In this paper, a series of experiments of drilling holes and slotting micro-channels on the 1 mm-thick BK7 or 1.1 mmthick B270 glass substrates are introduced by employing three types of Q-switched lasers with the wavelength of 1064, 355, and 266 nm. Firstly, by smearing the solution of NiSO4∙6H2O on the front surface of BK7 glass plates, we successfully realized drilling holes on the glass substrates by employing a 1064 nm fundamental Nd:YAG laser. Then, we also carried out the experiments of drilling holes by utilizing a normal third-harmonic-generation (THG) 355 nm Nd:YAG laser and a 266 nm FHG (forth-harmonic-generation) laser. It can be found that the diameters of drilled holes by utilizing a 355 nm laser are larger than those by utilizing a 266 nm laser, and the holes with both two wavelengths lasers did not change a lot when the exposure time of lasers was increased from 0.5 s to 30 s. Finally, the experiments of slotting micro-channels on B270 glass plates were undertaken by utilizing both a 355 nm laser and a 266 nm laser. It has been found that the cracks around slotted micro-channels become lesser when the moving speeds are increased for both experiments. The channel widths of using the 355 nm laser are around 10 times smaller than those of using the 266 nm laser. As a conclusion, among three kinds of lasers, the 355 nm laser may be the most suitable type for the glass micro-processing with high precision in practice.
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.
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.
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.
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.
A diode-pumped alkali laser (DPAL) has been regarded as one of the most potential candidates to achieve high power performances of next generation. In this paper, we investigate the physical properties of a rubidium cell side-pumped by a Laser-Diode-Array (LDA) in this study. As the saturated concentration of a gain medium inside a vapor cell is extremely sensitive to the temperature, the populations of every energy-level of the atomic alkali are strongly relying on the vapor temperature. Thus, the absorption characteristics of a DPAL are mainly dominated by the temperature distribution. In this paper, the temperature, absorption, and lasing distributions in the cross-section of a rubidium cell side-pumped by a LDA are obtained by means of a complicated mathematic procedure. Based on the original end-pumped mode we constructed before, a novel one-direction side-pumped theoretical mode has been established to explore the distribution properties in the transverse section of a rubidium vapor cell by combining the procedures of heat transfer and laser kinetics together. It has been thought the results might be helpful for design of a side-pumped configuration in a high-powered DPAL.
In this paper, we build a theoretical model to study a continues-wave (CW) Ho3+:BaY2F8 laser by considering both energy transfer up-conversion (ETU) and cross relaxation (CR) processes. The influences of the pump power, reflectance of an output coupler (OC), and crystal length on the output features are systematically analyzed for an end-pumped configuration, respectively. We also investigate how the processes of ETU and CR in the energy-level system affect the output of a Ho3+:BaY2F8 laser by use of the kinetic evaluation. The simulation results show that the optical-to-optical efficiency can be promoted by adjusting the parameters such as the reflectance of an output coupler, crystal length, and pump power. It has been theoretically demonstrated that the threshold of a Ho3+:BaY2F8 laser is very high for the lasing operation in a CW mode.
In the recent years, lasers around 1.6 μm are attracted much attention since their wavelengths fit the atmospheric transmission window and can be used for applications in a range of fields including laser radar, gas sensing, and free-space communications. As one of the lasing wavelengths of an Er:YAG medium is just located in the 1.6 μm region, such a laser has been gaining more and more extensive applications in the near infrared. Until now, rare literatures have been found in the MOPA (Master Oscillator Power Amplifier) study of a 1.617 μm Er:YAG laser because the effect of upconversion will become greater while a higher doping concentration is adopted. In this study, we theoretically analyze the amplification features of a 1.617 μm Er:YAG seed laser by using a multiple MOPA configuration. In the simulation, a kinetic model is established to investigate how the doping concentration, crystal length, and pump power affect the amplification efficiency of a seed laser. The results would be helpful to construct a feasible 1.617 μm laser system.
