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.
With the development of laser technology, nanosecond lasers have been widely used in material micromachining due to their advantages such as the narrow pulse width and high-power density. The high-order harmonic generation procedures have been invented to obtain 532, 355, and 266 nm radiations based on a 1064 nm Nd:YAG laser. In this paper, the influence of different sample moving speeds and laser power on the cutting effects were studied using three kinds of laser sources. It can be seen that the state of the cutting surface has not changed obviously when the laser power was increased. The self-defined cutting threshold, i.e., 2.25 W·s/mm, has been obtained by investigating the processing morphology with the power of 1.35 W at different sample moving speeds for both a 355 nm laser and a 266 nm laser. Increasing the laser power to 3.20 W, we obtained the cutting threshold of about 1.80 W·s/mm for a 355 nm laser. The scorching status of the surfaces cut by both a FHG laser and a SHG laser have been found to be more serious than that cut by a THG laser. The experiments have demonstrated that the machining efficiency increases with the laser power, but the cutting quality becomes worse at the same time. The results are thought to be useful for the PCB cutting applications in the industrial fields.
Although aluminum processing with lasers has become popular in industrial applications, machining some blind grooves or blind holes with a required size in aluminum sheets is also a difficult task for laser technicians. In this paper, blind grooves with the depth of about 0.1 mm and the width of less than 0.1 mm on a 0.24 mm thick aluminum sheet have been realized by using two kinds of nanosecond Q-switched lasers without burning the coating polymer layer. The effects of the laser wavelength, average power, and scanning speed on laser processing have been investigated in detail. The groove machining of aluminum sheets has been carried out at different laser power and machining speeds by use of two Q-switched lasers with the wavelengths of 532 nm and 355 nm. The experiment result shows that the faster the scanning speed, the better the processing efficiency. And the status of blind grooves processed by a 355 nm laser is cleaner and smarter. In summary, the optimal laser parameters for processing grooves on the aluminum surface are the peak power density of 2.27×108 W/cm2 with the scanning speed of 0.1 mm/s for a 355 nm nanosecond laser. The results of our study might be of great importance as a reference for processing blind grooves on aluminum sheets in some industrial applications.
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.
Silicon is one of the most important semiconductor materials and the basic material in the field of modern microelectronics, and it has been widely used in microelectronics and photovoltaic industries which are closely related to our daily life. Because the traditional silicon wafer cutting technology has some serious problems such as insufficient cutting accuracy, low efficiency, and serious pollution, the laser processing has been paid more and more attention in silicon wafer cutting applications in about recent fifteen years. Therefore, it is extremely important to develop the laser silicon wafer cutting procedure for the improvement of the laser silicon wafer processing technology. An algorithm named as constrained interpolation profile has been invented in computational fluid dynamics. It is actually a semi-Lagrangian method to solve hyperbolic partial differential equations, and has the advantages of the stable results, compact process, and low dissipation, etc. Focused Gaussian laser beams with the same energy of 200 μJ and pulse widths of 100 fs, 20 ps, and 0.5 ns, respectively, were irradiated on the surface of a silicon wafer. The physical properties of density, temperature, and pressure in both time and space domains were obtained by means of the algorithm of constrained interpolation profile in the laser processing simulation. The mechanisms of laser silicon wafer processing were studied in detail by analyzing the changes in physical properties of silicon material. The conclusions of this paper might be useful in the optimization of a silicon wafer cutting process by the use of a pulsed laser.
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.
Glass is one of the most important materials in industrial applications because of its high hardness, high thermal stability, and high transparency in the visible band. In general, it is very difficult to process glass with near-infrared, visible, and near-ultraviolet lasers. Physically speaking, the absorption coefficient of the glass sheet is one of the most crucial factors for processing efficiency, and it can be influenced by the temperature of a glass sheet. Therefore, to obtain the optimal processing efficiency, the influence of the temperature on the absorption coefficient should be studied in detail. In this paper, we theoretically and experimentally studied the relationship between the absorption coefficient and the temperature to improve the processing efficiency. A tunable near-ultraviolet Nd:YAG frequency-tripled harmonic laser with the wavelength ranging from 270 to 400 nm was utilized to measure the absorption coefficient, and a Peltier temperature controller was used to heat the glass sheet. It has been demonstrated that controlling the temperature is an efficient method to process the transparent glass sheet.
