Simulation Of Pulse Propagation Research Articles

Double-pulse-laser volumetric modification of fused silica: the effect of pulse delay on light propagation and energy deposition.

Volumetric modification of dielectrics by ultrashort laser pulses is a complex dynamic phenomenon involving material photoexcitation and associated nonlinear processes. To achieve control over modification, it is necessary to gain a deep insight into the dynamics of laser-excited processes that can be realized using double-laser-pulse experiments with different time separations supported by numerical simulations. In this paper, we apply this approach to investigate fused silica modification with femtosecond laser pulses that provides time-resolved information about the dynamic behavior of the laser-excited bandgap material. It is shown that the laser-generated free-electron plasma causes a shielding effect for the following pulse with a characteristic duration of ∼600 fs after the pulse action. Within this time interval, the second pulse produces a reduced modification as compared to a longer time separation between pulses. For double pulses with different energies, it was found that the volumetric modification is stronger when a lower-energy pulse couples with material first. This is explained by the combination of the effects of the re-excitation of self-trapped excitons, which are generated as a result of free electron recombination and associated light shielding. Experimental results are supported by numerical simulations of double laser pulse propagation in nonlinear media based on Maxwell's equations. Our findings offer a route for better controlling the inscription of 3D photonic structures in bulk optical materials.

Statistical Simulation of Laser Pulse Propagation in Cirrus Clouds Accounting for Multiple Scattering

Statistical Simulation of Laser Pulse Propagation in Cirrus Clouds Accounting for Multiple Scattering

Predicting behavior of photonic crystal fiber lasers using artificial neural networks

Simulating pulse propagation within fiber lasers is a difficult and computationally demanding task, which limits the ability to accurately capture their complex nonlinear dynamics. This paper leverages artificial intelligence (AI) and artificial neural networks (ANN) to predict the output pulse shape parameters for a ring cavity fiber laser, thus avoiding the need for traditional complex numerical calculations and reducing the overall computational cost. This study focuses on a dissipative soliton resonance (DSR) ring cavity fiber laser, incorporating a photonic crystal fiber (PCF) and mode locked by a real saturable absorber. The integration of the PCF into the laser cavity design enhances the control of both dispersion and nonlinearity, allowing for a greater range of output pulse shapes and parameters. The proposed approach demonstrates the effectiveness of artificial neural networks in predicting pulse parameters, and could pave the way for more efficient design and optimization of fiber lasers. The results of the study show that the ANN model can accurately predict the output pulse shape parameters for the DSR ring cavity fiber laser, and thus offers a promising tool for future research in the field.

Estimate the Attenuation and Simulation of dispersion Gaussian pulses propagation in a Single Mode Optical Fiber

we studied Attenuation in Fiber Optics, we used two type of Fibers (Plastic and glass) with length (0.5,5,20m) and (1,20,100m) respectively and used two wavelength laser (660nm, 850nm), we found attenuation increase with 850nm wavelength and 660nm wavelength are the best for the plastic fiber optics, in addition the attenuation which occur from axial gap, axes rotation, inclination angle, transversal displacement are investigated. Influence three values of linear dispersion on Pulse propagation along fiber at seam distance is investigated by simulation using Fourier Method using MATLAB.

Statistical simulation of laser pulse propagation in cirrus clouds with accounting for multiple scattering

Statistical simulation of laser pulse propagation in cirrus clouds with accounting for multiple scattering

Modeling of mode-locked fiber lasers and amplifiers with accurate saturable gain evaluation

We present a numerical model for mode-locked lasers and ultrafast nonlinear amplifiers in which the saturated gain profiles along active fibers are judiciously computed using experimental pump powers as input. This eliminates the need for approximating the gain profile by using a small-signal gain coefficient and saturation energy to simulate pulse propagation in active fibers. Our model shows good agreement with experiments involving mode-locked cavities at 1 µm with a silica glass host doped with ytterbium ions. Accurate results are also obtained for continuous-wave and mode-locked laser cavities around 2.8 µm, which uses ZBLAN fiber doped with erbium ions. In the case of Er:ZBLAN fiber, we use the model to show regions of stable mode-locking delivering a single pulse as output and how the spectral width changes with variation in doping concentration and fiber lengths. Our model enables accurate numerical modeling of mode-locked fiber lasers and ultrafast amplifiers, and can be useful in guiding the design of new architectures, understanding complex intracavity laser dynamics, and optimizing device output.

