Patent Publication Number: US-8531661-B2

Title: Optical device unit and detection apparatus

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to an optical device unit and a detection apparatus. 
     2. Related Art 
     In general, a Raman spectroscopic apparatus includes a detector for obtaining Raman spectra by detecting Raman scattering light depending on a detection target substance. The detection target substance can be specified by performing a spectroscopic analysis using the Raman spectra. However, the signal intensity of the Raman scattering light is typically weak, and its detection sensitivity is low. 
     JP-T-2008-529006 discloses a handheld Raman blood analyzer to provide surface-enhanced Raman scattering using gold colloid sol-gel/strips and increase the signal intensity of the Raman scattering light. 
     In addition, a localized plasmon can be generated by irradiating excitation light onto a metal surface. The electric field can be locally enhanced by combining the excitation light and the localized plasmon. It is envisaged that Raman scattering light is enhanced by the enhanced electric field in the surface-enhanced Raman scattering. 
     Japanese Patent No. 3482824 discloses a vertical cavity surface-emitting laser (VCSEL) capable of safely controlling a polarization surface in which excitation light can be provided using the VCSEL. 
     Optical absorption is generated by localized plasmon resonance when excitation light and localized plasmon are combined. For example, JP-A-2000-356587 discloses a technique of improving sensor sensitivity based on localized surface plasmon resonance using a substrate having a surface where metal micro particles are fixed. JP-A-2007-10648 discloses a localized plasmon resonance sensor having a resonance peak shifted to a long wavelength side and a resonance peak shifted to a short wavelength side. In addition, JP-A-2009-250951 discloses an electric field enhancement device including a micro resonator having a plurality of resonance areas in order to make it possible to resonate for a plurality of wavelengths. 
     A Raman spectroscopic apparatus typically includes an optical device having an electrical conductor such as a metal nano-structure where a detection target substance can be adsorbed. Raman scattering light caused by an enhanced electric field can be detected by guiding the target substance into the enhanced electrical field near the optical device. Depending on the type of target substance, or the type of optical device, a detection sensitivity of the Raman scattering light may be low. 
     SUMMARY 
     An advantage of some aspects of the invention is to provide an optical device unit and a detection apparatus capable of improving the detection sensitivity. 
     An aspect of the invention is directed to a detachable optical device unit to a detection apparatus, the optical device unit including: an optical device having an electrical conductor, the optical device being capable of enhancing Raman scattering light generated by receiving light from a light source of the detection apparatus; and a first guide unit that guides a gaseous sample to the optical device. 
     In the optical device unit of the aspect of the invention, the used optical device unit may be removed from the detection apparatus, and a new optical device unit may be installed in the detection apparatus. If the optical device unit is exchanged in this manner, it is possible to increase detection sensitivity of the detection apparatus while the gaseous samples attached to the first guide unit and the optical device do not influence the subsequent detection or measurement. 
     In the optical device unit of the aspect of the invention, the first guide unit may have a first fluid path that imports the gaseous sample from an import hole, and the first fluid path may have an inner wall surface that blocks an incident ray of external light between the import hole and the optical device. 
     As a result, external light rarely reaches the optical device, and a ratio of the external light (noise) with respect to the Raman scattering light (signal) decreases. Therefore, it is possible to improve a signal-to-noise ratio (S/N ratio) when the Raman scattering light is detected and increase the detection sensitivity. 
     The optical device unit of the aspect of the invention may further include a filter for removing dust in the air in the first fluid path, and the filter may block the external light. 
     As a result, dust and external light rarely arrive at the optical device due to the presence of the filter, and it is possible to increase the detection sensitivity. 
     The optical device unit of the aspect of the invention may further include an identification code that can be read by the detection apparatus and identifies the optical device. 
     As a result, the detection apparatus can recognize the type of the optical device or the gaseous sample detectable by the optical device. In a case where the detection apparatus carries out a spectroscopic analysis using Raman spectra, such a detection apparatus (Raman spectroscopic apparatus) can easily detect or specify the gaseous sample (target substance) corresponding to the optical device. 
     In the optical device unit of the aspect of the invention, the first guide unit may have a second fluid path connected to the first fluid path, and the second fluid path may rotate the gaseous sample in an area facing the optical device. 
     As a result, due to presence of the second fluid path of the guide unit, a possibility that the gaseous sample enters the optical device increases. Therefore, the signal intensity of the Raman scattering light becomes stable. For example, even when the amount of the gaseous sample is small, it is possible to easily detect or specify the gaseous sample (a target substance). 
     Another aspect of the invention is directed to a detection apparatus including: the optical device unit described above, a second guide unit connectable to the first guide unit; the light source; a first optical system that introduces the light from the light source into the electrical conductor of the optical device; and a detector that detects Raman scattering light from the light scattered or reflected by the electrical conductor, wherein the second guide unit guides the gaseous sample to the outlet duct. 
     As a result, by connecting the first guide unit of the optical device unit and the second guide unit of the detection apparatus, it is possible to provide a detection apparatus in which the optical device unit is exchangeable. 
     In the detection apparatus of the aspect of the invention, the electrical conductor of the optical device may include a first protrusion group having a plurality of protrusions, each of the plurality of protrusions of the first protrusion group may be arranged with a first period along a direction parallel to the virtual plane of the electrical conductor, and the first optical system introduces the light from the light source into the first protrusion group such that a component parallel to the virtual plane of a polarization direction of the light from the light source is parallel to an arrangement direction of the first protrusion group. 
     As a result, the enhanced electric field of the optical device can be increased by the first protrusion group. In addition, linearly-polarized light in which a component parallel to the virtual plane of the polarization direction is parallel to the arrangement direction of the first protrusion group can be incident to the optical device. As a result, propagation type surface plasmons can be excited. 
     In the detection apparatus of the aspect of the invention, each of the plurality of the protrusions of the first protrusion group may include a second protrusion group formed of an electrical conductor on a front surface of the first protrusion group, and each of a plurality of protrusions of the second protrusion group corresponding to any one of the plurality of protrusions of the first protrusion group may be arranged with a second period shorter than the first period along a direction parallel to the virtual plane. 
     As a result, the enhanced electric field in the optical device can increase also in the second protrusion group. 
     The detection apparatus of the aspect of the invention may further include a third protrusion group formed of a third electrical conductor on a surface between neighboring protrusions of the first protrusion group on a surface where the first protrusion group is arranged, and each of a plurality of protrusions of the third protrusion group may be arranged with a third period shorter than the first period along the direction parallel to the virtual plane between the neighboring protrusions of the first protrusion group. 
     As a result, the enhanced electric field in the optical device can increase also in the third protrusion group. 
     In the detection apparatus of the aspect of the invention, surface plasmon resonance in the event that a propagating direction of the light from the light source is inclined with respect to a normal line directed to the virtual plane may be generated in each of first and second resonance peak wavelengths, a first resonance peak wavelength band having the first resonance peak wavelength may have an excitation wavelength in surface-enhanced Raman scattering caused by the surface plasmon resonance, and a second resonance peak wavelength band having the second resonance peak wavelength may have a Raman scattering wavelength in the surface-enhanced Raman scattering. 
     As a result, surface plasmon resonance is generated in each of the first and second resonance peak wavelengths by the light incident to the first protrusion group in which protrusions are arranged with the first period. In this case, the incident angle of the light and the first period are set such that the first resonance peak wavelength band including the first resonance peak wavelength includes an excitation wavelength of surface-enhanced Raman scattering, and the second resonance peak wavelength band of the second resonance peak wavelength includes a Raman scattering wavelength in surface-enhanced Raman scattering. As a result, it is possible to improve an enhancement degree of the electric field in both the excitation wavelength and the Raman scattering wavelength. 
     The detection apparatus of the aspect of the invention may further include a second optical system that guides the Raman scattering light to the detector, and the detector may receive the Raman scattering light through the second optical system. 
     As a result, it is possible to efficiently receive the Raman scattering light using the second optical system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIGS. 1A to 1D  illustrate a configuration example of a detection apparatus including an optical device unit according to an embodiment of the invention. 
         FIGS. 2A to 2E  are explanatory diagrams of the principle of detecting Raman scattering light. 
         FIGS. 3A to 3D  illustrate a specific configuration example of a detection apparatus including an optical device unit according to an embodiment of the invention. 
         FIG. 4  is an exemplary block diagram illustrating the detection apparatus of  FIG. 3A . 
         FIGS. 5A and 5B  illustrate an exemplary structure of a vertical cavity surface-emitting laser (VCSEL). 
         FIG. 6  is an explanatory diagram illustrating characteristics of light sources. 
         FIGS. 7A to 7C  illustrate exemplary configurations of a guide unit and a discharge fluid path. 
         FIGS. 8A to 8E  are schematic explanatory diagrams illustrating a photolithographic technique. 
         FIGS. 9A to 9E  are schematic explanatory diagrams illustrating a manufacturing process of a metal nano-structure. 
         FIGS. 10A to 10C  are schematic explanatory diagrams illustrating an enhanced electric field formed in a metal nano-structure. 
         FIG. 11  is a schematic explanatory diagram illustrating two resonance peaks. 
         FIG. 12  is a perspective view illustrating a configuration example of a sensor chip. 
         FIG. 13  is a cross-sectional view illustrating the sensor chip of  FIG. 12 . 
         FIG. 14  illustrates an exemplary characteristic of a reflective light intensity of a sensor chip. 
         FIG. 15  is an explanatory diagram illustrating an excitation condition of surface plasmon polaritons. 
         FIG. 16  illustrates another exemplary characteristic of a reflective light intensity of a sensor chip. 
