Abstract

Recently, Lawandy et al. have observed laser action in a laser-pumped high-concentration dye solution with the addition of scattering particles. A quite different result has been found also: when a low-concentration pure-dye solution is excited, superradiance may appear, and with the addition of scatterers the threshold of superradiance is enhanced. Here we report an experimental study on the relation between the bandwidth of the emission and the gain length by using two kinds of gain area: point and line. For point excitation the laser beam was focused to a small point with a diameter less than 2 mm. In the other case the laser beam was focused by a cylindrical lens. Then the gain length was increased by an order of magnitude over that of the point excitation. We have tried two kinds of commercial TiO₂, particles with an average diameter of 1 μm and powdered TiO₂, and we have used homemade SrTiO₃ with particles with diameters of several micrometers.

© 1995 Optical Society of America