Theoretical and experimental analysis of two schemes for controllable transformation of short laser pulses coherence is presented: self phase-modulation in CCl4 with thermal nonlinearity and time-delay line. Such methods can be utilized in high-speed schemes of speckle-noise reduction for perspective systems or laser UV projective lithography.
Reciprocity inequalities (uncertainty relations) are studied for a finite light pulse with complex spatio-temporal structure and for statistical ensemble of such pulses. A possibility to create partially coherent pulses (and ensembles) with parameters close to minima of these inequalities both in temporal and spatial domains are discussed. The structure of optimal beams is analyzed from point of view of modal treatment of coherence (biorthogonal Karhunen-Loeve expansion).
Nonlinear self-action of light fields in a layer of cubic nonlinear medium can serve as a convenient tool for controllable coherence manipulation. In the present work this scheme is considered for partially coherent input light. Due to experimental requirements, we consider the model of multimode laser. For the purely phase statistics of the input beam (when the average intensity can be represented in factorized form I(r,t) equals I(r)I(t)), it is possible to find out rather simply the dependence of the effective number of (coherent) modes in output radiation on the input number of modes and the nonlinearity parameter.
Via solution of appropriate variational problem it is shown that light beams with Gaussian spatial profile and sufficiently short duration provide maximal destruction of global coherence under nonlinear self-modulation.
Some consequences of spatio-temporal symmetry for the deterministic decomposition of complex light fields into factorized components are considered. This enables to reveal interrelations between spatial and temporal coherence properties of wave. An estimation of average number of the decomposition terms is obtained in the case of statistical ensemble of light pulses.
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