Propagation Of Femtosecond Laser Pulses Research Articles

Efficient single-cycle mid-infrared femtosecond laser pulse generation by spectrally temporally cascaded optical parametric amplification with pump energy recycling.

We proposed spectrally temporally cascaded optical parametric amplification (STOPA) using pump energy recycling to simultaneously increase spectral bandwidth and conversion efficiency in optical parametric amplification (OPA). Using BiB3O6 and KTiOAsO4 nonlinear crystals, near-single-cycle mid-infrared (MIR) pulses with maximum energy conversion efficiencies exceeding 25% were obtained in simulations. We successfully demonstrated sub-two-cycle, CEP-stable pulse generation at 1.8 µm using a four-step STOPA system in the experiment. This method provides a solution to solve the limitations of the gain bandwidth of nonlinear crystals and the low conversion efficiency in broadband OPA systems, which is helpful for intense attosecond pulse generation and strong laser field physics studies.

The Effect of Turbulence on Generation of High-Intensity Light Channels during Femtosecond Laser Pulse Propagation along a 100-Meter Air Path

The Effect of Turbulence on Generation of High-Intensity Light Channels during Femtosecond Laser Pulse Propagation along a 100-Meter Air Path

Proposal of a novel analytical method for simultaneous ultra-broadband and ultrashort laser pulses generation in photonic crystal fibers with optimized manufacturing process

In this paper, a novel method for simultaneous ultra-broadband and ultrashort femtosecond laser pulse generation in silica photonic crystal fibers is investigated analytically using the fully vectorial effective index method (FVEIM). By reducing the impact of fifth and lower-order dispersions, the method produces narrower laser pulses and wider supercontinuum using a fixed soliton order over a specific distance of the fiber. Additionally, the larger effective areas utilized in this approach make the manufacturing process simpler compared to other samples. These simultaneous features represent the primary innovations of this study.

Manipulation of femtosecond laser filamentation by wire mesh amplitude mask

The results of numerical simulation on the propagation of high-power femtosecond laser pulses in air under conditions of the amplitude modulation are presented. Laser pulse amplitude modulation is realized by using the metal mesh-masks, which divide the initial laser beam into lower-energy parts (subbeams). We show that, in general, the beam energy partitioning by metal meshes reduces the total length of beam filamentation region in air, whereas the longitudinal continuity of the laser plasma distribution in the filaments is considerably improved. A strong dependence of the filamentation region parameters (starting coordinate, length, longitudinal continuity) on the position of the mesh-mask relative to the laser beam axis is also revealed. It turns out that under certain conditions, when the beam axis points to the mesh crossing, the spatial position of the filaments can be shifted further along the propagation path by increasing the size of the mesh cells. Alternatively, if the beam center exposes the mesh cell opening, the filamentation start coordinate decreases monotonically when the mesh becomes sparser. Additionally, the parameters of the filamentation region exhibit high sensitivity to the mesh wire thickness that can dominate the influence of mesh position and cell size.

Simulation of nonlinear propagation of femtosecond laser pulses in air for quantitative prediction of the ablation crater shape.

The utilization of sub-100 fs pulses has attracted attention as an approach to further improve the quality and precision of femtosecond laser microfabrication. However, when using such lasers at pulse energies typical for laser processing, nonlinear propagation effects in air are known to distort the beam's temporal and spatial intensity profile. Due to this distortion, it has been difficult to quantitatively predict the final processed crater shape of materials ablated by such lasers. In this study, we developed a method to quantitatively predict the ablation crater shape, utilizing nonlinear propagation simulations. Investigations revealed that the ablation crater diameters derived by our method were in excellent quantitative agreement with experimental results for several metals over a two-orders-of-magnitude range in the pulse energy. We also found a good quantitative correlation between the simulated central fluence and the ablation depth. Such methods should improve the controllability of laser processing with sub-100 fs pulses and contribute to furthering their practical application to processes over a wide pulse-energy range, including conditions with nonlinear-propagating pulses.

Review on Ultra-Long Distance Propagation of Femtosecond Laser Pulses for Remote Sensing Applications

Review on Ultra-Long Distance Propagation of Femtosecond Laser Pulses for Remote Sensing Applications

The condition of collapse stopping during propagation of high-power femtosecond laser pulses in an optical medium

The condition of collapse stopping during propagation of high-power femtosecond laser pulses in an optical medium

Nonlocality-driven switchable fast-slow light effect in hyperbolic metamaterials in epsilon-near-zero regime

The recent surge of optics of hyperbolic metamaterials (HMMs) has been fueled by their fascinating optical properties, one of the most intriguing being their strong optical nonlocality. In this work we demonstrate that in metal nanorod-based HMMs the nonlocality results in fast and slow light effects in the propagation of femtosecond laser pulses in close spectral vicinity of the HMM epsilon-near-zero regime. These effects are switchable via the angle of incidence and light wavelength. We elucidate that revealed dynamical phenomena stem from the zero-transmission points of HMM and related phase singularities caused by the destructive interference of the main optical wave and the additional wave mediated by the spatial dispersion of light in the HMMs.

