Patent Publication Number: US-2015085359-A1

Title: Microscope super-resolution illumination source

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The disclosure relates generally to illumination sources and more specifically, to alternative illumination sources for traditional optical microscopes. 
     2. Description of the Related Art 
     Traditional microscopy is diffraction-limited to spatial periods (p) larger than ˜λ/NA or separation between two points (Δx) larger than ˜0.5 to 0.8 times λ/NA where λ is the free space wavelength of the illuminating radiation and NA is the numerical aperture of the microscope&#39;s objective lens (see for instance the following publications: Feynman R P, Leighton R B, Sands M,  The Feynman Lectures on Physics , Addison-Wesley, Mass., Sixth Edition, Vol. I, pages 30-(1-5), 1977; Hecht E,  Optic , Addison Wesley, Mass., Third Edition, pages 439-472, 1998; Born M, and Wolf E,  Principles of Optics , Pergamon Press, Oxford, Fifth Edition, pages 418-424, 1975; Durant S, Liu Z, Steele J M, Zhang X, Theory of the transmission properties of an optical far-field superlens for imaging beyond the diffraction limit,  J. Opt. Soc. Am. B , vol. 23, pages 2383-2392, 2006). For instance, a typical optical microscope illuminated with a monochromatic source of illumination with λ=568 nm and NA=1.49, has a minimum resolvable values of p˜380 nm and Δx˜200 nm. 
     Optical images with sub-wavelength resolution have been achieved with several scanning techniques and non-scanning near-field approaches. Optical wide-field images with sub-wavelength resolution have also been obtained in the far-field by numerical reconstruction of the Moiré patterns formed directly in the image plane of the microscope or by using multilayer hyper-lenses. Surface waves of different nature have also being used to obtain far-field optical sub-wavelength resolution. However, all the above-mentioned optical imaging techniques require either special sample fabrication or intensive numerical image post-processing. 
     There is, therefore, a need for a non-scanning, far-field, optical imaging system with sub-wavelength resolution and method thereof that does not require special sample fabrication or intensive numerical image post-processing. 
     BRIEF SUMMARY OF THE INVENTION 
     A portable microscope super-resolution illumination (SRI) apparatus includes a two-dimensional (2D) array of individual sources of radiation distributed in the internal surface of a solid body. The microscope SRI apparatus further includes a power supply having an electronic circuit adapted to power and to control the array of individual sources of radiation. In one aspect of this embodiment, the individual sources of the microscope SRI apparatus emit radiation in the visible frequency range of the spectrum. In another aspect of this embodiment, the individual sources of the microscope SRI apparatus emit radiation in the infrared frequency range of the spectrum. In yet another aspect of this embodiment, the body housing has a shape selected from the group consisting of a cylinder, a paraboloid, an ellipsoid and a flat screen. 
     In another embodiment, a super-resolution microscope system can be provided. The super-resolution illumination (SRI) microscope system includes a conventional optical microscope and a portable microscope super-resolution illumination (SRI) apparatus adapted for use with the conventional optical microscope to provide direct observation of objects smaller than a wavelength of radiation used for illumination. The microscope SRI apparatus includes a two-dimensional (2D) array of individual sources of radiation distributed in the internal surface of a body housing, and a power supply with an electronic circuit designed to power and control the array of individual sources of radiation. In one aspect of this embodiment, the individual sources of the microscope SRI apparatus emit radiation in the visible frequency range of the spectrum. In another aspect of this embodiment, the individual sources of the microscope SRI apparatus emit radiation in the infrared frequency range of the spectrum. In yet another aspect of this embodiment, the body housing has a shape selected from the group consisting of a cylinder, a paraboloid, an ellipsoid and a flat screen. 
     Additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The aspects of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention. The embodiments illustrated herein are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown, wherein: 
         FIG. 1A  is a side view of an exemplary illustration of a hemisphere-shaped super-resolution illumination (SRI) source, in accordance with one embodiment of the present invention; 
         FIG. 1B  is a is a bottom view of an exemplary illustration of a hemisphere-shaped super-resolution illumination (SRI) source, in accordance with one embodiment of the present invention; 
         FIG. 2  is a block diagram illustrating the various components of a SRI microscope system, in accordance with one embodiment of the present invention; 
         FIG. 3A  is a side view of an exemplary illustration of a SRI source, according to an alternative embodiment of the present invention; 
         FIG. 3B  is a is a bottom view of an exemplary illustration of a SRI source, according to an alternative embodiment of the present invention; 
         FIG. 4  is an exemplary illustration of a cylindrical SRI source, according to yet another embodiment of the present invention; 
         FIG. 5  is an exemplary illustration of a cylindrical SRI source, according to an alternative preferred embodiment of the present invention; 
         FIGS. 6A and 6B  illustrate an instance of sub-wavelength resolution images obtained with a preferred embodiment of this invention in which  FIG. 6A  illustrates a real plane image and  FIG. 6B  illustrates a Fourier plane image obtained with a SRI-microscope arrangement corresponding to a sample with a period of 260 nm; 
         FIGS. 6C and 6D  illustrate an instance of sub-wavelength resolution images obtained with a preferred embodiment of this invention in which  FIG. 6C  illustrates a real plane image and  FIG. 6D  illustrates a Fourier plane image obtained with a SRI-microscope arrangement corresponding to a sample with a period of 220 nm; 
