Dynamic phenomena in laser cutting and cut quality

Coherent emission of light in the uv or vuv range can be obtained from an undulator or optical klystron by harmonic generation using an external laser. We show that if the input is a multimode laser (instead of an ideal monochromatic coherent wave) the kinetics of growth of the rms beam modulation is completely different from the one described by the usual Webster formula, and we find a simple analytical expression for a Gaussian input (large number of modes). Numerical calculations show that with 3 modes the result is already close to the Gaussian case, and that the frequency bandwidth increases as the square root of the harmonic number.