Broadly tunable single-frequency cw mid-infrared source with milliwatt-level output based on difference-frequency generation in orientation-patterned GaAs

A narrow-linewidth mid-IR source based on difference-frequency generation of an amplified 1.5 microm diode laser and a cw Tm-doped fiber laser in orientation-patterned (OP) GaAs has been developed and evaluated for spectroscopic applications. The source can be tuned to any frequency in the 7.6-8.2 microm range with an output power of 0.5 mW. The measured characteristics of the OP-GaAs sample demonstrate a high quality of the material.     

Optical parametric generation of a mid-infrared continuum in orientation-patterned GaAs

We have generated an ultrabroad mid-infrared continuum by using single-pass optical parametric generation (OPG) in orientation-patterned GaAs (OP-GaAs). The spectrum spans more than an octave, from 4.5 to 10.7 microm, measured 20 dB down from the peak. The 17.5 mm long, 0.5 mm thick, all-epitaxially-grown OP-GaAs sample with a 166.6-microm quasi-phase-matching period was pumped with 3.1-3.3 microm wavelength, 1 ps pulses up to 2 microJ in energy. The OPG threshold was observed at 55 nJ pump energy with the pump polarized along the [111] crystal direction. The slope efficiency near threshold was 51%, and the external conversion efficiency was as high as 15%.     

Long-wave IR chemical sensing based on difference frequency generation in orientation-patterned GaAs

The combination of continuous-wave difference frequency generation based on quasi-phase-matched (QPM) gallium arsenide with cavity ring-down spectroscopy is explored for use in spectroscopic and chemical sensing applications. The advent of QPM materials based on orientation-patterned GaAs (OP-GaAs) offers a significant advantage over traditional ferroelectric QPM materials of extended wavelength coverage into the spectroscopically important 8–12 μm region. In this work, the outputs from two tunable, external cavity diode lasers covering the 1.3 μm and 1.5 μm telecom bands were amplified then mixed in an orientation-patterned GaAs crystal, producing several microwatts of tunable radiation in the 7–9 μm region. We also evaluate the use of a low-power DFG source for use in cavity ring-down spectroscopy. PACS 82.80.Gk; 42.62.Fi; 42.70.Hj; 42.65.Ky     

A high power hybrid mid-IR laser source

An efficient hybrid mid-IR laser system comprising a thulium fibre laser, Ho:YAG solid state laser and a zinc germanium phosphide optical parametric oscillator is presented. A 790 nm diode pumped 1908 nm thulium fibre laser operating at 30 W pumps an RTP q-switched Ho:YAG laser emitting 17 W at 40 kHz and 2090 nm. The zinc germanium phosphide optical parametric oscillator efficiently converts this into the 3-5 μm region producing 10.1 W with 59% optical conversion efficiency and an M² = 1.5.     

Widely tunable midinfrared difference frequency generation in orientation-patterned GaAs pumped with a femtosecond Tm-fiber system

We demonstrate a midinfrared source tunable from 6.7 to 12.7 μm via difference frequency generation (DFG) in orientation-patterned GaAs, with 1.3 mW average output power. The input pulses are generated via Raman self-frequency shift of a femtosecond Tm-doped-fiber laser system in a fluoride fiber. We numerically model the DFG process and show good agreement between simulations and experiments. We use this numerical model to show an improved design using longer pump pulses.     

Measurement of the nonlinear coefficient of orientation-patterned GaAs and demonstration of highly efficient second-harmonic generation

Quasi-phase-matched (QPM) GaAs structures, 0.5 mm thick, 10 mm long, and with 61-mum grating periods, were grown by a combination of molecular-beam epitaxy and hydride vapor phase epitaxy. These were characterized by use of mid-IR second-harmonic generation (SHG) with a ZnGeP(2) (ZGP) optical parametric oscillator as a pump source. The SHG efficiencies of QPM GaAs and QPM LiNbO(3) were directly compared, and a ratio of nonlinear coefficients d(14)(GaAs)/d(33) (LiNbO(3))=5.01+/-0.3 was found at 4.1-mum fundamental wavelength. For input pulse energies as low as 50muJ and approximately 60-ns pulse duration, an internal SHG conversion efficiency of 33% was measured in QPM GaAs.     

