Measurements and assignments of new large offset CD3OH FIR laser lines

By using an acoustooptic modulator we extend the 300 MHz tunability of a waveguide CO₂ laser to 480 MHz. The CD₃OH was optically pumped by the 10R(32), 10R(34), and 10R(36) CO₂ laser lines, and 17 new FIR laser lines were discovered. The Stark effect on previously known FIR laser lines was investigated, and some tentative FIR laser lines assignments are suggested.     

Diagnostics of a Compact Discharge-Pumped XeCl Laser with BCl3 Halogen Donor

The results of a comprehensive study of a compact UV-preionized XeCl laser are presented. The subjects of this study were: discharge voltage and current measurements, dye laser probing of the active medium, and the mass spectrometry of gas mixture degradation products. It is shown that the gas lifetime was significantly improved when the laser was operated with BCl₃ as a halogen donor instead of commonly used HCl. By the dye laser absorption and gain probing, the temporal and spatial dependences of the densities for several plasma components, Ne*, Xe*, Xe⁺*, Cl^–, XeCl* and of ground state boron atoms were measured. Some aspects of plasma kinetics for uniform and constricted phases of the discharge are discussed. By the mass spectrometry of gas mixture degradation products on long-term operation of the laser device several gaseous (N₂, O₂, CO₂, H₂O, C₂H₄) and solid (NiCl₂, H₃BO₃) products were detected in the laser chamber. NH₄Cl was determined to be a stable fraction of the deposits on optics surfaces. The reasons for the improvement of gas lifetime for BCl₃-containing gas mixtures are discussed.     

Low cost fabrication of SiO2 optical waveguides by laser direct writing on Ti-doped Sol-Gel films

A commercial direct laser writing (DLW) system operating at 1070 nm was used to fabricate SiO₂ optical waveguides on silicon wafers. A Ti-doped SiO₂ Sol-Gel film was deposited on the SiO₂/Si substrate by the dip-coating technique, based on which SiO₂ optical waveguides were patterned by DLW using a Ytterbium fiber laser and followed by chemical etching. The effects of laser parameters and the preheated temperature of Sol-Gel films on the dimensions of optical waveguides were studied systematically. The differences of etching rate between laser irradiated and non-irradiated areas in Sol-Gel films preheated at various temperatures are characterized by measuring the thickness of the films. Results demonstrate that the available laser power density range for laser densification and the width of the patterned optical waveguides are influenced strongly by the preheated temperature of the Sol-Gel films. The width of the optimized optical waveguide in this work is 25 μm. The minimum propagation loss of the fabricated optical waveguides is 1.7 dB cm⁻¹ at the wavelength of 1550 nm.     

Laser micro-processing of amorphous and partially crystalline Cu45Zr48Al7 alloy

This paper presents a microstructural study of laser micro-processed high-purity Cu₄₅Zr₄₈Al₇ alloys prepared by arc melting and Cu-mould casting. Microprocessing of the Cu₄₅Zr₄₈Al₇ alloy was performed using a Rofin DC-015 diffusion-cooled CO₂ slab laser system with 10.6-μm wavelength. The laser was defocused to a spot size of 0.2 mm on the sample surface. The laser parameters were set to give 300- and 350-W peak power, 30% duty cycle and a 3000-Hz laser pulse repetition frequency (PRF). About 100-micrometer-wide channels were scribed on the surfaces of disk-shaped amorphous and partially crystalline samples at traverse speeds of 500 and 5000 mm/min. These channels were analysed using scanning electron microscopy (SEM) and 2D stylus profilometry. The metallographic study and profile of these processed regions are discussed in terms of the applied laser processing parameters. The SEM micrographs showed that striation marks developed at the edge and inside these regions as a result of the laser processing. The results from this work showed that microscale features can be produced on the surface of amorphous Cu–Zr–Al alloys by CO₂ laser processing.     

Multiwatt optically pumped ammonia laser operation in the 12–13 μm

Design and operating caracteristics of high pulse repetition rate NH₃ laser producing up to 20 W of average output power are described. The NH₃ laser, operating in the 12–13 μm region was optically pumped with a high pulse repetition rate TEA CO₂ laser. Dependences of the NH₃ laser output on the pump energy, ammonia and buffer gas pressures and pulse repetition rate have been studied. The conversion efficiency of up to 16% has been received.     

