Lithuanian Journal of Physics article / Lietuvos fizikos žurnalo straipsnis

GENERATION OF THz-RADIATION BY DIFFERENCE-FREQUENCY MIXING AT ONE- AND TWO-PHOTON RESONANCES
E. Gaižauskas^a, O. Balachninaitė^a, and O. Khasanov^b
^aLaser Research Center, Vilnius University, Saulėtekio 10, LT-10222 Vilnius, Lithuania
^bScientific-Practical Materials Research Center of the National Academy of Sciences of Belarus, P. Brovki 19, 220072, Minsk, Belarus
E-mail: eugenijus.gaizauskas@ff.vu.lt

Received 4 March 2014; accepted 29 May 2014

In this work, difference-frequency generation is theoretically analysed for the three-level quantum system, having forbidden in dipole approximation electronic and optically active vibration transitions from the ground state. Excitation of coherent phonon polaritons wave in the terahertz frequency range by an ultrashort optical pulse, being in the visible or near-infrared spectral regions, and injected pulse with frequency almost twice that of the pump is considered. Dynamics of terahertz radiation arising during excitation of both electronic and vibrational coherences at the two-photon and combined resonances in the ensemble of three-level quantum systems was evaluated.

Keywords: terahertz radiation, difference-frequency generation, two-photon resonance, coherent light and matter interaction
PACS: 42.6+5.-k,71.36.+c,78.20.-e

TERAHERCŲ SPINDULIUOTĖS GENERAVIMAS NAUDOJANT SKIRTUMINIO DAŽNIO MAIŠYMĄ ESANT VIENFOTONIAM IR DVIFOTONIAM REZONANSAMS

E. Gaižauskas^a, O. Balachninaitė^a, O. Khasanov^b
^aVilniaus universiteto Lazerinių tyrimų centras, Vilnius, Lietuva
^bBaltarusijos mokslų akademijos Mokslinis-praktinis medžiagotyros centras, Minskas, Baltarusija

Darbe teoriškai tiriama skirtuminio dažnio generavimo terahercų bangų ruože dinamika, naudojant keturbangį maišymą kvantiniame trijų lygmenų sistemų ansamblyje. Trijų lygmenų sistema šalia draustino (dipoliniu artiniu) šuolio iš pagrindinės į aukščiausią būseną turi ir optiškai aktyvų žemo dažnio šuolį į vibracinę būseną (fononą). Surištoji koherentinė elektromagnetinio lauko ir fononų būsena (poliaritoninė banga) sukuriama kaupinant skirtingų dažnių ultratrumpaisiais lazeriniais impulsais. Pirmasis dažnis ω_L matomame ar artimajame infraraudonųjų bangų ruože parenkamas taip, kad būtų tenkinama dvifotonio rezonanso sąlyga, o antrasis ω_P – artimas dvigubam kaupinimo dažniui (ω_P ~ 2ω_L). Kaupinimo artiniu įvertinta terahercų bangos generavimo dinamika demonstruoja optinio lyginimo (optical rectification, angl.) metodo realizavimo galimybes terpėse su centrine simetrija. Praktiškai pasiūlytas metodas galėtų būti taikomas technologiškai patraukliose optinio stiklo su įterptomis puslaidininkių nanodalelėmis terpėse, kurioms būdingi optiniai šuoliai į eksitonines būsenas, pasižymintys dideliu osciliatorių stipriu, o sužadinti koherentiniai eksitonai – ilga gyvavimo trukme, palyginti su ultratrumpųjų kaupinančių impulsų trukmėmis.

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