Energetic and thermal performance of high-gain diode-side-pumped Nd:YAG rods

We investigated the energetic and thermal performance of a diode-side-pumped Nd:YAG rod laser with up to 50 W power deposited as excess heat into a 3-mm-diameter, 10-cm-length rod. The rod design produces an extremely flat gain profile resulting in “textbook” expressions of thermal lensing and birefringence. Thermal and energetic measurements are compared to corresponding “textbook” theoretical expressions. Discrepancies between various published thermo-mechanical YAG parameters are resolved by a self-consistent set of measured and calculated data for rod thermal lens focal lengths, birefringence depolarization and ratio of heat to stored energy (χ). Measured thermal and energetic performance under lasing and nonlasing conditions are presented, which agree with published theoretical expressions and measurements. Compensation of rod thermal lensing with simple spherical concave lenses is demonstrated. In addition various methods for compensating birefringence depolarization are theoretically and experimentally analyzed and compared. Received: 19 July 1999 / Revised version: 22 October 1999 / Published online: 23 February 2000     

Thermal stress effects of the diode-end-pumped Nd:YLF slab

The thermal stress effects of the diode-end-pumped Nd:YLF slab laser crystals are numerically investigated. The theoretical model is established by considering the divergence of the pump beam in the slab and the additional heat generated in the upconversion. Using the three dimensional finite element analyses, accurate numerical solutions based on the theoretical model are achieved. Our analyses focuses on the thermal fracture damage of the Nd:YLF slab under both the lasing and non-lasing conditions, and the predicted values are compared with the experimental results.     

Thermal unbalance by an amplified spontaneous emission absorber in an Nd:YAG thin-disk laser

We investigate heat generation in a Nd:YAG thin-disk laser composite with an undoped anti-amplified spontaneous emission (ASE) cap and a side ASE absorber under lasing and nonlasing conditions. The heat load unbalance in three different regions induces a large transverse temperature inhomogeneity under the nonlasing condition. The additional heat fraction generated by the concentration quenching is observed.     

Measurement of the thermal lens of grazing-incidence diode-pumped Nd:YVO4 laser amplifier

The thermally induced lensing effects of a diode-pumped Nd:YVO₄ laser amplifier in a grazing incidence bounce geometry are carefully measured experimentally. Measurements of the thermal effects are interpreted by considering the diode-pumped amplifier region as a thick lens. A more detailed modeling was made of a quadratic refractive index lens duct for the normal to the bounce plane distribution. Due to the asymmetric pumping the thermal lens shows significant astigmatism. The ratio between dioptric powers in the plane normal to bounce and in the bounce plane is measured to be approximately 20. A nonlinear component of the power dependence of the lens is observed and related to the nonlinear heating induced by energy transfer upconversion. Measurements made under non-lasing conditions are used to infer thermal lensing behavior under lasing conditions and this allows optimization of optical resonator design.     

The influence of energy transfer upconversion on thermal loading in end-pumped Nd:GdVO4 laser

The influence of energy transfer upconversion on thermal loading in end-pumped Nd:GdVO₄ laser was investigated. The dependence of thermal loading on absorbed pump power and pump radius was discussed. Higher absorbed pump power and smaller pump radius resulted in more serious ETU effect, which cause more extra thermal loading. The experimental results indicated that ETU effect in Nd:GdVO₄ laser is a unneglectable mechanism to generate extra heat especially in end-pumped geometry     

Repetition-rate dependence of thermal loading in diode-end-pumped Q-switched lasers: influence of energy-transfer upconversion

The fractional thermal loading in diode-end-pumped Q-switched lasers was estimated from the theory of cavity stability. The experimental results show that the thermal loading depends on the pulse-repetition rate. This dependence is attributed to the effect of energy-transfer upconversion (ETU). A theoretical model including the ETU effect was developed to analyze the fractional thermal loading in end-pumped Q-switched lasers. The theoretical predictions were found to be in good agreement with the experimental data.     

