Abstract:
A portable spectral imaging microscope includes a probe head coupled via fiber optic cabling to a laser source and to a spectrograph. The probe head is coupled to a position controller that is mounted on a base suitable for positioning adjacent to a sample. The position controller has five degrees of freedom that permits one to adjust the position and direction of the probe head relative to the sample over a wide range of dimensions and angles. The entire probe head can be easily moved in order to precisely align the objective lens to stationary samples for simultaneous viewing and spectral analysis.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application is related to U.S. Provisional Application S/ No. 60/350,847 filed Jan. 22, 2002, which is hereby incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention generally relates to portable spectroscopic imaging microscopes, including portable Raman imaging microscope systems and portable fluorescence imaging microscope systems.  
           [0004]    2. Description of Prior Art  
           [0005]    Conventional spectral microscope systems allow a sample to be viewed through a video camera or an eyepiece. However, the sample must generally be fixed on a movable stage or table of the microscope and moved toward or away from the objective lens to achieve proper focus as disclosed, for example, in U.S. Pat. Nos. 5,194,912; 5,442,438; 5,479,252; 6,002,476 and 6,069,690. For some applications, such as samples in a vacuum chamber, in an oven, or located in a manufacturing process, one cannot use such conventional spectral microscope systems. U.S. Pat. No. 6,008,894 discloses a Raman spectroscopy probe for analyzing specimens in adverse environments requiring remote focusing of the probe, and suggests mounting the probe to achieve nanometer positional variations. U.S. Pat. No. 6,115,528 discloses a fiber optic based probe assembly for use in hostile environments, but the probe heads do not allow the sample to be directly viewed and thus do not allow the collection of either a single or multiple spectra from precisely identified locations within a sample, as visually viewed through the same objective lens used to collect the spectra. One system that does allow the collection of either a single or multiple spectra from precisely identified locations within a sample, as visually viewed through the same objective lens used to collect the spectra is disclosed in my earlier U.S. Pat. No. 6,310,686, which does suggest manual and machine-powered manipulation of a probe head containing the objective lens, but required spacing from the sample by less than 1 cm and did not disclose any mechanism for accurately positioning the probe head.  
           [0006]    Despite the variety of spectral microscopic systems that have been developed, there remains a need for a portable spectroscopic microscope system that is easily adapted to a variety of work environments and allows the simultaneous observation of the sample and acquisition of spectral information from the sample. There is a further need for a spectroscopic microscope system that can be used any angle and is sufficiently portable to be brought to a stationary sample rather than requiring that the sample be set on a translation stage for alignment to a fixed microscope objective. There is particularly a need for a portable spectroscopic microscope system having the forgoing mobility that requires no optical realignment upon movement of the system from one position to another.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    The forgoing needs are met by a spectroscopic microscope of the present invention. The microscope system comprises a source of spectral energy, typically taking the form of a laser that is coupled to a probe head containing an objective lens system for directing spectral energy from the source toward a sample. The coupling can include fiber optic elements, spatial filters, band pass filters, lenses, mirrors, and other optical transmission elements defining an optical path between the source of spectral energy and the objective lens. Any of the elements forming the optical path between the source of spectral energy and the objective lens can be included in the probe head. The spectral energy can take the form of white-light and/or expanded laser light.  
           [0008]    The microscope system also comprises collection elements coupled to the objective lens for receiving energy returned from the sample. The collection elements can also be located in the probe head and include an optical image collection device coupled to the collection elements for extracting a visual image of the sample. The optical image collection device can comprise a lens, a mirror, and a CCD camera driven by known software to produce a signal that can be supplied to a visual monitor for real-time optical observation and evaluation of the sample. For example, the visual image can be derived from a built-in video camera for viewing the sample that can take the form of either with a video monitor or CRT, or by using video frame grabbing software on a computer, such as a conventional PC.  
           [0009]    The microscope system also comprises a spectral collection device that is coupled to the collection elements for extracting a spectral characteristic of the sample. The spectral collection device can include a lens system, a spatial filter, a Rayleigh rejection filter, fiber optic elements and a spectrograph, preferably one capable of collecting Raman spectrographic information from the sample. Any of the elements of the spectral collection device can be included in the probe head so that movement of the probe head achieves coordinate movement of the location of the spectral characteristic extraction.  
