Generation Of Ultrashort Pulses Research Articles

Efficient computation of coherent multimode instabilities in lasers using a spectral approach

Coherent multimode instabilities are responsible for several phenomena of recent interest in semiconductor lasers, such as the generation of frequency combs and ultrashort pulses. These techonologies have proven disruptive in optical telecommunications and spectroscopy applications. While the standard Maxwell-Bloch equations (MBEs) encompass such complex lasing phenomena, their integration is computationally expensive and offers limited analytical insight. In this paper, we demonstrate an efficient spectral approach to the simulation of multimode instabilities via a quantitative analysis of the instability of single-frequency lasing in ring lasers, referred to as the Lorenz-Haken (LH) instability or the RNGH instability in distinct parameter regimes. Our approach, referred to as CFTD, uses generally non-Hermitian Constant Flux modes to obtain projected Time Domain equations. CFTD provides excellent agreement with finite-difference integration of the MBEs across a wide range of parameters in regimes of non-stationary inversion, including frequency comb formation and spatiotemporal chaos. We also develop a modal linear stability analysis using CFTD to efficiently predict multimode instabilities in lasers. The combination of numerical accuracy, speedup, and semi-analytic insight across a variety of dynamical regimes make the CFTD approach ideal to analyze multimode instabilities in lasers, especially in more complex geometries or coupled laser arrays.

Hydrothermal-assisted synthesis of reduced graphene oxide/zinc oxide nanocomposite for ultrashort pulse generation in 1.5 µm and 2.0 µm spectral regions

Our research focuses on synthesizing reduced graphene oxide/zinc oxide (rGO/ZnO) nanocomposite using hydrothermal techniques, which we then utilized as a saturable absorber (SA) to generate ultrashort pulses at wavelengths of 1.5 μm and 2.0 μm. A balanced twin detector approach investigated the nonlinear optical properties of rGO/ZnO nanocomposite, giving modulation depths of 4.06 % and 46.23 % at the 1.5 µm and 2.0 µm wavelength ranges, respectively. Stable mode-locked pulses with picosecond pulse widths and megahertz repetition rate were obtained after inserting the rGO/ZnO-coated arc-shaped fiber into an erbium-doped fiber laser (EDFL) and Thulium/Holmium-doped fiber laser (THDF) cavities. The pulse width and repetition rate differ between EDFL and THDFL, with EDFL generating an output soliton with a pulse width of 0.92 ps and a repetition rate of 18.19 MHz, and THDFL producing a pulse width of 1.36 ps and a repetition rate of 12.14 MHz. Upon assessment of their long-term stability, it was found that both generated lasers exhibited remarkable resilience, with signal-to-noise ratio (SNR) values surpassing 50 dB. Our study indicates the extraordinary broadband nonlinear features of rGO/ZnO nanocomposite. It presents a new opportunity to develop ultrashort nonlinear devices utilizing rGO/metal oxide-based nanocomposites.

Tunable in situ near-UV pulses by transient plasmonic resonance in nanocomposites.

We propose a concept for generation of ultrashort pulses based on transient field-induced plasmonic resonance in nanoparticle composites. Photoionization and free-carrier plasma generation change the susceptibility of nanoparticles on a few-femtosecond scale under the action of the pump pulse. This opens a narrow time window when the system is in plasmonic resonance, which is accompanied by a short burst of the local field. During this process, frequency-tunable few-fs pulses can be emitted. This paves a way to ultra-compact yet efficient generation of ultrashort pulses at short wavelengths.

Characterization and Mode-Locking of Erbium-Doped Fiber Laser for Ultra-Short Pulse Generation

In this work, the characteristics of a passively mode-locked laser based on a glass fiber doped with the rare-earth material erbium were investigated. This report explores the wavelength tuning capability of the fiber laser using a reflective diffraction grating placed within its cavity. The experiment demonstrates a wavelength tuning range of 1515 nm-1580 nm for a 50% out-coupling configuration and highlights the efficacy of the grating in achieving precise control over the laser’s output spectrum and power.

