Generation of Intense THz Pulsed Lasers Pumped Strongly by CO2 Pulsed Lasers

A theoretical method dealing with two intense laser fields interacting with a three-level molecular system is proposed. A discussion is presented on the properties of the solutions for time-independent and time-dependent absorption coefficients and gain coefficient on resonance for strong laser fields, based on analytic evaluation of the rate equations for a homogeneously broadened, three-level molecular system. The pump intensity range can be estimated according to the analytic expression of pump saturation intensity. The effects of pulse width, gas pressure and path length on the energy absorbed from pump light are studied theoretically. The results can be applied to the analysis of pulsed, optically pumped terahertz lasers.     

基于600—2000 nm抽运源的太赫兹相干光源的最新进展

最近几年,紧凑型、便携式、低廉、可调谐的太赫兹波源由于具有广泛的应用前景因而成为太赫兹领域的研究焦点.波长为600—2000 nm范围的近红外光源由于具有体积紧凑、价格低廉、频率可调谐和工作稳定的特点,所以频繁被选为太赫兹波产生的抽运源.本文着重从双波长可调谐抽运源、内腔光参量振荡器太赫兹发生器两个方面进行了较系统的阐述.分析表明,近红外相对中红外双波长抽运光源由于具有更紧凑的结构而成为研究热点;差频和非线性级联过程由于具有调谐范围宽的特点而成为产生太赫兹辐射的重要手段. 关键词： 太赫兹辐射 近红外波段 调谐宽度 非线性级联过程     

Theoretical Design of a Wedged Output Coupler Coated by Capacitive Strip-Grating for Optically Pumped Terahertz Lasers

An output coupler for optically pumped terahertz laser consisting of capacitive strip-grating and wedged high- resistivity silicon substrate is designed theoretically and its transmittance performance is also discussed. The etalon effects frequently occurring in previous experiments are effectively suppressed, and thus a fiat and accurate transmittance spectrum is obtained in a narrow wavenumber interval of 2 cm^-1 near a particular center wavenumber. Furthermore the transmittance sensitivity to the slight shift of substrate thickness is also completely eliminated. The wedged output coupler is easy to fabricate and its substrate may be used repeatedly to meet various transmittance requirements.     

An Efficient Photon Conversion Efficiency Ammonia Terahertz Cavity Laser

An efficient ammonia terahertz （THz） cavity laser is reported experimentally. Unlike the past design schemes such as hole couplers and freestanding mesh couplers, in our systems the input and output couplers are fabricated by depositing nickel capacitive metallic meshes on ZnSe and high-resistivity silicon substrates. Thus the couplers not only can be constructed as an F-P oscillator but also can be used as sealed windows that are easier to perform the adjustment of alignment with. To enhanceTHz laser output energy and photon conversion efficiency, the dominant factors such as pump intensity and gas pressure are investigated experimentally. Finally, a 1.35mJ terahertz radiation of ammonia laser with 90μm wavelength （3.33THz） operating at 1.09kPa pumped by a 402mJ TEA CO2 laser with 9R （16） line is generated, and photon conversion efficiencies of 6.5% are achieved.     

High energy optically pumped NH_3 terahertz laser with simple cavity

<正>A high energy pulsed terahertz(THz) laser is studied experimentally.The laser cavity simply consists of a quartz glass waveguide,a coated GaAs input window,and a crystal quartz output window.NH3 is filled in the cavity as gain medium,and pumped by an 8-J line-tunable transversely excited atmospheric(TEA) CO_2 laser.When 9R(16) transition acts as the pump line,55.6-mJ THz radiation(90μm) is obtained at 730-Pa NH_3 pressure.The corresponding conversion efficiency is 13.54%.Energy and optimal pressure of amplified spontaneous emission and laser oscillation are compared.     

基于光放大的长脉冲抽运太赫兹激光

为了获得较窄增益带宽、较大光强的太赫兹辐射,尝试了利用TEA CO₂激光器对6 W可调谐连续波CO₂种子激光实行双程光放大实验,以期望获得长脉冲、高峰值功率的抽运光.通过实验,获得了大约30倍的放大系数,放大光输出功率随种子光注入功率的增加而增加,其中10 P （20）支线表现更加突出,并且被放大的激光支线半峰全宽在14 μs左右.基于这种长脉冲抽运源,建立了一种产生脉冲太赫兹的动力学模型,给出了产生太赫兹辐射的饱和抽运光强表达式,确定了抽运光的光强范围.另外, 关键词： 激光物理 长脉冲 动力学模型 太赫兹激光     

Transmittance investigation on capacitive mesh on thick dielectric substrates as output windows for optically pumped terahertz lasers

This paper reports that an output window for optically pumped terahertz (THz) laser has been fabricated by depositing a capacitive nickel-mesh on a thick high-resistivity silicon substrate (approximating to 5 mm thick).Unlike the conventional process of depositing a gold film approximating to 100 nm on negative photoresist using electron-beam evaporation,a nickel film approximating to 1.5 μm thick is directly deposited on the clean surface of dielectric substrate using magnetron sputtering and then a positive photoresist is spun onto the nickel metal surface at 6000 r for 60 s.A transmittance spectrum of the output window in a certain frequency range (say,from zero to 1 THz) has been obtained by using THz time domain spectroscopy.Moreover a transmittance spectrum simulated numerically has also been estimated with respect to the output window using the transmission-line model (TLM) containing attenuation component from dielectric substrate.The simulation results show that the TLM can explain well the experimental curve in a certain frequency range from zero to 1 THz.Thus it is demonstrated that the improved optical component can be efficiently used as both output coupler and output window for optically pumped THz lasers.     

An Efficient Pulsed CH3OH Terahertz Laser Pumped by a TEA CO2 Laser

An efficient pulsed CH3OH terahertz （THz） laser pumped by a TEA CO2 laser is investigated experimentally. To improve photon conversion efficiency and THz laser energy, two cavity configurations of the TEA CO2 laser, which is external and semi-external, are evaluated. The pump intensities are about 4.7 MW/cm2 and 1.2 MW/cm2, respectively. Higher pump intensity and more stable single lines are obtained in the external cavity. For the 3.8 J pump energy of the 9P（16） transition in the external cavity, the maximum terahertz output energy with 570.5 μm wavelength at 160 Pa is 431 μJ. With a 6 J energy pulse in terms of a semi-external cavity, a 353 μJ terahertz emission （570.5 μm） is produced. The corresponding photon conversion efficiencies are 1.36% and 0.705%, increasing by a factor of about 2.