A diode pumped alkali laser (DPAL) provides a significant potential for construction of high-powered lasers in the future. To realize the scaling of a DPAL, heat management and flow field inside a vapor cell should be investigated. In this paper, a new kind of gas-flowing DPAL with a disc-type vapor cell was proposed. The gain medium of cesium and the buffer gas of ethane were filled in the vapor cell with the total pressure is about 1 atmosphere. The influence of the rotate speed of a cross-flow fan on the internal gas velocity, temperature, and output features of the laser was systematically studied. The corresponding experiment was carried out, and the output laser at 894.3 nm with power of 321 W was obtained.
Due to the rapid performance of taking away the generated heat of a diode pumped alkali laser (DPAL) system, a flowing diode pumped alkali laser (FDPAL) is thought to be helpful to mitigate the thermal effects and improve the power scaling ability of a DPAL system during the power scaling period. In general, a relatively perfect theoretical model for a FDPAL needs to take the laser kinetic, heat transfer, and computational fluid dynamics (CFD) into account at the same time. Until now, the commercial finite element method (FEM) soft can only simulate the fluid and thermal distributions in an alkali vapor cell for a FDPAL. The laser kinetic can only be effectively calculated by a coding soft. Therefore, the multi-physics coupling problem needs to be firstly tackled at the beginning of a design for a FDPAL system. In the paper, a loop iteration based co-simulation method is utilized to solve the multi-physics coupling problem during the simulation of a FDPAL. The temperature and fluid corresponded parameters of a FDPAL are obtained by a FEM soft. The laser kinetic corresponded parameters of a FDPAL are got by a coding soft. By constructing a java language based server, the calculated data of such two kinds of soft can be shared. Then, a main iteration based procedure with preset initial values is coded to control the running behavior and communication of the two kinds of soft. After several or several ten times loop iteration, the laser power, temperature distribution, and velocity distribution of a FDPAL can be theoretically investigated. It has been demonstrated that the co-simulation based calculating results show a good agreement with the experiment results.
A diode pumped alkali laser (DPAL) provides a significant potential for construction of high-powered lasers. To realize the scaling of a DPAL, heat management should be optimized. In this paper, a new kind of gas-flowing DPAL was proposed, in which a small cross-flow fan with diameter of 125 mm was set in the center of a cylindrical vapor cell whose diameter and thickness is 160 mm and 55 mm, respectively. The gain medium of cesium and the buffer gas of ethane were filled in the vapor cell with the total pressure is about 1 atmosphere. A mathematical model was constructed to systematically study the influence of the rotate speed on the internal temperature distribution and the output features of the laser. And then, the experimental study of the laser system was then carried out, in which the output laser at 894.3 nm with power of 32 W was obtained. The results show that both the velocity distribution and temperature distribution are greatly influenced by the rotate speed of the cross-flow fan, and then the heat generated from the DPAL can be took away efficiently, which is very important to the output performance of the laser system. These results indicate that this new type of gas-flowing DPAL might be a good choice for power scaling of DPALs.
KEYWORDS: Fluctuations and noise, Cesium, Semiconductor lasers, Gases, Diodes, Output couplers, Laser systems engineering, High power lasers, Alkali vapor lasers
A diode pumped alkali laser (DPAL) provides a significant potential for construction of high-powered lasers. To realize the scaling of a DPAL, heat management should be optimized. In this paper, a new kind of gas-flowing DPAL was proposed, in which a small cross-flow fan with diameter of 80 mm was set in the center of a cylindrical vapor cell whose diameter is 125 mm. The gain medium of cesium and the buffer gas of ethane were filled in the vapor cell with the total pressure is about 1 atmosphere. A mathematical model was constructed to systematically study the influence of the rotate speed, the heating temperature on the internal temperature distribution, and the output features of the laser.
In this paper, a widely tunable Cr:LiSAF laser with an external cavity was employed as the pump source. By using a triangular prism and double output couplers in the cavity, the line width can be narrowed and the pump center wavelength can be adjusted to the ideal value. The FWHM in spectrum of a pump laser can be narrowed to as small as 0.5 nm. The absorptivity of Ho:BYF at the center wavelength from 885 nm to 890 nm was measured, and the optimal pump center wavelength has been determined to 888.5 nm. Then the focal length of a focusing lens and the curvature radius of a laser output coupler have been optimized through a series of experiments. Finally, we have obtained the laser output at 3.9 μm with the optical-to-optical efficiency larger than 10% at the relatively low repetitive rate. The results might be helpful for the construction of a real laser system.
