Theoretical and Experimental Investigations of Diode-Pumped Tm:YAG Laser in Active Mirror Configuration

Based on the rate-equations of quasi-three-level lasers, we analyzed the threshold and the output power of longitudinally pumped Tm:YAG lasers in an active mirror configuration. In contrast to one-pass pumping, two-pass pumping in this configuration will result in a 24% decrease in threshold and 16% increase in slope efficiency. Using a 3-W diode-laser pumping in the active mirror configuration, we demonstrated a CW Tm:YAG laser and obtained 735 mW output power with a slope efficiency up to 49%. Using a Ti:sapphire laser to pump the same device, the threshold power was further reduced and the slope efficiency reached 59%.     

Cr,Tm:YAG晶体中的能量转移

通过对Cr:YAG、Tm:YAG和Cr,Tm:YAG晶体吸收光谱和发射光谱的比较,研究了Cr,Tm:YAG晶体中的能量转移过程.指出Cr3+→Tm3+能量转移过程中,无辐射能量转移占绝对优势.     

激光二极管端面抽运室温Tm,Ho:YLF连续固体激光器

报道了激光二极管端面抽运Tm，Ho：YLF固体激光器的输出特性.室温下，选用不同透过率的输出耦合镜进行了实验研究，确定了最佳输出耦合镜透过率为2%. 利用小孔扫描的方法，得到了激光远场的光强分布，证明激光为基横模输出，并且给出了热焦距随抽运功率的变化关系.通过在激光谐振腔内插入两个固体Fabry-Perot标准具的方法，获得了2μm激光的单频输出，阈值功率为250mW，在抽运功率为2.8W时，单频输出功率为118mW.此单频激光器可用作激光振荡器和激光放大器的种子源. 关键词： 激光光学 激光二极管 Tm Ho:YLF固体激光器 单频     

A kilowatt level diode-side-pumped QCW Nd:YAG ceramic laser

We demonstrate a kilowatt level Quasi-continuous-wave (QCW) diode-side-pumped Nd:YAG ceramic laser at 1064 nm. The laser system adopts a master oscillator power amplifier scheme (MOPA). The master oscillator contains two diode-pumped laser modules. Under the pump power of 2000 W, an output power of 686 W was obtained. After amplified by an identical ceramic laser module, a maximum output power of 1020 W was obtained under a total incident pump power of 3433 W, corresponding to an optical-optical conversion efficiency of 29.7%. At the maximal output power, the repetition frequency was measured to be 1 kHz and the pulse width was 114 μs. To the best of our knowledge, this is the first time to realize QCW side-pumped Nd:YAG ceramic laser system with output power above 1 kW.     

Tm：YAG晶体的光谱及激光特性研究

测试了Ｔｍ：ＹＡＧ晶体的室温吸收光谱和荧光光谱，计算了各吸收谱线的振子强度，并根据Ｊｕｄｄ－Ｏｆｅｌｔ理论了Ｔｍ：ＹＡＧ晶体的荧光跃迁截面和荧光寿命，用红宝石激光泵浦时，获得了波长２．０１μｍ能量４０ｍＪ的激光脉冲。     

Diode-pumped long-pulse-width Tm:YAG laser at room temperature

We report the pulsed-diode-pumped and acoustics-optically Q-switched operation of a long-pulse-width Tm:YAG laser at room temperature. Output energy for single pulse of 48 mJ is obtained under the incident pump energy of 217.3 mJ, corresponding to a slope efficiency of 30.2% and an optical conversion efficiency of 22.1%. For the Q-switched regime, maximum pulse energy of 3.25 mJ and the pulse width of 232.8 ns at the repetition rate of 30 Hz are achieved. The wavelength of the Q-switched laser is 2.013 μm. A beam quality factor of M ² < 1.4 is measured using the traveling 90/10 knife-edge method.     