         FIG. 17  is a perspective view illustrating a modified example of the sensor chip of  FIG. 12 . 
         FIG. 18  is a cross-sectional view illustrating the sensor chip of  FIG. 17 . 
         FIGS. 19A and 19B  are explanatory diagrams illustrating a technique for introducing incident light into a sensor chip with an inclination. 
         FIGS. 20A and 20B  are schematic explanatory diagrams illustrating a method of manufacturing an electrical conductor. 
         FIGS. 21A to 21C  are schematic explanatory diagrams illustrating peak extraction from Raman spectra. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, preferable embodiments of the invention will be described in detail. Embodiments of the invention described below are not intended to limit the scope of the invention described in the claims, and all of the configurations described in the embodiments of the invention are not necessarily indispensable as solving means of the invention. 
     1. Overview 
     1.1. Basic Configuration 
       FIGS. 1A to 1D  illustrate an exemplary configuration of a detection apparatus including an optical device unit according to an embodiment of the invention. As shown in  FIG. 1A , the optical device unit includes an optical device  4  and a guide unit  420  (first guide unit), and the detection apparatus includes the optical device unit, a discharge fluid path  423  (second guide unit), a light source A, an optical system, and a detector  5 . The optical device unit is detachable from the detection apparatus, and the guide unit  420  and the discharge fluid path  423  are connected thereto. 
     The optical system (first optical system) includes a half mirror  2  and an object lens  3 . The light source A may radiate light having a predetermined polarization direction. In addition, the light source A is not limited to the example in  FIG. 1A  but may include a plurality of light sources. In addition, the light source A may have directivity. Preferably, the light source A may have a light source with high directivity (for example, laser). 
     The half mirror  2  and the object lens  3  (in the broadest sense, the optical system) introduces the light from the light source A into the electrical conductor of the optical device  4 . In addition, the guide unit  420  guides the gaseous sample to the optical device  4 . The discharge fluid path  423  is guided to the optical device  4  and discharges the gaseous sample. The detector  5  detects the Raman scattering light from the light scattered or reflected by the electrical conductor. The detection apparatus may be called a Raman detection apparatus, and the detection apparatus further performing a spectroscopic analysis using Raman spectra may also be called a Raman spectroscopic apparatus. 
     The inventors have recognized that the gaseous sample is continuously attached to the optical device  4  and the guide unit  420  used in the Raman spectroscopic apparatus, and the signal intensity of the Raman scattering light caused by the enhanced electric field in the vicinity of the electrical conductor of the optical device  4  is not stable. In this regard, it is possible to increase the detection sensitivity of the detector  5  by separating the optical device  4  and the guide unit  420  and by improving the guide unit  420  in some cases. In addition, it is possible to improve the detection sensitivity by separating the optical device  4  and the guide unit  420  from the detection apparatus. In addition, it is possible to increase a possibility that the gaseous sample enters the optical device by improving the guide unit  420 . Therefore, it is possible to obtain a stable signal intensity of the Raman scattering light. The Raman scattering light and the enhanced electric field will be described below. In addition, the guide unit  420  will be described below. 
     In the example in  FIG. 1A , the optical path of the light Lin (incident light) from the light source A and the optical path of the light Lout (scattered light, reflective light) from the optical device  4  do not accurately represent the actual optical path. In other words, they are intended to only show presence of the optical path of the light Lin (incident light) from the light source A and presence of the optical path of the light Lout (scattered light, reflective light) from the optical device  4 . 
     In the example in  FIG. 1B , the detection apparatus may include a control unit  7  that variably controls the relative position between the optical device  4  and the light source A. Specifically, the control unit  7  may change the position of the light source A. In addition, the control unit  7  may include an operation unit such as an XY stage or may only transmit a signal to the operational unit. 
     The control unit  7  may change the position of the optical device  4 . In the example in  FIG. 1B , the control unit  7  changes the position of the light source A such that the optical axis Lax 1  of the light source A matches the optical axis Lax 2  of the object lens  3  (in the broadest sense, the optical axis of the optical system). 
     In this case, in practice, it is anticipated that the light Lin from the light source A is overlapped with the optical axis Lax 1  of the light source A and the optical axis Lax 2  of the object lens  3 . However, in the example in  FIG. 1B , the light Lin from the light source A is illustrated so as not to be overlapped with the optical axis Lax 1  of the light source A and the optical axis Lax 2  of the object lens  3 . In the example in  FIG. 1B , in order to illustrate that the optical axis Lax 1  of the light source A matches the optical axis Lax 2  of the object lens  3 , the light Lin from the light source A is illustrated so as not to be overlapped with the optical axis Lax 1  of the light source A and the optical axis Lax 2  of the object lens  3 . 
     In the example in  FIG. 1C , the control unit  7  changes the position of the light source A such that the optical axis Lax 1  of the light source A is deviated from the optical axis Lax 2  of the object lens  3 . In this case, in practice, it is anticipated that the light Lin from the light source A is overlapped with the optical axis Lax 1  of the light source A. However, in the example in  FIG. 1C , the light Lin from the light source A is illustrated so as not to be overlapped with the optical axis Lax 1  of the light source A. In the example in  FIG. 1C , in order to illustrate that the optical axis Lax 1  of the light source A does not match the optical axis Lax 2  of the object lens  3 , the light Lin from the light source A is illustrated so as not to be overlapped with the optical axis Lax 1  of the light source A. 
     In the example in  FIG. 1D , the detection apparatus may have a control unit  7  for variably controlling a relative position between the optical device  4  and the optical system. Specifically, the control unit  7  may change a position of the object lens  3 . It is possible to match the optical axis of the light source A with the optical axis of the object lens  3  by changing the position of the object lens  3 . Otherwise, the optical axis of the light source A may be deviated from the optical axis of the object lens. 
     1.2. Principle of Detection 
       FIGS. 2A to 2E  are explanatory diagrams illustrating the principle of detection in the Raman scattering light. The example in  FIG. 2A  illustrates Raman spectroscopy, in which, when the incident light (frequency ν) is irradiated onto a target molecule (in the broadest sense, a target substance), a significant amount of the incident light is scattered as Rayleigh scattering light, and a frequency ν or a wavelength of the Rayleigh scattering light is not changed. A part of the incident light is scattered as Raman scattering light, and the frequency (ν−ν′ and ν+ν′) or the wavelength of the Raman scattering light is reflected on the frequency ν′ (molecular vibration) of the target molecule. A part of the incident light is used to vibrate the target molecule to reduce energy. However, the vibration energy of the target molecule may be added to optical energy or vibration energy of the Raman scattering light. Such a shift (ν′) of the frequency is called a Raman shift. 
     The example in  FIG. 2B  illustrates a Raman spectrum in a case where the target molecule is a molecule of acetaldehyde. In other words, it is possible to specify a molecule of acetaldehyde by analyzing the Raman spectrum shown in  FIG. 2B . However, in a case where the amount of target molecules is small, the Raman scattering light is typically too weak to detect or specify the target molecule. In this regard, it is preferable that the Raman scattering light be enhanced by the enhanced electric field by adding the enhanced electric field. In addition, the Raman spectrum in  FIG. 2B  shows the Raman shift using the wave number. 
     The example in  FIG. 2C  illustrates an enhanced electric field formed when the incident light (irradiated light) is irradiated onto the metal fine-particle  20 . In a case where the incident light is irradiated onto metal fine-particles  20  (metal nano-particles) smaller than the wavelength of the incident light, the electric field of the incident light is applied to free electrons present on the surfaces of the metal fine-particles  20  to generate resonance. As a result, the electric dipole caused by the free electrons is excited within the metal fine-particles  20  so that an enhanced electric field stronger than the electric field of the incident light is formed in the vicinity of the metal fine-particles  20 . Such a phenomenon is unique in electric conductors such as metal fine-particles  20  smaller than the wavelength of the incident light. 
     The example in  FIG. 2D  illustrates surface-enhanced Raman scattering (SERS) when the incident light is irradiated onto the optical device  4 . The optical device  4  includes a substrate  100 . It is possible to provide a protrusion group  115  (in the broadest sense, a metal nano-structure) having a plurality of protrusions  110  by forming metal fine-particles  20  in convex portions  105  of the substrate  100 . It is possible to form an enhanced electric field between neighboring protrusions  110  (electrical conductors formed in the convex portions  105 ) of the protrusion group  115  by irradiating incident light onto such an optical device. If the target molecule enters the enhanced electric field, the Raman scattering light caused by the target molecule is enhanced by the enhanced electric field, and the signal intensity of the Raman scattering light becomes strong. In such surface-enhanced Raman scattering, it is possible to increase detection sensitivity even when the number of target molecules is insignificant. 
     Although the incident light is irradiated from the surface side (the electrical conductor side) of the optical device  4  in the example in  FIG. 2D , the incident light may be irradiated from the rear side (the substrate  100  side) of the optical device  4  as shown in  FIG. 2E . In the example in  FIG. 2E , it is possible to detect the Raman scattering light and the Rayleigh scattering light on the rear side of the optical device  4 . 
     The optical device  4  illustrated in  FIGS. 1A to 1D  preferably has a metal nano-structure as shown in  FIG. 2D . However, it may not be necessary to provide the enhanced electric field as shown in  FIG. 2C . 
