An EMQ-switched CO2 laser as a pump source for afar-infrared laser with a high peak power and a high repetitionrate

A modified current pulsed Q (EMQ)-switched CO₂ laser which is Q-switched by a mechanical beam chopper in combination with a pulsed discharge current is discussed. The laser produces a very stable output with a peak power greater than 1 kW at a repetition rate of 1000 p.p.s. for all transitions in the P and R branches of the CO₂ spectrum. A CH₃F laser pumped by the EMQ-switched laser produces 496 μm radiation in a 6.5 W peak, 100 ns pulses at 500 p.p.s. in the lowest loss EH₁₁ mode     

小型化高光束质量MgO: PPLN中红外光参量振荡器

为满足中红外激光的工程应用需求,研制了基于MgO: PPLN晶体的小型化高光束质量中红外光参量振荡器（MgO: PPLN-OPO）。泵浦源采用声光调Q Nd: YVO₄激光器,通过泵浦MgO: PPLN晶体,获得了高效率、高峰值功率中红外激光输出,在MgO: PPLN-OPO谐振腔中加入光阑,有效提高了中红外激光光束质量,整个激光器采用热电制冷与风冷相结合的散热方式,实现了激光器的小型化。实验结果表明:采用无水冷的声光调Q Nd: YVO₄激光器能够实现最高9.3 W的1.064 μm脉冲激光输出,光光转换效率为27.2%,峰值功率可达~27.5 kW;在Nd: YVO₄激光器泵浦下,MgO: PPLN-OPO实现了3.765 μm脉冲激光输出,在谐振腔中加入光阑后,MgO: PPLN-OPO的最高输出功率由1.20 W略降至1.08 W,但光束质量有明显提高,M_x2和M_y2因子分别从1.89和1.98优化至1.20和1.29,中红外激光脉冲宽度为8.4 ns,峰值功率达到~4.3 kW。     

Subnanosecond multi-gigawatt CO2 laser

A semiconductor switching technique has been utilized to produce 30-300 ps variable duration CO₂ laser pulses of 0.5-MW peak power. Eight passes through a 1.2-m long, UV-preionized, 3-atm TE CO₂ amplifier raise the output laser peak power to the 10¹⁰ W level. Sampling the amplifier gain in linear and saturated regimes using CO₂ laser radiation ranging from CW to 30 ps pulse length permits comparison with computer modeling of picosecond CO₂ pulse amplification. The potential for further peak power scaling of picosecond molecular lasers is discussed     

2 ns pulse width high repetition rate short cavity acousto-optically Q-switched Nd:YVO/sub 4/ laser

With a specially constructed miniature acousto-optical Q-switch, 2 ns pulses with 10.3 muJ energy and 5.13 kW peak power at 80 kHz repetition rate were obtained in an end pumped short cavity acousto-optically Q-switched Nd:YVO₄ laser. This is believed to be the shortest pulse width obtained in a solid-state laser by acousto-optical Q-switching. At 500 kHz repetition rate, 10 ns pulses were generated     

Diode-pumped ytterbium-doped Sr5(PO4)3F laser performance

The performance of the first diode-pumped Yb³⁺-doped Sr ₅(PO₄)₃F (Yb:S-FAP) solid-state laser is discussed. An InGaAs diode array has been fabricated that has suitable specifications for pumping a 3×3×30 mm Yb:S-FAP rod. The saturation fluence for diode pumping was deduced to be 5.5 J/cm ² for the particular 2.8 kW peak power diode array utilized in our studies. This is 2.5× higher than the intrinsic 2.2 J/cm ² saturation fluence as is attributed to the 6.5 nm bandwidth of our diode pump array. The small signal gain is consistent with the previously measured emission cross section of 6.0×10^-20 cm², obtained from a narrowband-laser pumped gain experiment. Up to 1.7 J/cm³ of stored energy density was achieved in a 6×6×44 mm Yb:S-FAP amplifier rod. In a free running configuration, diode-pumped slope efficiencies up to 43% (laser output energy/absorbed pump energy) were observed with output energies up to ~0.5 J per 1 ms pulse. When the rod was mounted in a copper block for cooling, 13 W of average power was produced with power supply limited operation at 70 Hz with 500 μs pulses     

