Efficient continuous-wave radiatively cooled cr(4+):forsterite lasers at room temperature

Results of a detailed experimental investigation aimed at reducing the thermal loading problem in a cw Cr(4+):forsterite laser at elevated temperatures are presented. From a Cr(4+):forsterite crystal with a differential absorption coefficient of 0.57 cm(-1), as much as 900 mW of cw output power has been obtained at 1.26 mum and at a crystal boundary temperature of 15 degrees C with an absorbed pump power of only 4.5 W at 1.06 mum. No chopping of the pump beam was necessary. An efficient radiative cooling technique was further employed to cool the laser and no subsequent power fading was observed. To the author's knowledge, the measured absorbed power slope efficiency of 29.5% represents the highest cw power performance reported to date from a Cr(4+):forsterite laser pumped by a Nd:YAG laser around room temperature. The role of the low differential absorption coefficient in the reduction of thermal loading is further elucidated by presenting comparative cw power performance data with a second Cr(4+):forsterite crystal having a differential absorption coefficient of 1.78 cm(-1) in the temperature range between 12 and 35 degrees C. Finally, some interesting multipulse effects of the laser observed in the millisecond regime during quasi-cw operation at 50% duty cycle are described.     

Efficient quasi-continuous-wave and passively Q-switched laser operation of a Nd3+:BaGd2(MoO4)4 cleavage plate

Pumped by a Ti:sapphire laser at 807 nm, efficient quasi-cw and passively Q-switched laser operations have been realized from a 1.1 mm thick, 1.2 at. % Nd(3+):BaGd(2)(MoO(4))(4) cleavage plate in a plano-plano cavity. When the absorbed pump power was 1060 mW, the achieved maximum quasi-cw output power was 580 mW. The slope efficiency and absorbed pump threshold power were 60% and 50 mW, respectively. Using a Cr(4+):YAG crystal with an initial transmission of 85% as the saturable absorber, a pulse laser with 3.0 microJ energy, 30 ns duration, and 52 kHz repetition rate has been obtained when the absorbed pump power was 1060 mW. The polarization characteristic and laser spectra of both the quasi-cw and passively Q-switched lasers have been measured.     

High-efficiency 1.06-µm output in a monolithic Nd:YVO(4) laser

A miniature 1.5-mm-long monolithic Nd:YVO(4) laser was end pumped with a Ti-sapphire laser. The Nd-doping density was 3 at. %. The maximum output power obtained with 885 mW of absorbed pump power was 495 mW at 1.064 μm. The maximum slope efficiency was 57%, and the output power was only slightly dependent on pump polarization. Laser diode pumping was also demonstrated. Thermal effects were observed to reduce the output power and required active cooling of the laser crystal.     

1.3at%Nd:YAG透明陶瓷的制备及激光性能研究

以高纯氧化物商业粉体为原料, 采用固相反应和真空烧结技术, 制备了高质量的1.3at%Nd:YAG透明陶瓷. 研究了室温下Nd:YAG透明陶瓷的显微结构、光谱及激光性能. 实验结果表明, Nd:YAG透明陶瓷主要以穿晶方式断裂; 平均晶粒尺寸为15μm, 且分布均匀; 晶粒中和晶界处没有检测到杂质和气孔存在, 且成分一致, 无偏析现象. 退火后样品在激光波长1064nm处的透过率高达82.4%; 主吸收峰位于808.6nm处, 峰值吸收系数为4.45cm^-1, 激光波长1064nm处的吸收系数为0.11cm^-1; 主荧光发射峰位于1064nm处, 半高宽为0.82nm, 荧光寿命为258μs. 用LD端面泵浦Nd:YAG陶瓷样品(泵浦源最大输出功率为1000mW), 获得了波长为1064nm的连续激光输出, 激光阈值约530mW, 斜率效率为23.2%, 最大泵浦吸收功率为731mW时, 最大输出功率为45mW.     

Directly Single-Diode-Pumped Continuous-Wave Yb(3+):YAG Laser Tunable in the 1047-1051-nm Wavelength Range

We have demonstrated tunability in a wavelength range of 1047-1051 nm, using the lowest pumping power known to us (1.4 W at 972 nm), for a cw single-diode-pumped Yb:YAG laser. The output power was 166 mW in the multimode regime and 73 mW in the fundamental transverse-mode regime. The laser efficiency was 12.8% and 21% with respect to the incident and the absorbed pump powers, respectively. The linewidth of the laser was Dlambda = 0.05-0.07 cm(-1) (1.5-2.1 GHz), which corresponds to two to three longitudinal cavity modes. A theoretical model of the laser has been developed. Experimental results are in good agreement with the theoretical model.     