         FIGS. 7A and 7B  illustrate two instances of sub-wavelength resolution images obtained with a preferred embodiment of this invention, in which images obtained with a SRI-microscope arrangement correspond to a sample with C nanotubes, which have a diameter of 40-60 nm and a sample of human blood placed on top of a glass slide; 
         FIG. 8  illustrates an external control circuit that powers and controls the plurality of radiation sources of the SRI source of the SRI-microscope arrangement; 
         FIG. 9A  is a side view of an exemplary illustration of a SRI source, according to an alternative embodiment of the present invention; and 
         FIG. 9B  is a bottom view of an exemplary illustration of a SRI source, according to an alternative embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention provide an alternative super-resolution illumination apparatus for use with conventional optical microscopes. In accordance with an embodiment of the present invention, a portable microscope super-resolution illumination (SRI) apparatus includes a two-dimensional (2D) array of individual sources of radiation distributed on the internal surface of a housing body. The microscope SRI apparatus further includes a power supply having an electronic circuit adapted to power and to control the array of individual sources of radiation. In one aspect of this embodiment, the individual sources of the microscope SRI apparatus emit radiation in the visible frequency range of the spectrum. In another aspect of this embodiment, the individual sources of the microscope SRI apparatus emit radiation in the infrared frequency range of the spectrum. In another embodiment, a super-resolution microscope system can be provided. The super-resolution illumination (SRI) microscope system includes a conventional optical microscope and a portable microscope super-resolution illumination (SRI) apparatus adapted for use with the conventional optical microscope to provide direct observation of objects smaller than a wavelength of radiation used for illumination. The microscope SRI apparatus includes a two-dimensional (2D) array of individual sources of radiation distributed in the internal surface of a body housing, and a power supply with an electronic circuit designed to power and control the array of individual sources of radiation. 
     Traditional microscopy is diffraction-limited to spatial periods (p) larger than ˜λ/NA or separation between two points (Δx) larger than ˜0.5 to 0.8 times λ/NA where λ is the free space wavelength of the illuminating radiation and NA is the numerical aperture of the microscope&#39;s objective lens. For instance, a typical optical microscope illuminated with a monochromatic source of illumination with λ=568 nm and NA=1.49, has a minimum resolvable values of p˜380 nm and Δx˜200 nm. However, by using the present invention, a simple substitution of the traditional source of illumination of the microscope by a visible-light super-resolution illumination source, super resolution with minimum values of p˜200 nm and Δx&lt;100 nm can be obtained. These values can be reduced using an ultraviolet SRI source. In another embodiment, the invention also results in an infrared wide-field nanoscope with λ=1.5 μm having similar resolution limit than that demonstrated using visible light, which is much smaller than the resolution limit of any existing infrared microscope. 
     As in conventional optical microscopes, the object under observation is placed over a glass slide. In a preferred and demonstrated embodiment of this invention, a visible-light SRI source is fabricated using 560 light emitting diodes (LED) distributed uniformly on the inner surface of a hemisphere having a diameter of 10 cm. The object under observation is illuminated in all directions for the light emitted by the LEDs, which includes light with very large incidence angles and which results in the demonstrated sub-wavelength resolution of the SRI-microscope system. In conventional microscopy, imaging occurs in the SRI-microscope system after collection by the microscope objective lens of the light directly diffracted by the object under observation. An alternative embodiment of this invention uses an ultraviolet or an infrared (wavelength ˜1.5 μm) SRI source. Notably, the use of an infrared SRI source can produce infrared images with unprecedented sub-wavelength resolution and therefore obtain features fabricated on top of a silicon wafer. 
     Referring to  FIG. 1 , a super resolution illumination (SRI) device  100  can include a body housing  112  in the shape of a hemisphere. The SRI body housing  112  can include an external surface  114  and an internal surface  116 . The SRI body housing  112  further can include a plurality of sources of radiation  118  (e.g., light emitting diodes (LEDs)) that are uniformly or non-uniformly distributed on the internal surface  116 . The LEDs  118  are electrically connected through a cable  122  to an external circuit  120  that powers and controls the LEDs  118  As illustrated in  FIG. 8 , external circuit  120  can include a power supply  802  with a DC to DC converter  804 , which provides the necessary energy to the rest of the electronics including the master controller  808 . The external circuit  120  further can include a function generator  806  coupled to the master controller  808  and an input buffer  811 . The external circuit  120  further can include an X/Y position LED control  810  coupled to the master controller  808  and an input buffer  812 . The output of the input buffers  811 ,  812  can be input to a selector/decoder  814  that distributes the power to the input of smart current control  816 . The smart current control  816  powers and controls the plurality of radiation sources  818  (e.g., LEDs  118 ). The smart current control  816  regulates the output power of one or more of the plurality of radiation sources  818  such that the sources of radiation  818  can be simultaneously powered, equally powered or not equally powered. For example, at least one of the individual sources of radiation  818  is powered at a different power level from the power level of other individual sources of radiation  818 . Although  FIG. 1  illustrates that the body housing  112  is in the shape of a hemisphere, the SRI device  100  is not limited to just the shape of a hemisphere. It is contemplated that body housing  112  can take the shape of a partial hemisphere with a top portion removed (as shown in  FIG. 3 ), the shape of a cylinder (as shown in  FIG. 4 ), the shape of a flat screen (as shown in  FIG. 9 ) and/or other geometric shapes. 