Simultaneous Q-switching and mode-locking in a diode-pumped Nd:YVO4-Cr4+:YAG laser

Parametric studies of passive Q-switching and mode-locking in a Nd ³⁺:YVO₄-Cr⁴⁺:YAG laser were theoretically carried out. Simultaneous mode-locking and Q-switching was also experimentally studied. It was found that over 90% of the output power could be mode-locked in a diode-pumped passively Q-switched Nd³⁺:YVO₄-Cr⁴⁺:YAG laser. The average pulse duration of the mode-locked pulse train was estimated to he around 110~150 ps. The highest peak power of a single pulse near the maximum of the Q-switched envelope was greater than 100 kW     

绿光泵浦的黄光波段可调谐窄线宽光学参量振荡器

为实现波长可调谐的窄线宽黄光波段激光输出,设计搭建了以倍频声光调Q Nd:YAG激光器的532 nm脉冲绿光输出为泵浦源、以II类相位匹配磷酸钛氧钾（KTP）晶体为非线性介质的折叠腔光学参量振荡器（OPO）。首先产生腔内振荡的近红外可调谐闲频光,在此基础上基于LBO晶体I类非临界相位匹配方式对OPO的闲频光进行内腔倍频,得到波长调谐范围587.2~595.2 nm的黄光波段输出。为改善OPO光谱特性,在OPO闲频光谐振腔内插入熔融石英标准具,有效压缩了OPO输出黄光的光谱线宽。绿光泵浦源脉冲重复频率10 kHz、平均功率24.0 W下在波长591.2 nm处获得了最高黄光输出功率2.89 W,光束质量因子M2=3.4,从532 nm泵浦光到黄光输出的转换效率为12.0%,脉冲宽度37 ns,对应峰值功率7.8 kW。此时黄光光谱半高全宽为0.15 nm,相比未在OPO腔内插入标准具自由运转状态下的光谱得到明显改善。     

Efficient high-power diode-end-pumped TEM00 Nd:YVO4 laser

We demonstrate a compact and efficient diode-end-pumped TEM₀₀ laser with output power of 25.2 W for 52 W of incident pump power by use of a single YVO₄ crystal with a Nd concentration of 0.3 at.%. In Q-switched operation 21-W of average power at a pulse repetition rate of 100 kHz and ~1.1-mT pulse energy at a pulse repetition rate of 10 kHz were produced. At 10 kHz, the pulse width is around 10 ns and the peak power is higher than 100 kW     

Fast axial flow CO2 laser excited by silent discharge

A fast axial flow CO₂ laser excited by silent discharge has been developed. With a new electrode system applied to the laser, homogeneous discharge of power density of up to 80 W/cm³ is obtained without applying any stabilization techniques on the discharge. An output laser power of 920 W in stable TEM₀₀ mode operation is attained with an efficiency of over 14%. Beam fluctuation common to fast axial flow lasers is suppressed by the combination of smooth gas flow and low CO₂ molar fraction     

High average and high peak brightness slab laser

A high average and high peak brightness Nd:YAG MOPA laser system composed of a laser-diode-pumped Nd:YAG master oscillator, flash-lamp-pumped slab power amplifiers and a phase conjugated mirror was developed. The system demonstrates an average output power of 235 W at a repetition rate of 320 Hz and a peak power of 30 MW at a pulse duration of 24 ns with M²=1.5. Both an average brightness of 7×10⁹ W/cm²·sr and a peak brightness of 1×10¹⁵ W/cm2·sr are achieved simultaneously. The system design rules that we confirmed suggest that by replacing lamp pumping in the amplifier with laser-diode pumping, an average output power of ~1 kW can be obtained at ~1 kHz with a higher average brightness of ~3×10¹⁰ W/cm²·sr and a higher peak brightness of ~3×10¹⁵ W/cm²·sr     

Measurements of intrinsic efficiency and parameters of an electronbeam pumped ArXe laser

