Ultra low-na refractive index profiling system and method for filtering out severely disturbing diffraction effects

A system for determining a refractive index profile of an optical object having a cylindrical surface and a longitudinal cylinder axis, the system comprising:

• (a) a measuring cell having a light entry surface, a light exit surface, and a cavity disposed therebetween configured to receive the optical object;
• (b) one or more light sources configured to emit one or more optical beams toward the measuring cell;
• (c) a stage configured to support the measuring cell;
• (d) an optical sensor configured to be positioned in a path of the one or more optical beams downstream of the light exit surface of the measuring cell;
• (e) a pinhole aperture selectively movable into and out of the path of the one or more optical beams upstream of the light entry surface of the measuring cell;
• and
• (f) a controller configured to:
• (i) initiate relative movement between the stage and the one or more light sources and optical sensor, with the pinhole aperture in the path of the one or more optical beams, to cause the one or more optical beams to impinge on the cylindrical surface of the optical object perpendicularly to the longitudinal cylinder axis at a first plurality of scanning locations,
• (ii) measure a first deflection function of the optical object based on detection by the optical sensor of the one or more optical beams after deflection by the optical object for each of the first plurality of scanning locations,
• (iii) initiate relative movement between the stage and the one or more light sources and optical sensor, with the pinhole aperture out of the path of the one or more optical beams, to cause the one or more optical beams to impinge on the cylindrical surface of the optical object perpendicularly to the longitudinal cylinder axis at a second plurality of scanning locations,
• (iv) measure a second deflection function of the optical object based on detection by the optical sensor of the one or more optical beams after deflection by the optical object for each of the second plurality of scanning locations,
• (v) merge at least a portion of the first deflection function with at least a portion of the second deflection function to obtain a composite deflection function, and
• (vi) calculate the refractive index profile of the optical object using the composite deflection function.