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.     

Efficient and compact intracavity-frequency-doubled YVO4/Nd:YVO4/KTP laser through analysis of the interaction length

In this paper, a stable end-pumped intracavity-frequency-doubled green laser was demonstrated. The interaction length of different pump systems before setting up the experiment was analyzed in order to find out an effective pump system. The experimental results indicate that the pump system in our configuration is beneficial to the efficient CW Nd lasers. A continue-grown composite crystal YVO₄/Nd:YVO₄, with Nd³⁺ concentration doping of 0.3 at.%, is used as laser medium. With an incident pump power of 27.5 W, as high as 7.2 W of CW output power at 532 nm was achieved. The optical-to-optical conversion efficiency of 26.2% was obtained in CW modes with a flat-flat cavity design.     

Effect of Nd3+ concentration on CW and pulsed performance of fiber-coupled diode laser pumped Nd:YVO4 laser at 1064 nm

The effect of Nd³⁺ concentration on the CW and Q-switched laser performances at 1064 nm from Nd: YVO₄ has been studied under diode laser pumping in identical laser configuration. The Nd³⁺ concentrations used were 1, 2 and 3 at.% in YVO₄ crystals. Under the CW operations we have compared the thermal lensing effect, slope efficiencies and also the beam quality at the fourth-order degeneracy configuration. Q-switching was done with the help of an acousto-optic modulator and we have compared the pulses obtained from Nd: YVO₄ laser with different doping concentration. It was found that the 1 at.%-doped crystal is the best, offering highest optical-to-optical conversion efficiency (55%), lowest fractional heat load (24%), highest pulse energy (80 μJ) and shortest pulse width (20 ns). It was also found that there was not much difference in performances for 2 and 3 at.%-doped crystals both in CW and Q-switched configurations.     

A comparative study of continuous laser operation on the F3/2-I9/2 transitions of Nd:GdVO4 and Nd:YVO4 crystals

A comparative study of Nd:GdVO₄ and Nd:YVO₄ crystal lasers pumped by a fiber-coupled diode array has been conducted at the ⁴F_3/2-⁴I_9/2 transitions wavelengths of 912 nm and 914 nm, as well as when intracavity frequency-doubled to 456 nm and 457 nm, respectively. At the fundamental wavelength of 912 nm and second harmonic wavelength of 456 nm, maximum output powers from the Nd:GdVO₄ crystal laser were 7.85 W and 4.6 W at a pump power of 29 W. All the results obtained from Nd:GdVO₄ were superior to those of Nd:YVO₄, indicating that Nd:GdVO₄ is a more efficient laser crystal than Nd:YVO₄ for laser operation on the ⁴F_3/2-⁴I_9/2 transitions.     

激光二极管抽运Nd:YVO4晶体的三维热效应分析

针对激光二极管抽运的以Nd:YVO4板条晶体为增益介质的激光器件,基于有限容积法数值分析各向异性介质的热传导方程,给出了Nd:YVO4晶体板条结构的热分布数值模型,并分别模拟仿真了808nm半导体激光器双端端面抽运,大面均匀抽运,大面周期分布抽运三种抽运结构,得到了Nd:YVO4板条晶体在这三种抽运结构下的非稳态时不同时刻的温度曲线和稳态时的三维温度分布切面图.     

全固态紫外激光器研究

本文报道了具有增强谐振倍频腔的全固态紫外激光器研究半导体激光二极管(LD)泵浦的Nd:YVO₄激光晶体产生波长为1064nm的近红外光,腔内倍频输出波长为532nm的绿光,再送入增强谐振腔进行四倍频,输出波长为266nm的深紫外激光产生深紫外激光的基频绿光输入阈值可低到2.5mW据我们所知,这是国内首次报道的全固态紫外激光器.     

Theoretical analysis and experimental research on thermal focal length of a YVO4/Nd:YVO4 composite crystal

This paper investigates the temperature field distribution and thermal focal length within a laser diode array (LDA) end-pumped YVO4/Nd:YVO4 rectangular composite crystal. A general expression of the temperature field distribution within the Nd:YVO4 rectangular crystal was obtained by analysing the characteristics of the Nd:YVO4 crystal and solving the Poisson equation with boundary conditions. The temperature field distributions in the Nd:YVO4 rectangular crystal for the YVO4/Nd:YVO4 composite crystal and the Nd:YVO4 single crystal are researched respec- tively. Calculating the thermal focal length within the Nd:YVO4 rectangular crystal was done by an analysis of the additional optical path differences (OPD) caused by heat, which was very identical with experimental results in this paper. Research results show that the maximum relative temperature on the rear face of the Nd:YVO4 crystal in the composite crystal is 150 K and the thermal focal length is 35.7 mm when the output power of the LDA is 22 W. In the same circumstances, the experimental value of the thermal focal length is 37.4 mm. So the relative error between the theoretical analysis and the experimental result is only 4.5%. With the same conditions, the thermal focal length of the Nd:YVO4 single crystal is 18.5 mm. So the relative rate of the thermal focal length between the YVO4/Nd:YVO4 crystal and the Nd:YVO4 crystal is 93%. So, the thermal stability of the output power and the beam quality of the YVO4/Nd:YVO4 laser is more advantageous than the laser with Nd:YVO4 single crystal.     