Thermal lensing measurements and thermal conductivity of Yb:YAB

By using holographic shear interferometry, we have measured the thermal lens in a diode-pumped Yb:YAB crystal, under lasing and non-lasing conditions, as a function of absorbed power. From these purely optical measurements we estimate the fractional thermal loading and the thermal conductivity of Yb:YAB. Knowledge of these thermal parameters is essential for the optimisation of Yb:YAB laser cavity designs. Received: 5 February 2002 / Final version: 22 November 2002 / Published online: 26 February 2003 RID="*" ID="*"Corresponding author. Fax +61-2/9850-8915, E-mail: Judith@ics.mq.edu.au     

LD抽运Nd:YVO4晶体中的上转换及其影响

对激光二极管抽运下Nd:YVO₄晶体中的上转换发光做了测量与分析,发现对应⁴G_7/2能级向下跃迁的上转换发光的主导机制为能量传递上转换.接着,对上转换对LD抽运Nd:YVO₄激光器运转的影响进行了理论分析,并特别讨论了上转换对热效应的影响. 关键词： 上转换 固体激光器 热效应     

Spontaneous emission evaluation in a photonic bandgap microcavity

This work is concerned with an electromagnetic model of a microresonator built in a dielectric periodical structure, with the purpose to achieve the control of spontaneous emission. The aim is to enhance the spontaneous emission into the lasing mode and to reduce it into the continuous spectrum of the nonlasing modes. An example of design of the microcavity structure is presented, together with the evaluation of the β-factor for various operating conditions.     

Ultrafast switching dynamics of nonlasing modes of vertical-cavity surface-emitting lasers

Single-mode vertical-cavity surface-emitting lasers (VCSELs) have been investigated with ultrafast optical modulation. After injection of a subpicosecond laser pulse into the VCSEL cavity, nonlasing modes were excited and produced optical beating in the emission of the VCSEL. After these oscillations have died down, when the VCSEL is operating at high power and when the injected laser pulses exceed a power threshold as well, the injected laser pulses can induce the lasing to switch to a normally nonlasing mode with crossed polarization. Our measurements of the decay time of the nonlasing modes at low injected pulse energy are consistent with the interpretation of this switching as enabled by increased lifetime of the nonlasing modes at high power.     

Properties of continuous-wave 1123 nm laser with diode-side-pumped Nd:YAG

Laser properties of diode-side-pumped Nd:YAG laser operating at 1123 nm are demonstrated. A 1.0 at % Nd-doped Nd:YAG rod with a size of Ø3 × 63 mm² is used as the active medium. Both radial and tangential thermal focal lengths of this side-pumped Nd:YAG rod are determined under lasing condition. The results show that the bifocusing strength of 1123 nm laser is larger than that of 1164 nm laser, and 1123-nm thermal focal lengths are shorter than those of 1064-nm laser due to higher quantum defect. Laser output performances of 1123 nm in terms of stability, output power and beam quality influenced by pump power at different cavity lengths are also discussed with a convex-piano cavity.     

Self-suppression of axial mode hopping by intracavity second-harmonic generation

Intracavity second-harmonic generation (SHG) in a single-frequency laser has an associated loss for adjacent nonlasing modes, from sum-frequency generation, that is greater than the loss from SHG for the lasing mode. Mode hopping is thereby suppressed, as the lasing mode dominates neighboring modes. We have investigated this behavior in a Nd:YAG laser with LBO intracavity frequency doubler, obtaining frequency tuning over more than 80 axial mode spacings, without mode hopping.     

Tomographic reconstruction of 2D-OH<Superscript>∗</Superscript>-chemiluminescence distributions in turbulent diffusion flames

A theoretical model on actively Q-switched Nd³⁺-doped quasi-three-level laser including the energy transfer upconversion and the ground state reabsorption is developed. The analytical expressions of the fractional thermal loading and the average output power are obtained, and the influence of ETU effects on laser performance for different repetition rate is analyzed. The average output power and the thermal focal length of the Q-switched 946 nm laser are acquired in experiment. The good agreement between the experimental data and theoretical results demonstrates the reliability of the theoretical model.     

Diode-pumped continuous-wave green upconversion lasing of Er(3+):LiLuF(4) using multipass pumping

Powerful green upconversion lasing of Er(3+):LiLuF(4) was achieved with a multipass pumping setup. The maximum output was 213 mW for Ti:sapphire laser pumping. Diode-pumped cw lasing at room temperature is demonstrated for the first time to the authors' knowledge.     

