arXiv subjects

Kevin Schwarz

Publications and source records attributed to Kevin Schwarz.

3 recordsLinked to original sources

arXiv2026

Low peak-power pulse compression in gas-filled Herriott cells in the 2 μm wavelength range

At laser wavelengths longer than the prominent 1 μm range of high-power ytterbium-doped lasers, nonlinear phase shifts produced in nonlinear media for spectral broadening and subsequent pulse compression decrease drastically. Consequently, at the 2 μm wavelength range, the threshold of the applicable peak power for pulse compression in gas-filled multipass cells increases. The common approach of choosing a Herriott multipass cell configuration close to the concentric resonator does not necessarily lead to the highest total nonlinear phase shift, due to a restriction of the total number of reflections on the cell mirrors of a given size. Therefore, an analytical approach is presented here to maximize the nonlinear phase shift for a given set of mirrors, considering lossless and dispersionless propagation. Furthermore, to achieve pulse compression with gas-filled multipass cells for relatively low peak powers at wavelengths around 2 μm, we developed a high-pressure gas cell and demonstrated experimentally pulse compression in the negative- and positive dispersion regimes, with achieved pulse durations of around 40 fs and 55 fs respectively.

physics.optics↗

arXiv2025

Characterizing Phishing Pages by JavaScript Capabilities

Phishers achieve large-scale attacks by using ready-to-deploy phishing websites (phishing kits) to rapidly launch campaigns that leverage specific data exfiltration, evasion, or mimicry techniques. In contrast, researchers and defenders continue to rely on manual analysis to identify features for kit fingerprinting. In this paper, we examine the link between a page's client-side behavior and the underlying phishing kit used, enabling automated aggregation of phishing pages. Our key insight is that client-side techniques make heavy use of browser APIs, which, in turn, differentiate underlying kits based on their feature sets. Using an instrumented browser and a URL fuzzing utility, we collected traces from 1,328,917 pages and recovered kit archives for 4,180 pages between August 2023 and January 2025. For the labeled subset, we find that clustering based on the set of browser APIs executed yields 98% accuracy in grouping them by the underlying kit. We also find that 434,495 phishing pages execute enough browser APIs to cluster into 9,306 clusters, compressing multi-lingual phishing pages across various domains into a single cluster. Our findings show that analysts and researchers can leverage the complexity of client-side phishing code to track phishers' kit deployments in the wild.

cs.CR↗

arXiv2022

Spectral broadening in convex-concave multipass cells

Since its first demonstration in 2016, the multi-pass spectral broadening technique has covered impressive ranges of pulse energy (3 $μ$J - 100 mJ) and peak power (4 MW - 100 GW). Energy scaling of this technique into the joule-level is currently limited by phenomena such as optical damage, gas ionization and spatio-spectral beam inhomogeneity. These limitations can be overcome by the novel multi-pass convex-concave arrangement, which exhibits crucial properties such as large mode size and compactness. In a proof-of-principle experiment, 260 fs, 15 $μ$J and 200 $μ$J pulses are broadened and subsequently compressed to approximately 50 fs with 90 % efficiency and excellent spatio-spectral homogeneity across the beam profile.

physics.optics↗