Performance improvement in a directly 879 nm dual-end-π-polarized-pumped CW and pulsed GdVO₄/Nd:GdVO₄ laser

A continuous-wave and Q-switched 10 kHz GdVO?/Nd:GdVO? laser by 879 nm laser-diode pumping was demonstrated. We combined dual-end-π-polarized-pumping, half-wave plate (HWP) insertion, composite laser crystals, and dual Q-switching techniques to obtain a 1.06 μm nanosecond laser with high temporal and spatial quality. A polarization beam splitter was used to divide the unpolarized pump beam into two linearly polarized beams to increase the absorption efficiency. The output performance was improved obviously by inserting a HWP into the cavity. The pulse duration was compressed and the peak power was increased for a doubly Q-switched laser, in contrast to a single acousto-optical Q-switched laser under the same conditions.     

Spectra and broad-spectral laser operation of a disordered Nd:LiLa(MoO4)2 crystal

The crystal characteristics of a disordered Nd:LiLa(MoO₄)₂ laser crystal were investigated in detail, including its structure, absorption, emission and Raman scattering spectra. Laser operation, end-pumped by an 808?nm diode laser, has been demonstrated in both a concave-plano and plane-parallel resonator cavity. A broad-spectral dual-peak laser emission at 1061?nm and 1060?nm with a full width at half maximum of 2?nm was obtained in the experiment. A maximum output power of 267?mW was obtained in the concave-plano cavity. However, in the plane-parallel cavity, laser output of 381?mW was obtained, giving a slope efficiency of 14.5%. The results lay the groundwork for Raman, mode-locked and tunable laser applications generated by a Nd:LiLa(MoO₄)₂ laser crystal.     

Comparison on performance of passively Q-switched laser properties of continuous-grown composite GdVO4/Nd:GdVO4 and YVO4/Nd:YVO4 crystals under direct pumping

The comparison on performance of passively Q-switched laser properties of continuous-grown composite GdVO(4)/Nd:GdVO(4) and YVO(4)/Nd:YVO(4) crystals under direct pumping to the emitting level was demonstrated. A Cr(4+):YAG crystal was used as saturable absorber. At an incident pump power of 10 W, the average output power, the pulse width, the repetition rate, the pulse energy, and the peak power for a GdVO(4)/Nd:GdVO(4) laser were 1.22 W, 48.1 ns, 121 kHz, 10.1 μJ, and 209.6 W, respectively. And for a YVO(4)/Nd:YVO(4) laser under the same conditions, these output characteristics were 1.26 W, 44.9 ns, 218 kHz, 5.8 μJ, and 128.7 W, respectively.     

635/808双波长低强度照射对术后创口愈合的影响(英文)

本文通过评估635/808双波长低强度激光照射对术后病人创口愈合的影响,以给临床应用提供病例参考。随机选取外科手术治疗的非恶性肿瘤患者60例,试验组和对照组各30例。试验组使用635nm/808nm双波长激光辅助切口治疗,对照组以波长635nm的He-Ne激光辅助治疗。激光器发出两路激光对受试者切口部位进行照射治疗,一路波长为(635±5)nm,光功率密度1～6.5mW/cm2,另外一路波长为(808±5)nm,光功率密度为11～32mW/cm2。激光照射治疗开始于手术结束24h之后,每天一次,每次照射15min,至治疗终点(出院或切口愈合拆线),双波长激光器最大功率密度控制在40mW/cm2以下(可调节),最大能量密度在36J/cm2以下(可调节)。He-Ne激光器输出功率最大为100mW,每天一次,每次照射15min,至治疗终点(出院或切口愈合拆线)。试验表明,635/808双波长低照度照射能够促进创口愈合,治疗效果好于He-Ne激光器。     

Comparative experimental investigation of thermal loading in continuous-wave cr(4 +):forsterite lasers