     2. Specific Example 
     2.1. Entire Configuration 
       FIGS. 3A to 3D  illustrate an exemplary configuration of the detection apparatus having the optical device unit in detail according to an embodiment of the invention. In the following description, like reference numerals denote like elements as in  FIG. 1 , and description thereof will not be repeated. In the example in  FIG. 3A , the optical device unit is integrated in the detection apparatus. In the example in  FIG. 3B , the optical device unit is extracted from the detection apparatus before the optical device unit is integrated. In the example in  FIG. 3C , the optical device unit for exchange is illustrated. In the example in  FIG. 3D , an entrance path of the external light is illustrated. In order to increase the detection sensitivity of the detection apparatus, the optical device unit is detachably integrated in the detection apparatus. By removing the used optical device unit from the detection apparatus and installing a new optical device unit in the detection apparatus, the gaseous sample attached to the guide unit  420  and the optical device  4  does not affect the subsequent detection or measurement. 
     The optical device unit of the detection apparatus in  FIG. 3A  includes a sensor chip  300  (in the broadest sense, the optical device  4 ) and a guide unit  420  (transport unit). The target substance is introduced from the inlet duct  400  (loading entrance or import hole) to the inner side of the guide unit  420  (first guide unit) and the discharge fluid path  423  (second guide unit) and discharged from the outlet duct  410  to the outer side of the guide unit  420  (first guide unit) and the discharge fluid path  423  (second guide unit). In the example in  FIG. 3A , the detection apparatus includes a fan  450  (in the broadest sense, suction unit) near the outlet duct  410  so that pressures within the inlet fluid path  421  (first fluid path) of the guide unit  420 , the fluid path  422  (second fluid path) in an area facing the sensor chip  300 , and the discharge fluid path  423  (third fluid path) are reduced as the fan  450  is operated. As a result, the target substance (gaseous sample) is imported to the guide portion  420 . The target substance passes through the fluid path  422  near the sensor chip  300  via the inlet fluid path  421  and is discharged from the discharge fluid path  423 . In this case, a part of the target substances are adhered to the surface of the sensor chip  300  (an electrical conductor). 
     The discharge fluid path  423  for guiding the gaseous sample to the outlet duct  410  may be connected to fluid path  422  (in the broadest sense, the guide unit  420 ) near the sensor chip  300 . In the example in  FIG. 3A , the discharge fluid path  423  and the fluid path  422  are connected through a connector  490  such as a flange or a coupler. 
     The sensor chip  300  can enhance the Raman scattering light generated by receiving the light from the light source A, and the fluid path of the guide unit  420  may be improved in order to increase a possibility that the gaseous sample is attached to or adsorbed on the surface of the sensor chip  300 . In a simple fluid path (not shown), the gaseous sample may pass through the sensor chip  300 . Therefore, the guide unit  420  may have a fluid path such that the gaseous sample is circulated around the vicinity of the surface of the sensor chip  300 . The circulated gaseous sample is difficult to directly go to the outlet duct  410  or the discharge fluid path  423  and may stay in the fluid path  422  near the sensor chip  300 . 
     As shown in  FIG. 3A , the gaseous sample can be circulated in the fluid path  422  (the second fluid path) in the vicinity of the sensor chip  300 . Due to the generation of rotating flow, the possibility in which the gaseous sample is entering the sensor chip  300  improves. Therefore, the signal intensity of the Raman scattering light becomes stable, and even in the case where the amount of the gaseous sample is small the gaseous sample (target substance) can be easily detected or specified. 
     As the target substance trace molecules such as a narcotic drugs, alcohol, or residual pesticides or pathogenic agents such as viruses may be envisaged. 
     Preferably, a possibility that the gaseous sample makes contact with the surface of the sensor chip  300  is high. Furthermore, the external light (not shown) does not reach the sensor chip  300  as long as possible. As shown in  FIG. 3A , the inlet fluid path  421  (first fluid path) of the guide unit  420  may have a reflecting structure. By reducing a ratio of the external light (noise) to the Raman scattering light (signal), it is possible to improve the signal-to-noise (S/N) ratio to detect the Raman scattering light, and thus, to enhance the detection sensitivity. 
     If the inlet fluid path  421  is straight, it is difficult to block the external light in the inlet fluid path  421 , so that the detection sensitivity may be degraded. 
     The example in  FIG. 3D  illustrates an optical path when the external light reaches the fluid path  422  in the vicinity of the sensor chip  300  through the inlet fluid path  421 . For example, as shown in  FIG. 3D , the external light is reflected by the inner wall of the inlet fluid path  421  three times. The inlet fluid path  421  has an inner wall surface for blocking the incident rays of the external light between the inlet duct  400  (import hole) and the sensor chip  300 . Through such a reflecting structure, the inlet fluid path  421  is provided with a light-blocking property. 
     Although the inlet fluid path  421  has a reflecting structure in the example in  FIG. 3A , the inner wall of the inlet fluid path  421  is preferably curved such that the resistance of the fluid path is reduced. In addition, the inner wall of the inlet fluid path  421  is preferably made of a material having a low light reflectance to increase the light blocking property. Furthermore, the discharge fluid path  423  (third fluid path) of the guide unit  420  also preferably has a structure capable of increasing the light blocking property. 
     The example in  FIG. 3D  illustrates an optical path (incident rays) when the external light reaches the fluid path  422  near the sensor chip  300  through the discharge fluid path  423 . For example, as shown in  FIG. 3D , the external light is reflected 3 times by the inner wall of the discharge fluid path  423 . The discharge fluid path  423  has an inner wall surface for blocking the incident rays of the external light between the outlet duct  410  and the sensor chip  300 . Through such a reflecting structure, the discharge fluid path  423  may be provided with the light blocking property. 
     In the example in  FIG. 3A , the inlet fluid path  421  (in the broadest sense, guide unit  420 , and in broadest possible sense, the optical device unit) may include a filter  426  (for example, the dust-removing filter) for removing dust in the air. The filter  426  preferably blocks the external light, and may serve as both the dust-removing filter and the light-blocking filter. In addition, the discharge fluid path  423  (in the broadest sense, the detection apparatus) may also include a filter  427  (for example, a light-blocking filter) for blocking the external light. 
     In the example in  FIG. 3A , the detection apparatus includes a covering  440 , and the covering  440  may store a sensor chip  300 . In addition, the detection apparatus includes a casing  500 , and the light source A, the half mirror  2 , the object lens  3 , and the detector  5  may be included in the casing  500 . The detector  5  includes a spectroscopic element  370  and an optical receiver element  380 . The spectroscopic element  370  may include etalon. Furthermore, the detection apparatus may include a condensing lens  360 , an optical filter  365 , a processing unit  460 , a power supply unit  470 , a communication connection plug  510 , and a power connection plug  520 . 
     In the example in  FIG. 3A , the detection apparatus has a hinge  480 , and the covering  440  can be opened/closed through the hinge  480 . While the covering  440  is opened, the used optical device unit may be removed. Alternatively, as shown in  FIG. 3B , while the covering  440  is opened, a new optical device unit may be integrated into the detection apparatus. In addition, the detection apparatus has a latching portion (not shown), and the optical device unit has a latched portion (not shown) corresponding to the latching portion so that the optical device unit can be positioned. In addition, the sensor chip detection element  310  may detect whether or not the sensor chip  300  (in the broadest sense, optical device unit) is suitably integrated into the detection apparatus.  FIG. 3C  illustrates an optical device unit for exchange, and the optical device unit may have encapsulation members  424  and  425  to prevent contamination of the guide unit  420  and the sensor chip  300 . The optical device unit may have an identification code  305  (for example, a bard code) for identifying the sensor chip  300 , and the sensor chip detection element  310  (for example, a barcode reader) may read the identification code  305 . 
     In the example in  FIG. 3A , the detection apparatus further includes a polarization control element  330  and a collimator lens  320  corresponding to the light source A. The light emitted from the light source A is collimated by the collimator lens  320  and plane-polarized by the polarization control element  330 . In addition, if a surface-emitting laser is employed as the light source to allow the plane-polarized light to be emitted, it is possible to omit the polarization control element  330 . 
     The light from the light source A is attracted to the direction of the sensor chip  300  by the half mirror  2  (dichroic mirror), condensed to the object lens  3 , and is incident to the sensor chip  300 . For example, a metal nano-structure is formed on the surface of the sensor chip  300 . From the sensor chip  300  Rayleigh scattering light and Raman scattering light are emitted from the sensor chip  300  by surface-enhanced Raman scattering. The Raman scattering light and the Rayleigh scattering light from the sensor chip  300  pass through the object lens  3  and are attracted to the direction of the detector  5  by the half mirror  2 . 
     In the example in  FIG. 3A , the light from the light source A reaches the front surface of the sensor chip  300  from the rear surface thereof, and the Rayleigh scattering light and the Raman scattering light are generated from the vicinity of the metal nano-structure, so that the Rayleigh scattering light and the Raman scattering light are radiated from the rear surface of the sensor chip  300  (refer to  FIG. 2E ). In addition, the arrangement of the sensor chip  300  in  FIG. 3  may be changed such that the light from the light source A directly reaches the front surface of the sensor chip  300  (refer to  FIG. 2D ). 
     In the example in  FIG. 3A , the Rayleigh scattering light and the Raman scattering light from the sensor chip  300  are condensed by the condensing lens  360  and reach the optical filter  365 . In addition, the Raman scattering light is extracted by the optical filter  365  (for example, a notch filter), and the optical receiver element  380  receives the Raman scattering light through the spectroscopic element  370 . The wavelength of the light passing through the spectroscopic element  370  can be controlled (selected) by the processing unit  460 . 
     The optical receiver element  380  receives the Raman scattering light through the optical system and the spectroscopic element  370 . The optical system (second optical system) includes a half mirror  2 , a condensing lens  360 , and an optical filter  365 . A Raman spectrum unique to the target substance is obtained by the spectroscopic element  370  and the optical receiver element  380 , and the target substance can be specified by checking the obtained Raman spectrum against the previously-stored data. 
