# US 5,703,689 A · Optical spectrometer

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- Number: US 5,703,689 A
- Document ID: US5703689A
- Status: Granted
- Kind: A
- Application number: 08/664,284
- Filed: 1996-06-11
- Granted: 1997-12-30
- Earliest claimed: 1996-06-11
- Assignees: Varian Associates, Inc.
- Inventors: Ronald Allan Powell
- Web page: https://patentgrep.com/patent/US5703689A

## CPC

- G01K 11/12: using changes in colour, translucency or reflectance
- G01J 5/20: using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices
- G01K: MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR (radiation pyrometry G01J5/00)
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)

## Abstract

A broadband optical detector is disposed to measure the total intensity I(.lambda., .alpha.) attributed to a portion of the optical spectrum passed by a sharp bandgap optical transmission element as the bandgap is caused to translate over a desired wavelength interval by a band gap control parameter, T. The differential spectrum of the incident optical radiation is recovered by the differentiation of I(.lambda., .alpha.) in respect to the parameter T.

## Claims

### Claim 1

The method for determining the spectrum of incident radiation comprising the steps of
(a) providing at least one layer of material, said material having a band gap energy, said layer being deposited onto a transparent substrate having a thickness sufficient to absorb all incident radiation above the band gap energy,
(b) controllably heating said layer in order to impose a temperature gradient across said material while projecting incident radiation through said layer,
(c) measuring the intensity of a portion of said incident radiation transmitted through said layer as a function of said temperature gradient across said material,
(d) differentiating said intensity with respect to temperature to obtain the differential intensity as a function of wavelength.

### Claim 2

The method for determining the differential spectral distribution of radiation incident upon a layer of material, said material characterized by a temperature dependent band gap energy, said layer being deposited onto a substrate, said substrate substantially transparent to said radiation, said layer having thickness sufficient to transmit only incident radiation having energy greater than said band gap, comprising:
controlling said layer to achieve a plurality of successive temperatures,
directing said radiation upon said layer,
measuring intensity of radiation transmitted through said layer for each of said plurality of temperatures of said layer,
determining a corresponding plurality of transmitted intensities in functional relationship to said plurality of temperatures,
analyzing said functional relationship in order to substantially provide a mathematical derivative of said functional relationship of said intensity as a function of said corresponding temperatures whereby the,
differential change of total radiation intensity transmitted by said material as a function of temperature is directly identifiable with said spectral distribution.

### Claim 3

Apparatus for determining the spectrum of incident radiation comprising:
a film of material, said material exhibiting a band gap and being of such thickness to absorb all incident radiation above the band gap, said material being deposited onto a radiation transparent heat sink substrate cooperating therewith to provide adequate thermal response:
means for heating said film so as to maintain a thermal gradient across said film,
means for detecting radiation intensity at a plurality of temperatures corresponding to said thermal gradient,
means for measuring transmitted intensity for each temperature of said plurality of temperatures,
means for collecting a plurality of intensity measurements corresponding to said plurality of temperature measurements,
means for determining a differential change in intensity corresponding to a differential change in temperature in order to determine a derivative function thereof.

### Claim 4

The method of acquiring a differential distribution of optical radiation, comprising the steps of:
(a) passing incident radiation through an optical discrimination element, whereby radiation below a cut-off wavelength is not transmitted, said cut-off wavelength being temperature dependent,
(b) detecting and recording the total intensity of transmitted radiation,
(c) causing the cut-off wavelength to change controllably in response to a changing the temperature of said optical discrimination element,
(d) repeating the steps (a) through (c) to obtain the total intensity of transmitted radiation as a function of cut-off wavelength,
(e) differentiating the total intensity of transmitted radiation as a function of cut-off wavelength with respect to cut-off wavelength whereby the distribution of optical radiation is obtained.