Results of a detailed experimental study aimed at reducing the thermal loading effects in room-temperature continuous-wave Cr(4+):forsterite lasers are presented. By using a Nd:YAG pump laser operated at 1.06 mum, the effect of the absorption coefficient and crystal cross-sectional area on the power performance of three crystals was compared between 12 and 36 degrees C. Experiments indicated that a low differential absorption coefficient significantly reduces the pump-induced thermal effects and cavity losses that would otherwise give rise to inefficient operation and increased temperature sensitivity. In particular, a Cr(4+):forsterite crystal with an absorption coefficient of 0.57 cm(-1) yielded as much as 900 mW of output power at 1.26 mum and a crystal temperature of 15 degrees C with an incident pump power of only 7.6 W. To the author's knowledge, the demonstrated slope efficiency of 30% represents the highest continuous-wave power performance reported to date from this laser system at elevated temperatures.     

Ammonia detection by using quantum-cascade laser photoacoustic spectroscopy

A pulsed quantum-cascade distributed-feedback laser, temperature tunable from -41 degrees C to +31.6 degrees C, and a resonant differential photoacoustic detector are used to measure trace-gas concentrations to as low as 66 parts per 10(9) by volume (ppbv) ammonia at a low laser power of 2 mW. Good agreement between the experimental spectrum and the simulated HITRAN spectrum of NH3 is found in the spectral range between 1046 and 1052 cm(-1). A detection limit of 30 ppbv ammonia at a signal-to-noise ratio of 1 was obtained with the quantum-cascade laser (QCL) photoacoustic (PA) setup. Concentration changes of approximately 50 ppbv were detectable with this compact and versatile QCL-based PA detection system. The performance of the PA detector, characterized by the product of the incident laser power and the minimum detectable absorption coefficient, was 4.7 x 10-9 W cm(-1).     

Thermally boosted pumping of neodymium lasers

Pumping at 885 nm from thermally excited ground-state levels directly to the Nd:YAG upper lasing level is experimentally demonstrated by use of a Ti:sapphire pump laser. This approach utilizes thermal energy contained within the laser medium to provide part of the pump energy required to achieve population inversion. Slope efficiency increased by 12% compared with traditional pump band excitation (lambda(pump) = 808 nm) and by 7% compared with ground-state direct pumping (lambda(pump) = 869 nm). The combined transition from the first and second thermally excited Stark components of the ground state ((4)I(9/2)) to the upper lasing level ((4)F(3/2)) has characteristics that make thermally boosted pumping a suitable candidate for use with diode lasers: reasonable absorption (1.8 cm(-1)) and bandwidth (2.7 nm FWHM). A model suggests that, compared with traditional 808-nm pumping, heat could be reduced by 40% by use of thermally boosted pumping.     

Diode-laser-pumped 1.328-mum Nd:Sr(5)(PO(4))(3) F laser and its intracavity frequency doubling

Nd:Sr(5) (PO(4))(3) F, known as Nd:S-FAP, is a new material for efficient, miniature diode-pumped solid-state lasers. By using a laser-diode pump operating at 805.4 nm, we successfully lased Nd:S-FAP at 1.328 mum. A slope efficiency of 33.5% and a laser threshold of 18.5 mW have been measured. By using KTP as an intracavity doubling crystal, we also achieved an intracavity frequency Nd:S-FAP laser at 0.664 mum with a threshold power of 18.2 mW, a TEM(00) mode red laser output power of 20.7 mW at 250 mW incident pump power corresponding to an optical efficiency of 8.3%. In addition, we discuss ways to improve efficiency by use of this material.     

～2 μm Tm3+/Yb3+-doped tellurite fibre laser

We present, for the first time, laser emission in the range 1.910–1.994 μm in Tm³⁺/Yb³⁺-doped tellurite fibre when pumped using an Yb³⁺-doped double-clad silica fibre laser operating at 1.088 μm. With this pump scheme there was strong pump excited state absorption (ESA) which caused upconversion emission at 800 nm and 480 nm due to the Tm³⁺: ³H₄ → ³H₆ and Tm³⁺: ¹G₄ → ³H₆ transitions, respectively. This strong ESA limited the maximum slope efficiency to 10% with respect to absorbed pump power, and the maximum output power to 67 mW. This is however the highest output power which has been achieved in a tellurite fibre laser so far. The lowest observed threshold was 114 mW for a 22 cm long fibre and a 90% reflective output coupler. Further power scaling was limited due to thermal damage at the pump end of the fibre. The optimum fibre length for this arrangement was around 16 cm but lasing was achieved in lengths ranging from <9 to 30 cm. Tellurite glass offers significant advantages over silicate and fluoride glasses which make it a very promising material for compact, medium power, near and mid-IR fibre lasers for range-finding, medical and atmospheric monitoring and sensing applications.     

