0

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.

ocrdu
  • 8,705
  • 21
  • 30
  • 42
iwantmyphd
  • 417
  • 1
  • 5
  • 17
  • What does the data sheet for the lock-in amplifier tell you? – Andy aka Jan 26 '18 at 18:07
  • @Andyaka There isn't one as far as I know. The manufacturer's website has basic specifications but no information about choosing reference frequencies. – iwantmyphd Jan 28 '18 at 00:26

2 Answers2

2

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.

D Duck
  • 2,041
  • 1
  • 8
  • 18
0

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).

Spehro Pefhany
  • 376,485
  • 21
  • 320
  • 842