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This study presents a novel way to increase the energy conversion efficiency of optical parametric amplification by eliminating the idler wave from the interaction using consecutive type-I and type-II amplification processes. By using the aforementioned straightforward approach the wavelength tunable narrow-bandwidth amplification with exceptionally high 40% peak pump-to-signal conversion efficiency and 68% peak pump depletion was achieved in the short-pulse regime, while preserving the beam quality factor of less than 1.4. The same optical layout can also serve as an enhanced idler amplification scheme.

Keywords: optical parametric amplification, absorption The amplification bandwidth of an optical parametric amplifier (OPA) defines the duration of the signal and idler pulse. Usually the OPA bandwidth is described by material dispersion and interaction geometry. The absorption of interacting waves is detrimental to the amplification process. However, even in the case of a large linear absorption of the idler wave it is still possible to get an effective amplification and a positive effect to the amplifier bandwidth. In the current work, we investigate the influence of idler wave linear losses on the OPA bandwidth.

Usually the absorption of interacting waves is detrimental to the parametric amplification process. We show that even in the case of large idler wave absorption it is possible to get highly efficient signal amplification as well as amplifier bandwidth enhancement due to back-conversion suppression. We numerically investigated the influence of the idler wave linear losses arising in the case of parametric amplification in 515 nm pumped BBO crystal tuned to signal amplification at 610 nm. The possibility to achieve ∼75% pump-to-signal energy conversion and amplification bandwidth of ∼900 cm-1 using collinear amplification scheme is demonstrated.

We demonstrate the formation possibilities of femtosecond highly localized few micron stationary beam in one transverse direction and hundreds of microns in perpendicular with the high focal depth via optical parametric amplification (OPA) process.

We demonstrate that using two nonlinear crystals cut for different phase matching types in an optical parametric amplification stage suppresses back-conversion, which results in considerable improvements of conversion efficiency and signal beam quality.

The bandwidth of the optical parametric amplification (OPA) defines the duration of the signal and idler pulse. In current work, we investigate the influence of the idler wave absorption to the OPA bandwidth.

In this paper we propose a method for pulsed conical wave parametric amplification (PCWPA) with subsequent spatio-temporal compression during propagation in free space. It is numerically demonstrated that Gaussian wave-packet can be reshaped into pulsed conical wave (PCW) just by means of lens and nonlinear crystal. We point out that performing the far field amplification of the PCW is the key for generation of localized PCWs with ultrahigh intensities. It allows to form ultra-intense and propagation invariant wave-packets capable to propagate over many Rayleigh range in the desired material. The method exploits achromatic phase matching and empowers the parametric amplification of bandwidths corresponding to few-cycle light pulses with Gaussian temporal spectrum. In contrast to ordinary chirped-pulse amplification technique it does not require a pulse compressor, thus greatly facilitates the parametric amplification of few-cycle light pulses.

The propagation of near-infrared ultra-short laser pulses in the regime of anomalous dispersion of transparent solids is associated with a host of self-induced effects including a significant spectral broadening extending from the ultraviolet into the infrared region, pulse self-compression down to few-cycle pulse durations, free and driven third harmonic generation, conical emission and the formation of stable filaments over several \(\mathop{\mathrm{cm}}\nolimits\) showing the emergence of conical light bullets. We review measurements performed in different experimental conditions and results of numerical simulations of unidirectional propagation models showing that the interpretation of all these phenomena proceeds from the formation of non-spreading conical light bullets during filamentation.

We study how the probability density function of a weak seed intensity is transformed in a nonlinear process such as optical parametric amplification. The character of the transformation strongly depends on the amplification regime accessed: in the small-gain (undepleted-pump) regime the statistics of the seed are transferred to the statistics of the amplified signal almost unaltered. In contrast, in the gain saturation regime the modification of the statistics is considerable. In particular, we demonstrate that rogue-wave-like (long-tailed) statistics of the seed are completely suppressed, and resulting probability distribution function of the amplified signal becomes Gaussian. The theoretical findings are supported by the experiments carried out in supercontinuum-seeded noncollinear optical parametric amplifier.