           [0010]    The spectroscopic microscope system of the present invention also comprises a base that is adapted to be situated adjacent to a sample for supporting the probe head containing at least some of the forgoing optical components above any convenient substrate in the vicinity of the sample. A position controller is coupled to the base and the probe head for adjusting the position of the objective lens and related optical components with respect to the sample. The relative position of the objective lens is ascertained at least in part by observation of the visual image of the sample derived from the optical image collection device.  
           [0011]    The source of spectral energy, which generally takes the form of a laser, and the spectrograph are coupled to the probe head by fiber optic cabling. The characteristics of these components, such as laser wavelength, bandwidth, power and spectrograph focal length, grating groove density, spectral resolution, spectral window and optical design, can be custom tailored to the specific needs of the samples to the tested. The probe head position is adjustable for alignment to stationary samples. The probe head can also be used at any angle, vertically and horizontally. The probe head can have a working distance from the sample of up to about 2.5 cm, so one can use the present invention to look through windows in vacuum systems, oven or gas handing systems, etc. The magnification and working distance of the probe head can be changed by replacing the objective lens system much as is done in conventional microscopes, using standard or custom microscope objectives.  
           [0012]    One of feature of a spectroscopic microscope of the present invention is that it incorporates both spectral and video image collection optics which are contained in a common probe head and both coupled to the sample through the same objective lens. Thus observation of the sample and acquisition of spectra can be performed simultaneously. Further any change of position of the probe that might affect a change in the spectra from the sample is automatically tracked by the video image.  
           [0013]    A further feature of spectroscopic microscope of the present invention is that it can be used any angle and brought to a stationary sample rather than requiring that the sample be set on a translation stage for alignment to a fixed microscope objective. Furthermore, when implemented using a collection fiber bundle containing multiple optical fibers (and an imaging spectrograph with sufficient resolution to separately view each fiber), a spectroscopic microscope of the present invention can be used to simultaneously collect multiple spectra, each originating from a different precisely defined location within the video field of view.  
           [0014]    The spectroscopic microscope of the present invention differs from a fiber coupled probe head used for collecting Raman spectra for industrial and laboratory process monitoring since the spectroscopic microscope of the present invention allows direct viewing of the sample from which spectra are collected. This is due to the fact that the spectroscopic microscope of the present invention includes built-in video camera that makes it possible to visually align the objective and thus insure that spectra are collected from a precisely identified region in a sample.  
           [0015]    These and other features and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following description of a preferred embodiment of the present invention that is shown in the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a block diagram of the functional elements of spectroscopic microscope of the present invention.  
         [0017]    [0017]FIG. 2 and FIG. 3 are ray diagrams of two possible implementations of the illumination, collection and video camera optics of the present invention.  
         [0018]    [0018]FIG. 4 is a sectional view of a probe head suitable for use in the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    A portable spectroscopic imaging microscope system  10  of the present invention is shown in block diagram form in FIG. 1. The system  10  includes a laser  12  coupled by a fiber optic cable  14  to a probe head  16 . The probe head  16  includes filter elements  18  and optical path defining elements  20  that direct energy from the fiber optic cable  14  to an objective lens  22  to illuminate a specimen or sample S. The probe head also includes collection optical path defining elements  24  that are arranged to intercept any desired spectral signal reflected, scattered or emitted by the illuminated sample S passing back through the objective lens  22 . The collection optic elements  24  direct a portion of the reflected, scattered or emitted signal to a CCD camera  26  to form a visual image signal of the sample S. The visual image signal is transmitted to a monitor  28  by way of a suitable cable  30 . The collection optics  24  also direct a portion of the reflected, scattered or emitted signal to filter elements  32  designed to allow only a desired band width of energy through to a spectrograph  34  that is coupled to the collection optics  24  in the probe head  16  by fiber optic cable  36 .  
         [0020]    The system  10  also includes a base  40  that can be positioned on any underlying substrate so as to be situated conveniently close to the specimen S. The base  40  generally supports a stand  42  that is generally vertical and defines a vertical or polar axis. A position controller  44  can be coupled to the base  40 , or the vertical stand  42 , and to the probe head  16  to permit the probe head  16  to be situated any desired location and aimed in any direction relative to the specimen S. The position controller  44  includes a height adjustor  45  that is capable of moving the probe head  16  vertically through a distance Y of 10 cm or more. The position controller  44  can also include first and second horizontal adjusters  46  and  47  that are capable of moving the horizontally through distances X and Z of 10 cm or more with micrometer accuracy. The position controller  44  can also include an azimuth angle adjuster  48  that can tilt the probe head  16  through an azimuth angle φ relative to the vertical or polar axis through a range of at least 45°. The position controller  44  can also include a polar angle adjuster  49  that can rotate the probe head  16  through a polar angle Θ relative to the base of at least 45°.  
