Diode-end-Pumped Nd:YAG Ceramic and Crystal Operation at 1,123 nm

We present a high-power diode-end-pumped continuous-wave Nd:YAG laser operating at 1,123 nm. Laser operation was carried out and compared using high optical quality Nd:YAG ceramics fabricated in-house and commercial Nd:YAG single crystals. At the absorbed diode pump powers of 23.2 and 28.0 W, output powers of 10.7 and 12.5 W at 1,123 nm were achieved for the employed ceramics and crystals as the laser material, which correspond to conversion efficiencies of 46.1% and 44.6%. For high-power lasers, the Nd:YAG ceramic has the advantage of a higher destructive threshold than that of commercial crystals.     

High-power and high optical conversion efficiency diode-end-pumped laser with multi-segmented Nd:YAG/Nd:YVO_4

A novel flat-flat resonator consisting of two crystals(Nd:YAG + Nd:YVO_4) is established for power scaling in a diode-end-pumped solid-state laser. We systematically compare laser characteristics between multi-segmented(Nd:YAG + Nd:YVO_4) and conventional composite(Nd:YAG + Nd:YAG) crystals to demonstrate the feasibility of spectral line matching for output power scale-up in end-pumped lasers. A maximum continuous-wave output power of 79.2 W is reported at 1064 nm, with M_x~2= 4.82, M_y~2= 5.48, and a pumping power of 136 W in the multi-segmented crystals(Nd:YAG + Nd:YVO_4). Compared to conventional composite crystals(Nd:YAG + Nd:YAG), the optical-optical conversion efficiency of multi-segmented crystals(Nd:YAG + Nd:YVO4) from 808 nm to 1064 nm is enhanced from 30% to 58.8%,while the laser output sensitivity as affected by the diode-laser temperature is reduced from 55% to 9%.     

All-solid-state continuous-wave doubly resonant all-intracavity sum-frequency mixer

A new resonator design for doubly resonant continuous-wave intracavity sum-frequency mixing is presented. We generated 212 mW of coherent radiation at 618 nm by mixing the radiation of a 1080-nm Nd(3+):YAlO(3) laser and a 1444-nm Nd(3+):YAG laser. Two different mixing resonator setups and several nonlinear-optical crystals were investigated. So far output is limited by unequal performance of the two fundamental lasers and coating problems of the nonlinear crystals.     

Efficient high-power self-frequency-doubling Nd:GdCOB laser at 545 and 530 nm

We report an efficient high-power self-frequency-doubling (SFD) Nd:GdCOB laser. The maximum output power is 3.01 W at a wavelength of 545 nm with an optical efficiency of 20.7%, which, to our knowledge, is the highest SFD laser output power and efficiency yet obtained. By optimizing the configuration and cut orientation of the Nd:GdCOB crystals, a SFD laser at a wavelength of about 530 nm was achieved with a maximum output power of 1.32 W. We propose that these SFD lasers will have promise in applications such as laser displays, medical treatment, spectroscopic analysis, etc.     

An efficient and high polarized single cavity Nd:YVO4 microchip laser

An efficient and high polarized microchip green laser with dual Nd:YVO4 crystals is reported. The microchip includes a half-monolithic Nd:YVO4-KTP chip and a second Nd:YVO4 crystal. With two 1 W diode lasers pumped, the output power of TEM₀₀ green laser is 430 mW, and the optical-to-optical conversion efficiency is nearly 21.5 %, when the c-axes of second Nd:YVO4 crystal rotated to 90° from the half-monolithic chip, the polarization ratio of output green laser is 130:1. This laser has the advantages of being simple and easily attainable at a low cost, and suitable for batch production.     

Compact corner-pumped Nd:YAG/YAG composite slab laser

Corner-pumping is a new pumping scheme in diode-pumped all-solid-state lasers, having such advantages as high pump efficiency, favorable pump uniformity and low cost. Compact corner-pumped Nd:YAG/YAG composite slab lasers at 1064 nm with low or medium output powers and high efficiency are demonstrated in this paper. Combined with intracavity frequency doubling by a LBO crystal, a corner-pumped Nd:YAG/YAG composite slab 532 nm green laser with a stable output is realized successfully. The experimental results show that corner-pumping can reduce laser costs greatly, release the thermal effects of slab crystals and improve the output beam quality, and that the new pumping scheme is feasible in the design of diode-pumped all-solid-state lasers with low or medium output powers.     

