Multispectral reflectometer
OwnerThornton Stearns, Subhash C. Sarkarinventors
Life of this patent
Estimating the term…
Abstract
A reflectometer for measuring absorption of light in selected regions of the light spectrum by a diffuse reflector. The reflectometer is adapted to precisely measure absorption resulting from the constituents present in body fluids. The sample to be measured is illuminated by a focussed light source at an angle of 45.degree. to its surface. The light diffusely reflected about the normal to the sample falls on a small round bundle of optical fibers. At the opposite end of the bundle, the fibers are arranged into a narrow rectangle. This rectangle forms the entrance slit for a concave holographic diffraction grating. The grating forms images of this entrance slit spectrally separated over a flat field suitable for recording the spectrum on film or on an array of discrete detectors.
Claims15
A system for measuring the absorption of light by a sample in selected regions of the light spectrum, comprising:
- means for illuminating the sample;
- a fixed fiber optic collector for directly collecting diffusely reflected energy from the sample, the optical fibers forming said collector being generally straight, short, grouped in a bundle, and extending from an entrance and that is generally circular to an exit end that is arranged in the shape of a rectangular slit, said entrance end being disposed immediately adjacent the sample so that said fibers each receive and transmit light from the entire sample, said entrance end of each of said fibers in said bundle having an acceptance angle that is at least as large as the associated optical exit angle of each of said fibers;
- a holographic, concave diffraction grating for dispersing the reflected energy projected onto it through the slit of the collector into its component wavelengths on a flat spectral plane, said light transmitted by said collector filling said grating;
- a photodetector array comprising a plurality of photodetectors located at the spectral plane for detecting the separated energy at its various wavelengths;
- and
- means for processing electrical signals generated by said photodetectors corresponding to the presence of light at the various wavelengths to obtain digital data corresponding to a reflectance value within a wavelength bandwidth, said means for processing comprising:
- means for generating control signals for controlling readout of said electrical signals from said photodetectors sequentially with subsets of said photodetectors being assigned to different wavelength bandwidths across said light spectrum and with readout of photodetectors in a given subset occurring in a predetermined period of time associated with that given subset;
- means for amplifying said electrical signals read out from said photodetector;
- analog means for integrating said amplified electrical signals for each of said predetermined periods of time during which electrical signals are being read out from one of said subsets of photodetectors which are positioned in said array so as to detect said separated energy in a given bandwidth;
- means for sampling and holding said integrated electrical signals after each said predetermined period of time;
- and
- means for converting said sampled and held integrated electrical signals into digital data.
A method for measuring the absorption of light by a sample in selected regions of the light spectrum, comprising the steps of:
- illuminating the sample with light from a light source;
- collecting optical energy reflected from the sample in a fiber optic collector formed as a fixed bundle of generally straight fibers with a generally circular entrance end, the optical fibers at the exit end of the collector being arranged in the shape of a rectangular slit;
- projecting the reflected energy passing through the rectangular slit onto a holographic, concave diffraction grating;
- separating the reflected energy into its component wavelengths on a flat spectral plane by reflecting the energy off the grating;
- detecting the separated energy by projecting the separated energy onto a photodetector array formed as a generally linear array of photodetector cells;
- and
- processing electrical signals generated by said projecting at each said cell of said photodetector array, said step of processing comprising the steps of:
- sequentially reading out said electrical signals from all of said photodetector cells of said photodetector array in a scan,
- processing portions of said read out of signals in time sequence from the start to the end of said scan where said time sequencing causes said portions to correspond to preselected groups of said cells and to bandwidths in the light spectrum;
- amplifying said electrical signal portions read out from said photodetector array;
- integrating sequentially in each said scan each of said amplified electrical signal portions from each of said groups of said cells for a predetermined period of time that corresponds to an associated one of said groups;
- sampling and holding said integrated electrical signal portions after each of said predetermined periods of time;
- and
- converting said sampled and held integrated electrical signal portions into digital data, said digital data corresponding to the absorption of light by said sample in said given bandwidth.
A circuit for processing the analog signals output from an array of photodetectors that are illuminated by linear light spectrum and where selectable groups of said photodetectors are associated with bandwidths within the spectrum and where the analog output of each of the groups of photodetectors is converted into a digital signal that measures the light energy incident on the photodetector array in the associated bandwidth, comprising
- means for scanning in each cycle of operation each photodetector in said array,
- means for generating control signals to sequentially readout in each said scan those portions of the electrical signals produced by photodetectors in each of said groups, said portions being sequentially read out from each and every group in predetermined periods of time each associated with one of said groups,
- means for integrating the electrical signal readout from all of the photodetectors in a given group independently of the readout of photodetectors in any other group,
- means for sampling and holding said integrated analog electrical signals from each group after the predetermined period of time associated with that group;
- and
- means for converting said sampled and held integrated electrical signals into digital data,
- all of said photodetectors in said array operating to produce said electrical signals during each of said scans.
Dependencies are inferred from the claim text.