You may try Spectral confocal technology.

Spectral confocal technology is a non-contact method used to measure surface height, particularly for micro and nano-scale measurements. It works by analyzing the spectrum of reflected light from a surface, where different wavelengths correspond to different heights.

Usually it been used to measure heights, but you can get intensity of different surface from the results, but maybe need some normalization to convert to the intensity of white light.