     In the example in  FIG. 3A , the processing unit  460  may turn on/off the power of the light source A. For example, the processing unit  460  may carry out the function of the control unit  7  shown in  FIG. 1B , and the processing unit  460  may variably control the position of the light source A. In addition, the processing unit  460  may send instructions to the detector  5  and the fan  450  other than the light source A shown in  FIG. 3A , and the processing unit  460  may control the detector  5  and the fan  450  as well as the light source A. In addition, the processing unit  460  may carry out the spectroscopic analysis using the Raman spectrum, and the processing unit  460  may specify the target substance. In addition, the processing unit  460  may transmit the detection result of Raman scattering light, the spectroscopic analysis result of the Raman spectrum is transmitted to an external device (not shown) connected to the communication connection plug  510 . 
     In the example in  FIG. 3A , the power supply unit  470  may supply power to the light source A, the detector  5 , the fan  450 , the processing unit  460  shown in  FIG. 3A . The power supply unit  470  may be configured using a secondary battery as well as a primary battery and an AC adaptor. In a case where the power supply unit  470  is configured using the secondary battery, an electric charger (not shown) connected to the power connection plug  520  may charge the secondary battery. In a case where the power supply unit  470  is configured using an AC adaptor, the AC adaptor is arranged in an external side of the detection apparatus and connected to the power connection plug  520 . In addition, the detection apparatus may include a display unit (the display unit  540  in the example in  FIG. 4 ), and the display unit may display the state of the power supply unit  470  (for example, out of battery, now charging, charging completed, power is being supplied). 
       FIG. 4  illustrates an exemplary block diagram of the detection apparatus of  FIG. 3A . In the following description, like reference numerals denote like elements as in  FIG. 3A , and description thereof will not be repeated. As shown in  FIG. 4 , the detection apparatus may further include a display unit  540 , a manipulation unit  550 , and an interface  530 . In addition, the processing unit  460  shown in  FIG. 3A  may include a central processing unit (CPU)  461 , random access memory (RAM)  462 , and read only memory (ROM)  463 . Furthermore, the detection apparatus may include a light source driver  15 , a spectroscopic driver  375 , an optical receiver circuit  385 , and a fan driver  455 . Hereinafter, an operational example of the detection apparatus shown in  FIG. 4  will be described. 
     In the example in  FIG. 4 , the CPU  461  may determine whether or not preparation to detect the Raman scattering light has been completed, and the CPU  461  may send a signal indicating that the preparation has been completed to the display unit  540 . In addition, the CPU  461  may send signals other than that signal to the display unit  540 . The display unit  540  may provide a user with various display contents in response to the signal (display signal) from the CPU  461 . 
     In the example in  FIG. 4 , the detection circuit  315  may extract the identification code  305  detected by the sensor chip detection element  310  as an electrical signal. The CPU  461  may receive the electric signal in a digital format and specify the type of the sensor chip  300  using a value thereof. Then, the CPU  461  may recognize that it is ready to detect the Raman scattering light. 
     In a case where the display unit  540  indicates that it is ready to detect the Raman scattering light, a user manipulates the manipulation unit  550  to initiate the detection of the Raman scattering light. In a case where the signal from the manipulation unit  550  (manipulation signal) initiates detection, the CPU  461  may actuate the light source A through a light source driver  15 . Specifically, the light source driver  15  (in the broadest sense, the CPU  461 ) may power on the light source A. In addition, the light source A may include a temperature sensor (not shown) and a light amount sensor (not shown). The light source A may send the temperature and the light amount of the light source A to the CPU  461  through the light source driver  15 . The CPU  461  may receive the temperature and the light amount of the light source A and determine whether or not the output of the light source A is stable. While the light source A is powered on, and after the output of the light source A becomes stable in some cases, the CPU  461  may actuate the fan  450  through the fan driver  455 . 
     In addition, the CPU  461  (in the broadest sense, the processing unit  460 ) may carry out the function of the control unit  7  shown in  FIG. 1B , and may variably control the position of the light source A through the light source driver  15 . Alternatively, the CPU  461  may variably control the position of the object lens  3  shown in  FIG. 1D  through the light source driver  15  or the lens driver (not shown). 
     In the example in  FIG. 4 , the fan driver  455  may power on the fan  450 . As a result, the target substance (gaseous sample) is suctioned into the guide unit  420  in  FIGS. 3A to 3D . In a case where the light source A in  FIG. 3A  is powered on, the light from the light source A reaches the sensor chip  300  in  FIGS. 3A to 3D  through the half mirror  2 . In response, the Rayleigh scattering light and the Raman scattering light are returned to the half mirror  2  from the sensor chip  300 . The Rayleigh scattering light and the Raman scattering light from the sensor chip  300  arrive at the optical filter  365  through the condensing lens  360 . The optical filter  365  blocks the Rayleigh scattering light and guides the Raman scattering light to the spectroscopic element  370 . The aforementioned process can be made using a fan  450  when the fluid path resistance from the inlet duct  400  (a loading entrance) to the guide unit  420  and the outlet duct  410  is relatively small. However, when the fluid path resistance is relatively large, a suction pump (not shown) may be used instead of the fan  450 . 
     In the example in  FIG. 4 , the spectroscopic driver  375  (in the broadest sense, the CPU  461 ) may control the spectroscopic element  370 . The spectroscopic element  370  may be made of a variable etalon spectroscope capable of changing the resonance wavelength. In a case where the spectroscopic element  370  is an etalon using Fabry-Perot resonance, the spectroscopic driver  375  may change (select) the wavelength of the light passing through the etalon while the distance between the two facing etalon plates is adjusted. Specifically, when the wavelength of the light passing through the etalon is set to a range from the first wavelength to the Nth wavelength, first, the distance between the two etalon plates is set such that the light of the first wavelength represents a maximum intensity. Then, the distance between the two etalon plates is set again such that the light having a second wavelength deviated by a half maximum full width from the first wavelength has a maximum intensity. In such a method, the light passing through the etalon is received by the optical receiver element  380  while the first wavelength, the second wavelength, the third wavelength, . . . , and the Nth wavelength are sequentially selected. 
     In the example in  FIG. 4 , the optical receiver circuit  385  (in the broadest sense, the CPU  461 ) may extract the light received from the optical receiver element  380  as an electric signal. The CPU  461  receives the electric signal in a digital format and stores the value thereof in the RAM  462 . Since the spectroscopic element  370  selectively guides the light in a range of the first wavelength to the Nth wavelength to the optical receiver element  380 , the CPU  461  can store the Raman spectrum in the RAM  462  in a digital format. 
     In the example in  FIG. 4 , the CPU  461  may compare the Raman spectral data unique to the target substance stored in the RAM  462  with the existing Raman spectral data stored in advance in the ROM  463 . The CPU  461  may determine what kind of material the target substance is based on the comparison result. The CPU  461  may send a signal indicating the comparison result or the determination result to the display unit  540 . As a result, the display unit  540  may notify a user of the comparison result or the determination result. In addition, the CPU  461  may output the data indicating the comparison result or the determination result from the communication connection plug  510 . The interface  530  may transmit/receive data to/from an external device (not show) connected to the CPU  461  and the communication connection plug  510  according to a predetermined standard. 
     In the example in  FIG. 4 , the CPU  461  may determine the state of the power supply unit  470 . In a case where the power supply unit  470  includes the primary battery or the secondary battery, the CPU  461  may determine whether or not the data indicating a voltage of the primary battery or the secondary battery are equal to or smaller than a predetermined value previously stored in the ROM  463 . The CPU  461  may transmit the signal indicating the determination result to the display unit  540 . As a result, the display unit  540  may allow a user to see the determination result (for example, out of battery, charging required) or an instruction based on the determination result. In addition, in a case where the power supply unit  470  includes the secondary battery, the CPU  461  may determine whether or not the secondary battery is being charged. 
     In the example in  FIG. 4 , the power supply unit  470  may transmit the state of the power supply unit  470  to the CPU  461 . In addition, the power supply unit  470  may supply power to the processing unit  460  including the CPU  461 . Although not shown in  FIG. 4 , the power supply unit  470  may supply power to the components of the detection apparatus such as the light source driver  15 , the optical receiver circuit  385 , and the light source group  1 . 
     2.2. Light Source 
       FIGS. 5A and 5B  illustrate a configuration example of a VCSEL. In the example in  FIG. 5A , an n-type DBR (Diffracted Bragg Reflector) layer is formed on an n-type GaAs substrate. An active layer and an oxidation constriction layer are provided at the center of the n-type diffracted Bragg reflector (DBR) layer. A p-type DBR layer is provided on the active layer and the oxidation constriction layer. An electrode is formed on the insulation layer by providing an insulation layer on the p-type DBR layer and the n-type DBR layer. The electrode is also formed on the rear side of the n-type GaAs substrate. In the example in  FIG. 5A , an active layer is interposed between the n-type DBR layer and the p-type DBR layer, so that a vertical resonator is formed, in which the light generated from the active layer is resonated between the n-type DBR layer and the p-type DBR layer. In addition, the VCSEL is not limited to the example in  FIG. 5A . For example, the oxidation constriction layer may be omitted. 