Light Interaction With an Ensemble of Quantum Dots [Guest Editorial

The quantum technologies series of articles started with the basics of quantum electromagnetics and then turned to deal with various promising applications. These range from the computation of the Casimir force to the analysis of interactions between electromagnetic waves and large molecules behaving as nanoantennas. Another article outlined the advantages of more futuristic higher level applications, such as quantum radars and lidars. Recent articles in the series covered device-level performance, including the quantum electrodynamics of plasmonic waveguides and construction of transmon qubits. Similarly, the present contribution, “Numerical Simulations of Laser Pulse Propagation in Quantum Active Media,” deals with the semiclassical analysis of field interaction with a collection of quantum dots, posing a heavy computational challenge. One typically sidesteps this by deriving a homogeneous behavior. But this leaves out interesting design opportunities. This article takes a different approach to the self-consistent analysis of a large ensemble of quantum dots. It combines analysis methods that are well known in the electromagnetics community together with predictor–corrector methods to solve for the evolution of the polarization of quantum dots. Interestingly, the approach correctly predicts experimentally observed behavior.

Dynamics and numerical simulation of optical pulses in the passively mode-locked Er-doped fiber laser

Passively mode-locked fiber laser has advantages of compactness, simplicity, flexibility and high quality of the output pulse, which provides an excellent research platform for the analysis of optical soliton characteristics. In this paper, the complex cubic Ginzburg–Landau equation (CGLE) is employed to simulate pulse propagation in passively mode-locked Er-doped fiber laser. We use barycentric interpolation collocation method to numerically solve the dark single soliton, dark two-soliton and bright two-soliton solutions, and study the effects of dispersion, nonlinear effects, gain and loss on optical pulse transmission. We discuss the dynamic characteristics of the bright two-solitons and dark two-solitons for the complex CGLE, respectively. The results is of great significance for the study of optical pulse transmission in fiber laser.

Heat pulse propagation and nonlocal phonon heat transport in one-dimensional harmonic chains

Phonons are the main heat carriers in semiconductor devices. In small devices, heat is not driven by a local temperature gradient, but by local points of heat input and removal. This complicates theoretical modeling. Study of the propagation of vibrational energy from an initial localized pulse provides insight into nonlocal phonon heat transport. We report simulations of pulse propagation in one dimension. The 1d case has tricky anomalies, but provides the simplest pictures of the evolution from initially ballistic toward longer time diffusive propagation. Our results show surprising details, such as diverse results from different definitions of atomistic local energy, and failure to exhibit pure diffusion at long times. Boltzmann phonon gas theory, including external energy insertion, is applied to this inherently time-dependent and nonlocal problem. The solution, using relaxation time approximation for impurity scattering, does not closely agree with the simulated results.

Ultrafast transverse and longitudinal response of laser-excited quantum wires.

We couple 1D pulse propagation simulations with laser-solid dynamics in a GaAs quantum wire, solving for the electron and hole populations and the interband and intraband coherences between states. We thus model not only the dynamical dipole contributions to the optical polarization (interband bound-charge response) but also the photo-generation and back-action effects of the net free-charge density (intraband free-charge response). These results show that solving for the dynamic electron and hole intraband coherences leads to plasma oscillations at THz frequencies, even in a 1D solid where plasma screening is small. We then calculate the transverse and longitudinal response of the quantum wire and characterize the dispersion relation for the e-h plasma. This approach allows one to predict the optoelectronic response of 1D semiconductor devices during and after exposure to resonant ultrashort pulses.

