If the angle between optical flat and surface to be tested is very small, then what is the difference of separation between optical flat and surface between two similar adjacent fringes?
(a) λ
(b) λ/2
(c) λ/3
(d) 3λ/2
I got this question in an interview for internship.
Question is from Interferometry Applied to Flatness Testing in division Measurement by Light-Wave Interference of Engineering Metrology