Measurements of the output energy and intrinsic efficiency of an electron-beam-pumped ArXe laser operating on the 1.73-μm line are reported. A 220-kV electron beam was used to pump either an 11×11×50 cm³ or an 11×11×25 cm³ active volume. Small-signal gain, nonsaturable loss, and saturation flux were deduced from a Rigrod analysis of the output energies as a function of output coupler reflectivity. Electron beam pump powers ranging from 2.2 to 16.2 kW/cm³ were employed. At a pump power of 2.2 kW/cm³ a small signal of 0.035 cm^-1 , a gain-to-loss ratio of 272, and a saturation flux of 2.1 kW/cm ² were determined. Intrinsic efficiencies of 4% were obtained at the lower pump powers. From the measurements of the laser output it is clear that the secondary electrons have a significant impact on the laser kinetics and efficiency     

Optical power limiting and stabilization based on a novel polymercompound

Optical power limiting and stabilization based on the two-photon absorption (TPA) mechanism is performed in a polymer solution excited by ~810 nm and ~7-ns laser pulses. The solute is a novel polymer, a poly(2,5-dialkoxy-p-phenylene ethynylene) derivative (EBO-OPPE). Using 1-cm path-length EHO-OPPE solution in chloroform of d₀=0.03 mol of repeat unit/liter as the nonlinear absorptive medium, the dynamic transmission changes from T=0.92 to 0.28 when the input intensity of the ~810-nm laser beam is increased from I₀=15 to 600 MW/cm² . The measured nonlinear absorption coefficient is 14.5 cm/GW. Optical power stabilization is demonstrated at an average input intensity level of I₀≈400 MW/cm² with a Δ≈±25% peak-power fluctuation of the laser pulse. After passing through the nonlinear medium, the output peak-power fluctuation is reduced to Δ≈±8%. The spectral-width effect of the input laser beam on the nonlinear absorption of the EHO-OPPE solution is investigated. For three different spectral structures of the input laser beam (single narrow spectral line, multiple spectral lines, and broad spectral band), measured values of TPA cross section for EHO-OPPE are σ₂=66, 80, and 101×10^-20 cm⁴/GW, respectively. This means that EHO-OPPE is one of the best known nonlinear absorptive materials for power limiting purposes     

High power and high focusing CWCO2 laser using anunstable resonator with a phase-unifying output coupler

A high-power and high-focusing continuous-wave (CW) CO₂ laser with a novel unstable resonator was developed. This resonator contains a step-wise variable reflecting output coupler named the phase-unifying output coupler and a total reflector. The laser was excited by a capacitive-barriered AC discharge called a silent discharge. A linearly polarized laser beam with a diffraction-limited divergence angle of 0.55 mrad was obtained. Very stable CW laser operation at an output power of 5 kW was achieved with a threshold discharge power of 10 kW and a slope efficiency of 18%     

激光二极管抽运Nd:YVO4晶体声光调Q 1342 nm激光器

报道了激光二极管抽运ＮｄｖＹＶＯ４ 晶体声光调Ｑ的１３４２ ｎｍ 激光器,在重复频率为１５ ｋＨｚ时,获得最大单脉冲能量为７１ μＪ,脉宽为５６ ｎｓ,峰值功率为１．２７ ｋＷ,平均功率达到１．１４ Ｗ 。利用二类非临界相位匹配的ＬＢＯ晶体腔外倍频,得到约３０ ｍ Ｗ 的６７１ ｎｍ 激光输出     

Tunable Cr4+:YSO Q-switched Cr:LiCAF laser

Tunable passive Q-switching (781 nm to 806 nm at 300 K) of a flash-lamp pumped Cr³⁺:LiCaAlF₆ (Cr:LiCAF) laser with a Cr⁴⁺:Y₂SiO₅ (Cr⁴⁺:YSO) broad-band solid-state saturable absorber has been realized. Typical pulse widths of the Q-switched laser output ranged from 40 ns to 80 ns, depending on the lasing wavelength. Spectral narrowing and reduced beam diameter with the use of the saturable absorber were observed. The ground state and the excited state absorption cross sections of the Cr⁴⁺:YSO absorber were found by bleaching experiments to be (7.0±1.4)×10^-19 cm² and (2.3±0.5)×10^-19 cm² at 694 nm, respectively. Numerical simulation was utilized to simulate the Cr:LiCAF passive Q-switching with Cr⁴⁺ :YSO solid-state saturable absorber     

