Laser Dynamics Research Articles

Transient behaviors of pulse breaking and recovering in a dispersion-managed mode-locked Yb fiber laser

Various pulse regimes have been discovered in mode-locked fiber lasers with carefully designed cavity setups. However, the transitions between different types of stable pulse solutions are rarely observed in a laser with the same cavity configuration. Here, we report on the experimental observation of the transformation from stretched pulses (SPs) to dissipative solitons (DSs) in an all-polarization-maintaining dispersion-managed mode-locked Yb fiber laser for the first time. By means of the time-stretch dispersive Fourier transform technique, the temporal and spectral dynamics of transient behaviors from pulse breaking to pulse recovering are identified in real time. It is revealed that the overdriven nonlinear effect induced by pump increase triggers the wave breaking of SPs, and the improved net-cavity dispersion originated from wavelength shift helps the self-recovering of DSs. Numerical simulations validate the experimental observations and bring insights to the understanding of transient nonlinear dynamics in ultrafast fiber lasers.

Influence of pressure and pulse energy on the expansion dynamics of nanoparticle-enhanced laser produced plasma

In the present work, we have studied the influence of pressure and pulse energy on the expansion dynamics of nanoparticle-enhanced laser produced plasma (NELPP) for two different metals, copper and aluminum. The targets were ablated using a Q-switched Nd:YAG laser operating at its primary wavelength of 1064 nm. The plasma imaging was recorded using the fast-gated ICCD camera. Although spectroscopic investigation of signal enhancement of emission line intensities in presence of nanoparticles (NPs), nanoparticle enhanced LIBS (NELIBS), has been performed extensively, expansion dynamics for NELIBS is not yet studied. We have carried out a detailed investigation of the plume propagation of NELPP for different pulse energies and ambient pressures. Temporal evolution of the distance of propagation of the plume front at different laser fluences and pressures shows a good agreement with the existing theoretical models. By comparing different plume propagation parameters, such as diameter, aspect ratio and expansion velocity, we have shown that the NELPP plume shows similar behavior as of LPP and its evolution can be explained with the existing models. Hence NPs, though influence the ablation process, do not alter the overall plume dynamics during the course of plasma evolution as observed for the two metals.

The Effect of Electron Escape Rate on the Nonlinear Dynamics of Quantum Dot Lasers under Optical Feedback

When theoretically investigating the nonlinear dynamics of quantum dot lasers (QDLs), the parameter value of the electron escape rate (Ce) is sometimes approximated to zero to simplify the calculation. However, the value of Ce is dependent on the energy interval between the ground state (GS) and the excited state (ES) in the conduction band and is affected by the operation temperature. As a result, such simplified approximation treatments may lead to inaccurate results. In this study, after considering the effect of Ce, we investigate the nonlinear dynamics of QDLs with and without optical feedback based on the asymmetric electron-hole carrier rate equation model. The simulation results show that without optical feedback, the lasing conditions for ES and GS in free-running QDLs are dependent on the value of Ce. A larger Ce is more helpful for the ES emission, and the GS emission will stop lasing if Ce is large enough. Through analyzing the dynamical characteristics of GS and ES in QDLs with optical feedback under different Ce values, it can be found that the dynamical characteristics are strongly correlative with Ce.

Spatiotemporal dissipative soliton resonances in multimode fiber lasers

Spatiotemporal mode-locking in multimode fiber lasers is intriguing for the complex nonlinear dynamics and the increase of theoretical energy limit. In this paper, we enrich spatiotemporal mode-locking with dissipative soliton resonances, a kind of solitons which is characterized by large pulse energy in single mode fiber lasers, and demonstrate their emergence in multimode fiber lasers by employing the reverse saturable absorption effect from real saturable absorbers. The spatiotemporal dissipative soliton resonances are expected to raise the energy limit further by the locking of dissipative soliton resonances in different transverse modes, whose energy is about twice the maximum single-mode energy in our results. Moreover, properties of spatiotemporal dissipative soliton resonances are investigated by tailoring parameters of the multimode fiber laser, where evolution and transformation of the proposed pulses including shaping and broadening are disclosed. The spatiotemporal dissipative soliton resonances in multimode fiber lasers may open up new avenue for high-power and spatiotemporally engineered coherent light fields in laser dynamics and nonlinear optics.

Suppression of modulation instability in VCSEL by external optical injection.

