Coherent Control of THz Wave Generation in Ambient Air

Abstract

Our study of THz wave generation in the pulsed laser induced air plasma with individually controlled phase, polarization, and amplitude of the optical fundamental wave (omega) and its second harmonic (2omega) indicates that the third-order nonlinear optical process mixing the omega and 2omega beams in the ionized plasma is the main mechanism of the efficient THz wave generation. The polarity and the strength of the emitted THz field are completely controlled by the relative phase between the omega and 2omega waves. The measured THz field amplitude is proportional to the pulse energy of the fundamental beam and to the square root of the pulse energy of the second-harmonic beam once the total optical pulse energy exceeds the plasma formation threshold. The optimal THz field is achieved when all waves (omega, 2omega, and THz waves) are at the same polarization in the four-wave-mixing process.

Determination of the carrier-envelope phase of few-cycle laser pulses with terahertz-emission spectroscopy

“…There, the transient electric currents responsible for the THz radiation have their origin either in ponderomotive forces 22 , the Coulomb force of an externally applied DC bias 5,6 , or an optical "AC bias" achieved by superimposing the light pulses with their own second-harmonic radiation 7,8,9,10 . The THz-wave generation mechanism for the latter has been discussed in terms of a four-wave-mixing (FWM) process 7,9,10 . For the present case where the pulse spectra are octave-spanning FWM results in a low-frequency (Ω → 0) polarisation:…”

“…In order to take full advantage of such pulses, it is crucial to measure 1,2,3,4 and stabilise 1,2 their carrierenvelope (CE) phase, i.e., the phase difference between the carrier wave and the envelope function. We introduce a novel approach to determine the CE phase by down-conversion of the laser light to the terahertz (THz) frequency range via plasma generation in ambient air, an isotropic medium where optical rectification (down-conversion) in the forward direction is only possible if the inversion symmetry is broken by electrical or optical means 5,6,7,8,9,10 . We show that few-cycle pulses directly produce a spatial charge asymmetry in the plasma.…”

Coherent control of plasma dynamics

“…T he concept of coherent control-precise measurement or determination of a process through control of the phase of an applied oscillating field-has been applied to many different systems, including quantum dynamics 1 , trapped atomic ions 2 , chemical reactions 3 , Cooper pairs 4 , quantum dots 5,6 and THz generation 7 to name but a few. A plasma wave is a coherent and deterministically evolving structure that can be generated by the interaction of laser light with plasma.…”

Study on the generation of Efficient Terahertz from cavity phase matching optical parametric oscillator with a GaAs Crystal sheet by CO2 laser

“…Terahertz (THz) sources can be used in many applications in environment detections, security inspections, biomedical diagnostics, and so on [1][2][3]. Among the variety of nonlinear crystals, GaAs meet the requirements for high transparency in both 10 µm band and relatively high transparency in the THz region.…”