I am trying to do a variation on the double slit experiment in order to see how interference patterns change if the relative amounts of light passing through each slit change. I think I have the apparatus figured out, but my experiment requires the laser to be passed through three polarizers. As a result, the intensity is greatly diminished. I currently own a laser pointer which cost me about $10 and was advertised at 5mW, though I am tending to doubt that because the beam is not much more powerful than a 1mW laser from Pasco Scientific. In any event, the majority of this lasers intensity is lost by the polarizers so that once it is time to measure interference, it is difficult for the photometer to pick up distinct, clear interference patterns (I am using a light sensor from Vernier). Does anybody know where I could buy an affordable laser, or laser pointer, which could give me reliable interference patterns even after being placed through all the polarizers? I am not horribly concerned with overall beam quality as I have found that my cheap laser pointer gives me clear interference, but is simply not powerful enough. I was thinking of buying something in the neighborhood of 15mW. Any thoughts on the subject would be appreciated.
Choosing the laser for your project consider 2 aspects:
1) Laser power: using 3 polarizers you need more power than 5 mW. In university didactic labs are commonly used He-Ne lasers for interference experiments, the one I used had a power about 150 mW and we had just one polarizer and a diffraction grating made of plastic (so don't be afraid of that power, it won't fry your hardware).
2) Photometer spectral sensibility: just like our eyes, photometer has a spectral sensibility which depends from the wavelength of incident radiation (e.g. our eye's top sensitivity is reached from green light, have you ever noticed that green laser pointers seems to be much brighter then red ?).
So in my opinion you should buy a 80-150 mW He-Ne laser for your experiment, or a laser not so powerful but at least of a WL which maximize detector sensitivity