# Fresnel Biprism

1. Nov 16, 2009

### v_pino

I'm doing a lab report on diffraction and interference. I've done several diffraction experiments (single slit, double slit, diffraction grating, Fresnel Biprism) to find the wavelength of the laser used. with Fresnel Biprism, wouldn't the refraction within the prism cause a change in wavelength? Or would it not matter? - would it go back to its original wavelength after the wave passes through and out of the prism?

thanks :)

2. Nov 16, 2009

### Woland

Well a prism refracts the light going through it. Different wavelengths would be refracted by different amounts (thats why white light turns into a rainbow). If you send a red laser in, it would still be red, just refracted, creating a virtual light source. With the biprism setup, you would get two virtual light sources which would interfere. Now from here I believe you would use the same diffraction formulas to find the spacing between the maxima, and from there you would solve for wavelength. I believe there is a tricky part where you need to calculate the spacing of the two virtual sources, because you cant measure them directly. I dont remember how :S

This is very brief, but please let us know if you need more detail.