Ultraviolet-to-millimeter-band supercontinua driven by ultrashort mid-infrared laser pulses

Abstract

Combined optical nonlinearity of bound and free electrons in a fast-ionizing medium driven by ultrashort, mid-infrared (mid-IR) pulses gives rise to a vast variety of ultrafast nonlinear-optical scenarios, producing bright, broadband radiation in spectral ranges as different as ultraviolet (UV) and terahertz (THz). Given its enormous bandwidth, a quantitative experimental analysis of this type of nonlinear response is anything but simple. Here, we confront this challenge by ultrabroadband spectral measurements performed across the spectral range from the UV to the millimeter-wave (MMW) band jointly with beam profile analysis in the THz-to-MMW band and direct time-domain field waveform characterization. As one of the most striking results, the nonlinear response of a fast-ionizing gas driven by a two-color field, consisting of a high-peak-power sub-100-fs mid-IR pulse and its second harmonic, is shown to provide a source of a bright multiband supercontinuum (SC) radiation, whose spectrum spans over about 14 octaves, stretching from below 300 nm all the way beyond 4.3 mm. The MMW-to-THz part of this SC is emitted, as direct measurements show, in the form of half-cycle field waveforms that can be focused to yield a field strength of ≈ 5 M V / c m . At least 1.5% of the MMW–THz supercontinuum energy is emitted in the MMW range, giving rise to MMW field strengths up to 100 kV/cm in the beam waist region.

ADVANCED PROGRESS ON Χ<SUP>(3)</SUP> NONLINEARITY IN CHIP-SCALE PHOTONIC PLATFORMS (INVITED REVIEW)

“…PC is a key technology for generating ultrashort pulses, which are widely used in optical communication systems [149], SC and frequency comb generation [150], ultrafast spectroscopy [151], and biology [152]. While many applications benefit from pulses with ultrashort duration and high average power, it is a challenge to simultaneously achieve both with a laser.…”

Powerful terahertz waves from long-wavelength infrared laser filaments

“…Since then, two more experiments on two-color filamentation have demonstrated the significant enhancement of the THz yield for 3.9 μm laser pulses 91 , 92 . In both of them, THz radiation was studied as a part of the broadband supercontinuum generated by 3.9 μm two-color laser pulses jointly with the supercontinuum of higher harmonics.…”

“…In the second experiment, carried out by Mitrofanov et al 92 , THz generation by 3.9 μm two-color laser pulses was studied in various gases (helium, argon, nitrogen, air, and krypton) under different pressures. Gases with a lower ionization potential were shown to provide a higher THz yield.…”

Intensity-surged and Bandwidth-extended Terahertz Radiation in Two-foci Cascading Plasmas

“…The temporal and spatial mixing of strong fundamental frequency (ω) and second harmonic (2ω) laser fields in gas-phase medium can produce a ultrashort terahertz (THz) pulse [1]. Given the absence of emitter damage and absorption, the two-color scheme is particularly promising for intense and broadband THz radiation [2][3][4]. The wonderful characteristics of the THz source has already been used in time-resolved terahertz spectroscopy [5][6][7] and transient absorption spectroscopy [8].…”