28.2 W波长锁定878.6 nm激光二极管共振抽运双晶体1064 nm激光器

报道了一种由波长锁定878.6 nm半导体激光器共振抽运两块不同掺杂浓度Nd:YVO4晶体串接的1064nm激光器,并与使用单块的低掺杂浓度晶体和高掺杂浓度晶体情况进行比较,实验表明利用波长锁定878.6nm半导体激光器共振抽运双晶体串接的方式,有利于降低晶体的热效应,提高光光转换效率.当抽运功率为40 W时,获得了28.2 W的1064 nm激光输出,光光转换率为70.5%,斜率效率为70.6%,相对吸收光的光光转换率76%,斜率效率为76.4%,同时该激光器在10?C—40?C的温度变化范围内具有极好的温度稳定性.     

Laser-diode pumped self-Q-switched microchip lasers

Optical properties of Cr,Yb:YAG, Cr,Nd:YAG crystals, and composite Yb:YAG/Cr:YAG ceramics self-Q-switched solid-state laser materials are presented. The merits of these self-Q-switched laser materials are given and the potentials of such lasers can be chosen by the applications. Cr,Yb:YAG and composite Yb:YAG/Cr:YAG ceramics self-Q-switched laser are conducted. Although several tens of kW peak power can be obtained with a monolithic microchip Cr,Yb:YAG laser, the experimental results show that the performance of this laser is limited by the absorption of Cr⁴⁺ ions at a pump wavelength of 940 nm and strong fluorescence quenching at high Cr concentration. Composite Yb:YAG/Cr:YAG ceramics are more suitable to realize high pulse energy and peak power (up to MW level) with optimized lasing and Q-switching parts. In addition, the instabilities induced by the multi-longitudinal mode competition in Cr,Nd:YAG and Cr,Yb:YAG microchip lasers are addressed. The different gain bandwidths of Yb:YAG and Nd:YAG play an important role in the instability of the output laser pulse trains. Stable laser pulses from the Cr,Yb:YAG microchip laser were obtained due to the antiphase dynamics. For the Cr,Nd:YAG microchip laser, the instability caused by the multi-longitudinal mode competition is an intrinsic property. Different transverse patterns were observed in Cr,Nd:YAG microchip lasers when a pump beam with larger diameter was used. Saturated inversion population distribution inside the gain medium plays an important role in the transverse pattern formation. Different transverse patterns were reconstructed by combining different sets of the Hermite-Gaussian modes.     

激光自倍频晶体研究和应用进展

激光自倍频晶体是一类同时具有激光和非线性效应的复合功能晶体。以激光自倍频晶体制作的全固态激光器具有体积小,调整方便,稳定性高等优点。自1970年代以来,以LiNbO3,YAl3(BO3)4倍频晶体为基质的激光自倍频晶体实现了自倍频激光运转。近年来,以RECa4O(BO3)3(RECOB)为基质的激光自倍频晶体受到重视和广泛研究。本文从对激光晶体、非线性光学晶体及激光自倍频晶体的基本要求出发,在综述激光自倍频晶体研究历史的基础上,讨论了激光自倍频晶体中的基波和倍频光,探讨了NYAB和Nd:GdCOB一类晶体中晶体长度,Nd3+浓度和效率之间的关系。理论估算表明,当浓度适当,晶体长度10mm时,这两类晶体的光–光转换效率可达30%以上。本文总结了NYAB系列晶体的研究历程及RECOB系列激光自倍频研究的思路及取得的成果。在最近10年中,利用山东大学生长的Yb:YAB晶体,获得1.1 W自倍频绿光,光光转换效率为10%;在RECOB体系中,比较了各种晶体的特点,选定Nd:GdCOB为主要研究对象,经过晶体掺钕浓度和长度关系,位相匹配方向、膜系及热工程等多方面研究,获得了1.36 W的545 nm绿光输出,光–光转换效率为17.1%;输出功率为1.03 W时,半小时功率波动不超过1%。这是目前为止,Nd3+离子激光自倍频晶体的最好结果。文章最后介绍了激光自倍频晶体的可能应用。通过理论和实验分析,认为到目前为止Nd:GdCOB是以Nd3+为激活离子最后的激光自倍频晶体,而在Yb3+为激活离子时,Yb:YAB晶体最佳。     

First-Stokes Wavelengths at 1175.8 and 1177.1 nm Generated in a Diode End-Pumped Nd:YVO_4/LuVO_4 Raman Laser

A diode end-pumped acousto-optic Q-switched Nd:YVO_4/LuVO_4 Raman laser is demonstrated. Both YVO_4 and LuVO_4 can work as Raman gain, and slightly different active vibration modes of both crystals can result in different first-Stokes wavelengths. The output characteristic as the Raman competition between YVO_4 and LuVO_4 crystals for the laser systems with both shared cavity and coupled cavity is experimentally investigated.For the shared cavity, simultaneous Raman conversion in both YVO_4 and LuVO_4 crystals is achieved with dualwavelength emission at 1175.8 and 1177.1 nm. The maximum output power of 1.03 W and the conversion efficiency of 10.3% are obtained. The 0.84 W single first Stokes wavelength at 1177.1 nm with LuVO_4 Raman conversion is achieved with the coupled cavity. The results show that the coupled cavity with short Raman cavity can obtain a narrow pulse width. The separated laser crystal and Raman gain media with different vanadates in shared cavity have advantages in achieving dual-wavelength lasers with small frequency intervals.     

