Design and performance of reflective terahertz air-biased-coherent-detection for time-domain spectroscopy

Ho, I‐Ting; Guo, Xiaoyu; Zhang, Xicheng

doi:10.1364/oe.18.002872

Cited by 88 publications

(43 citation statements)

References 35 publications

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“…Quantum cascade lasers [7] provide a continuous wave source tunable in this spectral window. Pulses can also be produced by photoconductive switches [8,9] or via laser-induced air plasma generation [10][11][12]. However, to obtain stable and intense electric fields combined with femtosecond temporal resolution, the workhorse approach relies on the generation of coherent field transients by frequency mixing processes in nonlinear crystals [13,14].…”

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confidence: 99%

Coherent Field Transients below 15 THz from Phase-Matched Difference Frequency Generation in 4H-SiC

Fischer

Bühler

Kurihara

et al. 2017

Conference on Lasers and Electro-Optics

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We experimentally demonstrate tunable, phase-matched difference frequency generation covering the spectral region below 15 THz using 4H-SiC as a nonlinear crystal. This material combines a non-centrosymmetric lattice and strong birefringence with broadband transparency at low optical frequencies. Thorough refractive index measurements in the terahertz spectral range allow us to calculate phase-matching conditions for any near-infrared pump laser source. 4H-SiC is also exploited as a detector crystal for electro-optic sampling. The results allow us to estimate the effective second-order nonlinear coefficient. The generation of coherent radiation in the spectral region between 5 and 15 THz is a major challenge for solid-state sources, despite its relevant interest for the study of fundamental excitations in condensed matter systems. In fact, the corresponding energy range from 20 to 60 meV includes various molecular vibrations [1][2][3], as well as optical phonons in solids [4,5] and low-energy collective modes in correlated materials such as superconductors [6]. Quantum cascade lasers [7] provide a continuous wave source tunable in this spectral window. Pulses can also be produced by photoconductive switches [8,9] or via laser-induced air plasma generation [10][11][12]. However, to obtain stable and intense electric fields combined with femtosecond temporal resolution, the workhorse approach relies on the generation of coherent field transients by frequency mixing processes in nonlinear crystals [13,14]. A typical setup is based on difference frequency generation (DFG) driven by an ultrafast laser system. Unfortunately, in the elusive spectral region between 5 and 15 THz, most nonlinear crystals applied for DFG such as GaSe, AgGaS 2 (AGS), and BBO, exhibit strong optical phonon resonances that lead to reststrahlen bands where radiation cannot penetrate into the material [see Fig. 1(a)]. In addition, isotropic materials such as ZnTe are lacking birefringence and, therefore, do not allow adjustment of phase matching. Furthermore, organic nonlinear crystals [15] show heavily structured spectra in the frequency range of interest and display inherently low damage thresholds. Recently, preliminary investigations by Naftaly et al.[16] suggested 4H-SiC as a crystal suitable for nonlinear optics in the multi-terahertz range. So far, this outstanding material has received little attention in experimental works that are limited to the demonstration of nonlinear properties in the near infrared [17], mid-infrared DFG above the optical phonon frequencies [18], and emission of 1 THz radiation from 6H-SiC [19].In this Letter, we experimentally demonstrate the application of 4H-SiC for the generation of ultrashort field transients tunable between 5 and 15 THz, and its use as an electro-optic sampling (EOS) crystal.SiC exhibits a large plurality of polymorphs with hexagonal, cubic, and rhombohedral symmetry [20]. Owing to its technological relevance, high-quality synthetic crystals of 4H-SiC are available. Its lattice, sketched in...

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confidence: 99%

Coherent Field Transients below 15 THz from Phase-Matched Difference Frequency Generation in 4H-SiC

Fischer

Bühler

Kurihara

et al. 2017

Conference on Lasers and Electro-Optics

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“…17, producing a ultra-broadband THz pulses whose bandwidth is limited solely by the duration of the optical pulses. Details of the experimental setup can be found in Ref.…”

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“…The THz pulse is detected by the method of air-biased coherent detection. 17 A third portion of the fundamental beam is frequency doubled to 400 nm in a BBO crystal and used to photoexcite the samples at a pump fluence of 800 lJ=cm 2 . Experiments are performed under a dry N 2 purge to avoid absorption by water vapor.…”

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confidence: 99%

Ultrabroadband terahertz conductivity of Si nanocrystal films

Cooke

Meldrum

Jepsen³

2012

Applied Physics Letters

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The terahertz conductivity of silicon nanoparticles embedded in glass with varying density is studied with ultra-broadband terahertz spectroscopy on picosecond time scales following fs optical excitation. The transition from relatively isolated charge carriers to densities which allow inter-particle transport is clearly observed. For the times immediately following carrier injection, we observe Drude-like long range transport that is rapidly replaced with a localized response on picosecond time scales. The localized response can be very well described by a phenomenological Drude-Smith model, verifying the applicability of this simple model to the conductivity of nanoparticle ensembles over the entire THz spectral window.

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“…Moreover, recent results show that femtosecond laser-induced gas plasma exhibits a remarkable ability to detect pulsed (broadband) THz waves through nonlinear optical processes [10,11]. The use of air (or selected gases) as both the broadband THz wave emitter and THz wave sensor provides superior bandwidth covering the entire THz gap and well-beyond [12]. Potential applications include nonlinear spectroscopy and imaging, as well as remote sensing and identification.…”

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confidence: 99%

Coherent Polarization Control of THz Waves Generated from Asymmetrically Ionized Gases

Dai¹,

Karpowicz²,

Zhang³

2011

J. Phys.: Conf. Ser.

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Design and performance of reflective terahertz air-biased-coherent-detection for time-domain spectroscopy

Cited by 88 publications

References 35 publications

Coherent Field Transients below 15 THz from Phase-Matched Difference Frequency Generation in 4H-SiC

Coherent Field Transients below 15 THz from Phase-Matched Difference Frequency Generation in 4H-SiC

Ultrabroadband terahertz conductivity of Si nanocrystal films

Coherent Polarization Control of THz Waves Generated from Asymmetrically Ionized Gases

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