Build-up time of the random laser in R6G dye solution with TiO 2 scatters

Abstract

The dynamic properties of the laser emission are very important in studying the characteristics of the laser and may reveal the underlying operating mechanism. Here we report a more precise measurement of the build-up time of random laser pumped by picosecond pulse laser. The build-up time is defined as the time delay from the peak of the pumping pulse to that of the emission. The random laser is R6G dye solutions with nanometer size TiO ₂ as the scatterer. Various dye concentrations and scatterer density are tried and measured. A specially customized fiber and a streak camera with a spectrometer are employed to make the simultaneous measurement. The fiber has two branches and the lengths of both branches are made equal with a difference of much less than 1 mm. The dispersion of the fiber, which introduces much error in the results, is also measured and later compensated in the following data processing. The streak camera with spectrometer can catch the random laser pulse and the pumping pulse signal in one shot with a resolution of less than 2 picoseconds. The results show that the build-up time changes evidently with the dye concentration, while it changes a little along with the scatterer density. The pulse width almost remains the same in our experiment considering the errors.