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Register a new userTime-resolved observation of coherent excitonic nonlinear response with a table-top narrowband THz pulse wave
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By combining a tilted-pulse-intensity-front scheme using a LiNbO3 crystal and a chirped-pulse-beating method, we generated a narrowband intense terahertz (THz) pulse, which had a maximum electric field of more than 10 kV/cm at around 2 THz, a bandwidth of about 50 GHz,and frequency tunability from 0.5 to 2 THz. By performing THz-pump and near-infrared-probe experiments on GaAs quantum wells, we observed that the resonant excitation of the intraexcitonic 1s-2p transition induces a clear and large Autler-Townes splitting. Our time-resolved measurements show that the splitting energy observed in the rising edge region of electric field is larger than in the constant region. This result implies that the splitting energy depends on the time-averaged THz field over the excitonic dephasing time rather than that at the instant of the exciton creation by a probe pulse.
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The lack of available table-top extreme ultraviolet (XUV) sources with high enough fluxes and coherence properties have limited the availability of nonlinear XUV and x-ray spectroscopies to free electron lasers (FEL). Here, we demonstrate second harmonic generation (SHG) on a table-top XUV source for the first time by observing SHG at the Ti M2,3-edge with a high harmonic seeded soft x-ray laser (HHG-SXRL) [1,2]. Further, this experiment represents the first SHG experiment in the XUV. First-principles electronic structure calculations are used to confirm the surface specificity and resonant enhancement of the SHG signal. The realization of XUV-SHG on a table-top source with femtosecond temporal resolution opens up tremendous opportunities for the study of element-specific dynamics in multi-component systems where surface, interfacial, and bulk-phase asymmetries play a driving role in smaller-scale labs as opposed to FELs.
We have created a nonequilibrium population of antiferromagnetic spin-waves in Cr2O3, and characterized its dynamics, using frequency- and time-resolved nonlinear optical spectroscopy of the exciton-magnon transition. We observe a time-dependent pump-probe line shape, which results from excitation induced renormalization of the spin-wave band structure. We present a model that reproduces the basic characteristics of the data, in which we postulate the optical nonlinearity to be dominated by interactions with long-wavelength spin-waves, and the dynamics to be due to spin-wave thermalization.
We propose a scheme to measure the mass of a single particle using the nonlinear response of a 2D nanoresonator with degenerate eigenmodes. Using numerical and analytical calculations, we show that by driving a square graphene nanoresonator into the nonlinear regime, simultaneous determination of the mass and position of an added particle is possible. Moreover, this scheme only requires measurements in a narrow frequency band near the fundamental resonance.
Coherent Raman scattering spectroscopy is studied purposely, with the Gaussian ultrashort pulses as a hands-on elucidatory extraction tool of the clean coherent Raman resonant spectra from the overall measured data contaminated with the non-resonant four wave mixing background. The integral formulae for both the coherent anti-Stokes and Stokes Raman scattering are given in the semiclassical picture, and the closed-form solutions in terms of a complex error function are obtained. An analytic form of maximum enhancement of pure coherent Raman spectra at threshold time delay depending on bandwidth of probe pulse is also obtained. The observed experimental data for pyridine in liquid-phase are quantitatively elucidated and the inferred time-resolved coherent Raman resonant results are reconstructed with a new insight.
Since its first demonstration in the sixties, coherent anti-Stokes Raman scattering (CARS) has become a powerful spectroscopic sensing tool with broad applications in biology and chemistry. However, it is a complex nonlinear optical process that often leads to the lacks of quantitative data outputs. In this letter, we observe how CARS signal builds up gradually and demonstrate how to control its deferral with laser-pulse shaping. A time-resolved three-color CARS that involves a pair of driving broadband femtosecond pulses and delayed shaped probe pulse is realized experimentally. Driving pulses are tuned to the Raman-resonance onto the vibrational ring modes of pyridine and benzene molecules. As a result, CARS-buildup is deferred in picoseconds as delayed probe pulse width varies from 50 down to 10 cm-1. With off-resonant driving of water molecules this effect, in contrary, does not occur. Laser control predicting deferred resonant processes can serve as a novel and important species-specific indicator in, e.g., machine learning applications for future nonlinear optical spectroscopy.
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