Cr，Tm∶YAG晶体中的能量转移

通过对Ｃｒ∶ＹＡＧ、Ｔｍ∶ＹＡＧ和Ｃｒ，Ｔｍ∶ＹＡＧ晶体吸收光谱和发射光谱的比较，研究了Ｃｒ，Ｔｍ∶ＹＡＧ晶体中的能量转移过程．指出Ｃｒ３＋→Ｔｍ３＋能量转移过程中，无辐射能量转移占绝对优势．     

LD-pumped actively Q-switched Tm,Ho:YLF laser at room temperature

We have investigated acoustic-optical Q-switched Tm,Ho:YLF laser end-pumped by a laser-diode. At room temperature, a 2.067 μm wavelength pulsed output is realized. Average output power, single pulse energy and pulse-width are measured at different incident pump powers and pulse repetition frequencies. When the incident pump power is 2.8 W, a maximum average output power of 189 mW is obtained at the repetition frequency of 9 kHz, and this corresponds to an optical conversion efficiency of 6.8%. The maximum single pulse energy of 65μJ, the shortest pulse-width with full-width at half-maximum (FWHM) of 138 ns and the maximum peak power of 470 W are obtained at the pulse repetition frequency of 1 kHz.     

纵向泵浦Tm：YAG激光器的理论研究

用准三能级系统速率方程对纵向泵浦Ｔｍ：ＹＡＧ激光器的阈值，效率和激活介质最佳长度进行了计算和分析，讨论了温度对Ｔｍ：ＹＡＧ激光器输出特性的影响。     

Design and performance of a composite Tm:YAG laser pumped by VBG-stabilized narrow-band laser diode

A 2-μm composite Tm:YAG laser pumped with a narrow-band laser diode was presented. The temperature distribution and thermal lens in the Tm:YAG were numerically simulated by a finite element method and the results were used to design the special cavity, in order to achieve a high efficiency and stable output. With a 25-W incident pump power, we obtained a maximum output power of 11 W at 2018.5 nm, corresponding to a slope efficiency of 51.3% and an optical-to-optical efficiency of 44.5%, respectively. The beam quality was measured to be M_x~2= 1.8 and M_y~2= 1.6.     

Diode-end-pumped linear-polarized single-frequency Tm:YAG laser at room temperature

By using two solid uncoated etalons, we present a diode-pumped linear-polarized single-frequency Tm:YAG laser operating at 2 μm. Placing one 0.1 mm F-P etalon at nearly Brewster angle in the cavity, the linear-polarization laser is achieved. The other 1 mm F-P etalon was turned in the range of very small angle, single-longitudinal-mode (SLM) could be obtained. The maximum output power of linear-polarized single-frequency laser of 60 mW is achieved at the wavelength of 2013 nm. The degree of the polarization is over 30 dB. Long-term frequency stability was also investigated, with the results of wavelength fluctuation about 2.55 × 10⁻¹³ m within 3 min and frequency change about 18.86 MHz, corresponding to a frequency stability of 1.27 × 10⁻⁷.     

Quasi-CW diode pumped Nd:KGW laser at low temperature

We have studied the laser performance of Nd: KGW and Nd: YAG rods by monitoring the 1.06 μm laser emission at 78.5 K and 300 K. Our observations indicate that the laser efficiency from Nd: KGW is much higher than from Nd: YAG at these two temperatures. The laser threshold in Nd: KGW is lower at 78.5 K than at 300 K but it is always lower than that in Nd:YAG.     

Achieving single-longitudinal-mode output about Tm:YAG laser at room temperature

We report on the single-longitudinal-mode Tm:YAG laser with a volume Bragg grating pumped by laser diode at room temperature. The maximum SLM power of 142 mW was achieved under incident pump power of 3.22 W. The central wavelength was 2012.6 nm accords with the resonant wavelength of the VBG. Three cavity lengths were used to achieve high efficiency and clear spectrum. The maximum output power were measured to be 450.5, 451.4, and 457.3 mW at incident pump power of 3.22 W, corresponding to a slope efficiency of 17.1, 16.9, and 16.7% for the cavity length of 30, 40, and 50 mm, respectively. 40 mm cavity length having the cleanest spectrum among the three was used for SLM laser with one 1 mm F-P etalon inserted into the cavity.     