RT-CW Operation of InGaN multi-quantum-well structure laser diodes

The continuous-wave operation of InGaN multi-quantum-well (MQW) structure laser diodes (LDs) was demonstrated at room temperature with a threshold current of 25 mA, a threshold voltage of 5.8 V, an output power of 30 mW and a high operating temperature of 100°C. The energy differences between the absorption and the emission energy of the InGaN MQW structure LDs were as large as 220 meV at RT. A deep localized state (the localization energy is >100 meV) was formed in the InGaN well layer due to the InGaN phase separation during the growth. Both the spontaneous emission and the stimulated emission of the LDs originated from these deep localized energy states. The far field pattern showed a higher order transverse mode of the entire 5-μm-thick epitaxial layer stack, with air and sapphire as the upper and lower cladding layers, respectively.     

High-Power Continuous-Wave Diode-Pumped Nd:YAlO(3) Laser that Emits on Low-Gain 1378- and 1385-nm Transitions

Efficient operation of a diode-pumped Nd:YAlO(3) laser on low-gain 1378- and 1385-nm transitions is reported for the first time, to our knowledge. A three-mirror folded cavity with a prism yielded a cw laser output power of 800 mW for an absorbed pump power of 11 W. The laser beam was TEM(00). We managed to eliminate the instabilities in the output power by purging the cavity of water vapor with nitrogen.     

A highly efficient graphene oxide absorber for Q-switched Nd:GdVO4 lasers

We demonstrated that graphene oxide material could be used as a highly efficient saturable absorber for the Q-switched Nd:GdVO4 laser. A novel and low-cost graphene oxide (GO) absorber was fabricated by a vertical evaporation technique and high viscosity of polyvinyl alcohol (PVA) aqueous solution. A piece of GO/PVA absorber, a piece of round quartz, and an output coupler mirror were combined to be a sandwich structure passive component. Using such a structure, 104 ns pulses and 1.22 W average output power were obtained with the maximum pulse energy at 2 μJ and a slope efficiency of 17%.     

Polarization-resolved study of diode-pumped passively Q-switched Nd:GdVO4 lasers

By using the natural birefringence of an a-cut Nd:GdVO(4) crystal, we experimentally investigate laser operation under different light polarizations (pi- and sigma-polarized emissions) and compare their performance. The laser performance is further compared with a diode-pumped c-cut Nd:GdVO(4) laser of the same parameters. We show experimentally that the c-cut Nd:GdVO(4) laser could have good passively Q-switched performance in a low-pump-power region but is influenced by other intrinsic laser effects, such as the thermally induced cavity losses; its performance is severely degraded under high pump power. The best passively Q-switched performance obtained in our experiments is from the a-cut pi-polarized laser, which gives the narrowest pulse of 5.4 ns with the highest peak power of 20 kW. Our experimental results show that, to achieve the best performance of the passively Q-switched laser operation, an overall consideration of laser parameters is important.     

Diode-pumped passively mode-locked multiwatt Nd:GdVO4 laser with a saturable Bragg reflector

We report a first demonstration, to our knowledge, of a cw passively mode-locked Nd:GdVO4 laser (k = 1063 nm). A relaxed saturable Bragg reflector was used. The laser generates pulses of 9.2 ps at a repetition rate of 119 MHz. As much as 5.4 W of average power was realized with a slope efficiency of 25.7%.     

Diode-laser-pumped tunable 896-939.5-nm neodymium-doped fiber laser with 43-mW output power

A diode-laser-pumped neodymium-doped fiber laser is presented. For a launched pump power of 85 mW, the fiber laser had a cw output power of 43 mW, which is approximately an order of magnitude greater output power than any previously reported diode-pumped neodymium fiber laser operating on the(4)F(3/2)-(4)I(9/2) transition, which covers the 900-950-nm region. The fiber laser had a threshold power of 10 mW and a slope efficiency of 58% with respect to launched pump power. Tuning with a diffraction grating was obtained from 896 to 937 nm with narrow-band output powers as high as 32 mW. Emission was also obtained at 939.5 nm with use of a fiber Bragg grating as the output reflector.