[PDF]    https://doi.org/10.3952/physics.v58i1.3652

Open access article / Atviros prieigos straipsnis

Lith. J. Phys. 58, 62–75 (2018)
SPATIAL AND TEMPORAL COHERENCE IN OPTICAL PARAMETRIC DEVICES PUMPED WITH MULTIMODE BEAMS
Valdas Pašiškevičiusa, Valerijus Smilgevičiusb, Rytis Butkusb, Riaan Coetzeea, and Fredrik Laurella
aDepartment of Applied Physics, Royal Institute of Technology, Roslagstullsbacken 21, 10691 Stockholm, Sweden
bLaser Research Center, Vilnius University, Saulėtekio 10, 10223 Vilnius, Lithuania
E-mail: vp@kth.se

Received 16 January 2018; accepted 22 March 2018

We investigate the emergence of spatial and temporal coherence for the fields in the noncritical nondegenerate parametric second-order down-conversion process pumped with low spatial and temporal coherence beams. It is shown that in this scenario, which is of considerable practical importance, the parametric gain in the near field breaks down into an ensemble of mutually incoherent beamlets containing parametric waves. The field generated in a single beamlet is fully spatially coherent. The size of such coherent parametric gain regions is governed by the near-field spatial coherence radius of the pump, which also acts as a parameter, restraining the linear diffraction of the parametric waves generated in the nonlinear interaction. Furthermore, we experimentally demonstrate how the spatial and temporal coherence can be substantially enhanced by manipulating the spatial field correlation of the multi-longitudinal and multi-transversal mode pump.
Keywords: optical parametric generators and oscilliators, nonlinear optical ferroelectric structures, temporal and spatial photon correlations, spatial and temporal coherence
PACS: 42.65.Lm, 42.65.Yj, 42.70.Mp

DAUGIAMODŽIAIS LAZERIAIS KAUPINAMŲ OPTINIŲ PARAMETRINIŲ DAŽNIO KEITIKLIŲ SPINDULIUOTĖS ERDVINIS IR LAIKINIS KOHERENTIŠKUMAS
Valdas Pašiškevičiusa, Valerijus Smilgevičiusb, Rytis Butkusb, Riaan Coetzeea, Fredrik Laurella

aKarališkasis technologijos institutas, Stokholmas, Švedija
bLazerinių tyrimų centras, Vilnius, Lietuva

Darbe tiriamas erdvinio ir laikinio koherentiškumo atsiradimas ir vystymasis neišsigimusio antros eilės parametrinio šviesos generavimo procesuose, realizuotuose feroelektriniuose dariniuose, kurie kaupinami daugiamodžių lazerių spinduliuote. Darbe parodoma, kad šiomis sąlygomis, kurios yra aktualios praktiniams taikymams, parametrinės spinduliuotės erdvinis skirstinys kristale užgimsta kaip tarpusavyje nekoreliuotų parametrinės spinduliuotės gijų ansamblis, kur pavienė tos spinduliuotės gija turi visišką erdvinį koherentiškumą. Mažas kaupinimo erdvinio koherentiškumo spindulys, būdingas didelės energijos daugiamodžių lazerių spinduliuotei, lemia parametrinio stiprinimo gijų skersinius matmenis ir padeda apriboti tiesinės difrakcijos sukeliamą parametrinės spinduliuotės gijų išplitimą. Remdamiesi šiais pastebėjimais mes eksperimentiškai pademonstravome, kad manipuliuojant daugiamodžio kaupinimo lauko erdvinėmis koreliacijomis netiesiniame kristale įmanoma padidinti generuojamos parametrinės spinduliuotės erdvinį ir laikinį koherentiškumą.


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