         [0021]    [0021]FIGS. 2 and 3 show two alternative optical arrangements that can be employed in the probe head  16 . Additional optical arrangements are possible and FIGS. 2 and 3 are intended to merely be exemplary. In FIG. 2, an illuminating collimated beam of light  51  travels from a source, not shown, toward a mirror  52 , which redirects the illuminating beam  51  toward a small area at the center of a holographic notch filter or dichroic optical filter  53 . The illuminating beam is again reflected by the filter  53  along a principal axis of the probe head  16  through a beam splitter  54 . The beam splitter  54  can be a long-pass filter to transmit laser and spectral light while reflecting shorter wavelength light. The illuminating beam is preferably in the visible or near infrared region of the spectrum, and so continues in a straight line through the beam splitter  54  toward the objective lens system  55  that focuses the illuminating beam on a selected portion  6  of the sample or specimen S. The exact location of the selected portion  6  and the angle of incidence of the illuminating beam on the specimen S is determined by the position controller  44  shown in FIG. 1. Additionally, the direction of the principal axis of the probe head  16  is also determined by the position controller  44 .  
         [0022]    As a consequence of the illumination of the specimen S by the illuminating beam, the specimen S reflects, scatters or emits some of the energy at the same or longer wavelength. Some of this reflected, scattered or emitted light is collected by the objective lens system  55  and directed back toward the beam splitter  54 , which reflects the shorter wavelength light and a small percentage of the laser light toward the input lens  57  of a video camera  58  that allows one to directly view the sample and focal spot of laser. The specimen S also reflects, scatters or emits some of the energy in the longer wavelength infrared spectral region of the spectrum. This spectral region is of particular interest as it is characteristic of molecular vibrational fundamentals of the various materials that form the specimen S. Some of this longer wavelength light is collected by the objective lens system  55  and directed back through the beam splitter  54 . To achieve this, the beam-splitter  54  can be either a long-pass filter that will transmit longer wavelength spectral light like Raman spectra and fluorescence while reflecting shorter wavelength light. The beam-splitter  54  can also be an anti-reflective coating beam-splitter to transmit the laser and spectral light of interest while reflecting a small percentage of light to the video camera  58 . The longer wavelength light continues through the filter  53 , which acts to exclude a wide range of wavelengths that are undesirable, leaving merely the wavelengths of interest  59  which can be directed to a suitable instrument for spectral analysis.  
         [0023]    In the arrangement shown in FIG. 3, an illuminating collimated beam of light  61  travels from a source, not shown, toward a mirror  62 , which redirects the illuminating beam  61  toward a small area at the center of a holographic notch filter or dichroic optical filter  63  in a manner similar to FIG. 2. The illuminating beam  61  is again reflected by the filter  63  along a principal axis of the probe head  16  to a beam splitter  70 . The beam splitter  70  can be either a short-pass filter to reflect laser and spectral light while transmitting shorter wavelength light and small percentage laser light or a neutral reflective beam splitter to reflect laser and spectral light while transmitting a small percentage of light. The illuminating beam  61  is redirected along a second principal axis of the probe head  16  toward the objective lens system  65  that focuses the illuminating beam on a selected portion  6  of the sample or specimen S. Again, the exact location of the selected portion  6  and the angle of incidence of the illuminating beam  61  on the specimen S can, be determined by a position controller  44  as shown in FIG. 1.  
         [0024]    Some of the reflected, scattered or re-emitted light is collected by the objective lens system  65  and directed back through the beam splitter  70  to the input lens  67  of a video camera  68  that allows one to directly view the sample and focal spot of the illuminating beam  61 . Some longer wavelength light is collected by the objective lens system  65  and directed back to the beam splitter  70  where it is redirected back along the first principal axis of the probe head  16 . The longer wavelength light again continues through the filter  63 , which acts to exclude a wide range of wavelengths that are undesirable, leaving merely the wavelengths of interest  69  which can be directed to a suitable instrument for spectral analysis. Since the direction of the principal axis of the probe head  16  is determined by the position controller  44 , the point from which the reflected, scattered or re-emitted light is collected by the objective lens system  65  is also determined by the position controller  44  of FIG. 1.  
