A. Stabinis

Conversion of topological charge of optical vortices in a parametric frequency converter

Abstract It is shown that sum-frequency generation of light beams with vortices allows to construct vortices of different topological charges. An optical parametric amplifier enables to produce a vortex with opposite topological charge (to the reverse vortex). In this way, a frequency converter can be seen as a prototype of an optical processor which allows to produce simple arithmetical operations with topological charges of the interacting vortices.

Effective sum frequency pulse compression in nonlinear crystals

Abstract Sum frequency (SF) generation in the case of strong energy exchange and group velocity mismatch may lead to very effective SF pulse compression. The conditions needed for effective compression of SF pulses are found. It is possible to produce SF pulses the duration of which is sufficiently smaller than the initial duration of the pump pulses and almost the total energy of the pump pulses is converted into the SF wave. By this technique the 3 ps pump pulses (λ=1.06 μm) can be converted into a ≈3 cm KDP crystal to a 200 fs SF pulse (λ=0.53 μm) if the intensity of the pump pulses is ≈3 GW/cm 2 .

Angular structure formation in single-pass optical parametric generators pumped by intersecting beams

Investigation results of angular structure formation in a picosecond traveling-wave optical parametric generator (OPG) based on a KDP crystal (type II phase matching) pumped by intersecting beams are presented. It is demonstrated that the angular structure of the OPG output radiation is controlled by pump geometry. Frequency-tuned diffraction-limited output even in a single-pass OPG was observed.

NONCOLLINEAR SECOND-HARMONIC GENERATION IN PERIODICALLY POLED KTIOPO4 EXCITED BY THE BESSEL BEAM

Frequency doubling in periodically poled KTiOPO(4) excited by the Bessel-like distribution of the fundamental radiation has been investigated. Theoretical analysis and experiments show that the use of noncollinear geometry provides new possibilities for engineering nonlinear interactions in periodically poled crystals. We demonstrate conversion of the ring-shaped fundamental mode to the axial second-harmonic beam with 30% efficiency for 220-muJ Q -switched Nd:YAG pulses.

Two-beam pumped travelling-wave optical parametric generator

Abstract The investigation results of a subnanosecond travelling-wave optical parametric generator (OPG) based on KDP crystal (type II phase matching) pumped by two intersecting beams are presented. It is found that the broad angular and frequency spectrum of OPG caused by noncollinear interactions can be significantly reduced by means of the double phase matching in the field of two pump beams. Two-beam pump technique should be very promising in picosecond and subpicosecond travelling-wave OPG to produce bandwidth- and diffraction-limited output.

Optical parametric oscillation excited by an incoherent conical beam

Abstract The operation of a KTP optical parametric oscillator pumped by an incoherent conical beam is demonstrated for the first time. The incoherent conical beam was produced by nonaxial excitation of a multimode fiber. It is shown that the OPO output radiation pattern in the far field consists of a coherent central spot (signal) and an incoherent ring (idler). The incoherence of the pump was transferred to the idler wave in accordance with theoretical predictions. By adjusting the OPO cavity mirrors, the lowest-order mode as well as higher-order transverse modes were easily selected in the central spot.

OPTICAL PARAMETRIC OSCILLATOR PUMPED BY A BESSEL BEAM

We demonstrate operation of a KTP optical parametric oscillator (OPO) pumped by a Bessel beam for the first time to our knowledge. It is shown that the output of the OPO has a transverse profile, which is consistent with noncollinear phase-matching relations defined by a conical pump. The central spot and ring related to the pair of signal and idler beams were generated in the OPO. By adjusting the OPO cavity mirrors, we easily selected the lowest-order mode as well as the higher-order transverse modes in the central spot. Bessel beam pumping was shown to be useful, providing tubular beam coupling into OPO cavity modes. The OPO threshold pump energy was ~100 muJ in a 6-ns pulse.

Free-space propagation of overlapping light vortex beams

The propagation of a combined beam consisting of two noncoaxial vortex beams is investigated. It is demonstrated that the vortical properties of the combined beam under diffraction depend on propagation length as well as on amplitude ratio of individual beams.

Ultrabroad Bandwidth of Optical Parametric Amplifiers

Optical parametric chirped pulse amplifiers (OPCPAs) are widely recognized and rapidly developing devices for high-power femtosecond pulse generation. In this paper we reveal the main issues of OPCPA gain bandwidth extension for amplification of pulses with octave-spanning spectra.

Characterization of phase modulated ultrashort pulses using single-shot autocorrelator

Abstract It is shown that the spatial properties of the second harmonic (SH) beam produced by a single-shot autocorrelator arrangement provide information about pulse spectrum and phase along with that about the pulse envelope. The intensity distribution in the beam, after free propagation over some distance, is equivalent to the autocorrelation trace of a pulse which has passed a negatively dispersive medium of a certain length. In the case of a regularly chirped pulse the beam exhibits cylindrical focusing (or defocusing) and the beam waist corresponds to the halfwidth of the autocorrelation trace of an optimally compressed pulse.