     In general, in an embodiment of this invention, a two-dimensional (2D) array of individual sources of radiation  118  are distributed on the internal surface  116  of a body housing  112 , which has an arbitrary shape. As shown in  FIGS. 1 ,  3 - 4  and  9  in an embodiment of this invention the individual sources of radiation  118 ,  318 ,  418 ,  918  are LEDs. Moreover, the individual sources of radiation can be selected from the group consisting of omnidirectional LEDs, highly directional LEDs and ultra-bright LEDs. In an alternative embodiment of this invention as illustrated in  FIG. 5 , the individual sources of radiation are optical fibers  508 , which have a first end  518  that connects to the internal surface  516  of the body housing  512 . A second end  520  of the optical fibers  508  is coupled to a large illumination source (not shown). In yet another aspect of the embodiment, the body housing has a shape different than a hemisphere such as a cylinder, a paraboloid, an ellipsoid or a flat screen. 
     Referring to  FIG. 2 , a block diagram illustrating the various components of a SRI microscope system  200 , in accordance with one embodiment of the present invention is provided. The SRI device  100  can include a body housing  112  in the shape of a hemisphere. The SRI body housing  112  can include an external surface  114  and an internal surface  116 . The SRI body housing  112  further can include a plurality of light emitting diodes (LEDs)  118  that are distributed on the internal surface  116 . The LEDs  118  are electrically connected through a cable  122  to an external circuit  120  that powers and controls the operation of the LEDs  118 . The SRI device  100  is positioned on top of a traditional glass slide  206  used in conventional microscopes  202 . In this way, the SRI device  100  substitutes for the traditional illumination source of conventional microscopes  202  and provides a collimate beam impinging perpendicularly on the glass slide  206  that contains the object under observation  208 . The object under observation  208  is then illuminated by the light emitted in all directions by the plurality of LEDs  118  of the SRI device  100 , which includes radiated light that have very large incidence angles. The illumination by the light that has very large incidence angles, which is emitted in all directions results in the demonstrated sub-wavelength resolution of the SRI-microscope system  200 . Similar to conventional microscopy, imaging occurs in the SRI-microscope system  200  after collection by the microscope objective lens  204  of the light directly diffracted by the object under observation  208 .  FIGS. 6 and 7  demonstrate the sub-wavelength resolution capabilities of the SRI-microscope system  2 . It is known that the observation of extended diffraction features instead of spots in the Fourier plane image results in sub-wavelength resolution (see for instance the following publications: C. J. Reagan, R. Rodriguez, S. Gourshetty, L. Grave de Peralta, and A. A. Bernussi, Imaging nanoscale features with plasmon-coupled leakage radiation far-field superlenses, Optics Express, vol. 20, page 20827, 2012; L. Grave de Peralta, C. J. Reagan, and A. A. Bernussi, SPP Tomography: a simple wide-field nanoscope, Scanning, vol. 35, page 246, 2013; R. Lopez-Boada, C. J. Reagan, D. Dominguez, A. A. Bernussi, and L. Grave de Peralta, Fundaments of optical far-field subwavelength resolution based on illumination with surface waves, Optics Express, vol. 21, page 11928, 2013). The collection of numerous bright spots  614 ,  634  observed in the Fourier plane images  610  and  630  shown in  FIGS. 6B and 6D  constitute an extended diffraction feature obtained with a SRI-microscope system  200 . This illustrates a good correlation with the sub-wavelength resolution images  602  and  622  shown in  FIGS. 6A and 6C . Real, wide-field images of the object under observation  208  with nano-resolution are formed analogically, without need of sample tagging, intensive computation and/or scanning by the microscope&#39;s lenses  204 . 
     Other relevant variations are allowed in this invention with respect to the arrangement used in the experimental demonstration of a preferred embodiment of this invention described above. In other embodiments, the wavelength of the radiation emitted by the individual sources  118  can also be in the ultraviolet and/or infrared spectral range. A preferred embodiment of this invention uses an infrared SRI device  100  having LEDs  118  that emit infrared radiation with a wavelength in the range of λ˜1.2-1.5 μm. Silicon (Si) is transparent at these wavelengths; therefore, a common optical microscope  202  in combination with such an infrared SRI device  100  can be transformed in a super resolution infrared microscope  200  capable to image nanostructures fabricated on top of a Si wafer. Such a super resolution infrared microscope  200  will have numerous applications in the semiconductor industry. 
     Another preferred embodiment of this invention uses a more sophisticated electronic circuit  120  to power and control the 2D array of individual sources of radiation  118  distributed on the internal surface  116  of a body housing  112 . Separate control of individual LEDs  118  may allow both spatial filtering and time multiplexing techniques that result in additional imaging capabilities for an embodiment of this invention. 
     Testing has established that the minimum observable period p using this invention is given by the following Equation (1): 
     
