Patent Application
20080049234
The colorimetric three-dimensional microscopy system according to the invention is schematically illustrated in
A first possible embodiment of such a tunable light source 10 consists of an intense broad-band light source, which is filtered with an electrically or mechanically switchable filter with the above described spectral characteristics. Possible embodiments of such light sources include a high-intensity white LED, or a high-pressure gas discharge lamp with a sufficiently wide spectrum to cover all visible wavelengths (e.g. metal halide lamps).
Another possible embodiment of a tunable light source is a monochromatic light source such as a Ti:Sapphire laser system, whose wavelength and intensity are swept at high speed over the desired range, so that an averaged, effective spectrum as described above is obtained. The speed of this sweep must be so high that the detector sees a complete spectrum during the time of one fringe period of the OCT signal.
The light from the light source 10 is coupled into the multi-mode optical fiber 11, and is guided to the input of an optical interferometer, such as a Michelson, a Mach-Zehnder, or a Kösters interferometer. The interferometer type used for illustrative purposes in
An alternative, non-mechanical depth-scanning mechanism consists of using a fixed relative position of reference mirror and object, and by realizing the depth scanning through a dispersive optical element and electronic scanning of a one- or two-dimensional image sensor in the photodetector device, as known from FD-OCT, and as described for example by R. A. Leitgeb et al. in “Performance of Fourier domain vs. time domain optical coherence tomography,” Optics Express, vol. 11, pp. 889-894, March 2003.
If the axial extent of an object under study is larger than a few ten micrometer, it becomes necessary to adapt the focus of the imaging lens (not shown) used in the OCT setup illustrated in
A tunable light source 20 is used, whose emission properties can be electrically controlled, in order to produce three emission spectra S1, S2 and S3. The total spectral system response with these three emission spectra correspond to the three CIE tristimulus curves shown in
It is also possible to use different lenses 27 and 31, while still obtaining dynamic coherent focus, by placing a compensation plate 28 in the reference beam path on the optical subsystem module 25. The properties of this compensation plate are chosen such that it provides for identical thicknesses and refractive properties in the reference as well as in the object beam path.
The beam splitter 23 recombines the reflected light from the reference beam path and the object beam path to a detection beam path, where the interfering light is focused with an detector imaging lens 33 onto the plane of a image sensor 34. As described above, the OCT image sensor 34 is capable of demodulating separately for each pixel the incident light, which is temporally modulated according to the axial movement of the optical subsystem module 25.
The average size of the speckles in the image sensor plane 34 varies as a function of the optical aperture 32 in the detection beam path. For optimum contrast, the average speckle size should be in the range of the effective photosensitive area of the single detector pixels. As a consequence, the aperture 32 should be chosen such that the average speckle size has optimum size. Since all components determining the optical magnification of the OCT microscope are contained in the optical subsystem module 25, a different value of the optical magnification can be realized by simply replacing one module 25 for another module 25, having a different set of lenses 31 and 27. All other parts of the OCT microscope according to the present invention are not affected.
If the object under study reflects or scatters only a small amount of light back into the interferometer, the light from the reference beam path should be correspondingly reduced, in order to improve the contrast of the detected signal in the sensor plane 34. A neutral density plate 29 arranged in the reference beam path can achieve this. The transmission ratio of said neutral density plate 29 must be chosen in way that results in optimum signal contrast for different types of objects.
If the average propagation speed of the light in the object volume under study is differing significantly for the three spectral distributions S1, S2 and S3 of the tunable light source, i.e. if the refractive index n(λ) shows significant variation as a function of the wavelength λ, the effect of optical dispersion will become manifest: The three depth scans measured with the three illumination spectra S1, S2 and S3 will exhibit a different depth scale. This is illustrated in the left part of
Once the corresponding salient signal features in three measurements M1, M2 and M3 have been determined, the different coordinate segments of the depth axis z of the three data sets are adapted to each other, so that the salient signal features in the three measurements coincide, as indicated on the right side of
A further problem of prior art optical microscopy can be successfully addressed by a microscopy system according to the invention: In the presence of absorbing layers whose characteristics depend on the wavelength and the depth coordinate, it has not been possible until today to obtain a true-color volumetric representation of a microscopic scene. This problem is illustrated in
| Number | Date | Country | |
|---|---|---|---|
| 60839424 | Aug 2006 | US |
