Conical Third-Harmonic Generation in Normally Dispersive Media

Abstract

It is shown, both theoretically and experimentally, that in normally dispersive media under tight-focusing conditions third harmonic is generated by six-wave mixing rather than via common third-order frequency tripling. Though far-field pattern of third-harmonic signal was an axially symmetric ring for a wide range of the material wave vector mismatch and laser beam focusing conditions, in some cases the generation of more complex beams has been found possible. Results of simulations of the proposed model qualitatively correspond well with experimental data for the calculated values of third- and fifth-order nonlinear susceptibilities of sodium.

Temporal dynamics of the internally generated radiations in a two-photon excited four-level potassium atom

“…four-level schemes in alkalis) interacting coherently with a number of fields, either externally applied or internally generated by the atomic system, has received attention, as indicated by [2][3][4][5][6][7][8][9][10][11] (see, in particular, the review article [4] on Na and references therein). A specific case concerns an excitation scheme whereby strong nanosecond (ns) or femtosecond (fs) laser pulses, tuned near a two-photon resonance, are used in order to study the atomic system dynamics, in combination with the propagation of the emitted radiation, in a vapour cell [12][13][14]. Interesting and promising studies, based on the off-resonantly excited atoms by truncated optical ns laser pulses, investigating an atomic system's dynamics have also been implemented [6,15].…”

“…in the visible and ultraviolet (UV) spectral regions [1,14]. In [13] conical THG was interpreted as a sixwave mixing process rather than a four-wave one. Hence, under strong focusing conditions a high-order multi-wave mixing process seems to take place, while for maximum conversion efficiency, phase matching is required (the phase velocities of the fundamental and the generated TH waves have to be equal).…”

“…Under such conditions it has been possible to observe conical third harmonic generation (THG) [13,14]. The production of THG can be seen as an important and well-established experimental technique that can up-convert the coherent output of laser sources to shorter wavelengths, i.e.…”

“…Interesting and promising studies, based on the off-resonantly excited atoms by truncated optical ns laser pulses, investigating an atomic system's dynamics have also been implemented [6,15]. Wellknown nonlinear phenomena, such as partially coherent amplified spontaneous emission (ASE), stimulated hyper Raman scattering (SHRS) and coherent parametric four-wave mixing (PFWM), result from such excitation schemes [2][3][4][5][7][8][9][10][11][12][13][14]. These partially coherent processes appear when the laser is tuned on or off an atomic resonance, giving rise to forward and backward propagating radiations [16].…”

Emissions from high-density potassium atoms excited by either nanosecond or femtosecond laser pulses

“…Thus, the nonlinear wave mixing in gaseous media [1][2][3] has been widely used for a variety of applications, such as the frequency conversion of laser radiation, the optical quantum memory induction and the internal emission of strong coherent fields [4][5][6][7][8][9][10][11][12]. Parametric light generation [1,13], stimulated hyper Raman scattering (SHRS), amplified spontaneous emission (ASE) [1,3], six-and four-wave mixing (FWM) [2,8,14,15] and third-harmonic generation [16] are the most widely studied nonlinear processes that take place in these atomic systems. In addition, the laser-atom interaction, with co-propagating beams, may result in destructive quantum interference (QI) between the pump and emitted radiation, in the ns (nanosecond) or fs (femtosecond) excitation case [1-9, 11, 12, 15].…”