Simple Short-Pulse CO<Subscript>2</Subscript> Laser Excited by Longitudinal Discharge without High-Voltage Switch

We have developed a longitudinally excited CO₂ laser without a high-voltage switch. The laser produces a short laser pulse similar to those from TEA and Q-switched CO₂ lasers. This system, which is the simplest short-pulse CO₂ laser yet constructed, includes a pulsed power supply, a high-speed step-up transformer, a storage capacitor, and a laser tube. At high pressure (4.2 kPa and above), a rapid discharge produces a short laser pulse with a sharp spike pulse. In mixed gas (CO₂: N₂: He = 1: 1: 2) at a pressure of 9.0 kPa, the laser pulse contains a spike pulse of 218 ns and has a pulse tail length of 16.7 μs.     

Pulsed CH<Subscript>3</Subscript>OH Terahertz Laser Emission Pumped by a TEA CO<Subscript>2</Subscript> Laser

A simple terahertz (THz) cavity and a TEA CO₂ laser for the optically pumped THz emission is studied experimentally. To obtain high peak power of pump laser, pressure ratios of gas mixture in the cavity of the TEA CO₂ laser are discussed. When CH₃OH are pumped by the 9P(16) and 9P(36) CO₂ laser lines, the generation of terahertz radiation with energy as high as 353 μJ and 307 μJ are obtained, respectively. The corresponding photon conversion efficiencies are 0.705% and 0.29%. Meanwhile, higher peak power of pump laser effectively improves the photon conversion efficiency. And the optimum THz laser pressure increases with narrower pulse width of pump laser.     

An injection-locked single-mode tea CO2 laser for SMM laser pumping

A D₂O laser has been developed for collective Thomson scattering measurements of ion temperature in high temperature plasmas. A pulse duration and a spectral width of a high power D₂O laser has been successfully controlled for this purpose, by using a TEA CO₂ laser injection-locked by an etalon-tuned TEA CO₂ laser as a pump source.     

CO2 laser-induced hot electron effects in n-InSb

The influence of a 3-μsec wide CO₂ laser pulse on the Shubnikov-de Haas (SdH) effect in a 1.4 × 10¹⁵ cm^?3 sample of n-InSb has been investigated at a lattice temperature of 1.8 K. During the time the sample is illuminated the SdH amplitudes are found to decrease with increasing laser power. For a peak incident power of about 1 watt, the SdH oscillatory behavior corresponds to that measured at a lattice temperature of 4.6 K for the non-illuminated sample. These results form the first direct and quantitative evidence for electron heating induced by CO₂ laser radiation and permit the evaluation of a phenomenological energy relaxation time.     

Fast Discharge Circuit for Longitudinally Excited CO2 Laser

In a longitudinally excited CO₂ laser with a short laser pulse, similarly to TEA and Q-switched CO₂ lasers, a fast discharge is very important. We investigated the use of a fast discharge circuit to obtain a high spike laser pulse in a longitudinally excited CO₂ laser. We compared a traditional capacitor-transfer circuit having a buffer capacitance of 700 pF with our direct-drive circuit in which the buffer capacitance is removed. The direct-drive circuit produced a fast discharge and a high spike laser pulse. We also investigated the effect of a resistance connected in parallel with the discharge tube to eliminate low discharge current after the main discharge. A low resistance of 1 kΩ or less acted as a shunt resistance. The shunt resistance was effective in decreasing the energy of the laser pulse tail at high gas pressure.     

Relation Between Discharge Length and Laser Pulse Characteristics in Longitudinally Excited CO2 Laser

A longitudinally excited CO₂ laser pumped by a fast discharge emits a short laser pulse, similarly to TEA and Q-switched CO₂ lasers. We investigated the relation between the discharge length and the laser pulse characteristics to develop a longitudinally excited CO₂ laser producing a high spike laser pulse. We examined discharge lengths of 30, 45, and 60 cm, using the same mirrors and the same excitation circuit with the same input energy. A longer discharge length increased the discharge volume and improved the laser output energy. However, the longer discharge length caused a long discharge formation time (a slow fall time of the discharge voltage) due to the higher discharge impedance, which resulted in a long laser pulse tail. Therefore, the longitudinally excited CO₂ laser had optimum conditions for obtaining a high spike laser pulse effectively.     

High power ns FIR Raman pulses in NH3 pumped by a short pulse tail-free CO2 oscillator

By using a short pulse CO₂, tail free, broadband laser it is possible to produce a compressed, high power FIR pulse in a pure Raman system when a suitable pressure and Raman cell length are used. In this way we have obtained 4ns (70KW) emission around the sR(3,0) NH₃ line pumped by 130 mJ (23ns) 9P20 CO₂ line. More resonant transitions can be also compressed at a suitable high pressure also if they show a large optical pumping and cascade processes at low pressure.     