A serious rust phenomenon has been observed in an enclosed laser cavity. To figure out the reason which induces the rust, some experiments were carried out by recording the variation of the temperature and relative humidity at different positions. Thus, the vapor density can be numerically deduced by using the measured physical features. To avoid the undesirable rust phenomena occurring again, the exchange windows were chiseled out on an inner cover of the enclosed laser cavity in order to decrease the difference between the vapor density inside the cover and that outside the cover, which relates to the efficiency of dehumidification. The results validate that such a difference of the vapor density is a function of the area of exchange windows. Then, the curves of the vapor density versus the area of exchange windows have been plotted. It has been demonstrated that adding the area of exchange windows, which were pasted by some particulate air filters to prevent external dust particles from entering, on an inner cover might be a feasible method to avoid rust near the water cooling elements. Such a study might be useful for laser technicians to pay much more attention to the protection of undesirable vapor-induced rusting.
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.
Laser processing plays a key role in treating a lot of materials. The visible nanosecond laser processing based on a tripartite-interaction system has been proved to be an effective method of processing materials with high optical transparency, which has the advantages of low cost, high efficiency, and simplicity over the direct processing by using a femtosecond laser. However, further studies on the theoretical mechanism and parameter optimization keep to be rear for the hybrid tripartite-interaction laser processing. In this study, we have carried out the confirmatory experiment and numerical simulation of laser processing with a tripartite-interaction system, which includes a visible nanosecond laser (19 ns@532 nm), a piece of transparent glass, and a copper foil. The experiment indicates that drilled holes can be obtained on the glass sheets by using the visible nanosecond laser. The numerical results, which have been obtained by an approach named as constrained interpolation profile, reveal that the processing mechanism is based on the heat conduction, generation of stress and ablation between the glass and the copper foil. Our results could to be useful for the development of visible nanosecond laser processing in industrial applications.
It has always been difficult to process a metal film with high reflectivity in the field of manufacture, industry, medicine, and military, etc. Since much of the laser energy can be reflected especially when the reflectance of the target film surface is high, it is hard to process such a metallic film by laser radiation as the energy absorbed by the film material is very little. In this paper, we used a nanosecond pulsed laser to scribe some patterns on a smooth titanium (Ti) film, and investigated the surface morphology of a Ti film ablated by different laser spot sizes and laser energy. In our experiments, it has been found that the Ti film can be efficiently processed although the surface reflectance of the Ti film is about 57% at the wavelength of 532 nm. We also see that the processing range of the Ti film will decrease when the diameter of a laser beam increases. The experimental results show that the ablated status of the surface of a Ti film for a just-focus beam is much better than that for a defocus beam under the same laser power. Furthermore, the higher the laser power, the larger the processed area. By using the optimal parameters we obtained, we also produced some hole matrices and line patterns on a glass-based Ti film by employing a short pulsed laser. The processed samples were observed with a reflecting microscope and a transmitting microscope, respectively. Our research results can play an important role in the selection of laser parameters for laser processing of some materials with a high reflectivity.