Propagation of High-Power Phase-Modulated Femtosecond Laser Pulses in Air in the Self-Channeling and Filamentation Modes

Propagation of High-Power Phase-Modulated Femtosecond Laser Pulses in Air in the Self-Channeling and Filamentation Modes

Self-channeling of spatially modulated femtosecond laser beams in the post-filamentation region

The propagation of high-intensity femtosecond laser pulses in air under conditions of superposed spatial phase modulation is considered theoretically. The numerical simulations are carried out on the basis of the reduced form of a nonlinear Schrödinger equation for a time-averaged electric field envelope. Initial spatial modulations are applied to pulse wavefront profiling by a staggered ( T E M 22 ) phase plate, which is simulated numerically. The dynamics of laser pulse self-focusing, filamentation, and post-filamentation self-channeling after the phase plates with variable phase jumps is studied. We show that, with specific phase modulations, the pulse filamentation region in air can be markedly shifted further and elongated compared with a nonmodulated pulse. Moreover, during the post-filamentation propagation of spatially structured radiation, the highly localized light channels are formed, possessing enhanced intensity and reduced angular divergence, which enables post-filamentation pulse self-channeling on the distance multiple exceeding the Rayleigh range.

Emission of conical THz radiation induced by bichromatic pumpXwaves in an air plasma

The $X$-wave formation during the propagation of bichromatic femtosecond laser pulses in an air plasma filament and THz radiation generation has been investigated both experimentally and theoretically. We found that in this case the pump waves as well as THz radiation propagate as $X$ waves at the same group velocity. Therefore, the cone angle of generated THz radiation could be estimated using the $X$-wave dispersion law. Hence, the proposed model allows an alternative characterization of generated THz radiation based on the frequency-angular spectra of pump waves registered after propagation in the created plasma filament.

Propagation of phase-modulated high-power femtosecond laser pulses in the self-channeling and filamentation mode in air

Propagation of phase-modulated high-power femtosecond laser pulses in the self-channeling and filamentation mode in air

Time-frequency analysis of light-bullet dynamics during femtosecond filamentation in the anomalous dispersion regime

In this paper, we investigate the light-bullet dynamics during femtosecond laser filamenation in an anomalous dispersion regime based on the experimentally observed blueshifted resonant radiation (RR) in fused silica. A numerical simulation is performed and well reproduces the pronounced asymmetric feature of the RR spectra. By applying a time-frequency analysis to the propagating laser field, this specific spectral feature is found to be closely connected to the positively chirped property of RR in the time domain. In the context of the effective three-wave mixing model, this temporal chirp character of the RR is ascribed to the variable phase-matching conditions, which can be traced back to the accelerative propagation of the light bullet during its formation. Our work provides a deep understanding of the spatiotemporal dynamics of femtosecond laser-pulse propagation in condensed media.

Temporal visualization of femtosecond laser pulses with single-edge transport in turbid media via Monte Carlo simulation.

We study the propagation of femtosecond laser pulses with a single (front or rear) edge or dual edge through turbid media via Monte Carlo simulation. The results show that both the transmitted pulses spread on the basis of the incident pulse width ${t_{p}} = {{100}}\;{\rm{fs}}$, arising from the scattering effect. Further, the broadening width of the incident laser with a dual-edge pulse is wider than that of the incident laser width a single-edge pulse. The effect of the scattering particles on the front edge and the rear edge of the femtosecond laser can be distinguished in the time domain for femtosecond laser pulses through turbid media with the optical depth (OD) less than 10. In this scattering regime, the front-edge pulse scattered by the particles contributes more to diffused photons, but the effect of the scattering particles on the front edge and the rear edge of the femtosecond laser cannot be discriminated in turbid media with the OD more than 10, where the scattering is dominated by multiple scattering.

