First measurement of 12 Optical Density with 1 nm resolution

In the last few years, optical coating technologies have made significant progress which allows depositing hundreds of layers with perfect control, hence emphasizing a generation of complex optical filters with ultimate performances.


Such balance now requires upgrading of 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 characterization Apparatus (SALSA). Thanks to the use of a SuperK EXTREME supercontinuum laser, for the first time to our knowledge, SALSA measured within the spectral range (400 nm–1650 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 for a new generation of spectrophotometric tools.

With the tunable and accurate spectral filtering from the supercontinuum laser, SALSA allows the measurement of angularly and spectrally resolved scattering patterns in the same 400 nm-1650 nm range.

The detection limit for BRDF and BTDF is the air diffraction level on the whole range of analysis and measurement accuracy is guaranteed to be better than 1%, which is the ultimate level of worldwide scattering metrology.

Figure 1: First broadband transmission measurement down to OD 12
Figure 2: Measurement of spectrally and angularly resolved scattering function for a complex optical filter (>100 layers) compared to modeling. The color scale is logarithmic.

This work has been realized thanks to the support of the French National Direction of Armament (Direction Générale de l’Armement) and the French National Space Center (CNES), Professor Michel LEQUIME, and Dr. Myriam Zerrad, Institut FRESNEL –  CONCEPT Group