Phase Evolution and THz Emission from a Femtosecond Laser Filament in Air

Abstract

AbstractThe recent progress in the study of waveform-controlled terahertz (THz) generation from air plasma at SIOM is reviewed. Carrier envelope phase (CEP) stabilized Infrared (center wavelength \({\sim }1.8\,\upmu \)m) few-cycle laser pulses are produced through a home-built three-stage optical parametric amplifier (OPA) system pumped by a Ti:Sapphire laser amplifier and a hollow-fiber compressor filled with argon gas. By focusing the few-cycle pulses into the ambient air, THz radiation is generated from the produced filament. THz waveform can be controlled by varying the filament length and the CEP of driving laser pulses. Calculations using the photocurrent model and including the propagation effects well reproduce the experimental results, and the origins of various phase shifts in the filament are elucidated. Such waveform-controlled THz emission is of great importance due to its potential application in THz sensing and coherent control of quantum systems. For the application of measuring the CEP of few-cycle laser pulses, the evolution of THz waveform generated in air plasma provides a sensitive probe to the variation of the initial CEP of propagating intense few-cycle pulses. The number and positions of the inversion of THz waveform are dependent on the initial CEP, which is near 0.5\(\uppi \) constantly under varied input pulse energies when two inversions of THz waveform in air plasma become one. This provides a method of measuring the initial CEP in an accuracy that is only limited by the stability of the driving few-cycle pulses.KeywordsOptical Parametric AmplifierCarrier Envelope PhaseDrive Laser PulseGouy Phase ShiftCarrier Envelope Phase StabilityThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.