Intracavity second-harmonic generation at 320 nm of an actively Q-switched Pr:LiYF4 laser

We demonstrate pulse laser operation of a Pr:LiYF(4) laser pumped by InGaN laser diodes (444 nm) using an acousto-optic modulator. We obtained a maximum laser peak power of 167 W (4 μJ/pulse) with a pulse width of 24 ns at an 11 kHz repetition rate for a 63 nm wavelength. Employing an 8 mm long lithium triborate nonlinear crystal in the laser cavity, we obtained a maximum peak power of 55 W (2.7 μJ/pulse) at 320 nm, which corresponds to a conversion efficiency of 69% with respect to the fundamental laser energy. The UV laser pulse width was 36 ns.     

A high efficiency coaxial pulse tube cryocooler operating at 60 K

In recent years, improved efficiency of pulse tube cryocoolers has been required by some space infrared detectors and special military applications. Based on this, a high efficiency single-stage coaxial pulse tube cryocooler which operates at 60 K is introduced in this paper. The cryocooler is numerically designed using SAGE, and details of the analysis are presented. The performance of the cryocooler at different input powers ranging from 100 W to 200 W is experimentally tested. Experimental results show that this cryocooler typically provides a cooling power of 7.7 W at 60 K with an input power of 200 W, and achieves a relative Carnot efficiency of around 15%. When the cooling power is around 6 W, the cryocooler achieves the best relative Carnot efficiency of around 15.9% at 60 K, which is the highest efficiency ever reported for a coaxial pulse tube cryocooler.     

A 1319 nm diode-side-pumped Nd:YAG laser Q-switched with graphene oxide

We have demonstrated a diode-side-pumped Q-switched Nd:YAG laser operating at 1319?nm with a saturable absorber of graphene oxide fabricated by the vertical evaporation method. The 1319?nm Q-switched laser pulses were realized with average output power of 820 mW, pulse width of 2?μs and repetition rate of 35?kHz. The pulse energy and peak power were 23.4?μJ and 11.7?W, respectively when the optical pump power was 232?W. The experimental results indicate that graphene oxide is an effective saturable absorber for Q-switched lasers.     

Near-diffraction-limited, high-energy, high-power, diode-pumped laser using thermal aberration correction with aspheric diamond-turned optics

We achieved a 1.3× diffraction-limited output beam with a pulse energy of 0.76 J at 60 Hz (average power of 46 W) at 1.064 μm from a diode-pumped Nd:YAG master oscillator power amplifier rod laser using a diamond-turned aspheric optic to compensate thermally induced phase distortion of the gain medium. The output was frequency doubled in KTP to 30 W (0.5-J pulse energy) and 2.4× diffraction-limited at 532 nm.     

Diode-end-pumped passively Q-switched Nd:YAG crystal laser with V:YAG saturable absorber at 1319 and 1338 nm

A diode-end-pumped passively Q-switched Nd:YAG laser with a V:YAG saturable absorber emitting at 1319 and 1338?nm was demonstrated for the first time. A maximum output power of 286?mW was obtained with minimum pulse duration of 13.2?ns and the highest repetition rate was 15?kHz under an incident pump power of 7.7?W. The calculated highest peak power and pulse energy were 2.1?kW and 29?μJ, respectively.     

Theoretical and experimental study of a gas-coupled two-stage pulse tube cooler with stepped warm displacer as the phase shifter

A compact and high efficiency cooler working at liquid hydrogen temperature has many important applications such as cooling superconductors and mid-infrared sensors. This paper presents a two-stage gas-coupled pulse tube cooler system with a completely co-axial configuration. A stepped warm displacer, working as the phase shifter for both stages, has been studied theoretically and experimentally in this paper. Comparisons with the traditional phase shifter (double inlet) are also made. Compared with the double inlet type, the stepped warm displacer has the advantages of recovering the expansion work from the pulse tube hot end (especially from the first stage) and easily realizing an appropriate phase relationship between the pressure wave and volume flow rate at the pulse tube hot end. Experiments are then carried out to investigate the performance. The pressure ratio at the compression space is maintained at 1.37, for the double inlet type, the system obtains 1.1 W cooling power at 20 K with 390 W acoustic power input and the relative Carnot efficiency is only 3.85%; while for the stepped warm displacer type, the system obtains 1.06 W cooling power at 20 K with only 224 W acoustic power input and the relative Carnot efficiency can reach 6.5%.     

