CC BY
9THz-I-8
Terahertz emission from ionized air under single-color filamentation
L.V. Seleznev, G.E. Rizaev, D.V. Pushkarev, A.V. Koribut, Y.A. Gerasimova, Y.V. Grudtsyn, S.A. Savinov, Y.A. Mityagin, D.V. Mokrousova, A.A. Ionin
P.N. Lebedev Physical Institute of RAS, 53 Leninski pr., Moscow, Russia
The presentation shows the results of an experimental study of the THz emission in the plasma of a single-color filament. The different wavelengths of filamented laser pulse (940, 740, and 370 nm) are used in the study. Particular attention is paid to the study of the frequency-angular distribution of the THz emission within 0.1 - 3 THz spectral range. It is shown that different spectral components of THz radiation have various angular distribution. It is shown that an increase in the laser beam number aperture leads to a growth in the THz emission divergence (Fig.1), especially in its low-frequency range.
a " . ■ ■ ■
- ■ ■
■ ■
■ AA ■ • ■
M* A AAA • ' • •• A 1« : ■ A • ■
: • A • A A •
• • • •
• A «A A A •
■ 0.1 THz
• 0.3 THz
A 0.5 THz
-20 0 20 Angle, degree
b
r
v
i ■
• A
A •
A A«
■ 0.1 THz
• 0.3 THz
A 0.5 THz
T 1 THz
-10 0 10 Angle, degree
Fig.1. Angular distribution of different spectral components of THz radiation observed at various beam number aperture 2 10-2 (a) and 5 10-3.
The study showed a significant effect on the THz radiation characteristics of the initial wavelength of laser pulse. Transformation of frequency-angular THz emission spectrum produced by single-color (740 nm) laser filament plasma under an external electrostatic field of various strength is experimentally studied also. While there is no any static electric field, THz emission is predominantly generated in the low-frequency spectral range around 0.1 THz and propagates within a hollow cone. When the electric field is applied, the transition from the hollow cone to a filled one is observed with the field strength rise, THz emission frequency being within of 0.3 - 0.5 THz. Higher frequency emission of ~1 THz fills the whole cone with the emission maximum along the laser filament axis. The angular distribution for the low-frequency THz emission depends significantly on the laser pulse energy in contrast to the case of no electric field. An increase in the laser pulse energy leads to a decrease of the propagation angles for low-frequency THz emission and to disappearance of the local minimum in the angular distribution on the propagation axis.
The research is supported by RFBR grant 20-02-00114.
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