小型高重复频率TEACO2激光器的研究

本文叙述了一种小型高重复频率TEACO2激光器,其激光模式为TEM00,远场发散全角≤4mard,基模激光能量87.8mJ,脉冲宽度36.5ns,基模激光峰值功率>0.9MW,激光重复频率130Hz(最高重复频率255Hz),能以50Hz的重复频率连续长期工作,其工作寿命>1×107次.     

RF激励CO2激光器功率控制器

描述了小型RF激励CO     

A Highly Sensitive Multi-element HgCdTe e-APD Detector for IPDA Lidar Applications

An HgCdTe electron avalanche photodiode (e-APD) detector has been developed for lidar receivers, one application of which is integrated path differential absorption lidar measurements of such atmospheric trace gases as CO₂ and CH₄. The HgCdTe APD has a wide, visible to mid-wave-infrared, spectral response, high dynamic range, substantially improved sensitivity, and an expected improvement in operational lifetime. A demonstration sensor-chip assembly consisting of a 4.3 μm cutoff HgCdTe 4 × 4 APD detector array with 80 μm pitch pixels and a custom complementary metal–oxide–semiconductor readout integrated circuit was developed. For one typical array the APD gain was 654 at 12 V with corresponding gain normalized dark currents ranging from 1.2 fA to 3.2 fA. The 4 × 4 detector system was characterized at 77 K with a 1.55 μm wavelength, 1 μs wide, laser pulse. The measured unit gain detector photon conversion efficiency was 91.1%. At 11 V bias the mean measured APD gain at 77 K was 307.8 with σ/mean uniformity of 1.23%. The average, noise-bandwidth normalized, system noise-equivalent power (NEP) was 1.04 fW/Hz^1/2 with a σ/mean of 3.8%. The measured, electronics-limited, bandwidth of 6.8 MHz was more than adequate for 1 μs pulse detection. The system had an NEP (3 MHz) of 0.4 fW/Hz^1/2 at 12 V APD bias and a linear dynamic range close to 1000. A gain-independent quantum-limited SNR of 80% of full theoretical was indicative of a gain-independent excess noise factor very close to 1.0 and the expected APD mode quantum efficiency.     

光泵CF4 16微米激光器

本文介绍了由 TEA CO_2激光器的9R(12)跃迁线泵浦冷却的 CF_4分子,获得 16μm激光输出。泵浦光用限孔光阑得到TEMoo单横模,由低气压CO_2增益池压缩线宽,并与光泵腔良好的模式匹配下,以700mJ的泵浦源能量获得25mJ左右的16μm激光输出能量。光量子转换效率达7％左右。激光脉宽窄于150ns,该器件可在约0.5Hz重复率下,以20mJ的输出能量运转数千次。     

高频激励横流CO2激光器的实验研究

本文在实验上在气压为120mba、100mba和80mba,气压比为CO2:N2:Ar=7:46.5;46.5,间隙为20mm,26mm和27mm,电极直径为12mm、长为700mm的情况下,对网络的高频传输特性,间隙高频放电的伏安特性及激光功率输出特性进行了一定的研究,在国内首次得到高频激励横流CO2激光器400W的激光输出.注入功率密度达20W/cm3,与相同条件下的直流针板式激光器相比最大注入功率提高了约一倍,最大电光转换效率为9%.     

High Efficient, Intense and Compact Pulsed D2O Terahertz Laser Pumped With a TEA CO2 Laser

A high efficient, intense and compact pulsed D₂O terahertz laser is presented, which is pumped by a multi-transverse mode TEA CO₂ laser. For D₂O gas as the active medium, with the cavity length of 120 cm, pulse energy of the THz laser has been investigated as the variation of pump energy and gas pressure. When the pump energy was 1.41 J, the maximum single pulse energy of 6.2 mJ was achieved at the wavelength of 385 μm. Photon conversion efficiency as high as 36.5% was obtained when laser operated at the maximum output energy. As the pump energy was raised from 0.57 to 1.41 J, the optimum pressure was slightly changed from 400 to 700 Pa. The THz pulse consisted of a spike pulse with pulse width of 120 ns and a tail pulse with pulse width of about 170 ns. The peak power of the spike pulse is about 44.3 kW. Comparing with the occurring time and pulse width of pump pulse, 70 ns delay and 10ns broadening were observed in the THz spike pulse.     

A compact, highly stable CW CO2 laser without brewster windows

We describe an open resonator, quasi sealed-off; 70cm cavity length CO₂ laser with very high stability of power and frequency, which lases on 96 lines from 9R42 (2W) to 10P52 (5W) with a power of >11W on 9R20, 9P20, 10R20 and 10P20, plus on 18 hotband lines with ≈2W. This laser was used successfully to pump an FIR ring laser [1] enabling an FIR power stability of ΔP/P ≈ 10^?4 by use of a simple PI control loop, thus demonstrating its superb frequency stability.     

