I wish to obtain the refractive index of a smooth surface using only a laser of given wavelength and a light sensor. I thought of using the Pfund method (attached), but I can't understand how the light sensor would fit in instead of the paper. I must use the sensor by the way. Can this be done on a horizontal table and then detected using a sensor?
Keeping in mind that a surface cannot have a refractive index, but rather the bulk material which has that surface,
what shape is the material you're measuring, and do you get to modify it? If, for example, it's a planar solid (front and back faces parallel), point the laser at an angle and measure the lateral displacement of the output beam. Given that and the thickness of the material, it's easy to calculate the index.
As to Pfund's method: it depends critically on having some sort of diffuser at the entrance point of your light source. You can't aim a collimated (laser) beam at an angle which would produce total internal reflection at the far side, for reasons which should be obvious. So with paper (in contact with the surface!), or roughened surface, or a little translucent white paint applied, somehow you disperse the light right at the entrance surface.