Dynamics Of Femtosecond Pulses Research Articles

Self-interaction of ultrashort pulses in an epsilon-near-zero nonlinear material at the telecom wavelength.

Dynamics of femtosecond pulses with the telecom carrier wavelength is investigated numerically in a subwavelength layer of an indium tin oxide (ITO) epsilon-near-zero (ENZ) material with high dispersion and high nonlinearity. Due to the subwavelength thickness of the ITO ENZ material, and the fact that the pulse's propagation time is shorter than its temporal width, multiple reflections give rise to self-interaction in both spectral and temporal domains, especially at wavelengths longer than at the ENZ point, at which the reflections are significantly stronger. A larger absolute value of the pulse's chirp strongly affects the self-interaction by redistributing energy between wavelengths, while the sign of the chirp affects the interaction in the temporal domain. It is also found that, when two identical pulses are launched simultaneously from both ends, a subwavelength counterpart of a standing-wave state can be established. It shows robust energy localization in the middle of the sample, in terms of both the spectral and temporal intensity distributions.

High-energy femtosecond pulse shaping, compression, and contrast enhancement using multicore fiber

Nonlinear spatiotemporal dynamics of femtosecond pulses in a hexagonal seven-core silica fiber pumped by a sub-μJ 370fs Er:fiber chirped pulse amplification (CPA) system were studied. Nonlinear pulse shaping and compression in the central core and pedestal coupling to the outer cores were directly measured by frequency-resolved optical gating. Further compression of the pulses spectrally broadened in the multicore fiber down to 53fs was demonstrated. Two orders of magnitude contrast enhancement of the pulses after compression was observed.

Panoramic-reconstruction temporal imaging for seamless measurements of slowly-evolved femtosecond pulse dynamics

Single-shot real-time characterization of optical waveforms with sub-picosecond resolution is essential for investigating various ultrafast optical dynamics. However, the finite temporal recording length of current techniques hinders comprehensive understanding of many intriguing ultrafast optical phenomena that evolve over a timescale much longer than their fine temporal details. Inspired by the space-time duality and by stitching of multiple microscopic images to achieve a larger field of view in the spatial domain, here a panoramic-reconstruction temporal imaging (PARTI) system is devised to scale up the temporal recording length without sacrificing the resolution. As a proof-of-concept demonstration, the PARTI system is applied to study the dynamic waveforms of slowly evolved dissipative Kerr solitons in an ultrahigh-Q microresonator. Two 1.5-ns-long comprehensive evolution portraits are reconstructed with 740 fs resolution and dissipative Kerr soliton transition dynamics, in which a multiplet soliton state evolves into a stable singlet soliton state, are depicted.

Femtosecond filamentation of optical vortex in a medium with anomalous group velocity dispersion

Within the framework of the slowly varying wave approximation method, the pictures of spatio-temporal dynamics of femtosecond pulse in a ring beam with phase singularity were obtained during propagation in CaF 2 crystal with anomalous group velocity dispersion. We show formation of tubular structure of the beam and explain reasons of its appearance. Fluence and linear plasma concentration dependencies on propagation distance are analyzed.

Comparison of femtosecond pulse dynamics in a PCF amplifier with backward and forward pump schemes

A comparative study of femtosecond pulse dynamics in a photonic crystal fiber amplifier with backward and forward pump schemes is demonstrated experimentally and numerically. The output power, pulse duration and spectrum width of the amplified soliton pulse at different pump powers under the two pump schemes are discussed. The results show that the evolution of the soliton pulse shape in the temporal and spectral domains is also dependent on the direction of pump besides the output power. A narrower pulse duration and spectral width (i.e. smaller time-bandwidth-product), the much less nonlinearity accumulation (i.e. smaller B-Integral value) and a higher output power can be obtained in the backward pump scheme compared to that in the forward pump scheme. The physical origin can be explained by the interaction among group-velocity dispersion, self-phase modulation and nonuniform gain distribution along the fiber due to different end-pump directions. The results provide convincing support to choose the backward pump scheme rather than the forward pump scheme in soliton amplification region in a femtosecond fiber amplifier.

