Pulse Trapping Research Articles

Dissimilar soliton molecule formed by dissipative pulses in a single-mode mode-locked fiber laser

Soliton molecules, or also known as optical bound states, are the most representative example of solitons’ particle nature and have given birth to diverse light-matter analogies. Despite detailed research on regular bound states, the soliton molecule synthesis of dissimilar pulses has rarely been reported. Here, soliton molecules formed by dissimilar dissipative solitons are demonstrated in a single-mode mode-locked fiber laser, with an in-depth analysis of their evolution dynamics. This novel bound state features pulse trapping between two ultrafast vector pulses with distinct pulse properties including energy, duration, and chirp, leading to unique temporal and spectral profiles. This laser provides an optimal platform for studying complex interactions between different types of dissipative solitons. The findings here can provide new degrees of freedom for the generation of optical soliton molecules and can fuel applications in optical information processing, metrology, and spectroscopy.

Crowd control of ions in the Astral analyzer.

Space charge effects are the Achilles' heel of all high-resolution ion optical devices. In time-of-flight mass analyzers, these may manifest as reduction of resolving power, mass measurement shift, peak coalescence, and/or transmission losses, while highly sensitive modern ion sources and injection devices ensure that such limits are easily exceeded. Space charge effects have been investigated, by experiment and simulation study, for the astral multi-reflection analyzer, incorporating ion focusing via a pair of converging ion mirrors, and fed by a pulsed extraction ion trap. Major factors were identified as the resonant effect between ~103 ions of similar m/z in-flight and the expansion of trapped packets of ~104-5 ions prior to extraction. Optimum operation and compensated ion mirror calibration strategies were then generated and described based on these findings.

Pulse Trapping and Harmonic Oscillations in the Presence of a Dark Soliton in Optical Fibers

Pulse Trapping and Harmonic Oscillations in the Presence of a Dark Soliton in Optical Fibers

Autonomous nanorobots with powerful thrust under dry solid-contact conditions by photothermal shock

Nanorobotic motion on solid substrates is greatly hindered by strong nanofriction, and powerful nanomotors‒the core components for nanorobotic motion‒are still lacking. Optical actuation addresses power and motion control issues simultaneously, while conventional technologies with small thrust usually apply to fluid environments. Here, we demonstrate micronewton-thrust nanomotors that enable the autonomous nanorobots working like conventional robots with precise motion control on dry surfaces by a photothermal-shock technique. We build a pulsed laser-based actuation and trapping platform, termed photothermal-shock tweezers, for general motion control of metallic nanomaterials and assembled nanorobots with nanoscale precision. The thrust-to-weight ratios up to 107 enable nanomotors output forces to interact with external micro/nano-objects. Leveraging machine vision and deep learning technologies, we assemble the nanomotors into autonomous nanorobots with complex structures, and demonstrate multi-degree-of-freedom motion and sophisticated functions. Our photothermal shock-actuation concept fundamentally addresses the nanotribology challenges and expands the nanorobotic horizon from fluids to dry solid surfaces.

Machine-learning iterative optimization for all polarization-maintaining linear cavity Er:fiber laser.

All polarization-maintaining (PM) linear cavity mode-locked fiber lasers are promising ultrafast laser sources due to their compactness and environmental robustness. Here, we demonstrate a linear cavity fiber laser with all-PM configuration experimentally and investigate the mode-locking formation of the laser using a machine-learning iterative optimization method based on the Gaussian process. The optimization algorithm can converge rapidly after only 30 runs. Using the optimized parameters, we simulate the generation of mode-locked pulses from noise. The output spectrum and pulse energy are highly consistent with the experiment. Furthermore, we describe the intracavity dynamic evolution under group velocity mismatch. We then show that the pulse trapping induced by cross-phase modulation leads to the overcompensated time synchronization between the orthogonally polarized components.

Propagation dynamics of elliptical super-Gaussian bullets in nonlinear metamaterial waveguide

The characteristics of an optical beam propagating in a medium should be preserved for many applications related to fiber optic communication. The phenomenon of self-trapping due to adequate balance among linear and nonlinear effects may preserve the characteristics of an optical beam. In this work, we perform a theoretical investigation on the propagation of a spatiotemporal elliptical super-Gaussian beam in a Kerr nonlinear metamaterial waveguide. We follow the Lagrangian variational method and numerical analysis using the appropriate trial function for the input elliptical super-Gaussian beam and analyze the self-trapping and deformation of the propagating beam in metamaterials. We obtain special conditions to observe the self-trapping and stabilize the dynamics of the elliptical super-Gaussian beam in both negative and positive index regimes of the metamaterial. It is found that in the negative index regime of metamaterial, the phenomenon of self-trapping may exist in the normal dispersion regime with defocusing Kerr nonlinearity. However similar to the conventional medium, the robust balance among the anomalous dispersion and focussing Kerr nonlinearity supports the self-trapping in the positive index regime. There is a critical optical power for the input beam to observe the pulse trapping phenomena. This power is found to be a function of the super-Gaussian parameter as well as the ellipticity of the input beam. The period of self-trapping is also a function of the super-Gaussian parameter and the ellipticity of the input beam.

