Meaning
Metrology system for mapping the spatial distribution of birefringence and phase retardation across an optical component. Images at two distinct spectral points are captured by dual wavelength imaging polarimetry to resolve phase ambiguities that occur when retardation exceeds a single wavelength. This capability is required for qualifying large-format glass blanks used in lithography.
Phase Evaluation
Optical retardation often wraps around if the physical thickness or stress is high enough to shift the phase by more than one cycle. When dual wavelength imaging polarimetry is applied, the synthetic wavelength generated by the difference between the two sources provides a much larger unambiguous range. The pixel-by-pixel map reveals internal stress concentrations that a single-point sensor would overlook.
Data from both wavelengths are combined to produce a continuous phase map without discontinuities.
Resolution Limit
Spatial detail is determined by the sensor array and objective magnification.
Inspection Throughput
Rapid data acquisition allows for hundred-percent inspection of precision optics before they move to the assembly stage. Using dual wavelength imaging polarimetry at the prototype phase identifies whether a cooling cycle in the glass furnace is too fast. If these stress patterns are not caught during the initial pilot, the resulting parts may crack during high-power laser operation.
