Hello All,
I am currently building a stabilized Helium Neon laser that uses a 3 mode t ube and stabilizes the optical frequency by monitoring a beat frequency bet ween the modes. The beat frequency is 450-600 kHz and is sensed from the wa ste beam at the back of the laser tube. For a prototype I used an amplified moderately high speed Si detector that fed into a 12 bit 125 MSPS DAC. Th is data was then sent to the computer , bandpass filtered and Fourier trans formed to determine the signal frequency. This frequency was then fed into a PID algorithm whose output controlled a heater that would heat the tube t o stabilize its length.
Question: Can you suggest and analog solution to frequency detection that could work in this scenario? It does not need to be exceedingly fast since the PID loop time constant is on the order of seconds. I've noticed that Analog Devices has an IC for Freq to Voltage conversion. A PLL may be usef ul as well. Not looking for specifics, just suggestions as to the best pat h forward.
Thank you,
Brad Kimbrough