Diode-pumped doubly Q-switched mode-locked YVO4/Nd:YVO4 laser with AO and GaAs saturable absorber

By using both acousto-optic (AO) modulator and GaAs saturable absorber, a diode-pumped doubly Q-switched and mode-locked (QML) YVO₄/Nd:YVO₄ laser is presented. The average output power and the pulse width of the Q-switched envelope have been measured. The Q-switch pulse energy of the doubly QML laser are higher than that only with GaAs. The stability of the QML laser with the dual-loss-modulation is significantly improved if compared to that only with GaAs.The experimental results show that the doubly QML YVO₄/Nd:YVO₄ laser has nearly 80% modulation depth and deeper than that of the singly passively QML pulse. The doubly Q-switched mode-locked pulse inside the Q-switched envelope has a repetition rate of 111 MHz and its pulse width is estimated to be about 700 ps. By using a hyperbolic secant square function and considering the Gaussian distribution of the intracavity photon density, the coupled equations for diode-pumped dual-loss-modulated QML laser is given and the numerical solutions of the equations are in good agreement with the experimental results.     

High-efficiency Nd:YVO4 laser emission under direct pumping at 880 nm

We report a high-efficiency Nd:YVO₄ laser pumped by an all-solid-state Q-switched Ti:Sapphire laser at 880 nm in this paper. Output power at 1064 nm with different-doped Nd:YVO₄ crystals of 0.4-, 1.0- and 3.0-at.% under the 880 nm pumping was measured, respectively. Comparative results obtained by the traditional pumping at 808 nm into the highly absorbing ⁴F_5/2 level were presented, showing that the slope efficiency and the threshold with respect to the absorbed pump power of the 1.0-at.% Nd:YVO₄ laser under the 880 nm pumping was 17.5% higher and 11.5% lower than those of 808 nm pumping. In a 4-mm-thick, 1.0-at.% Nd:YVO₄ crystal, a high slope efficiency of 75% was achieved under the 880 nm pumping, with an optical-to-optical conversion efficiency of 52.4%.     

A novel prism beam-shaping laser diode bar end-pumped TEM<Subscript>00</Subscript> mode Nd:YVO<Subscript>4</Subscript> laser

A beam-shaping diode end-pumped TEM₀₀ mode CW Nd:YVO₄ laser is presented. A special beam-shaping element made up of isosceles right-angled prism pieces is adopted to realize beam symmetric. Two cylinder lenses are used to couple the shaped beam into a 3 × 3 × 9 mm Nd:YVO₄ crystal with 0.3 at % neodymium doping. By using this laser system, we have achieved 6.1 W CW laser operated in single transverse mode at 1064 nm with 95.2% reshaping efficiency and 25.6% optical-optical conversion efficiency.     

High power diode single-end-pumped Nd:YVO4 laser

A fiber-coupled diode-single-end-pumped Nd:YVO₄ laser with an Nd:YVO₄ crystal of 0.3 at% doping concentration and 3×3×10 mm³ dimensions was reported. 14.850 W of continuous-wave output power in an M² factor of 1.12 was obtained under pump power of 27.365 W, with an optical conversion efficiency of 60.49%, and a slope efficiency of 64.5%.     

Influence of neodymium concentration on the strength of thermal effects in continuous-wave diode-pumped Nd:YVO4 lasers at 1064 nm

The influence of neodymium ion concentration on the continuous-wave power performance of diode-pumped Nd:YVO₄ lasers was experimentally investigated by using three crystals of approximately the same total absorption but different Nd concentrations of 0.5, 1, and 3 at.%. In situ measurements indicate that strong thermal lensing occurs in the highly doped sample (3 at.% Nd) and precludes scaling of the output power to large values. Results also show that undesirable thermal effects are dramatically reduced with decreasing active-ion concentration. The best power performance was obtained with a 10-mm-long Nd:YVO₄ sample that had 0.5 at.% Nd. In this case, up to 6.5 W of continuous-wave output power was obtained at 1064 nm by using a 3% transmitting output coupler.     

全固化自锁模飞秒Ti:S激光器实验研究

首次在国内系统报道了以腔内LBO倍频Nd:YVO₄激光器为泵浦源的全固化自锁模飞秒钛宝石激光器的实验结果.设计了一种热不敏腔内LBO倍频线性折叠腔结构,获得到了25.5%的光转换效率,泵浦功率为22W时得到了5.6W的基模绿光输出功率;以该激光器为泵浦源,在线性Z型腔的基础上,使用了一种能够通过改变腔内凹面聚焦镜折叠角消除象散的方法,直接由钛宝石激光器得到了脉冲宽度为22fs、功率为300mW的光脉冲.整个激光系统稳定性好,噪音明显低于Ar³⁺激光器的泵浦情况.     