Transform-Limited Sub-100-fs Cr:ZnS Laser with a Graphene-ZnSe Saturable Absorber

In this work, we present ultrashort pulse generation from passively mode-locked Cr:ZnS laser with a monolayer graphene-coated ZnSe substrate exhibiting high nonlinearity. The femtosecond Cr:ZnS laser produces output power up to 330 mW at a 233 MHz repetition rate. Even in the presence of an uneven negative dispersion profile, the enhanced self-phase modulation by the ZnSe substrate of the graphene saturable absorber enables the polycrystalline Cr:ZnS laser to produce slightly chirped 99 fs pulses at 2373 nm. With extracavity dispersion compensation using a mixture of 3 mm and 2 mm thick ZnSe plates, the pulse width was compressed from 99 fs to 73 fs, resulting in an improved time–bandwidth product from 0.431 to 0.318. Assuming a sech2 pulse shape (0.315), the pulses were almost transform-limited. These results indicate that utilizing a graphene saturable absorber on a substrate with high nonlinearity presents an effective method for developing sub-100 fs solid-state lasers within the mid-IR spectral range.

Crystallization in the TeO2 - Ta2O5 - Bi2O3 system: From glass to anti-glass to transparent ceramic

Glass samples belonging the TeO2 - Ta2O5 - Bi2O3 (TTB) system are prepared by conventional melt-quenching technique and the corresponding vitreous domain is identified. A crystallization study of the 80 TeO2 - 10 Ta2O5 - 10 Bi2O3 glass composition versus temperature shows structural transitions from glass to the stabilization of an unreported translucent anti-glass phase and eventually to a fully transparent crystalline ceramic in both the visible and infrared ranges. The structure and microstructure of the anti-glass and ceramic phases are characterized by Powder X-Ray Diffraction, Electron Back-Scatter Diffraction, Transmission Electron Microscopy and Raman spectroscopy. The optical properties of undoped and Er3+-doped transparent samples are also discussed. Up-conversion green emission band shows that the glass intensity is about 2 and 4 times more intense than that of the anti-glass and the ceramic, respectively. Furthermore, a large spectral bandwidth of 105 nm is found in the anti-glass sample. The advantageous spectroscopic characteristics found here, together with the good thermal stability of these samples, suggest that the anti-glass phase has potential applications as amplification medium for the generation of ultrashort (femtoseconds) pulses.

Spectral stability of elliptic solutions to the short-pulse equation

The short pulse (SP) equation describes the propagation of ultrashort optical pulses in nonlinear media and possesses a Lax pair of the Wadati–Konno–Ichikawa (WKI) type. In this paper, using integrability, we examine the spectral stability of elliptic solutions to the SP equation. Firstly, we analytically give an explicit description of the spectrum of the WKI-Lax operator to the SP equation for elliptic potentials. Then, by constructing the squared-eigenfunction connection between the non-standard linear stability problem (LZ=ΛZ′) and the Lax spectral problem, we prove that the elliptic solutions are spectrally stable with respect to subharmonic perturbations.

Transparent nanopaper for ultrashort pulse generation in the near-infrared region.

Transparent nanopaper (T-paper) can be applied in the field of electromagnetic shielding materials, antistatic materials, composite conductive materials, electric pool materials, super capacitors, and thermal management systems. However, this kind of T-paper has not been employed in ultrafast photonics yet. For the first time, to our knowledge, transparent electrical nanopaper is used in fiber lasers, different from the conventional pulsed fiber laser, which operates in the Q-switched regime under low pump power and then in the mode-locked regime under high pump power. Mode-locking is achieved first with a pulse duration of 550fs under low pump power (166mW). When further increasing the pump power up to 198mW, the proposed fiber laser can be converted from a mode-locked to Q-switched state, which is a result of the two-photon absorption effect. The proposed fiber laser based on T-paper can be potentially applied in optical tomography, metrology, spectroscopy, micro-machining technology, and biomedical diagnostics.