The dynamics of a broad area semiconductor vertical-cavity surface-emitting laser (VCSEL) is analytically and numerically investigated considering the linewidth enhancement factor resulting in the modulation instability of a spatially homogeneous generation mode. We find the aperture width depends on the parameters of the laser system, above which the modulation instability leads to chaotic filamentalization of the optical field and complicates the practical application of such lasers. We show that using the external optical injection of small amplitude, it is possible both to transform chaotic filaments into regular stationary spatial optical structures (stripes and hexagons) and to stabilize the broad-area VCSELs.

Dynamics of two-level laser models with cavity loss modulation and delayed feedback

In 1982, Arecchi et al. [Phys. Rev. Lett. 49, 1217 (1982)PRLTAO0031-900710.1103/PhysRevLett.49.1217] proposed a simple two-level laser model to interpret the first evidence of chaos and generalized multistability in a Q-switched CO2 laser. In this framework, laser dynamics is described by means of a set of two ordinary differential equations for the photon number and the population inversion between the two resonant levels. A sinusoidal function accounts for cavity loss modulation. In this work, we first prove the existence of a periodic orbit for the original two-level non-autonomous laser. Then, we transform this model into a four-dimensional autonomous dynamical system to provide a mathematical analysis that confirms the seminal results already obtained. Finally, by replacing the sinusoidal loss modulation with a delayed function of photon number, we confirm the occurrence of chaos and multistability for such a delayed model with delay times of the order of the reciprocal of the modulation frequencies.

Intrinsic Spectrum Analysis of Laser Dynamics Based on Fractional Fourier Transform

The intrinsic spectrum that results from the coupling of spontaneous emission in a laser cavity can determine the energy concentration and coherence of lasers, which is crucial for optical high-precision measurements. To date, it has been difficult to analyze the intrinsic spectrum in high-speed laser dynamics processes, especially under the condition of fast wavelength sweeping. In this work, a new method to analyze the laser intrinsic spectrum is proposed with laser energy decomposition into a series of chirp-frequency signals, which is realized by fractional Fourier transform (FRFT) of the coherently reconstructed laser waveform. The new understanding of the energy distribution of lasers contributes to accurate characterization of laser dynamic parameters in the time-frequency domain. In a proof-of-concept experiment, the time-frequency dynamic process of a commercial wavelength-swept laser is tested for different wavelength-scanning speeds, and the most suitable measurement time window width required for the narrowest FRFT-based spectrum is also explored. The proposed analysis method of laser dynamic parameters will promote the understanding of laser dynamics and benefit optical precision measurement applications.

The effect of optical polarized feedback on dynamics of quantum dot semiconductor lasers

The effect of optical polarized feedback on dynamics of quantum dot semiconductor lasers

Modulational instability and nonlinear dynamics of femtosecond lasers in transparent materials with non-Kerr nonlinearities

Femtosecond laser inscription in transparent materials is a physical process that finds widespread applications in material engineering, particularly in laser micromachining technology. In this process, the nonlinear optical response of the transparent material can be either intrinsic or induced by multiphoton ionization processes. In this work, a generic model is considered to describe the dynamics of femtosecond laser filamentation in transparent materials characterized by non-Kerr nonlinearities, focusing on the influence of multiphoton ionization processes in the generation of an electron plasma of inhomogeneous density. The mathematical model consists of a complex Ginzburg–Landau equation with a generalized saturable nonlinearity, besides the residual nonlinearity related to multiphoton ionization processes. This generalized complex Ginzburg–Landau equation is coupled to a rate equation for time evolution of the electron plasma density, where multiphoton ionizations are assumed to be the sole processes controlling the generation of the electron plasma. Dynamical properties of the model are discussed starting from the continuous-wave regime, where a modulational-instability analysis enables us to determine the stability conditions of continuous-wave modes in the system. The analysis reveals a dominant tendency of continuous-wave stability for relatively large values of the multiphoton ionization order K, provided the femtosecond laser operates in the anomalous dispersion regime. Numerical simulations of the mathematical model feature a family of wavetrains composed of self-focused, well-separated, pulse-shaped optical filaments whose repetition rates are shortened but amplitudes are increased, with an increase in K. Simulations suggest that such nonlinear wavetrain structures do not need the transparent material to be intrinsically nonlinear and that they may also be favored solely by the nonlinearity induced by multiphoton ionization processes in a linear transparent material.

