Method and Apparatus for Hyperspectral Imaging

Abstract

A method and apparatus for the generation of hyperspectral images for an object consisting of a broad band light projection systems, a means of modulating the wavelength of the light, one or more sensors for observing the reflected light, one or more electronic means of synchronizing and extracting data from the sensor, one or more sensors for registering position, one or more calibration methods for rationalizing the data, and one or more algorithms for analyzing the data to produce the hyperspectral image.

Claims

1) A method for hyperspectral imaging of an object or objects using a CHIRP modulation, the method comprising a light source of sufficient bandwidth and brightness, a tunable optical filter, such as an acousto-optic-transmission filter, with driver capable of CHIRPING, brightfield or darkfield illumination optics, lens of sufficient resolution to measure the samples, imaging optics, one or more sensor(s) of sufficient sensitivity and readout rate to enable sampling of the CHIRP signal, hardware and software to enable the creation of the CHIRP source and demodulation of the CHIRP signal, calibration method for normalizing the spectroscopic response, and hardware and software required for synchronizing data sampling with location of sample.

2) A method for hyperspectral imaging of an object or objects using a CHIRP modulation, the method comprising a light source of sufficient bandwidth and brightness, a tunable optical filter, such as an acousto-optic-transmission filter, with driver capable of CHIRPING, brightfield or darkfield illumination optics, lens of sufficient resolution to measure the sample, galvanometric scanner(s) with mirrors and programmable driver capable of scanning entire field of view, imaging optics, one or more sensor(s) of sufficient sensitivity and readout rate to enable sampling of the CHIRP signal, hardware and software to enable the creation of the CHIRP source and demodulation of the CHIRP signal, calibration method for normalizing the spectroscopic response, and hardware and software required for synchronizing data sampling with location of sample.

3) A method for hyperspectral imaging of an object or objects using a CHIRP modulation, the method comprising a light source of sufficient bandwidth and brightness, a tunable optical filter, such as an acousto-optic-transmission filter, with driver capable of CHIRPING, brightfield or darkfield illumination optics, lens of sufficient resolution to measure the sample, combination of rotating polygon scanner(s) with galvanometric mirror(s) and programmable driver capable of scanning entire field of view, imaging optics, one or more sensor(s) of sufficient sensitivity and readout rate to enable sampling of the CHIRP signal, hardware and software to enable the creation of the CHIRP source and demodulation of the CHIRP signal, calibration method for normalizing the spectroscopic response, and hardware and software required for synchronizing data sampling with location of sample.

4) A method for hyperspectral imaging of an object or objects using a CHIRP modulation, the method comprising a light source of sufficient bandwidth and brightness, a tunable optical filter, such as an acousto-optic-transmission filter, with driver capable of CHIRPING, brightfield or darkfield illumination optics, lens of sufficient resolution to measure the sample, combination of rotating polygon scanner(s) with galvanometric mirror(s) and scanning stage(s) and programmable driver capable of scanning entire field of view, imaging optics, one or more sensor(s) of sufficient sensitivity and readout rate to enable sampling of the CHIRP signal, hardware and software to enable the creation of the CHIRP source and demodulation of the CHIRP signal, calibration method for normalizing the spectroscopic response, and hardware and software required for synchronizing data sampling with location of sample.

5) A method for hyperspectral imaging of an object or objects using a CHIRP modulation, the method comprising a light source of sufficient bandwidth and brightness, a tunable optical filter, such as an acousto-optic-transmission filter, with driver capable of CHIRPING, brightfield or darkfield illumination optics, lens of sufficient resolution to measure the sample, combination of rotating polygon scanner(s) with galvanometric mirror(s) and scanning stage(s) and programmable driver capable of scanning entire field of view, imaging optics, one or more sensor(s) of sufficient sensitivity and readout rate to enable sampling of the CHIRP signal, hardware and software to enable the creation of the CHIRP source and demodulation of the CHIRP signal, calibration method for normalizing the spectroscopic response, hardware and software required for synchronizing data sampling with location of sample, and programmable sampling methodology to enable variable density sampling, area reconstruction of spectrally sampled areas, and optimized sampling speed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 A possible system layout consisting of a light source, imaging and collimation optics, full and partially reflective mirrors, a tunable wavelength filter, a sensor capable of measuring the structured light across multiple wavelengths, multiple electronic drivers capable of synchronizing the wavelength filter with the sensor, and a computer system that will be used to synchronize, gather and analyze data. In this system layout, the wavelength filter is on the illumination leg of the apparatus.

