Optical spectrophotometer with wavelength modulation

Details Optical spectrophotometer with wavelength modulation Optical spectrophotometer with wavelength modulation

1992-02-25

1993-07-27

Evans, F. L.

Optics: measuring and testing

By dispersed light spectroscopy

Utilizing a spectrometer

356334, 356346, 356352, G01J 306, G01J 318, G01J 326

Patent

active

052314626

ABSTRACT:
A spectrophotometer useful for measuring absorption or emission bands of a substance irradiated with optical radiation, comprises a light source for producing the optical radiation, a monochromator for isolating light of wavelength (W) from the optical radiation and which modulates the wavelength (W) by a predetermined wavelength amplitude (.delta.W), and a photodetector for detecting the intensity of light passing through the monochromator and for producing a measuring signal in response thereto. The monochromator operates under the control of an electronic control unit which produces a control signal that causes the monochromator to scan across a portion of the spectrum of the optical radiation at a frequency (f.sub.2) to transmit a narrow band of radiation at the wavelength (W). The control unit includes a modulation generator which produces a signal that causes the monochromator to modulate the wavelength (W) by the predetermined wavelength amplitude (.delta.W) at a frequency (f.sub.1). The spectrophotometer also includes an electronic evaluation unit which amplifies an a.c. component of the measuring signal that is attributable to the wavelength modulation in synchronization with the signal produced by the modulation generator. In one preferred embodiment, the monochromator comprises a diffraction grating and a drive unit which causes the diffraction to rotate about a pivot axis and which superimposes an oscillatory motion on the rotational movement. In another preferred embodiment, the monochromator comprises a Fabry-Perot resonator and a drive unit which adjusts the optical length of the Fabry-Perot resonator under the control of the control unit.

REFERENCES:
patent: 3565567 (1971-02-01), Rains
patent: 3832558 (1974-08-01), Fern et al.
patent: 4051371 (1977-09-01), Dewey, Jr.
Hieftje et al, Applied Spectroscopy, vol. 26, No. 6 Nov./Dec. 1972, pp. 624-631.
T. Izumi et al, "Repetitive-scanning Derivative spectrometer as a monitor of environmental air pollution," Applied Optics, vol. 22, No. 22 Nov. 15, 1983.

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