Abstract:
The invention aims to improve the spatial resolution in a multi-focus type electrophoresis apparatus that irradiates a capillary array from both ends thereof with laser beams. The invention relates to an electrophoresis apparatus in which capillaries at both ends of a capillary array are irradiated respectively with laser beams, and each of the two laser beams traverses multiple capillaries. In the electrophoresis apparatus, the laser beams are coaxially introduced into the capillary array from the both ends thereof to travel in a direction vertical to axis of each capillary and horizontal to the aligrnent plane of the capillary array; and a λ/4 plate and a polarizer are arranged on the laser beam optical axes. According to the invention, the total width of the incident laser beams is made narrow, generation of pseudo signals is prevented, and an analysis performance is improved.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a technology for separating and analyzing nucleic acids, proteins and the like by electrophoresis. The present invention relates to, for example, a capillary electrophoresis device. 
         [0003]    2. Description of the Related Art 
         [0004]    An electrophoresis method using a capillary has been used for such purposes as determination of DNA base sequences and base lengths. Multiple capillaries are required to be irradiated with exciting light in a capillary electrophoresis device, and methods for irradiating the multiple capillaries with light include a multi-focus method disclosed in Japanese Patent Application Publication No. 2001-324472. 
         [0005]    In this method, samples each containing fluorescently-labeled DNA are introduced into the respective capillaries, and the capillaries are irradiated with a laser beam so that the laser beam can be transmitted through the multiple capillaries aligned in line. The capillary array is formed of the multiple capillaries aligned on a planar substrate, and a capillary in any one end or capillaries in both ends of a capillary array are irradiated with a laser beam. The laser beam is successively transmitted from one capillary to the next, thereby traversing the capillary array. The fluorescently-labeled DNA generates fluorescence by the laser beam with which the capillaries are irradiated. The luminescence generated from the capillary array is detected by a light detection device. By measuring the fluorescence generated by the capillaries one by one, DNA analyses on the samples introduced into the respective capillaries can be conducted. Analyses on proteins can be performed in the same manner. 
         [0006]    In the multi-focus method, laser instability is caused by reflected and transmitted feedback light. Specifically, in a case where the capillary array is irradiated with a laser beam from only one end thereof, there is a problem that reflected light from a surface of the capillary array returns to a laser oscillator, and destabilizes laser oscillation thereof. On the other hand, in a case where the capillary array is irradiated with laser beams from both ends thereof, there is a problem that not only reflected light from the surfaces of the capillary array but also light having passed through the capillary array returns to a laser oscillator, and destabilizes laser oscillation thereof. In order to solve these problems, Japanese Patent Application Publication No. 2001-324472 shows a method in which angles are formed in the laser beams introduced into both ends of the capillary array. 
       SUMMARY OF THE INVENTION 
       [0007]    The present inventors conducted studies to improve the analysis performance of the multi-focus method, and, as a result, found out the following problems. 
         [0008]    As described in Japanese Patent Application Publication No. 2001-324472, in order to prevent from capillaries, laser beams may be introduced from both ends of a capillary array with its optical axis inclined at a certain angle, and be controlled to meet each other around the center of the capillary array where the laser beams from both the ends have almost the same irradiation intensity. In this case, however, the laser beams from both the ends do not meet each other in a vicinity of either of the ends of the capillary array. Consequently, the capillaries are irradiated with the laser beam thicker in appearance than each of the laser beams originally radiated. 
         [0009]    Additionally, in a case where a laser beam is inclined to axes of the capillaries so as to prevent reflected feedback light, the incident laser beam is reflected in an interface between air and an external wall of each of the capillaries, and in an interface between gel and an internal wall of each of the capillaries. The reflected light beams are each also inclined to the axes of the capillaries, and thus is reflected multiple times, thereby generating multiple reflected light beams along axes different from an axis of the incident laser beam. As a result, the apparent diameter of the laser beam is large. 
         [0010]    A laser beam with which the capillaries are irradiated is actually thick, and additionally, an intensity distribution of this laser beam is not expressed as an ideal Gaussian curve, but has a wide bottom. Thereby, a spectral shift is observed in measured data and a large pseudo signal is generated after matrix conversion of the data. 