Laser processing is a technique based on the interaction between a laser and the substance for cutting, drilling, cleaning, welding, and other operations on metallic or non-metallic materials. It is widely used in some important fields of the national economy such as automobiles, microelectronics, electrical appliances, aviation, metallurgy, medical treatment, and machinery manufacturing. In the process of high-powered laser processing, a large amount of plasma will be generated and there will be the obvious inverse Bremsstrahlung absorption (IBA) near the plasma plume. The effect of laser processing will be significantly deteriorated due to the absorption of laser photons and changes in light intensity distribution. Besides, laser-induced plasma is produced during the interaction between a high-powered laser and materials. Also, it has the very important value in the research of analyzing the high-powered laser processing. To fully understand the laserinduced plasma, this paper uses the Hilbert procedure to numerically investigate the plasma generated in the laser processing. The method firstly acquires the images corresponding to the fringes of a Mach–Zehnder interferometer by using the detection after a probe laser beam passing through the plasma plume. Then, a series of operations such as the spectrum shift, unwrap, and Abel inverse transformation are performed after a fast Fourier transform (FFT). Finally, the density distribution of plasma can be calculated. This methodology provides a new algorithm for the research of laserinduced plasma, and it also valuable for the understanding the high-powered laser processing process.
Because of the low thermal conductivity of the mixture gases in an alkali vapor cell, the temperature of the pumping area of an alkali vapor cell can be extremely high than that of other area. Therefore, thermally-induced effects, such as, consumption of atomic alkali, degradation of output power, glass window contamination by the products of the optically chemical reaction between atomic alkali and buffer gases, etc. can be observed in high temperature heated diode pumped alkali lasers (DPALs) in the case of high power pumping. Generally, a flowing diode pumped alkali laser (FDPAL) system is thought to be a useful way to mitigate thermal effects in a DPAL system. In the paper, a mathematical model of a flowing diode pumped cesium laser (FDPCL) was constructed to systematically study the temperature distribution, the flow filed distribution, and the impacts of pressure of the buffer gases on output power of a FDPCL, etc. The laser kinetics, heat transfer, and computational fluid dynamics (CFD) are both taken into account at the same time during the simulation. The multi-physics coupling method was utilized to solve such three physics induced problem during the simulation. It has been demonstrated that the temperature distribution of a FDPCL system depends on the distribution of gas flow filed, a gas flow method can decrease thermal effects in a DPAL system, and the output power of a DPAL can be improved by increasing the velocity of gas flow filed.
In this paper, a mathematic model is established for the end-pumped continuous-wave cesium vapor laser. The threedimensional calculation of amplified spontaneous emission (ASE) is presented. The ASE flux is calculated from every point through all possible paths inside the medium. We systemically investigate the influences of the cell radius, cell length, and cell wall temperature on ASE. The results show that the ASE effect can be decreased by adjusting these key factors. To the best of our knowledge, there have not been any reports on the ASE estimation in an end-pumped DPAL so far.
KEYWORDS: Nd:YAG lasers, Absorption, Refractive index, Rod lasers, Solid state lasers, Ray tracing, Finite element methods, Laser beam diagnostics, Reflectors
LD-side-pumping schemes for a solid-state laser offer the advantages of both high pump efficiency and high output power. However, thermally-induced lens has been known to severely affect the performance of high-powered solid-state lasers. To solve the problem, a systematic simulation model was developed by combining two procedures of ray tracing and finite element method (FEM) together to explore the thermal lens characteristics of a high-powered Nd:YAG laser. The relationship between the spatial heat density distribution and thermally-induced refractive index distribution was investigated by taking an inhomogeneous pentagonal pumping into account. The influence of a pentagonal pumping on the characteristics of the thermal lens focal length of a laser rod was studied afterwards. According to the results, if the volume average heat density of a laser rod is kept as a constant, the focal lengths of a thermally-induced lens in the pentagonal pumped laser rods will be shorter than those of the homogeneously pumped laser rods with different rod diameters. It has also been demonstrated that the focal lengths of both pumping cases are not sensitive to the variation of the rod diameter. The study is thought to be helpful for the design of a high-powered solid-state laser.
In order to satisfy the requirements of laser irradiation and laser ranging over the long distance, and to realize the miniaturization, the modularization and the engineering application of 1J high-energy DPSSL circuit system, a laser driving circuit system is designed according to the laser work patterns of one oscillator stage and two amplification stages. The system includes many parts, such as the integrated power supply circuits, the corresponding LD drivers of three stages, the signal control circuits, the Q switched circuits, the receiving circuits and the temperature control circuits, etc. It possesses the characteristics of 28VDC input power source, working frequency 25Hz,driving laser output 1J, working stable and reliable, thermal management optimization and small size as well as light weight. The study promotes the comprehensive technical specifications of the platform load effectively and can also provide a valuable reference for the miniaturization of high energy DPSSL circuit system.
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