Experiment under ambient light I performed the following experiment for Faraday rotation, Verdet constant etc.

http://www.teachspin.com/instruments/faraday/

However, I have a concern. Does the external light actually affect the results of the experiment? As in under an ambient light? I fear that it might affect due to the receiver being a photodiode. But I am not too sure. 
 A: As long as your ambient light is consistent and lower power than your experiment light source it shouldn't be a problem. 
As you rotate the angle of the polarisation filter you will eventually detect a peak at the detector--this angle will be different from the polarisation angle when the solenoid is turned off, indicating Faraday rotation. Like most optics experiments, this peak is best observed in minimal ambient light conditions. In other words ambient light adds noise but does not change the result.
A: I think you don't need to worry about the effect of the ambient light assuming 


*

*the source and detector you used are the same (or roughly the same) as in the specifications, and

*you used the non-standard strategy (i.e. setting the relative angle between the polarizers to be $\pi/4$) as described in the "Experiments" section

*the ambient light was not fluctuating too much. 


The receiver being a classical photodiode (instead of an avalanche type diode) and with the impinging optical power level $\sim 1$ mW, the effect of background light should be negligible. 
