Generation Of Femtosecond Pulses Research Articles

Bright-dark soliton solutions and their elastic interaction analysis for a reduced integrable spin Hirota–Maxwell–Bloch equation

Under consideration is a reduced integrable spin Hirota–Maxwell–Bloch (rsHMB) equation, which may have potential applications in describing femtosecond pulse propagation through an erbium doped fiber. With the aid of symbolic computation, we establish the N-fold Darboux transformation (DT) of rsHMB equation based on its known 2 × 2 matrix spectral problem. As an application of the resulting DT, we can get bright-dark soliton and breather solutions of rsHMB equation. Through graphical and asymptotic analysis, the soliton elastic collisions are shown and discussed graphically, and some important soliton physical features including wave velocity, amplitude and energy are analyzed. The consequences and properties presented in this paper may be helpful to comprehend the transmission of optical soliton in erbium doped fiber.

Exact chirped solutions for the generalized nonlinear Schrödinger equation in highly-nonlinear optical fibers

This study examines the generalized nonlinear Schrödinger equation for the propagation of femtosecond pulses in highly-nonlinear optical medium with polynomial Kerr nonlinearity and arbitrary higher-order non-Kerr components. The polynomial complete discriminant system is used to obtain exact solutions and chirped soliton solutions of complete types of nonlinear Schrödinger equation. Exact solutions can be of three types: soliton solutions, singular solutions, and elliptic function double periodic solutions. The model is also visualized under specific parameter values, and the classical two-dimensional diagrams of exact solutions and chirped soliton solutions are given to prove the existence of solutions.

Theoretical analysis of self-phase-modulation-enabled spectral selection in hollow-core fibers: effect of ionization

We propose the generation of wavelength-tunable femtosecond pulses with µJ energy based on spectral broadening in hollow-core fibers (HCFs) filled with noble gas. A proper combination of gas type, gas pressure, and the HCF core radius ensures that the broadened spectrum consists of isolated spectral lobes; the selection of the outermost spectral lobes produces nearly transform-limited pulses. We performed a detailed numerical investigation of this method based on an antiresonant HCF with a 20 µm core radius filled with 17.3 bar Xe gas. By using 1.03 µm, 200 fs pulses with up to 20 µJ energy as the excitation pulse, this method can produce 100 fs pulses tuned from 0.74 to 1.25 µm with up to 5 µJ pulse energy. Further energy scaling is limited by the onset of ionization, which reduces the wavelength tuning range and causes a significant spectral blue shift. Increasing the input pulse energy beyond 45 µJ creates a strong spectral lobe peaking in the wavelength range of 0.92–0.95 µm with >10µJ energy. These results represent a two orders of magnitude improvement in the pulse energy compared to current tunable femtosecond sources based on nonlinear wavelength conversion in solid-core optical fibers.

Lab‐on‐Fiber Based on Optimized Gallium Selenide for Femtosecond Mode‐Locked Lasers and Fiber‐Compatible Photodetectors

Although the physicochemical properties of gallium selenide (GaSe) have been widely investigated, the property and application exploration of GaSe‐coupled fiber devices are still in its infancy. There are obvious challenges, namely, selecting from multiple GaSe phases and effectively coupling to the unique fiber structure. Herein, lab‐on‐fiber (LOF) based on optimized GaSe is proposed to be used for robust femtosecond pulse generation and fiber‐compatible photodetection. First, based on density functional theory (DFT) calculations, ε‐GaSe is selected as a preferable model material for its suitable band structures, low work function, and high damage threshold. Benefiting from the fiber‐compatible ε‐GaSe combined with micro–nano processing, stable femtosecond soliton pulse (≈303 fs, 16.67 MHz, 51.64 dB) output and multiwavelength (520, 808, and 1550 nm) detection are realized in LOF. These results pave the way for optics research of polyphase semiconductors and design of integrated all‐fiber devices.

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.

Spectrally combined four-diode-pumped femtosecond Ti:sapphire laser with 16.3 nJ pulse and its application to video-rate coherent anti-Stokes Raman scattering spectro-microscopy.

We demonstrate the generation of high-energy femtosecond pulses by a spectrally combined four-diode-pumped Ti:sapphire laser with semi-conductor saturable absorber mirror mode locking. To achieve energy scaling, the laser cavity was extended using a design based on the Herriott multipass cell. The laser operates at a 17.5 MHz repetition rate and generates pulses with energies as high as 16.3 nJ and 80 fs in duration. The signal-to-noise ratio at the fundamental frequency showed an extinction ratio of >50 dB relative to the carrier. This compact single laser was applied to video-rate forward and backward coherent anti-Stokes Raman scattering spectro-microscopy with a pixel dwell time of 122 ns, which is the lowest dwell time ever achieved, to the best of our knowledge.

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

High-precision phase plate for targeted generation of pseudorandom femtosecond pulses

The targeted generation of fs pulses is essential for a variety of applications and it is routinely carried out by 4f pulse shapers. However, this seemingly simple task is complicated by hidden experimental limitations, such as modulator crosstalk or pixelation. We present an approach to overcome this issue by using a high-precision phase plate with a phase change characterized with λ/500 precision. We generated pseudorandom pulses using a 4f pulse shaper by using a structured PMMA plate with the high-precision predefined shape made by the SPDT machine. We study the accuracy, reproducibility, as well as the sufficiency, and limits of the method. The generated pulses are characterized using the FROG method. The reconstructed pulses’ shapes and their spectral phases are compared to the results of simulations.

