REFRACTION OF AN ELECTROMAGNETIC PROBE WAVE IN A LASER-PLASMA

A method for reconstructing the refraction angle of electromagnetic pr obe radiation, based on a field-visualisation interferogram, was propo sed and implemented in laser plasma experiments. A reconstruction of t he refraction angle involved determination of partial derivatives of a n interference phase shift partial derivative delta/partial derivative x and partial derivative delta/partial derivative y at each point of the wavefront reconstructed from an interferogram. An example is given of an analysis of a laser-plasma interferogram obtained on irradiatio n of an aluminium target with a 2 ns pulse from a powerful Nd:YAG lase r of 25 J energy and 527 nm wavelength (the intensity on the target su rface was similar to 10(14) W cm(-2)). The refraction angle of the pro be radiation reached similar to 3 degrees and the maximum electron den sity in the plasma was similar to 2.6 x 10(20) cm(-3). The proposed me thod for reconstructing the refraction angle makes it possible to visu alise the structure of an inhomogeneity in the investigated object and to answer unambiguously the question of the cause of the appearance o f an 'opaque zone', observed in experiments on laser plasmas and Z pin ches.