Superluminal and slow femtosecond laser pulses in hyperbolic metamaterials in epsilon-near-zero regime

Flourish of optics of hyperbolic metamaterials (HMMs) is stimulated by their exotic optical properties. Here, we demonstrate resonant changes of the group retardation and superluminal-like propagation of femtosecond laser pulses in nanorod-based HMMs in the vicinity of epsilon-near-zero spectral point responsible for the transition between topologically distinct elliptic and hyperbolic light dispersions. Resonant dynamics of ultrashort pulses appears in a unique case when their spectral components are in both dispersion regimes simultaneously. Our findings suggest HMMs as a powerful platform for future ultrafast photonics and are pivotal for growing nonlinear optics of hyperbolic media.

Generation of wideband tunable femtosecond laser based on nonlinear propagation of power-scaled mode-locked femtosecond laser pulses in photonic crystal fiber* *Project supported by the National Natural Science Foundation of China (Grant No. 61805274), the Major Program of the National Natural Science Foundation of China (Grant No. 12034020), and Research Foundation of Inner Mongolia University of China (Grant No. 21200-5215108).

We implement an experimental study for the generation of wideband tunable femtosecond laser with a home-made power-scaled mode-locked fiber oscillator as the pump source. By coupling the sub-100 fs mode-locked pulses into a nonlinear photonic crystal fiber (NL-PCF), the exited spectra have significant nonlinear broadening and cover a spectra range of hundreds of nm. In experiment, by reasonably optimizing the structure parameters of NL-PCF and regulating the power of the incident pulses, femtosecond laser with tuning range of 900–1290 nm is realized. The research approach promotes the development of femtosecond lasers with center wavelengths out of the traditional laser gain media toward the direction of simplicity and ease of implementation.

Electronic and vibrational processes in absorbing liquids in femtosecond laser sub- and filamentation regimes: ultrasonic and optical characterization

The ultrasonic characterization of the propagation of femtosecond laser pulses in pure transparent water and colored phenol-red dye solutions at variable concentrations indicates their thermoacoustic pressure generation due to intrinsic multi-photon absorption in the low-power sub-filamentation regime and sub-linear pressure response of sub-critical plasma via free-carrier absorption in the filamentation regime. Multi-photon absorption appears to be concentration dependent for water and dye solutions, while plasma absorption demonstrates a universal trend for all these liquids. In the filamentation regime, through the non-linear laser-matter interactions, not only new optical frequencies (intense white-light supercontinua) were generated, but supercontinuum-based ultrafast broadband spectroscopy in the filaments also revealed many additional transient absorption bands of the dye molecules, induced via power-dependent and concentration-independent stimulated Raman scattering.

Nonlinear beam self-imaging and self-focusing dynamics in a GRIN multimode optical fiber: theory and experiments.

Beam self-imaging in nonlinear graded-index multimode optical fibers is of interest for many applications, such as implementing a fast saturable absorber mechanism in fiber lasers via multimode interference. We obtain a new exact solution for the nonlinear evolution of first and second order moments of a laser beam of arbitrary transverse shape carried by a graded-index multimode fiber. We have experimentally directly visualized the longitudinal evolution of beam self-imaging by means of femtosecond laser pulse propagation in both the anomalous and the normal dispersion regime of a standard telecom graded-index multimode optical fiber. Light scattering out of the fiber core via visible photo-luminescence emission permits us to directly measure the self-imaging period and the beam dynamics. Spatial shift and splitting of the self-imaging process under the action of self-focusing are also revealed.

Rotational quantum beat lasing without inversion

In standard lasers, light amplification requires population inversion between an upper and a lower state to break the reciprocity between absorption and stimulated emission. However, in a medium prepared in a specific superposition state, quantum interference may fully suppress absorption while leaving stimulated emission intact, opening the possibility of lasing without inversion. Here we show that lasing without inversion arises naturally during propagation of intense femtosecond laser pulses in air. It is triggered by the combination of molecular ionization and molecular alignment, both unavoidable in intense light fields. The effect could enable inversionless amplification of broadband radiation in many molecular gases, opening unusual opportunities for remote sensing.

Engineering black titanium dioxide by femtosecond laser filament

We propose an approach, by utilizing the propagation of femtosecond laser pulses in the filamentation region in air, to achieve black titanium dioxide (TiO2), a promising material for efficient photocatalysis. It is found that the black TiO2 engineered by femtosecond laser filament in both solution and air environments shows significantly improved absorption in a broad spectral range from 400 to 2500 nm. In addition, the engineered black TiO2 shows a certain degree of enhanced absorption in the microwave range. The structural and elemental analyses of the processed TiO2 suggest that the absorption enhancement is mainly ascribed to the filament-induced disorder and dopant impurity in the surface layer of crystalline TiO2. Our technique provides an alternative way to engineer black TiO2 with the capability of absorbing the solar energy across a broad spectrum that can be useful for various applications in optoelectronics and photochemistry.