Abstract-Terahertz emission from a weakly-coupled GaAs/AlGaAs superlattice biased into three different modes of current self-oscillations

AIP Advances

G. K. Rasulova,  I. V. Pentin,  G. N. Goltsman

Electroluminescence spectrum of three coupled SL mesas (black line) measured at 8 K. Inset displays the reference square pulses of 1 V height and 330 Hz repetition rate (blue) and the pulsed current response (yellow) where the self-oscillations of current appear in half a period of the applied pulses. The EL spectrum of the SL sample with two coupled mesas11 is shown by blue line.

https://aip.scitation.org/doi/10.1063/1.5116014

Radio-frequency modulated terahertz (THz) emission power from weakly-coupled GaAs/AlGaAs superlattice (SL) has been increased by parallel connection of several SL mesas. Each SL mesa is a self-oscillator with its own oscillation frequency and mode. In coupled non-identical SL mesas biased at different voltages within the hysteresis loop the chaotic, quasiperiodic and frequency-locked modes of self-oscillations of current arise. THz emission was detected when three connected in parallel SL mesas were biased into the frequency-locked and quasiperiodic modes of self-oscillations of current, while in the chaotic mode of those it falls to the noise level.

Abstract-Optical excitation of surface plasmons and terahertz emission from metals

I. V. Oladyshkin, D. A. Fadeev, and V. A. Mironov

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.100.085421

We propose a microscopic theory of terahertz (THz) radiation generation on metal gratings under the action of femtosecond laser pulses. In contrast to previous models, only low-frequency currents inside the metal are considered without involving electron emission and acceleration. The presented model generalizes thermal mechanism of THz response for the case of structured surfaces, when temperature gradients inside the electron gas can be enhanced by excitation and absorption of surface plasmons. Performed numerical calculations reproduce specific experimental features like delayed character of THz response and low conversion efficiency when the grating depth is too large.

• 
• 
• 
• 

Abstract-Study of terahertz emission from nickel (Ni) films of different thicknesses using ultrafast laser pulses

M. Venkatesh, S. Ramakanth, A. K. Chaudhary, and K. C. James Raju
https://www.osapublishing.org/ome/abstract.cfm?uri=ome-6-7-2342

The nickel (Ni) films of three different thicknesses, 65 nm, 135 nm and 1018 nm, were deposited by the RF magnetron sputtering technique. These films were subjected to femtosecond laser pulses of ~140 fs duration at 80 MHz repetition rate for generation of terahertz (THz) radiation. The obtained electromagnetic radiation was detected using photoconductive antennas by a sampling technique. The THz generation mechanism of Ni films is attributed to the ultrafast demagnetization process and its time depends on the Gilbert damping factor. The ascertained values of the Gilbert damping parameter of Ni films using ferromagnetic resonance (FMR) measurements lies between 0.011 and 0.0069. We have observed that the amplitude of emitted THz radiation from Ni films is proportional to Gilbert damping factor of films. The amplitude of emitted THz radiation from 65 nm Ni film is 1.19 and 1.66 times higher than 135 and 1018 nm films.

© 2016 Optical Society of America

Full Article  |  PDF Article

Abstract-Terahertz emission from laser-induced microplasma in ambient air

Terahertz emission from laser-induced microplasma in ambient air Fabrizio Buccheri and Xi-Cheng Zhang  »View Author Affiliations

Optica, Vol. 2, Issue 4, pp. 366-369 (2015)
http://dx.doi.org/10.1364/OPTICA.2.000366

http://www.opticsinfobase.org/optica/abstract.cfm?uri=optica-2-4-366

View Full Text Article

Enhanced HTML    Acrobat PDF (127

The integration of ambient air plasmas as source and sensor in terahertz time-domain techniques allows spectral measurements covering the elusive terahertz gap (0.1–10 THz), further increasing the impact of those scientific tools in the study of the four states of matter. In this article we describe the experimental study of the terahertz emission from a laser-induced plasma of submillimeter size. The main direction of emission is almost orthogonal to the laser propagation direction, unlike that of elongated plasmas. We show that laser pulse energies lower than 1 μJ are sufficient to generate measurable terahertz pulses from ambient air. This significant decrease in the required laser energy will make plasma-based terahertz techniques more accessible to the scientific community.

© 2015 Optical Society of America

Abstract-Effect of an external electric field on the coherent terahertz emission from multiple filaments in air

• Sergey I. Mitryukovskiy, 
• Yi Liu, 
• Bernard Prade, 
• Aurélien Houard, 
• André Mysyrowicz

http://link.springer.com/article/10.1007/s00340-014-5830-1

We describe the terahertz emission from multiple filaments in air in the presence of an external electric field. A strong enhancement of the radiated terahertz energy is obtained by the combined effect of terahertz field interference and presence of a static electric field.