         [0025]    One commercially available probe head  16  is shown in FIG. 4. Light of the correct laser source wavelength starts at the exit end  73  of optical fiber  74  in support  71 , and is collimated by lens  72 . The collimated laser beam  81  passes through the band-pass filter  76  in support  75 . The band-pass filter  76  controls the wavelength deviation of the source light  81  directed toward the sample S. After passing the band-pass filter  76 , the collimated laser beam  81  reflects off of mirror  82  toward filter  83  in support  84 . The optical filter  83  can be an interference filter or long pass filter designed to highly reflect wavelengths of the laser beam  81  and transmit light having a wavelength longer than the laser source. Alternatively, the optical filter  83  can be a holographic notch filter designed to highly reflect wavelengths of the laser beam  81  and transmit light having a wavelength that is either longer or shorter than the laser source. The reflective character of the filter  83  highly reflects the laser light beam  81  toward the objective lens system  85  and toward the sample S. The monochromatic laser light is scattered by the sample S creating a Raman signal that is typically about 1 part in 1 million of the reflected and scattered incident light.  
         [0026]    The Raman spectrum appears as light that is shifted to longer wavelength from the source laser beam  81 . The observed wavelength shifts are produced by molecular vibrational fundamentals of the various materials found in the sample S. The portion of scattered, reflected, and Raman or fluorescence light are collected and recollimated by the same objective lens  85  and directed parallel to the optical axis P of the probe head through the beam splitter  86 . The beam splitter  86  reflects a small percentage of the collected and recollimated light to video camera lens  87  in video camera  88 . The video camera  88  allows direct viewing of the sample S and focal spot of the laser beam  81  on the sample. Most of the collected and recollimated light is transmitted by the beam splitter  86  toward the filter  83 . Filter  83  rejects substantially all of the source laser light and transmits Raman scattering or fluorescence light, which have a longer wavelength than the source laser.  
         [0027]    Still, some un-rejected light at about the wavelength of the source laser beam  81  is usually able to pass through filter  83 . The un-rejected light of about the wavelength of the source laser coming through filter  83  can swamp some details of the Raman or fluorescence signal. A focusing lens  90  held by support  97  projects an image of the recollimated beam from the sample S into an aperture  91  at an entrance end  92  of spatial filter  100 . The spatial filter  100  acts to further extinguish the un-rejected light at about the wavelength of the source laser beam  81 . Within the spatial filter  100 , a first lens  93  is positioned to focus on the aperture  91 , so that any radiation passing through the aperture  91  is again collimated within spatial filter housing  99 . An interference filter or holographic notch filter  94  is selected to further reflect light at the laser wavelength and transmit Raman or fluorescence signals. A second lens  95  collects the signal passing through the filter  94  and focuses the signal on an entrance end  96  of optical fiber bundle  97  held in holder  99 . The fiber bundle  97  carries the Raman or fluorescence signal to the spectrograph and detector, not shown.  
         [0028]    Thus both the initial illuminating laser beam  81  and the recollimated beam transmitted by the beam splitter  86  toward the filter  83  are aligned with the axis P of the probe head  16 . Any movement of the probe head  16  has the effect of moving both the focal point of the illuminating beam  81 , and the area from which scattered and reflected light are collected and recolliminated by the objective lens system  85 . Further, despite any movement of the probe head, the collected and recolliminated light still travels parallel to the probe head axis P. Thus, the illumination and collection of information from a specimen S can be controlled by the control of a single position controller  44 . This enables the probe head  16  to be brought to the sample S rather than requiring the sample to be set on a translation stage for alignment to a fixed microscope objective as was commonly the practice with the prior art. Since the probe head  16  incorporates both spectral and video image collection optics coupled to the sample through the same objective lens, the built-in video camera  88  makes it possible, using the position controller  44  of FIG. 1, to visually align the objective lens system  85  and the principal axis X to the precise region of a sample S for spectral collection. A variety of readily interchangeable standard microscope objectives can be employed to better control the focusing.  
         [0029]    Although the invention has been described in detail with reference to a preferred embodiment, variations and modifications exist within the scope and spirit of the invention as described and defined in the following claims.