Nonlinear optical features in core–shell ZIF-8@ZIF-67 for ultrashort pulse generation in Yb- and Er-doped fiber lasers

Nonlinear optical features in core–shell ZIF-8@ZIF-67 for ultrashort pulse generation in Yb- and Er-doped fiber lasers

Generation of noise-like pulse using nickel-based metal-organic framework saturable absorber

We experimentally demonstrate the generation of noise-like pulse (NLP) in an erbium-doped fiber laser using a metal-organic framework (MOF)-based saturable absorber. To fabricate the device, a tapered fiber was coated with MOF material, nickel 1,3,5-benzene-tricarboxylic acid (Ni-H3BTC) using a spin-coating method. The fabricated Ni-H3BTC-MOF saturable absorber exhibited 4.5% modulation depth and 30.3 MW/cm2 saturation intensity. A mode-locked erbium-doped fiber laser operated in the NLP regime was successfully achieved at 1564.90 nm central wavelength having 3-dB bandwidth of 19.96 nm, repetition rate of 9.02 MHz, and signal-to-noise ratio of 57.17 dB at 248 mW pump power. The characteristics of the NLP was confirmed by the spike width of 148 fs riding on a pedestal pulse duration of 26.67 ps. The estimated value of its damage threshold was experimented to be beyond 4.69 GW/cm2. These results infer that MOF-based saturable absorber can be an alternative material for the generation of ultrashort pulses.

Effect of dispersion and nonlinearity on ultrashort optical pulse propagation in long-period fiber grating: An analytical investigation

Long-period fiber grating is widely used as an optical component in photonics communication technology. The optical pulse propagation in grating has been studied mostly numerically and some number of studies carried out experimentally. The detailed analytical investigation has not been reported due to the complexity of the mathematical equations. Here, we have investigated analytically the effect of dispersion and nonlinearity on ultrafast optical pulse propagation in long-period fiber grating and derived the expression for transmitted optical pulses because the detailed analytical investigation has not been reported by any authors. The results of the study show how grating-induced overall dispersion and nonlinearity-induced self-phase modulation (SPM) modify the shape of the ultrashort optical pulses when it’s propagating through a length of the grating. The combined effects of dispersion and SPM on the optical pulse evaluation are also analyzed. From the plotted graphs it is investigated that the dispersion of the grating distorted the pulse shape whereas SPM shifts the pulse towards the higher time scale. It is also investigated that the distorted optical pulse due to dispersion is reshaped by the nonlinearity introduced in the medium due to the combined effect of dispersion and SPM. Optical pulse compression, optical limiting and pulse reshaping are also illustrated as a function of excitation intensity.

All-Solid-State Ultrashort Pulse Generator by Capacitive Chopping Circuit

High-voltage ultrashort pulse (HVUSP) is attaching more attention to advanced biomedicine. In this paper, a capacitive chopping circuit (CCC) topology with all-solid-state switches is proposed, which can generate adjustable HVUSP with high power efficiency. Dual capacitors of opposite polarity are connected in series with the load, thus cutting off the discharge loop of a single capacitor and chopping out a narrow pulse with adjustable width. The CCC can be stacked modularly for higher amplitude. The working principle is analyzed and the power efficiency under different working conditions is simulated, along with existing modularized HVUSP generation topologies. Finally, an 8-staged all-solid-state prototype based on the proposed CCC topology is developed. The adjustability of pulse parameters and staged performance are tested. The pulse width can be compressed to less than 10ns at 6.5kV. Output parameters can satisfy HVUSP electroporation in the biological scene.

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.

