arXiv subjects

Frank Wise

Publications and source records attributed to Frank Wise.

13 recordsLinked to original sources

arXiv2026

Partial parabolic amplification in rare-earth-doped optical fiber

Nonlinear amplification is a powerful technique for generating ultrashort laser pulses with high peak power in fiber systems. However, the diversity of nonlinear amplification approaches and their inherent complexities present significant challenges to achieving a unified understanding and further scaling of peak power and pulse energy while preserving ultrashort durations. Here, we report the results of a systematic optimization with respect to seed pulse duration that elucidates the dynamics of nonlinear amplification and allows identification of distinct propagation regimes. As part of this analysis, we identify a new regime, termed partial parabolic amplification, which achieves 50-fs pulse duration and yields higher peak power than any other nonlinear amplification regime known to date. An initial experimental demonstration of partial parabolic amplification produces 50-fs and 2.2-uJ pulses with a 25-um-core Yb fiber amplifier, corresponding to a 30-MW peak power. In contrast to other nonlinear amplification techniques, practical energy scaling beyond 10 uJ and 200 MW should be achievable with available gain fibers with larger mode areas, which would fill a gap in existing fiber laser capabilities that would directly impact material processing, nonlinear bio-imaging, and other applications.

physics.optics↗

arXiv2026

Analysis and control of Raman phonon dynamics for enhanced optical frequency conversion

Raman phonons are quantized molecular motions that arise from the inelastic scattering of light and mediate a wide range of spectroscopic and nonlinear optical phenomena. These can play a major role in frequency-conversion processes, but commonly-used theoretical treatments based on the Raman gain spectrum largely neglect the phonons and their dynamical interaction with the field. In this work, we clarify the physical role of Raman phonons within a recently-developed time-domain framework based on the Raman-induced index modulation, and show that phonons correspond to the oscillatory component of the Raman-induced index modulation. The analysis further reveals a linear phonon-mediated interaction embedded within Raman scattering, in which optical fields couple through wave-vector matching with existing phonons. This mechanism underlies, but has been neglected in, coherent Stokes and anti-Stokes scattering, as well as molecular modulation. Building on this insight, we introduce a phonon-controlled approach that enables efficient conversion into a selected Stokes order by tuning the wave-vector-matching relation between the driven phonons and the targeted Raman process, and we confirm the approach by numerical simulations that consider realistic Raman dynamics. These results provide a clearer physical interpretation of Raman phonons and their dynamics, and offer new strategies for controlling Raman interactions.

physics.optics↗

arXiv2026

Highly-efficient perturbative Raman shifting by engineering the nonlinear temporal response

Raman scattering underlies a broad range of spectroscopic and light-generation techniques, yet its conventional description, based on the Raman gain spectrum, accurately describes only long-pulse, steady-state dynamics. We present a time-domain theoretical approach that provides a unified and physically-transparent description of Raman interactions across all temporal regimes. It enables direct visualization of Raman temporal dynamics and accounts for spectrotemporal aspects of Raman phenomena, which cannot be addressed by prior theories. In particular, molecules with strong Raman responses do not produce an efficient soliton self-frequency shift in gas-filled hollow-core fibers. The time-domain analysis exposes temporal and spectral distortions from the Raman response that impact frequency-shifting detrimentally, and identifies how these distortions can be suppressed by reducing the Raman interaction to a perturbation on the electronic response. Experiments that employ gas mixtures with tunable Raman fractions of the nonlinear response demonstrate up to a four-fold increase in quantum efficiency (from 20 to 80%) compared to the pure molecular gas, and unity-efficiency Raman shifting will be possible. The new time-domain framework uncovers phenomena that are inaccessible through the decades-old frequency-domain treatment of Raman scattering, and it applies to Raman interactions in solids, liquids, and gases on various timescales.

physics.optics↗

arXiv2026

Raman-enhanced spectral compression of high-energy femtosecond laser pulses in molecular gases

