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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) - Exceptionally high THz energy densities generated from organic crystals pumped with mid-infrared pulses
摘要： Optical Parametric Chirped-Pulse Amplification (OPCPA) is an emerging laser technology, providing a flexibility in operating wavelengths and power upscaling. Here, we investigate THz generation in organic crystals (DAST) by optical rectification (OR) of intense Mid–Infrared (MIR) pulses. The broadband spectrum exceeds several octaves when pumped by 100 fs, 3.9 μm OPCPA pulses. We report on an extraordinarily high THz energy density of 3.1 mJ/cm2 and crystal damage threshold > 150 mJ/cm2.
关键词： optical rectification,OPCPA,mid-infrared pulses,THz generation,organic crystals
更新于2025-09-11 14:15:04
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Oscillatory behaviour in the energy and nonlinear optical rectification spectra of elliptic quantum rings under electric field: influence of impurity and eccentricity
摘要： We have theoretically investigated the electronic properties and nonlinear optical rectification spectra of GaAs/AlGaAs anisotropic quantum ring, modelled by an outer ellipsis and an inner circle, in connection to the presence of a donor off-centre impurity, structural distortions and in-plane electric field. The one-electron energy spectrum and wave functions are found using the adiabatic approximation and the finite element method within the effective-mass model. The energy spectrum of the ring reveals an anomalous oscillatory behaviour in the region of relatively small values of the electric field (< 12 kV/cm) followed by linear Stark effect at higher field values. We showed that this unusual behaviour is strongly affected by the ratio of the outer/inner ring radii, the displacement of the inner circle (eccentricity) along the x or y axis and the impurity presence. The related nonlinear optical rectification spectra present maxima whose positions mirror this oscillatory behaviour and consequently can be used as an excellent tool to distinguish the presence of an impurity or the direction of the eccentricity.
关键词： nonlinear optical rectification,eccentricity,Quantum ring,donor impurity,electric field
更新于2025-09-09 09:28:46
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[IEEE 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz2018) - Nagoya, Japan (2018.9.9-2018.9.14)] 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Optical Rectification of a 100W Average Power Ultrafast Thin-Disk Oscillator
摘要： We demonstrate THz generation by optical rectification in GaP crystals using excitation average power levels exceeding 100 W. The laser source is a state-of-the-art diode-pumped Yb:YAG modelocked thin-disk laser, capable of generating 120 W at 13.4 MHz directly from a one-box oscillator, without the need for any amplification stages. In this first demonstration, we measured a maximum average power of 78 μW at a central frequency of 0.8 THz. This first result shows that optical rectification of high average power (100 W class) ultrafast sources is within reach, and paves the way towards Watt-level, ultrafast laser pumped THz sources.
关键词： optical rectification,ultrafast lasers,GaP crystals,high average power,THz generation
更新于2025-09-09 09:28:46
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Scanning frequency comb microscopy—A new method in scanning probe microscopy
摘要： A method for superimposing a microwave frequency comb (MFC) on the DC tunneling current in a scanning tunneling microscope (STM) is described in which a mode-locked laser is focused on the tunneling junction. The MFC is caused by optical rectification of the regular sequence of laser pulses due to the nonlinear current-voltage characteristics of the tunneling junction. Hundreds of harmonics, at integer multiples of the laser pulse-repetition frequency, are generated with a metal tip and sample. However, the harmonics have less power with a resistive sample due to the loss in its spreading resistance. The microwave power is greatest at a tip-sample distance that is unique for each sample resistivity. This distance may be set by using different pairs of the applied DC bias and the set-point for the DC tunneling current. However, the laser, and not the applied DC bias or the DC tunneling current, is the source of energy for the MFC so they are not required. Feedback control of the tip-sample distance may be based on maximizing the attowatt-level microwave power of the harmonics, which have a signal-to-noise ratio of 20 dB. This method shows promise for nondestructive carrier profiling of semiconductors with true sub-nanometer resolution which is essential in the continued progress below the 40-nm technology node. It may enable carrier profiling with 2-D materials such as graphene, and it also shows promise for finer resolution in images of biological materials or other resistive samples.
关键词： optical rectification,microwave frequency comb,resistive sample,feedback control,scanning tunneling microscope
更新于2025-09-04 15:30:14