Behavioral studies of gain and saturation energy density in a N2 laser with corona preionization

By the use of an oscillator-amplifier (OSC-AMP) TE N₂ laser system, both operating with corona preionizers, the laser parameters (small-signal gain g ₀ and saturation energy density E _s) have been measured at different N₂ gas pressure and for different states of the AMP preionizer. The details of our measurements are presented. In addition, the effect of He buffer gas on the laser parameters has also been investigated; it was found that both laser parameters remain almost constant up to 150 Torr of He gas pressure, indicating that He mainly affects the discharge uniformity. Finally, with the variation of the N₂ laser gain values in the literature, we found that the g ₀-N₂-laser parameter depends strongly on the length of the laser channel. Based on the most recent measurements, a graph showing this dependency is introduced.     

Efficient 1.06 μm laser operation in an unprocessed Nd3+:BaGd2(MoO4)4 cleavage microchip

A 1.2 mm thick microchip cleaved from a 1.2 at.% Nd³⁺: BaGd₂(MoO₄)₄ crystal was used as the laser gain medium directly. The laser cavity mirrors were coated on the microchip without cutting and polishing. In the 1.06 μm quasi-CW laser operation, the microchip was pumped by a Ti:sapphire laser with a duty cycle of 10%, the threshold is 10 mW, and the slope efficiency is 50%. In the CW laser operation pumped by a diode laser, the threshold and slope efficiency are 140 mW and 33%, respectively. The results demonstrate that the unprocessed surfaces of the cleaved microchip have good enough flatness and parallelism for laser operation.     

Comparison of surface films formed on titanium by pulsed Nd:YAG laser irradiation at different powers and wavelengths in nitrogen atmosphere

The nitridation of titanium (Ti) caused by a Q-switched Nd:YAG laser under nitrogen gas atmosphere was investigated in situ using X-ray photoelectron spectroscopy (XPS). A laser having a wavelength of 1064 nm and 532 nm (SHG mode) was irradiated on a titanium substrate in an atmosphere-controlled chamber, and the substrate was then transported to an XPS analysis chamber without exposing it to air. The characteristics of the surface layer strongly depend on the laser power. When the power is relatively low, a titanium dioxide layer containing a small amount of nitrogen is formed on the substrate. Laser irradiation beyond a certain laser power is required to obtain a stoichiometric titanium nitride (TiN) layer. A TiN layer and an oxynitride layer with a TiO_xN_y-like structure are formed as the topmost and the lower surface layer, respectively, when the laser power exceeds this threshold value. The threshold laser power strongly depends on the wavelength of the laser, and this threshold value for the 532-nm laser is quite lower than that for the 1064-nm laser.     

Cr3+,Yb3+,Er3+共掺磷酸盐铒玻璃转镜调Q激光性质研究

研究了Cr³⁺,Yb³⁺,Er³⁺共掺磷酸盐铒玻 璃转镜调Q激光性质.三种Er₂O₃掺杂浓度的激光实验结果表明，在Er₂O₃名义掺杂浓 度为0.5wt％时，玻璃的综合激 光性质最好，重复频率为0.1Hz时，它的激光阈值功率为14.5mJ，最大输出能量为9.6mJ ，斜率效率为0.55％.在同种实验条件下，比较了Cr14和Kigre公司生产的QE-7S激光性质参数，实验表明，前者激光阈值功率稍低，而后者的斜率效率和最大输出功率略高. 关键词： 3+-Yb³⁺-Er³⁺共掺')" href="#">Cr³⁺-Yb³⁺-Er³⁺共掺 磷酸 盐玻璃 光谱性质 激光性质     

Study on Fe-Al-Si in situ composite coating fabricated by laser cladding

Fe-Al-Si in situ composite coating was fabricated on the surface of ASTM A283Gr.D steel by laser cladding with the preplaced powder. The influence of powder composition, laser power and scanning speed on microstructure, microhardness and wear resistance were investigated in this paper. The results show that Fe-Al-Si in situ composite coating with the good metallurgical bond mainly consists of Fe, SiO₂ and Al₂Fe₃Si₄ intermetallic compound. With the increase of laser power and scanning speed, the grain size of coating gets the minimum value. With the increase of laser power and scanning speed, microhardness and wear resistance both get the peak vaule, and their value are three times and 3.5 times those of substrate, respectively. The optimum parameters are followed as: the ratio of the preplaced composite powder: 8:1:1, laser power: 1600 W and scanning speed: 400 mm/min.     

