Enhancement of THz Generation by Two-Color TW Laser Pulses in a Low-Pressure Gas
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Enhancement of THz Generation by Two-Color TW Laser Pulses in a Low-Pressure Gas Мaxim М. Nazarov 1 & Alexander V. Mitrofanov 1,2,3 & Dmitry A. Sidorov-Biryukov 1,3,4 & Mikhail V. Chasсhin 1,4 & Pavel A. Shcheglov 1 & Alexey M. Zheltikov 1,3,4,5 & Vladislav Ya. Panchenko 1,2,4 Received: 29 September 2019 / Accepted: 20 March 2020/ # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
We identify experimental conditions for efficient generation of THz pulses by high power near IR laser radiation: 2 TW, 30 fs, 800-nm laser pulses with their second harmonic were slightly focused in a low-pressure gas cell in such a way to avoid multiple filamentation and excessive ionization. This two-color scheme yields a microjoule level of THz pulses which is two orders of magnitude higher than the signal generated in the atmosphere of ambient air. Keywords Low pressure . Terawatt . Two-color . Filament . THz . Chirp . Plasma absorption . Saturation
1 Introduction Short pulses of electromagnetic radiation with an electric field strength of more than 1 MV/cm are increasingly used for particle acceleration, characterization of electron bunches, and strong-field laser-matter interaction studies. Such intense electromagnetic fields can be obtained now in the terahertz (THz) frequency range [1–5]. Long cycles of THz fields provide a more efficient driver for charged particles, enabling unique regimes of particle acceleration and powerful diagnostic tools for ultrashort electron bunches. Rapidly progressing short-pulse laser technologies allow efficient THz generation, offering an attractive alternative to large-scale free-electron-laser–based THz beamlines. Nonlinear crystals remain the most efficient source of high-field THz radiation reaching energy * Мaxim М. Nazarov [email protected]
1
National Research Center “Kurchatov Institute”, Moscow 123182, Russia
2
FSRC “Crystallography and Photonics” of the RAS, Leninsky Av. 59, Moscow 119333, Russia
3
Russian Quantum Center, Novaya 100, Skolkovo, Moscow Region 143025, Russia
4
Physics Department, M.V. Lomonosov Moscow State University, Moscow 119991, Russia
5
Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843, USA
Journal of Infrared, Millimeter, and Terahertz Waves
conversion efficiencies as high as 10−2 [6]. However, due to the limitations of the available crystal apertures and breakdown threshold of the material, this method of THz generation cannot be scaled to the multi-terawatt (TW)- and petawatt (PW)-peak–power laser pulses which have become available in many laboratories worldwide during the last decade. Ablation of metal foil by laser pulses is another method of intense THz field generation [7]. This method allows one to generate terahertz pulses with an energy of hundreds of microjoules. Unfortunately, it is limited by the need to continuously change the position of the target to avoid changes in conversion efficiency due to surface degradation, and it requires complicated optics to collimate THz radiation
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