Second harmonic generation of femtosecond laser pulses of central wavelength 1000 nm, 1100 nm and 1300 nm using ZnO nanorods

In this work high density ZnO nanorods were grown on glass substrate by using a two-step method. In the first step, drop-casting method was used for growth of seed layer by taking Zinc Acetate Dihydrate as precursor. In the second step, ZnO nanorods were prepared through Chemical Bath Deposition process on this seed layer by taking Zinc Nitrate as precursor. Field Emission Scanning Electron Microscope study was done to study the morphology of grown ZnO nanorods. From this study the average diameter and length of nanorods were found to be 33 nm and 270 nm respectively. These nanorods are successfully used for second harmonic generation (SHG) of femtosecond laser pulses of central wavelengths like 1000 nm, 1100 nm and 1300 nm. Discussion is given on the significance of this result along with its potential application.

On the dynamics of soliton waves in a generalized nonlinear Schrödinger equation

The main objective of the present paper is to investigate the dynamics of soliton waves in a generalized nonlinear Schrödinger (GNLS) equation. To achieve such a goal, the real and imaginary portions of the GNLS equation are first extracted using a complex wave transformation. Solitons and Jacobi elliptic structures of the governing model, describing the propagation of femtosecond pulses in nonlinear optical fibers, are then constructed through applying the modified Jacobi elliptic expansion method (MJEEM). In the end, by employing a series of 2 and 3D-dimensional numerical representations, it is exposed that the width of bright and dark solitons respectively decreases and increases, while the amplitude of both waves decreases with the increase of nonlinear parameters.

Optical soliton solutions of (1 + 1)- and (2 + 1)-dimensional generalized Sasa–Satsuma equations using new Kudryashov method

In this paper, we aim to derive new soliton solutions of (1+1)- and (2+1)-dimensional generalized Sasa–Satsuma equations via the new Kudryashov method. In optical fiber transmission systems, the Sasa–Satsuma equation describes the effects of third-order dispersion, self-steepening and stimulated Raman scattering in the propagation of ultrafast pulses. The considered equations are encountered in various physical applications such as ultra-short and femto-second pulse propagation in optical fibers and dynamics of deep water waves. So, investigation of the novel solutions of the equations is one of the important topics. We have successfully extracted some soliton solutions for the considered equation. The various graphs of the obtained solutions have been depicted in the figures by selecting appropriate parameters. The singular and bright soliton solutions have been revealed in the figures. All acquired solutions have been confirmed to satisfy the considered equations. The results show that the approach may be used to find exact solutions to various nonlinear evolution equations. The new solutions and the paper results may enrich the understanding of the wave propagation in the optical fibers and may shed light on new studies.

Two Analytical Schemes for the Optical Soliton Solution of the (2 + 1) Hirota–Maccari System Observed in Single-Mode Fibers

In this scientific research article, the new Kudryashov method and the tanh-coth method, which have not been applied before, are employed to construct analytical and soliton solutions of the (2+1)-dimensional Hirota–Maccari system. The (2+1)-dimensional Hirota–Maccari system is a special kind of nonlinear Schrödinger equation (NLSEs) that models the motion of isolated waves localized in a small part of space, and is used in such various fields as fiber optics telecommunication systems, nonlinear optics, plasma physics, and hydrodynamics. In addition, the Hirota–Maccari system defines the dynamical characters of femtosecond soliton pulse propagation in single-mode fibers. Analytical solutions of the model are successfully acquired with the assistance of symbolic computation utilizing these methods. Finally, 3D, 2D, and contour graphs of solutions are depicted at specific values of parameters. It is shown that the new Kudryashov method and the tanh-coth method are uncomplicated, very effective, easily applicable, reliable, and indeed vital mathematical tools in solving nonlinear models.

Periodic and localized waves in parabolic-law media with third- and fourth-order dispersions.

Considering the higher-order nonlinearity is essential in a broad range of real physical media as it significantly influences the wave dynamics in these systems. We study the propagation of femtosecond light pulses inside an optical fiber medium exhibiting higher-order dispersion and cubic-quintic nonlinearities. Pulse evolution in such a system is governed by a higher-order nonlinear Schrödinger equationincorporating second-, third-, and fourth-order dispersions as well as cubic and quintic nonlinearities. The periodic and solitary wave solutions are identified using the equationmethod. Results presented indicated the potentially rich set of periodic waves in the system under the combined influence of higher-order dispersive effects and cubic-quintic nonlinearity. The velocity of these structures is uniquely dependent on all orders of dispersion. Conditions on the optical fiber parameters for the existence of these exact stable solutions are found by analytical stability analysis.

