Soliton formation in a femtosecond optical parametric oscillator

Cascaded nonlinearity induced spatial domain effects in a high power femtosecond optical parametric oscillator

We have investigated the effect of cascaded optical nonlinearity on the spatial beam properties of a femtosecond optical parametric oscillator (OPO). The OPO was operated with a tunable phase mismatch by varying the angle of the nonlinear crystal. The cascaded nonlinearity induced self-focusing and defocusing changed resonator's stability and impacted mode properties. With tuning of a phase mismatch, the calculated parabolic part of cascaded nonlinearity lens focal length changes from f ∼ 30 mm (D ∼ 33 m^-1 at Δθ ∼ -0.5^o) to infinity and back to f ∼ -110 mm (D ∼ -9 m^-1 at Δθ ∼ 0.9^o) in the LBO nonlinear crystal. Such high power nonlinear lenses in a cavity operated near its stability limit promoted the generation of axially asymmetric or pass-to-pass unstable resonator modes. It was shown that phase mismatched optical parametric oscillation changes the physical character of the resonator from linear to ring-like with two nonlinear crystals having two different focusing powers. Calculations showed that the QCN induced spatial nonlinear phase should lead to severe longitudinal chromatic aberrations for broad spectrum pulses. A numerical simulation in XYZ spatial domain and calculations using ABCD matrix approach confirmed the physical mechanisms underlying the experimental results and allowed for the interpretation of the observed effects.

Multi-soliton formation in femtosecond degenerate optical parametric oscillators

Multi-soliton formation is observed theoretically and experimentally in femtosecond degenerate optical parametric oscillators (OPOs). We show that when the pulse energy of the pump source of a femtosecond OPO is increased to a certain level, the existing soliton will move towards the leading edge of pump pulses due to the enhanced nonlinear acceleration, and the undepleted pump energy will support the generation of more solitons. We have successfully observed the generation of double solitons and triple solitons in experimental demonstrations with the measured pulse characteristics agreeing well with the theoretical ones. The generation of multi-soliton sources may stimulate many novel applications, including data storage, telecommunication, and all-optical signal processing.

Efficiency signal conversion parameter to evaluate astigmatic femtosecond-optical parametric oscillator cavities

In this work, we define the efficiency signal conversion numerical parameter, V_eff, useful to evaluate the operation efficiency of femtosecond-Optical Parametric Oscillator (fs-OPO) cavities considering the astigmatism effect. For the validation of the V_eff, we have performed experimental measurements. We present different high efficiency home-made singly resonant fs-OPO cavities, with signal tuneability from 1.1 µm to 1.6 µm based on a 0.5 mm Periodically Poled Lithium Niobate doped with MgO (MgO:PPLN) crystal. We have also defined the pump energy threshold per crystal unit length, ζ_p,th. Pump threshold, achieved by following the V_eff, was 142 mW at 810 nm, and ζ_p,th = 2.10 nJ/mm, the lowest value, in comparison with other studies. The V_eff is based on an ABCD matrix Gaussian beam propagation method, which calculates the mode coupling between the pump and signal beams along the crystal under different cavity configurations taking into account the astigmatism. The model was compared and tested with 3 different experimental singly resonant fs-OPO ring cavity configurations that we have defined as single-folded, two-folded, and direct-pump cavity.

Spectrotemporal dynamics of a picosecond OPO based on chirped quasi-phase-matching

We report on the first experimental investigation of the spectral dynamics of a synchronously pumped optical parametric oscillator (OPO) by use of dispersive Fourier transformation. For standard pumping rates, we observe a reproducible steady-state pulse-to-pulse spectrum. However, at high pumping levels, the OPO delivers pulse trains with nontrivial oscillatory spectral patterns. So as to benefit from a tailored broadband gain spectrum, the investigated OPO contains a chirped quasi-phase matching (QPM) nonlinear crystal. We explore the specific impacts of using such a remarkable parametric amplification medium where nonlinearly coupled frequencies vary with position. Depending on the QPM chirp rate sign, a red- or blue-shift of the emitted wavelength occurs when the OPO is switched on, leading to different spectral steady-states. These singular spectrotemporal dynamics are evidenced and explained for the first time.

Ultra-broadband pulse evolution in optical parametric oscillators

Ultrashort-pulse evolution inside a optical parametric oscillator is described by using a nonlinear-envelope-equation approach, eliminating the assumptions of fixed frequencies and a single χ((2)) process associated with conventional solutions based on the three coupled-amplitude equations. By treating the interacting waves as a single propagating field, the experimentally-observed behaviors of singly and doubly-resonant OPOs are predicted across near-octave-spanning bandwidths, including situations where the nonlinear crystal provides simultaneous phasematching for multiple nonlinear processes.

Body-centered cubic dissipative crystal formation in a dispersive and diffractive optical parametric oscillator

We show that coupling diffraction and chromatic dispersion lead to body-centered cubic and hexagonally packed cylinders of dissipative optical crystals in a degenerate optical parametric oscillator. The stabilization of these crystals is a direct consequence of the interaction between the modulational and the quasi-neutral modes.

Walking cavity solitons

A family of walking solitons is obtained for the degenerate optical parametric oscillator below threshold. The loss-driven mechanism of velocity selection for these structures is described analytically and numerically. Our approach is based on understanding the role played by the field momentum and generic symmetry properties and, therefore, it can be easily generalized to other dissipative multicomponent models with walk off.

Parametric Generation of Tunable Light from Continuous-Wave to Femtosecond Pulses

By exploiting nonlinear optical effects, a technology of unprecedented flexibility for the production of tunable coherent light has been developed. Referred to as optical parametric generation, it provides sources with spectral coverage extending all the way from the ultraviolet to the mid-infrared, and with temporal coverage extending over all time domains from the femtosecond pulse to the continuous wave. Such sources generate coherent light of outstanding optical quality and are now finding wide-ranging applications.

Solitons of singly resonant optical parametric oscillators

Single resonant parametric oscillators including intracavity quadratic and cubic nonlinearities are described in the mean-field limit with a cubic and quintic complex Ginzburg-Landau equation. Following our model, simple design criteria are derived for the generation of solitonlike pulses and beams for singly resonant optical parametric oscillators.

Excitation and bistability of self-trapped signal beams in optical parametric oscillators

In a doubly resonant degenerate optical parametric oscillator below threshold the signal beam can be trapped in the form of stable bright temporal or spatial solitons. We characterize these soliton families and discuss how to excite them.

Pulse-train generation through modulational instability in intracavity second-harmonic generation

We show, taking dispersion into account, that second-harmonic generation in a cavity can be modulationally unstable. In the monostable mode of operation this instability might predominate with respect to self-pulsing instabilities, leading to the generation of stable solitarylike pulse trains.

Noncritically phase-matched Ti:sapphire-pumped femtosecond optical parametric oscillator based on RbTiOAsO(4)

The operation of a Ti:sapphire-laser-pumped femtosecond optical parametric oscillator based on the new nonlinear material RbTiOAsO(4) is described. Oscillation has been observed for pump powers as low as 50 mW, and output powers as high as 185 mW have been measured. With intracavity prisms for dispersion compensation, transformlimited pulses of less than 70-fs duration have been produced. Under noncritical phase matching, a signal (idler) tuning range over 110 nm (330 nm) is demonstrated with pump tuning.