The dynamic speckle-based wavemeter

Based on a previously devised speckle-based set-up for probing minute wavelength changes for a coherent field [1], [2] we will here present the first experiments where these changes are resolved on a millisecond time scale. The setup is based on probing the lateral shift of a speckle pattern arising from a slanted rough object, the speckle displacement being linearly proportional to the wavenumber change. Thus, by shearing the speckle pattern across a grating-like structure [3],[4] and [5], a frequency proportional to the frequency of the wavelength change can be derived as will the irradiance. Thus, a cordial display of the complex field amplitude may be obtained with a high temporal resolution and a reasonable spectral resolution. The spatial filter is here preliminarily implemented by recording the speckle pattern with a CMOS array with subsequent digital image processing mimicking the use of a spatial filter.