共查询到20条相似文献,搜索用时 15 毫秒
1.
In this letter, we describe a coherent subpicosecond terahertz (THz) spectroscopy system based on nonresonant optical rectification for the generation of THz radiation. We studied the two-photon absorption (TPA) of ZnTe induced by femtosecond laser pulses via THz generation, and its influence on the generation of THz radiation. Experimental results demonstrated that the intensity of pump beam against TPA must be traded off to get an optimum generation of THz radiation. As an example, we measured absorption spectrum of water vapor by time-domain spectroscopy (TDS) in the frequency range from 0.5 to 2.5 THzwith a high overall accuracy. 相似文献
2.
A survey on the mechanisms of powerful terahertz (THz) radiation from laser plasmas is presented.Firstly,an analytical model is described,showing that a transverse net current formed in a plasma can be converted into THz radiations at the plasma oscillation frequency.This theory is applied to explain THz generation in a gas driven by two-color laser pulses.It is also applied to THz generation in a tenuous plasma driven by a chirped laser pulse,a few-cycle laser pulse,a DC/AC bias electric field.These are well verified by particle-in-cell simulations,demonstrating that THz radiations produced in these approaches are nearly single-cycles and linear polarized.In the chirped laser scheme and the few-cycle laser scheme,THz radiations with the peak field strength of tens of MV/cm and the peak power of gigawatt can be achieved with the incident laser intensity less than 10 17 W/cm 2. 相似文献
3.
根据光整流效应,利用超快激光脉冲泵浦GaSe晶体实现了0.2~2.5 THz的宽带太赫兹辐射输出。禁带中的电子在两个800 nm光子的作用下激发到导带中形成自由载流子,进而吸收所产生的太赫兹辐射,最终导致太赫兹的输出随泵浦功率的增加而趋于饱和。为了研究双光子吸收对太赫兹输出的影响,测量了800 nm处的GaSe晶体的双光子吸收系数,结果为 0.165 cm/GW。通过对太赫兹输出实验数据的拟合,得到GaSe晶体中自由载流子对太赫兹输出的吸收截面为1×10-15 cm2。本文的研究结果可用于优化GaSe晶体在强激光泵浦下的太赫兹转换效率。 相似文献
4.
V. G. Bespalov V. N. Krylov S. E. Putilin D. I. Stasel’ko 《Optics and Spectroscopy》2002,93(1):148-152
Generation of a coherent electromagnetic radiation in the far IR (THz) spectral range upon excitation of a semiconductor InAs crystal by 70-fs Ti: sapphire laser pulses is studied. The effect of a magnetic field of different orientation on generation in the submillimeter-wavelength range is analyzed. Placing the crystal into the magnetic field of an optimized permanent magnet with a strength of 5 kOe aligned along the surface of the semiconductor increased the power of generated radiation by a factor of six compared with that in the absence of the field. For the average pump-laser output power of 150 mW and repetition rate of 80 MHz, the average power of the THz radiation reached 100 nW. For detection of ultrashort pulses of the THz radiation, we used, for the first time, a highly sensitive uncooled optoacoustic detector, which detected signals with a power lower than 1 nW. 相似文献
5.
A. G. Stepanov 《Optics and Spectroscopy》2009,107(4):529-533
Factors that lead to a decrease in the width and the mean frequency of the spectrum of terahertz (THz) radiation that were
observed in recent experiments on optical rectification of powerful (∼0.5 TW) femtosecond laser pulses with a tilted amplitude
front in a lithium niobate crystal are considered. A simple method is proposed that allows one to avoid the above transformation
of the spectrum and to ensure a high efficiency of generation of THz radiation when laser pulses with a power of several TW
are used. 相似文献
6.
We report the generation of tunable, narrow-band, few-cycle and multicycle coherent terahertz (THz) pulses from a temporally modulated relativistic electron beam. We demonstrate that the frequency of the THz radiation and the number of the oscillation cycles of the THz electric field can be tuned by changing the modulation period of the electron beam through a temporally shaped photocathode drive laser. The central frequency of the THz spectrum is tunable from ~0.26 to 2.6 THz with a bandwidth of ~0.16 THz. 相似文献
7.