模块化固体开关脉冲功率源触发技术

为满足高功率脉冲源小型化和高重复频率运行的研制需要,提出了一种基于固体开关(可控硅)的电感隔离型高压脉冲发生器触发控制设计方案。这种方案采用光纤收发器件及其驱动电路和高耐压脉冲变压器,研究了固体开关脉冲功率源控制技术中的触发信号高压隔离、光分多路及脉冲变压器分立或并联使用等关键技术。给出了单模块触发控制电路的设计及测试结果:5级LC回路在每级充电电压4 kV输入时,实现最终32 kV的输出,功率源模块输出/输入电压转换效率达到80%。同时对其应用特点进行了分析和讨论。     

High-resolution cavity-tuned ringdown spectrometer using a narrow-bandwidth pulsed laser source

A novel method of cavity ringdown spectroscopy is proposed to achieve high spectral resolution with tunable narrow bandwidth pulsed lasers. We demonstrate a cavity-tuned ringdown configuration in which only a single cavity mode is kept excited near the carrier frequency of a narrow bandwidth pulse laser. This is done simply by making a cavity resonance actively track the frequency reference served by the cw injection seed of the pulsed laser source. We present the servo mechanism used in the cavity resonance tracking, reliable procedures for transverse mode matching, and the evidence of single longitudinal mode excitation. The spectrometer performance is tested to record weak molecular overtone features of acetylene around the wavelength of 570 nm, showing cavity tracking stability within 5-MHz uncertainty which overcomes the bandwidth limit of pulsed laser sources itself. PACS 42.62.Fi; 42.60.Da; 33.20.Kf     

模块化固体开关脉冲功率源触发技术

为满足高功率脉冲源小型化和高重复频率运行的研制需要,提出了一种基于固体开关（可控硅）的电感隔离型高压脉冲发生器触发控制设计方案。这种方案采用光纤收发器件及其驱动电路和高耐压脉冲变压器,研究了固体开关脉冲功率源控制技术中的触发信号高压隔离、光分多路及脉冲变压器分立或并联使用等关键技术。给出了单模块触发控制电路的设计及测试结果：5级LC回路在每级充电电压4 kV输入时,实现最终32 kV的输出,功率源模块输出/输入电压转换效率达到80%。同时对其应用特点进行了分析和讨论。     

Deposition of mass-selected cluster ions using a pulsed arc cluster-ion source

A PACIS (pulsed arc cluster-ion source) developed for high average cluster-ion currents is presented. The performance of the PACIS at different operational modes is described, and the suitability for cluster-deposition experiments is discussed in comparison with other cluster-ion sources. Maximum currents of mass-selected cluster ions of 3–6 nA of small Si_n ^- (n=4–10) clusters and 0.3–0.5 nA of large Al_n ^+/- (n=20–70) clusters are achieved. The mass-selected cluster ions are soft-landed on a substrate at residual kinetic energies lower than 1 eV/atom, and the samples are characterized by X-ray photoelectron spectroscopy and scanning tunneling microscopy. First results on the soft landing of “magic” Si₄ ^- clusters on graphite are presented. Received: 30 May 2001 / Accepted: 14 June 2001 / Published online: 2 October 2001     

Carbon isotopomers measurement using mid-IR tunable laser sources

Recent developments of two mid-infrared tunable laser spectrometers dedicated to carbon isotope ratio determination are presented. First, a field deployable quantum cascade laser-based sensor is described, along with line selection strategy for (13/12)CO(2) ratio measurements. Secondly, an instrument architecture based on difference frequency generation is presented. The analyses of fundamental limitations, specifically temperature and pressure stability, and water vapor collision broadening, are detailed.     

Carbon isotopomers measurement using mid-IR tunable laser sources

Recent developments of two mid-infrared tunable laser spectrometers dedicated to carbon isotope ratio determination are presented. First, a field deployable quantum cascade laser-based sensor is described, along with line selection strategy for ^13/12CO₂ ratio measurements. Secondly, an instrument architecture based on difference frequency generation is presented. The analyses of fundamental limitations, specifically temperature and pressure stability, and water vapor collision broadening, are detailed.     

