Triggering for a heterodyne interferometer

Details Triggering for a heterodyne interferometer Triggering for a heterodyne interferometer

2004-12-14

2009-02-17

Lee, Hwa (Andrew) S (Department: 2886)

Optics: measuring and testing

By light interference

Having light beams of different frequencies

Reexamination Certificate

active

07492464

ABSTRACT:
A method for triggering a heterodyne interferometer having two acousto-optical modulators in separate light paths, a receiver generating an analog signal and a downstream A/D converter converting the analog signal into a digital signal is described. The one acousto-optical modulator is triggered at a modulation frequency f1and the other acousto-optical modulator is triggered at another modulation frequency f2, the difference between modulation frequencies f1and f2forming a heterodyne frequency fHetand the analog signal being converted into the digital signal in the A/D converter at sampling frequency fa. In such a heterodyne interferometer, a fixed ratio of modulation frequencies is maintained, and they are prevented from shifting due to aging and drift by forming at least two of the frequencies of modulation frequencies f1, f2and sampling frequency fafrom a fundamental frequency fqartzof a common oscillator. As a result, it is also possible for sampling frequency fato be in a fixed phase ratio to the differential frequency of modulation frequencies f1, f2, of heterodyne frequency fHet. Measurement accuracy is increased because sampling is performed at a constant phase, independently of drift and aging.

REFERENCES:
patent: 6249155 (2001-06-01), Hartman et al.
patent: 2003/0199115 (2003-10-01), Mattox
patent: WO 02/37684 (2002-05-01), None

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