Electric Power Research Institute Incorporated

Sri International

Thomas F Gallagher

David E Cooper

John P Watjen

Clinton B Carlisle

Gary R Janik

FM laser spectroscopy apparatus includes a single modulator for modulating a laser beam with first and second modulation signals (.omega..sub.1, .omega..sub.2). The two modulation signals are generated by mixing a signal from a first oscillator (.omega..sub.1 +.omega..sub.2)/2 and a signal from a second oscillator (.omega..sub.1 -.omega..sub.2)/2 and producing the two modulation signals (.omega..sub.1, .omega..sub.2). The modulator produces three groups of sidebands on the laser beam at the laser frequency plus and minus the two modulation frequencies and at plus and minus the difference between the two modulation signal frequencies. The apparatus provides practical high frequency FM spectroscopy as required for the observation of pressure broadened spectral features.

Frequency modulation spectroscopy using dual frequency modulation and

A phase-matched resonant waveguide modulator suitable for very high frequency modulation and applications such as FM laser spectroscopy is described. The width of a crystal modulator section of the waveguide is chosen so that the operating frequency is just above cut-off to achieve optical and RF phase velocity matching at high frequencies such as 10 GHz by virtue of the dispersion of the waveguide near cut-off. The waveguide contains air in opposite end sections so that those sections are below cut-off and the microwave is evanescent, with the result that the end sections preferably are open for ease of optical coupling to the waveguide.

Resonant cavity optical modulator

A spectroscopic technique in which the sample under investigation is probed with a generally monochromatic beam of light which has been modulated at two distinct modulation frequencies. The double modulation produces a plurality of sidebands, and the two modulation frequencies are related to one another such that a selection of sidebands falls into two groups of closely spaced component sidebands. A first group is disposed in frequency at the spectral feature of interest and serves to probe the spectral feature. The other group is disposed in frequency remote from the feature and serves as a reference group. Within each group the component sidebands are offset from one another by a characteristic offset frequency, which can be considerably less than the width of the spectral feature under investigation. After interaction with the sample the doubly modulated beam is passed on to a photodetector, which in combination with appropriate signal processing apparatus detects a signal at the characteristic offset frequency representative of the spectral feature.

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Charlottesville, VA, United States of America

Thomas F Gallagher