arXiv subjects

Spencer W. Jolly

Publications and source records attributed to Spencer W. Jolly.

At least 19 recordsLinked to original sources

arXiv2026

Optimization of vacuum acceleration with radially polarized laser beams having phase aberrations

The strong electric fields from tightly-focused and ultrashort laser beams have always been discussed as a way to accelerate charged particles without any need for a medium or external cavity. Radially-polarized light is one way to do this, motivated by the emergence of longitudinal electrical fields with tight focusing. However, the laser pulse will generally quickly overtake the electrons under its influence, and every-other half-cycle will decelerate the electrons in effect partially reversing the acceleration. In this work we present the effect of optical aberrations, primarily spherical aberration, and how despite their purely spatial nature they can significantly optimize the net acceleration, and advantageously allow for longer pulses to drive this optical field-based process. We discuss the optical physics responsible for this increase in performance and find optimal aberration profiles using a stochastic algorithm.

physics.optics↗

arXiv2026

Space-time excitation creates soliton trains in multimode fibers

In this work, we show that injecting a single space-time-coupled light pulse-beam into a multimode graded-index fiber generates a train of multimode solitons. Space-time couplings excite the spatial modes with distinct temporal profiles. Due to nonlinear interactions, with a properly chosen input power these profiles split into several unique multimode solitons. In the case of a spatially chirped input pulse, two solitons composed of modes $LP_{01}$ and $LP_{11}$ are formed. In the case of the injection of a space-time optical vortex, characterized by its topological charge $\ell$, a train composed of $|\ell| + 1$ multimode solitons is generated. Their energy and modal composition are directly determined by the absolute value of the topological charge.

nlin.PS↗

arXiv2025

Space-time singularities in spatially-chirped Laguerre-Gaussian beams of any order

The electric field distributions and space-time singularity curves are computed for ultrashort pulsed Laguerre-Gaussian laser beams having spatial chirp. Due to the breaking of cylindrical symmetry by the spatial chirp, the singularities trace complicated curves in space-time, which also vary for different combinations of radial and vortical orders. Analytical solutions are mostly presented along with a recipe for numerically calculating higher orders. The behavior of the singularities upon propagation is also shown, along with a discussion of the extension towards few-cycle pulses. These results are an example of how a simple physical scenario can result in highly complicated singular behavior in space-time.

physics.optics↗

arXiv2025

Agile laser wavelength tuning using dynamic targeting

Tunable lasers are essential and versatile tools in photonics, with applications spanning telecommunications, spectroscopy, and sensing. Advancements have aimed to expand tuning ranges, suppress mode hopping, and enable photonic integration. In this work, we explore the adaptation of dynamic targeting, a technique originally developed to stabilize lasers under optical feedback, as a method for achieving agile, fast, and continuous wavelength tuning. By adjusting the feedback rate and phase, we enable a stable and controlled frequency shift. We experimentally demonstrate reliable and reproducible tuning over 2.1 GHz using a free-space optical setup. Simulations further suggest that this approach could extend the tuning range to tens of GHz, with a potential scan speed exceeding $10^{17}$ Hz/s. These results highlight dynamic targeting as a promising route toward agile frequency control in semiconductor lasers.

physics.optics↗

arXiv2025

Accessing different higher-order modes with nonlinear modal energy transfer under simple realistic tuning of initial conditions

The initial conditions in multi-mode fibers pumped by ultrashort laser pulses strongly determine the following nonlinear optical interactions. In this work we firstly compare the detailed spatial mode content of simple initial conditions, transverse offset and tilt. We then show how those initial conditions can both be used to achieve a nonlinear modal energy transfer into higher-order spatial modes of a model graded-index fiber, with their own slight differences and advantages. Going beyond purely spatial initial conditions, we introduce nonlinear modal energy transfer results using spatial chirp at the input facet, whereby the different temporal envelopes of the spatial modes allow for tuning the nonlinear modal energy transfer process. Our results open up investigations into higher-dimensional tuning of nonlinear processes in multi-mode fibers using initial conditions.

physics.optics↗

arXiv2025

Enhanced spatiotemporal optical vortices and vortex chains from Hermite-Gauss modes with a tilted pulse front

Hermite-Gaussian (HG) beams are standard modes delivered by continuous or pulsed lasers systems, and pulse-front tilt is one of the most common, detrimental or beneficial, spatiotemporal couplings affecting ultrashort pulses. Combining them, we show that focusing a pulsed HG beam with a tilt generates an elliptical spatiotemporal optical vortex (STOV), or a chain of them. The elliptical STOVs differ from standard STOVs in an additional spatial chirp that is manifested as a wave front temporal rotation, and results in an enhanced transverse orbital angular momentum. The longitudinal field is significantly larger than that of normal STOVs, and may also take the form of an elliptical STOV. Our concept greatly simplifies previous arrangements for the generation of STOVs, whose additional features make them attractive for improving their applications in electron trapping and acceleration, or as driving fields for the generation of higher-order harmonics and other interactions with matter.