Probing drift velocity dispersion in MAPbI3 photovoltaic cells with nonlinear photocurrent spectroscopy.

Conventional time-of-flight (TOF) measurements yield charge carrier mobilities in photovoltaic cells with time resolution limited by the RC time constant of the device, which is on the order of 0.1-1 µs for the systems targeted in the present work. We have recently developed an alternate TOF method, termed nonlinear photocurrent spectroscopy (NLPC), in which carrier drift velocities are determined with picosecond time resolution by applying a pair of laser pulses to a device with an experimentally controlled delay time. In this technique, carriers photoexcited by the first laser pulse are "probed" by way of recombination processes involving carriers associated with the second laser pulse. Here, we report NLPC measurements conducted with a simplified experimental apparatus in which synchronized 40ps diode lasers enable delay times up to 100 µs at 5kHz repetition rates. Carrier mobilities of ∼0.025cm2/V/s are determined for MAPbI3 photovoltaic cells with active layer thicknesses of 240 and 460nm using this instrument. Our experiments and model calculations suggest that the nonlinear response of the photocurrent weakens as the carrier densities photoexcited by the first laser pulse trap and broaden while traversing the active layer of a device. Based on this aspect of the signal generation mechanism, experiments conducted with co-propagating and counter-propagating laser beam geometries are leveraged to determine a 60nm length scale of drift velocity dispersion in MAPbI3 films. Contributions from localized states induced by thermal fluctuations are consistent with drift velocity dispersion on this length scale.

Dual-state vector soliton in mode-locked fiber laser

Vector soliton originates from the soliton trapping dynamics via cross-phase modulation (XPM) which has been used to achieve supercontinuum, optical switching and optical analog of gravity-like potentials. Dual-state vector soliton (DSVS) is reported in mode-locked fiber laser under appropriate birefringence. Two vector soliton states emitted alternatively display double-peak and Lorentz-shaped spectral profile, respectively. The two orthogonally polarized components of the double-peak spectrum exhibit obvious redshift and blueshift, respectively, while the frequency shift for the other state is limited even with the reversed shift direction, which illustrates a unique vector soliton evolution dynamic. DSVS originates from the pulse trapping induced by XPM, as well as the periodical evolution and frequency shift induced by self-phase modulation under dispersion-managed condition. The vector period-doubling phenomenon will further enrich the understanding about soliton, and also guide the design of mode-locked laser.

Zero ac Stark frequency shift of an atom trapped in pulsed laser light* *Reported at the IV International Conference on Ultrafast Optical Science (28 September–October 2020, Lebedev Physical Institute of the Russian Academy of Sciences, Moscow, Russia).

We report a theoretical analysis of the spectral properties of atoms localised in an optical pulsed trap. It is shown that this analysis can be carried out using the correlation coefficient calculated from the averaged dynamics of atomic excitation by resonant probe laser light in the presence of a nonresonant pulsed field. It follows from calculations that at a laser pulse duration of 8 ps, atoms can be trapped at a zero shift in the D2 line transition frequency of the Rb atom, caused by the ac Stark effect. This configuration can be used to build optical frequency standards without the need for localising laser radiation at the ‘magic’ wavelength.

XPM‐Induced Vector Asymmetrical Soliton with Spectral Period Doubling in Mode‐Locked Fiber Laser

AbstractCross phase modulation (XPM) can induce soliton trapping in nonlinear medium, which has been employed to achieve vector soliton, optical switching, and optical analog of gravity‐like potentials. Here, the first observation of a novel soliton operation is reported whose wavelength exhibits redshift and blueshift periodically in a mode‐locked fiber laser under appropriate birefringence and dispersion map. XPM dominates the dynamics by inducing and sustaining the vector asymmetrical soliton (VAS) with spectral period doubling, and exhibits a unique trajectory of pulse trapping. The XPM‐induced VAS is an idiosyncratic steady state featured with asymmetry in the model based on the coupled Ginzburg–Landau equation, which depicts the distinct pulse features in comparison with vector soliton, soliton molecule, and traditional period‐doubling evolutions. The two orthogonal polarized directions of mode‐locked fiber laser can be regarded as the XPM‐coupled dissipative resonators guiding the further study of the optical nonlinear dynamics and chaos for soliton, which is helpful to laser design and brings useful insights into nonlinear science and applications.

