Terahertz Spectroscopy

Baxter, Jason B.; Guglietta, Glenn

doi:10.1021/ac200907z

Cited by 412 publications

(280 citation statements)

References 285 publications

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“…To study the dynamic THz response of graphene, we utilize ultrafast timeresolved THz spectroscopy 25,38,39 , which has established itself as a powerful all-optical experimental technique for directly probing the relaxation and cooling dynamics of photoexcited carriers (see Methods section). A 60-fs ultrafast optical pump pulse at 800 nm wavelength injects hot carriers into the graphene sample.…”

Section: Resultsmentioning

confidence: 99%

Microscopic Origins of the Terahertz Carrier Relaxation and Cooling Dynamics in Graphene

et al. 2015

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The ultrafast dynamics of hot carriers in graphene are key to both understanding of fundamental carrier-carrier interactions and carrier-phonon relaxation processes in two-dimensional materials, and understanding of the physics underlying novel high-speed electronic and optoelectronic devices. Many recent experiments on hot carriers using terahertz spectroscopy and related techniques have interpreted the variety of observed signals within phenomenological frameworks, and sometimes invoke extrinsic effects such as disorder. Here, we present an integrated experimental and theoretical programme, using ultrafast timeresolved terahertz spectroscopy combined with microscopic modelling, to systematically investigate the hot-carrier dynamics in a wide array of graphene samples having varying amounts of disorder and with either high or low doping levels. The theory reproduces the observed dynamics quantitatively without the need to invoke any fitting parameters, phenomenological models or extrinsic effects such as disorder. We demonstrate that the dynamics are dominated by the combined effect of efficient carrier-carrier scattering, which maintains a thermalized carrier distribution, and carrier-optical-phonon scattering, which removes energy from the carrier liquid.

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Section: Resultsmentioning

confidence: 99%

Microscopic Origins of the Terahertz Carrier Relaxation and Cooling Dynamics in Graphene

et al. 2015

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“…[4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] We also highlight that spectroscopy at terahertz frequencies has a much longer tradition than we can possibly cover in this review article. In the spirit of Felix Franks' comments regarding the value of ''old literature'', 19 we point out references that provide good summaries of previous work throughout this review.…”

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confidence: 99%

Terahertz Time-Domain and Low-Frequency Raman Spectroscopy of Organic Materials

2015

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With the ongoing proliferation of terahertz time-domain instrumentation from semiconductor physics into applied spectroscopy over the past decade, measurements at terahertz frequencies (1 THz [ 10 12 Hz [ 33 cm À1) have attracted a sustained growing interest, in particular the investigation of hydrogen-bonding interactions in organic materials. More recently, the availability of Raman spectrometers that are readily able to measure in the equivalent spectral region very close to the elastic scattering background has also grown significantly. This development has led to renewed efforts in performing spectroscopy at the interface between dielectric relaxation phenomena and vibrational spectroscopy. In this review, we briefly outline the underlying technology, the physical phenomena governing the light-matter interaction at terahertz frequencies, recent examples of spectroscopic studies, and the current state of the art in assigning spectral features to vibrational modes based on computational techniques.

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“…To study the dynamic THz response of graphene, the ultrafast time-resolved THz spectroscopy [106,109,110] is used, which has established itself as a very powerful all-optical experimental technique for directly probing the relaxation and cooling dynamics of photoexcited carriers, because it is sensitive to both the number of carriers and their distribution in energy. The details of the experimental set-up are provided in Ref.…”

Section: Optical Pump and Thz Probe DI Erential Transmission Spectramentioning

confidence: 99%

Relaxation Dynamics in Graphene

Malić

Knorr

2013

Graphene and Carbon Nanotubes

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In this thesis, the relaxation dynamics of nonequilibrium carriers in graphene is investigated. Based on the density matrix approach, the interaction of carriers with light, phonons and electrons is theoretically modelled. The resulting time-, momentum-, and angle-resolved simulation of the carrier dynamics enables the interpretation of recent experimental observations. Typically, the carrier relaxation has been accessed via high-resolution pump-probe experiments. Common to all studies is a bi-exponential decay of the pump-induced differential transmission (DT) spectrum. The fast decay component in the range of few tens of femtoseconds is assigned to an ultrafast Coulomb-dominated carrier redistribution towards a hot Fermi-Dirac distribution, whereas the slower decay component in the range of a picosecond reflects the equilibration between the electron and the phonon system. However, many studies report a zero-crossing after the initial decay in the transient DT spectrum, where the second decay component characterizes the recovering of the DT signal. In very good agreement with recent pump-probe experiment performed by the group of Prof. Manfred Helm (Helmholtz-Zentrum Dresden-Rossendorf), a microscopic explanation for the occurrence of transient negative differential transmission in graphene is found, where a detailed interplay of intraand interband absorption processes on the transient DT in graphene is investigated. In particular, phonon-assisted intraband processes are shown to lead to an enhanced absorption giving rise to the experimentally observed zero-crossing from positive to negative DT signals.In collaboration with the group of Prof. Theodore B. Norris (Michigan University, USA), theoretical studies combined with ultrafast time-resolved THz spectroscopy were performed to systematically investigate the hot-carrier dynamics in an array of graphene samples. The theory calculates explicitly the time-dependent response of the system to a THz probe pulse. The calculations reveal that the observed dynamics can be accounted for qualitatively without including any fitting parameters, phenomenological models or extrinsic effects. Specifically, the hot-carrier dynamics are governed by the coupling of extraordinarily efficient carrier-carrier and carrier-phonon interactions. Furthermore, the theory demonstrates that the simple Drude model is insufficient to fully account for the THz interactions.Beside pump-probe studies, the thesis presents the absorption spectra of mono-and bilayer graphene including the impact of the fully momentum-dependent optical and Coulomb matrix elements. In agreement with recent experiments, the absorbance of graphene is characterized by a frequency-independent value in the near-infrared spectral region and a pronounced peak in the ultraviolet region resulting from interband transition. In contrast to the linear band structure of graphene, the energy dispersion of bilayer graphene exhibits four parabolic bands resulting in interesting optical features: The absorbance exhibits in...

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Terahertz Spectroscopy

Cited by 412 publications

References 285 publications

Microscopic Origins of the Terahertz Carrier Relaxation and Cooling Dynamics in Graphene

Microscopic Origins of the Terahertz Carrier Relaxation and Cooling Dynamics in Graphene

Terahertz Time-Domain and Low-Frequency Raman Spectroscopy of Organic Materials

Relaxation Dynamics in Graphene

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