Quantum description of free electron laser radiation and nonlinear amplitude equations

A relativistic quantum mechanical model to describe the quantum free electron laser dynamics has been developed. Neglecting the spin of electrons in the impacting beam, this model is based on the Klein–Gordon equation coupled to the Poisson equation for the space-charge potential and the wave equation for the transverse components of the radiation field. Furthermore, a system of coupled nonlinear envelope equations for the slowly varying amplitudes of the electron beam distribution and the radiation field has been derived. The fundamental system of basic equations has been cast into a suitable hydrodynamic formulation. In the framework of the hydrodynamic representation, a new dispersion relation has been derived and analyzed in both the quantum and the quasi-classical regimes, where the space-charge oscillations of the electron beam are taken into account.

Editorial: Semiconductor laser dynamics and its applications

Editorial: Semiconductor laser dynamics and its applications

Synchronized time lens based temporal magnifier assisted by the phase lock loop.

We propose a synchronized time lens based temporal magnifier for the characterization of an ultrafast pulse, which is assisted by the phase lock loop (PLL) to actively lock the repetition rates of the pump laser and signal laser. A feedback control system combining a proportional-integral (PI) circuit and a piezoelectric transducer (PZT) inside the signal laser cavity is used to synchronize the repetition rates between the pump and signal lights. Benefitting from the PLL technique, the temporal position of the signal pulse remains as the numerical aperture of the time lens system, and therefore it has a high short-time stability for pulse measurement. This synchronized time lens based temporal magnifier can record single-shot pulses within continuous round trips. By engineering the dispersion of the pump, signal, and idler lights, we demonstrate a 200× magnification of the signal pulse. Our technique offers a simple synchronized method in a time lens system for ultrafast temporal characterization, which provides new insights into the observation of the fiber laser dynamics.

Dynamics of a dispersion-tuned swept-fiber laser

Dynamics of a dispersion-tuned swept-fiber laser

Numerical simulation of linewidth compression dynamics of external-cavity semiconductor laser

We theoretically simulate the linewidth compression dynamics of the semiconductor laser with a single external-cavity feedback. The evolution time from the periodic oscillation state to the equilibrium state is calculated by tracking the change of the intrinsic linewidth. The influences of the external-cavity length and feedback level are also explored. The linewidth evolution time of the external-cavity semiconductor laser can be extended with longer external cavity length and higher feedback level. Simultaneously, the intrinsic linewidth can be compressed while the side mode suppression ratio will be decreased. The simulation work show that the dynamic linewidth compression can be obtained by single external-cavity feedback, and nevertheless it is difficult to achieve the single-frequency output, which can instruct the design of the dynamical parameter tuning of the external-cavity semiconductor laser.

Ion expansion dynamics of laser induced multi-elemental plasmas

Ablation of multi-elemental materials by nanosecond lasers is often used to deposit oxide thin films. Understanding the ablation plume dynamics is of utmost importance to gain a detailed insight into thin film growth of materials with a complex composition. In this study, the plume expansion dynamics of several compound materials (AuCu, La0.33Ca0.67MnO3, and LiMn2O4) were characterized by measuring the angular-dependent kinetic energy (KE) distributions of ionic plasma species produced by KrF- and XeCl-excimer laser ablation in vacuum. The distributions of the lightest plume ions were found to differ fundamentally from those of other ions. The latter are similar to the energy distributions observed in single-component plumes and represent a low-energy peak and high-energy tail, while those for the lightest ions consist of at least two distinct peaks. These observations can be explained by assuming the formation of a dynamic double layer (DL) at the front of the plasma giving rise to different acceleration rates for light and heavier ions. As a consequence, heavier elements stay longer within the dynamic DL and gain larger KEs that leads to the observed ion separation. Extending these considerations into three dimensions yields an anisotropic acceleration concept for the plasma ions with high acceleration rates and longer presence within the DL normal to the target surface and lower acceleration rates and shorter time in the parallel direction.

Dual Regime Mode-Locked and Q-Switched Erbium-Doped Fiber Laser by Employing Graphene Filament-Chitin Film-Based Passive Saturable Absorber.

We investigate the dynamics of high energy dual regime unidirectional Erbium-doped fiber laser in ring cavity, which is passively Q-switched and mode-locked through the use of an environmentally friendly graphene filament-chitin film-based saturable absorber. The graphene-chitin passive saturable absorber allows the option for different operating regimes of the laser by simple adjustment of the input pump power, yielding, simultaneously, highly stable and high energy Q-switched pulses at 82.08 nJ and 1.08 ps mode-locked pulses. The finding can have applications in a multitude of fields due to its versatility and the regime of operation that is on demand.