Atom femtosecond optical trap based on spectrally filtered laser radiation

We have examined the use of alkali metal (rubidium) vapour for spectral filtering of broadband pulsed laser light that is used to produce a femtosecond pulsed optical dipole trap. It has been shown that, even at large detuning of the centre emission frequency from the frequency of atomic transitions, spectral components present in the wings of the laser emission line are capable of heating localised atoms, thus reducing their lifetime in the atomic trap. Using atomic vapour for filtering the laser emission spectrum, we have suppressed its spectral components resulting in heating. This has made it possible to increase the lifetime of atoms in the pulsed optical dipole trap to a value comparable to their lifetime in an optical trap formed by narrow-band cw laser light.

Atom femto trap: experimental realization

In this work, we demonstrate the trapping of rubidium (Rb) atoms in a pulsed optical dipole trap formed by femtosecond laser radiation with a pulse duration as small as 70 fs. The atom localization in such trap strongly depends on the heating of the atoms caused by the momentum diffusion due to the dipole force fluctuations. The atom femto traps can be used for localization of atoms others than alkaline and alkaline earth atomic elements by conversation of pulsed laser radiation of visible or near infrared to UV spectral.

Dynamic bouncing mode cavity for integratable broadband light trapping and release

We propose a dynamic process based on a new structure of bouncing mode cavity to realize integratable long-term light pulse trapping and release on a waveguide. To break the delay-bandwidth limit, the idea of a bouncing mode cavity is to bind a guided light pulse bouncing back and forth inside. Being compatible with complementary metal-oxide-semiconductor (COMS) processing, an optimized boundary mirror design with an ultra-low loss and a broad bandwidth is presented. Using the dynamic bouncing mode cavity composed of a switchable boundary mirror, the simulation of controlled optical pulse storage is demonstrated on a two-dimensional waveguide. The results show that the long lifetime of 32 ns and the wide bandwidth of 16.11 THz can be obtained simultaneously. All the results are verified with finite-difference time-domain numerical calculation. With progress in manipulating the optical properties of materials, this approach may contribute to integrated photonic devices for optical information processing.

ДИНАМИКА ВИБРОЗАЩИТНЫХ СИСТЕМ С УПРАВЛЯЕМЫМ МЕХАНИЗМОМ НАЛОЖЕНИЯ СВЯЗЕЙ

In the paper there are presented the applied theory elements of new basic models of vibration-proof systems with additional controlled devices of intermittent functioning – a mechanism of connection imposition and a pulse trap. 
 The ultimate options of control resulting in jumping changes of a system structure when control occasionally increases sharply and becomes a zero result. The sequential alternation of control data defines so-called an indirect pulse control of the parameters of damping and stiffness of an additional (controlled) elastic-damping link of intermittent action. At that, irrespective of the type of the controlled links used, such as a damper of viscous resistance, a friction damper or elastic damper the achieved effect of vibration protection under all other equal conditions will be equal. 
 These controlled links imitate the operation of connection imposition mechanism, that is, they block occasionally a vibration protection system that allows improving considerably its dynamic properties at the expense of a new parameter defining the length of such blocks. In particular, it is possible to consider also the imitation of the operation of a pulse trap realizing instant (pulse) blocks of the system as a result of which the rate of the object protected is occasionally zero.
 Basic investigation results of dynamic properties of these systems:
 - Resonance phenomena are eliminated (in steady-state oscillation modes of the object oscillation decrease monotonously with the frequency increase of kinematic harmonic disturbance);
 - Transients caused by initial conditions or random fluctuations of external disturbances damp within the limits of one period of impact, that is, the process is carried out which is characterized as “one shock – one oscillation”; 
 - System invariance with respect to power disturbances as a result of periodic blockings increases considerably and, as a consequence it is possible to decrease the stiffness of a bearing elastic component without fear for stability loss; 
 - Energy costs for realization of indirect pulse control are connected only with the “switch on-switch off” process which may be programmed through components of the system state in a relative motion by means of the actualization of system design properties.

Central Ramsey fringe identification by means of an auxiliary optical field

We propose and demonstrate a simple technique for identifying the central Ramsey fringe of pulsed coherent population trapping resonance. An auxiliary optical field is applied during the free evolution time. It suppresses the nearby fringes but does not change the amplitude of central fringe practically, which marks it out clearly. The theory based on the density matrix equations for the Λ-system configuration of levels and Ramsey interrogation that takes into account the auxiliary optical field is presented and compared to the experiment with 87Rb atoms. We also propose a technique for improving the middle- and long-term stability of compact atomic clocks.

