The Dynamic Behaviour Analysis of Up－Conversion Luminescence in ErP_5O_（14） Glass

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Effect of XeCl laser irradiation on the defect structure of Nd:YAG crystals

This paper presents the effect of XeCl laser irradiation on Nd:YAG single crystal samples with various number of pulses at different repetition rates and laser fluences. Effects of the irradiation on the optical and structural properties of the crystal are analyzed by UV–vis-NIR spectroscopy. Annihilation of some point defects of the crystal structure is observed following laser irradiation at a fluence of 100 mJ cm⁻² with 100 and 500 pulses. Increasing the laser fluence and pulse numbers leads to saturation and new defects are found to be formed in the crystal. Additional absorption spectra of the irradiated samples show that oxygen vacancies in the Nd:YAG crystals are removed during the low-dose irradiation. The laser irradiation is compared to the thermal annealing process for Nd:YAG crystal modification. Additional absorption spectrum of an annealed sample reveals that induced negative absorption band at 236 nm is correlated with the annihilation of the oxygen vacancy center. Our results also demonstrate that XeCl laser treatment has several advantages upon annealing at high temperatures in the Nd:YAG crystal quality improvement. Thus, the present work can give a new approach to modify Nd:YAG crystals to be used in a wide variety of solid-state laser engineering.     

Absorption and thermal study of dental enamel when irradiated with Nd:YAG laser with the aim of caries prevention

It is widely recognized that Nd:YAG can increase enamel resistance to demineralization; however, the safe parameters and conditions that enable the application of Nd:YAG laser irradiation in vivo are still unknown. The aim of this study was to determine a dye as a photoabsorber for Nd:YAG laser and to verify in vitro a safe condition of Nd:YAG irradiation for caries prevention. Fifty-eight human teeth were selected. In a first morphological study, four dyes (waterproof India ink., iron oxide, caries indicator and coal paste) were tested before Nd:YAG laser irradiation, under two different irradiation conditions: 60 mJ/pulse and 10 Hz (84.9 J/cm²); 80 mJ/pulse and 10 Hz (113.1 J/cm²). In a second study, the enamel surface and pulp chamber temperatures were evaluated during laser irradiations. All dyes produced enamel surface melting, with the exception of the caries indicator, and coal paste was the only dye that could be completely removed. All irradiation conditions produced temperature increases of up to 615.08°C on the enamel surface. Nd:YAG laser irradiation at 60 mJ/pulse, 10 Hz and 84.9 J/cm² promoted no harmful temperature increase in the pulp chamber (ANOVA, p < 0.05). Among all dyes tested, the coal paste was an efficient photoabsorber for Nd:YAG irradiation, considered feasible for clinical practice. Nd:YAG laser at 84.9 J/cm² can be indicated as a safe parameter for use in caries prevention.     

Laser ablation and desorption from calcite from ultraviolet to mid-infrared wavelengths

3 ) at wavelengths ranging from the ultraviolet to the mid-infrared, including a Nd:YAG laser operated at the fundamental, second and third harmonics, and a tunable infrared free-electron laser (wavelength range 2.5–8 μm). The threshold for ablation and the topography of the irradiated spot were characterized by scanning electron microscopy. A clear indication of two distinct excitation mechanisms was observed, namely, cracks and fractures followed by exfoliation at ultraviolet to near-infrared wavelengths, in contrast to evaporative holes and scattered droplets in the mid-infrared. Plume emission/absorption spectroscopy, plume transmission and photoacoustic beam deflection were used to characterize the ablation plasma. The composition of atoms, molecules, or particles in the ablation plumes also has a distinctive variation as a function of the wavelength. The excitation mechanisms leading to ablation appear to be defect activation at ultraviolet to near-infrared wavelengths, molecular impurity absorption and resonant vibrational absorption of the calcite at mid-infrared. Received: 5 December 1996/Accepted: 6 January 1997     