Energy deposition dynamics of femtosecond pulses in water

We exploit inverse Raman scattering and solvated electron absorption to perform a quantitative characterization of the energy loss and ionization dynamics in water with tightly focused near-infrared femtosecond pulses. A comparison between experimental data and numerical simulations suggests that the ionization energy of water is 8 eV, rather than the commonly used value of 6.5 eV. We also introduce an equation for the Raman gain valid for ultra-short pulses that validates our experimental procedure.

Study of femtosecond soliton dynamics in photonic crystal fiber using the moment method

We investigate the dynamics of femtosecond solitons in photonic crystal fibers (PCFs) by including high-order dispersion terms until to sixth-order in the generalized nonlinear Schrödinger equation, in addition to the nonlinear effects of the self phase modulation, self steepening and Raman scattering. We calculate theoretically the pulse parameters using the moment method. In the case of the fundamental soliton, our computed equations are coupled and difficult to solve analytically. However, we use the finite difference method to calculate numerically pulse parameters using an initially hyperbolic secant pulse at 1550-nm with different peak powers along 10m-PCF. Our numerical results show that the nonlinear regimes allow obtaining pulse compressions and initial pulse amplitudes. Furthermore, we remark a pulse broadening, and weak shifts of the peak power positions and frequencies in the critical and dispersive regimes. The use of an initial chirp provides a better pulse compressions and especially for low input powers. Also, the initial positive chirp reduces the optimal compression position lengths, while the negative one increases them. Therefore, we conclude that our theoretical calculations and numerical simulation results show that the moment method associated with the finite differences method is effective for the study of femtosecond pulse dynamics in PCFs.

Propagation dynamics of femtosecond pulse through subwavelength metallic hole arrays

We have studied the frequency-dependent transmission time delay of femtosecond (fs) laser pulses through subwavelength hole arrays in aluminum films using the up-conversion technique. The pulse delays measured at different wavelengths mainly follow the far-field transmission profile of the surface-plasmon polariton (SPP) resonances. Temporal delays of 60 and 100 fs were found at the major SPP resonance in the single-layer and double-layer samples. A coupled-SPP transmission model is used to explain the temporal dynamics of the transmission process. Our experiment shows that the weak coupling between the SPP waves on different metal-dielectric interfaces leads to the large temporal delay of the transmitted pulses.

Interpretation of the spectrally resolved far field of femtosecond pulses propagating in bulk nonlinear dispersive media

It has previously been realized that angle-resolved spectra (or far-field spectra) reflect in detail the complex dynamics of femtosecond pulses propagating in nonlinear dispersive media [J. Opt. Soc. Am. B 22, 862 (2005)], and thus represent a potentially useful experimental diagnostic tool. In this paper we extend an effective three-wave mixing approach previously applied to nonlinear X-waves [Phys. Rev. Lett. 92, 253901 (2004)] to the analysis of far-field spectra. Theoretical justification for the approach is presented, and a practical method is proposed that makes it possible to interpret all features of far-field spectra, and to extract quantitative information about the underlying intra-pulse dynamics.

Dynamics of femtosecond pulses with a continuous spectrum in nonlinear waveguides

Dynamics of femtosecond pulses with a continuous spectrum in nonlinear waveguides

Polarization dynamics of femtosecond pulses propagating in air.

Polarization dynamics of femtosecond light pulses propagating in air is studied by computer simulation. A rich variety of dynamics is found that depends on the initial polarization state and power of the pulse. Effects of polarization on the plasma and supercontinuum generation are also discussed.

Nonlinear propagation dynamics of an ultrashort pulse in a hollow waveguide

We present a theoretical investigation of the self-focusing dynamics of femtosecond pulses in a hollow waveguide. We show that transverse effects play an important role in these dynamics, even for pulses that are significantly below the critical power for self-focusing in free space, and that excitation of higher-order modes of the waveguide results in the spreading of the pulse in time. Inclusion of self-steepening and space-time focusing in our model is necessary for properly capturing the pulse dynamics.

Method for analyzing the propagation dynamics of femtosecond pulses with a continuum spectrum in transparent optical media

Method for analyzing the propagation dynamics of femtosecond pulses with a continuum spectrum in transparent optical media