         [0011]    In a fragment analysis using a capillary electrophoresis device for the purposes of human identification and the like, reduction of this false signal is demanded. To meet this demand, the width of an incident laser beam on capillaries needs to be narrow. Incident laser beams from both end sides of the capillaries has the smallest diameter when these laser beams form one straight line, which is the ideal condition. 
         [0012]    When orthogonal projections of the above two incident laser beams with respect to a plane formed by the capillary array are not substantially parallel to each other, the total diameter of these two laser beams joined together is larger than that of two laser beams coaxially emitted. Due to such large laser beam diameter, spatial resolution in fluorescence detection may be reduced. More specifically, in electrophoresis, DNA compositions are spatially separated in accordance with molecular weights while moving inside a capillary, and thus DNA bands are generated inside the capillary. In such electrophoresis, however, the large laser beam diameter may cause a reduction in resolution detection capability for these DNA bands. 
         [0013]    In order to avoid such problem, it is desired that the centers of the two laser beams overlap each other in the vicinity of the center of the capillary array. By thus emitting the two laser beams, enlargement of the laser beam diameter can be suppressed to the minimum. 
         [0014]    An object of the present invention is to improve spatial resolution in an electrophoresis device employing the multi-focus method in which a capillary array is irradiated with laser beams from both end sides thereof. 
         [0015]    The present invention relates to a configuration of an electrophoresis device in which capillaries at both ends of a capillary array are irradiated respectively with laser beams, and each of the two laser beams traverses the plurality of capillaries. In the configuration: the laser beams are coaxially introduced into the capillary array from the both ends thereof to travel in a direction vertical to axis of each capillary but horizontal to the alignment plane of the capillary array; and a quarter wavelength plate and a polarizer are arranged on the laser beam optical axes. 
         [0016]    According to the present invention, width of incident laser beams is made narrow, generation of false signal is prevented, and an analysis performance is improved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a schematic diagram of an electrophoresis device according to one example. 
           [0018]      FIGS. 2A and 2B  are schematic diagrams of an optical system of a first embodiment of the present invention where a solid state laser source is used. 
           [0019]      FIG. 3  is a schematic diagram of reflected feedback light and transmitted feedback light. 
           [0020]      FIGS. 4A and 4B  are schematic diagrams showing laser polarization directions according to a first embodiment of the present invention. 
           [0021]      FIGS. 5A and 5B  are schematic diagrams of an optical system of a second embodiment of the present invention where a solid state laser source is used. 
           [0022]      FIG. 6  is a characteristic curve diagram of a beam splitter according to the second embodiment of the present invention. 
           [0023]      FIGS. 7A and 7B  are schematic diagrams of an optical system of a third embodiment of the present invention where a solid state laser source is used. 
           [0024]      FIGS. 8A and 8B  are schematic views of an optical system of a fourth embodiment of the present invention where a solid state laser source is used. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    Description will be given below of the above described and other innovative characteristics and advantages of the present invention in consideration of the drawings. However, the drawings are provided mainly for the explanatory purpose, and are not intended to limit the present invention. 
         [0026]    In the following examples, disclosed is an electrophoresis device which is capable of blocking transmitted feedback light and reflected feedback light. In the electrophoresis device, a capillary array having a plurality of capillaries aligned in a plane is irradiated at both ends thereof respectively with laser beams; each of the laser beams is then transmitted through the capillaries from one to another so as to traverse the capillaries, thereby generating luminescence in each of the capillaries; and the luminescence thus generated is detected. In the electrophoresis device, the laser beams are coaxially introduced into the capillary array from the both ends thereof to travel in a direction vertical to the axis of each capillary and horizontal to the alignment plane of the capillary array, and a quarter wavelength plate and a polarizer are arranged on the axis of the laser beams so as to block transmitted feedback light and reflected feedback light. 
         [0027]    Additionally, disclosed is an electrophoresis device a capillary array having a plurality of capillaries aligned in a plane is irradiated at both ends thereof respectively with laser beams; each of the laser beams is then transmitted through the capillaries from one to another so as to traverse the capillaries, thereby generating luminescence in each of the capillaries; and the luminescence thus generated is detected. In the electrophoresis device, the capillary array is irradiated from both ends thereof with two laser beams so that optical axes of the laser beams overlap each other, the quarter wavelength plate is arranged so that each of transmitted feedback light and reflected feedback light passes through the quarter wavelength plate twice, and the polarizer is arranged so as to be reached by the transmitted feedback light and reflected feedback light whose phases is rotated by 90 degrees through the quarter wavelength plate. 
