A tunable random laser with a bendable poly (dimethylsiloxane) (PDMS) substrate was described. The substrate is prepared based on soft lithography from lotus leaf, which have the similar surface structure with lotus leaf such as micropapilla. The micro-papilla on the surface of the substrate will provide efficient multiple scattering for the photon generated from gain medium, and the coherent random lasing is emerging because photon form closed-loop path among micropapilla via the scattering. The wavelength of the random laser emission spectrum can be tuned as wide as 26.0 nm by changing the pump position due to the diverse distribution of the micro-scale features on the soft substrate. The random laser provides a promising solution toward the realization of many laser based applications such as integrating optical biosensors on chips, probing micro-scale structural alterations and developing a multi-color even white random laser.
Stimulated Raman Scattering (SRS) is important method of laser frequency conversion. Optical frequency-comb is a special kind of SRS which output multiple Stokes beam simultaneously, and lasers with mutiple wavelength have broad applications. In this paper, the optical frequency-comb generated by SRS of CO2 is presented and the spectral range covers from 0.4 μm to 1.5 μm. Research also indicates that the characteristics of optical frequency-comb depends on the wavelength of pumping laser. For instance, the SRS photon conversion efficiency pumped by 1064 nm laser is high at 1248nm, 1510nm but that pumped by 532 nm laser is high at 574nm, 624nm 683nm. The different features are compared and analyzed by the use of the mechanism of four-wave mixing and the change of SRS gain coefficient with Stokes wavelength.
The kinetic behaviors of 6p[1/2]0, 6p[3/2]2 ,and 6p[5/2]2 were examined under the ultrahigh pumped power. These processes were detected by the way of time-resolved fluorescence and ASE spectra. A theory of energy-pooling is presented under the focused condition. There are three types of energy-pooling processes. The first type is energy-pooling ionization. The obvious ionization can be observed whenever the laser prepared state is the 6p[1/2]0, 6p[3/2]2, or 6p[5/2]2 state. The second type is energy-pooling with big energy difference. The energy-pooling collision between the two 6p[1/2]0 atoms can produce one 5d[3/2]1 atom and one 6s’[1/2]0 atom when the prepared state is 6p[1/2]0. The third type is energy-pooling with small energy difference. The way of generation of five secondary 6p states is energy-pooling instead of collision relaxation.
After the multiphoton ionization of sodium-argon mixture, time-resolved atomic emission spectrum is used to experimentally study the unusual phenomenon of the obviously different broadening between Na D1 and D2 lines spectra. The primary reason for the unusual broadening of Na D2 line is that the spectral line of Ar I 588.9 nm overlays with Na D2 line (589.0 nm) after ionization, and the serious self-absorption on Na D2 line is the secondary reason. Although there is difference of population between 32P3/2 and 32P1/2 states, the experiment result demonstrates that the difference between Na D lines in radiation channel will not affect the broadening of spectral profile.
We have demonstrated a high peak power electro-optically cavity-dumped (CD) laser and a high energy picosecond regenerative amplifier (RGA) at 1342 nm. Their output power, pulse energy, pulse widths, and peak power were reported, respectively. For CD operation, the maximum pulse energy was 0.308 mJ at 1 kHz with the pulse width of 23.3 ns. The corresponding peak power was 13.2 kW. The maximum pulse energy of 0.243 mJ was extracted from RGA at 1 kHz under the seeded pulse energy of 250 pJ, resulting in its total optical gain of 9.7×105 . Its pulse width was estimated to be 43.8 ps, corresponding to a peak power of 5.55 MW.
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