Diffraction & Interference: Investigating Wavelengths with Fresnel Biprism

[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 :)

 

[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 can't measure them directly. I don't remember how :S

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

 

[sir-pinski]

Great job on your lab report! To answer your question, yes, the refraction within the prism can cause a change in wavelength. This is known as chromatic dispersion, where different wavelengths of light are refracted at different angles due to their different speeds in the prism. However, in most cases, the change in wavelength is small and can be neglected. This is because the prism is designed to minimize chromatic dispersion and maintain the original wavelength of the light passing through it. So, for your experiment, the wavelength of the laser should go back to its original value after passing through and out of the prism. Keep up the good work!