High-energy bow tie multi-pass cells for nonlinear spectral broadening applications

Multi-pass cells (MPCs) have emerged as very attractive tools for spectral broadening and post-compression applications. We discuss pulse energy limitations of standard MPCs considering basic geometrical scaling principles and introduce a novel energy scaling method using a MPC arranged in a bow tie geometry. Employing nonlinear pulse propagation simulations, we numerically demonstrate the compression of 125 mJ, 1 ps pulses to 50 fs using a compact 2 m long setup and outline routes to extend our approach into the Joule-regime.

Numerical simulation of laser-generated Rayleigh wave pulses propagation in the machined surface with residual stress using finite-difference method

Laser-excited broadband Rayleigh wave propagation behaviors can be used for characterizing material surface characteristics non-destructively. The present paper is concerned with the Rayleigh wave propagation in the machined surface with a damaged layer with residual stress. Biot’s theory of small deformations affected by initial stress forms the basis for this study. Taking ground silicon wafer as an example, we adopted a staggered finite-difference (FD) scheme for numerical simulation. By comparing the dispersion images with the theoretical dispersion curves of Rayleigh wave, the accuracy of the FD algorithm is verified. Then, some two-layer models without or with residual compressive stress are utilized to further analyze the dispersion energy characteristics of Rayleigh waves in the machined surface. The results indicate that damage layer thickness and damage degree determine the main Rayleigh wave high-order mode and the energy of the high-order mode, respectively. In addition, residual compressive stress can reduce the phase velocity of the Rayleigh wave to a small extent. Meanwhile it can significantly increase the total energy of the Rayleigh wave which excited by the same excitation source. This paper will provide a valuable reference for laser ultrasonic evaluation of residual stress on the machined surface.

Numerical Simulations of Laser Pulse Propagation in Quantum Active Media: Using a semiclassical model

Active media are materials that consist of quantum systems, such as atoms, impurities, or quantum dots, and are characterized by strong resonant absorption and re-emission of radiation. In this article, we present a general framework for the numerical simulation and analysis of time-dependent radiation-induced phenomena in active media. The formulation used is based on the solution of semiclassical Maxwell–Bloch equations describing the evolution of each quantum element under the effect of external and re-emitted radiation. Within these Maxwell–Bloch equations, the coupling of quantum systems to classical Maxwellian fields poses computational challenges due to the strong nonlinearities involved. In contrast to traditional mesh-based solvers, we adopt an electric field integral-operator approach that can reliably account for near-field effects—including self-radiation—and is scalable to large systems. We then focus on media based on large numbers of quantum dots and demonstrate various physical effects arising from the near-field coupling, including polarization modulations and superradiance.

Seed source for plasma compression in the long wavelength infrared

Two color laser pulses are used to form an air plasma and generate broadband infrared radiation suitable as a seed for backward Raman amplification of CO2 laser pulses. Broadband radiation in the atmospheric window from 8 to 14 μm is observed. The infrared radiation is characterized using a long wavelength grating spectrometer specially designed to accept an ionizing laser filament at its input plane. The long wavelength infrared yield is greatly enhanced by chirping the drive pulse, but this affects the spectrum as well. Unidirectional pulse propagation simulations suggest that this is due in part to the dependence of the nonlinear refractive index on the pulse duration.