physics.optics↗

arXiv2025

Propagation of space-time optical vortices in multimode fibers

The non-intuitive spatiotemporal modal content of space-time optical vortices (STOVs) is calculated in a graded-index fiber supporting a large number of propagating modes. We discuss how a fiber supporting many modes allows to truly couple higher-order STOVs, the number of modes necessary to support a STOV of a certain order, and conversely the truncation effect in a few-mode fiber. Based on the excited modes and their temporal profiles, we show numerical results for the linear and nonlinear propagation of STOVs in multimode fibers, specifically the linear space-time beating at short propagation distances, and the nonlinear trapping effect between modes producing stable states on long propagation distances. Our results underline how STOVs present a rich platform for multimode nonlinear optics and technology.

physics.optics↗

arXiv2024

Influence of Feedback Phase on Time Delay Signature and Chaos Bandwidth in a Laser subject to Dual Optical Feedback

Semiconductor lasers subject to optical feedback can behave chaotically, which can be used as a source of randomness. The optical feedback, provided by mirrors at a distance, determines the characteristics of the chaos and thus the quality of the randomness. However, this fixed distance also shows itself in the intensity, an unwanted feature called the Time Delay Signature (TDS). One promising solution to suppress the TDS is using double optical feedback. We study this system numerically in this paper. In particular, we focus on the impact of the feedback phase, a sub-wavelength change in the position of the mirrors, on the TDS and chaos bandwidth (CBW) of the system. We show that by precisely setting the feedback parameters, including the feedback phases, the TDS can be suppressed, and that the feedback phase control is necessary rather than optional to robustly suppress the TDS. In addition, it is possible to suppress the TDS without loss of the CBW. At strong feedback rates the system can restabilize, and one can switch between a chaotic and steady state by changing only the feedback phase. Finally, we relate the feedback phase sensitivity to interference between the two delayed signals. This system is promising for applications of chaotic lasers as one can either suppress the TDS or increase the CBW.

physics.optics↗

arXiv2024

Modeling the focusing of a radially-polarized laser beam with an initially flat-top intensity profile

Radially-polarized light beams present very interesting and useful behavior for creating small intensity spots when tightly-focused, and manipulating nanostructures or charged particles. The modeling of the propagation of such vector beams, however, is almost always done using the lowest-order fundamental radially-polarized beam due to the complexity of vector diffraction theory. We show how a flat-top radially-polarized beam can be modeled analytically using a sum of higher-order beams, and describe a number of interesting qualities, and compare to numerically-solved integral descriptions.

physics.optics↗

arXiv2024

Transverse orbital angular momentum imparted upon focusing spatio-temporally coupled ultrashort pulses

A focusing system such as a single lens or a spherical mirror imparts intrinsic transverse orbital angular momentum (OAM) to spatiotemporal (ST) coupled fields the ST intensity distribution of which presents ST covariance. This fact may greatly simplify the experimental setups used to date to impart transverse OAM. We evaluate analytically the imparted transverse OAM as a function of the focal length and the covariance. The focused fields with transverse OAM include elliptical ST vortices and rotating pulses without any ST phase singularity such as the "lighthouse" pulse. We provide closed-form, analytical expressions for these fields valid at any propagation distance from the focusing system, which are of interest in applications such the interaction of these fields with matter. In general, focusing of ST coupled fields with intensity covariance generates mixed fields with ST vortices and rotating pulse-fronts, where one or another feature dominates depending on the input field.

physics.optics↗

arXiv2024

Relativistic electrons from vacuum laser acceleration using tightly focused radially polarized beams

We generate a tabletop pulsed relativistic electron beam at 100 Hz repetition rate from vacuum laser acceleration (VLA) by tightly focusing a radially polarized beam into a low-density gas. We demonstrate that strong longitudinal electric fields at the focus can accelerate electrons up to 1.43 MeV by using only 98 GW of peak laser power. The electron energy is measured as a function of laser intensity and gas species, revealing a strong dependence on the atomic ionization dynamics. These experimental results are supported by numerical simulations of particle dynamics in a tightly focused configuration that take ionization into consideration. For the range of intensities considered, it is demonstrated that atoms with higher atomic numbers like krypton can optimally inject electrons at the peak of the laser field, resulting in higher energies and an efficient acceleration mechanism that reaches a significant fraction of the theoretical energy gain limit.

physics.optics↗

arXiv2023

Generation of ultrashort light pulses carrying orbital angular momentum using a vortex plate retarder-based approach

We use a vortex retarder-based approach to generate few optical cycles light pulses carrying orbital angular momentum (known also as twisted light or optical vortex) from a Yb:KGW oscillator pumping a noncollinear optical parametric amplifier generating sub-10 fs linearly polarized light pulses in the near infrared spectral range (central wavelength 850 nm). We characterize such vortices both spatially and temporally by using astigmatic imaging technique and second harmonic generation-based frequency resolved optical gating, respectively. The generation of optical vortices is analyzed, and its structure reconstructed by estimating the spatio-spectral field and Fourier transforming it into the temporal domain. As a proof of concept, we show that we can also generate sub-20 fs light pulses carrying orbital angular momentum and with arbitrary polarization on the first-order Poincaré sphere.