Two-photon excitation properties of a class of novel organic dye chloride

We present the two-photon excited (TPE) upconverted fluorescence and lasing efficiencies of a class of new pyridinium chloride having donor-π-acceptor (D-π-A) structure. Based on the excitation upon 40 ps laser pulses at 1064 nm, the experimental results showed that: the red-shift of TPE fluorescence emission peaks and the TPE fluorescence lifetime were gradually increased with the enhancement of electron-donating capability of the donor. To a certain extent, the enhanced donor would increase the two-photon pumped (TPP) upconversion lasing efficiencies, but the overlong alkyl chains would result in decreased lasing efficiencies. We could obtain TPE fluorescence lifetime of 754 ps, TPP upconversion lasing efficiency of ∼8.4%, and TPA cross-section of 6.14 × 10⁻⁴⁹cm⁴s/photon in these compounds.     

Two-frequency lasing in the Nd:YLF laser with a lens-shaped active element and longitudinal diode pumping

In the laser with lens-shaped Nd:YLF [100] active element, the dependence of polarization and frequency of the radiation on the cavity length is studied under conditions of longitudinal diode pumping. The conditions at which birefringence in the Nd:YLF active element allows two-frequency lasing are determined.     

The thermal effect in diode-end-pumped continuous-wave 914-nm Nd:YVO4 laser

The thermal effect and the heat generation in diode-end-pumped continuous-wave 914-nm Nd:YVO₄ lasers are investigated in detail. A theoretical model of a diode end-pumped solid-state laser is constructed to analyse the influence of fractional thermal loading on the thermal effect in the Nd:YVO₄ laser based on finite element analysis. The thermal focal lengths and the end-surface deformations of laser rods in Nd:YVO₄ quasi-three-level and four-level lasers are measured and compared with the results obtained by ordinary interferometry for the demonstration of higher thermal loading in 914-nm laser. Finally the fractional thermal loading in the Nd:YVO₄ quasi-three-level laser is calculated by matching the experimental and the simulated end deformations.     

Yb3+:YAG片状激光器的温度效应及金刚石窗口冷却设计

 基于准三能级速率方程分析了Yb³⁺:YAG 片状激光器的温度效应，结果表明随着激光介质的温度由300 K升高到400 K，激光器的储能提取效率由43%下降到26%。提出了利用热传导性能及优异的金刚石窗口对激光片的两端面进行冷却设计。模拟结果表明对掺杂11.6 %厚度为1.2 mm的激光片在泵浦功率密度为15 kW/cm²，重复频率为10 Hz的条件下，要将最高温度控制在可接受的范围内（比如320 K），周围冷却水的对流换热系数不应小于2 kW/(m²·K）。模拟结果还表明，在相同的热功率密度和冷却条件下，减小激光片的厚度同时增加抽运光的传输次数可以明显的降低激光片的温度。     

Spontaneous-emission spectrum of the nonlasing supermodes in semiconductor laser arrays

It is shown that the interference between amplified spontaneous emission into the nonlasing supermode and the laser field of a semiconductor laser array causes spatial hole burning, which couples the dynamics of the amplified spontaneous emission with the laser field. In particular, phase locking between the amplified spontaneous emission and the lasing mode leads to the formation of a spectral triplet composed of in-phase relaxation oscillation sidebands and an out-of-phase line at the lasing frequency.     

霍尔推力器热模型研究

为了对霍尔推力器的热分析研究提供准确的能耗加载条件,开展了霍尔推力器稳态工况下的热模型研究。基于等离子体理论,分析放电室内各项能量损耗机理,并建立各能量损耗与推力器工作参数、性能参数和结构参数的相关函数,系统地得到了霍尔推力器的完整热模型。以LHT100推力器为研究对象,热模型计算结果显示:额定工况下束流能量损耗约889 W,壁面能量损耗约300 W,阳极能量损耗约44 W,电离能量损耗约43 W,辐射能量损耗约34 W等。以此能量损耗作为热边界条件进行有限元分析,并开展热平衡试验进行验证,计算结果与试验结果吻合较好,最大误差小于5%。