We demonstrate a simple method for infrared few optical-cycle pulse generation, which is based on collinear visible-to-infrared frequency conversion and involves difference-frequency generation and subsequent two-step optical parametric amplification. The numerical simulations and experiments using BBO crystals show an efficient frequency down conversion of visible ∼20 fs pulses from a commercial blue-pumped noncollinear optical parametric amplifier yielding 1.2–2.4 μm tunable sub-100 μJ pulses with duration of 3 to 5 optical-cycles. The proposed method could be readily extended to generate few optical-cycle pulses in the mid-infrared spectral range (up to 5.5 μm) using, e.g., LiIO3 and LiNbO3 crystals, as demonstrated by the numerical simulations. In these crystals, even shorter, two-optical-cycle mid-infrared pulses could be obtained at particular wavelengths where group velocity matching between the signal and idler waves is achieved.

The general concepts for generation and amplification of the X-pulses in optical parametric amplifiers under the plane-wave and localised (Bessel beam, or more generally, X-pulse) pump are reviewed. It is shown numerically and experimentally that X-pulse phase-matching gives rise to spontaneous emergence of the localised light structures in the regime of the parametric frequency down-conversion. The parametric amplification technique of localised waves is extended to the chirped X-pulse optical parametric amplification concept, which allows one to achieve few optical cycle, high-peak power localised wave packets for laser—matter interactions.

We report on four-wave optical parametric amplification of the ultrashort ultraviolet light pulses in bulk fused silica and CaF 2 . Exact phase-matching in these isotropic media is achieved by means of non-collinear interaction with cylindrical beam focusing. Four-wave optical parametric amplifier efficiently operates in the UV spectral range with 1-ps laser pulses, delivering amplified signal energy exceeding 50 μJ using millijoule pump pulses in the visible (527 nm). Results of scanning of the parametric gain profile suggest that broad amplification bandwidth as wide as ∼20 nm (at FWHM) under these experimental settings is achieved, which might support amplification of sub-10-fs ultraviolet pulses with central wavelength around 330 nm. It is also shown experimentally and verified theoretically that the parametric gain profile exposes a distinct inhomogeneity and its bandwidth notably broadens due to effects of self- and cross-phase modulation imposed by the intense pump beam.

We report on efcient generation of the ultrashort ultraviolet light pulses by means of phase-matched four-wave optical parametric amplication and four-wave difference frequency mixing in UV-transparent solids with cubic nonlinearity. Broadband four-wave optical parametric amplication around 330 nm is investigated theoretically and demonstrated experimentally in optically isotropic materials, such as fused silica and CaF2 crystals. The results suggest that powerful broadband ultraviolet pulses as short as 7.5 fs (in the transform limit) could be amplied in the eld of milijoule 1-ps visible pulses. Efcient generation of 1-ps pulses at the 3rd (351 nm), 5th (211 nm), and, in particular, 6th (176 nm) harmonics of the Nd:glass laser is experimentally demonstrated through non-collinearly phase-matched four-wave difference-frequency mixing in fused silica, CaF2 and MgF2 crystals.

We have studied filamentation of 1-ps laser pulses in a scattering medium (aqueous suspension of 2-μm polystyrene microspheres) and compared filamentation dynamics to that in pure water. Our results indicate that light scattering does not alter filamentation dynamics in general, but rather results in farther position of the nonlinear focus, shorter filament length, and the development of speckle structure in the peripheral part of the beam. The experimental observations are qualitatively reproduced by the numerical model which accounts for diffraction, self-focusing, multiphoton absorption, and light scattering introduced through a stochastic diffusion and diffraction term.

We report on filamentation and supercontinuum generation in polycrystalline ZnSe by intense femtosecond laser pulses whose center wavelength is tunable in the 1.5–2.4 μm range. By varying the input pulse energy, single and multiple filamentation regimes were accessed, as verified by the measurements of near field intensity distributions. Along with supercontinuum generation, efficient simultaneous generation of broadband second, third, and fourth harmonics is observed. We uncover that extremely efficient harmonics generation stems from randomly quasi phase matched three wave mixing processes, which are facilitated by filamentation of the input beam, as verified by the spectral and energy conversion dynamics, and by polarization measurements.

In this paper we review the conditions needed for the localization and stationarity of a wave packet during propagation in a linear transparent medium. The requirements on the dimensionality and spatiotemporal frequency content for wave packets with such characteristics are discussed. In particular, we demonstrate how the localization of the stationary two-dimensional solution of the propagation equation depends on the features and shape of its spatiotemporal spectral bandwidth. The spatiotemporal properties of the one-dimensional (1D) spatial and 1D temporal beams stationarily propagating in dispersive materials are illustrated both in the normal and in the anomalous dispersion regime. Published version

We present an investigation of supercontinuum, third and fifth harmonics generation in transparent dielectrics with few optical-cycle pulses at 2 µm, revealing a negligible role of higher order nonlinearities for intensities up to 15 TW/cm2.