     For example, the light source A shown in  FIG. 1A  is preferably a VCSEL (in the broadest sense, surface-emitting laser) capable of emitting light to a direction perpendicular to the substrate surface (the optical axis Lax 1  of the light source) by resonating the light in a direction perpendicular to the substrate surface. By using the VCSEL, it is possible to configure a light source which is monochromic (single wavelength) and plane-polarized. In addition, the VCSEL can be miniaturized and suitable for incorporating into a portable detection apparatus. In addition, from the structure of the VCSEL, it is possible to form a resonator without cleaving the substrate during the manufacturing process and inspect the characteristics of laser, which is suitable for mass production. Furthermore, the VCSEL can be manufactured with lower cost than those of other semiconductor laser devices, and 2-dimensional array type VCSEL can be provided as well. Furthermore, since the threshold current of the VCSEL is small, it is possible to reduce power consumption in the detection apparatus. In addition, it is possible to modulate the VCSEL in a high speed even using a low electric current, and reduce the width of the characteristic change for the temperature change of the VCSEL. In addition, it is possible to simplify the temperature control unit of the VCSEL. 
     By modifying the example in  FIG. 5A , the VCSEL can provide a stable polarization surface (in the broadest sense, a polarization direction). In this case, instead of the polarization control element  330  in  FIG. 3A  the light source A (vertical cavity surface-emitting laser) may have a distorting portion as disclosed in Japanese Patent No. 3482824. In the example disclosed in Japanese Patent No. 3482824, the distorting portion  19  is disposed in the vicinity of the resonator  10 B of the VCSEL. According to Japanese Patent No. 3482824, the distorting portion  19  generates birefringence and dependence on polarization of the gain within the resonator  10 A by distorting the anisotropic stress to the resonator  10 B. As a result, it is possible to provide a stable polarization surface. 
     In the example in  FIG. 5B , a plan view of the VCSEL is illustrated, in which the light source A has a distorting portion. In the example in  FIG. 5B , the light source A can radiate light having a polarization direction DA. 
       FIG. 6  is an explanatory diagram illustrating a characteristic of light sources. In the example in  FIG. 6 , characteristics of lasers that can be used in the light source are represented as a table. Although a VCSEL is suitable for the light source of the detection apparatus as described above, the detection apparatus may employ other kinds of laser as illustrated in  FIG. 6 , or light sources other than the laser. 
     2.3. Guide Unit 
       FIGS. 7A to 7C  illustrate an exemplary configuration of the guide unit and the discharge fluid path  423 . As shown in  FIG. 7A , the fluid path  422  in the vicinity of the sensor chip  300  may have a cylindrical structure. The cylindrical structure includes an inner peripheral surface  422   a  and a plane  422   b  perpendicular to the inner peripheral surface  422   a  so that the gaseous sample can be rotated in a direction (horizontal direction) parallel to the plane (in the broadest sense, virtual plane) of substrate  100  (in narrow meaning, the electrical conductor) on the inner peripheral surface  422   a  (wall surface). Rotation of the gaseous sample in a direction parallel to the virtual plane (for example, horizontal cross-sectional surface) of the electrical conductor may be called horizontal rotation or transversal rotation. The inlet of the fluid path  422  in the vicinity of the sensor chip  300  is connected to the outlet of the inlet fluid path  421 , and the outlet of the fluid path  422  in the vicinity of the sensor chip  300  is connected to the inlet of the discharge fluid path  423 . The inflow direction of the gaseous sample to the inlet of the fluid path  422  from the outlet of the inlet fluid path  421  is approximated to a direction parallel to the plane  422   b , so that the gaseous sample is apt to rotate in a horizontal direction. In addition, as shown in  FIG. 7A , a rotating flow in a horizontal direction may be mainly generated, and a rotating flow in a vertical direction may be generated. The gaseous sample stays in the vicinity of the sensor chip  300 , and then, is discharged from the discharge fluid path  423 . Since the gaseous sample passes through the vicinity of the enhanced electric field near the sensor chip  300  several times, a possibility that the gaseous sample enters the enhanced electric field increases. 
     As shown in  FIG. 7B , the fluid path  422  near the sensor chip  300  may have a cavity-shaped structure. The cavity-shaped structure has an inner spherical surface  422   c . The gaseous sample can be rotated in a direction (vertical direction) perpendicular to the virtual plane of the electrical conductor on the inner spherical surface  422   c  (wall surface). Rotation of the gaseous sample in a direction perpendicular to the virtual plane (for example, a horizontal cross section) of the electrical conductor may be called vertical rotation or longitudinal rotation. Since the inflow direction of the gaseous sample from the outlet of the inlet fluid path  421  to the inlet of the fluid path  422  is approximated to a direction perpendicular to the plane  422   b , the gaseous sample is apt to rotate in a vertical direction. In addition, as shown in  FIG. 7B , the rotation flow in a vertical direction is mainly generated, and the rotation flow in a horizontal direction may be generated. 
     In the example in  FIG. 7C , the inlet fluid path  421  may have a helical structure. The gaseous sample enters the fluid path  422  from the inlet fluid path  421 . In this case, since the inlet fluid path  421  has a helical structure, a rotating gaseous sample enters the fluid path  422 . Therefore, since the gaseous sample may further rotate in the fluid path  422 , a possibility that the gaseous sample stays in the enhanced electric field near the electric conductor further increases. In addition, the inlet fluid path  421  can block the external light, and the inner wall of the inlet fluid path  421  is preferably made of a material having low light reflectivity to increase the light blocking property. In the example in  FIG. 7C , the guide unit  420  (in the broadest sense, optical device unit) may have a relay path  423   a  connectable to the discharge fluid path  423 . 
     The discharge fluid path  423  may have a helical structure as shown in  FIG. 7C . In addition the inlet fluid path  421  shown in  FIG. 7A  may have a helical structure. 
     2.4. Optical Device (Metal Nano-Structure According to a Photolithographic Technique) 
       FIGS. 8A to 8E  are schematic explanatory diagrams illustrating a photolithographic technique. In the example in  FIG. 8A , an optical interferotype exposure apparatus using ultraviolet laser is schematically illustrated, and continuous wave (CW) laser having a wavelength of 266 nm and an output power of 200 mW may be used as the light source. The light from the ultraviolet laser is reflected at the mirror via a shutter and splits into both sides of the half mirror. The two light beams split from the half mirror are reflected at the mirror and pass through the object lens and the pinhole so that the diameters of the light beams are enlarged. An exposure pattern may be formed by irradiating the light from the ultraviolet laser having an enlarged beam diameter onto a mask, and the exposure pattern may be irradiated onto the substrate  100  where a photoresist has been coated. In this case, since the exposure patterns from both masks are interfered with each other, an interference pattern can be formed on the photoresist (substrate  100 ). In addition, it is possible to recognize the exposure pattern on a monitor using a half mirror or a CCD camera. 
     After a predetermined interference pattern (in the broadest sense, a predetermined exposure pattern) is exposed on the photoresist (substrate  100 ), it is possible to leave only a desired part of the photoresist by developing the photoresist. Then, the substrate  100  may be etched to as much as the necessary amount by immersing it into an etching solution or through dry etching. After the etching, the photoresist remaining on the substrate  100  may be removed. As a result, it is possible to manufacture the surface of the substrate  100  in a fine embossed shape. Then, it is possible to form a metal nano-structure by adding metal fine-particles as an electrical conductor on the surface of the substrate  100 . An overview of the manufacturing process of the metal nano-structure will be described below (refer to  FIGS. 9A to 9E ). 
     In the example in  FIG. 8B , a substrate  100  having a metal nano-structure is illustrated in a plan view and a cross-sectional view. In this example, the substrate  100  (metal nano-structure) includes a protrusion group  115  including a plurality of protrusions  110 , and a plurality of protrusions  110  (metal fine-particles  20 ) are periodically arranged in a one-dimensional space. 
     Also in the example in  FIG. 8C , the substrate  100  having a metal nano-structure is illustrated in a plan view and a cross-sectional view. In this example, a plurality of protrusions  110  (metal fine-particles  20 ) are periodically arranged in a two-dimensional space. In the example in  FIG. 8D , the substrate  100  having a metal nano-structure is illustrated as an electron microscope photograph in a perspective view and corresponds to  FIG. 8C . In the example in  FIG. 8D , the substrate  100  having a metal nano-structure is illustrated in a plan view as a scanning electro microscopy (SEM) photograph, and corresponds to  FIG. 8C . For example, a period (pitch) of a plurality of protrusions  110  containing gold (Au) is set to approximately 140 nm. 
     In addition, the metal nano-structure may be formed using an electron beam exposure apparatus instead of the optical interferotype exposure apparatus. While the electron beam exposure apparatus is advantageous in view of a higher exposure freedom in comparison with the optical interferotype exposure apparatus, the optical interferotype exposure apparatus is advantageous in view of higher productivity of the optical device in comparison with the electron beam exposure apparatus. 
       FIGS. 9A to 9E  are schematic explanatory diagrams illustrating a manufacturing process of the metal nano-structure. In the following description, like reference numerals denote like elements as in  FIG. 8B , and description thereof will not be repeated. For example, the metal nano-structure illustrated in  FIG. 8C  may be manufactured, specifically, as described below. As shown in  FIG. 9A , the substrate  100  has a photoresist  101 . The photoresist  101  is coated on the substrate  100  using a spin coat, and then, dried. In order to expose the predetermined pattern on the photoresist  101  an optical interferotype exposure apparatus as shown in  FIG. 8A  may be used. For example, a positive photoresist may be used as the photoresist  101 , and the thickness of the photoresist  101  may be set to 1 μm. In the example in  FIG. 9A , the light beams from two directions are irradiated onto the photoresist  101 , and each of the two light beams has an exposure pattern having a lattice shape. It is possible to form various interference patterns using a crossing angle between the two light beams. In addition, the size of the interference pattern may be reduced to a half of the wavelength of the ultraviolet laser in the optical interferotype exposure apparatus. A latent image generated by the interference pattern is formed in the photoresist  101 , and the photoresist  101  is developed. As a result, it is possible to form a photoresist pattern as shown in  FIG. 9B . 
