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Hier finden Sie wissenschaftliche Publikationen aus den FraunhoferInstituten. Simulation of laser speckle patterns generated by random rough surfaces
 Holst, G.C. ; Society of PhotoOptical Instrumentation Engineers SPIE, Bellingham/Wash.: Infrared Imaging Systems: Design, Analysis, Modeling, and Testing XXXI : 27 April  8 May 2020, Online Only Bellingham, WA: SPIE, 2020 (Proceedings of SPIE 11406) ISBN: 9781510635890 ISBN: 9781510635906 Paper 1140609, 14 S. 
 Conference "Infrared Imaging Systems  Design, Analysis, Modeling, and Testing" <31, 2020, Online> 

 Englisch 
 Konferenzbeitrag 
 Fraunhofer IOSB () 
 Speckle pattern; spectral density; rough surface; sea surface 
Abstract
Laser speckle patterns typically occur when a laser beam with a narrow spectral linewidth is reflected by smallscale rough surfaces. These intensity patterns are of great interest for active imaging techniques such as gatedviewing, optical coherence tomography, or any other measurement techniques involving laser illumination. In addition to turbulence effects, surface roughness elevation plays an important role in this process. This paper presents the 2D simulation of isotropic smallscale rough surfaces with the corresponding objective speckle patterns, caused only by the reflection of laser light by those surfaces. In addition, laser speckles generated from sea surfaces, whose structures are anisotropic due to the effect of wind, are also shown. The numerical procedure for the simulation of the (material/sea) surface roughness is based on Fast Fourier Transform (FFT). Our method can simulate surfaces with given power spectral density or autocovariance function (ACF ). The most common are the Gaussian and exponential ACF's. Thereby, the rootmeansquare (rms) of surface heights and the correlation length are the main roughness descriptors for surfaces. A surface realization, using a fractal powerlaw for the spectral density, is also shown. For the simulation of the sea surface roughness, the main input parameters for the wave power spectrum are wind speed, wind direction and fetch. The simulation of the speckle patterns comprises the freespace propagation of a Gaussianshaped laser beam in forward direction, the subsequent reflection at the rough surface, which introduces fluctuations in the wave phase, and the backward propagation of the reflected laser beam. The method is similar to that of the laser beam propagation in a turbulent atmosphere that uses a 2D spatial field of phase fluctuations (phase screens), whereas here, only a single 2D phase screen is considered that defines the reflective medium.