Coherence analyses / Measurement of 4D coherence function
The high degree of coherence is one of the most important characteristics of laser light which allows for numerous applications. Using Young’s double slit experiment only the basic coherence properties of a beam can be measured as the entire spatial coherence function is four-dimensional.
We pursue the formalism of the Wigner distribution function representing the Fourier transform of the mutual coherence function, which includes all information on the spatial coherence properties of the radiation field. The Wigner distribution function can be accessed experimentally by caustic scans and is reconstructed by an algorithm mapping the measured beam profiles into a four-dimensional phase space. As a result, the global degree of coherence, coherence lengths and beam characteristics such as wavefront, 4D propagation matrix and M² value can be deduced easily.
The method of the Wigner distribution function is suitable for laser beams in a broad spectral range from NIR to EUV and soft x-rays.
B. Schäfer, K. Mann:
“Characterization of an ArF excimer laser beam from measurements of the Wigner distribution function”, New J. Phys. 13 (2011)
B. Schäfer et al:
“FEL beam characterization from measurements of the Wigner distribution function”, Nucl. Instr. Meth. Phys. Res. 654 (2011)
T. Mey et al:
“Wigner distribution measurements of the spatial coherence properties of the free electron laser FLASH”, Opt. Expr. 20 (2011)
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