Asymmetric orientational writing dependence on polarization and direction in Li2O–Nb2O5–SiO2 glass with femtosecond laser irradiation

Strong birefringence photo-induced by the femtosecond laser irradiation and a sensitivity to the orientation of the laser movement versus the laboratory reference (i.e., difference between rightward and leftward or between upward and downward) have been demonstrated in 32.5Li₂O–27.5Nb₂O₅–40SiO₂ glass. An asymmetry with the orientation of the laser scanning was firstly observed by one of the authors in 2003 in pure silica (Poumellec et al. in Opt Express 11:1070, 2003). Here, we show in addition that this asymmetric orientational sensitivity is dependent on the direction of laser polarization and the laser scanning (i.e., when the direction is horizontal or vertical). In particular, no asymmetric writing is detected when both laser scanning and polarization directions are vertical. These observations are not explained by the available model.     

Yb:Y2O3透明陶瓷的光学性能研究

介绍了一种基于纳米粉末真空烧结技术的新型固体激光材料——Yb：Y₂O₃多晶陶瓷的制备工艺、物理化学特性、能级结构和光谱特性，并与Yb：YAG单晶进行了对比.采用紧凑型有源镜激光器(CAMIL)的抽运方式，验证了Yb：Y₂O₃透明陶瓷的激光输出性能.在35W的最大抽运功率下，得到波长1078 nm，功率10.5 W 的连续激光输出，斜率效率达到37.5%.实验中还观察到激光输出波长随抽运功率增加而红移以及随输出耦合镜变化而漂移的现象.Yb：Y₂O₃多晶陶瓷是一种理想的激光材料，不仅具有与Yb：YAG单晶同样优秀的物理化学性能和光谱特性，而且其热导率和发射带宽约为Yb：YAG单晶的两倍，非常适合于高亮度激光器和超短脉冲激光器领域的发展应用. 关键词： 2O₃陶瓷')" href="#">Yb:Y₂O₃陶瓷 陶瓷激光器 透明陶瓷     

A comparative study on diode-pumped single-frequency Tm:YAG and Tm:GdVO<Subscript>4</Subscript> lasers

In this paper, we present experimental results concerning on the laser characteristics of Tm:YAG laser and Tm: GdVO₄ laser. At room temperature, the maximum output power of Tm:YAG laser and Tm:GdVO₄ laser is 210 and 145 mW, respectively. High efficiency can be achieved for both lasers at room temperature. Nevertheless, compared with Tm:GdVO₄ laser, Tm:YAG laser can operate on single frequency with high power easily. As much as 60 mW of 2013.9 nm single-longitudinal-mode (SLM) laser was achieved for Tm:YAG laser. For Tm:GdVO₄ laser 51 mW of 1919.7 nm SLM laser was achieved. The SLM Tm:YAG laser is better for using as a seed laser for coherent wind measurements and differential absorption LIDAR systems.     

Pressure dependence of laser oscillation and superfluorescent emission from an optically pumped CF4 laser

Experiments on pressure dependence of a CF₄ laser have been carried out to elucidate dynamic characteristics of CF₄ molecules pumped by CO₂ lasers. The results are followed by a model calculation which characterizes collisional quenching of the energy levels related to the stimulated emission. The enhancement of the laser output induced by buffer-gas addition, which was found under specific conditions, is discussed in relation to the competition between laser and superfluorescent emissions.     

Laser cleaning of particle and grease contaminations on the surface of optics

In the high power laser facility, surface contaminations on the optics will worsen the laser beam quality and damage the optics. Particle and grease contaminations are two of the usual contaminations on the surface of optics. In this work, the 1064-nm laser induced plasma shockwave cleaning is utilized to remove SiO₂ particle contaminations on the K9 glass surface. The results indicate the removal ratio can reach above 95%. The effects of parameters (particle position, laser gap distance and laser energy) on the cleaning efficiency have been studied in the case of single pulse laser cleaning. In addition, CO₂ laser (10.6 μm) is utilized to remove the dimethylsilicone oil contaminations on the gold-coated K9 glass surface. The results show that CO₂ laser can effectively remove the dimethylsilicone oil by properly controlling the laser parameters. The cleaned area increases with the increased laser power or irradiation time when the other parameters are constant.     

