Abstract-Terahertz Response from a Silicon Surface with Deposited Nanosized Gold Particles

• A. S. Sinko, 
• K. A. Moldosanov, 
• P. M. Solyankin, 
• I. A. Ozheredov, 
• A. P. Shkurinov, 

https://link.springer.com/article/10.3103%2FS875669901905008X

Terahertz emission spectra of the surface of silicon crystals with different types of conductivity were experimentally recorded upon excitation by femtosecond laser pulses at various temperatures. The observed features in the terahertz spectra of the silicon surface correspond to the energy structure of the impurity centers determining the type of conductivity of the sample. Comparison was made with the results obtained in the case of deposition of gold nanoparticles on a semiconductor surface. The spectral features of the surface with deposited nanoparticles are discussed using the terahertz re-emission mechanism in two-phonon absorption.

Abstract-Application of a Terahertz Multi-Frequency Radiation Source Based on Quantum-Cascade Lasers for Identification of Substances Basing on the Amplitude-Spectral Analysis of the Scattered Field

V. N. Aksenov, A. A. Angeluts, A. V. Balakin, E. M. Maksimov, I. A. Ozheredov, A. P. Shkurinov

https://link.springer.com/article/10.1007/s11141-018-9854-y

We demonstrate the possibility of using a multi-frequency terahertz source to identify substances basing on the analysis of relative amplitudes of the terahertz waves scattered by the object. The results of studying experimentally the scattering of quasi-monochromatic radiation generated by a two-frequency terahertz quantum-cascade laser by the surface of the samples containing inclusions of absorbing substances are presented. It is shown that the spectral features of absorption of these substances within the terahertz frequency range manifest themselves in variations of the amplitudes of the waves at frequencies of 3.0 and 3.7 THz, which are scattered by the samples under consideration.

Abstract-Ultrabroad terahertz spectrum generation from an air-based filament plasma

V. A. Andreeva, O. G. Kosareva, N. A. Panov, D. E. Shipilo, P. M. Solyankin, M. N. Esaulkov, P. González de Alaiza Martinez, A. P. Shkurinov, V. A. Makarov, L. Bergé, and S. L. Chin

https://journals.aps.org/prl/accepted/4507aYb8Wf411d4d98f601634b2a9b1dd8b3ddd05

We have solved the long standing problem of the mechanism of terahertz (THz) generation by a two-color filament in air and found that both neutrals and plasma contribute to the radiation. We reveal that contribution from neutrals by four-wave mixing is much weaker and higher in frequency than the distinctive plasma lower frequency contribution. The former is in the forward direction while the latter is in a cone and reveals an abrupt downshift towards near the plasma frequency. Ringshaped spatial distributions of the THz radiation are shown to be of universal nature and they occur in both collimated and focusing propagation geometries. Experimental measurements of the frequency-angular spectrum generated by 130-fs laser pulses agree with numerical simulations based on a unidirectional pulse propagation model.

Abstract-Transformation of terahertz spectra emitted from dual-frequency femtosecond pulse interaction in gases

                   

                                                      

A. V. Borodin, N. A. Panov, O. G. Kosareva, V. A. Andreeva, M. N. Esaulkov, V. A. Makarov, A. P. Shkurinov, S. L. Chin, and X.-C. Zhang  »View Author Affiliations

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-38-11-1906

We demonstrate that the two basic physical mechanisms of terahertz (THz) generation in a femtosecond filament, namely, the free electron photocurrent and the nonlinear polarization of neutrals, can be identified through the spectral analysis of THz radiation. The contribution from the photocurrent peaks at the units of THz, while the neutrals yield the peak at the tens of THz. We suggest the practical implementation of such spectral analysis by varying the initial transform-limited laser pulse duration.

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