Laser intensity stabilization

[ssmoke]

I'm working with a setup involving a collimated laser (Thorlabs model CPS180), two polarizers, a beam splitter, and 2 photo-diodes. While measuring the intensity of the laser via LabView, without changing any of the components, I find the intensity varies by 0.2mV for the first hour of measurement. it increases for about the first half hour, then decreases for the next 15 minutes before even starting to stabilize. This seems like very odd behavior, even if the laser needs some time to warm up.

For my experiment, it is important that the laser be stable to within a few hundreths of a milliVolt. Do you think the problem is with my laser, photo-diode, or even the LabVIEW program?

If the problem is with my laser, is there a simple way to stabilize the intensity?

 

[Mr Boom]

You might want to check the supply voltage to the laser to make sure it isn't changing, hence changing your wavelength and power a bit. I'm also not sure how the polarization ratio in these lasers changes as they warm up. Are you monitoring it after you pass it through your optics?

 

[Andy Resnick]

Do you know if the laser is operating within specifications? Thorlabs didn't provide much information, but I found this which may be useful:

http://www.ilxlightwave.com/appnotes/AN 5 REV02 LD Characteristics Overview.pdf

 

[ssmoke]

I think most of my measurements have been taken with at least one polarizer.

 

[Gordianus]

You mentioned how much the laser intensity changed, but not the average value (i.e the relative change). How large was it?