Dynamics and spectroscopy of the laser plume from solid targets

The dynamics and the spectral kinetic characteristics of the plume emerging in the vicinity of graphite targets, pressed pellets consisting of zirconium oxide powder stabilized with yttrium (YSZ) and yttrium-aluminum oxides with neodymium (YAO:Nd), and single-crystal YAG:Cr are studied. The targets are irradiated in air at room temperature using a repetitively pulsed CO₂ laser with a wavelength of 10.6 μm, a peak power of up to 9 kW, a pulse energy of 1.69 J, and a pulse duration of 330 μs at a level of 0.1. The plume propagates normally to the target surface at an angle of 45° relative to the laser radiation. The spectral kinetic characteristics of the plume luminescence are discretely measured along the entire length. It is demonstrated that the plumes of all targets (except for the single-crystal YAG:Cr) represent the flows of a weakly nonequilibrium gas plasma with a temperature of 10 kK (graphite) and 3.1–4.7 kK (YSZ and YAO:Nd pressed pellets). The plume size is determined by the peak power of the laser pulse. The luminescence of the two-atom radicals (C₂ in graphite; ZrO and YO in YSZ; and YO, AlO, and NdO in YAO:Nd) dominates in all of the plumes. A single radical (YO) and the spectral lines of atoms and atomic ions are observed in the YAG:Cr plume. A relatively high temperature of the graphite plume is maintained owing to the energy of the exothermic reaction involving the association of carbon atoms and the energy of the vibrationally excited molecules resulting from this reaction. Original Text ? Astro, Ltd., 2006.     

Transient colour centre in YAG : Nd

Formation of a transient absorption centre is demonstrated in YAG : Nd monocrystals on intensive irradiation in the near UV spectrum region. Spectral distribution has been studied of their absorption coefficient, their decay kinetics was also followed. Activation energy of the decay process was determined from the temperature dependence. The transient absorption centre possessing the character of V-centres exsrcise, in view of the spectral course of their absorption coefficient, a certain amount of influence upon the efficiency of the YAG : Nd laser.     

Characterization of Nd Doped Films Prepared by Femtosecond Pulsed Laser DepositionSCIEI北大核心CSCD

Thin films of Nd : YAG and Nd : Glass were prepared on Si (100) substrate by pulsed laser deposition technology. The morphology of film surface and cross section, composition, absorption spectrum and photoluminescence (PL) spectra of films were investigated by scanning electron microscope (SEM), energy disperse spectroscopy (EDS), Fourier transform infrared spectrometer(FTIR), optical parametric oscillator(OPO) and grating spectrometer. The results show that both Nd : YAG films and Nd : Glass films grown on the substrates at room temperature are amorphous. Nd : YAG films grown by PLD contain Nd element with 0. 15 at. % stoichiometric proportion. The absorption spectrum of bulk Nd : YAG target rather than deposited films exhibit two absorption peaks at 750 and 808 nm. There are no evident peaks in the photoluminescence spectra curve of Nd : YAG films. However, the photoluminescence spectra of Nd : Glass films with two sharp peaks at the wavelength of 877 and 1 064 nm are observed. It indicates that Nd is doped into glass host as optically active Nd3+ ions when Nd : Glass films grow at room temperature. But for Nd : YAG films, Nd don't incorporate into YAG host as Nd3+ ions.     

10 kHz detection of CO2 at 4.5 microm by using tunable diode-laser-based difference-frequency generation

A compact, high-speed tunable, diode-laser-based mid-infrared (MIR) laser source has been developed for absorption spectroscopy of CO2 at rates up to 10 kHz. Radiation at 4.5 microm with a mode-hop-free tuning range of 80 GHz is generated by difference-frequency mixing the 860 nm output of a distributed-feedback diode laser with the 1064 nm output of a diode-pumped Nd:YAG laser in a periodically poled lithium niobate crystal. MIR absorption spectroscopy of CO2 with a detection limit of 44 ppm m at 10 kHz is demonstrated in a C2H4-air laminar diffusion flame and in the exhaust of a liquid-fueled model gas-turbine combustor.     

Coherence Time Measurement of Picosecond Pulses Using Reverse Saturable Absorption in Lead Phthalocyanine

ＣｏｈｅｒｅｎｃｅＴｉｍｅＭｅａｓｕｒｅｍｅｎｔｏｆＰｉｃｏｓｅｃｏｎｄＰｕｌｓｅｓＵｓｉｎｇＲｅｖｅｒｓｅＳａｔｕｒａｂｌｅＡｂｓｏｒｐｔｉｏｎｉｎＬｅａｄＰｈｔｈａｌｏｃｙａｎｉｎｅＬＩＦｅｎｇＳＯＮＧＹｉｎｇｌｉｎＹＡＮＧＫｕｎＬＵＩＳｈｕｔｉ...     