强太赫兹源是太赫兹科学技术发展的关键,其中大能量强场太赫兹脉冲源在超快物态调控、新型电子加速器等领域具有重要的应用前景.超快超强激光与等离子体相互作用是近年来发展起来的一种新型的强场太赫兹辐射产生途径.本文报道了利用超强飞秒激光脉冲与金属薄膜靶作用产生太赫兹辐射的实验结果,研究了激光能量和离焦量对靶后太赫兹辐射能量的影响,并通过监测激光背向散射光谱,定性揭示了其变化规律与不同光强下的电子加热机制的相关性.实验表征了太赫兹辐射的频谱、偏振及聚焦光斑情况.测量结果表明,实验产生了脉冲能量达458μJ、聚焦场强高达GV/m量级的超宽带太赫兹辐射,为开展极端太赫兹脉冲与物质相互作用研究提供了一种新的强场太赫兹光源. 相似文献
8.
We systematically study the optimization of highly efficient terahertz(THz) generation in lithium niobate(LN)crystal pumped by 800 nm laser pulses with 30 fs pulse duration. At room temperature, we obtain a record optical-to-THz energy conversion efficiency of 0.43% by chirping the pump laser pulses. Our method provides a new technique for producing millijoule THz radiation in LN via optical rectification driven by joule-level Ti:sapphire laser systems, which deliver sub-50-fs pulse durations. 相似文献
9.
范文慧 《中国光学快报(英文版)》2011,(11):40-45
An overview of the major techniques to generate and detect THz radiation so far,especially the major approaches to generate and detect coherent ultra-short THz pulses using ultra-short pulsed laser,has been presented.And also,this paper,in particularly,focuses on broadband THz spectroscopy and addresses on a number of issues relevant to generation and detection of broadband pulsed THz radiation as well as broadband time-domain THz spectroscopy (THz-TDS) with the help of ultra-short pulsed laser.The time-dom... 相似文献
10.
D. M. Lubenko V. F. Losev Yu. M. Andreev G. V. Lanskii 《Bulletin of the Russian Academy of Sciences: Physics》2017,81(10):1239-1243
Results from model studies of the possibility of creating a source of high-power picosecond pulses of terahertz radiation via optical rectification and phase-matched down conversion of femtosecond pulses of Ti:Sapphire lasers in a nonlinear LBO crystal are presented. Modified Sellmeier equations are used in calculations. It is shown that the lengths of coherence for the generation of THz radiation at frequencies higher than 0.5 THz are more than 0.5 mm, allowing the technologically simple production of periodic structures. The maximum length of coherence is achieved for s–s type interactions in the XY plane. Phase-matched s–f type down conversion is possible only in the XY plane, including noncritical spectral matching conditions. Maximum efficiency can be expected for three-wave interactions with the polarization of interacting waves parallel to Z axis. 相似文献
11.
Determination of third-order nonlinearity in ZnTe by use of femtosecond laser pulses 总被引:1,自引:0,他引:1
Qi-Rong Xing Fang-Lin Mao Li-Ying Lang Zhuan Wang Kai Wang Shu-Xin Li Lu Chai Qing-Yue Wang 《Optics & Laser Technology》2005,37(6):475-477
Third-order nonlinearity induced by femtosecond pulses in ZnTe is investigated experimentally. We employ the transmission z-scan technique, using femtosecond pulses at 810 nm, to determine Kerr-type nonlinearity in ZnTe. The implications of our results to the terahertz (THz) radiation generation are discussed. 相似文献
12.
电子动力学及相干辐射的强场调控与阿秒探测是强场物理与阿秒物理领域中的重大课题。通过同步探测阿秒辐射和太赫兹辐射,文章作者首次实现了阿秒精度的太赫兹产生动力学的探测与控制,表明阿秒物理与太赫兹技术的结合有助于深入理解强场驱动下太赫兹产生机制和电子再散射动力学,展示了利用双色场控制电子波包相干相位,实现超快物理过程强场调控的可能。文章作者所提出的精确刻画太赫兹时域瞬时电场方案,有助于推动极化敏感的太赫兹谱学研究。可以预期,阿秒脉冲与太赫兹源技术不会局限于原子分子物理领域。实现阿秒物理与太赫兹技术之间的互为抽运与探测,将会极大地推动化学、材料科学、凝聚态物理等领域的高时空分辨的超快动力学探测。 相似文献
13.