     As shown in  FIG. 9B , the substrate  100  includes a portion protected by the photoresist pattern and a portion unprotected by the photoresist pattern. Then, the portion unprotected by the photoresist pattern is etched to form a concave portion  104  in the substrate  100  as shown in  FIG. 9C . Then, by removing the photoresist  101  remaining in the substrate  100  the convex portion  105  of the substrate  100  shown in  FIG. 9D  is exposed. Then a metal film containing metal fine-particles  20  is formed on the substrate  100  using a sputtering apparatus. Although a thin metal film is formed on the entire area of the substrate  100  in an initial state, a lot of metal fine-particles  20  are gradually adhered in the vicinity of the convex portion  105  so that a plurality of protrusions  110  (metal nano-structure) can be formed in the metal film as shown in  FIG. 9E . 
     If plane-polarized laser light is irradiated onto the protrusion group  115  including a plurality of protrusions  110  (the metal nano-structure), localized plasmons are excited by the polarization direction of the laser light, and a strong enhanced electric field is formed in the gap between the neighboring protrusions  110  in the protrusion group  115 . The gap between the neighboring protrusions  110  in the protrusion group  115  can be controlled using the thickness of the metal film. The size of the gap serves as a main factor for controlling the strength of the enhanced electric field. 
     The metal fine-particle  20  or the metal film may be formed of aurum (gold) (Au), silver (Ag), copper (Cu), aluminum (Al), palladium (Pd), platinum (Pt), or alloy thereof (a combination thereof). Preferably, the metal fine-particles  20  or the metal film may be formed of gold (Au) or silver (Ag) to make it easier to generate the localized plasmon, the enhanced electric field, or the surface-enhanced Raman scattering. 
       FIGS. 10A to 10C  are schematic explanatory diagrams illustrating the enhanced electric field formed from the metal nano-structure. In the following description, like reference numerals denote like elements as in  FIG. 2D , and description thereof will not be repeated. The target molecule (gaseous sample) is suctioned to the inner side of the guide unit  420  from the inlet duct  400  as shown in  FIG. 3A  and reaches the fluid path  422  in the vicinity of the sensor chip  300  (in the broadest sense, the optical device  4 ). In the example in  FIG. 10A , the optical device  4  includes a metal nano-structure. If the light Lin (incident light) is irradiated from the light source to the metal nano-structure, the enhanced electric field is formed in the gap of the convex portion  105 . In the example in  FIG. 10B , an irradiation range of the light Lin (incident light) is illustrated as a dotted line. In addition, in a case where the target molecule enters the enhanced electric field, the Raman scattering light is generated including information on the frequency of the target molecule. In addition, the Raman scattering light is enhanced by the enhanced electric field, and the surface-enhanced Raman scattering is generated. Although the incident light is irradiated from the rear side (the substrate  100  side) of the optical device  4  in the example in  FIG. 10A , the incident light may be irradiated from the surface side of the sensor chip  300  (the convex portion  105  side), as shown in  FIG. 10C . 
     If the gap between the convex portions  105  becomes small and the height of the convex portion  105  (the depth of the concave portion  104 ) becomes large, generally, the enhanced electric field shown in  FIG. 10A  becomes strong. In addition, as the intensity of the light Lin (incident light) becomes higher, the enhanced electric field becomes strong. However, if the gap between the convex portions  105  is too narrow, the probability in which the target molecule enters the gap (enhanced electric field) becomes low. Therefore, the gap between the convex portions  105  can be set to several nm to several tens nm, for example. Further, if the height of the convex portion  105  (the depth of the concave portion  104 ) becomes large, the time in which the target molecule exits from the gap (enhanced electric field) after entering the gap (enhanced electric field) can be increased, and the detection signal or the Raman spectrum representing the Raman scattering light becomes stable. 
     In addition, the wavelength of the light Lin (incident light) may be selected based on the type of the metal of the metal nano-structure. In a case where the metal nano-structure is formed of gold (Au), the wavelength of the light Lin may be set to 633 nm. In addition, in a case where the metal nano-structure is formed of silver (Ag), the wavelength of the light Lin may be set to 514 nm. In addition, it is possible to select the wavelength of the light Lin depending on the type of the target molecule. In addition, in a case where the gaseous sample contains impurities other than the target molecule, the wavelength of the light Lin may be set to 780 nm in order to suppress fluorescence of the impurities. 
     2.5. Surface Plasmon Resonance Peak 
     When the light Lin (incident light) is irradiated onto the metal nano-structure (in the broadest sense, an electrical conductor) of the optical device  4  illustrated in  FIG. 10C , typically, only a single broad surface plasmon resonance peak exists. Therefore, it is necessary to set the position of the resonance peak to a suitable position in consideration of the excitation wavelength (equal to the Rayleigh scattering wavelength) and the Raman scattering wavelength. Therefore, if the resonance peak wavelength is set to a value between the excitation wavelength and the Raman scattering wavelength, it is possible to anticipate the electric field enhancement effect in both the excitation process and the Raman scattering process. However, since the resonance peak is broad, the intensity of the resonance is reduced in individual processes, and it can be said that the enhancement degree of the entire process is not sufficient. In this regard, it is possible to improve the detection sensitivity and the sensor sensitivity by introducing the incident light to the optical device  4  with an inclination to generate two resonance peaks and setting the two resonance peaks as the excitation wavelength and the Raman scattering wavelength. 
     In order to implement a high-sensitivity sensor chip  300  (in the broadest sense, the optical device  4 ) by applying the surface-enhanced Raman scattering, it is preferable that the enhancement degree of the local electric field (hereinafter, simply referred to as an enhancement degree) increases as large as possible. The enhancement degree α can be expressed as the following Equation (1) (M. Inoue, K. Ohtaka, J. Phys. Soc. Jpn., 52, 3853 (1983). In the Equation (1), αray denotes an enhancement degree using the excitation wavelength, and αram denotes the enhancement degree using the Raman scattering wavelength.
 
α=αray×αram  (1)
 
     Based on the Equation (1) described above, it is possible to increase the enhancement degree in the course of the surface-enhanced Raman scattering by simultaneously increasing both the enhancement degree in the excitation process and the enhancement degree in the Raman scattering process. Therefore as shown in  FIG. 11 , it is possible to generate two resonance peaks that are strong only in the vicinity of the excitation wavelength and the Raman scattering wavelength. As a result, it is possible to increase the enhancement effect of the local electric field by a synergy effect of both scattering processes. 
       FIG. 12  is a perspective view illustrating a configuration example of the sensor chip. As shown in  FIG. 12 , the sensor chip  300  includes a substrate  100  (base material) and a protrusion group  115  (a first protrusion group). The protrusion group  115  having a plurality of protrusions  110  contains an electrical conductor, and the electrical conductor is typically formed of metal (for example, gold (Au)) or may be formed of a semiconductor (for example, poly-silicon). 
     A plurality of protrusions  110  are periodically arranged in the first direction D 1  along the plane of the substrate  100  (in the broadest sense, a virtual plane). Here, the plane of the substrate  100  is the surface  120  of the substrate  100  where the protrusion group  115  is formed, and may be a plane parallel to the surface  120 . More specifically, each protrusion  110  of the protrusion group  115  is formed to have a convex shape from the surface  120  of the substrate  100  in a cross-sectional shape of the arrangement direction of the protrusions (first direction D 1 ). The convex shape may include a rectangular shape, a trapezoidal shape, a circular arc shape. For example, a cross-sectional shape defined by complicated curves as shown in  FIGS. 8D and 9E  may be used. For example, as shown in  FIG. 12 , the protrusion group  115  is formed to have a parallel stripe shape in the second direction D 2  perpendicular to the first direction D 1  as seen in a plan view for the substrate  100 . 
       FIG. 13  is a cross-sectional view illustrating a sensor chip in  FIG. 12 . The cross section of this cross-sectional view is perpendicular to the plane of the substrate  100  and parallel to the arrangement direction of the protrusion group  115  (first direction D 1 ). As shown in  FIG. 13 , the direction normal to the plane of the substrate  100  is set to a third direction D 3 . 
     In the example in  FIG. 13 , the substrate  100  has a glass substrate  130  and a metal thin film  140  formed on the glass substrate  130 . For example, the metal thin film  140  has a thickness equal to or larger than 150 nm. In the example in  FIG. 13 , the cross-sectional shape of the protrusion group  115  is rectangular (approximately rectangular), and the protrusions  110  having a first height H 1  are arranged with a first period P 1  along the first direction D 1 . A metal lattice  150  (periodically embossed metal structure) is formed by the metal thin film  140  and the protrusion group  115 . The first period P 1  is preferably set to a range between 100 and 1000 nm, and the first height H 1  is preferably set to a range between 10 and 100 nm. In addition, the glass substrate  130  may be substituted with a quartz substrate, a sapphire substrate. The substrate  100  may be formed using a metal plate. 
     The incident light Lin including plane polarization may be incident to the sensor chip  300 . The direction (polarization orientation) of the plane polarization is parallel to the surface parallel to the first direction D 1  and the third direction D 3 . In the example in  FIG. 13 , the incident light Lin is incident with an inclination with respect to the metal lattice  150  including the metal thin film  140  and the protrusion group  115  (in the broadest sense, an electrical conductor). Specifically, if the inclination angle is set to θ, θ&gt;0. The incident light is incident such that an angle between the direction incident to the cross section in  FIG. 13  and the direction opposite to the third direction D 3  (an angle with respect to the normal line directed to the plane of the substrate  100 ) becomes θ. 
