I have to measure the depth of the cavity in an object which is in the micrometer(10^-6 m) order. I'm given a laser, mirrors, neutral density filters, photodiode, and the object which is to be measured. Can anyone suggest scientific articles that are related to this problem provided with the materials aforementioned? As I was browsing the internet, I also found a few related articles like the light section method and measuring the width of a hair using interference patterns. However they didn't make use of ND filters.