- 标题
- 摘要
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Carrier-Induced Coherent Phonon Softening in Bismuth
摘要： With performing time-resolved pump-probe experiments with ultrashort pulses from a mode-locked Ti:sapphire laser, we report on the carrier-induced softening and dephasing of coherent phonon oscillations in the bismuth crystal. As the lattice displacement becomes severe at high pump power, a frequency shift can occur due to the lattice anharmonicity term. We clari?ed from the measurements done by varying the pulse duration that the phonon softening at high pump intensity in bismuth originates from the electron-interaction of photoexcited carriers not from the phonon anharmonicity. We also ?nd that the coherent phonon dephasing is accelerated at high carrier densities.
关键词： Pump-probe,Coherent phonon,Phonon softening
更新于2025-09-23 15:22:29
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Optical modulation of coherent phonon emission in optomechanical cavities
摘要： Optomechanical (OM) structures are well suited to study photon-phonon interactions, and they also turn out to be potential building blocks for phononic circuits and quantum computing. In phononic circuits, in which information is carried and processed by phonons, OM structures could be used as interfaces to photons and electrons thanks to their excellent coupling efficiency. Among the components required for phononic circuits, such structures could be used to create coherent phonon sources and detectors, but more complex functions remain challenging. Here, we propose and demonstrate a way to modulate the coherent phonon emission from OM crystals by a photothermal effect induced by an external laser, effectively creating a phonon switch working at ambient conditions of pressure and temperature and the working speed of which is only limited by the build-up time of the mechanical motion of the OM structure. We additionally demonstrate two other modulation schemes: modulation of harmonics in which the mechanical mode remains active but different harmonics of the optical force are used, and modulation to and from a chaotic regime. Furthermore, due to the local nature of the photothermal effect used here, we expect this method to allow us to selectively modulate the emission of any single cavity on a chip without affecting its surroundings in the absence of mechanical coupling between the structures, which is an important step toward freely controllable networks of OM phonon emitters.
关键词： phonon switch,coherent phonon emission,photothermal effect,Optomechanical structures,phononic circuits
更新于2025-09-23 15:21:21
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Coherent Coupled-Mode Phonon Emission in a Photoexcited Charge-Density-Wave System
摘要： Photoexcitation the quasi-one-dimensional of charge-density-wave (CDW) system, blue bronze (K0.3MoO3), with near-infrared femtosecond pulses, results in both a low-frequency, broadband THz surface emission from the photo-Dember effect, and a narrow-band emission from a TO phonon doublet centered at 1.5 THz below ~100 K in the CDW state. The polarization dependence of the phonon emission leads us to propose a surface-field/quadrupole excitation mechanism, distinct from the typical mechanisms for phonon emission in other materials. A coupled-oscillator model with a transient suppression of the mode coupling can reproduce the detailed temporal and spectral characteristics of the emission.
关键词： charge-density-wave,photo-Dember effect,coupled-oscillator model,THz emission,coherent phonon emission
更新于2025-09-16 10:30:52
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Stability of the light-induced hidden charge density wave state within the phase diagram of
摘要： The femtosecond transient optical spectroscopy is employed to study the relaxation dynamics of the equilibrium and hidden metastable charge-density-wave states in single crystals of 1T-TaS2?xSex as a function of the Se doping x. Similar to pristine 1T-TaS2, the transition to a hidden phase is observed at low temperature after a quench with a single 50 fs laser pulse, in the commensurate Mott phase up to x = 0.6. The photo-induced hidden-phase formation is accompanied by a notable change in the coherent phonon spectra, and particularly the collective amplitude mode. While the temperature stability of the hidden phase is only slightly dependent on the Se content, the creation-threshold ?uence strongly increases with Se content from 1 to ～4 mJ/cm2, which is attributed predominantly to the change in optical absorption coef?cient at the laser excitation wavelength, and not an increased barrier of the hidden state with increasing Se.
关键词： hidden phase,charge-density-wave states,1T-TaS2?xSex,coherent phonon spectra,femtosecond transient optical spectroscopy
更新于2025-09-10 09:29:36