     Preferably, the plane polarization is parallel to the surface parallel to the first direction D 1  and the third direction D 3 . However, the plane polarization may be nonparallel to the plane parallel to the first direction D 1  and the third direction D 3 . In other words, the plane polarization may contain a polarization component parallel to the surface parallel to the first direction D 1  and the third direction D 3 . In addition, the polarization direction of the plane polarization may be set by the distorting portion in  FIG. 5B , the polarization control element  330  in  FIG. 3A . 
       FIG. 14  illustrates an exemplary characteristic of the reflective light intensity of the sensor chip.  FIG. 14  illustrates an exemplary characteristic in the event that the metal lattice  150  is formed of silver Ag, the incident angle θ of the light for the metal lattice  150  is set to 3°, the polarization direction of the light is perpendicular to the groove direction of the metal lattice  150  (second direction D 2 ), the cross section of the protrusion  110  has a rectangular shape (approximately rectangular), the first period P 1  is set to 500 nm, and the first height H 1  is set to 20 nm. In the example in  FIG. 14 , the abscissa denotes the wavelength of the reflective light, and the ordinate denotes the reflective light intensity (a ratio with respect to the incident light intensity). 
     In the example in  FIG. 14 , two resonance peaks of the surface plasmon polaritons (SPP) exist in the metal lattice  150 . For example, a single resonance peak wavelength λp 1  is positioned in the vicinity of 515 nm, and the other resonance peak wavelength λp 2  is positioned in the vicinity of 555 nm. It is possible to obtain a significant enhanced Raman scattering effect by matching or adjusting the two resonance peak wavelengths λp 1  and λp 2  to the vicinity of the excitation wavelength λ 1  and the Raman scattering wavelength λ 2 , respectively. For example, in a case where Argon laser having a wavelength of 515 nm is used as the excitation wavelength λ 1 , it is possible to strongly enhance the Raman scattering light in the vicinity of a wavelength of 555 nm (Raman shift of 1200 to 1600 cm −1 ). 
       FIG. 15  is an explanatory diagram illustrating an excitation condition of the surface plasmon polaritons. The reference numeral C 1  in  FIG. 15  denotes a distribution curve of the surface plasmon polaritons (for example, a distribution curve at the interface between the air and gold (Au)), and the reference numeral C 2  denotes a light line. In  FIG. 15 , the period of the metal lattice  150  is set to a first period P 1 , and the wave number 2π/P 1  of the lattice vector in this case is illustrated on the abscissa. 
     First, a relationship between the metal lattice  150  and the excitation condition will be described. If the wave number of the incident light Lin is denoted by ki, and the incident angle is denoted by θ, the wave number of the primary evanescent wave in the arrangement direction of the metal lattice  150  (the first direction D 1  in  FIG. 13  or the opposite direction of the first direction D 1 ) is set to 2π/P 1 ±ki·sin θ. The surface plasmon polaritons are excited when the wave number 2π/P 1 ±ki·sin θ of the evanescent wave and the wave number of the surface plasmon match each other. That is, the excitation condition of the surface plasmon polaritons is determined by the cross point between the straight line indicating a condition for generating the evanescent wave and a distribution curve of the surface plasmon polaritons. 
     In C 3  in  FIG. 15 , as a comparison example, a straight line indicating a condition for generating the evanescent wave when light is incident perpendicularly (θ=0) to the metal lattice  150  is illustrated. As shown in C 3 , the wave number of the evanescent wave in this case is represented as 2π/P 1 . The straight line C 3  is a line extending on the position of the wave number of the lattice vector, and intersects with the distribution curve C 1  of the surface plasmon polaritons. In this case, a single cross point exists, and a resonance peak corresponding to the frequency ω 0  (angular frequency) is generated. 
     In C 4  and C 5 , a straight line indicating a condition for generating the evanescent wave is illustrated. In a case where light is incident with an angle θ (θ&gt;0) with respect to the metal lattice  150 , the wave number of the evanescent wave can be expressed as 2π/P 1 ±ki±sin θ. The straight line C 4  corresponds to 2π/P 1 +ki·sin θ, and the straight line C 5  corresponds to 2π/P 1 −ki·sin θ. Such straight lines C 4  and C 5  extend from the position of the wave number of the lattice vector with an inclination angle θ, and intersect with the distribution curve C 1  of the surface plasmon polaritons at two points (frequencies ω+ and ω−). Therefore, the two resonance peaks corresponding to the frequencies ω+ and ω− are represented as resonance peak wavelengths λp 1  and λp 2 . 
     Two resonance peak wavelengths λp 1  and λp 2  are set using the excitation condition of the surface plasmon polaritons, and the two resonance peak wavelengths λp 1  and λp 2  can be used in the surface-enhanced Raman scattering. Specifically, first, the distribution curve C 1  is obtained using a rigorous coupled wave analysis (RCWA) (L. Li and C. W. Haggans, J. Opt. Soc. Am., A10, 1184-1189 (1993)). The distribution curve C 1  is unique to the type of the metal, the type of the medium, or a cross-sectional shape of the metal lattice  150 . Then, a predetermined lattice period (for example, the first period P 1 ) and a predetermined incident angle θ are determined depending on the Raman shift of the target substance. That is, the first resonance peak wavelength λp 1  is set in the vicinity of the excitation wavelength λ 1  (Rayleigh scattering wavelength), and the second resonance peak wavelength λp 2  (λp 2 &gt;λp 1 ) is set in the vicinity of the Raman scattering wavelength λ 2 . In addition, the predetermined first period P 1  and the predetermined incident angle θ may be set such that the straight line C 4  passes through the cross point between the distribution curve C 1  and ω=ω+(λ=λp 1 ), and the straight line C 5  passes through the cross point between the distribution curve C 1  and ω=ω−(λ=λp 2 ). 
     In the example in  FIG. 14 , the first resonance peak wavelength band BW 1  including the first resonance peak wavelength λp 1  includes the excitation wavelength λ 1  in the surface-enhanced Raman scattering. The second resonance peak wavelength band BW 2  including the second resonance peak wavelength λp 2  includes the Raman scattering wavelength λ 2  in the surface-enhanced Raman scattering. Since the first period P 1  and the incident angle θ are set such that the resonance peak wavelength bands BW 1  and BW 2  include the resonance peak wavelengths λ 1  and λ 2 , respectively, it is possible to improve the electric field enhancement degree in the excitation wavelength λ 1  and the electric field enhancement degree in the Raman scattering wavelength λ 2 . 
     Here, the resonance peak wavelength bands BW 1  and BW 2  are bandwidths at the predetermined reflective light intensity, and may be a half-maximum full width of the peak. In addition, although λ 1 =λp 1  and λ 2 =λp 2  in  FIG. 14 , λ 1  may be different from λp 1 , and λ 2  may be different from λp 2 . 
       FIG. 16  illustrates another exemplary characteristic of the reflective light intensity of the sensor chip.  FIG. 16  illustrates an exemplary characteristic in the event that the metal lattice  150  is formed of gold (Au), the incident angle θ of the light with respect to the metal lattice  150  is set to 5°, the polarization direction of the light is perpendicular to the groove direction of the metal lattice  150  (second direction D 2 ), the cross section of the protrusion  110  is rectangular (approximately rectangular), the first period P 1  is set to 500 nm, and the first height H 1  is set to 40 nm. 
     In the example in  FIG. 16 , a single resonance peak wavelength λp 1  is positioned in the vicinity of 545 nm, and the other resonance peak wavelength λp 2  is positioned in the vicinity of 600 nm. It is possible to obtain a significant enhanced Raman scattering effect by adjusting or matching the two resonance peak wavelengths λp 1  and λp 2  in the vicinities of the excitation wavelength λ 1  and the Raman scattering wavelength λ 2 , respectively. 
     In the example in  FIG. 16 , compared to the example in  FIG. 14 , two resonance peaks are slightly broad and shallow. However, in comparison with the case where only a single resonance peak is used, the effect of enhancing the signal of the surface-enhanced Raman scattering is excellent. In addition, it is possible to suppress surface degradation caused by oxidation and sulfurization by using gold (Au). 
       FIG. 17  is a perspective view illustrating a modified example of the sensor chip of  FIG. 12 . Hereinafter, like reference numerals denote like elements as in  FIG. 12 , and description thereof will not be repeated. In the example in  FIG. 12 , the incident light Lin is preferably plane-polarized such that a component parallel to the plane of the substrate  100  of the polarization direction (the orthograph with respect to the plane of the substrate  100  of the polarization direction) is parallel to the arrangement direction of the first protrusion group  115  (first direction D 1 ). As a result, a compression wave of the free electron plasma is generated by the plane polarization along the first direction D 1 , and it is possible to excite the surface plasmon propagating along the arrangement direction of the first protrusion group  115 . 
     In the example in  FIG. 17 , a second protrusion group  205  formed of metal may be included on the top surface  220  of the first protrusion group  115 . Each of a plurality of protrusions  200  of the second protrusion group  205  is arranged with a second period P 2  (P 2 &lt;P 1 ) shorter than the first period P 1  along the direction parallel to the plane of the substrate  100  (first direction D 1 ). 
     In addition, in the example in  FIG. 17 , a third protrusion group  215  formed of metal may be included in the surface between the neighboring protrusions  110  of the first protrusion group  115  on the surface where the first protrusion group  115  is arranged (the bottom surface  230  between the neighboring protrusions  110  of the first protrusion group  115 ). Each of a plurality of protrusions  210  of the third protrusion group  215  is arranged with a third period P 3  (P 3 &lt;P 1 ) shorter than the first period P 1  along the direction parallel to the plane of the substrate  100  (first direction D 1 ). 
