Strong-field four-wave mixing in an optically-pumped methylfluoride laser

Continuously tunable coherent radiation in the 9.8-10.1 μm region has been obtained by pumping ¹²CH₃F and ¹³CH₃F with a 10-atmosphere CO₂ laser. Pulse energies up to 2.5 mJ were observed. The experimental conditions were similar to those used for optically-pumped Raman FIR lasers, and simultaneous emission of tunable FIR radiation was also observed. Under some circumstances, a fixed-frequency mid-infrared component was also present. A detailed theoretical analysis of the RFWM process that produces the mid-infrared emission is presented. It is based on a six-level density matrix model. The importance of FIR cascade and refilling transitions, as well as double-Raman transitions, is demonstrated. Contributions to the MIR gain resulting from both degenerate and nondegenerate parametric processes are analyzed. The pressure dependence of the MIR emission was studied, both theoretically and experimentally, and the possibility of pressure switching between tunable and fixed-frequency operating modes is discussed     

A tunable far infrared laser

A continuously tunable far infrared (FIR) laser has been demonstrated; experimental results are presented. A high-pressure (10-12 atm) continuously tunable CO2TE laser is used to pump Raman transitions in CH3F; the generation of continuously tunable radiation in the250-300 mum wavelength range is reported. Accurate frequency and bandwidth measurements have been made and the FIR bandwidth in superradiant emission isapprox4-5GHz. Consequently, the generation of frequency tunable, subnanosecond pulses in the FIR appears feasible. The generation of tunable laser radiation from 150 to 1000 μm by stimulated Raman scattering should be possible using higher pump intensity and/or other gases.     

Far-infrared raman laser with high intensity laser pumping

Theoretical and experimental results are presented for a pulsed far-infrared (FIR) molecular gas laser with high intensity laser pumping. In these FIR lasers, high intensity pumping is found to produce stimulated Raman emission at very large offsets (up to 30 GHz) from resonance with the intermediate state. A theoretical, density matrix model is developed for these lasers to account for simultaneous Raman emission on rotational levels in the ground and excited vibrational states (double Raman resonance). This theoretical approach is necessary in the case of off-resonant, high intensity pumping. Theory predicts the FIR emission frequency, the FIR laser gain, and the pump threshold intensity as a function of pump laser frequency. Experimental results are obtained onP-,Q-, andR-branch transitions in¹²CH3F and¹³CH3F using a single-mode, grating tuned CO2TEA pump laser with an intensity of up to 40 MW/cm². Good agreement is obtained between theory and experiment for the observed values of FIR emission frequency and pump threshold intensity. These results indicate that a widely tunable (150-1200 mum), pulsed FIR CH3F laser could be constructed with a tunable, multiatmospheric CO2pump laser of modest power (about 2-5 MW).     

Near- to far-infrared tunable Raman laser

The importance of stimulated Raman scattering of tunable laser beams in molecular fluids for generating powerful infrared radiation tunable from the near to the far infrared (FIR) is demonstrated. Main criteria (frequency shift, transparency, and Raman gain) leading to the choice of the best Raman medium for a given tunable laser are discussed. For the high power (400-1000 MW), monochromatic (0.02 cm^-1), and broadly tunable (0.72-1.09 mum) ruby pumped dye laser described here, gaseous hydrogen is chosen for the1-10 mum wavelength region yielding powers ranging from 1 to 200 MW. For mid-infrared (IR) generation (10-18 mum), one more Raman shifting in liquid nitrogen permits one to obtain up to 1.7 mJ in the 16 μm region. For longer wavelengths the use of resonantly enhanced stimulated Raman scattering in hydrogen fluoride gives rise to the generation of powerful radiation (2 times 10^{17}photons per pulse of 2.5 ns duration) tunable over half of the40-250 mum spectral range.     

Single line high efficiency tunable fir generation by resonant four-wave mixing in CH3 pumped by a multiatmosphere tunable CO2 laser

By pumping CH₃F with a high pressure tunable TE-CO₂ laser, the resonant four-wave mixing process (RFWM) generates a very efficient tunable single line FIR emission at the Raman frequency. This result is strictly related to the spectroscopic structure of the CH₃F molecule. By means of this process, a tunable FIR emission on a 0.1 cm^?1 bandwidth 150 kW (8 mJ) single line, is obtained which can be used for many FIR multiphoton applications.     

