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?