physics.optics↗

arXiv2023

Coupling to multi-mode waveguides with space-time shaped free-space pulses

Guided wave optics, including most prominently fiber optics and integrated photonics, very often considers only one or very few spatial modes of the waveguides. Despite being known and utilized for decades, multi-mode guided wave optics is currently rapidly increasing in parallel with technological improvements and better simulation tools. The physics of multi-mode interactions are usually driven by some initial energy distribution in a number of spatial modes. In this work we introduce how, with free-space input beams having space-time couplings, the different modes can be excited with different complex frequency or time profiles. We cover fundamentals, the coupling with a few simple space-time aberrations, different waveguides, and a number of technical nuances. This concept of space-time initial conditions in multi-mode waveguides will provide yet another tool to study the rich nonlinear interactions in such systems.

physics.optics↗

arXiv2023

Control of vortex orientation of ultrashort optical pulses using spatial chirp

Introducing a spatial chirp into a pulse with a longitudinal vortex, such as a standard pulsed Laguerre-Gauss beam, results in a vortex pulse with an arbitrary orientation of the line phase singularity between longitudinal and transverse, depending on the amount of chirp. Analytical expressions are given for such pulses with arbitrary topological charge valid at any propagation distance.

physics.optics↗

arXiv2023

Impact of feedback time-distribution on laser dynamics

Time-distributed optical feedback in semiconductor lasers has gained attention for its ability to produce high-quality chaos and effectively suppress the time-delay signature. However, the fundamental impact of the distribution of feedback in time on laser dynamics remains unexplored. In this paper, we investigate this topic by using fiber Bragg grating (FBG) feedback. We theoretically study the laser response using FBGs of different lengths but similar reflectivity, effectively stretching the impulse response over a longer period while maintaining its overall shape. We observe that above a critical value corresponding to a grating length of approximately $1$\,cm, fluctuations in laser stability emerge. We attribute this phenomenon to the damping of relaxation oscillations when the zeros of the FBG reflectivity spectrum align with the laser side lobes around the relaxation oscillation frequency. We also uncover an asymmetrical dynamical behavior of the laser for positive and negative frequency detuning. We deduce that this asymmetry is a characteristic feature of FBG feedback and delve into the specificities that trigger such behavior.

physics.optics↗

arXiv2023

Clarifying the impact of dual optical feedback on semiconductor lasers through analysis of the effective feedback phase

Time-delayed optical feedback is known to trigger a wide variety of complex dynamical behavior in semiconductor lasers. Adding a second optical feedback loop is naturally expected to further increase the complexity of the system and its dynamics, but due to interference between the two feedback arms it was also quickly identified as a way to improve the laser stability. While these two aspects have already been investigated, the influence of the feedback phases, i.e. sub-wavelength changes in the mirror positions, on the laser behavior still remains to be thoroughly studied, despite indications that this parameter could have a significant impact. Here, we analyze the effect of the feedback phase on the laser stability in a dual-feedback configuration. We show an increased sensitivity of the laser system to feedback phase changes when two feedback loops are present, and clarify the interplay between the frequency shift induced by the feedback and the interferometric effect between the two feedback arms.

physics.optics↗

arXiv2023

Ultrashort laser pulses with chromatic astigmatism

Ultrashort laser pulses are described having chromatic astigmatism, where the astigmatic phase varies linearly with the offset from the central frequency. Such a spatio-temporal coupling not only induces interesting space-frequency and space-time effects, but it removes cylindrical symmetry. We analyze the quantitative effects on the spatio-temporal pulse structure on the collimated beam and as it propagates through a focus, with both the fundamental Gaussian beam and Laguerre-Gaussian beams. Chromatic astigmatism is a new type of spatio-temporal coupling towards arbitrary higher complexity beams that still have a simple description, and may be applied to imaging, metrology, or ultrafast light-matter interaction.

physics.optics↗

arXiv2022

Performance and control strategy of an integrated tunable laser with a single intra-cavity AMZI filter

Asymmetric Mach-Zehnder interferometers (AMZIs) can, in principle, enable continuous wavelength tuning of a laser when used as an intra-cavity filter. Their simplicity and good compatibility with generic foundry platforms are major advantages. However, the difficulty to develop a well-defined and robust control strategy is an important drawback which restricts the use-cases of these tunable lasers. Here, we make an in-depth investigation of the tunability properties of a laser including a single-stage AMZI in its cavity. We find that due to imperfections of Electro-Optic Phase Modulators (EOPMs), the dependence of the phase variation with the applied voltage is not linear. Because integrated EOPMs cannot be individually calibrated, these nonlinearities prevent a precise and independent tuning of the phase and amplitude of the AMZI transfer function, and thus continuous tuning cannot be reliably achieved. To overcome this issue, we propose a refined control strategy which allows for semi-continuous tuning. With this approach, we demonstrate a piece-wise continuous tuning of the emission wavelength by taking advantage of the coupling between amplitude and phase in the AMZI response. With our refined control strategy, we achieve tuning of the emission wavelength over the full free spectral range (FSR) of the AMZI.

physics.optics↗