Nonlinear pulse propagation in gas-filled waveguides has attracted substantial attention over the past decade, and a variety of capabilities have been reported. However, there is no prior report of spectral compression in gas-filled waveguides or cavities, which would offer a natural route for scaling to much higher pulse energies than have been reached in solid structures. Here we report a high-energy spectral-compression technique based on nonlinear propagation in gas-filled capillaries. With 0.1- to 1-mJ pulses, compression of the spectral width by a factor up to 12 (from 60 nm to 5 nm) is demonstrated. Key to this advance is recognition that the process plays out differently in gases than in solids. In a noble gas (Ar), we find that even small structure in the spectrum, which is mapped to the time profile, of the input pulse can degrade the compression process. We identify the delayed Raman response of molecular gases (N2O and N2) as a mechanism that smooths and symmetrizes the nonlinear index modulation, which reduces the impact of spectral asymmetry and fine structure and enhances the fidelity of the compressed peak. The technique can be implemented with a capillary filled with ambient air, for sub-millijoule operation without a dedicated gas system. These results initiate a new direction in the optics of gas-filled waveguides and establish Raman-enhanced spectral compression as a robust route to high-energy narrowband optical sources, with potential impact in a broad range of applications.

physics.optics↗

arXiv2024

A simple accurate way to model noise-seeded ultrafast nonlinear processes

Noise can play an important role in nonlinear pulse propagation. It is not only the origin of fluctuations in supercontinuum but can also determine the generated signal amplitude and phase, as seen in phenomena such as noise-seeded four-wave mixing and spontaneous Raman scattering. Current models rely on input-pulse shot noise and Raman Langevin term to simulate noise-seeded Kerr effects and spontaneous Raman scattering, respectively. However, they cannot accurately simulate any nonlinear effects exhibiting asymmetries, for example, between spontaneous Stokes and anti-Stokes generation, or in amplification with emission and absorption cross sections. Moreover, combining these two techniques does not lead to accurate modeling of both effects simultaneously, especially in unsaturated Raman operational regimes or supercontinuum where spontaneous Raman emission noise plays a crucial role. To resolve this issue, we propose a new modified shot-noise model by directly introducing noise into the pulse propagation equation. It minimally modifies current models that contain only stimulated terms.

physics.optics↗

arXiv2024

Efficient, broadly-tunable source of megawatt pulses for multiphoton microscopy based on self-phase modulation in argon-filled hollow-core fiber

An exciting recent development for deep-tissue imaging with cellular resolution is three-photon fluorescence microscopy (3PM) with excitation at long wavelengths (1300 and 1700 nm). In the last few years, long-wavelength 3PM has driven rapid progress in deep-tissue imaging beyond the depth limit of two-photon microscopy, with impacts in neuroscience, immunology, and cancer biology. However, wide adoption of 3PM faces challenges. Three-photon excitation (3PE) is naturally weaker than two-photon excitation, which places a premium on ultrashort pulses with high peak power. The inefficiency, complexity, and cost of current sources of these pulses present major barriers to the use of 3PM in typical biomedical research labs. Here, we describe a fiber-based source of femtosecond pulses with multi-megawatt peak power, tunable from 850 nm to 1700 nm. Compressed pulses from a fiber amplifier at 1030~nm are launched into an antiresonant hollow-core fiber filled with argon. By varying only the gas pressure, pulses with hundreds of nanojoules of energy and sub-100 fs duration are obtained at wavelengths between 850 and 1700 nm. This approach is a new route to an efficient, robust, and potentially low-cost source for multiphoton deep-tissue imaging. In particular, 960-nJ and 50-fs pulses are generated at 1300 nm with a conversion efficiency of 10\%. The nearly 20-MW peak power is an order of magnitude higher than the previous best from femtosecond fiber source at 1300~nm. As an example of the capabilities of the source, these pulses are used to image structure and neuronal activity in mouse brain as deep as 1.1 mm below the dura.

physics.optics↗

arXiv2023

Spectral Speckle Customization

Speckle patterns are used in a broad range of applications including microscopy, imaging, and light-matter interactions. Tailoring speckles' statistics can dramatically enhance their performance in applications. We present an experimental technique for customizing the spatio-spectral speckled intensity statistics of optical pulses at the output of a complex medium (a disordered multimode fiber) by controlling the spatial profile of the input light. We demonstrate that it is possible to create ensembles of independent speckle patterns with arbitrary statistics at a single wavelength, simultaneously at decorrelated wavelengths, and even tailored statistics across an entire pulse spectrum.

physics.optics↗

arXiv2022

Direct Observation of Thermalization to a Rayleigh-Jeans Distribution in Multimode Optical Fibers

