Dynamic surface roughness profiler

Abstract

A dynamic profiler is presented that is capable of precision measurement of surface roughness in the presence of significant vibration or motion. Utilizing a special CCD camera incorporating a micro-polarizer array and a proprietary LED source, quantitative measurements were obtained with exposure times of <100 µsec. The polarization-based interferometer utilizes an adjustable input polarization state to optimize fringe contrast and signal to noise for measurement of optical surfaces ranging in reflectivity from 1 to 100%. A new phase calculation algorithm is presented that nearly eliminates phase-dependent errors resulting in shot noise limited performance. In addition to its vibration immunity, the system's light weight, <5 kg, compact envelope, 24 x 24 x 8 cm, integrated alignment system, and multiple mounting options facilitate use both directly resting on large optical surfaces and directly mounted to polishing equipment, stands, gantries and robots. Measurement results presented show an RMS repeatability <0.005 nm and an RMS precision < 0.1nm which are achieved without active vibration isolation.

Vibration insensitive extended range interference microscopy

“…7. In this case the measured step size varied roughly 60 nm between the two measurements, whereas the noise in the phase essentially limits the repeatability when using the calculated step size [23]. In this example the vibration largely results in a pistoning movement.…”

Fringe-print-through error analysis and correction in snapshot phase-shifting interference microscope

“…Interferometry is the industry standard metrology method for optical surface [1] and roughness measurement [2]. The phase-shifting interferometer (PSI) was introduced by Brunning [3] to achieve accurate metrology in 1974, PSI and its variations have been widely used in optical measurement [1,4,5].…”