Patent ID: 8013985

Claim:
A method of measuring a refractive index profile of a transparent cylindrical object having a central axis, a radial coordinate r, an outer edge at a radius r=R and an actual refractive index profile η i (r) at a wavelength λ, the method comprising: transmitting a radiation beam having a wavelength λ through the cylindrical object in a direction transverse to the central axis for different heights relative to the central axis; detecting positions of the transmitted radiation beam relative to the cylindrical object and converting the positions to corresponding deflection angles to form a measured deflection function ψ m ; and numerically fitting a target deflection function ψ t to the measured deflection function ψ m within a first object region that does not include the outer edge by varying yet unknown radius R and yet unknown refractive index η i to obtain an estimated refractive index profile η* i (r) over a second object region equal to or greater in size than the first object region.