We study the second-harmonic generation in quadratic nonlinear media with localized spatial modulation of χ(2) response. We demonstrate that the emission of Čerenkov second-harmonic takes place only when the fundamental beam illuminates the region of χ(2) variation. This proves that the sharp modulation of the χ(2) nonlinearity constitutes a sufficient condition for the emission of Čerenkov second harmonic in bulk materials. Our calculations are in excellent agreement with simple analytical approach utilizing the concept of reciprocal vectors representing the Fourier spectrum of the modulation of χ(2).
[Show abstract][Hide abstract] ABSTRACT: Nanosecond Čerenkov-type conical beam at 628 nm is obtained by intracavity sum frequency mixing (SFM) of 1064 and 1534 nm in KTiOAsO<sub>4</sub> (KTA) crystal. The 1534 nm signal generated by the KTA optical parametric oscillation (OPO), respectively, interacts with the orthogonally polarized 1064 nm radiations by the nonlinear Čerenkov SFM, emitting two red rings with cone angles of 11.4° and 16.0°, respectively. Multidomain structure observed in the KTA crystal can account for the corresponding phenomenon. The KTA crystal simultaneously serves as OPO medium and Čerenkov radiation emitter in this experiment, indicating that it is a promising multifunctional nonlinear crystal material. Furthermore, the naturally grown crystal combined with intracavity Čerenkov-type configuration will provide a simple and compact approach, opening a door for the wide application of nonlinear Čerenkov radiation sources due to its cost-effectiveness.
[Show abstract][Hide abstract] ABSTRACT: Nonlinear optical Cerenkov emission represents the type of noncollinear parametric process where the direction of the generated wave is defined by the longitudinal phase matching condition . In the simplest case of Čerenkov second harmonic generation (ČSHG), the radiation of the doubled frequency is observed at the angle defined as cosθ= 2k1/k2cosa, where k1 and k2 denote the wave vectors of the fundamental and the second harmonic (SH) waves, respectively, and a is the incident angle of the fundamental wave. Recently the ČSHG has attracted lots of attention because of the efficient noncollinear SHG eliminating the necessity of filtering out the incident wave in all-optical signal processing. Moreover, it also enables the spatial control of the generated wave front, e.g. forming the radially polarized Bessel beam.
International Quantum Electronics Conference; 05/2013
[Show abstract][Hide abstract] ABSTRACT: We demonstrate a method to generate enhanced nonlinear Cherenkov radiation (NCR) in the bulk medium by utilizing the total reflection on the physical boundaries inside the crystal. This is the experimental demonstration of enhanced NCR by a sharp chi((2)) modulation from 0 to 1, and a new way for generating enhanced NCR in addition to using the waveguide structures and the ferroelectric domain walls, which also possesses a better beam quality for applications. (C) 2013 Optical Society of America
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