Physical source realization of complex source pulsed beams

Complex source pulsed beams (CSPB) are exact wave-packet solutions of the time-dependent wave equation that are modeled mathematically in terms of radiation from a pulsed point source located at a complex space-time coordinate. In the present paper, the physical source realization of the CSPB is explored. This is done in the framework of the acoustic field, as a concrete physical example, but a similar analysis can be applied for electromagnetic CSPB. The physical realization of the CSPB is addressed by deriving exact expressions for the acoustic source distribution in the real coordinate space that generates the CSPB, and by exploring the power and energy flux near these sources. The exact source distribution is of finite support. Special emphasis is placed on deriving simplified source functions and parametrization for the special case where the CSPB are well collimated.     

500 nm continuous wave tunable single-frequency mid-IR light source for C-H spectroscopy

A computer controlled tunable mid-IR light source, based on single resonant difference frequency generation (DFG), is experimentally investigated. The DFG process is pumped by an external cavity tapered diode laser, tunable over a spectral range of 30 nm. Grating feedback to the single mode channel of the tapered diode narrows the spectrum and allows for tuning of the emitted spectrum in the range from 780 to 810 nm. The DFG process takes place intra-cavity in a high finesse diode pumped 1064 nm solid state Nd:YVO₄ laser cavity, using periodically poled LiNbO₃ as the nonlinear material. Based on this new approach, a tunable single-frequency output power exceeding 3 mW was obtained in the mid-IR tuning range from 2.9 to 3.4 ??m.     

紧凑型爆炸脉冲电源

采用等效电路模型程序——BCYSSYS对系统参数进行优化,设计了04型爆磁压缩发生器及用04型发生器驱动的紧凑型爆炸脉冲电源。紧凑型爆炸脉冲电源长度小于1.2 m,直径0.4 m,质量约100 kg。实验结果表明:04型爆磁压缩发生器能够在3μH电感负载上获得脉宽约10μs、峰值为100 kA的脉冲大电流输出;当负载电阻为8.7Ω时,输出电功率大于20 GW。典型实验结果与采用BCYSSYS程序得到的计算结果吻合较好,验证了BCYSSYS程序用于爆炸脉冲电源理论设计的可行性。     

紧凑型爆炸脉冲电源

采用等效电路模型程序——BCYSSYS对系统参数进行优化,设计了04型爆磁压缩发生器及用04型发生器驱动的紧凑型爆炸脉冲电源。紧凑型爆炸脉冲电源长度小于1.2 m,直径0.4 m,质量约100 kg。实验结果表明：04型爆磁压缩发生器能够在3 μH电感负载上获得脉宽约10 μs、峰值为100 kA的脉冲大电流输出;当负载电阻为8.7 Ω时,输出电功率大于20 GW。典型实验结果与采用BCYSSYS程序得到的计算结果吻合较好,验证了BCYSSYS程序用于爆炸脉冲电源理论设计的可行性。     

A point pulsed light source

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 48, No. 1, pp. 160–162, January, 1988.     

高阶模抑制型MILO慢波结构高频特性分析北大核心CSCD

理论分析了高阶模抑制型磁绝缘线振荡器(MILO)慢波结构,推导了其各分区电磁场分布.通过对场分布的进一步分析可以发现,角向开槽使得原始MILO结构中的两个简并的HEM11模式去简并,分裂成为极化方向与开槽方向垂直或平行的两个模式;通过改变慢波结构叶片间开槽角向位置相对关系,可以破坏高阶模式之间π模谐振关系,从而抑制高阶模式的起振,使器件稳定工作在基模.     

Neutron powder diffraction studies at high pressure using a pulsed neutron source

Abstract

High-pressure neutron-diffraction experiments using the time-of-flight (TOF) method are presented. We first introduce the helium-gas pressure system at Argonne's Intense Pulsed Neutron Source (IPNS) with the Special Environment Powder Diffractometer (SEPD). The results for TIBa₂CuO₆₊₈, and La_2?x, Sr_x, CuO_4–8 are briefly reviewed. We then introduce the present situation in Japan. We have been developing a high-pressure system on high-resolution powder diffractometer (HRP) which was much improved recently and renamed VEGA at KEK. The best resolution of 0.45% was obtained at VEGA. The preliminary results for YBa₂, Cu₄O₈, and HgBa₂, CuO₄₊₈, are presented and compared with the SEPD data.