[0011] FIG. 2 A possible system layout consisting of a light source, imaging and collimation optics, full and partially reflective mirrors, a tunable wavelength filter, a sensor capable of measuring the structured light across multiple wavelengths, multiple electronic drivers capable of synchronizing the wavelength filter with the sensor, and a computer system that will be used to synchronize, gather and analyze data. In this system layout, the wavelength filter is on the imaging leg of the apparatus.

[0012] FIG. 3 A modulation/demodulation scheme in which the modulation occurs via hardware drivers and the demodulation occurs through an optimized software program using off the shelf hardware components.

[0013] FIG. 4 A modulation/demodulation scheme in which the modulation occurs via hardware drivers and the demodulation occurs through an optimized set of hardware/electronics components.

DETAILED DESCRIPTION OF INVENTION

[0014] Reference is made herein to the attached drawings. Like reference numerals are used throughout the drawings to explain elements of the hyperspectral measurements instrument. For the purpose of presenting a brief and clear description of the invention, the preferred embodiments will be discussed as used for the measurement of reflectivity of a sample. The figures are intended for representative purposes only and should not be considered limiting in any aspect.

[0015] Referring to FIG. 1, a light source capable of broadband illumination 1 is projected onto the sample area 2. The light passes through a tunable wavelength filter 3, set of collimated or near collimating optics 4, a beam splitting/half silvered mirror 5, and imaging optics 6. The wavelength of the tunable filter 3 is modulated by driver 7; specifically, the filter is changed systematically through a series of wavelengths in a repeated fashion, such that the repetition rate becomes its own frequency base. The lower frequency repetition rate, or base carrier, when combined with the higher frequency wavelength sweep, represents a CHIRP signal. As such, all wavelengths are represented by a common frequency with known phase relationship based upon the programmed modulation; a simple representation of the Fourier components of the illumination is shown by the relationship 8. The reflected light from sample 2 is gathered by the same imaging optics 6, and is reflected off the beam splitting/half silvered mirror 5 into a galvanometric mirror pair 9. For this representation of the invention, the galvanometric mirror pair 9 enable either a full or partial imaging of the sample area 2. The imaging light is transfer through one or more mirrors 10, one or more conditioning optics 11, and into one or more sensors 12. For this embodiment, the sensor 12 can either be sampled fast enough, such that the highest represented frequency in the illumination is captured or the sensor 12 can be programmed to sub sample at the (or multiple thereof) repeat frequency with known phase offsets. The subsequent data stream will be represented by Fourier components 13, similar to the Fourier components of the illumination leg 8. The sensor data stream can either be analyzed by a computer with custom software or custom electronics 14. Additionally, the positions and/or movements of the galvanometric mirrors 9 are synchronized with the data stream in 14, thus enabling the reconstruction of the areal reflectance from the sample 2. The end result is a data cube representing X and Y locations defined by the galvanometric mirrors 9 and reflectance value representing the wavelength dependence of the sample; the reflectance data will need to be normalized with respect to a known sample in order to remove the wavelength dependence of the light source.

[0016] An alternative embodiment of the apparatus is presented in FIG. 2; for this incarnation, the wavelength tunable filter 7 is inserted into the imaging leg of the apparatus instead of the illumination leg as described in FIG. 1. Operation of the wavelength modulation, data sampling, and analysis schemes may occur in an identical fashion as described above. The apparatus described in FIG. 1 has inherent advantages in terms of stray light filtering that do not exist in the apparatus described in FIG. 2; however, natural extensions of the apparatus described in FIG. 2 enables more flexibility in the choice of light source 1 and associated optics 4, 5, 6. Specifically, items 1, 4, and 5 can be removed from the apparatus described in FIG. 2, replaced with ambient diffuse lighting, and the apparatus will perform in a similar manner. Additionally, even though embodiments show in FIG. 1 and FIG. 2 are brightfield configurations, darkfield configurations of the system can obviously be made.

[0017] Referring to FIG. 3, one implementation of a method for modulation and demodulation is presented. Within this scheme, the modulation occurs via hardware drivers and the demodulation occurs through an optimized software program using off the shelf hardware components. This approach stores all sampled data into computer memory, which is later recalled for demodulation and subsequent analysis. The demodulation happening via software can occur by either a Fourier analysis of the represented frequencies or by mixing a software representation of the modulated signal with the measured data stream. A strict phase relationship between the CHIRP, modulation, and sensor sampling frequency must be maintained.

[0018] Referring to FIG. 4, an alternative method of modulation and demodulation is presented. Specifically, within this scheme, the modulation occurs via hardware drivers and the demodulation occurs through an optimized set of hardware and/or electronics components. In this approach, the signal used to drive the CHIRP production is fed directly in to the optimized electronics, enabling the extraction of reflected light as a function of the wavelength sweep.

REFERENCES

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