Polarization-dependent laser action in a two-dimensional random medium

We examined laser action in a two-dimensional amplifying and scattering medium consisting of random array of dye-doped plastic fiber. When the excitation pulse energy was increased, the parallel emission component to the fiber first reached the laser threshold showing spectral collapse, and then further increase in the excitation pulse energy resulted in the subsequent laser action in the perpendicular component. Two-beam spatial-correlation measurement was performed to examine the gain regions. It was found that the size of the gain region is different between the two polarization components. Experimental results on the threshold and the gain region are discussed on the basis of simple rate equations.