         [0028]    Additionally, disclosed is the electrophoresis device in which a solid state laser is used as a source of the laser beams. 
         [0029]    Additionally, disclosed is the electrophoresis device in which a laser beam oscillated by a laser source is split into two laser beams by a beam splitter, the capillary array is irradiated with the two laser beams from both ends thereof, the polarizer is arranged in a route of the laser beam before the laser beam is split, and the quarter wavelength plate is arranged in each of routes of the laser beams after the laser beam is split. 
         [0030]    Additionally, disclosed is the electrophoresis device in which, a laser beam oscillated by a laser source is split into two laser beams by a non-polarizing beam splitter (Non-polarizing half mirror), the capillary array is irradiated with the two laser beams from both ends thereof, and the polarizer and the quarter wavelength plate are arranged in a route of the laser beam before the laser beam is split. 
         [0031]    Additionally, disclosed is the electrophoresis device in which, a laser beam oscillated by a laser source is split into two laser beams by a beam splitter, the capillary array is irradiated with the two laser beams from both ends thereof, and the polarizer and the quarter wavelength plate are arranged in each of routes of the laser beams after the laser beam is split. 
         [0032]    Additionally, disclosed is the electrophoresis device in which, the laser beam is reflected by a mirror having a reflection characteristic in which phases of s-polarization light and p-polarization light are kept unchanged. 
       EXAMPLE 1 
       [0033]      FIG. 1  is a schematic view of an electrophoresis device according to this example. A configuration of this apparatus will be described with reference to  FIG. 1 . 
         [0034]    This apparatus is comprised of: a detection portion  116  used for optically detecting samples; a thermostatic chamber  118  used for maintaining capillaries at a constant temperature; a auto sampler  125  used for transporting various containers to the cathode end of the capillaries; a high-voltage power supply  104  used for applying a high voltage to the capillaries; a first ammeter  105  used for detecting a current generated by the high-voltage power supply; a second ammeter  112  used for detecting a current flowing in an anode electrode; a capillary array  117  formed by one or more capillaries  102 ; and a pump mechanism  103  used for injecting polymer into the capillaries. 
         [0035]    The capillary array  117  is a replaceable member including 24 capillaries, and includes a load header  129 , the detection portion  116 , and a capillary head. When a measurement method is changed, the capillary array is replaced, and lengths of the capillaries are adjusted. Additionally, the capillary array  117  is replaced with a new one when there is damage to, or deterioration in quality of the capillaries. 
         [0036]    Each of the capillaries is formed of a glass tube having an internal diameter of several ten to several hundred micrometers, and having an external diameter of several hundred micrometers. A surface of the capillary is coated with polyimide so as to be increased in strength. However, a light-irradiated portion of the capillaries to be irradiated with a laser beam is removed of the polyimide coating so that luminescence inside the capillary can easily come out. The inside of the capillary  102  is filled with a separation media so that imparted sample travels in different migration speeds during electrophoresis. While both fluid separation mediums and non-fluid separation media exist as separation mediums, a fluid polymer is used as the separation medium in this example. 
         [0037]    The detection portion  116  is a member which acquires information depending on samples, and is irradiated with exciting light to emit light having wavelengths depending on samples. The vicinities of the light-irradiated portions of the 24 capillaries are fixedly arrayed on an optical flat plane with tolerances of several micrometers. During electrophoresis, the capillaries are irradiated from both ends thereof with two laser beams positioned substantially coaxially to each other, and the two laser beams successively pass through all of these light-irradiated portions. By these laser beams, information light (fluorescence having wavelengths depending on samples) is generated from the samples, and travels through the light-irradiated portions to the outside. This information light is detected by an optical detector  115 , and the samples are analyzed. 
