Triggering for a heterodyne interferometer

摘要

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; in this method, the one acousto-optical modulator is triggered at a modulation frequency f₁ and the other acousto-optical modulator is triggered at another modulation frequency f₂, the difference between modulation frequencies f₁ and f₂ forming a heterodyne frequency f_Het and the analog signal being converted into the digital signal in the A/D converter at sampling frequency f_a. 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, f₂ and sampling frequency f_a from a fundamental frequency f_quartz of a common oscillator. As a result, it is also possible for sampling frequency f_a to be in a fixed phase ratio to the differential frequency of modulation frequencies f₁, f₂, of heterodyne frequency f_Het. Measurement accuracy is increased because sampling is performed at a constant phase, independently of drift and aging.