3.77-5.05-/spl mu/m tunable solid-state lasers based on Fe/sup 2+/-doped ZnSe crystals operating at low and room temperatures

Spectroscopic properties and lasing of Fe:ZnSe and co-doped Fe:Cr:ZnSe crystals in the mid-infrared spectral range were studied at room and low temperatures. Using a free-running Er:YAG laser as a pump source, the output energy of the thermoelectrically cooled Fe:ZnSe laser was 142 mJ with 30% slope efficiency at T=220 K. Passive Q-switched oscillation of Er:YAG laser with Fe:ZnSe crystal was demonstrated and used as a pump source for a Fe:ZnSe laser system. Room-temperature (RT) gain-switched lasing of Fe:ZnSe was achieved in microchip and selective cavity configurations using Q-switched Er:YAG and Raman-shifted Nd:YAG lasers as pump sources. The microchip laser threshold of 100 mJ/cm/sup 2/ was demonstrated using a Fe:ZnSe crystal without any reflection coatings. A slope efficiency of 13%, oscillation threshold of 1.3 mJ, and tunable oscillation of Fe:ZnSe laser systems over 3.95-5.05 /spl mu/m spectral range were realized at RT.     

Intracavity 1.549-μm pumped 1.634-μm Er:YAG lasers at 300 K

A novel method of generating 1.634-μm laser action from Er:YAG crystals pumped intracavity by an Er:glass laser emitting at 1.549 μm is described. Operation of the Er:glass laser at 1.549 μm (red shifted from the standard 1.532 μm, but with comparable output) at 500 K was obtained using mirrors with tailored spectral reflectivities. Several Er:YAG crystals ranging in concentration from 0.3% to 2% and in length from 1 cm to 8 cm were lased in the intracavity pumping arrangement. All the Er:YAG crystals lased in the ⁴I_13/2 :Y1(6544 cm^-1)-⁴I_15/2:Z6(424 cm ^-1) 1.634-μm transition at 300 K     

Acoustooptic Q-switching of erbium lasers

Experiments were performed on Q switching of erbium lasers at 3 μm with an acoustooptical modulator. Different laser crystals of YAG:Er and YSGG:Cr:Er have been investigated. The highest fraction of single pulse Q-switch energy to free-running mode energy was 1%. Pulse durations of 50 ns were obtained. Multiple switching with up to 14 Q-switch peaks per flashlamp pulse could be generated, containing up to 19% of the energy of the free-running mode     

子脉冲序列模式Er∶YAG激光消融牙本质的实验观察

研制了一台子脉冲序列模式Er∶YAG激光器,获得了每秒80个和100个子脉冲高能量激光输出,开展了不同脉冲宽度的子脉冲对离体牙本质的激光消融实验。实验中使用的是子脉冲序列模式激光器,其重复频率为20 Hz,脉冲包络能量为45 mJ,子脉冲宽度分别为20,30,40,50μs,在无冷却水雾条件下分别对比了子脉冲宽度对牙本质消融量、牙髓腔温升和坑洞组织形貌的影响。结果表明:在相同的激光脉冲能量下,较窄的子脉冲宽度不仅能够增加消融量,降低牙髓腔温升,从而延长操作时间,而且可以获得更好的消融坑洞组织形貌,牙小管的开放程度较高,有利于黏接修复治疗。     

Performance of a Cr:YAG laser

We report on the performance of a Cr⁴⁺:YAG laser, tunable over the range from 1.32 to 1.53 μm, under different operating conditions. Laser action has been achieved by pumping with a Nd:YAG laser in the Q-switched mode and cw mode and with a Cr:Nd:GSGG laser in the long pulse mode. Slope efficiencies up to 22% in the Q-switched mode have been achieved. The lowest threshold was 30 mJ for the long pulse pumped mode. Excited state absorption seems to limit the tuning range and the output characteristics     

Er3+2.79μm激光器转镜调Q系统的特性分析

当YSGG、GGG、GSGG、YAG、YLF作为基质材料时，Er3+的4I11/2 能级和4I13/2 能级之间能够跃迁产生2.7~3μm的激光，该波段激光在医疗、军事等方面有着重要的应用价值。在790nm泵浦光作用下，Er:YSGG作为工作物质可产生2.79μm激光。通过构建Er:YSGG能级跃迁的速率方程，对转镜调Q激光器的系统特性进行了理论分析，并在此基础上进行数值模拟，得出了在给定激光工作物质参数的情况下，系统的各个变量对转镜调Q激光器性能的影响。这些结论将为类似实验的设计和改进提供理论指导。     