         [0038]    Capillary cathode electrode  127  are fixed to the respective capillaries  102  through metallic hollow electrodes  126 , whereby the capillaries have tips thereof protruding from the respective hollow electrodes  126  by about 0.5 mm. Additionally, all of the hollow electrodes  126  of capillaries are, as one body, mounted on the load header  129 . Furthermore, all of the hollow electrodes  126  are electrically connected to the high-voltage power supply  104  installed in a main body of the apparatus, and thereby operate as cathode electrodes when it is necessary to apply a voltage, that is, when electrophoresis, sample introduction or the like is carried out. 
         [0039]    Ends (the other end portions) of the capillaries, which are opposite to the capillary cathode electrode  127 , are bundled together as one by the capillary head. The other end portions of the capillaries are members detachably attached in a pressure-resistant and air-tight condition in one bundle. The capillary head can be connected to a block  107  in a pressure-resistant and air-tight condition. Then, insides of the capillaries are filled with unused polymer by a syringe  106  from the other end portions. Replacement of polymer inside the capillaries is made every time measurement is newly conducted, so that performances of measurement can be enhanced. 
         [0040]    The pump mechanism  103  is comprised of: the syringe  106 ; and a mechanism system used for pressuring the syringe  106 . The block  107  is a connecting portion for causing the syringe  106 , the capillary array  117 , an anode buffer container  110 , and a polymer container  109  to communicate with one another. 
         [0041]    An optical detection portion is comprised of: a light source  114  used for illuminating the detection portion  116 ; and an optical detection device  115  used for detecting luminescence inside the detection portion  116 . When the optical detection portion detects samples separated by electrophoresis in the capillaries, the light source  114  irradiates the light-irradiated portions of the capillaries, and the optical detection device  115  detects luminescence from the light-irradiated portions. 
         [0042]    The thermostatic chamber  118  is covered with a heat insulating material and a heating/cooling mechanism  120  controls the temperature so that a temperature inside the thermostatic chamber  118  can be kept constant. Additionally, a fan  119  circulates and stirs air inside the thermostatic chamber  118 , whereby temperatures of the capillary array  117  are kept uniform and constant regardless of positions thereof. 
         [0043]    The auto sampler includes three electric motors and linear actuators, thereby being capable of moving in three axial directions, namely, vertical, horizontal, and depth directions. A moving stage  130  of the auto sampler  125  can carry at least one container thereon. The moving stage  130  is provided with an electrically-driven grip  131 , by which a container can be held and released. Consequently, the auto sampler  125  can transport a buffer container  121 , a washing container  122 , a waste-liquid container  123 , and a sample plate  124  being a sample container to the cathode electrode as necessary. Note that unnecessary containers are stored in a predetermined storage in the apparatus. 
         [0044]    The apparatus main body  101  is used in a state connected to a control computer  128  via a communication cable. Through the control computer  128 , an operator can control functions of the apparatus, and can receive data detected by the detection device in the apparatus. 
         [0045]      FIGS. 2A and 2B  are schematic views showing a detection portion of a capillary array, an optical detection portion, and introduction routes of laser beams in this example. A shutter and a filter are publicly known elements in this technical field, and are omitted for simplification.  FIG. 2A  is a side schematic view, and  FIG. 2B  is a front schematic view. 
         [0046]    The optical detection portion in this example includes: a solid state laser  201  which oscillates a laser beam  202 ; a beam splitter  205  which splits the laser beam  202 ; reflecting mirrors  203  each of which changes a travelling direction of a laser beam; and laser condensing lenses  206  which condense laser beams toward the detection portion of the capillary array. Immediately after the solid-state laser  201 , a polarizer  204  such as a sheet polarizer or a polarizing cube is arranged which is an optical element transmitting only light polarized in one direction. Additionally, two wavelength plates (quarter wavelength plate)  207  are arranged on both ends of the capillary array so that linear polarization of the laser beam  202  can be changed into circular polarization light before the laser beam  202  reaches capillaries  208 . There, DNA is detected through observation of fluorescence emitted from the detection portion. 
