We found that many peaks in squeezing spectrum are odd number harmonics of 50Hz. Matteo suggested they are 50Hz square wave and related to thorlabs PD power supply. We are using thorlabs PD for OPO lock(PDA05CF2) and MZ lock(PDA100A-EC). We can use battery or another PD for check.

 

Matteo suggested they are 50Hz square wave and related to thorlabs PD power supply. 

We are using thorlabs PD for OPO lock(PDA05CF2) and MZ lock(PDA100A-EC).

We can use battery or another PD for check.