arXiv subjects

TJ Hammond

Publications and source records attributed to TJ Hammond.

8 recordsLinked to original sources

arXiv2025

Addressing modulational instability in anti-resonant hollow-core fibers for pulse compression

When pulses propagate in gas-filled anti-resonant hollow-core fibers (AR-HCFs) modulational instability (MI) can lead to pulse break-up and loss of coherence. In pulse broadening and compression schemes, MI is a parasitic effect that induces significant shot-to-shot fluctuations of the peak power of compressed pulses and increases rapidly over a narrow range of input pulse energies. In this work we use experimental studies and supporting numerical simulations to compare two AR-HCFs that are chosen to enhance or suppress MI. We demonstrate that judicious selection of the wall thickness of the anti-resonant elements (AREs) can drastically reduce the MI gain, thereby increasing the limit of pulse energy scaling of stable ultrafast pulse compression.

physics.optics↗

arXiv2025

Supercontinuum Generation in 1-decanol

Although solids have been recently used in ultrafast experiments for spectral broadening due to their relatively high nonlinearity, their sensitivity to damage limits their long-term stability. Liquids are a possible alternative to solids as a nonlinear medium because of their comparable nonlinearity and resistance to permanent damage. We generate a supercontinuum in 1-decanol that spans more than an octave from the visible to the near-infrared regime. We measure the nonlinear index of refraction of 1-decanol and find a significant $n_4$ contribution. This contribution leads to a nonlinearity comparable to CS$_2$ (a frequent reference for nonlinear optics) in high-intensity regimes while being significantly less volatile and toxic. We find this supercontinuum spectrum to be stable for at least 30 minutes.

physics.optics↗

arXiv2025

Influence of Kerr Anisotropy in Parametric Amplification

Four-wave parametric amplification can be extended to the TW/cm$^2$ regime using femtosecond pump pulses to amplify nearly octave spanning pulses with gain $> 20$~mm$^{-1}$, which we call Kerr instability amplification. Cross-polarized wave generation exploits Kerr anisotropy to induce a transient intensity-dependent polarization evolution. In this work, we combine Kerr instability amplification with cross-polarized wave generation to simultaneously amplify and rotate the output polarization of a signal beam, and we explore laser and crystal parameters to control the resulting polarization. In 1~mm MgO(100), we amplify linearly polarized light by $2000\times$ orthogonal to the pump and seed polarization. The parametric amplification and polarization rotation offers excellent pulse contrast enhancement for future high-power laser systems. Furthermore, the polarization provides an additional observable to study the nonlinear dynamics occuring in this extreme ultrafast light-matter interaction.

physics.optics↗

arXiv2024

Stimulated Raman Spectroscopy with Tunable Visible Broadband Probe Pulse Generated by Kerr-Instability Amplification

Femtosecond, broadband stimulated Raman spectroscopy is a popular approach to measuring molecular dynamics with excellent signal-to-noise and spectral resolution. We present a new method for broadband stimulated Raman spectroscopy that employs Kerr-instability amplification to amplify the supercontinuum spectrum from sapphire and create a highly tunable Raman probe spectrum spanning from 530 to 1000 nm (-6000 to 2800 cm^(-1)). Our method, called Kerr-instability amplification for broadband stimulated Raman spectroscopy (KAB-SRS) provides an alternative to optical parametric amplifiers by producing a broader and more tunable spectrum at a significantly reduced cost to OPA implementations. We demonstrate the effectiveness of KAB-SRS by measuring the stimulated Raman loss spectrum of 1-decanol.

physics.optics↗

arXiv2023

Phase of Kerr-based few-cycle parametric amplification

Kerr instability amplification can amplify over an octave of spectrum, a broad bandwdith supporting few-cycle pulses. However, dispersion management in this regime is crucial to maintain the ultrashort pulse duration. In our simulations, we find that the dispersion of Kerr instability amplification is near zero at the pump wavelength, and can be compensated pre-amplification to generate near-transform-limited amplified few-cycle pulses. We also find the phase of the amplified pulse depends on the seed phase and is independent of the pump, and does not significantly depend on the pump intensity. We discuss chirping the seed pulse to avoid saturation, a route for generating sub-mJ few-cycle pulses from the Kerr nonlinearity.

physics.optics↗

arXiv2023

Single-stage few-cycle pulse amplification

Kerr instability can be exploited to amplify visible, near-, and mid-infrared ultrashort pulses. We use the results of Kerr instability amplification theory to inform our simulations amplifying few-cycle pulses. We show that the amplification angle-dependence is simplified to the phase matching condition of four-wave mixing when the intense pump is considered. Seeding with few-cycle pulses near the pump leads to broadband amplification without spatial chirp, while longer pulses undergo compression through amplification. Pumping in the mid-IR leads to multi-octave spanning amplified pulses with single-cycle duration not previously predicted. We discuss limitations of the amplification process and optimizing pump and seed parameters to maximize amplification.

physics.optics↗

arXiv2023

Supercontinuum amplification by Kerr instability

The versatility of optical parametric amplifiers make them excellent sources for next-generation ultrashort strong-field physics experiments, however phase matching considerations limit the available bandwidth. We demonstrate supercontinuum amplification in a four-wave optical parametric amplifier by Kerr instability. Experimentally, we amplify spectra that span nearly an octave without spatial chirp, with two-cycle transform limited pulse duration. We also theoretically explore regimes that demonstrate single-cycle amplification in the near infrared.

physics.optics↗

arXiv2012

XUV Frequency Combs via Femtosecond Enhancement Cavities

We review the current state of tabletop extreme ultraviolet (XUV) sources based on high harmonic generation (HHG) in femtosecond enhancement cavities (fsEC). Recent developments have enabled generation of high photon flux (1014 photons/sec) in the XUV, at high repetition rates (>50 MHz) and spanning the spectral region from 40 nm - 120 nm. This level of performance has enabled precision spectroscopy with XUV frequency combs and promises further applications in XUV spectroscopic and photoemission studies. We discuss the theory of operation and experimental details of the fsEC and XUV generation based on HHG, including current technical challenges to increasing the photon flux and maximum photon energy produced by this type of system. Current and future applications for these sources are also discussed.

physics.optics↗