We report on the experimental proof-of-principle demonstration of the ultrashort pulse single-pass beta-barium borate, BBO optical parametric amplifier pumped by two mutually incoherent laser sources. We show that the amplified signal at 1054 nm gains energy from both pump pulses with wavelengths of 680 and 527 nm, respectively, with overall energy conversion of 36%, and exhibits low wavefront distortions and improved energy stability in the gain saturation regime.

A novel and promising light pulse compression technique based on frequency conversion in nonlinear crystals is reviewed and discussed in some detail. Five- to sevenfold compression of light pulses of different wavelengths and initial pulse widths providing an intensity conversion rate as high as 400% is demonstrated. It is shown that adaptively tilted pulses ensure modification of group velocity mismatch of interacting pulses in a medium and significantly extend the list of suitable crystals as well as the pulse compression rate. The results of 1.3 ps tilted pulse compression up to 150 fs due to second- and third-harmonic generation in BBO II and KDP I crystals, respectively, are presented.

We demonstrate that conditions of group velocity mismatch required for nonlinear pulse compression in the ultraviolet can be achieved using pulses with properly tilted fronts. We also show that nonlinear compression of third-harmonic pulses can be performed in type I phase matching configuration. Experimentally we demonstrate the 351-nm pulse compression from 1.3 ps down to 140 fs using the frequency tripling scheme with predelay time.

We have experimentally demonstrated the generation of a powerful femtosecond pulse at 264 nm, starting with a picosecond pulse from a Nd:glass laser and using a nonlinearly compressed second-harmonic pulse. Fourth-harmonic pulses with durations between 130–370 fs have been generated in KDP and BBO crystals of various lengths. The consistency of the numerical and experimental data indicates that group-velocity mismatch and two-photon absorption are the main factors limiting the efficiency of the frequency quadrupling process with femtosecond pulses.

In this paper we illustrate how the localization of the stationary two-dimensional solution of the propagation equation strongly depends on the features of its spatio-temporal spectral bandwidth. We especially investigate the role of the ultra-broad temporal support and of the spatial bandwidth of the spectrum on the high localization in one spatial dimension of "Bessel-like" or "blade-like" beams, quasi-stationarily propagating in normally dispersive materials, and potentially interesting for microfabrication applications. © 2013 Optical Society of America.

We experimentally study filamentation and supercontinuum generation in a birefringent medium [beta-barium borate (β-BBO) crystal] pumped by intense 90 fs, 1.8 μm laser pulses whose carrier wavelength falls in the range of anomalous group velocity dispersion of the crystal. We demonstrate that the competition between the intrinsic cubic and cascaded-quadratic nonlinearities may serve as a useful tool for controlling the self-action effects via phase matching condition. In particular, we found that spectral superbroadening of the ordinary polarization is linked to three-dimensional self-focusing and formation of self-compressed spatiotemporal light bullets that could be accessed within a certain range of either positive or negative phase mismatch. In the extraordinary polarization, we detect giant spectral shifts of the second harmonic radiation, which are attributed to a light bullet-induced self-phase matching.

We propose a method for ultrashort pulse parametric visible-to-infrared frequency conversion. Our experiment demonstrate generation of sub-30-fs, sub-100 μJ pulses, broadly tunable across the infrared (1.1-3 μm) spectral range.

We present the results of theoretical, numerical and experimental study on transformation of chirped pulse spatio-temporal characteristics, when pump and signal pulse fronts are not matched during the amplification in noncollinear optical parametric chirped-pulse amplifier.

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.

We experimentally study the statistics of the white-light continuum generated by focusing of 130 fs, 800 nm pulses in a sapphire plate and show that the statistical distributions of the spectral intensity of the blue-shifted continuum components obey the extreme-value statistics. This rogue-wave-like behavior is detected only within a narrow input-pulse energy interval. By the use of numerical simulations, we show that the observed rogue-wave-like behavior is associated with pulse splitting and build-up of intense trailing pulse. The extreme events are thereafter suppressed by the intensity clamping.

Optical rogue waves, recently discovered by Solli et al. [1] constitute a fascinating topic in modern nonlinear optics. Until now, most of the knowledge on optical rogue waves is brought by the studies of supercontinuum generation in optical fibers under different operating conditions. However extreme-value statistics, the most prominent manifestation of rogue waves, is also inherent to various nonlinear optical systems, and to ultrashort pulse filamentation in particular [2].

