Re: photodiode amplifier with notch/highpass filter?

mattias.olsen@xxxxxxxxx wrote:

To give you a little more background on my problem, it is an
experiment in brillouin scattering spectroscopy.
In my setup, there are two lasers, one is chopped at 35 kHz and the
other at 25 kHz.
The desired signal is light scattered from the second beam to the 1st
by a nonlinear interaction in the sample, and will have a component at
the sum frequency of 60kHz.

Selectivity will be easier to get with the difference frequency.

I chose these frequencies because the lockin I have cannot accept a
reference below 25 kHz, and also behaves poorly when the input has
strong components at lower frequencies.

That's weird for a lock-in--are you sure it isn't broken? Most lock-ins work best around 1 kHz and degrade fairly rapidly above and below there.

It's almost as easy to build a lock-in as it is to make a biquad.

Cheers,

Phil Hobbs
.