Femtosecond laser induced luminescence in hierarchically structured NdIII, YbIII, ErIII co-doped upconversion nanoparticles: Light-matter interaction mechanisms from experiments and simulations

Fundamental studies of light-matter interactions are important for basic knowledge and in applications. Thanks to advances in experimental and theoretical methods, nowadays it is possible to perform such studies in a broad dynamic range, covering timescales from that of elementary interactions to real time. In the present work, we perform an experimental-theoretical study of light intensity-dependent femtosecond and CW-laser induced frequency upconversion in hierarchically structured core-multishell nanoparticles co-doped with NdIII, YbIII, and ErIII. Upconversion spectra recorded with CW and femtosecond excitation are qualitatively similar whereas the intensity dependence of upconversion depends on excitation mode (CW or femtosecond). To further assess the observed intensity dependence, we perform light-matter interaction simulations in the dynamic range from 100 fs to 3 ms for 18-level system describing the UCNPs, including nine levels of the NdIII, two of the YbIII, and seven of the ErIII ions and a classical model for the excitation source. The calculated time- and intensity-dependent energy level population are compared with measured spectra to understand CW vs femtosecond laser-induced upconversion. To further discuss the differences between CW and femtosecond laser-induced light-matter interactions for the systems studied here, we perform semi-classical pulse propagation simulations and ultrafast pump-probe measurements to study how the light source bandwidth, relative to the absorption linewidth, influence light absorption and transmission and further connect these results with the intensity dependence. Overall, we report our progress toward mechanistic studies of light-matter interaction and photophysical pathways following femtosecond excitation and UCNPs.

Numerical simulation of arterial pulse propagation using autonomous models

We present a model of the fluid flow between elastic walls simulating arteries actively interacting with the blood. The lubrication theory for the flow is coupled with the pressure and shear stress from the walls. The resulting nonlinear partial differential equation describes the displacement of the walls as a function of the distance along the flow and time.

Multiphoton-Absorption-Excited Up-Conversion Luminescence in Optical Fibers

We experimentally demonstrate a previously unforeseen nonlinear effect in optical fibers: up-conversion luminescence generation excited by multiphoton absorption of femtosecond infrared pulses. We directly estimate the average number of photons involved in the up-conversion process, by varying the wavelength of the pump source. We highlight the role of nonbridging oxygen hole centers and oxygen-deficient center defects and directly compare the intensity of side-scattered luminescence with numerical simulations of pulse propagation.

Original Solution of Coupled Nonlinear Schrödinger Equations for Simulation of Ultrashort Optical Pulse Propagation in a Birefringent Fiber

This paper discusses approaches to the numerical integration of the coupled nonlinear Schrödinger equations system, different from the generally accepted approach based on the method of splitting according to physical processes. A combined explicit/implicit finite-difference integration scheme based on the implicit Crank–Nicolson finite-difference scheme is proposed and substantiated. It allows the integration of a nonlinear system of equations with a choice of nonlinear terms from the previous integration step. The main advantages of the proposed method are: its absolute stability through the use of an implicit finite-difference integration scheme and an integrated mechanism for refining the numerical solution at each step; integration with automatic step selection; performance gains (or resolutions) up to three or more orders of magnitude due to the fact that there is no need to produce direct and inverse Fourier transforms at each integration step, as is required in the method of splitting according to physical processes. An additional advantage of the proposed method is the ability to calculate the interaction with an arbitrary number of propagation modes in the fiber.

Periodic transmission and control of pulses in solid mechanics and nonlinear optics

Nonlinear physical models play an important role in basic research of solid mechanics and nonlinear optics. In this study, a high-order variable coefficient nonlinear Schördinger equation, which can be used to simulate pulse propagation in various media, is analytical investigated. Using the bilinear method, analytical solution is obtained. Pulse propagation characteristics are analyzed, and the influences of relevant physical parameters on pulse propagation are discussed. Results have an impact on related physical sciences, engineering and other fields.

Mid-infrared two-octave spanning supercontinuum generation in a Ge–Se–Te glass suspended core fiber

We report on both the fabrication and the application of a Ge–Se–Te glass-based suspended core fiber for mid-infrared supercontinuum generation. A two-octave spanning mid-infrared light source (from 3.25 to 13 µm) is experimentally demonstrated by pumping the chalcogenide fiber with sub-100 fs pulses at 8.6 µm. Numerical simulations of nonlinear pulse propagation as well as fiber properties are also provided and support experimental measurements.