Generation of strong terahertz fields exceeding 8 MV/cm at 1 kHz and real-time beam profiling

Abstract

We demonstrate high-field (>8 MV/cm) terahertz generation at a high-repetition-rate (1 kHz) via two-color laser filamentation. Here, we use a cryogenically cooled femtosecond laser amplifier capable of producing 30 fs, 15 mJ pulses at 1 kHz as a driver, along with a combination of a thin dual-wavelength half-waveplate and a Brewster-angled silicon window to enhance terahertz generation and transmission. We also introduce a cost-effective, uncooled microbolometer camera for real-time terahertz beam profiling with two different modes.

Nonlinear distortion of intense THz beams

“…While for many new applications it is important to increase the THz yield further [13][14][15], little attention has been paid so far to spatial characteristics of the generated THz beam, even though different methods are available for the measurement of beam properties [16][17][18]. The spatial emission characteristics of air plasma THz sources have recently been studied [18,19], but less detailed experiments have been performed for TPFP in LN [20]. It was shown theoretically that distortions in the imaging system can lead to strongly distorted THz beam profiles [8], but possible nonlinear effects were not considered.…”

High field terahertz emission from relativistic laser-driven plasma wakefields

“…2 In the laser-based schemes, THz pulses with field strength > 8 MV/cm at 1 KHz repetition rate have been generated via two-color laser filamentation. 3 Single-cycle THz pulse with field strength up to 36 MV/cm can be generated by optical rectification of a midinfrared laser in a large-size nonlinear organic crystals assembly. 4 In addition, other methods that have produced high field THz pulses include difference frequency mixing process of two near-infrared lasers in second-order nonlinear crystals, but only with components > 20 THz, 5 and optical rectification in lithium niobate (LiNbO 3 ) crystals with tilted laser front, but mostly limited to < 1.5 THz.…”

Scheme to extend the range of electro-optic sampling of an intense terahertz field

“…An intense THz radiation field can be produced by overlapping the second harmonics onto the fundamental beam and then focusing into the air to form plasma, where four-wave rectification and a photocurrent model are used to explain the underlying physics [6,7]. Under optimized conditions, the field intensity of the plasma induced THz emission can reach 8 MV/cm [8] at a repetition rate of 1 kHz. The method of difference frequency mixing of two infrared (IR) laser pulses has produced the strongest THz field of 108 MV/cm [9], but in a relatively higher frequency range of >20 THz.…”