Narrow bandwidth emission from a mirrorless, far infrared, 13CH3F laser

Frequency tuning and linewidth measurements are reported for a pulsed, mirrorless, kilowatt-power-level, far-infrared (FIR) ¹³ CH₃F laser operating at 245 GHz. The pump laser is an etalon tunable, single-mode CO₂ TEA laser. The FIR frequency spectrum was measured with 2.5-MHz resolution on individual 100-ns laser output pulses using harmonic mixing techniques. The linewidth of the amplified spontaneous emission was found to be surprisingly narrow, about 15 MHz. Frequency tuning of the FIR laser, as the pump laser frequency is tuned, is nonlinear, possibly due to inhomogeneous broadening of the gain by the K-level substructure of the rotational states. These results indicate that heterodyne receivers capable of single-shot frequency measurements can be important tools for investigating the properties of Raman FIR lasers     

光泵CH3F和D2O远红外脉冲激光器

本文叙述了无镜远红外激光器的结构及其实验结果。用可调谐TEA CO_2激光器作为泵浦源,其输出能量在9P(20),9R(22)线上均可达1J左右。用CO_29P(20)线泵浦CH_3F分子,获得了能量为0.5mJ,波长为496μm的激光输出;用9R(22)线泵浦D_2O分子,获得了能量为1mJ,波长为385μm的激光输出。输出能量和波长是分别用热电堆和Fabry-Perot干涉仪测量的。     

光泵CH3F和D2O远红外脉冲激光器

自1970年T.Y.Chang报道了光泵CH_3F远红外激光器以来,至今已发现有几十种工作物质,可在远红外波段产生1000多条激光线。远红外激光器有广泛的应用,在等离子体诊断中,通过Thompson散射,可确定Tokamak中离子密度和温度;在半导体中,可用来确定载流子浓度和杂质浓度;作为标准波长,可构成频率链的一环;在军事上,远红外激光可用于亚毫米通讯;用远红外激光照射石英晶体,可产生频率为几THz的声子,在     

Ge-As-Se-Te硫系玻璃的飞秒激光损伤特性

Ge-As-Se-Te（GAST）硫族化物玻璃拥有超过20 μm的超宽透射范围,是一种可应用于中红外（MIR）和远红外(FIR)波段的优良光学材料。通过熔融淬火法制备了Ge_xAs_40?xSe₄₀Te₂₀（x = 0、10、20、30、40 mol%）系列硫系玻璃,采用不同波长（800 nm,3 μm和4 μm）、功率和重复频率的飞秒激光辐照硫系玻璃,利用扫描电子显微镜（SEM）和拉曼光谱等手段研究了GAST的激光损伤特性。研究结果发现,Ge_xAs_40-xSe₄₀Te₂₀玻璃的激光诱导损伤阈值（LIDT）随着样品中Ge含量的增加而增加,在800 nm下Ge₃₀As₁₀Se₄₀Te₂₀玻璃的LIDT达到最高40.16 mJ/cm2。随着飞秒激光波长增加,系列玻璃的LIDT也逐步增加,Ge₃₀As₁₀Se₄₀Te₂₀在4 μm激光辐照下LIDT达到81.09 mJ/cm2。此外,研究结果表明样品LIDT随着激光的脉冲辐照数量和重复率的增加将逐渐减小。     

Tunable solid-state laser action in Ce3+:LiSrAlF6

Continuously tunable UV laser operation of cerium-doped LiSrAlF ₆ (Ce³⁺:LiSAF) between 285 and 297 nm is demonstrated. At the peak operating wavelength of 290 nm, output energies of 1.3 mJ with slope efficiencies of 17% have been obtained     

Methanol and the optically pumped far-infrared laser

New results on the generation and spectroscopic analysis of optically pumped far-infrared (FIR) laser emission from CH₃OH have been obtained as part of a systematic study of methanol isotopomers as FIR laser sources utilizing the extended line coverage available from a recently developed high-resolution CO₂ laser of high efficiency. For normal CH₃OH, six new short-wavelength lines have been found using a 2 m long Fabry-Perot FIR laser cavity. Accurate heterodyne frequency measurements are reported for 14 CH₃OH FIR laser lines, nearly all above 100 cm^-1, as well as accurate frequency offsets for most of the corresponding CO₂ pump lines. Spectroscopic assignments are presented for nine high-frequency FIR laser lines in four pump systems     

Continuously tunable optically pumped high-pressure DF → CO2transfer laser

The operational characteristics of a continuously tunable DF → CO2transfer laser optically pumped with radiation from a pulsed DF laser are experimentally and theoretically studied. The pump radiation is absorbed by DF in a high-pressure DF/CO2/He gas mixture, and subsequent V-V energy transfer to the CO2ν3mode provides the CO2laser population inversion. Continuous tuning of the CO2laser frequency between five CO2line centers from 29.14 to 29.30 THz has been demonstrated, using a 12 atm gas mixture. The maximum pulse energy was about 0.8 mJ. In experiments with a two-mirror CO2laser resonator, pulse energies up to 6 mJ and 35 percent slope quantum efficiency have been obtained at 10 atm gas pressure. The gas mixture typically contained 0.5 percent DF, 5 percent CO2, and 94.5 percent He, but this was not critical. Computer simulations based on a rate equation model of the laser have given results which are in reasonable agreement with those obtained experimentally.     

