Instantaneous measurement of the intensity distribution of a focused high power laser pulse

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Abstract
A digitalized TV system controlled by a microprocessor allows the focused intensity distribution of laser pulses to be determined instantaneously. The use of silicon mosaic vidicons at 1.06 μm is discussed and their performance is compared with that obtained using photographic methods. The linearity response of the vidicon is very good provided a preillumination system is used. Dynamic ranges of 64, and 255 x 255 pixels are analysed. This system allows the minimum cross-section Smin of the focused laser intensity distribution to be measured five seconds after each laser shot, with an accuracy of ± 4 % for absolute values, and ± 2 % for relative variations of Smin . The usefulness of this system is amply demonstrated in a graphical plot of the variation in the number of ions formed, as a function of laser intensity for the four-photon ionization of Cs atoms