Q-switch regime of 3-μm Er:YAG lasers

A mathematical model, based exclusively on spectroscopic data concerning radiative, nonradiative, and energy transfer processes, is proposed and used to simulate the Q-switch regime of a 3-μm Er:YAG laser. The connection between the main energy transfer mechanisms that make possible generation on the self-saturated transition ⁴I _11/2→⁴I_13/2 (upconversion from ⁴I_13/2 and ⁴I_11/2 and cross relaxation from ⁴S_3/2) and the giant pulse characteristics are discussed. The radiative as well as nonradiative losses during optical pumping and giant pulse generation are defined and evaluated. A particular attention is given to the frustrated total internal reflection (FTIR) Q-switch which demonstrated real qualities for 3-μm erbium lasers. The reasons responsible for experimental performances of Q-switched Er:YAG lasers inferior to those predicted by the mathematical modeling are analyzed     

2.94um Er:YAG电光调Q激光器及应用研究

随着2.94 激光在医学中的应用日益广泛,控制工作激光参数提高医疗安全性能显得尤为重要,因此对工作的激光进行调Q是很有必要的。文中介绍了利用双布儒斯特角切割的LiNbO3晶体作为电光Q开关的Er:YAG调Q激光器,在工作频率5Hz,脉冲泵浦能量92J条件下,获得了脉宽103 ~110ns,能量达到87mJ的调Q脉冲激光输出。并分别在静态和调Q模式下对龋牙进行了窝洞制样,利用扫描电子显微镜对样本扫描,对比显示调Q激光制样的效果更好。     

动态Cr,Tm,Ho：YAG激光器的实验研究

本文报道Ｑ开关Ｃｒ，Ｔｍ，Ｈｏ：ＹＡＧ激光器的实验研究，研究了Ｃｒ、Ｔｍ、Ｈｏ：ＹＡＧ激光器的调Ｑ工作的一系列特性，并分析了多脉冲产生的机制，获得了单脉冲能量６０ｍＪ的２．１μｍ的稳定调Ｑ激光输出，通过倍频途径测得了茯倍频光的光脉冲半宽度３５ｎｓ。     

Solid-state laser pumping of 1.5-μm optical amplifiers andsources for lightwave video transmission

An optical power amplifier and a laser source are demonstrated at 1.5 μm. A diode-pumped Nd:YAG laser is used as the pumping source for an Er/Yb co-doped gain medium. The power scaling advantages of this approach are demonstrated. Up to +21 dBm of output power is obtained from the Er/Yb amplifier and up to +19 dBm is obtained from the laser source. The Er/Yb power amplifier was deployed in a 42-channel AM link with 40 km of fiber, and an optical loss budget of 18 dBm was demonstrated     

Compositionally tuned 0.94-μm lasers: a comparative lasermaterial study and demonstration of 100-mJ Q-switched lasing at 0.946and 0.9441 μm

A new and innovative composite laser material Nd:YAG_xYSAG_1-x has been developed with several objectives in mind; tunability, efficiency, and minimization of the deleterious effects of amplified spontaneous emission (ASE) in Q-switched operation. Wavelength tuning to the requisite wavelength 0.9441 μm was achieved by using the technique referred to as compositional tuning; that is, using nonstoichiometric laser materials to shift the wavelength for precise tuning. Laser efficiency was achieved by studying the physics of 0.94-μm transitions in nonstoichiometric materials; i.e., by examining the effects of the host on the linewidth and cross section of of 0.94 μm neodymium (Nd) transitions, ASE was minimized by choosing materials with a small ratio of 1.06- to 0.94-μm peak cross sections. A comparative study of six different Nd-doped mixed garnet laser material systems was performed to meet the objectives above. Within these six material systems, over 20 laser materials were spectroscopically analyzed. The optimal laser material was found to be Nd:YAG_xYSAG_1-x, which has been demonstrated to lase at the preselected wavelength of 0.9441 μm, an important wavelength for remote sensing of water vapor. Operating this laser on the ⁴F_3/2→⁴I_9/2 transition in Nd:YAG_0.18YSAG_0.82 at 0.9441 μm, has produced for the first time over 100 mT in the Q-switched mode. This represents one of the few lasers that have been designed to operate at a specific, user-preselected wavelength     

激光蚀除生物组织的影响因素

为深入研究激光和生物组织的相关参数对激光蚀除生物组织过程的影响规律,在McKenzie三层结构模型的基础上,提出了包含碳化层、干化层、脱水层、凝结层和正常组织在内的激光蚀除生物组织多层结构模型,并进行了数值模拟与分析。结果表明,蚀除速度与激光功率密度呈近似线性关系;碳化层、干化层和凝结层的厚度皆随激光功率密度的增加而减小,并逐渐趋于定值;而脱水层的厚度则随激光功率密度的增加而增大,并逐渐趋于定值。波长为2.94μm的Er∶YAG激光蚀除生物组织时,组织热损伤的总厚度小于波长为10.6μm的CO2激光造成的损伤,更适合用于激光外科手术。     

Ho:YAG laser pumped by 1.9-μm diode lasers

A 21-μm Ho:YAG laser end pumped by 1.9-μm diode lasers has generated nearly 0.7-W CW output power. Laser operation was maintained even with Ho:YAG heat sink temperatures in excess of 60°C     