Passive mode-locking performance comparison between composite and single Nd:YVO4 crystals

The mode-locked performances of composite and conventional Nd:YVO₄ crystals were demonstrated with a semiconductor saturable absorber mirror. For the conventional crystal, power saturation was observed when the pump power exceeded 5.31 W, while for the composite crystals, the output power increased linearly with the pump power, showing good thermo-mechanical performances. The maximum average output power of 1.2 W was achieved by a composite crystal at an incident pump power of 7.09 W. The largest pulse energy of 34.6 nJ and the highest peak power of 4.9 kW with a pulse duration of 7 ps were also obtained by the same composite crystal while the non-composite crystal got the shortest pulse duration of 5.3 ps. The theoretical analysis on pulse duration for different laser media is in agreement with the experimental result.     

High power 2 MHz passively Q-switched nanosecond Nd:YVO4/Cr4+:YAG 914 nm laser

We report a high-power, high-repetition-rate end-pumped passively Q-switched Nd:YVO4/Cr4+: yttrium aluminum garnet 914 nm laser. The maximum output power of 3.8 W at 914 nm is achieved at 2 MHz with the absorbed pump power of 25.2 W. The highest single pulse energy of a pulsed 914 nm laser reaches 2.3 μJ with a pulse width of 27.1 ns.     

Watt-level Q-switched Nd:LuVO4 laser based on a graphene oxide saturable absorber

The demonstration is reported of a diode-pumped passively Q-switched Nd:LuVO₄ laser at 1064 nm using a transmission-type graphene oxide as the saturable absorber. The graphene oxide saturable absorber with a modulation depth of 10% was fabricated using a vertical evaporation method. With a pump of 11.5 W, a maximum output power of 1.353 W was obtained with 186-ns pulse duration and 336.7-kHz repetition rate, corresponding to a maximum pulse energy of 4 μJ per pulse.     

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.     

斯特林型高频脉冲管制冷机的实验研究

介绍了一台单级U型高频脉冲管制冷机的实验装置和实验结果.制冷机冷端无负荷最低温度达到了38.31 K,此结果为目前国内单级斯特林型高频脉冲管制冷机所达到的最低温度.当输入电功率200 W时,在50 K有0.6 W制冷量;当输入电功率为250 W时,在80 K有4.25 W的制冷量.这为40 K以下深低温,大冷量的斯特林型脉冲管制冷机的研制做出了有益的探索.通过分析压缩机运行频率对制冷机的最低温度和制冷量的影响,得出了在液氮温区针对特定的制冷温度,压缩机存在的一个最佳工作频率.在此工作频率下,压缩机和脉冲管耦合后,制冷机能够获得较高的效率.     

Midinfrared laser source with high power and beam quality

A simple scheme for generation of high power in the midinfrared is demonstrated. By using a 15 W thulium-doped fiber laser emitting at 1907 nm to pump a Q-switched Ho:YAG laser, we obtained 9.8 W at 2096 nm at a 20 kHz pulse repetition rate with excellent beam quality. The output of this laser was used to pump a doubly resonant zinc germanium phosphide based optical parametric oscillator, and we obtained 5.1 W average power in the 3-5 microm range with M2 approximately = 1.8.     

Non-linear switching based on dual-core non-linear optical fiber couplers with XPM and Raman intrapulse applied to femtosecond pulse propagation

In this work, we investigated the optical switching process for three shapes of femtosecond pulses (soliton, Gaussian and super-Gaussian) propagating inside a symmetrical dual-core non-linear directional coupler by simulating their propagation via the coupled non-linear Schrödinger equations. In all simulations, we considered the dispersive effects of second and third order, besides the self-phase modulation and self-steepening non-linear effects. We studied three scenarios for each of the three pulse shapes under investigation. In the first scenario, we added only cross-phase modulation (XPM); in the second approach, we added only Raman scattering; in the third one, we combined both. The study was performed for distinct polarization modes and for different values of the Raman factor, with power range varying from 1 to 300 W. We noted that the XPM non-linear effect results in a decrease in the critical power threshold, whereas the Raman scattering causes an increase. For the first scenario (only XPM effect), the critical power threshold reduced from 113.72 to 104.69 W for the soliton pulse, from 111.49 to 100.77 W for the Gaussian and from 92.79 to 80.47 W for the Super-Gaussian pulse shape. For the second scenario (only Raman scattering), the critical power increased for a Raman factor varying from 1 to 10 fs, and the three pulse shapes reached thresholds above 150 W from a 5 fs factor, reaching more than 200 W for the super-Gaussian pulse as the Raman factor increased. For the third scenario (with both effects combined), we highlight that for a fixed XPM factor of 2, the critical power remained unchanged with the variation of the Raman factor. Hence, we observed that the Super-Gaussian pulse reached lower values for critical power when compared to the other pulse shapes.     