       
         
           
             
               
                 
                   p 
                   &gt; 
                   
                     λ 
                     
                       na 
                       + 
                       N 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     where n is the refractive index of the medium on top of the glass slide  206 . In the visible frequency range, for example, evaluating Eq. (1) for n˜NA˜1.5 gives a minimum observable period of p˜λ/3, which corresponds to p˜190 nm for λ=568 nm. Moreover, in the infrared frequency range, evaluating Eq. (1) for n˜NA˜3.5 gives a minimum observable period of p˜λ/7, which corresponds to p˜215 nm for λ=1.5 μm. This result is in contrast to the minimum period observable with a traditional microscope, which is diffraction-limited to p˜λ/NA˜λ/1.5, or periods of ˜380 nm and 1000 nm, for wavelengths of 568 nm and 1.5 μm, respectively. This represents more than a 100% increase in the resolution of a conventional optical microscope by substituting a SRI device  100  for the original source of illumination. The periodic structures observed in the images illustrated in  FIG. 6  are a demonstration of the super resolution capabilities of this invention as the period of the observed photonic crystals is p˜260-220 nm, which is below the minimum observable period of ˜380 nm when using a conventional microscope. The minimum observable period corresponds to a microscope angular bandwidth of Δk=2k max , where k max =2π/p; therefore, using ΔxΔk≈2π, the expected Rayleigh resolution limit of this invention is given by the following Equation (2): 
     
       
         