Nitrogen-doped graphene quantum dots for femtosecond ultrafast pulsed fiber lasers

Nitrogen-doped graphene quantum dots (N-GQDs) are a new class of quantum dot with unique electronic properties, whose electrons transport and biochemical properties have been extensively studied. However, the optical properties of N-GQDs, especially their nonlinear optical response and applications in ultrafast photonics and photoelectronic, need to be further explored. The nonlinear optical response and ultrafast carrier dynamics of N-GQDs in an aqueous solution are systematically investigated in this work. N-GQDs have an ultrafast carrier cooling delay of about 143 fs in the visible range. In the study of the nonlinear optical response of N-GQDs, the saturable absorption is transformed into reverse saturable absorption as the incident pulse intensity increases, which makes N-GQDs an effective saturable absorber for ultrashort pulse generation in mode-locked Er-doped fiber lasers. Our results may lead to further investigations into the optical properties of N-GQDs and demonstrate potential opportunities for ultrafast photonic applications.

Ultra-Short Laser Pulses Propagation Through Mouse Head Tissues: Experimental and Computational Study

We present a prototype and verification of a multichannel laser system applicable to optogenetic research. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In vivo</i> photostimulation of neural cells expressing photoconvertible phytochromes or opsins requires enough light irradiation delivery to the brain that cannot be supported by continues-wave (CW) light sources. The use of ultra-short pulsed (USP) lasers operating in the second near-infrared region (II-NIR) and allowing nonlinear activation and deactivation of the photoactuators is a promising method that allows to increase the penetration depth and provide spatio-temporal localisation of radiation in tissues. This study aimed to investigate the efficiency of USP light propagation in the skin, skull, and brain of the mouse head, as well as to compare it with the corresponding CW radiation propagation in the 750–830 nm and 1086–1183 nm wavelength ranges. The experimental results and computer modelling demonstrate that about 10–12% of the initial laser radiation can reach the brain tissues. These results prove that under certain conditions, the USP laser radiation can reach a penetration depth with required power that will be sufficient for non-linear activation of opsins/phytochromes in the brain of living animals.

Exact soliton solutions and stability analysis to (3 + 1)-dimensional nonlinear Schrödinger model

In this research, a dynamical (3 + 1)-dimensional nonlinear Schrödinger model (NLSM) is under consideration which is used to model the propagation of ultra-short optical pulses in highly-nonlinear media. This aforementioned model has been widely applied in Bose–Einstein condensates, nonlinear optical fiber communication plasma physics, hydrodynamics, elastic media and other diversified areas of mathematical physics and engineering. This study has two main objectives. Firstly, to obtain some novel solutions in the shape of singular, dark, periodic and plane wave solutions that are innovative and not previously found in the literature. Secondly, an amended extended tanh-function method with modulation instability (MI) is used for this model. As far as we know, this has never been investigated in this manner. The 2-D, 3-D and contour plots have been defined using the required parametric values to support the results of physical compatibility. According to the examined results, the method used in this study to retrieve consisting and conventional solutions is efficient and more immediate in computing and can be thought of as a useful tool in resolving more difficult problems that arise in the field of engineering, physics, mathematics and fiber optics.

Generation of Ultrashort Pulses in XUV and X-ray FELs via an Excessive Reverse Undulator Taper

The pulse duration in short-pulse schemes for Self-Amplified Spontaneous Emission Free Electron Lasers (SASE FELs) is limited by the FEL coherence time. A recently proposed concept allows to overcome the coherence time barrier and to obtain much shorter pulses. When the lasing part of an electron bunch is much shorter than the coherence time, one can suppress the radiation in the long main undulator while preserving microbunching within that short lasing slice. Then, a short radiation pulse is produced in a relatively short radiator. A possible suppression method, an excessive reverse undulator taper, is discussed and illustrated numerically in this paper. We also performed the first experimental tests of this method at the soft X-ray FEL user facility FLASH. The measured pulse duration approaches 1 fs (FWHM) at the wavelength of 5 nm.

Tm:CALGO lasers at 2.32 µm: cascade lasing and upconversion pumping.

