Comparison of various emissions from the laser dye solution under picosecond laser pulse pumping

We experimentally measured the spectral and the temporal properties of various emissions from the Rhdamine 6G dye solution pumped by picosecond laser pulses. These emissions involve the transverse amplified spontaneous emission (ASE), the longitudinal ASE, the longitudinal ASE coupled with partial and stronger coherent feedback, and the random laser. The random laser is made by adding TiO2 nanopowder to the dye solution as scatterer. The spectral and the temporal shapes and widths of these emissions are measured using a spectrometer and a streak camera combined with a CCD. The transverse ASE and the longitudinal ASE have similar spectral widths, while the longitudinal ASEs coupled with the coherent feedback show narrowed spectral widths. The pulse shapes and widths of the longitudinal ASE with coherent feedback show how the coherent feedback comes to existence. The experimental results show clearly the effect of the degree of the coherent feedback on the spectral narrowing. The spectra and the pulses of the random laser of some scatterer densities are presented, showing that the random laser without sharp peaks also has partial coherent feedback in it at certain scatterer densities in the weak scattering regime.