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首页> 外文会议>Terahertz and Gigahertz Electronics and Photonics V >Generation of multi-cycle THz-pulses via optical rectification in periodically inverted GaAs
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Generation of multi-cycle THz-pulses via optical rectification in periodically inverted GaAs

机译：在周期性倒置的砷化镓中通过光整流产生多周期太赫兹脉冲

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摘要

We demonstrate an efficient room temperature source of narrow-bandwidth terahertz (THz) radiation using femtosecond pump pulses and periodic GaAs structure as a nonlinear material. In the past, several THz generation schemes exploited optical rectification in nonlinear crystals using femtosecond laser technology. Most of them generated single-cycle THz-pulses with broad bandwidth, using nonlinear crystals shorter than the phase-matching coherence length. Recently a novel technique to generate multi-cycle THz-pulses in the pre-engineered domain structure of periodically-poled lithium niobate (PPLN) crystals has been demonstrated. Quasi-phase matching (QPM) structures such as PPLN consist of a periodic system of domains of inverted crystal orientation. The sign of second order nonlinear polarization generated by femtosecond pulses is inverted at domain boundaries. If domain length is comparable with coherence length, QPM between THz-wave and nonlinear polarization extends the interaction length between THz and optical pulses. In the present work, using periodic GaAs structures we have achieved exceptionally high photon as well as energy conversion efficiency: 3 % and 0.07% respectively. We have examined two different types of periodic QPM GaAs samples: diffusion-bonded GaAs wafers and all-epitaxially-grown orientation-patterned GaAs crystals with 3-10 mm thicknesses. The incident optical pulse energy was in the micro-Joule range and pulse duration was ～100 fsec. We measured spectral properties of THz radiation using Michelson interferometer and a bolometer. Narrow-bandwidth (～100GHz) THz output, tunable between 1 and 3 THz, was achieved. THz frequency was tuned either by tuning the light source wavelength between 2 and 4.4 μm, or by selecting GaAs samples with different QPM periods. Our theoretical analysis, based on known GaAs dispersion properties, shows good agreement between the measured and predicted THz frequencies.
机译：我们演示了使用飞秒泵浦脉冲和周期性GaAs结构作为非线性材料的窄带宽太赫兹（THz）辐射的高效室温源。过去，几种太赫兹产生方案利用飞秒激光技术在非线性晶体中利用光学整流。他们中的大多数使用短于相位匹配相干长度的非线性晶体来产生具有宽带宽的单周期太赫兹脉冲。最近，已经证明了一种新技术，可在周期性极化的铌酸锂（PPLN）晶体的预设计域结构中生成多周期THz脉冲。诸如PPLN的准相位匹配（QPM）结构由倒置晶体取向域的周期性系统组成。飞秒脉冲产生的二阶非线性极化的符号在畴边界处反转。如果畴长与相干长度相当，则太赫兹波和非线性极化之间的QPM会延长太赫兹与光脉冲之间的相互作用长度。在目前的工作中，使用周期性的GaAs结构，我们获得了极高的光子和能量转换效率：分别为3％和0.07％。我们研究了两种不同类型的周期性QPM GaAs样品：扩散结合的GaAs晶片和厚度为3-10 mm的全外延生长的取向图案GaAs晶体。入射光脉冲能量在微焦耳范围内，脉冲持续时间约100 fsec。我们使用迈克尔逊干涉仪和测辐射热仪测量了太赫兹辐射的光谱特性。实现了窄带宽（〜100GHz）的THz输出，可在1至3 THz之间调节。通过将光源波长调节在2到4.4μm之间，或者选择具有不同QPM周期的GaAs样品，可以调谐THz频率。我们基于已知的GaAs色散特性的理论分析表明，测得的和预测的THz频率之间具有良好的一致性。

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