         [0047]    The detection portion of the capillary array is formed by having 24 capillaries  208  fixedly aligned on a reference base  209 . Each of the capillaries is formed of a quartz glass tube coated with a polymer thin film. In the detection portion, polymer coating is removed and is set in a state where quartz is exposed. Internal and external diameters of the quartz glass tube are 50 μm and 320 μm, respectively, and an external diameter of each of the capillaries including the polymer thin films is 363 μm. A pitch between each adjacent ones of the capillaries is equal to the capillary external diameter, and is 363 μm, and a width of the capillary array is 8.7 mm obtained by multiplying 363 μm by 24. A plane formed by central axes of the 24 capillaries on the reference base  209 , and a virtual plane obtained by extending the above plane to the whole space will be referred to as capillary-array aligned plane. Additionally, a virtual straight line existing on the capillary-array aligned plane, being vertical to the capillary axes of the 24 capillaries, and penetrating the center of the detection portion will be hereinafter referred to as an optical-axis base axis  210 . 
         [0048]    The laser beam  202  oscillated from the solid state laser  201 , which is a light source of a laser beam, is changed in travelling direction by the reflecting mirror  203 , passes through the polarizer  204 , and is split into two beams by the beam splitter  205 . The split laser beams are changed in travelling direction by the reflecting mirrors  203 , and are introduced from both end sides of the detection portion of the capillary array. 
         [0049]    Here, reflected and transmitted feedback light which are considered as a problem in this example will be schematically described by using  FIG. 3 . In this drawing, for the purpose of facilitating understanding of the reflected light and the transmitted light from the capillary array, incident light entering the capillary array is illustrated in a state slightly inclined with respect to a straight line vertical to the capillary axes. 
         [0050]    When a laser beam enters the capillary array, reflection of the incident laser beam occurs in an interface between air and an external wall of each of the capillaries, and in an interface between gel and an internal wall of each of the capillaries. Particularly in the firstly mentioned air/external-wall interface, a refractive index is large, and an intensity of the reflected light is therefore high. Since there are two air/external-wall interfaces per capillary, reflection in the air/external-wall interfaces occurs 48 times in the capillary array formed of the 24 capillaries. If reflected feedback light  301  from this capillary array reaches the laser source, it destabilizes laser. 
         [0051]    Additionally, transmitted feedback light  302  is transmitted light transmitted through the capillary array and emitted from an end side of the capillary array opposite from the side which the laser beam has entered. The transmitted feedback light  302  attenuates for amount equal to the reflected light, as compared to the incident light. If this transmitted feedback light  302  reaches the laser source, it destabilizes laser. 
         [0052]    As a countermeasure against the feedback light, this example employs a configuration where, as show in  FIG. 2 , each laser beam  202  irradiates the detection portion of the capillary array after passing through the laser condensing lens  206  and the wavelength plate (quarter wavelength panel)  207 . Here, the laser beam is condensed by the laser condensing lenses  206  (f=60 mm). Additionally, the wavelength plates (quarter wavelength panel)  207  change linear polarization of the laser beams  202  into circular polarization light. The laser beams  202  introduced from both ends of the detection portion of the capillary array is parallel to the capillary-array aligned plane, and is coaxial with respect to the optical-axis base axis  210 . 
         [0053]    A capillary which is located at one end of the capillary array and into which a laser beam is introduced will be hereinafter referred to as a first capillary. A distance between one of the laser condensing lenses  206  and the corresponding first capillary is 62 mm. The laser beam introduced into the first capillary is successively transmitted through one capillary to the next, and traverses the 24 capillaries. 
         [0054]    A laser beam (transmitted feedback light) transmitted through the detection portion of the capillary array also passes through the wavelength plate (quarter wavelength panel) which is on the opposite side of the capillary array. That is, the laser beam  202  having been circularly polarized by one of the wavelength plates (quarter wavelength panel) is linearly polarized again by the other wavelength plate (quarter wavelength panel). At this time, a direction of this linear polarization is rotated 90-degrees from a direction of linear polarization of the laser beam  202  before being introduced into any one of the wavelength plates (quarter wavelength panel). The transmitted feedback light takes the same route as the incident laser beam, and reaches the polarizer  204  arranged immediately before the solid state laser  201 . Here, the laser beam having passed through the wavelength plates (quarter wavelength panel)  207  twice is blocked by the polarizer  204 , and the transmitted feedback light cannot reach the light source. 
