Boosting terahertz-radiation power with two-color circularly polarized midinfrared laser pulses

Abstract

A way to considerably enhance terahertz radiation, emitted in the interaction of intense mid-infrared laser pulses with atomic gases, in both the total energy and the electric-field amplitude is suggested. The scheme is based on the application of a two-color field consisting of a strong circularly polarized mid-infrared pulse with wavelengths of 1.6 ÷ 4 µm and its linearly or circularly polarized second harmonic of lower intensity. By combining the strong-field approximation for the ionization of a single atom with particle-in-cell simulations of the collective dynamics of the generated plasma it is shown that the application of such two-color circularly polarized laser pulses may lead to an order-of-magnitude increase in the energy emitted in the terahertz frequency domain as well as in a considerable enhancement in the maximal electric field of the terahertz pulse. Our results support recently reported experimental and numerical findings. arXiv:1810.08834v1 [physics.atom-ph]

Bright single-cycle terahertz source based on gas cells irradiated by two-color laser pulses

“…2. Thus, the quasi-static electric field induced inside the cell by the plasma oscillation grows with the atomic concentration and the laser wavelength, the latter agrees with the known data and calculations of two-color THz emission in mid-infrared fields [18,20,21]. The dependence of the electric field distribution on the cell size is less trivial: at 50µm the field is mostly concentrated near the cell edges where it oscillates spatially in the y-direction with a relatively small period.…”

“…The corresponding plasma wavelengths λ p = 2πc/ω p are 40 and 13µm determine the number of oscillations in the electron distribution function per cell size L. Finally the laser wavelength determines the initial photoelectron velocity (see e.g. [21] for details) v 0 ≈ keE 0 λ/(2πm e c) with k ≈ 0.1. These three tendencies are unambiguously presented on the distributions of Fig.…”

“…The relative electric field amplitude in ( 3) is taken = 0.22 corresponding to a 5% relative intensity of SH. When both the fundamental and the SH fields are circularly polarized, the value of α does not affect the resulting plasma dynamics in a spatially homogeneous gas [21]. In our calculations below we use a rectangular two-dimensional cell which makes results α-dependent.…”

“…Over the past years the ω − 2ω scheme has been extensively studied employing different field polarization states and wavelengths [16,17,18,19]. According to recent theoretical predictions [20,21], application of mid-infrared two-color pulses instead of conventionally used 800-nm radiation may help increasing the THz emitted energy by one order of magnitude or even more. This foreseeing enhancement can make THz sources of interest for fundamental experiments in AMOP physics and for other applications requiring nonlinear regimes of interaction.…”

QPROP with faster calculation of photoelectron spectra

“…Two-color setups were simulated already with previous versions of Qprop in Refs. [14,15,16,17,18,19,20,21,22]. Here, we include illustrative examples that can be easily customized.…”