Low‐wavelength emission of Nd‐doped lasers

This paper gives an overview of the results obtained with diode‐pumped Neodymium‐doped crystals operating below 900 nm. Operation at such low wavelengths requires considering the strong thermal population of the lower level of the laser transition. Based on a theoretical study and simulations, the paper presents the challenges related to the design of these three‐level lasers. Experimental results are given with Nd:YAG and Nd:vanadate crystals. It is explained how to deal with the line competition with emission at 946 nm or 912 nm. Finally, intracavity second‐harmonic generation is presented. The output powers reach a few hundred mW at wavelengths below 450 nm. Hence, the paper demonstrates the potential of Nd‐doped diode‐pumped solid‐state lasers for applications in the blue range, in replacement of gas lasers such as helium‐cadmium lasers.     

Comparison of cw laser performance of Nd:KGW, Nd:YAG, Nd:BEL, and Nd:YVO4 under laser diode pumping

4 crystals under low-power laser diode end-pumping. Output power dependencies on the pump power and the pump wavelength of these diode-pumped solid state lasers were investigated. The high Nd³⁺ concentration of the Nd:KGW samples used in our measurements as well as up-conversion and exited-state absorption processes in Nd:KGW cause the reduced laser output power dependence on the pump wavelength which was experimentally observed. At pump levels up to 270 mW a slope efficiency of η_sl≈46% was reached for the Nd:KGW laser. Nd:KGW microchip laser operation with a slope efficiency of η_sl≈50% was demonstrated. Thermal lensing in Nd:KGW at pump powers up to 3 W was measured. Received: 4 August 1997     

大口径谐振腔式固体激光中的动力学不稳定性研究

大口径谐振腔式固体激光定标到足够高功率后,由于非稳定腔内激光不对称振荡导致介质上激光强度横向不均匀,激光提取与介质产热耦合会引起激光输出功率和光束质量在时域上的不稳定性。针对三种激光器构型:Nd:YAG薄片、Yb:YAG薄片和浸入式液冷叠片激光器,通过理论分析与数值模拟揭示了其各自不同的光热耦合机制及其影响因素,给出了激光输出的瞬态演化规律。结果表明,前两种构型中基于激光动力学的光热耦合具有饱和效应,其动力学不稳定性只出现在特定参数区间,可以通过恰当的设计加以避免;第三种构型中动力学不稳定性表现出明显的阈值特征,在强光状态下只能通过减少冷却液吸收系数来抑制。     

Tunable continuous-wave laser at quasi-three-level with a disordered Nd:LGS crystal

A diode-pumped tunable CW Nd(3+):LGS laser at quasi-three-level has been demonstrated. The output power up to 403 mW at the central wavelength of 904 nm was obtained, corresponding to a slope efficiency of 29.7%. Taking advantage of the broad emission spectrum of the disordered crystal Nd:LGS, we tuned the laser wavelength within the spectral range of 899.8 to 906.6 nm with an etalon inserted into the V-type cavity. To the best of our knowledge, it is the first time to obtain a tunable laser based on the (4)F(3/2)-(4)I(9/2) transition of Nd(3+)-doped crystals.     

Comparative study on the laser performance of two Yb-doped disordered garnet crystals: Yb:CNGG and Yb:CLNGG

Continuous-wave (CW) and passively Q-switching laser performance of the Yb:CNGG and Yb:CLNGG disordered garnet crystals are compared. CW output powers of 6.3 and 7.5?W are generated from the Yb:CNGG and Yb:CLNGG lasers, with slope efficiencies measured to be 63 and 74?%, respectively. In passively Q-switched operation, the average output power reaches 2.0 and 3.1?W, with slope efficiencies of 56 and 65?%, for the Yb:CNGG and Yb:CLNGG lasers, respectively. Laser pulses of 9.5?ns in duration are generated with the two Yb lasers, with the highest pulse energy and peak power amounting to 166.7???J and 17.5?kW for the Yb:CNGG laser, and 133.0???J and 14.0?kW for the Yb:CLNGG laser. In respects of efficient laser operation and power scaling, the Yb:CLNGG proves to be advantageous over Yb:CNGG, whereas the Yb:CNGG is superior to Yb:CLNGG in energy storage capacity.     