在DCF光纤中放大的背向自发拉曼散射的增益特性

光脉冲沿色散补偿光纤（DCF）传输会产生背向自发拉曼散射,当入纤激光功率大于阈值时,出现放大的背向自发拉曼散射现象。实验发现,反斯托克斯（ASR）和斯托克斯（SR）自身脉冲光纤拉曼放大的阈值泵浦峰值脉冲功率是18．2W和14．5W．当入纤激光功率为52W时,背向SR和ASR散射的增益分别为12dB和7dB。放大的反斯托克斯和斯托克斯背向自发拉曼散射时域曲线上的阈值时间位置随激发功率的增大而前移并具有规律性。     

Passively Q-switched Yb3+:YCa4O(BO3)3 laser with InGaAs quantum wells as saturable absorbers

A diode-pumped Yb:YCOB laser at 1086 nm is passively Q switched by using InGaAs quantum wells as saturable absorbers and utilizing the Bragg mirror structure as an output coupler. With an absorbed pump power of 9.2 W the laser produces pulses of 100 ms duration with average pulse energy of as much as 165 microJ at a pulse repetition rate of 7 kHz.     

Theoretical and experimental study on passive mode-locking composite Nd:GdVO4/Nd:GdVO4/Nd:GdVO4 lasers

Stable passive mode-locking multi-segment composite Nd:GdVO₄ lasers with a semiconductor saturable absorber mirror were demonstrated for the first time. For the composite crystals, the output power increased linearly with the increase of the incident pump power, showing excellent thermo-mechanical performances. While for the conventional crystal, power saturation was observed when the incident pump power exceeded 8.79 W. The maximum average output power of 1.465 W was achieved by Nd(0.1%):GdVO₄/Nd(0.5%):GdVO₄/Nd(1%):GdVO₄ composite crystal at an incident pump power of 9.28 W. The largest pulse energy of 14.90 nJ and the highest peak power of 0.53 kW with a pulse duration of 28.0 ps were also obtained by using the same composite crystal, revealing that the multi-segment composite crystal with a proper combination of Nd³⁺-doped concentrations could obtain the optimal laser performance.     

The effect of passive Q-switching observed in an erbium-doped fiber laser at a low pumping power

The effect of passive Q-switching was observed in an erbium fiber laser at a pumping power below 100 mW. The phenomenon is explained by a cascade process of the Rayleigh light scattering and the induced Mandelshtam-Brillouin scattering in a fiber resonator of the laser. In the Q-switched mode, the laser produced giant output pulses with a duration below 15 ns, a peak power up to 200 W, and a repetition period of 300–500 μs. The proposed Q-switching mechanism is inferred from the characteristic features of the laser pulse oscillograms measured at a ∼1 ns resolution. Previously, this effect was observed only in high-power fiber lasers at a pumping power of ∼2 W.     

Passively Q-Switched Diode-Pumped Continuous-Wave Nd:YAG-Cr(4+):YAG Laser with High Peak Power and High Pulse Energy

A high peak power and high pulse energy passively Q-switched diode-pumped cw Nd:YAG laser at 1.064-mum wavelength has been demonstrated with Cr(4+):YAG crystal as the saturable absorber. The average output power of 7-12 W and pulse duration of 100-250 ns was obtained with kilohertz repetition rates. The highest peak power and pulse energy obtained were 30 kW and 3.4 mJ, respectively. All the output resulted from the TEM(00) mode with M(2) < 1.1. The thermal lensing effect of the saturable absorber was investigated, demonstrating that it played an important role in optimization of the output.     

Generation of deep ultraviolet narrow linewidth laser by mixing frequency Ti:sapphire laser at 5 kHz repetition rate

We demonstrate a scheme to generate deep ultraviolet source by the single-stage high-power Ti:sapphire laser with linewidth of 0.05 nm cryogenically operating at repetition rate of 5 kHz. The fundamental laser was tuned by an intracavity birefringent filter and three etalons with an output power greater than 8 W, corresponding to about 17% optical efficiency. The pulse width was 112 ns and M2<1.1. By using the nonlinear crystals BiB3O6 and KBe2BO3F2, the output power of 2.2 W at second harmonic and 8.5 mW at fourth harmonic laser of about 195 nm were produced. This compact high-repetition rate laser with narrow linewidth would be a promising tunable source for spectroscopy.     

空调压缩机驱动高效同轴脉冲管制冷系统

介绍了为实际应用而开发的低成本、高效率、长寿命的制冷系统：空调压缩机驱动的单级同轴脉冲管制冷机。实验获得了３８．４Ｋ的最低温度，制冷量３Ｗ／５０Ｋ，大于６Ｗ／８０Ｋ，输入功率约６２０Ｗ，启动过程操作简单、降温快、运行稳定。