Laser damage is becoming more and more important part to consider in design of laser systems among these decade years, for high-power lasers are widely used in industry production, medicine, signal detection, and any other departments. There are two research directions of laser damage: one is the damage caused by ultra-short pulse, the other is that caused by ultraviolet beams. These two types of laser are usually combined to irradiate materials. Laser Induced Periodic Surface Structures (LIPPS) are special phenomena which can change many physical characters of materials, for example, surface absorptivity. LIPPS are usually caused by ultra-short pulse, as a step of laser processing. This paper will reveal the damage caused by ultra-short and ultraviolet beams, especially when they lead to LIPPS.
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.
Diode pumped alkali laser (DPAL) with hydrocarbon buffer gases has the features of low threshold and high efficiency. The chemical reaction between alkali and hydrocarbon gases affects the life time of DPAL. In this paper, a method based on Fourier transform infrared spectroscopy and Lambert-Beer law is adopted to find a safe temperature at which DPAL runs for a long term. A theoretical model is established to figure out ways to reduce the peak temperature in the cell window. The results indicates that 170 °C is a safe temperature. Although the absorbance of the cell window to the pump light and alkali laser is lower, there is temperature increase. Small light-transmitting area and air blowing on the windows can reduce the peak temperature effectively. Cooling the cell window is essential and critical in a long-term running DPAL.
A self-heated diode-pumped alkali laser (SDPAL) with a microfabricated alkali cell is proposed. Based on Beach’s model and finite-element analysis theory, the output characteristics of a cesium self-heated laser are studied. The results indicate that an SDPAL with a cell length of 2 mm is feasible. The output power of a typical SDPAL is ∼Watt level. Rapid heat convection around the mini cell can increase the output power. At the same time, the utilization ratio of the pumping light will decrease. A heating experiment is also conducted to validate the theoretical model. When pumping power of 0.69 W is illuminated on the light absorber, the cell temperature can reach 76.4°C with a single-side heated structure. The results show that with a mini vapor cell, SDPAL can be portable and competitive when ∼Watt-level laser with wavelength of alkali D1 line is required.