Diode-laser-array end-pumped 14.3-W CW Nd:GdVO4 solid-state laser at 1.06 μm

A diode-laser-array end-pumped efficient CW Nd:GdVO₄ laser at 1.06 μm has been developed. A low-order-mode output power of 14.3 W was obtained at the maximum available pump power of 26 W, giving an optical conversion efficiency of 55% and an average slope efficiency of 62%. The laser output beam quality factor at full pump power was determined to be M²<1.8. It is also shown that only lightly doped Nd:GdVO₄ crystals are suitable for high-power end-pumped lasers. Received: 4 May 1999 / Published online: 29 July 1999     

Lasers for materials processing: specifications and trends

An overview is given of the types of lasers dominating the field of laser materials processing. The most prominent lasers in this field are the CO₂ and the Nd: YAG laser. The domain of CO₂ lasers is applications which demand high laser powers (up to 30 kW are available at present), whereas the domain of Nd:YAG lasers is micro-machining applications. In the kilowatt range of laser output power, the two types of lasers are in competition. New diffusion-cooled CO₂ laser systems are capable of output laser powers of several kilowatts, with good beam qualities, while still being quite compact. The output power and beam quality of Nd:YAG lasers has been improved in recent years, so that Nd:YAG lasers are now an alternative to CO₂ lasers even in the kilowatt range. This is especially true for applications that demand optical fibre transmission of the laser beam, which is possible with Nd:YAG laser light but not with the longerwavelength light emitted by CO₂ lasers. The main problem in solid-state lasers such as Nd:YAG is the thermal lensing effect and damage due to thermal stresses. In order to reduce thermal loading, cooling has to be enhanced. Several alternative geometries have been proposed to reduce thermal loading and, by this, thermal lensing effects. There are now slab and tube geometries which allow much higher output powers than the conventionally used laser rods. A very new scheme proposes a thin slab whose cooled side is also used as one of the laser mirrors, so that thermal gradients occur mainly in the direction of the beam propagation and not perpendicular to it, as is the case in the other geometries. As well as CO₂ and Nd:YAG lasers, semiconductor laser diodes are very promising for direct use of the emitted light or as pump sources for Nd:YAG and other solid-state lasers. When packaging together thousands of single laser diodes, output powers of several kilowatts can be realized. Major problems are collimation of the highly divergent laser beams and cooling of the laser diode bars.     

端面泵浦双Nd: YVO4激光器中热效应对腔稳定性的影响

利用多个激光晶体串接方式可以提高固体激光器的输出功率. 发展双Nd: YVO₄晶体激光器, 将晶体的端面镀膜作为谐振腔的端面镜, 构成了平行平面谐振腔. 对平行平面谐振腔的等效腔进行了理论分析, 结果表明激光晶体吸收泵浦光产生的热透镜效应对保持腔的稳定性起到了重要的作用. 在国内首次进行了双端泵浦双Nd: YVO₄激光器的实验研究, 在抽运功率为 20.74 W时获得了11 W的1064 nm TEM00模激光输出, 其光-光转化效率约为53%. 并且对于不同掺杂浓度下的实验结果进行了讨论.     

紧凑型激光二极管抽运全固态355 nm连续波紫外激光器

报道了一台激光二极管端面抽运Nd:YVO₄晶体内腔三倍频355 nm激光连续输出的全固态紫外激光器.激光腔采用紧凑型简单凹平直腔,腔长仅为70 mm.利用两块LBO晶体进行腔内倍频、和频,当注入抽运功率为2527 W时,获得最大功率为306 mW的355 nm连续波输出,光光转换效率为012％,输出功率短期不稳定性为53%,355 nm激光输出光束质量良好.通过采用内腔倍频技术和设计合理的腔参数,实现了中小功率连续输出的全固态紫外激光器的小型化、便携化,进一步拓宽了紫外激光器 关键词： 激光二极管端面抽运 内腔三倍频 连续波 355 nm激光     

Single rod efficient Nd:YAG and Nd:YALO lasers with average output powers of 46 and 47 W in diffraction limited beams with M<1.2 and 100 W with M<3.7

Using a new resonator concept guaranteeing fundamental mode operation, flashlamp pumped Nd lasers with average output powers of 46 and 47 W for the two materials were realized with beam qualities better than 1.2*DL. Due to the absence of thermally induced birefringence the efficiency of the Nd:YALO laser was up to 1.85% and thus 1.5 times higher than that of the realized Nd:YAG laser. The Nd:YALO laser output is linear polarized. Average output power of 100 W could be extracted from a Nd:YAG single rod oscillator with a beam quality of better than 3.7×DL.