Efficient diode-pumped Nd:YVO4 continuous-wave laser at 1.34 μm

We report a high-power continuous-wave(cw) diode-pumped efficient 1.34 μm Nd:YVO₄ laser. The laser properties of a low Nd³⁺-doped concentration of the Nd:YVO₄ crystal operating at 1.34 μm formed with a simple plane-concave cavity have been demonstrated. With the incident pump power of 22 W, an output power of 8.24 W was obtained, giving an optical conversion efficiency of 37.5% and slope efficiency of 40%. The thermal effects of cw end-pumped solid-state lasers were studied.     

Laser performance of grown-together YVO4/Nd:YVO4 composite crystal at continuous-wave 914 nm

We demonstrated a diode-end-pumped continuous-wave 914 nm laser using a novel grown-together YVO₄/Nd:YVO₄ crystal for the first time. A maximum output power at 914 nm of 7.5 W with an optical-optical efficiency of 16.3% and a slope efficiency of 24.3% was obtained when the incident pump power was 46.2 W. The beam quality factor M ² was 3.2 at the output power of 6.0 W. The quality and specification of the grown-together composite YVO₄/Nd:YVO₄ crystal should be improved. Meanwhile, energy-transfer upconversion spectrum of the composite YVO₄/Nd:YVO₄ crystal laser was also investigated.     

A novel orthogonally linearly polarized Nd:YVO4 laser

We presented a novel orthogonally linearly polarized Nd:YVO₄ laser. Two pieces of a-cut grown-together composite YVO₄/Nd:YVO₄ crystals were placed in the resonant cavity with the c-axis of the two crystals orthogonally. The polarization and power performance of the orthogonally polarized laser were investigated. A 26.2-W orthogonally linearly polarized laser was obtained. The power ratio between the two orthogonally polarized lasers was varied with the pump power caused by the polarized mode coupling. The longitudinal modes competition and the corresponding variable optical beats were also observed from the orthogonally polarized laser. We also adjusted the crystals with their c-axis parallele to each other, and a 40.7-W linearly polarized TEM₀₀ laser was obtained, and the beam quality factors were M²_x=1.37 and M²_y=1.25.     

Experimental determination of effective stimulated emission cross-section in a diode pumped Nd:YVO4 micro-laser at 1064 nm with various doping concentrations

A practical method is described and used for determination of the effective stimulated emission cross-section (σ_e) in an operating diode pumped Nd:YVO₄ micro-laser at 1064 nm with various doping concentrations. In this method a micro-laser is formed by keeping a small piece of the sample in a plane–plane resonator under semi-monolithic configuration and a fiber coupled diode laser (808 nm) was used for pumping. The pump power induced thermal lensing effect was used to make the cavity stable. In thermally stabilized solid-state lasers the cavity parameters change dynamically with the pump power and hence the overlap integrals become a function of the absorbed pump power. In our method the overlap integrals were estimated by measuring the thermal lens focal length at the threshold. The value of σ_e of Nd:YVO₄ crystal with different doping concentrations obtained by this method were in well agreement with the reported values.     

激光二极管端面抽运的1.34μm Nd:YVO4平凹腔型激光器

理论上分析了端面抽运的1.34μm Nd:YVO₄平凹腔型激光器的各项参数；实验 上实现了LD端面抽运的1.34μm Nd:YVO₄平凹腔型激光器的运转. 关键词： 固体激光 4晶体')" href="#">Nd:YVO₄晶体 平凹腔     

Optical losses in YVO4: RE (RE = Nd3+, Er3+, Tm3+) laser crystals

The relevance of processes contributing to depletion of pump and upper laser levels has been assessed based on experimental data obtained during measurement of excited state absorption, steady state emission and dynamics of excited states as a function of excitation power and activator concentration. It has been concluded that the excited state absorption in YVO₄: Nd and YVO₄: Er is not significant except for that from the ⁴ I _11/2 level of Er³⁺. In these systems, the interionic processes are dominant. In particular, the reported decrease of the YVO₄: Er laser slope efficiency when the Er³⁺ concentration increased from 0.5 to 1 at % is due mainly to the up-conversion by energy transfer from the pump level and upper laser level. Excited state absorption cannot contribute to depletion of excited states involved in the ³ F ₄-³ H ₆ laser operation near 1800 nm in the YVO₄: Tm crystal. However, the heavy doping required to enhance the cross-relaxation process which feeds the upper laser level brings about the migration-accelerated energy transfer to energy sinks.     

Influence of the laser-diode temperature on crystal absorption and output power in an end-pumped Nd:YVO<Subscript>4</Subscript> laser

In this work, we studied the influence of heat loaded into the laser crystal in an end-pumped solid-state Nd:YVO₄ high power laser. We have shown experimentally that the optimum value of the laser-diode temperature for the maximum pump power absorption by the Nd:YVO₄ crystal and the maximum Nd:YVO₄ laser output power are approximately similar to that of a system of the low power type, but by increasing the pump power, different values can be obtained.