We review the generation of broadband THz radiation from femtosecond photo‐induced gas plasmas, with an emphasis on the highly efficient “AC‐bias” case where the plasma is generated and driven by a superposition of fundamental and second‐harmonic optical fields. The dependence on experimental parameters such as pulse energy, air pressure, polarization and focusing are presented, and compared to the predictions from semi‐quantitative models for the THz generation process, namely (i) a microscopic photocurrent model and (ii) a four‐wave mixing model. We also employ these models to the case of few‐cycle pulses, where the observed THz emission is related directly to the carrier‐envelope phase of the pulses, and hence provides a mechanism with which to measure this phase.} 相似文献
14.
Femtosecond far-infrared radiation pulses in the THz spectral range were observed as a consequence of the energy modulation of 1.7 GeV electrons by femtosecond laser pulses in the BESSY storage ring in order to generate femtosecond x-ray pulses ("femtoslicing"). In addition to being crucial for diagnostics of the laser-electron interaction, the THz radiation itself is useful for experiments where intense ultrashort THz pulses of well-defined temporal and spectral characteristics are required. 相似文献
15.
The insertion of three continuous-wave optical frequencies in a low-dispersion optical fibre resulted in the generation of a high-repetition-rate train of ultra-short pulses and its simultaneous wavelength conversion. Two of the frequencies were spaced by ∼0.17 THz and multi-wave mixing generated a frequency comb to which is associated a train of 1.6 ps pulses. Wave-mixing between the generated comb and the third input optical frequency then converts the pulse train into different wavelengths. The Split-Step Fourier method was applied to numerically simulate the generation/wavelength conversion and results are in good agreement with experiments. 相似文献
16.
超快强激光在光学介质(如空气)中传播时由于克尔自聚焦效应和等离体散焦效应动态平
衡会发生一种独特的非线性激光成丝现象。激光成丝过程会诱导一些独特的物理现象,如非线性
光频转换产生超连续光谱、等离子体诱导高压放电、锥形辐射等,在大气传感、天气控制等研究
领域具有重要的应用前景。本文针对飞秒激光大气成丝过程中与传输介质相互作用所诱导的非线
性发光过程,介绍了激光大气成丝所产生的超连续光谱(白光)激光、谐波产生和太赫兹波辐射
三种非线性光频转换现象,并着重探讨了太赫兹波辐射的物理机理、研究现状和应用前景。 相似文献
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19.
利用飞秒激光脉冲在生长于二氧化硅衬底上的W/CoFeB/Pt和Ta/CoFeB/Pt两类铁磁/非磁性金属异质结构中实现高效、宽带的相干THz脉冲辐射.实验中, THz脉冲的相位随外加磁场的反转而反转,表明THz辐射与样品的磁有序密切相关.为了考察三层膜结构THz辐射的物理机制,分别研究了构成三层膜结构的双层异质结构(包括CoFeB/W, CoFeB/Pt和CoFeB/Ta)的THz辐射.实验结果都与逆自旋霍尔效应相符合, W/CoFeB/Pt和Ta/CoFeB/Pt三层膜结构所辐射的THz强度优于同等激发功率下的ZnTe (厚度0.5 mm)晶体.此外,还研究了两款异质结构和ZnTe的THz辐射强度与激发光脉冲能量密度的关系,发现Ta/CoFeB/Pt的饱和能量密度略大于W/CoFeB/Pt的饱和能量密度,表明自旋电子在Ta/CoFeB/Pt中的界面积累效应相对较小. 相似文献
20.
The results of a theoretical analysis of the generation of broadband radiation in the infrared and terahertz spectral ranges
upon the excitation of plasma in air by two femtosecond pulses at the fundamental and second-harmonic frequencies of a Ti-sapphire
laser are presented. It is found that the appearance of long-wavelength radiation in a strong field of pulses of different
frequencies can be described in terms of strongly anharmonic oscillations of optical electrons, whereby electrons are pulled
far away from their atoms; these oscillations are accompanied by cascade transitions of electrons from their ground state
to a bound excited state, followed by a transition to the continuum. It is shown that the generated infrared and terahertz
radiation appears in the form of pulses containing a few oscillations of the light field. The efficiency of terahertz generation
varies periodically with an increase in the interaction length of the femtosecond pulses of different frequencies. 相似文献