Unveiling Laser Radiation of Multiple Optical Solitons by Nonlinear Fourier Transform

AbstractMode‐locked fiber lasers are applied in versatile scientific fields and exhibit a rich diversity of nonlinear dynamics. However, the nontrivial coexistence of solitons and embedded dispersive wave radiation prevents unveiling the real nonlinear dynamics in mode‐locked fiber lasers, such as multiple solitons interaction. Here, nonlinear Fourier transform (NFT) is applied as a signal processing tool to reveal nonequilibrium multiple soliton dynamics. It is feasible to isolate solitons from the continuous wave background in a fiber laser. The real‐time coherent homodyne detection methodology is used to measure the full‐field dynamic evolution of multiple solitons, including multiple solitons buildup and sequentially nonequilibrium evolution with complex splitting, drifting, and collision processes. With the approach of inverse NFT, the corresponding various pure solitons buildup and collision are reconstructed. The eigenvalue probability distributions are used to classify different lasing regimes. Moreover, the controllable multiple solitons drifting is achieved and characterized by using all‐optical methods. Experimental results suggest that NFT can be used to identify localized soliton nonequilibrium evolution excluding dispersive wave radiation influence, which provides a new window into the physics of the underlying laser dynamics and uncovers real soliton interaction in dissipative nonlinear systems.

Prototype of a phonon laser with trapped ions

We propose a tunable phonon laser prototype with a large trapped ion array, where some of the ions are effectively pinned by optical tweezers, thus isolating a subset of ions that mimics an acoustic cavity used as a phonon lasing resonator. The cavity loss can then be controlled by the tweezer strength and the ``wall thickness'', the number of pinned ions for isolation. We pump the resonator by applying blue-sideband lasers, and investigate the lasing dynamics of the ``cavity'' motional modes such as threshold behavior, population distribution, the second-order coherence, and linewidth narrowing. This scheme can be generalized to multimode resonators, for which we report the mode competition phenomenon and lasing mode multistability. Our work provides an excellent platform for acoustic quantum state manipulation, paving the way towards phonon-mediated quantum computing, communications, and metrology.

Dynamics of surface-plasmon lasing in planar metal gratings on semiconductor.

We investigate the dynamics of surface plasmon (SP) lasing in Au gratings fabricated on InGaAs with a period of around 400 nm, which locates the SP resonance near the semiconductor energy gap and facilitates efficient energy transfer. By optically pumping the InGaAs to reach the population inversion required for the amplification and the lasing, we observe SP lasing at specific wavelengths that satisfy the SPR condition depending on the grating period. The carrier dynamics in semiconductor and the photon density in the SP cavity was investigated from the time-resolved pump-probe measurement and the time resolved photoluminescence spectroscopy, respectively. Our results reveal that the photon dynamics is strongly correlated with the carrier dynamics and the lasing build-up is accelerated as the initial gain proportional to the pumping power increases, and this trend is satisfactorily explained using the rate equation model.

Parity-time symmetry breaking optical nanocircuit.

Gain and loss balanced parity-time (PT) inversion symmetry has been achieved across multiple platforms including acoustics, electronics, and photonics. Tunable subwavelength asymmetric transmission based on PT symmetry breaking has attracted great interest. However, due to the diffraction limit, the geometric size of an optical PT symmetric system is much larger than the resonant wavelength, which limits the device miniaturization. Here, we theoretically studied a subwavelength optical PT symmetry breaking nanocircuit based on the similarity between a plasmonic system and an RLC circuit. Firstly, the asymmetric coupling of an input signal is observed by varying the coupling strength and gain-loss ratio between the nanocircuits. Furthermore, a subwavelength modulator is proposed by modulating the gain of the amplified nanocircuit. Notably, the modulation effect near the exceptional point is remarkable. Finally, we introduce a four-level atomic model modified by the Pauli exclusion principle to simulate the nonlinear dynamics of a PT symmetry broken laser. The asymmetric emission of a coherent laser is realized by full-wave simulation with a contrast of about 50. This subwavelength optical nanocircuit with broken PT symmetry is of great significance for realizing directional guided light, modulator and asymmetric-emission laser at subwavelength scales.