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How do you choose the reference frequency when using a lock-in amplifier?

I want to measure the amount of lateral deflection of a laser reflected by a surface that will be oscillating very slightly. I'm going to modulate the laser at a set frequency, and send the trigger signal and the signal from a position-sensitive detector to the lock-in amplifier.

At the moment, I'm not sure how quickly the surface will be oscillating, or how much, hence this measurement. My first guess is to choose a reference frequency that is many times the rate that the surface will be oscillating (for instance, 100x), in order to ensure the lock-in detects the variation of the signal, but I don't know how to optimize this for a clean measurement.

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  • \$\begingroup\$ What does the data sheet for the lock-in amplifier tell you? \$\endgroup\$
    – Andy aka
    Jan 26, 2018 at 18:07
  • \$\begingroup\$ @Andyaka There isn't one as far as I know. The manufacturer's website has basic specifications but no information about choosing reference frequencies. \$\endgroup\$
    – iwantmyphd
    Jan 28, 2018 at 0:26

2 Answers 2

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Mike Meade's classic book Lock-in Amplifiers:principles and applications is freely available from https://www.sites.google.com/site/lockinamplifiers/ or from https://archive.org/details/Lock-inAmplifiersPrinciplesAndApplications

You need to read this first.

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Avoid any known disturbance frequencies and their harmonics and the upper limit frequency. The Lock-in, of course, acts as a very narrow-band filter (if you make it too narrow you'll lose signal, of course).

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