Pulsed laser noise analysis and pump-probe signal detection with a data acquisition card

Werley, Christopher A.; Teo, Stephanie M.; Nelson, Keith A.

doi:10.1063/1.3669783

Cited by 55 publications

(40 citation statements)

References 13 publications

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“…To monitor the light intensity in perpendicular and parallel channels from the Wollaston prism, we recorded the signal simultaneously from two separate photodiodes with the output connected to gated integrators and a data acquisition card/ PC data acquisition system [13]. The pump beam was chopped at half the 1 kHz repetition rate, and the normalized and balanced difference signal was recorded as…”

Section: Methodsmentioning

confidence: 99%

Distortion-free enhancement of terahertz signals measured by electro-optic sampling II Experiment

et al. 2014

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Three methods for distortion-free enhancement of electro-optic sampling measurements of terahertz signals are tested. In the first part of this two-paper series [J. Opt. Soc. Am B 31, 904-910 (2014)], the theoretical framework for describing the signal enhancement was presented and discussed. As the applied optical bias is decreased, individual signal traces become enhanced but distorted. Here we experimentally show that nonlinear signal components that distort the terahertz electric field measurement can be removed by subtracting traces recorded with opposite optical bias values. In all three methods tested, we observe up to an order of magnitude increase in distortion-free signal enhancement, in agreement with the theory, making possible measurements of small terahertzinduced transient birefringence signals with increased signal-to-noise ratio.

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Section: Methodsmentioning

confidence: 99%

Distortion-free enhancement of terahertz signals measured by electro-optic sampling II Experiment

et al. 2014

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“…The EO sampling optical beam was variably delayed, attenuated using a half-wave plate and polarizer, directed through a hole in the second THz parabolic reflector, and overlapped with the THz pulse in the GaP crystal. The transmitted EO sampling beam was then passed through a quarter wave plate and polarizing beam splitter, and the signals were detected using balanced photodiodes and analyzed using a National Instruments Data Acquisition card 48 . …”

Section: Methodsmentioning

confidence: 99%

THz generation using a reflective stair-step echelon

et al. 2016

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We present a novel method for THz generation in lithium niobate using a reflective stair-step echelon structure. The echelon produces a discretely tilted pulse front with less angular dispersion compared to a high groove-density grating. The THz output was characterized using both a 1-lens and 3-lens imaging system to set the tilt angle at room and cryogenic temperatures. Using broadband 800 nm pulses with a pulse energy of 0.95 mJ and a pulse duration of 70 fs (24 nm FWHM bandwidth, 39 fs transform limited width), we produced THz pulses with field strengths as high as 500 kV/cm and pulse energies as high as 3.1 µJ. The highest conversion efficiency we obtained was 0.33%. In addition, we find that the echelon is easily implemented into an experimental setup for quick alignment and optimization.

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“…In these measurements, the local detection time of the picosecond terahertz pulse was synchronized with the pump pulse such that the whole terahertz waveform experienced the same time delay after photoexcitation [29]. To reduce experimental errors due to laser drift, we simultaneously measured the transmitted terahertz electric field waveform E 0 ðtÞ without optical excitation and the optical-pump-induced change of the field ΔE τ ðtÞ via electro-optic sampling using a data acquisition card [16,17,30]. The resulting ratio −ΔE τ =E 0 (referred to as "differential field") approximately represents the PC, Δσ τ;1 (Refs.…”

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confidence: 99%

Semiconducting-to-Metallic Photoconductivity Crossover and Temperature-Dependent Drude Weight in Graphene

et al. 2014

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We investigate the transient photoconductivity of graphene at various gate-tuned carrier densities by optical-pump terahertz-probe spectroscopy. We demonstrate that graphene exhibits semiconducting positive photoconductivity near zero carrier density, which crosses over to metallic negative photoconductivity at high carrier density. These observations can be accounted for by the interplay between photoinduced changes of both the Drude weight and carrier scattering rate. Our findings provide a complete picture to explain the opposite photoconductivity behavior reported in (undoped) graphene grown epitaxially and (doped) graphene grown by chemical vapor deposition. Notably, we observe nonmonotonic fluence dependence of the photoconductivity at low carrier density. This behavior reveals the nonmonotonic temperature dependence of the Drude weight in graphene, a unique property of two-dimensional massless Dirac fermions. DOI: 10.1103/PhysRevLett.113.056602 PACS numbers: 72.80.Vp, 72.40.+w, 73.40.Qv, 78.20.−e Charge carriers in graphene mimic two-dimensional (2D) massless Dirac fermions with linear energy dispersion, resulting in unique optical and electronic properties [1]. They exhibit high mobility and strong interaction with electromagnetic radiation over a broad frequency range [2]. Interband transitions in graphene give rise to pronounced optical absorption in the midinfrared to visible spectral range, where the optical conductivity is close to a universal value σ 0 ¼ πe 2 =2h [3]. Free-carrier intraband transitions, on the other hand, cause lowfrequency absorption, which varies significantly with charge density and results in strong light extinction at high carrier density [4]. In addition to this density dependence, the massless Dirac particles in graphene are predicted to exhibit a distinctive nonmonotonic temperature dependence of the intraband absorption strength, or Drude weight, due to their linear dispersion [5,6]. This behavior contrasts with the temperature-independent Drude weight expected in conventional systems of massive particles with parabolic dispersion [7,8]. Although the unique behavior of the Drude weight in graphene has been considered theoretically, experimental signatures are still lacking.The intrinsic properties of Drude absorption in graphene can be revealed by studying its dynamical response to photoexcitation. In particular, optical-pump terahertz-probe spectroscopy provides access to a wide transient temperature range via pulsed optical excitation, and allows measurement of the ac Drude conductivity by a timedelayed terahertz probe pulse [9]. This technique has been applied to study transient photoconductivity (PC) in graphene, but conflicting results have been reported [9][10][11][12][13][14][15]. Positive PC was observed in epitaxial graphene on SiC (Ref.[15]), while negative PC was seen in graphene grown by chemical vapor deposition (CVD) [11][12][13][14]. It has been argued that the opposite behavior in these samples arises from their different charge densities. Here we study...

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Pulsed laser noise analysis and pump-probe signal detection with a data acquisition card

Cited by 55 publications

References 13 publications

Distortion-free enhancement of terahertz signals measured by electro-optic sampling II Experiment

Distortion-free enhancement of terahertz signals measured by electro-optic sampling II Experiment

THz generation using a reflective stair-step echelon

Semiconducting-to-Metallic Photoconductivity Crossover and Temperature-Dependent Drude Weight in Graphene

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