     As a result, the propagation type surface plasmon is excited by the first protrusion group  115 , and the localized surface plasmon is excited by that propagation type surface plasmon in the second protrusion group  205  or the third protrusion group  215 . As a result, it is possible to further improve the electric field enhancement degree in the excitation wavelength λ 1  and the Raman scattering wavelength λ 2 . 
     The protrusions  200  and  210  of the second protrusion group  205  and the third protrusion group  215 , respectively, are formed such that a cross-sectional shape in the arrangement direction of the protrusions  200  and  210  (first direction D 1 ) has a convex shape from the top surface  220  and the bottom surface  230 . The convex shape includes a rectangular shape, a trapezoidal shape and a circular arc shape. For example, as shown in  FIG. 17 , the second protrusion group  205  or the third protrusion group  215  is formed to have a stripe shape parallel to the second direction D 2  as seen in a plan view with respect to the substrate  100 . The second protrusion group  205  and the third protrusion group  215  may be formed of the same metal as that of the first protrusion group  115  or may be formed of other metal materials. 
       FIG. 18  is a cross-sectional view illustrating the sensor chip of  FIG. 17 . The cross section of  FIG. 18  is perpendicular to the plane of the substrate  100  and parallel to the first direction D 1 . As shown in  FIG. 18 , the protrusions  200  having a second height H 2  from the top surface  220  (the second protrusion group  205 ) are arranged with a second period P 2  shorter than the first period P 1 . The protrusions  210  (the third protrusion group  215 ) having a third height H 3  from the bottom surface  230  are arranged with a third period P 3  shorter than the first period P 1 . For example, the second period P 2  or the third period P 3  is preferably set to be equal to or shorter than 500 nm, and the second height H 2  or the third height H 3  is preferably set to be equal to or shorter than 200 nm. In addition, the third height H 3  may be set to be H 3 &gt;H 1  or H 3 ≦H 1 . 
     In the example in  FIG. 18 , the arrangement direction of the second protrusion group  205  or the third protrusion group  215  is the same as the arrangement direction of the first protrusion group  115  (the first direction D 1 ). However, the arrangement direction of the second protrusion group  205  or the third protrusion group  215  may be different from the first direction D 1 . In this case, the second period P 2  or the third period P 3  becomes the arrangement period in the first direction D 1 . 
     As described above, using the first protrusion group  115 , propagation type surface plasmons having two resonance peaks in the excitation wavelength λ 1  (Rayleigh scattering wavelength) and the Raman scattering wavelength λ 2  are excited. The surface plasmons propagate along the surface of the metal lattice  150  and excite the localized surface plasmons in the second protrusion group  205  or the third protrusion group  215 . In addition, the localized surface plasmons excite the enhanced electric field between the protrusions  200  and  210  of the second protrusion group  205  or the third protrusion group  215 , and the surface-enhanced Raman scattering is generated by the interaction between the enhanced electric field and the target substance. In this case, since the interval between the protrusions  200  and  210  of the second protrusion group  205  or the third protrusion group  215  is narrow, a strong enhanced electric field is excited between the protrusions  200  and  210 . For this reason, regardless of whether the number of target substances adsorbed between the protrusions  200  and  210  is singular or plural, it is possible to generate the surface-enhanced Raman scattering by the enhanced electric field. 
     2.6. Incident Angle 
       FIGS. 19A and 19B  are explanatory diagrams illustrating a technique for introducing incident light into a sensor chip  300  with an inclination. Hereinafter, the like reference numerals denote like elements as in  FIG. 1B , and description thereof will not be repeated. In the example in  FIG. 19A , the incident light Lin is inclined with respect to the sensor chip  300  by deviating an optical axis Lax 1  of a light source from an optical axis Lax 2  of an object lens  3 . In the example in  FIG. 19B , the optical axis Lax 1  of the light source matches with the optical axis Lax 2  of the object lens  3 , and the sensor chip  300  is inclined with respect to the optical axis Lax 2  of the object lens  3  so that the incident light Lin is inclined with respect to the sensor chip  300 . 
     In the example in  FIG. 19A , the sensor chip  300  is disposed on the support  430  perpendicularly to the optical axis Lax 2  of the object lens  3 . In addition, the incident light Lin is incident to the object lens  3  in parallel to the optical axis Lax of the object lens  3  by separating the optical axis Lax 1  of the single activated light source from the optical axis Lax 2  of the object lens  3  in a predetermined distance. The predetermined distance is a distance at which the incident angle of the incident light Lin with respect to the sensor chip  300  becomes θ by refraction in the object lens  3 . The light Lout from the sensor chip  300  is incident to the object lens  3  and guided to the half mirror  2  in  FIGS. 1A to 1D  by the object lens  3 . 
     In the example in  FIG. 19B , an angle between the normal line of the plane of the sensor chip  300  (the plane of the substrate  100 ) and the optical axis Lax 2  of the object lens  3  is set to θ. In addition, the incident light Lin from the single activated light source is incident along the optical axis Lax 2  of the object lens  3 . Then, the incident light Lin is incident to the sensor chip  300  with an incident angle θ without being refracted by the object lens  3 . In order to incline the sensor chip  300 , as shown in  FIG. 19B , the support  430  may be inclined. In addition, the support surface of the support  430  may be inclined by modifying the example in  FIG. 19B . 
     2.7. Optical Device (Metal Nano-structure Using Deposition) 
       FIGS. 20A and 20B  are schematic explanatory diagrams illustrating a method of manufacturing an electrical conductor. For example, a method of manufacturing a metal nano-structure using a photolithographic technique as shown in  FIG. 8A  is called a top-down technique, in which the metal nano-structure has a regular arrangement structure and also has a gap where an enhanced electric field is generated. In contrast, the metal nano-structure having an independent island shape formed through deposition has an irregular size or shape, and a gap where the enhanced electric field is generated is also irregular. That is, there is a place where the enhanced electric field is strong and a place where the enhanced electric field is weak, and a polarization direction of the incident light Lin also has freedom. However, since the metal nano-structure formed through deposition has a condition that a strong enhanced electric field is generated in some places, variations in the manufacturing can be advantageously absorbed. 
     For example, it is possible to manufacture a metal nano-structure through deposition using a vacuum deposition machine. As an exemplary deposition condition, borosilicate may be employed in the substrate  100 . In addition, silver (Ag) may be employed as deposition metal, and the silver (Ag) may be heated and deposited on the substrate  100 . In this case, the substrate  100  is not necessary to be heated, and the heating/deposition rate may be set to 0.03 to 0.05 nm/sec. 
       FIG. 20A  schematically illustrates a process of forming an island. At the initial stage of the deposition island, a seed of silver (Ag) is formed on the substrate  100 . At the growth stage of the deposition island, silver (Ag) is grown from the seed and increases in size. At the completion stage of the deposition island, while a distance between neighboring islands is reduced, the vacuum deposition may stop before the neighboring islands stick to each other. 
     In  FIG. 20B , an electron microscope photograph of the metal nano-structure manufactured in practice is illustrated. In general, Ag islands of approximately 25 nm are formed such that each of them is isolated. If deposition is carried out further, the Ag islands are connected to each other, and finally, form a film. Typically, it is necessary to deposit the islands in a regular film shape. However, in this case, it is preferable that the independent Ag islands be narrowly formed with a high density as long as possible. 
     As the plane-polarized light is irradiated onto such a metal nano-structure, a strong enhanced electric field is formed in the vicinity of the gap between the deposition islands while the position or the direction of the gap is not constant. The thing contributing to the enhanced electric field is a P-polarized wave of the incident light Lin matching with the direction of the gap. A strong enhanced electric field may be formed by the polarization direction, or a slightly weak enhanced electric field may be formed. 
     2.8. Spectroscopic Analysis 
       FIGS. 21A to 21C  are schematic explanatory diagrams illustrating peak extraction of the Raman spectrum.  FIG. 21A  illustrates a Raman spectrum detected when excitation laser is irradiated onto a certain substance, in which the Raman shift is expressed using a wave number. In the example in  FIG. 21A , it is recognized that a first peak (883 cm −1 ) and a second peak (1453 cm −1 ) are characteristic. By checking the obtained Raman spectrum against the data stored in advance (for example, checking the light intensity and the Raman shift of the first peak, and against the light intensity and the Raman shift of the second peak), it is possible to specify the target substance. 
       FIG. 21B  illustrates a signal intensity (white circle) when a spectrum around the second peak is detected by the optical receiver element  380  using a spectroscopic element  370  having a low resolution (40 cm −1 ).  FIG. 21C  illustrates a signal intensity (white circle) when a spectrum around the second peak is detected by the optical receiver element  380  using a spectroscopic element  370  having a high resolution (10 cm −1 ). When the resolution is high such as 10 cm −1 , it becomes easy to accurately specify the Raman shift (black circle) of the second peak. 
     While the embodiments of the invention have been described in detail in the foregoing description, it will be appreciated by those skilled in the art that various modifications can be made without substantially departing from the novel matter and effects of the invention. Therefore, such various modifications are intended to be included in the scope of the invention. For example, through the description and the drawings, the terminologies referred to at least once together with other words which may be broader or have the same meaning may be substituted for other terms in any parts of the description or the drawings. In addition, configurations or operations of the optical device, the detection apparatus and the analysis apparatus may be variously modified without limitation to the embodiments of the invention. 
     The entire disclosure of Japanese Patent Application No. 2010-205510, filed Sep. 14, 2010 is expressly incorporated by reference herein.