Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Reexamination Certificate
2002-06-04
2004-11-30
Evans, F. L. (Department: 2877)
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
C250S205000, C362S231000
Reexamination Certificate
active
06825930
ABSTRACT:
BACKGROUND
Applications in medicine, science, and engineering commonly use microscopy to determine information about a given sample. Such applications likewise exploit spectroscopic information when analyzing a sample. In particular, the optical response of a sample often depends on the spectral content of light illuminating the sample, and that spectral dependence provides additional information about the sample or components therein. Not surprisingly, it is often desirable to obtain both spatial and spectral information about a sample to more accurately identify or characterize different regions or components of the sample. For example, one may want to spatially resolve the optical response of a sample (e.g., the optical transmission) as a function of illumination light at a particular wavelength or superposition of wavelengths. Furthermore, the image of a sample at a particular wavelength or superposition of wavelengths may be useful in distinguishing and spatially isolating one component of the sample from other components of the sample.
In such applications, however, it is important that light intensity variations in the detected image can be properly associated with the sample. Accordingly, variations in the relative spectral content of the illumination light across its spatial profile should be minimized or carefully calibrated. Furthermore, any spectroscopic imaging system should provide robust and reliable performance, and efficiently exploit the available illumination light.
SUMMARY
The invention features a multi-spectral microscopy system for illuminating a sample with light of a selectable spectral content and generating an image of the sample in response to the illumination. The selection of the spectral content of the illumination and the image detection can be performed through an electronic control system. The multi-spectral microscopy system includes a multispectral illuminator that provides output radiation having the selectable spectral content. A preferred set of optical arrangements for the multispectral illuminator generates the output radiation so that the spectral content of the output radiation is substantially uniform across its transverse profile. In particular, the absolute intensity of the output radiation may vary across its transverse profile, but the relative spectral content of the radiation is substantially uniform across the transverse profile. Furthermore, the multispectral illuminator can include monitoring optics and a corresponding detector array that independently monitors the output in each spectral band of the radiation produced by the multispectral illuminator. The monitoring provides calibration, feedback, and/or source aging information to insure robust and reliable performance for the multispectral illuminator. The multi-spectral microscopy system also includes a microscope which illuminates the sample with light derived from the output of the multispectral illuminator, and beam modification optics, which modify the output from the lamp prior to the microscope to increase the light efficiency of the microscope and fully exploit field of view and resolution of the microscope. In preferred embodiments, the beam modifications optics provide independent and selectable control over the spot size and divergence cone of the illumination pattern on the sample.
We will now summarize different aspects, features, and advantages of the invention.
In general, in one aspect, the invention features a multispectral illuminator for providing EM radiation with a selectable frequency content. The multispectral illuminator includes: a dispersive element which during operation provides an angular dispersion for incident EM radiation; a light source array including an array of light sources providing EM radiation at different wavelengths; and an optical system having an optical power. The optical system is positioned relative to the source array and the dispersive element to image the dispersive element at infinity with respect to the light source array for at least one of the different wavelengths in a paraxial approximation. The position of each light source along the array and the angular dispersion of the dispersive element are selected to cause at least a portion of the EM radiation from the source array incident on the dispersive element through the optical system to propagate along a common direction.
Embodiments of the multispectral illuminator may include any of the following features.
The optical system can include any of a singlet lens, a composite lens system, and one or more curved reflective surfaces.
During operation, the optical system may collimate the EM radiation emerging from each light source within a preset cone angle and direct the collimated radiation from each light source to be coextensive on the diffractive element.
The optical system can define a focal length for at least one of the different wavelengths, and the light source array and the diffractive element can be each spaced from the optical system by a distance substantially equal to the focal length.
The spatial extent of the dispersive element can define an aperture stop for the optical system. For example, the dispersive element can include an iris for varying the spatial extent of the dispersive element.
The optical system and the dispersive element can cause the EM radiation propagating along the common direction to have a spatial distribution that is substantially wavelength independent.
The common direction can be substantially collinear with a chief ray from a central one of the light sources.
The dispersive element can be a reflective dispersive element (e.g., a reflective grating). For example, the reflective dispersive element can direct the radiation back to the optical system along the common direction, and the optical system can focus the radiation received from the reflective dispersive element to a spot in an image field. The image field may be substantially coplanar with a plane defined by the source array. Also, the common direction may be substantially perpendicular to a plane defined by the source array. The source array may include a substrate supporting the light sources, and the spot in the image field may coincide with an aperture in the substrate. The light sources may extend along an axis, and the aperture can lie along the light source axis. Alternatively, the aperture can lie above or below the light source axis. The optical system may form a telecentric imaging system based on the reflection by the dispersive element. The multispectral illuminator may further include an optical fiber positioned to receive the focused radiation from the aperture in the substrate.
Alternatively, the dispersive element may be a transmissive dispersive element (e.g., a transmission grating). The multispectral illuminator may further include a second optical system position to receive the radiation from the transmissive dispersive element propagating along the common direction and focus that radiation to a spot in an image field. The common direction may be substantially perpendicular to a plane defined by the source array. The two optical systems may form a telecentric imaging system.
The second optical system may define a focal length, and the transmissive dispersive element and the image field can be each spaced from the second optical system by a distance substantially equal to the focal length of the second optical system. The multispectral illuminator may further include an optical fiber positioned to receive the focused radiation from the spot in the image field.
The multispectral illuminator can further include an electronic controller coupled to the array of light source for selectively adjusting the EM radiation provided by each light source.
The EM radiation provided by the array of light sources may span wavelengths within the range of 400 nm to 1000 nm.
The source array may includes a substrate supporting the light sources, and each light source may include at least one light emitting diode (LED) mounted on the substrate. For example, each light sourc
Cronin Paul J.
Fantone Stephen D.
Miller Peter J.
Orband Daniel
Cambridge Research and Instrumentation, Inc.
Evans F. L.
Fish & Richardson P.C.
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