Silicon cluster formation in the laser ablation of SiO at 308 nm

Neutral silicon cluster formation in the laser (308 nm) ablation of silicon monoxide was investigated through the analysis of composition and dynamics of the ablation plume under different laser fluence conditions. The neutral species were ionized by a second laser (193 nm) and the positionized species detected by TOF-MS (time-of-flight mass spectrometry). At low laser fluences, plume composition is dominated by SiO; above 0.6 J/cm² Si, SiO and Si₂ have comparable intensity and Si_n (n≤7) clusters are observed. Flow velocities and temperatures of the ejected species are nearly mass-independent, indicating that the plume dynamics are close to the strong expansion limit, implying a collisional regime. Through the relation between the estimated values of terminal flow velocity and surface temperature, u_T²∝T_S, it is found that, at low laser fluences, the surface temperature increases linearly with laser fluence, whereas, at the laser fluence at which Si_n clusters are observed, the increase of temperature is below the linear dependence. The population distribution of the ejected Si_n provides some indication of a formation mechanism based on condensation. Analogies between the ablation behavior of silicon monoxide and silicon targets are considered. PACS 82.30.Nr; 81.05.Gc; 78.70.-g     

A computer model of a transverse discharge cw CO laser

A kinetic model has been developed for the investigation of the novel performance of a CO laser, on which efficient extraction of laser power was obtained by exciting a subsonic gas mixture of CO/N₂/He/O₂ through transverse dc discharge. Kinetic equations for direct excitation by electron impact, V-V and V-R/T energy transfer, and stimulated emission are coupled with a semi-one-dimensional flow model. Careful consideration is devoted especially to the V-V transfer process of CO–N₂ and N₂–N₂. The laser power was calculated by a constant gain method. The laser output performance, examined as a function of gas mixture ratio, temperature, flow velocity, and discharge current, was in good agreement with the experiment.     

Laser cleaving on glass sheets with multiple laser beams

A multiple laser system consisting of CO₂ line-shaped and Nd-YAG pulsed lasers was applied to cleave a soda-lime glass substrate in this study. Due to an increase of absorption coefficient of the wavelength of 1.06 μm for Nd-YAG laser on the soda-lime glass at high temperatures, the glass sheets were preheated by the CO₂ line-shaped laser and followed with the pulsed Nd-YAG laser to generate a mixture fracture mode on the substrate. The stress distribution on the glass substrate cleaved by the multiple laser beams has been analyzed. An uncoupled thermal–elastic analysis based on the finite-element method (FEM) was made. The numerical results show that the stress field of the fracture region is caused by a complex stress state and the cleavages are significantly affected by the pulsed laser. A clean cut of the soda-lime glass substrate could be obtained due to a large shear stress state on the cutting direction with the pulsed laser radiated on the glass substrate.     

Laser-induced nonthermal fragmentation of C60 studied by semiclassical dynamics simulation

Photofragmentation of the C₆₀ fullerene induced by ultrafast laser pulses is studied by semiclassical dynamics simulation. The simulation study is focused on the excitation below the continuum levels. A laser pulse of 40 fs (FWHM) with an effective photon energy of 2.0 eV and different intensities was selected to interact with the C₆₀ fullerene. The simulation results show that averaged fragmentation size distribution over groups of initial geometries selected at random exhibits a power law pattern with the peak at C₂ at high laser pulse intensities. The threshold for the C₆₀ fragmentation was determined. The simulation finds that as many as 55 electrons are excited from the occupied molecular orbitals to unoccupied molecular orbitals upon the laser irradiation and that the number of the fragments significantly depends on the number of electrons excited. Finally, the temperature examination seems to suggest that the nonthermal effect may play a significant role in laser fragmentation of the C₆₀ fullerene.     

A comparative study on diode-pumped continuous wave Tm:Ho:YVO<Subscript>4</Subscript> and Tm:Ho:GdVO<Subscript>4</Subscript> lasers

In this paper, we presented experimental results concerning on the laser characteristics of two microchip lasers emitting in the 2 μm range, Tm:Ho:YVO₄ microchip laser and Tm:Ho:GdVO₄ microchip laser. At a heat sink temperature of 283 K, the maximum output power of Tm:Ho:YVO₄ laser and Tm:Ho:GdVO₄ laser is 47 and 34 mW under absorbed pump power of 912 mW, respectively. High efficiency can be achieved for both lasers at room temperature. Nevertheless, compared with Tm:Ho:GdVO₄ laser, Tm:Ho:YVO₄ laser can operate on single frequency with high power easily. At the heat sink temperature of 288 K, as much as 16.5 mW of 2052.3 nm single-longitudinal-mode (SLM) laser was achieved for Tm:Ho:YVO₄ laser. Under the same condition, only 8 mW of 2048.5 nm SLM laser was achieved for Tm:Ho:GdVO₄ laser.