In this study, we analyze the characteristics of a micro-cavity laser with the size one-order larger than the lasing wavelength by employing the finite-difference time-domain (FDTD) methodology. The simulation results have been obtained under the conditions with different materials and structures of the oscillator. It is seen that the power leakage from the side wall depends on the material and structure of a micro-cavity laser system. The wall material of the micro-cavity is assumed to be BK7 glass, silver, and copper, respectively. The results indicate that the side power leakage with the wall material of BK7 glass is much more serious than those with the wall materials of silver and copper. In addition, it is demonstrated that the cavity structure is also a key factor that influences the output features of such a laser.
In this paper, we introduce a new model to analyze the absorption efficiency of the laser medium for a diode side-pumped alkali laser (DSPAL). In the model, a ray trace method is employed to analyze the pump laser propagating route inside a diffusing chamber. In addition, the method, which is used to determine the total absorbed power of an alkali vapor cell, is named as the infinite convergence approach (ICA) while the random reflection is assumed to take place at the inner surface of a ceramic reflector. By considering the increase of a slit size will give rise to both increase of the input power and decrease of the reflection of the ceramic wall, we deduce that there must be an optimum slit width corresponding to the maximum absorption efficiency.
As two main atomic alkalis, rubidium (Rb) and cesium (Cs) have the similar energy-level structures. The energy transfer caused by collisions between rubidium and cesium atoms is a crucial factor for a vapor system. When such a vapor is irradiated with one component of rubidium resonance doublet, energy transfer will be induced by inelastic collisions between the excited rubidium atoms and the unexcited rubidium atoms, and between the excited rubidium atoms and the unexcited cesium atoms as well. It is noteworthy that the energy transfer between atomic rubidium and cesium is performed as cross relaxation. In this study, we theoretically investigate the effects of cross relaxations between the upper-state levels of atomic rubidium and cesium on the population distribution of the gas media. It has been demonstrated that the intensity of cross relaxations in this system is too weak to greatly affect the population distributions of atomic rubidium and cesium under the different temperatures. The conclusion might be helpful to better understand the physical features of alkalis.
Although the concept of the mode filling factor (also named as “mode-matching efficiency”) has been well discussed decades before, the concept of so-called overlap coefficient is often confused by the laser technicians because there are several different formulae for various engineering purposes. Furthermore, the LD-pumped configurations have become the mainstream of solid-state lasers since their compact size, high optical-to-optical efficiency, low heat generation, etc. As the beam quality of LDs are usually very unsatisfactory, it is necessary to investigate how the mode filling factor of a laser system is affected by a high-powered LD pump source. In this paper, theoretical analyses of an end-pumped laser are carried out based on the normalized overlap coefficient formalism. The study provides a convenient tool to describe the intrinsically complex issue of mode interaction corresponding to a laser and an end-pumped source. The mode filling factor has been studied for many cases in which the pump mode and the laser mode have been considered together in the calculation based on analyses of the rate equations. The results should be applied for analyses of any other types of lasers with the similar optical geometry.
A diode-pumped alkali laser (DPAL) is one of the most promising candidates of the next-generation high-powered laser sources. Until now, a single-heater structure has been widely adopted to control the temperature of an alkali vapor cell in plenty of the DPAL studies. However, for an end-pumped DPAL using a single heater, most pump power can be absorbed by the gain media near the entrance window of a cell due to the large absorption cross section of atomic alkali. As a result, the temperature in the pumping area around the inputted window will be much higher than those in the other positions of the vapor cell. Such a large temperature gradient would bring about some negative influences on the output performance of a DPAL. Additionally, in the worst case, the inputted cell window may even be damaged, especially when the pump intensity becomes very high. To solve the problem, we put forward a new scheme by using a gradient heating process in which several heaters are simultaneously utilized to anneal an alkali vapor cell. In this technique, the temperature at the entrance window is set to be lower than that of the other side. Using this novel method, one can not only achieve a homogeneous absorption of pump energy along the cell axis, but also decrease the possibility of the window damage in the DPAL configuration. The theoretical simulation of the laser output features by use of multiple heaters has been carried out, and the optimum condition in temperature gradient is also discussed in this paper.
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