Time-varying beam quality factor and mode evolution in TEA CO2 laser pulses

The time evolution of the transversal modes in a TEA CO₂ laser cavity has been investigated from the analysis of the time-varying beam quality factor M² of the emitted pulses. The experiments reveal a significant change in this parameter during the pulse evolution, which can be translated into an evolution of the modes of the laser cavity to reach a nearly stationary behavior. Attention is focused on both the appearance of a particular mode and the duration of its growing process     

RF excitation of a flowing gas CO2 waveguide laser

Investigation of an RF excited CO₂ waveguide laser in flowing gas operation is reported. Power extraction of 0.8 W/cm with an efficiency of 10.3% has been achieved. Using W.W. Rigrod's analysis (1965), values of the small-signal gain α₀ and saturation parameter I_s have been determined for different excitation levels and for different pressures of the amplifying medium. The parameters α₀ and I_s, have been determined as 0.6%/cm and 10.4 kW/cm ², respectively, at 125 torr and 100 W/cm³ RF loading power. These values are close to those reported for sealed-off RF CO₂ waveguide lasers with xenon added to the gas mixture     

Picosecond CO2 laser-pulse generation and amplification

The generation of 30-ps 10-μm laser pulses from an optical-free-induction-decay (OFID) 10-μm CO₂ laser system and the first realization of a UV-preionized high-pressure CO₂-laser-pulse amplifier with Ernst-electrode profiles for these ultrashort CO₂ laser pulses are described. For a given transverse electric discharge width, the Ernst profile makes it possible to position the UV-radiation sources nearer to the discharge than with the Rogowski or Chang profile. A more homogeneous preionization of the discharge area is possible. Thus, the amplifier works up to 15 bar with a laser-gas mixture of 5:5:90 (CO₂:N₂:He). The authors amplified 30-ps OFID 10-μm CO₂-laser pulses up to ten times by passing through the amplifier twice. Thus, 10-μm OFID pulse energies of 1 mJ were achieved. With the amplifier used as an oscillator, a maximum output energy of 600 mJ was obtained in longitudinal-multimode operation for 50-ns pulses     

LaserQswitching by a PLZT shutter

The application of a polycrystalline ferroelectric ceramic Pb1-xLax(ZryTiz)1-(x/4)O3(called PLZT) electrooptic shutter is described for controlling the giant pulse emission of a ruby laser. The PLZT material hady = 65percent,z = 35percent, and the value ofxwas in the vicinity of 8 percent. Half-wave retardation switching was not possible with the PLZT shutter when 10-ns rise-time 70-ns-duration voltage pulses (fastQswitching) were applied. The increase insertion loss, due to less than half-wave retardation, resulted in laser pulsewidths that were wider and contained less energy than predicted by fastQ-switching theory. Since the PLZT material was damaged at relatively low power densities of between 5.6 to 8.5 MW/cm², respectively, its use is restricted toQ-switching small output power.     

Simultaneous emission of the HF and N2 lines from aplasma cathode TEA laser

Simultaneous laser action from HF and N₂ is obtained, from a plasma cathode TEA laser, for the first time. The sliding discharge along the surface of a dielectric is used as a plasma cathode, for the main volumetric discharge. The laser operates at atmospheric pressure, with a gas mixture of SF₆:C₃H₈:N₂:He. For a typical flow rate ratio of 0.27:0.024:0.2:19.8 1 min^-1, it produces simultaneously 160 mJ HF and 0.6 mJ N₂ laser outputs at 0.43% and 1.4×10^-3% efficiencies respectively, at the moderate charging voltage of 28.5 kV. These output characteristics are obtained from a small active discharge volume and length of 10⁶ cm³ and 38 cm respectively. These values extend the performance, recently reported in the literature, of a sliding discharge HF/N₂ laser with corresponding simultaneous energy outputs of 12 mJ HF and 1.1 mJ N₂, to a higher energy output level, thus making the device suitable for a broader range of applications. This novel dual wavelength HF/N₂ laser system presented, can be particularly convenient for medical experiments, where the IR beam can be used for tissue ablation, while the UV beam can be used as the excitation source for fluorescence spectroscopic measurements, for the evaluation of the ablation process. Details are presented on the dependence of the laser performance parameters, such as output energy, discharge voltage and current and structure of the laser output pulses on the mixture composition and the circuit parameters