Theoretical gain spectrum of far-infrared Raman lasers

The four-level density matrix theory of the Raman FIR laser is extended to include arbitrary pump and emission field strengths and arbitrary pump frequency offsets from resonance. The results accommodate the full range of spectral variation that is observed when CH₃F Raman FIR lasers are operated at widely differing values of the rotational quantum number J. The extended theory is also useful for optimizing the temperature and pressure of these broadly tunable lasers to achieve maximum spectral coverage     

Tunable alexandrite lasers

Wavelength tunable laser operation has been obtained from the solid-state crystal alexandrite (BeAl2O4:Cr³⁺) over the continuous range from 701 to 818 nm. The tunable emission was observed at room temperature and above in a homogeneously broadened, vibronic, four-level mode of laser action. In this mode the laser gain cross section increases from7 times 10^{-21}cm²at 300K to2 times 10^{-20}cm²at 475K, which results in improved laser performance at elevated temperatures. Efficient 2.5 percent, low-threshold (10 J) operation has been obtained with xenon-flashlamp excitation of the 6 mm diameter × 76 mm length laser rods. Output pulses of greater than 5 J and average power outputs of 35 W have been demonstrated, limited by the available power supply. The emission is strongly polarizedEparallelb, with a gain that is 10 times that in the alternate polarization. The 262 μs, room-temperature fluorescence lifetime permits effective energy storage andQ-switched operation. TunableQ-switched pulses as large as 500 mJ have been obtained with pulsewidths ranging between 33 and 200 ns depending on the laser gain. Laser action has also been demonstrated on the high-gain (3 times 10^{-19}cm²emission cross section)Rline at 680.4 nm and is also polarizedEparallelb. This three-level mode is analogous to the lasing in ruby except that the stimulated emission cross section in alexandrite is ten times larger than for ruby.     

Analysis of CH3OH far infrared laser lines optically pumped by sequence band and isotopic CO2lasers

Assignments are presented for seven far infrared (FIR) laser lines of CH3OH pumped by theS-9P(31),18-10R(24),13-9R(26), and13-9P(16)CO2laser lines, plus an interesting speculation for the FIR line pumped by the18-9P(12)CO2line. Frequencies have been deduced to a substantially improved accuracy of ±0.001 cm^-1from IR and FIR spectroscopic combination differences for most of the assigned lines as well as three other predicted transitions. In addition, accurate frequencies are given for 13 predicted FIR laser transitions which are expected from the IR spectrum to be pumped by three¹⁶O¹²C¹⁸O laser lines.     

Characterization of new FIR laser lines from CD3-rockingand asymmetric CD3 deformation modes of 13CD3OD

In this paper, we report new optically pumped far-infrared (FIR) laser lines from the in-plane CD₃-rocking and asymmetric CD ₃ deformation absorption vibrational bands of ¹³CD ₃OD. A waveguide CO₂ laser of wide tunability (290 MHz) was used as the pump source, and a Fabry-Perot open cavity as the FIR laser resonator. Optoacoustic absorption spectrum was used as a guide to search for new FIR laser lines. We could observe 13 new laser lines in the range 103-491 μm. The lines were characterized according to wavelength, relative polarization, relative intensity, and optimum working pressure. The transferred lamb-dip technique was used to measure the frequency absorption transition for both new and previously reported laser lines     

High-power operation and scaling behavior of CW optically pumped FIR waveguide lasers

High-power far infrared (FIR) laser operation at the 10- 100 mW level is described for wavelengths throughout the 40 μm-1.22 mm spectral region. These data correspond to order of magnitude improvements in converting CO2laser energy into FIR laser output. This improved FIR laser performance is attributed to a waveguide laser geometry with reduced losses for the CO2pump and also to a new method of output coupling. The basic design concept of the efficient laser resonator is discussed as well as the prospect for further increases in laser performance through improved efficiency and sealing.     

Performance of a Cr:YAG laser

We report on the performance of a Cr⁴⁺:YAG laser, tunable over the range from 1.32 to 1.53 μm, under different operating conditions. Laser action has been achieved by pumping with a Nd:YAG laser in the Q-switched mode and cw mode and with a Cr:Nd:GSGG laser in the long pulse mode. Slope efficiencies up to 22% in the Q-switched mode have been achieved. The lowest threshold was 30 mJ for the long pulse pumped mode. Excited state absorption seems to limit the tuning range and the output characteristics     

Frequency measurements of optically pumped far-infrared laser lines

In this work, we report the frequency measurements of optically pumped far-infrared (FIR) laser lines. We use the heterodyne technique of mixing FIR laser radiation and microwave radiation on a metal-insulator-metal (MIM) point contact tunnel diode, to determine the FIR laser frequencies. The two FIR laser systems, consisting of CO₂ waveguide pump lasers and Fabry-Perot FIR laser cavities, and MIM diode were developed by us. To check the system, we have measured some FIR laser line frequencies previously reported in the literature. An average fractional frequency reproducibility of ±7×10^-7, between our measurements and the previous ones, permit us to use our system to measure five new FIR laser frequencies     

双光路快速调谐脉冲CO2激光器

报道了一种采用双路高速伺服电机驱动光栅选线的方式,实现9~11 μm CO₂激光快速调谐输出。双光路谱线切换时间小于100 μs,单光路谱线切换时间小于50 ms。激光器输出谱线达70条,其中9P （20）、9P （28）单脉冲输出能量大于100 mJ,9R （30）、9P （40）单脉冲能量大于90 mJ,激光脉冲宽度小于100 ns,重复频率为20 Hz。