           
             
               
                 
                   
                     Δ 
                      
                     
                         
                     
                      
                     x 
                   
                   &gt; 
                   
                     λ 
                     
                       2 
                        
                       
                         ( 
                         
                           NA 
                           + 
                           n 
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     As such, the Rayleigh resolution limit of this invention, Δx, is half of the value of the minimum observable period, p. For instance, evaluating Eq. (2) for n˜NA˜1.5 and n˜NA˜3.5 gives Δx˜k/6 and Δx˜λ/14, respectively, which corresponds to Δx˜95 nm and Δx˜107 nm, for λ=568 nm and λ=1.5 μm, respectively. This result is in contrast to the resolution limit of traditional microscopes, which are diffraction-limited to Δx˜λ/2NA, or ˜190 nm and ˜500 nm, for wavelengths of 568 nm and 1.5 μm, respectively. It should be noted that using a simple SRI source containing ultraviolet LEDs  118  would reduce the Rayleigh resolution limit of a common optical microscope to Δx˜50 nm, which is in the resolution range of a very sophisticated state of the art optical microscopy. 
     Referring to  FIGS. 3A and 3B , a super resolution illumination (SRI) device  300  can include a body housing  312  in the shape of a partial hemisphere with a top portion removed, which defines an equatorial region  302  of a hemisphere. The SRI body housing  312  can include an external surface  314  and an internal surface  316 . The SRI body housing  312  further can include a plurality of sources of radiation  318  (e.g., light emitting diodes (LEDs)) that are uniformly distributed on the internal surface  316 . Similar to the SRI device  100  of  FIG. 1 , the LEDs  318  are electrically connected through a cable  322  to an external circuit  320  that powers and controls the LEDs  318 . In the embodiment of  FIGS. 3A and 3B , an aperture or opening  304  in the top of the hemisphere advantageously allows a user of the SRI-microscope system  200  to visually observe the object under observation  208  while the SRI device  300  is in use. 
     Referring to  FIG. 4 , a super resolution illumination (SRI) device  400  can include a body housing  412  in the shape of a cylinder  402 . The SRI body housing  412  can include an external surface  414  and an internal surface  416 . The SRI body housing  412  further can include a plurality of sources of radiation  418  (e.g., light emitting diodes (LEDs)) that are distributed on the internal surface  416 . Similar to the SRI device  100  of  FIG. 1 , the LEDs  418  are electrically connected through a cable  422  to an external circuit  420  that powers and controls the LEDs  418 . In the embodiment of  FIG. 4 , an aperture or opening  404  in the top of the cylinder advantageously allows a user of the SRI-microscope system  200  to visually observe the object under observation  208  while the SRI device  400  is in use. 
     Referring to  FIG. 5 , a super resolution illumination (SRI) device  500  can include a body housing  512  in the shape of a cylinder  502 . Numerous optical fibers  508  can be uniformly distributed from the external surface  514  of body housing  512  to the internal surface  516  of body housing  512  that has a cylinder shape  502 . A first end  518  of each fiber  508  connects to the internal surface  516  of the cylinder shape  502 , which a second end  520  of each fiber is coupled to a large illumination source (not shown). 
     Referring to  FIGS. 9A and 9B , a super resolution illumination (SRI) device  900  can include a body housing  912  in the shape of a flat screen  902 . The SRI body housing  912  can include an external surface  914  and an internal surface  916 . The SRI body housing  912  further can include a plurality of sources of radiation  918  (e.g., light emitting diodes (LEDs)) that are distributed on the internal surface  916 . Similar to the SRI device  100  of  FIG. 1 , the LEDs  918  are electrically connected through a cable  922  to an external circuit  920  that powers and controls the LEDs  918 . In one embodiment, a total of 36 LEDs were used to obtain enhanced resolution of the conventional microscope. In another embodiment, a total of 120 LEDs were used to obtain enhanced resolution of the conventional microscope. In yet another embodiment, a total of 1000 LEDs were used to obtain enhanced resolution of the conventional microscope. 