         [0055]    Additionally, as well as the transmitted feedback light, the reflected feedback light cannot reach the light source. Specifically, a laser beam (reflected feedback light) having been reflected by the detection portion of the capillary array again passes through the wavelength plate (quarter wavelength panel) which the laser beam has already passed through. That is, the laser beam  202  having been circularly polarized by the one of the wavelength plates (quarter wavelength panel) becomes linearly polarized again by the same wavelength plate (quarter wavelength panel). At this time, a direction of this linear polarization is rotated 90-degrees from a direction of linear polarization of the laser beam  202  before being introduced into any one of the wavelength plates (quarter wavelength panel). The reflected feedback light goes back a route which the laser beam  202  came, and reaches the polarizer  204  arranged immediately before the solid state laser  201 . Here, the laser beam having passed through the wavelength plates (quarter wavelength panel)  207  twice is blocked by the polarizer  204 , and the reflected feedback light cannot reach the light source. 
         [0056]    Here, polarization of the feedback light will be described in detail by use of  FIGS. 4A and 4B . The polarization of laser beam  202  before being introduced into the capillaries is linear polarization, and a direction of the polarization is a polarization direction  401 . Linear polarization of the laser beam  202  is changed into circular polarization  403  by the wavelength plate (quarter wavelength panel)  207  provided before the capillaries  208 , before the laser beam  202  reaches the capillaries  208 . A crystal axis of each of the wavelength plates (quarter wavelength panel)  207  is rotated 45-degrees in respect to the polarization direction  401 . The reflected feedback light  301  occurs from the laser beam  202  introduced into the capillaries  208 . Polarization of the reflected feedback light  301  is circular polarization  403 , and is changed back into linear polarization by passing through the wavelength plate (quarter wavelength panel)  207  again. At this time, a polarization direction of this linear polarization is a polarization direction  404 . The polarization direction  404  is rotated 90-degrees from the polarization direction  401  which is the linear polarization of the laser beam  202  before being introduced into any one of the wavelength plates (quarter wavelength panel)  207 . 
         [0057]    Moreover, the polarization of transmitted feedback light  302  from the capillaries  208  is circular polarization  405 , which is changed back into linear polarization through the wavelength plate (quarter wavelength panel)  207  on the other side of the capillaries  208  that the laser beam  202  have entered. At this time, a polarization direction of this linear polarization is changed into a polarization direction  406 . The polarization direction  406  is rotated 90-degrees from the polarization direction  401  which is the linear polarization of the laser beam  202  before being introduced into any one of the wavelength plates (quarter wavelength panel)  207 . 
         [0058]    As has been described above, in this example, the reflected feedback light and the transmitted feedback light can be blocked through the countermeasure against the feedback light. Consequently, an electrophoresis device in which the laser beam  202  introduced from both ends of the capillary array is parallel to the capillary-array aligned plane, and are coaxial to the optical-axis base axis can be provided without causing instability in the laser source due to the feedback light. The laser beams are coaxially introduced into the capillary array from the both ends thereof to travel in a direction vertical to axis of each capillary but horizontal to the alignment plane of the capillary array. Thereby, width of the incident laser beams entering the capillaries is made narrow, generation of false signal is prevented, and an analysis performance is improved. 
         [0059]    Additionally, a solid state laser is employed as the light source in this example. Since solid state lasers of some types are very unsusceptible to feedback light, configuration of the above laser beam optical axes is facilitated. 
       EXAMPLE 2 
       [0060]    In this example, unlike Example 1, a wavelength plate (half wavelength plate)  207  is provided immediately after the polarizer  204 . Example 2 will be described below while focusing on differences thereof from Example 1. 
         [0061]      FIGS. 5A and 5B  are schematic views showing a detection portion of a capillary array, an optical detection portion, and introduction routes of laser beams in this example. 
         [0062]    In this example also, the laser beam  202  passes through the wavelength plate (half wavelength panel)  207  firstly, thereby becomes circular polarization light, and then, is introduced into the capillary array. Reflected feedback light and transmitted feedback light occurring as a result of the laser beam introduced into the capillary array pass through the wavelength plate (half wavelength panel)  207  again, is thereby changed back into linear polarization with its polarizing direction rotated 90-degrees from polarizing direction of the laser beam  202  first emitted, and then, is blocked by the polarizer  204 . 
         [0063]    However, it is necessary to prevent deformation of the circular polarization light by use of a non-polarizing beam splitter  501  at this time. A characteristic of the non-polarizing beam splitter  501  is shown in  FIG. 6 . In this characteristic, in a certain wavelength, both s-polarization light and p-polarization light show a reflectance of 50% and a transmittance of 50%, and phases of the lights are kept unchanged. 