We report on the first laser operation of a disordered Tm:CaGdAlO4 crystal on the 3H4 → 3H5 transition. Under direct pumping at 0.79 µm, it generates 264 mW at 2.32 µm with a slope efficiency of 13.9% and 22.5% vs. incident and absorbed pump power, respectively, and a linear polarization (σ). Two strategies to overcome the bottleneck effect of the metastable 3F4 Tm3+ state leading to the ground-state bleaching are exploited: cascade lasing on the 3H4 → 3H5 and 3F4 → 3H6 transitions and dual-wavelength pumping at 0.79 and 1.05 µm combining the direct and upconversion pumping schemes. The cascade Tm-laser generates a maximum output power of 585 mW at 1.77 µm (3F4 → 3H6) and 2.32 µm (3H4 → 3H5) with a higher slope efficiency of 28.3% and a lower laser threshold of 1.43 W, out of which 332 mW are achieved at 2.32 µm. Under dual-wavelength pumping, further power scaling to 357 mW at at 2.32 µm is observed at the expense of increased laser threshold. To support the upconversion pumping experiment, excited-state absorption spectra of Tm3+ ions for the 3F4 → 3F2,3 and 3F4 → 3H4 transitions are measured for polarized light. Tm3+ ions in CaGdAlO4 exhibit broadband emission at 2.3 - 2.5 µm making this crystal promising for ultrashort pulse generation.

Chaotic Internal Dynamics of Dissipative Optical Soliton Molecules

AbstractWhen a laser cavity supports the propagation of several ultrashort pulses, these pulses can form compact bound states called soliton molecules. Soliton molecules are fascinating objects of nonlinear science, presenting striking analogies with their matter molecule counterparts. The relative timing and phase between the copropagating pulses are the most salient internal degrees of freedom of the soliton molecule. The soliton pair, composed of two identical pulses, constitutes the chief soliton molecule of fundamental interest. Its two major internal degrees of freedom allow self‐oscillating soliton molecules, which have been recurrently observed. However, despite theoretical predictions, the low‐dimensional chaotic dynamics of a soliton‐pair molecule remain elusive. This article reports the observation of chaotic soliton‐pair molecules within an ultrafast fiber laser by means of a direct measurement of the relative optical pulse separation with sub‐femtosecond precision in real time. Moreover, it demonstrates an all‐optical control of the chaotic dynamics followed by the soliton molecule by injection of a modulated optical signal that resynchronizes the internal periodic vibration of the soliton molecule. The fast error‐free switching between ordered and chaotic soliton molecules enabled by pump current sweeping and external injection highlights the potential prospects of all‐optical logic gates and chaotic communication using soliton molecules.

Soliton interactions and Yang–Baxter maps for the complex coupled short‐pulse equation

AbstractThe complex coupled short‐pulse equation (ccSPE) describes the propagation of ultrashort optical pulses in nonlinear birefringent fibers. The system admits a variety of vector soliton solutions: fundamental solitons, fundamental breathers, composite breathers (generic or nongeneric), as well as so‐called self‐symmetric composite solitons. In this work, we use the dressing method and the Darboux matrices corresponding to the various types of solitons to investigate soliton interactions in the focusing ccSPE. The study combines refactorization problems on generators of certain rational loop groups, and long‐time asymptotics of these generators, as well as the main refactorization theorem for the dressing factors that leads to the Yang–Baxter property for the refactorization map and the vector soliton interactions. Among the results obtained in this paper, we derive explicit formulas for the polarization shift of fundamental solitons that are the analog of the well‐known formulas for the interaction of vector solitons in the Manakov system. Our study also reveals that upon interacting with a fundamental breather, a fundamental soliton becomes a fundamental breather and, conversely, that the interaction of two fundamental breathers generically yields two fundamental breathers with a polarization shifts, but may also result into a fundamental soliton and a fundamental breather. Explicit formulas for the coefficients that characterize the fundamental breathers, as well as for their polarization vectors are obtained. The interactions of other types of solitons are also derived and discussed in detail and illustrated with plots. New Yang–Baxter maps are obtained in the process.