       FIGS. 6A and 6B  illustrate optical images with sub-wavelength resolution obtained during an experimental demonstration of an embodiment of this invention.  FIG. 6A  is a real plane image  602 , and  FIG. 6B  is a Fourier plane image  610 , which correspond to photonic crystals with a period of 260 nm, which were obtained with a SRI-microscope system  200 .  FIG. 6C  is a real plane image  622 , and  FIG. 6D  is a Fourier plane image  630 , which correspond to photonic crystals with a period of 220 nm, which were obtained with a SRI-microscope system  200 . The square symmetry of the photonic crystal structure  606 ,  626  is clearly illustrated in the real plane images  602  and  622 . The spots  604 ,  624  are image artifacts that disappear when the image  602 ,  622  are magnified. These structures are invisible for a traditional optical microscope; however, they are clearly visible using a preferred embodiment of this invention. This demonstrates the subwavelength resolution capabilities of this invention. Each bright spot  614  and  634  observed in the Fourier plane images  610  and  630  corresponds to an individual source of radiation (e.g., a LED) in the SRI device  100  used in this experimental demonstration of a preferred embodiment of this invention, which has a uniform distribution of LEDs in the internal surface  116  of the body housing  112  that has the shape of a hemisphere. 
       FIGS. 7A and 7B  show optical images with sub-wavelength resolution obtained during an experimental demonstration of a preferred embodiment of this invention. The images were obtained with a SRI-microscope system  200  and correspond to a sample  710  with carbon nanotubes  712 , which have diameters of 40-60 nm and a sample of human blood  720  placed on top of a glass slide  206 . Single carbon nanotubes  712  are clearly observed in  FIG. 7A . Piled disk-shaped red cells  722  and an ameba-shaped white cell  724  at the center of the image are observed in  FIG. 7B . In addition, a rich sub-cellular internal structure of the white cell  724  is clearly observed. 
     In operation, the visible-light SRI device  100  used to obtain the images illustrated in  FIGS. 6 and 7  includes 560 LEDs  112  distributed in the internal surface  116  of a body housing  112  in the shape of a hemisphere with a diameter of 10 cm. The LEDs  118  where electrically connected in series and simultaneously and equally powered through a common cable  122 . A simple electronic circuit  120  was implemented to allow for control of the intensity illumination of the SRI device  100 . A more elaborated electronic circuit  120  may allow for control of individual LEDs by increasing the imaging capabilities of the preferred embodiment of this invention. In the experimental demonstration of this invention, the conventional illumination of a Nikon inverse optical microscope  202  is substituted for the visible-light SRI device  100 . This change with respect to the conventional optical microscopy  202  resulted in the observed super resolution. As shown in  FIG. 2 , the visible-light SRI device  100  was just on top of the glass slide  206  with the object under observation  208 . The immersion oil microscope objective lens  204 , with a numerical aperture of NA=1.49 and magnification λ100, was in optical contact with the bottom surface of the glass slide  206 . The object under observation  208  was then illuminated by the light emitted in all directions by the LEDs  118 , which included light with very large incidence angles. This procedure resulted in the demonstrated sub-wavelength resolution of the SRI-microscope system  200 . Similar to traditional microscopy, imaging occurs in the SRI-microscope system  200  after collection by the microscope objective lens  204  of the light directly diffracted by the object under observation  208 . Real, wide-field images of the object under observation  208  with sub-wavelength resolution were formed analogically, without the need of sample tagging, intensive computation or scanning, by the microscope&#39;s lenses. 
     Some variations are allowed in this invention with respect to the arrangement used in the experimental demonstration of a preferred embodiment of this invention described above. As illustrated in  FIGS. 3-4 , the shape of the body housing  312  where the LEDs  318  are distributed can be different from a hemisphere  312 .  FIG. 3  illustrates an alternative embodiment of this invention where the LEDs  318  are uniformly distributed in the internal surface  316  of the equatorial region  302  of a hemisphere shape.  FIG. 4  illustrates another instance of this invention where the LEDs  418  are uniformly distributed in the internal surface  416  of a solid cylinder  402 . In both variations of this invention the aperture  304  on the top of the body housing  312  permits a user of the SRI-microscope system  200  to visually observe of the object under observation  208  while the SRI apparatus  300 ,  400  is in use. 
     The invention has been described with respect to certain preferred embodiments, but the invention is not limited only to the particular constructions disclosed and shown in the drawings as examples, and also comprises the subject matter and such reasonable modifications or equivalents as are encompassed within the scope of the appended claims.