Diffraction losses of Nd:YAG and Yb:YAG laser crystals

Based on space-dependent rate equations, the lowest threshold input power for a diode end-pumped solid-state laser is obtained for the pump spot size w_p→0. However, as the pump beam waist is decreased, the thermally induced effects in the laser rod would be very high. Diffraction losses caused by radial and tangential variations of refractive index have been analyzed and compared for the Nd : YAG and the Yb : YAG at room temperature (300 K) and liquid-nitrogen temperature (77 K).     

Tm:YAG晶体光谱的温度特性及荧光的温度淬灭

通过测量不同温度下Ｔｍ：ＹＡＧ晶体的吸收光谱、荧光光谱和荧光寿命发现,温度是影响Ｔｍ：ＹＡＧ晶体光谱特性的重要因素。温度升高不仅引起Ｔ：ＹＡＧ晶体吸收光谱、荧光光谱的加宽和新光谱线的产生,而且引起荧光淬灭现象的发生。     

Characterization of spectral hole depth in Tm3+:YAG within cryogenic temperature range

In this paper, spectral hole depth dependence on temperature below 10 K in Tm³⁺:YAG crystal is investigated in detail. A novel model is proposed to analyze the temperature dependence on spectral hole. By using the proposed model, we theoretically deduce the temperature dependence of spectral hole depth. The results are compared with experimental results and they are in good agreement. According to the theoretic results, the optimum temperature in experiment can be found.     

Pulsed and cw Cr,Tm:YAG laser with simultaneous diode and flashlamp excitation

A Cr,Tm:YAG laser, under simultaneous flashlamp and diode laser excitation, was demonstrated. With respect to diode pumping a cw-output power of 35 W with a slope efficiency of 20% was achieved. With flashlamp excitation pulse energies up to 465 mJ were realised. This operation was supported by simultaneous diode pumping to bring the laser close to threshold. Repetition rates up to 10 Hz were demonstrated with this simultaneous pumping mode of the Cr,Tm:YAG laser crystal.     

Experimental study of high-power pulse side-pumped Nd:YAG laser

The paper reports on the characterization of a compact and simple side-pumped 0.538 J×100 Hz pulse Nd:YAG laser. A side-pumping configuration with 100 laser diode bars is used in the laser head. We also experimentally studied the laser performance of the diode-pumped Nd:YAG laser head in the free running and Q-switched operation under different repetition rates.     

Diode-pumped actively Q-switched Tm:YAG ring laser operation at room temperature

2-μm lasers with high pulse energy and long pulse width of hundreds of nanoseconds are needed urgently in the accurate wind velocity lidar systems. This paper presents the acoustic-optical Q-switched Tm:YAG laser performance in a pulsed-laser-diode end-pumping figure-eight ring resonator structure. Pulse energy and pulse width are investigated with the increasing of the incident pump energy at different repetition rate operation. Maximum energy of 4.6 mJ with the pulse width of 179.2 ns and 3.57 mJ with pulse width of 184.4 ns are obtained at the repetition rate of 20 and 100 Hz, respectively. Under free-running and Q-switched operation, the peak output wavelength is 2.014 μm at all time, and the beam quality factors are lower than 2 times diffraction-limited measured by a knife-edge traveling method.     

Cr,Tm,Ho∶YAG激光器的理论模拟

为了使CTH∶YAG激光器的设计得到更好的优化，从晶体光谱吸收特性、离子间能量转移过程及准三能级运转方式对CTH∶YAG激光器的工作特性进行了理论分析；依据速率方程理论建立了CTH∶YAG激光器运转的理论模型.模拟能量输出与试验结果较好的吻合，验证了此理论模型描述CTH∶YAG激光器运转规律的合理性.模拟结果表明：CTH∶YAG激光器的激光脉冲输出与泵浦有较长的时间延迟且伴随较强的驰豫振荡，冷却温度对激光输出产生较大的影响.