OPTICAL SMOOTHING OF THE HIGH-POWER PHEBUS ND-GLASS LASER USING THE MULTIMODE OPTICAL FIBER TECHNIQUE

The use of an optical fiber for the coherence reduction at the laser front-end changes the common point laser source into an extended source. The required optical arrangement taking into account the divergence of the extended source beam is described. The smoothing efficiency is measured by the reduction of one order of magnitude of the contrast of the energy modulations in the focal spot. The output power is limited to 4 TW, which is about half the laser capability, by a saturation-like effect in the large amplifier section. It is believed that the hot spots of the instantaneous speckle patterns in the glass lead to nonlinear losses, responsible for the observed power limitation. This hypothesis is supported by the measurement of the transmission of laser glass samples on a separate experiment with high intensity picosecond pulses.