Since 1961, when Franken and his collaborators experimentally discovered second-harmonic generation (SHG) [1], the process of SHG has been widely investigated leading first to important contributions by many authors, who derived the now well-known theory described in nonlinear optics books. It was realized long time ago that the use of short light pulses for SHG gives rise to special effects, like the broadening of the generated light pulse due to the group velocity mismatch between the fundamental (FH) and second-harmonic (SH) pulses, predicted by Comly and coworkers [2] and observed for the first time by Shapiro [3]. Typically SHG is investigated or used at or near the phase-matching condition, in such a way to maximize the conversion efficiency. More recently the study of propagation phenomena in phase-mismatched second-harmonic processes has attracted considerable interest, in particular for the investigation of the effect on the generated pulse shape. However, typically mentioned studies were done in the case when the plane wave approximation is valid and SHG could be recognized as one-dimensional problem.

We present experimental and numerical investigations of optical extreme (rogue) event statistics recorded in the regime of femtosecond pulse filamentation in water. In the spectral domain, the extreme events manifest themselves as either large or small extremes of the spectral intensity, justified by right- or left-tailed statistical distributions, respectively. In the time domain, the observed extreme events are associated with pulse splitting and energy redistribution in space and therefore are exquisitely linked to three-dimensional, spatiotemporal dynamics and formation of the $X$ waves.

This paper concerns the theoretical, numerical, and experimental study of the second-harmonic-generation (SHG) process under conditions of phase and group-velocity mismatch and aims to demonstrate the dimensionality transition of the SHG process caused by the change of the fundamental wave diameter. We show that SHG from a narrow fundamental beam leads to the spontaneous self-phase-matching process with, in addition, the appearance of angular dispersion for the off-axis frequency components generated. The angular dispersion sustains the formation of the short X pulse in the second harmonic (SH) and is recognized as three-dimensional (3D) dynamics. On the contrary, the large-diameter fundamental beam reduces the number of the degrees of freedom, does not allow the generation of the angular dispersion, and maintains the so-called one-dimensional (1D) SHG dynamics, where the self-phase-matching appears just for axial components and is accompanied by the shrinking of the SH temporal bandwidth, and sustains a long SH pulse formation. The transition from long SH pulse generation typical of the 1D dynamics to the short 3D X pulse is illustrated numerically and experimentally by changing the conditions from the self-defocusing to the self-focusing regime by simply tuning the phase mismatch. The numerical and experimental verification of the analytical results are also presented. © 2011 American Physical Society.

We study experimentally and numerically the spatiotemporal dynamics of the multiple filament arrays excited by self-focusing of intense elliptical laser beams in fused silica. Our results demonstrate that although multiple filament arrays emerge as apparently regular patterns in the space domain, the spatiotemporal dynamics of the individual filaments is governed by the input-beam power and the input-beam ellipticity. In the case of moderate input-beam ellipticity, the individual filaments propagate in curved trajectories arising from skewed (spatiotemporal) coherence. The spatiotemporal propagation dynamics is regularized by increasing the input-beam ellipticity, and in part due to permanent modifications of fused silica that occur under intense irradiation. In this case, strong pulse reshaping and shock-front generation are observed, which yields a regular array of very short ($l5$ fs) superluminally propagating localized peaks in the leading front, followed by the subpulses centered on the input-pulse top, and trailed by subluminally propagating pulses with rather complex transverse intensity distribution.

We show that cascading of the second-order processes under large group-velocity mismatch can lead to the efficient compression of pulses at fundamental frequency in the type II phase-matched second-harmonic-generation process. We demonstrate that any of three interacting pulses can be compressed if the proper ratio of intensities of the o- and e-polarized pump pulses is chosen on input. We experimentally achieved compression of o-polarized pulses from 1.3 ps down to 280 fs with energy conversion close to 50% when a conventional second-harmonic compressor with unbalanced intensities of the pump pulses was used.

Nearly transform-limited femtosecond pulses tunable from 635 to 3000 nm were generated by a traveling-wave type II phase-matching barium borate parametric generator pumped by the self-compressed second harmonic of a Nd:glass laser. A total conversion efficiency of 10% with output pulses as short as 200 fs has been achieved. Numerical simulation indicated that the relative amount of energy contained in the output pulse wings was reduced by ~4 × 104 compared with that in the pump.

