EXTREME optical metrology: First broadband measurement of a 12 optical density with 1 nm resolution

In the last few years, optical coating technologies have made significant progresses which allow to deposit hundreds of layers with a perfect control, hence emphasizing a generation of complex optical filters with ultimate performances. Such balance now requires to upgrade the metrological tools for accurate characterization of absorption and scattering, stress and birefringence…

Within this context, the Scattering Group of Institut FRESNEL designed and developed a Spectral and Angular Light Scattering characterisation Apparatus (SALSA). Thanks to the use of a SuperK EXTREME supercontinuum laser, for the first time to our knowledge, SALSA measured within the whole CCD range (400 nm – 1000 nm) and with a 1 nm resolution the spectral transmission of filters down to 10-12 levels (equivalent to 12 Optical Density) in the rejection band whereas the state of the art was limited to OD 6 for such a wide range of analysis. This paves the way towards a new generation of spectrophotometric tools.

With a tunable and accurate spectral filtering of the supercontinuum laser, SALSA allows the measurement of angularly and spectrally resolved scattering patterns in the same 400 nm -1000 nm range. Detection limit for BRDF and BTDF is the air diffraction level on the whole range of analysis and measurements accuracy is guaranteed to be better than 1%, which is the ultimate level of world wide scattering metrology.

First Broad band transmission measurement down to OD 12
Measurement of spectrally and angularly resolved scattering function for the calibration of SALSA. Detectivity is limited by air diffraction level on the whole CCD range