Wide single-mode tuning of a 3.0- 3.8-mum, 700-mW, continuous-wave Nd:YAG-pumped optical parametric oscillator based on periodically poled lithium niobate

A new optical parametric oscillator (OPO) for the mid-infrared wavelength region of 3-3.8mum with an idler output power of up to 1.5 W has been developed. The singly resonant OPO is pumped by a single-mode, 10-W, continuous-wave Nd:YAG laser and consists of a bow-tie ring cavity with a fan-out periodically poled lithium niobate crystal and a low-finesse intracavity air-spaced etalon. The single-frequency idler output can be continuously tuned over 24 GHz with 700-mW power by tuning of the pump laser. The tuning was demonstrated by recording of an absorption line of ethane with photoacoustic spectroscopy.     

Application of mid-infrared laser radiation for lithotripsy

The perforation effects of Er:YAG (2940 nm) and Ho:YAG (2100 nm) lasers radiation on human urinary stones model made from compressed plaster and real human samples were compared in vitro. For mid-infrared laser radiation delivery the special COP/Ag hollow glass waveguides were used. From the interaction experiments the perforation rates were derived and compared for both lasers. From the results it can be evaluated that Er:YAG laser radiation is favourable in comparison with Ho:YAG laser in case of artificial samples perforation efficiency.     

Demonstration of room-temperature laser action at 2.5 mum from Cr(2+):Cd(0.85)Mn(0.15)Te

Room-temperature laser action from Cr(2+)-doped Cd(0.85)Mn(0.15)Te has been demonstrated for what is believed to be the first time. We achieved pulsed laser operation centered at ~2.5mu m by pumping into the mid-infrared absorption band of Cr(2+) ions by use of the 1.907- mum output of a H(2) Raman-shifted Nd:YAG laser. The output of the free-running Cr(2+):Cd(0.85)Mn(0.15)Te laser had a width of ~50 nm (FWHM), and the slope efficiency was calculated to be 5.5% under nonoptimum conditions.     

Picosecond laser ablation of nano-sized WTi thin film

Interaction of an Nd:YAG laser, operating at 532 nm wavelength and pulse duration of 40 ps, with tungsten-titanium (WTi) thin film (thickness, 190 nm) deposited on single silicon (100) substrate was studied. Laser fluences of 10.5 and 13.4 J/cm² were found to be sufficient for modification of the WTi/silicon target system. The energy absorbed from the Nd:YAG laser beam is partially converted to thermal energy, which generates a series of effects, such as melting, vaporization of the molten material, shock waves, etc. The following WTi/silicon surface morphological changes were observed: (i) ablation of the thin film during the first laser pulse. The boundary of damage area was relatively sharp after action of one pulse whereas it was quite diffuse after irradiation with more than 10 pulses; (ii) appearance of some nano-structures (e.g., nano-ripples) in the irradiated region; (iii) appearance of the micro-cracking. The process of the laser interaction with WTi/silicon target was accompanied by formation of plasma.     

Nd3+:Er3+:KY(WO4)2激光晶体的生长和光谱特性

采用熔盐法从K2 WO4助熔剂体系生长出尺寸为 4 5mm的Nd3 :Er3 :KY(WO4) 2 透明晶体。从晶体中切割出Ф3× 11 9mm的激光器件 ,测量了晶体的紫外 -近红外的吸收光谱 ,从吸收光谱图上可以看到 ,晶体存在着 974 88nm ;80 1 0 (798 12 ,80 3 95 )nm ;74 8 5 (75 3 5 ,74 3 4 9)nm ;6 5 3 6 1nm ;5 86 6 5nm ;5 18 6(5 4 5 0 3,5 2 1 32 ,4 89 35 )nm ;4 5 2 80nm ;4 0 7 81nm ;36 7 2 2 (377 2 4 ,36 6 4 ,35 8 0 2 )nm九个吸收峰带 ,对各个吸收峰带按照Er3 和Nd3 离子的能级跃迁进行了归属。同时采用Edinburgh InstrumentF92 0荧光光谱仪在室温下对晶体进行了荧光测试研究。研究结果表明 ,共掺Nd3 离子可以增强Er3 :KY(WO4) 2 对半导体激光器泵浦源 (80 0nm)的吸收。     

连续激光二极管端面抽运Nd:YAG激光器噪声研究

以连续激光二极管端面抽运NdYAG激光器为实验模型,研究了该激光器中输出激光强度噪声、频率噪声和场分布噪声的特性,并根据实验数据推算出NdYAG晶体的粒子上能级寿命随温度变化为1.83μsK,发射截面随温度变化为-0.146×10-19cm2K。     

Wavelength conversion of nanosecond pulses to the mid-IR in photonic crystal fibers

We investigate degenerate four wave mixing with nanosecond pulses in fused silica photonic crystal fibers. Phase-matching curves are calculated taking into account the material and waveguide dispersion. Experiments with a nanosecond pulsed Nd:YAG pump laser and relatively short fiber lengths show more than an octave spanning conversion to idler and signal wavelengths at 3.105 μm and 0.642 μm, respectively. Conversion efficiency depends on the fiber length and pump intensity and is limited in our experiments by damage of the fiber input facet. Our results represent a new stretch towards the limit of the silica transmission window in the mid-infrared (IR).     