         [0064]    In this example, the number of the wavelength plates (quarter wavelength panel)  207  used in the apparatus can be set to one. 
       EXAMPLE 3 
       [0065]    In this example, unlike Example 1, the laser condensing lenses  206  and wavelength plates (quarter wavelength panel)  207 , which are provided on both ends of the capillary array in Example 1, are provided before reflection mirrors  701 . Example 3 will be described below while focusing on differences thereof from Example 1. 
         [0066]      FIGS. 7A and 7B  are schematic views showing a detection portion of a capillary array, an optical detection portion, and introduction routes of laser beams in this example. 
         [0067]    In designing the electrophoresis device, once a laser diameter and an f-value of each condensing lens, which are necessary for focusing the laser beam  202  toward the capillaries, are determined, a distance between the corresponding laser condensing lens  206  and the first capillary  208  cannot be shortened. As a result, spatial restriction in the apparatus designing arises. 
         [0068]    In this example, the laser condensing lenses  206  and the wavelength plates (quarter wavelength panel)  207  are provided before reflecting mirrors  701 . As a result, a spatial allowance is produced while the distance between the corresponding laser condensing lens  206  and the first capillary  208  is secured, whereby downsizing of the apparatus is achieved. Note that the reflection mirror  701  has a reflection characteristic in which phases of s-polarization light and p-polarization light are respectively kept unchanged. 
       EXAMPLE 4 
       [0069]    In this example, further downsizing of Example 3 is achieved. Example 4 will be described below while focusing on differences thereof from Example 3. 
         [0070]      FIGS. 8A and 8B  are schematic views showing a detection portion of a capillary array, an optical detection portion, and introduction routes of laser beams in this example. 
         [0071]    In this example, in order to provide a further downsized apparatus, the routes taken by the laser beam  202  in Example 3 are positioned to have angles which are not 90 degrees. While an angle between light incident to and reflected from the reflecting mirror  203  is set to 90 degrees by setting each of the incidence and reflection angles to 45 degrees in Example 3, the laser beam  202  can be positioned with arbitrary angles being formed therein in this example. Thereby, the laser beam  202  can be positioned without restriction, and further downsizing of the apparatus can be achieved. Note that deformation of the circular polarization light should be prevented by using a non-polarizing beam splitter  501 . Additionally, the reflection mirrors  701  have a reflection characteristic in which phases of s-polarization light and p-polarization light are respectively kept unchanged. 
         [0072]    While the examples of the present invention have been described hereinabove, the present invention is not limited to these examples, and those skilled in the art will understand that various alterations can be made thereto within the scope of the invention described in the scope of claims. Appropriate combinations of the respective examples are also included in the scope of the present invention. 
       DESCRIPTION OF REFERENCE NUMERALS 
       [0073]      101  . . . apparatus main body,  102  and  208  . . . capillaries,  103  . . . pump mechanism,  104  . . . high-voltage power supply,  105  . . . first ammeter,  106  . . . syringe,  107  . . . block,  108  . . . check valve,  109  . . . polymer container,  110  . . . anode buffer container,  111  . . . electrode (GND),  112  . . . second ammeter,  113  . . . electrically-driven valve,  114  . . . light source,  115  . . . optical detection device,  116  . . . detection portion,  117  . . . capillary array,  118  . . . thermostatic chamber,  119  . . . fan,  120  . . . heating/cooling mechanism,  121  . . . buffer container,  122  . . . washing container,  123  . . . waste-liquid container,  124  . . . sample plate,  125  . . . auto sampler,  126  . . . hollow electrode,  127  . . . capillary cathode electrode,  128  . . . control computer,  129  . . . load header,  130  . . . moving stage,  131  . . . grip,  201  . . . solid-state laser,  202  . . . laser beam,  203  . . . reflecting mirror,  204  . . . polarizer,  205  . . . beam splitter,  206  . . . laser condensing lens,  207  . . . wavelength plate (quarter wavelength panel),  209  . . . reference base,  210  . . . optical-axis base axis,  301  . . . reflected feedback light,  302  . . . transmitted feedback light