Generation of spatially incoherent short pulses in laser-pumped neodymium stoichiometric crystals and powders

We have developed mirrorless quasi-monochromatic laser sources made of stoichiometric neodymium compounds (Nd0.75:La0.25P4O15 and NdCl3· 6H2O) pumped by nanosecond laser pulses. We find that short subnanosecond and narrow-bandwidth (0.15-nm) pulses are generated in both compounds when they are pumped at high intensities. This emission is spatially incoherent as shown by a speckle statistics analysis. Its origin is discussed in terms of collective effects. This shows that poor optical materials with strongly quenched emission may be useful for generating incoherent short pulses.