An improved mirror alignment control for dynamically aligning the reflecting mirrors bounding the optical path in an interferometer comprises a closed loop servo control which utilizes a two frequency laser beam to provide phase comparison between beams traversing differing portions of the optical paths in the interferometer to determine alignment of the mirrors, said phase comparison providing a correction signal to direct multi-axial alignment of at least one of the mirrors.

Dynamic mirror alignment control

Real time high speed high resolution hyper-spectral imaging. (a) electromagnetic radiation collimating element (16), collimating electromagnetic radiation (44) emitted by objects (12) in a scene or a sample (14); (b) optical interferometer (18), receiving and dividing collimated object emission beam, generating interference images, and piezoelectrically determining and changing magnitude of optical path difference of divided collimated object emission beam; optical interferometer (18) includes: beam splitter (20'), fixed mirror (22), movable mirror (24), piezoelectric motor (26), displacing movable mirror (24) along axis (60), distance change feedback sensor (28), sensing and measuring change in distance of movable mirror (24) along axis (60), piezoelectric motor controller (30), actuating and controlling piezoelectric motor (26); and thermo-mechanically stable optical interferometer mount (32A); (c) camera optics (34), focusing interference images of each optical path difference; (d) detector (36), recording interference images; (e) central programming and signal processing unit (38), and (f) display (40).

Real time high speed high resolution hyper-spectral imaging

A spectrometric method is disclosed which uses a novel tunable laser as a monochromatic light source to carrying out spectrometry efficiently. As the tunable laser, a tunable laser is used which comprises a laser resonator so provided therein with a laser medium 14 capable of laser oscillation in a predetermined range of wavelength and a birefringent acousto-optic element 100 and which is capable of wavelength selection by selecting a frequency of an acoustic wave to be generated in the birefringent acousto-optic element 100 by means of a piezoelectric element 22 connected to a RF power source 20. The tunable laser is used instead of a spectroscopic light source and a monochromator in a conventional spectrophotometer to thereby carry out spectrometry efficiently. In case of detecting Raman scattered light no influence of fluorescence without using a spectroscope, a tunable laser 140 is controlled by a controlling device 141 to sweep a wavelength of a monochromatic light beam LB with which a sample S is irradiated while alternately switching the wavelength between a first frequency υ ex1 and a second frequency υ ex2 having a frequency difference Δυ ex relative to the first frequency υ ex1 . The resulting scattered light emanated from the sample S is detected by a photodetector 145 through an interference filter 144 which transmits light having an obsrvation frequency υ ob . Output of the photodetector 145 is subjected to phase synchronous detection by a lock-in amplifier 146 and processed by a signal processor 147 to obtain a Raman spectrum ot the sample S.

Spectrometric method and apparatus for spectrometry

A wavelength reference device (110) for tuning a tunable Fabry-Perot filter and/or a tunable VCSEL (105) to a desired frequency, where the device uses a Fizeau interferometer (125) and a position sensitive detector (130), with the position sensitive detector (130) being used to measure the location of the maximum reflected power from the interferometer (125), whereby to determine the wavelength of laser radiation for tuning the device (110).

Wavelength reference device

A tunable optical cavity constructed from a fixed mirror and a movable mirror is disclosed. A circuit applies an electrical potential between first and second electrically conducting surfaces thereby adjusting the distance between the fixed and movable mirrors. The fixed mirror and the moveable mirror are positioned such that the mirrors form the opposite ends of the optical cavity. The distance between the fixed mirror and the moveable mirror is a function of the applied electrical potential. The thermally induced vibrations are reduced by utilizing an electrical feedback circuit that measures the distance between the mirrors. The feedback circuit dynamically changes the potential between the substrate and the support member so as to reduce fluctuations in the cavity resonance frequency.

Tunable Fabry-Perot filters and lasers utilizing feedback to reduce frequency noise

A stabilizer for the relative mirror separation and inclination in a Michelson (two beam) or a Fabry-Perot (multiple beam) interferometer that generates at least three reference beams and in one embodiment an optional monitor beam. The reference beams are disposed substantially around the interferometer signal beam and are directed through the interferometer. The resultant intensity from the interference within each reference beam (transmission) is detected and compared to a fixed reference, in one embodiment the monitor beam. Based upon the ratio of reference intensity to fixed reference, the mirror position is controlled to maintain a constant spacing with respect to the wavelength of the reference source. A stepped mirror surface in the interferometer is used in one embodiment and provides a constant difference between effective mirror spacing encountered by a signal beam and the spacing encountered by reference beams. A servo system is provided to adjust mirror spacing to maintain a constant transmission ratio for each of the reference beams in response to distortion in the interferometer or changes in reference wavelength. A method of stabilizing a Michelson and a Fabry-Perot interferometer utilizing reference beams derived from an independent reference source of nearly monochromatic radiation is also disclosed.

Ronald L. Schwiesow

Papers

Stabilization mechanism for optical interferometer