Observation of Temporal Solitons in Second-Harmonic Generation with Tilted Pulses (original) (raw)
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Temporal solitons in (2) materials with tilted pulses
Journal of The Optical Society of America B-optical Physics, 1999
We investigate the possibility of obtaining temporal bright solitons in three-wave parametric interaction by using the pulse tilt to modify the effective dispersion of the nonlinear crystal. We show that, in the largebeam approximation, the temporal evolution of the tilted pulse can be described by (1 ϩ 1)-dimensional equations, which account for the tilt by means of effective group-velocity mismatch and dispersion coefficients. Numerical calculations show that the soliton regime is accessible in several experimental conditions. The limit of the (1 ϩ 1)-dimensional approximation is investigated with the aid of a (2 ϩ 1)-dimensional model.
Temporal modulational instability of spatial solitons in second-harmonic generation
Nonlinear Guided Waves and Their Applications, 2004
Spatial solitons in second-harmonic generation show regular, high-frequency, temporal modulation 1.5-times above threshold. The result is interpreted as the first observation of their temporal modulational instability. Simulations indicate that instability is seeded by quantum noise.
Journal of the Optical Society of America B, 1998
The spectral and temporal characteristics and optical-conversion efficiency of ϳ150-fs laser pulses at 400 nm generated by second-harmonic generation (SHG) of a regeneratively amplified mode-locked Ti:sapphire laser were investigated both theoretically and experimentally. The theoretical investigation was done by taking into account cubic nonlinearity, pulse walk-off, group-velocity dispersion, Kerr nonlinearity, quadratic broadening, frequency chirping of the fundamental pulse, and higher-order nonlinear mixing such as backconversion and optical parametric processing. The experimental studies of the effects of crystal length and pumping intensity on the pulse duration, the spectrum, and the optical-conversion efficiency of the SHG were carried out in BBO and LBO crystals of various thicknesses and compared with the theory. It was found that in a nontransform-limited pulse, the most significant contribution to the temporal and spectral distortion of the ϳ150-fs SHG pulses is mainly due to the chirping of the fundamental beam and self-phase modulation at high pumping intensity and long crystal length. The optimum crystal length and pumping intensity for obtaining a high optical-conversion efficiency and a pure spectrum in SHG are also calculated and experimentally investigated. It was found that a transform-limited fundamental pulse is essential to obtain a high conversion efficiency and to preserve the temporal profile of the second-harmonic pulse. It is also found that for a nontransform-limited ϳ150-fs pulse, a 0.5-0.6-mm BBO crystal and a modest pumping intensity of ϳ40 GW/cm 2 are the most suitable for SHG.
Asymmetric spatio-temporal optical solitons in media with quadratic nonlinearity
Optics Communications, 1998
We find exact one-parameter families of stationary two-dimensional light bullets in the form of solitons localized in space and time in diffractive and dispersive nonlinear media under conditions for second-harmonic generation. We study the shape and various features of the solitons, including their stability during propagation, with emphasis on the general case of unequal group-velocity dispersions for the fundamental and second-harmonic waves when the transverse spatio-temporal shape of the solitons is asymmetric. It is shown that, when propagating in two-dimensional geometries, most of the spatio-temporal solitons are dynamically stable. q 1998 Elsevier Science B.V. All rights reserved. 0030-4018r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved.
Observation of multiple soliton generation mediated by amplification of asymmetries
Physical Review E, 2003
We report the experimental observation of the formation of multiple optical quadratic solitons in a process mediated by the amplification of minute asymmetries in the diffraction properties of the input light. Experiments were conducted in phase-matched second-harmonic generation in a bulk crystal of periodically poled potassium titanyl phosphate pumped at 1064 nm. The different mechanisms that influence the process were investigated numerically, and the pulsed nature of the pump light was found to play a key role in the observed light distributions.
Optical Materials Express, 2013
We discuss a novel method for generating octave-spanning supercontinua and few-cycle pulses in the important mid-IR wavelength range. The technique relies on strongly phase-mismatched cascaded second-harmonic generation (SHG) in mid-IR nonlinear frequency conversion crystals. Importantly we here investigate the so-called noncritical SHG case, where no phase matching can be achieved but as a compensation the largest quadratic nonlinearities are exploited. A self-defocusing temporal soliton can be excited if the cascading nonlinearity is larger than the competing material self-focusing nonlinearity, and we define a suitable figure of merit to screen a wide range of mid-IR dielectric and semiconductor materials with large effective second-order nonlinearities d eff . The best candidates have simultaneously a large bandgap and a large d eff . We show selected realistic numerical examples using one of the promising crystals: in one case soliton pulse compression from 50 fs to 15 fs (1.5 cycles) at 3.0 µm is achieved, and at the same time a 3-cycle dispersive wave at 5.0 µm is formed that can be isolated using a long-pass filter. In another example we show that extremely broadband supercontinua can form spanning the near-IR to the end of the mid-IR (nearly 4 octaves).