Recent years have witnessed a resurgence of interest in nonlinear multimode optical systems where a host of intriguing effects have been observed that are impossible in single-mode settings. While nonlinearity can provide a rich environment where the chaotic power exchange among thousands of modes can lead to novel behaviors, at the same time, it poses a major challenge in terms of understanding and harnessing these processes to advantage. Over the years, statistical models have been developed to macroscopically describe the response of these complex systems. One of the cornerstones of these theoretical formalisms is the prediction of a photon-photon mediated thermalization process that leads to a Rayleigh-Jeans distribution of mode occupations. Here we report the use of mode-resolved measurement techniques to make the first direct observations of thermalization to a Rayleigh-Jeans power distribution in a multimode optical fiber. We experimentally demonstrate that the underlying system Hamiltonian remains invariant during propagation while power equipartition takes place among degenerate groups of modes - all in full accord with theoretical predictions. Our results may pave the way toward a new generation of high-power optical sources whose brightness and modal content can be controlled using principles from thermodynamics and statistical mechanics.

physics.optics↗

arXiv2021

Efficient soliton self-frequency shift in hydrogen-filled hollow-core fiber

We report a study of soliton self-frequency shifting in hydrogen-filled hollow-core fiber. The combination of hydrogen and short 40-fs input pulses underlies clean and efficient generation of Raman solitons between 1080 and 1600 nm. With 240-nJ input pulses, the Raman soliton energy ranges from 110 to 20 nJ over that wavelength range, and the pulse duration is approximately 45 fs. In particular, 70-nJ and 42-fs pulses are generated at 1300 nm. Numerical simulations agree reasonably well with experiments and predict that microjoule-energy tunable pulses should be possible with higher-energy input pulses.

physics.optics↗

arXiv2021

Multimode Mamyshev Oscillator

We present a spatiotemporally mode-locked Mamyshev oscillator. A wide variety of multimode mode-locked states, with varying degrees of spatiotemporal coupling, are observed. We find that some control of the modal content of the output beam is possible through the cavity design. Comparison of simulations to experiments indicates that spatiotemporal mode-locking is enabled by nonlinear intermodal interactions and spatial filtering, along with the Mamyshev mechanism. This work represents a first exploration of spatiotemporal mode-locking in an oscillator with the Mamyshev saturable absorber.

physics.optics↗

arXiv2020

Starting Dynamics of a Fully Electronically Controlled Linear Mamyshev Oscillator

We start an environmentally-stable linear Mamyshev oscillator with electronically-controlled modulated pump and a moving filter. It delivers a 21-nJ pulse that becomes 65 fs in duration after a compressor. Reliable starting into stable mode-locking is found achievable with a modulated mode-locked state observed only when the modulation frequency is larger than 70 kHz. To avoid the damage of the gain fiber, two Faraday rotators are introduced. Besides, we have studied several aspects toward obtaining successful starting.

physics.optics↗

arXiv2019

Nonlinear ultrafast fiber amplifiers beyond the gain-narrowing limit

Ultrafast lasers are becoming increasingly widespread in science and industry alike. Fiber-based ultrafast laser sources are especially attractive because of their compactness, alignment-free setups, and potentially low costs. However, confining short pulses within a fiber core leads to high intensities, which drive a host of nonlinear effects. While these phenomena and their interactions greatly complicate the design of such systems, they can also provide opportunities for engineering new capabilities. Here, we report a new fiber amplification regime distinguished by the use of a dynamically-evolving gain spectrum as a degree of freedom: as a pulse experiences nonlinear spectral broadening, absorption and amplification actively reshape both the pulse and the gain spectrum itself. The dynamic co-evolution of the field and excited-state populations supports pulses that can broaden spectrally by almost two orders of magnitude and well beyond the gain bandwidth, while remaining cleanly-compressible to their sub-50-fs transform limit. Theory and experiments provide evidence that a nonlinear attractor underlies the management of the nonlinearity by the gain. Further research into the mutual, pulse-inversion propagation dynamics may address open scientific questions and pave the way toward simple, compact fiber sources that produce high-energy, sub-30-fs pulses.

physics.optics↗

arXiv2016

Commentary (invited update) to article "Spatiotemporal optical solitons", by B. A. Malomed, D. Mihalache, F. Wise, and L. Torner, J. Opt. B: Quantum Semiclass. Opt. 7, R53-R72 (2005)

This is an invited short update of the topic covered by the review article, which aims to briefly survey progress made in theoretical and experimental studies of multidimensional solitons since the publication of the review. The Commentary was invited as an addition to the original review article that will be reprinted in an e-book celebrating the 50th anniversary of Journal of Physics B (incorporating Journal of Optics B: Quantum and Semiclassical Optics).

physics.optics↗