Broadband field-resolved terahertz detection via laser induced air plasma with controlled optical bias

Abstract

Abstract:We report a robust method of coherent detection of broadband THz pulses using terahertz induced second-harmonic (TISH) generation in a laser induced air plasma together with a controlled second harmonic optical bias. We discuss a role of the bias field and its phase in the process of coherent detection. Phase-matching considerations subject to plasma dispersion are also examined.

Terahertz field induced near-cutoff even-order harmonics in femtosecond laser

“…( 14) requires (ϕ 2 t /ϕ 2 σ + ϕ 2 σ )/2 > 256, necessitating ϕ σ > 23, suggesting a femtosecond pulse should contain as least 9 cycles within its FWHM. The range of ϕ σ also naturally satisfies both conditions that η = ϕ τ /ϕ σ 1 and e ϕtϕτ /ϕ 2 σ 1 to derive ( 16) from (15). In general, the scheme favors the use of large ϕ σ , which also helps suppress the sideband caused by the finite pulse width.…”

“…Gases are continuously renewed, do not show appreciable dispersion, and lack phonon resonances due to the absence of an ordered structure [12]. Among such schemes, it is worth mentioning airbreakdown coherent detection [13], air-biased coherent detection [14] (ABCD), optically biased coherent detection [15], and THz radiation enhanced emission of fluorescence [16]. In particular, ABCD exploits a thirdorder nonlinear process named electric-field-induced second harmonic (EFISH) generation.…”

Phase-Insensitive Scattering of Terahertz Radiation

“…Such beating leads to a phase-and amplitude-modulated signal at the second harmonic of the optical probe. Overlapping this signal to a coherent field at the second-harmonic of the probe pulse, either induced by spectral broadening of the high intensity probe in air [7], by electric field-induced second harmonic generation of the probe via an external DC electric field [8], or by employing a second-order nonlinear crystal [10] leads to coherent detection of the THz field. In a recent publication, we investigated such a four-wave-mixing process in condensed matter (specifically, diamond), demonstrating counter-propagating phase-matched THz-NIR (near infrared) mixing [11].…”

Micro-Slit Based Coherent Detection of Terahertz Pulses in Biased, Solid State Media

“…It has been shown that coherent (field-sensitive) detection schemes can be obtained exploiting TFISH in air either via the beating of the generated second harmonic signal with supercontinuum components, or by adding an external, oscillating bias field to the interaction [3]. This last technique is largely employed as a broadband THz detection scheme and is named Air Biased Coherent Detection (ABCD) [4]. The ABCD, due to the low dispersion of air, can record THz fields with extremely large bandwidth (>20 THz), yet require bulk setups and cannot be easily miniaturized.…”

“…(3,4) into Eq. (2), we can then write the following expression for the measured intensity of the induced second harmonic as a function of the incident THz field and applied bias field:…”