Thermo-optic nonlinearity of the laser dye LDS 867 under low power CW laser excitation

Temporal profiles for measuring threshold of random lasers pumped by ns pulses

“…When the pump energy is increased to higher value, more molecules are excited to a high level and the probability of stimulated emission is increased. Simultaneously, strong laser field generates the reduction of the environment refraction index in the pump area by the nonlinear effect 43 – 45 , indicating a lager transport speed of photon. And the laser-induced refractive index gradient is induced, meaning an effective poor cavity to further decrease optical path and the loss (Detailed information shown in Supporting Information) 46 – 48 .…”

“…As a result, lasing resonance can be built-up in a shorter time before photons leave the gain regime 42 , resulting in narrowing of the linewidth and more intense emission and quickly reduction of the delay time. After the pump power reaching the lasing threshold, the gain is larger than the loss from the random system and lasing resonance is formed based on the coupling role of several nonlinear optical effects (saturation absorption 49 , 50 , large refraction index gradient for optical cavity 51 , 52 , stimulated Raman scattering 38 , 40 , self-phase modulation 43 , 53 – 57 , et al . ), which may induce a relative stable delay time (more detailed information seen in the Supplementary Information).…”

“…), which may induce a relative stable delay time (more detailed information seen in the Supplementary Information). In particular, self-phase modulation process in laser cavities can shorten the pulses and improve mode-locking stability (more detailed information seen in the Supplementary Information) 43 , 53 – 57 . The stimulated Raman scattering process may play a role of seed at several wavelengths, which attributes to the random lasing with several spikes, meaning a stable delay time.…”