Speckle-based wavemeter

A spectrometer based on the application of dynamic speckles will be disclosed. The method relies on scattering of primarily coherent radiation from a slanted rough surface. The scattered radiation is collected on a detector array and the speckle displacement is monitored during a change in the incident wavelength.

The change of wavelength gives an almost linear phaseshift across the scattering surface resulting in an almost linear shift of the speckle pattern, which is subsequently monitored. It is argued that frequency changes close to 100 MHz can be probed using a common CMOS array. Experiments showing agreement with theoretical predictions will be given.

An extension of the method, with which fast wavelength changes in the GHz regime can be probed, will be discussed but not experimentally verified. This method relies on shearing the dynamic speckle pattern across a cylindrical lens array as it’s well-known within spatial filtering velocimetry.