板条型脉冲Nd∶YAG激光器的研究

本文研制了尺寸为124×12×6mm~3的Nd:YAG晶体板条型脉冲激光器,自由振荡单脉冲输出24J,器件总体效率2.5％,电光调Q单脉冲输出860mJ,脉宽12～15ns,Q开关效率72％。     

Evaluation of Er, Cr:YSGG laser for hard tissue ablation: an in vitro study

The use of erbium,chromium:yttrium-scandium-gallium-garnet (Er, Cr:YSGG) laser with a wavelength of 2.78 μm for hard bone tissue ablation was evaluated. The surface morphology and microstructure changes of bone tissue treated with Er, Cr:YSGG were analyzed as compared to those treated with diamond drill.The influence of fluence on ablation rate and ablation efficiency as well as microstructure was also examined.The results show that Er, Cr:YSGG laser can perform bone perforation that is more fine and presented a lot of unique advantages compared to traditional methods. An approximately linear relationship was observed between the ablation rate/ablation efficiency and radiant exposure.Increasing the radiant exposure irradiated on bone tissue will produce stronger thermal injury around the crater and result in microstructure changing.     

Tissue ablation through water with erbium: YAG lasers

We report the dynamics of vapor cavities generated by 200 microseconds long Er:YAG laser pulses under water and in gelatin. Acoustic transients were detected at the beginning of the laser pulse and when the cavity collapsed. Cavity expansion and collapse, and the associated acoustic transients are possible ablation mechanisms with the Er:YAG laser. Shortening of the pulse duration is suggested to minimize long range under water tissue damages.     

2.79 μm YSGG:Cr:Er laser pumped at 790 nm

2.79 μm quasi-CW laser operation at room temperature was achieved from a YSGG:Cr:Er crystal. The output from the crystal, which was longitudinally pumped with a Ti:sapphire laser at 790 nm, was self-terminating. Under quasi-CW pumping, the length of the emitted pulses decreased exponentially with increasing pump power. The self-terminating behavior is explained by thermal effects with a computer simulation of the population mechanisms in the crystal. This simulation considers not only the common cross-relaxation and up-conversion processes, but also the inverse processes. They turn out to be of the same importance as the normal processes. The YSGG:Cr:Er crystal depends so critically on the laser parameters that it is an ideal candidate for testing the system of rate equations     

Spectroscopy, modeling, and laser operation of thulium-dopedcrystals at 2.3 μm

Pulsed room-temperature lasers based on the thulium 2.3-μm ³H₄-³H₅ transition have been achieved in 1.5% Tm:YAG, 2% Tm:LuAG, and 1.5% Tm:YLF crystals using a pulsed alexandrite laser at 785 nm as the pump source in a collinear geometry. The absorbed energy thresholds (slope efficiencies) for 1.5% Tm:YAG, 2% Tm:LuAG, and 1.5% Tm:YLF lasers are measured to be 1.2 mJ (14%), 1.8 mJ (13%), and 1.0 mJ (18%), respectively, which are in good agreement with the theoretically predicted results. The experimental results indicate 1.0 mJ thulium to be the most optimum concentration for 2.3-μm laser action. The thulium lasers are tuned around 2.3 μm using an intracavity single birefringent plate of quartz     

LD脉冲抽运的被动调Q Nd:YVO4激光器的研究

报道在LD脉冲抽运的Nd：YVO4激光器中插入Cr^4＋：YAG,获得稳定的调Q激光输出。在输出镜透过率T=10％时,插入Cr^4＋：YAG的调Q阈值为19．1mJ,在抽运能量为34mJ时,测得脉冲宽度为38ns,输出能量为0．34mJ。实验研究了脉冲宽度随抽运能量的变化,并比较了不同透过率输出镜条件下Cr^4＋：YAG调Q的输出能量和调Q效率随抽运能量的关系。实验还把Cr^4＋：YAG换成BDN染料片,获得了比Cr^4＋：YAG调Q还窄的10ns左右的脉冲,并根据Cr^4＋：YAG和BDN染料片的调Q机理对一些实验现象作出合理的解释。     

Efficient selection of high-order Laguerre-Gaussian modes in a Q-switched Nd:YAG laser

Intra-cavity binary phase elements are incorporated into a Q-switched Nd:YAG laser resonator to obtain efficient high-order transverse mode selection. The resonator configuration is analyzed using the propagation-matrix diagonalization method and the Fox-Li algorithm, and a simple model for predicting the relative output powers of the selected modes is developed. The predicted results are verified experimentally with binary phase elements for selecting the TEM/sub 01/, TEM/sub 02/ and TEM/sub 03/, degenerate Laguerre-Gaussian modes. The output energy per pulse was 15 mJ for the TEM/sub 01/, 16.5 mJ for TEM/sub 02/ and 18.3 mJ for TEM/sub 03/, all higher than the 10 mJ for the TEM/sub 00/. The performance in Q-switched operation was found to be similar to that in free-running operation. The numerical calculations, experimental procedure and experimental results are presented.