Luminescence sensitization in Nd-Cr-Ce doped yttrium aluminates

Energy transfer from Ce to Cr in YAG is radiative and relatively inefficient. If excited below 500 nm, the opposite transfer is dominant. YAP: Ce, Cr showed relatively efficient CeCr transfer only. The sensitization of Nd³⁺ luminescence by Ce³⁺ ions depends on the overlap of the Ce³⁺ emission band with Nd³⁺ absorption lines. Cr³⁺Nd³⁺ transfer is characterized by an expressive non-radiative portion. It is inefficient in YAG but very efficient in YAP. No UV-induced colour centres were found in YAG: Nd, Cr grown under Ar-H₂ atmosphere and doped with 10^–3 wt. % Cr, but at a higher Cr concentration anomalous absorption between UV absorption edge and 650 nm was stabilized. Ce³⁺ admixture in YAG:Nd, Cr and/or reducing treatment of the crystals facilitate the decomposition of the centres. The decomposition is accompanied with a strong Nd³⁺ luminescence. Therefore, YAG: Nd, Ce, Cr is an advisable active laser material. On the other hand the same centre in YAP: Nd, Cr seemed to be more stable even in the presence of cerium ions.     

液体介质快脉冲电压下击穿特性研究

设计了液体介质快脉冲击穿试验装置和电压电流测量系统，研究了重复频率、电极形状及电极间距与介质击穿场强、击穿电压和击穿时延等击穿特性参数的关系，比较了变压器油、十二烷基苯、蓖麻油三种典型液体绝缘介质在直流及快脉冲电压作用下的绝缘性能。结果表明:短脉冲持续时间下液体绝缘材料有异常高的击穿场强；重复脉冲串作用下的击穿场强比单个脉冲下明显减小，重复频率2 kHz时击穿场强减小了约30％；电极头半径大小对击穿也有影响，半径R＝5 mm时，击穿电压最高；击穿时延随击穿场强减小而变长，在其他条件相同的情况下，测得击穿时延随机波动；蓖麻油的快脉冲电压绝缘性能最好，变压器油次之。     

Lasers effects on enamel for caries prevention

The aim of this study was to ascertain whether laser irradiation is able to reduce caries incidence. For this purpose, the effects of laser on enamel and on fluoride uptake were discussed. Current literature regarding the preventive effect of laser irradiation on dental hard tissue has been reviewed. An evaluation of the results of the available in vitro and in vivo studies on the efficacy of anticaries and induced changes on enamel by laser irradiation were also performed. Articles were selected using the Medline, Web of Science, Embase, and Cochrane databases, and the results of these studies were described. The most common lasers employed for caries prevention on enamel are Nd:YAG; CO₂; Er:YAG; Er,Cr:YSGG; and argon. The percentage of inhibition of dental caries varied from 30 to 97.2%, and the association with fluoride has demonstrated the best results on inhibition of caries development. Laser irradiation under specific conditions can change the crystallographic properties of apatite crystals, increasing the acid resistance of lased enamel. The combined treatment of laser irradiation with fluoride propitiates an expressive fluoride uptake, reducing the progression of carieslike lesions, and this treatment is more effective than laser or fluoride alone. Available data suggest that lasers combined with fluoride is a promising treatment in caries prevention.     

Efficient all-solid-state mid-infrared optical parametric oscillator based on resonantly pumped 1.645 μm Er:YAG laser

We first report an all-solid-state tunable mid-infrared singly resonant optical parametric oscillator based on a 1532 nm laser diode resonantly pumped, Q-switched 1.645 μm Er:YAG laser. An MgO-doped periodically poled lithium niobate was used as the nonlinear material. At the pulse repetition frequency of 2 KHz, a maximum overall average output power of 0.95 W with pump power of 2.8 W was achieved, corresponding to a conversion efficiency of 34% and a slope efficiency of 38%. The temperature tuning was performed giving signal and idler ranges of 2.67 to 2.71 μm and 4.18 to 4.31 μm, respectively.