Coherent XUV Multispectral Diffraction Imaging in the Microscale

The rapid growth of nanotechnology has increased the need for fast nanoscale imaging. X-ray free electron laser (XFEL) facilities currently provide such coherent sources of directional and high-brilliance X-ray radiation. These facilities require large financial investments for development, maintenance, and manpower, and thus, only a few exist worldwide. In this article, we present an automated table-top system for XUV coherent diffraction imaging supporting the capabilities for multispectral microscopy at high repetition rates, based on laser high harmonic generation from gases. This prototype system aims towards the development of an industrial table-top system of ultrafast soft X-ray multi-spectral microscopy imaging for nanostructured materials with enormous potential and a broad range of applications in current nanotechnologies. The coherent XUV radiation is generated in a semi-infinite gas cell via the high harmonic generation of the near-infrared femtosecond laser pulses. The XUV spectral selection is performed by specially designed multilayer XUV mirrors that do not affect the XUV phase front and pulse duration.

Design and analysis of recurrent neural networks for ultrafast optical pulse nonlinear propagation.

In this work, we analyze different types of recurrent neural networks (RNNs) working under several different parameters to best model the nonlinear optical dynamics of pulse propagation. Here we studied the propagation of picosecond and femtosecond pulses under distinct initial conditions going through 13 m of a highly nonlinear fiber and demonstrated the application of two RNNs returning error metrics such as normalized root mean squared error (NRMSE) as low as 9%. Those results were further extended for a dataset outside the initial pulse conditions used on the RNN training, and the best-proposed network was still able to achieve a NRMSE below 14%. We believe that this study can contribute to a better understanding of building RNNs employed for modeling nonlinear optical pulse propagation and of how the peak power and nonlinearity affect the prediction error.

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.

Simulation of femtosecond pulse in a Kerr-lens mode-locked Ti:sapphire laser

The Kerr-lens mode-locking (KLM) is known as a suitable method for generation of femtosecond pulses and mode-locked Ti:sapphire laser is now widely used sources of stable, energetic femtosecond pulses. We will present the simulation of KLM in Ti:sapphire laser cavities with a folded-cavity four-mirror by applying the ABCD ray-tracing technique for a Gaussian beam. Simulations will be performed for an asymmetric resonator design. Based on the numerical analysis, we will find the optimum design parameters (slit position, gain cavity spacing, gain medium position) for KLM.

Phase portraits and optical soliton solutions of coupled Sasa–Satsuma model in birefringent fibers

The main purpose of this paper is to discuss the optical soliton solutions and phase portraits of the coupled Sasa–Satsuma model in nonlinear optics. This model is usually used to describe the propagation of femtosecond pulses in optical fibers. By using traveling wave transformation, the coupled Sasa–Satsuma model is simplified into the coupled nonlinear ordinary differential equations. After that, the coupled nonlinear ordinary differential equations are transformed into two-dimensional planar dynamic system with the Hamiltonian system. According to the bifurcation theory of planar dynamical system, the phase portrait of two-dimensional dynamical system is drawn. What is more, some very important optical soliton solutions are also constructed. In order to explain the propagation of optical solitons, three-dimensional diagrams, two-dimensional diagrams and the contour plots of the obtained solutions are drawn by using Maple software.

High coherent supercontinuum generation in nitrobenzene liquid-core photonic crystal fiber with elliptical air-hole inner ring

A nitrobenzene liquid-core photonic crystal fiber (NLC-PCF) with eight elliptical air-holes in the innermost ring of the cladding is proposed in this work, and this fiber structure can contribute to flexibly adjusting dispersion and constraining the fiber core. The appreciable dispersion is realized by adjusting the structural parameters of NLC-PCF, which is characterized by three zero-dispersion wavelengths (ZDWs), flat dispersion with the fluctuation of fewer than 40 ps nm−1 km−1, and high nonlinearity as high as 5500 W−1 km−1. The propagation of femtosecond pulse and supercontinuum generation (SCG) in NLC-PCF is studied numerically when the pump wavelength is located in the normal and abnormal dispersion region near different ZDW through solving the generalized nonlinear Schrödinger equation (GNLSE) by the split-step Fourier method. The numerical results show that a highly coherent supercontinuum (SC) spanning from 1.3 to 2.8 µm is obtained when the pump pulse with the center wavelength of 1810 nm, the peak power of 1000 W, and pulse width of 50 fs propagated in the 5 cm long NLC-PCF. This research can find applications in the fields of novel liquid-core PCF design and ultrashort pulse propagation.

A novel common-path scheme for fourth harmonic generation by ultrashort laser pulses

A new compact common-path scheme for Fourth-Harmonic Generation (FHG) of femtosecond laser pulses is proposed here. Guidelines for selection of non-linear crystals and birefringent crystals used for delay pre-compensation are derived based on approximation of non-saturated sum-frequency mixing of Gaussian pulses. We experimentally demonstrate the scheme and study its performance for a different combinations of BBO nonlinear crystals for the case of generation of sub-200 nm deep ultraviolet pulses by FHG of pulses delivered by a Ti:Sapphire ultrafast laser. Pulses with duration between 130 fs and 370 fs and pulse energy of 19 to 85 μJ were generated. It is shown, that in addition to its compactness and intrinsic stability, the scheme allows a superior spectrum and pulse quality.