CO2 detection with CNx thin films deposited on porous silicon

In recent years, porous silicon (PSi) has attracted a great deal of attention for sensing applications. However, the high reactivity of PSi surfaces causes serious problems of stability. In this work, we developed new thin films that can serve as stabilizer of PSi for CO₂ gas sensors development. PSi surface was coated with carbon nitride (CN_x) film which is one of the most important interfering to stabilize the PSi layer. CN_x film was deposited by pulsed laser ablation. The effect of CO₂ gas on the sensor response was investigated for different polarization voltages. The electrical properties of (Al/CN_x/PSi/Si) structure were modified in the presence of the gas. The device shows a high sensitivity against CO₂ gas. Furthermore, the current variation of the sensor as a function of time has been investigated. The results show that the Al/CN_x/PSi/Si structure becomes stable after the first two weeks.     

Mini-optically pumped NH3 cavity laser wide band emission at 67.2 µm

The spectral characteristics of mini-optically pumped NH₃ cavity laser emission at 67.2µm was studied. It was found that the spectrum of 67.2µm emission was duality. With low power CO₂-9R(30) pumping condition (lp<1MW/cm²), the spectrum appeared to be two wide FIR laser lines (～4.6GHz for each line), which were the result of competition of multi-Raman processes. With high power pumping condition (lp>2MW/cm²), the spectrum extended to be a very wide band (～14GHz), which was the result of the combination of the competition and interaction enhancement of Raman processes. The wide band spectral characteristics of 67.2 µm would be significant to the tuning of NH₃ OPFIRL.     

Study of Optimal Cavity Parameter in Optically Pumped D2O Gas Terahertz Laser

Heavy water gas (D₂O gas) which owns special structure property, can generate terahertz radiation by optically pumping technology, and its 385 μm wavelength radiation can be widely used. In this research, on the base of semi-classical density matrix theory, we set up a three-level energy system as its theoretical model, a TEA-CO₂ laser 9R (22) output line (λ?=?9.26 μm) acted as pumping source, D₂O gas molecules were operating medium, the expressions of pumping absorption coefficient G _p and Terahertz signal gain coefficient G _s were deduced. It was shown that the gain of Terahertz signal was related with the energy-level parameters of operating molecules and some operating parameters of the Terahertz laser cavity, mainly including cavity length. By means of iteration method, the output power density of Terahertz pulse signal was calculated numerically. Changing the parameter of cavity length and keeping others steady, the relationship curve between the output power intensity (Is) of Terahertz pulse laser and the operating cavity length (L) was obtained. The curve showed that the power intensity (Is) increased with cavity length (L) in a certain range, but decreased when the length (L) exceeded some value because of the absorption effect, and there was an optimal cavity length for the highest output power. We used a grating tuned TEA-CO₂ laser as pumping power and a sample tube of variable length in 70–160 cm as terahertz laser operating cavity to experiment. The results of theoretical calculation and experiment matched with each other, and it is helpful for miniaturizing terahertz laser volume to make it practical.     

脉冲激光对星载探测器的干扰和损伤分析

该文采用高斯光束辐照半无限固体的温升模型,研究了探测器表面温升与激光干扰和损伤阈值的变化关系。发现脉冲CO2激光对探测器的干扰和损伤与脉宽无关,只与脉冲能量密度有关,探测器表面温升与入射激光脉冲能量密度成正比关系,干扰阈值比损伤阈值要低一个数量级。通过理论分析,求出了干扰和损伤星载HgCdTe探测器所需CO2激光的脉冲能量。定性分析结果表明高平均功率重频脉冲激光更容易对星载探测器造成有效干扰和永久性损伤。     

Longitudinally Excited CO<Subscript>2</Subscript> Laser with Short Laser Pulse like TEA CO<Subscript>2</Subscript> Laser

We have developed a longitudinally excited CO₂ laser with a short laser pulse similar to that of TEA and Q-switched CO₂ lasers. A capacitor transfer circuit with a low shunt resistance provided rapid discharge and a sharp spike pulse with a short pulse tail. Specifically, a circuit with a resistance of 10 M Ω provided a spike pulse width of 103.3 ns and a pulse tail length of 61.9 μs, whereas a circuit with a shunt resistance of 100 Ω provided a laser pulse with a spike pulse width of 96.3 ns and a pulse tail length of 17.2 μs. The laser pulses from this longitudinally excited CO₂ laser were used for processing a human tooth without carbonization and for glass marking without cracks.      

Gas breakdown with nanosecond CO2 laser radiation

The thresholds for CO₂ laser induced breakdown and their variation with pulse width have been measured at various pressures for Ar, N₂ and an 8/1/1 laser mixture of He/CO₂/N₂ using 3–40 ns duration pulses. These measurements indicate that excited state production plays a dominant role in determining the threshold for nanosecond duration pulses. This has been confirmed by the good agreement obtained between the measured and theoretical thresholds.