Optical-parametric-oscillator solitons driven by the third harmonic
Physical Review E, 2004
We introduce a model of a lossy second-harmonic-generating (χ (2) ) cavity externally pumped at the third harmonic, which gives rise to driving terms of a new type, corresponding to a cross-parametric gain. The equation for the fundamental-frequency (FF) wave may also contain a quadratic self-driving term, which is generated by the cubic nonlinearity of the medium. Unlike previously studied phase-matched models of χ (2) cavities driven at the second harmonic (SH) or at FF, the present one admits an exact analytical solution for the soliton, at a special value of the gain parameter. Two families of solitons are found in a numerical form, and their stability area is identified through numerical computation of the perturbation eigenvalues (stability of the zero solution, which is a necessary condition for the soliton's stability, is investigated in an analytical form). One family is a continuation of the special analytical solution. At given values of parameters, one soliton is stable and the other one is not; they swap their stability at a critical value of the mismatch parameter. The stability of the solitons is also verified in direct simulations, which demonstrate that the unstable pulse rearranges itself into the stable one, or into a delocalized state, or decays to zero. A soliton which was given an initial boost C starts to move but quickly comes to a halt, if the boost is smaller than a critical value C cr . If C > C cr , the boost destroys the soliton (sometimes, through splitting into two secondary pulses). Interactions between initially separated solitons are investigated too. It is concluded that stable solitons always merge into a single one. In the system with weak loss, it appears in a vibrating form, slowly relaxing to the static shape. With stronger loss, the final soliton emerges in the stationary form.
Few-cycle solitons in short strongly phase-mismatched frequency conversion crystals
2011
Cascaded nonlinearities have attracted much interest, but ultrafast applications have been seriously hampered by the simultaneous requirements of being near phase matching and having ultrafast femtosecond response times. Here we show that in strongly phase-mismatched nonlinear frequency conversion crystals the pump pulse can experience a large and extremely broadband self-defocusing cascaded Kerr-like nonlinearity. The large cascaded nonlinearity is ensured through interaction with the largest quadratic tensor element in the crystal, and the strong phase-mismatch ensures an ultrafast nonlinear response with an octave-spanning bandwidth. We verify this experimentally by showing few-cycle soliton compression with noncritical cascaded second-harmonic generation: Energetic 47 fs infrared pulses are compressed in a just 1-mm long bulk lithium niobate crystal to 17 fs (under 4 optical cycles) with 80% efficiency, and upon further propagation an octave-spanning supercontinuum is observed. Such ultrafast cascading is expected to occur for a broad range of pump wavelengths spanning the near-and mid-IR using standard nonlinear crystals.
Stabilization of spatiotemporal solitons in second-harmonic-generating media
2009
We report the results of a systematic analysis of the existence and stability of spatiotemporal (twodimensional) solitons (STSs) in the model of a planar waveguide with the intrinsic v ð2Þ nonlinearity. Fundamental obstacles to the creation of STSs under physically realistic conditions are the normal sign of the group-velocity dispersion (GVD) at the second harmonic (SH), and the significant group-velocity mismatch (GVM) between the SH and fundamental-frequency (FF) components. To construct STS solutions in a numerical form, we adjust the iterative method, which was recently used for finding temporal (one-dimensional) v ð2Þ solitons in a similar setting. We identify effective existence borders for the STSs, within which the energy loss to the generation of extended ''tails" in the SH component (due to the normal sign of the GVD) is negligible. It is demonstrated that the existence region can be made much broader by means of the GVD-management and GVM-management techniques. We also explore interactions between the STSs, and find robust two-soliton bound states, with a moderate separation in the longitudinal (temporal) direction. Head-on collisions between the STSs are always destructive.
Physical Review A, 2019
We studied generation and dynamics of solitonic pulses, platicons, at normal group velocity dispersion due to the pump amplitude modulation. We proposed, that if the required frequency of amplitude modulation is too large for available modulators, it is possible to use subharmonic phase modulation for platicon generation. It was also demonstrated that it is possible to control the repetition rate of platicons by tuning modulation frequency. Tuning range for platicons was found to be much wider than for bright solitons. We also studied the influence of the high-order dispersion on platicon properties. It was shown that both third-order dispersion and pump modulation govern platicon dynamics making it quite different from dynamics of dissipative Kerr solitons. Third-order dispersion was also shown to affect significantly the optimal conditions for the platicon generation and repetition rate tuning range.