Waveform-Controlled Terahertz Radiation from the Air Filament Produced by Few-Cycle Laser Pulses

Abstract

Waveform-controlled terahertz (THz) radiation is of great importance due to its potential application in THz sensing and coherent control of quantum systems. We demonstrated a novel scheme to generate waveform-controlled THz radiation from air plasma produced when carrier-envelope-phase (CEP) stabilized few-cycle laser pulses undergo filamentation in ambient air. We launched CEP-stabilized 10 fs-long (~1.7 optical cycles) laser pulses at 1.8 μm into air and found that the generated 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.

Analytical description of generation of the residual current density in the plasma produced by a few-cycle laser pulse

“…This experiment, specifically, revealed the sinusoidal dependence of the amplitude of the THz field on the CEP of the laser pulse, which was later confirmed in further experiments. 17,[20][21][22] In these experiments, laser pulses with a longer wavelength (1:8 lm) and fewer ($1:5) field periods were used. The dependence of the generated THz radiation on CEP of the laser pulse opens up additional opportunities of controlling the amplitude, waveform, and polarization of THz pulses and allows one to realize a comparatively simple method of controlling and measuring CEP by means of detecting the THz radiation.…”

Intense broadband THz generation from femtosecond laser filamentation

“…By applying a helical electrical field along a plasma region, Lu et al [10] could generate an elliptically polarized THz wave. An intense THz generation can also be generated from air plasma driven by an intense few-cycle laser pulse [11,12] . The effect of the carrier envelope phase of few-cycle laser pulses on THz emission was predicted by Wu et al [11] and later on experimentally demonstrated by Bai et al [12] .…”

“…An intense THz generation can also be generated from air plasma driven by an intense few-cycle laser pulse [11,12] . The effect of the carrier envelope phase of few-cycle laser pulses on THz emission was predicted by Wu et al [11] and later on experimentally demonstrated by Bai et al [12] . A four-wave rectification method by focusing the fundamental wave (FW) and second-harmonic wave (SHW) of an amplified Ti:Sapphire laser into air was reported in 2000 by Cook et al to generate more than 3 orders stronger THz signal compared with only FW pumping [13] .…”

Extremely asymmetric electron localization in H2+controlled with a THz field

“…We utilize a terahertz (THz) pulse [22][23][24][25][26][27] to steer the electron motion between the two protons after an ultrashort UV laser pulse is used to excite the electron wave packet onto the dissociative 2pσ u state. Both the THz and UV pulses are linearly polarized.…”