Extreme UV Light Generation Through Dispersive Wave Trapping in a Tapered Gas-Filled Hollow Fiber

In this letter, we demonstrate how the soliton–plasma interaction initiates trapping of the generated dispersive waves (DWs) in an experimentally feasible tapered He-filled hollow-core anti-resonant fiber (HC-ARF). We show that the taper gradient strongly influences the pulse trapping dynamics and thus determines the intensity and blueshift of the trapped DW. This process leads to an efficient DW generation down to 100 nm with a 3.4-octave supercontinuum spanning 100–1150 nm (2.73 PHz) by tapering a 36- $\mu \text{m}$ core HC-ARF to 18 $\mu \text{m}$ under 19-bar He, pumped at 800 nm with 6- $\mu \text{J}$ pulse energy. The proposed fiber taper structure could be an alternative route to generate light in the extreme ultra-violet (EUV) spectral range using moderate gas pressure and relatively low pulse energy.

Generation of Fusion Neutrons under the Interaction of Accelerated Deuterons with a Heavy Hydrogen Flow in a Plasma Trap with a Pulsed Magnetic Field

A scheme for the generation of thermonuclear neutrons in a pulsed trap with magnetoinertial plasma confinement is proposed. Neutrons are primarily produced in the center of the trap in the hottest zone of the plasma. This zone is formed in the area of intersection of two opposite axial flows of deuterons and a heavy hydrogen jet injected perpendicular to the axis of the trap. The evaluation shows that the thermonuclear process of neutron generation prevails over direct interactions of the “beam-beam” and “beam-plasma” type.

Indirect Control of Oscillations: Elements of Theory

A brief review of the main research areas in the field of controlled vibration protection systems is given. It is shown that Vibration systems with indirect control processes of oscillations allow with a minimum expenditure of energy to ensure programmable switching parameters and structures, in which the dissipative restoring and inertial forces generated on the basis of active impact. Within synthesis of indirect control the chains of new auxiliary mathematical constructs for finding optimal synthesizing functions of the elastic-damping units parameters control are obtained. It enabled to separate a base model with intermittent damping and base model with impulse trap. As a result of the study, based on the harmonic balance method, the dynamic properties of the basic model with intermittent damping, calculation formulas are obtained for determining the parameters of the compensation effect and calculating the dynamic coefficient. It is established that, with an optimal sequence of damping switching, the resonant phenomena are eliminated, and the transient processes decay within one period of the kinematic perturbation. The basic model with a pulse trap imitates the limiting variant of intermittent damping and realizes the process of superimposing constraining bonds, the sequence and duration of which are new variables essentially increasing controllability. And for indirect pulse control, there exicts a certain minimum of power consumption independent of the achieved effect of vibration protection. A regulated increase in the duration of the application of the restraining coupling in the low-frequency region and a decrease in this duration in the high-frequency region provides a monotonically decreasing dependence on the dynamic coefficients over the entire frequency range. An example of a solution to the optimization problem of controlling the damping process for a basic model of a vibration isolation system is considered. It is established that intermittent damping is an indispensable feature of the optimality of the vibration isolation system: the damper switches on when the sign of the object's speed has changed and turns off when the object's displacement sign has changed.

Suppression of Dick Effect in Ramsey-CPT Atomic Clock by Interleaving Lock.

The Dick effect is one of the main limitations of short-term frequency stability for most atomic clocks operating in the pulsed mode. Rather than employing better local oscillators with ultralow phase noise, using the interleaving lock technique to eliminate the dead time is a promising approach to suppress the Dick effect. In this paper, we demonstrate the suppression of the Dick effect by the interleaving lock technique in a pulsed Ramsey-coherent population trapping clock with two identical Cs atomic ensembles. The Dick effect is expected to be reduced by a factor of 24 theoretically. The measured short-term Allan deviation is improved from at 1 s to at 1 s. What is even more remarkable is that the Allan deviation curve exhibits slope from 0.01 to 2 s.

Symmetric autobalanced Ramsey interrogation for high-performance coherent-population-trapping vapor-cell atomic clock

We report a high-performance pulsed coherent population trapping (CPT) Cs cell atomic clock using the implementation of a symmetric auto-balanced Ramsey (SABR) interrogation sequence. The latter method is found to reduce the light-power induced frequency shift by an order of magnitude compared to a previous experiment using a simple auto-balanced Ramsey interrogation. The contribution of this shift to the clock frequency stability is now rejected in the 10−16 range at 104 s averaging time. Additional tricks, including a compensation method to reduce the laser amplitude noise contribution and the generation of novel error signals for local oscillator frequency and phase correction, have been implemented using a FPGA-based digital electronics board in order to improve the clock short-term stability by a of factor 2. The Allan deviation of the SABR-CPT clock, extracted from a selected 3 × 104 s-long dataset, is 2 × 10−13 τ−1∕2 and averages down to the level of 2.5 × 10−15 at 104 s. These results are encouraging to stimulate the development of hot cell CPT-based clocks for industrial, scientific, and instrumentation applications.