Terahertz wave is generally an electromagnetic wave at the wavelength of 0.1-10 THz (30-3000 μm). The terahertz laser is a new type of radiation source with many unique advantages and has broad applications. Generally, the size of a normal laser cavity is from a few of to several hundred millimeters, and the size of a micro-cavity is mainly from a few of to several hundred micrometers in the wavelength region of ultraviolet, visible, and near-infrared. However, if the wavelength increases to the terahertz region, the wavelength is of the order of the micro-cavity size. The power distributions inside and outside the cavity of a terahertz laser are significantly different from those for a conventional laser cavity. In this paper, a theoretical model is established to study the outputted and leaked power of a micro-cavity in the terahertz band. We assume that the wavelength of an emission terahertz source is 240 μm and simulate the output features of a micro-cavity laser with the Finite-Difference Time-Domain (FDTD) algorithm. The output characteristics of a micro-cavity have been analyzed by using two types of material and different thicknesses of the sidewall. It has been found that when the thicknesses of both silver and aluminum sidewalls are reduced to around 16 μm, the power leaking from the micro-cavity begins to increase with the decrease of the sidewall thickness. In this way, the sidewall no longer restrains terahertz radiation inside the cavity. The simulation results might be referred for the design of a terahertz laser with the micro-cavity.
To minimize the effect of thermally-induced distortion and avoid the reabsorption phenomenon caused by the atomic alkali inside an alkali vapor cell (generally several or several ten millimeters long) in a diode-pumped alkali laser (DPAL) system, a novel concept of thin-disk DPALs in which alkali is sealed in a symmetric thin-disk cell has recently been proposed by referring a solid-state thin-disk laser. In this paper, we construct a theoretical model to study a V-pumped thin-disk DPAL system where the pump beam propagates along a V-shaped path. The influence of the thickness and the radius of a thin-disk cell, the incident angle of a pump beam, and the cell temperature on the output features of a thin-disk DPAL is studied by employing this model. In addition, we also investigate the effects of the profile of a pump beam such as a flat-top beam or a Gaussian beam on the uniformity of the temperature distribution and output power of a thin-disk DPAL. It has been demonstrated that a V-pumped DPAL might be better than an end-pumped DPAL. With respect to the uniformity of temperature distribution at the end-windows of a cell, the results reveal that a flat-top beam holds out a considerable merit compared with a Gaussian beam.
The diode-pumped alkali laser (DPAL) is a new type of high-powered laser sources which has been paid much attention in recent years. The fluorescent spectra can be used to investigate how the collisions between atomic rubidium and various buffer gases are affected when a sealed rubidium vapor cell is pumped by a LD. In this study, the cross sections between the fine-structure levels of atomic rubidium in a vapor cell were first theoretically deduced by using a gas kinetic procedure. And then, the sensitized fluorescence was experimentally obtained by means of a series of spectral measurements. Finally, the influence of the temperature on the cross section between the fine -structure levels of atomic rubidium was studied with the systematical analyses. The results are thought to be helpful for deeply understanding the theoretical characteristics of a DPAL at the atomic physics level.
A diode pumped alkali laser (DPAL) provides a significant potential for construction of high-powered lasers. Until now, a series of models have been established to analyze the kinetic process and most of them are based on the end-pumped alkali laser system in which the vapor cell are usually cylindrical and cuboid. In this paper, a mathematic model is constructed to investigate the kinetic processes of a diode pumped thin-disk cesium vapor laser, in which the cesium vapor and the buffer gases are beforehand filled in a sealed glass cell with a thin-disk structure. We systemically study the influences of the cell temperature and cell thickness on the output features of a thin-disk DPAL. Further, we study the thin-disk DPAL with the W-shaped resonator and multiple-disk configuration. To the best of our knowledge, there have not been any similar reports so far.
KEYWORDS: Semiconductor lasers, Laser systems engineering, Thermography, Diodes, Absorption, High power lasers, Laser applications, Cesium, Physics, Analytical research
As one of the most hopeful candidates to achieve high power performances, a diode-pumped alkali laser (DPAL) has attracted a lot of attention in the last decade. Comparing with a diode end-pumped alkali laser (DEPAL), a diode side-pumped alkali laser (DSPAL) has great potentiality to realize an even-higher output of alkali lasers. However, there are few related researching studies concern DSPAL. In this paper, we introduce a theoretical model to investigate the physical features of a double-directions side-pumped alkali laser. The distributions of the population density, temperature, and absorption power at the cross section of a vapor cell are systematically studied. The analyses should be valuable for design of a steady high-powered DPAL.
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