Powerful ultrashort laser pulses reveal surprising features on the nature of light and matter interactions. Intense optical field modifies the refractive index of the medium through the optical Kerr effect and gives rise to self-focusing, self- and cross-phase modulation, spectral broadening, electron plasma generation, etc. The phenomenon, which couples these effects as a whole, is called femtosecond filamentation [1]. High-power laser beams break-up into multiple filaments (MFs) [2]. This process is governed by the growth of the wave-front perturbations that lead to random filament distribution over a given transverse plane. However, most of the applications require precise filament localization, and high MF pattern reproducibility is of paramount importance.

Here we report spontaneous conical wave formation in quadratic and cubic nonlinear media, demonstrating how the characteristics of the formed conical wave strictly depend on those of the pumping source.

We propose a method for amplification of complex localized ultrashort wave packets ($\mathsf{X}$ pulses or $\mathsf{X}$ waves). We present an analytical derivation and numerical simulations of broadband parametric amplification of chirped $\mathsf{X}$ pulses in a noncentrosymmetric medium with quadratic nonlinearity. Our results suggest that $\mathsf{X}$ pulses with particular spatial and temporal chirps can be efficiently amplified in an optical parametric amplifier and compressed down to a few tens of femtoseconds during free-space propagation.

We investigated the intensity-dependent loss properties of nonlinear crystals by using subpicosecond laser pulses at 264 and 211 nm. Two-photon absorption coefficients for potassium dihydrogen phosphate, beta-barium borate, and lithium triborate crystals were obtained from the intensity-dependent transmission measurements.

We present a short overview of recent advances in ultrashort pulse four-wave optical parametric amplification in transparent condensed bulk media with Kerr nonlinearity. Highly efficient (10% to 15% pump-to-signal energy conversion) four-wave optical parametric amplification in water and fused silica is experimentally demonstrated. The amplification process highly benefits from 1-dimensional spatial soliton propagation regime, which sets in under proper combination of cylindrical beam focusing and noncollinear phase matching geometry with millijoule pumping. Under these operating conditions, strong four-wave coupling quenches catastrophic beam break-up and filamentation, and the setup operates reasonably below the damage threshold of the nonlinear medium. The proposed methodology offers a number of advantages as compared to guided-wave configurations in gaseous media.

High-energy light pulses that are tunable from 1.1 to 2.6 mum, with a duration as short as 14.5 fs were generated in a type II phase-matching beta-BaB(2)O(4) traveling-wave parametric converter pumped by 18-fs pulses obtained from a Ti:sapphire laser with chirped-pulse amplification, followed by a hollow-fiber compressor.

Laser-pulse filamentation in Kerr media induced by a strongly elliptic input beam leads to breakup into a periodic array of filaments. In the plane of the filament array we observe strong Stokes and anti-Stokes emission at large angles. For 1 ps input pulses the measured angles are found to support two different phase-matching configurations: one nontransversally phase matched and the other perfectly phase matched. Shorter 200 fs pulses give rise to group-velocity-matched Raman conversion.

An appearance of nondiffracting X-waves from quantum noise parametric amplification by the Bessel beam pump is investigated. The numerical simulation results in ADP crystal and preliminary experimental data are presented.

We report on highly efficient four-wave optical parametric amplification in a water cell pumped by an elliptically shaped, ultrashort pulsed laser beam under non-collinear phase-matching configuration. Energy conversion from pump to parametric waves as high as 25 % is obtained owing to the achievement of 1-dimensional spatial-soliton regime, which guarantees high intensity over a large interaction length and ensures high beam quality.

Nonlinear pulse compression under special conditions of large group-velocity mismatch (GVM) and strong energy exchange suggested for the first time 8 years ago [1,2], was demonstrated to be a simple and efficient method to generate powerful femtosecond pulses via frequency doubling of picosecond Nd-laser pulses in KDP crystal. However, the direct transfer of this technique to other wavelengths or other well-developed laser sources (Ti:sapphire, for instance) encounters serious problems related to the lack of nonlinear crystals with suitable dispersive properties. To this regard, the use of tilted pulses offers unique possibility to adjust the GVM in a nonlinear crystal for a particular wavelength [3,4].

Three-dimensional reconstruction of light wave-packets with complex spatio-temporal profiles is obtained by means of a second order cross-correlation scheme with a transverse and temporal resolution of few tens of microns and of femtoseconds respectively.

We study the impact of the beam diameter on the spectrum of the instability in second harmonic generation, and we report direct evidence of a quantum origin of the instability of a spatial soliton. © 2005 IEEE.