arXiv subjects

Çağrı Erciyes

Publications and source records attributed to Çağrı Erciyes.

3 recordsLinked to original sources

arXiv2026

Pair beams unlock beyond-terawatt attosecond free-electron laser pulses

Free-electron lasers (FELs) generate the brightest coherent X-ray pulses available, enabling atomic-resolution and femtosecond-timescale studies across physics, chemistry, and biology. Realising their full potential at extreme peak powers and attosecond pulse durations critically depends on sustaining coherent gain across the full bunch length. Yet, the quasi-static longitudinal space-charge field in the ultrahigh-current regime imprints a slice-dependent energy detuning that quenches gain growth, so that current schemes typically sustain efficient lasing only across a limited fraction of the bunch. Here we demonstrate that a quasi-neutral electron-positron pair beam cancels this self-field and enables full-bunch high-gain lasing in ultracompressed beams without external compensation. Three-dimensional particle-in-cell simulations in a single-pass, untapered undulator confirm the mechanism across operating regimes: in the soft X-ray regime, the pair beam reaches $1.85\,\mathrm{TW}$ at $345\,\mathrm{as}$ with enhanced odd-harmonic emission and improved spatial coherence, while the electron-only beam fails to saturate; and a high-harmonic pair-cascade configuration yields ${\sim}10\,\mathrm{TW}$ in isolated ${\sim}3.5\,\mathrm{as}$ spikes with coherent amplification extending to photon energies of ${\sim}177\,\mathrm{keV}$. These results establish a new operating regime for ultrahigh-power attosecond light sources and open a direct route to coherent gamma-ray emission ($\geq\!100\,\mathrm{keV}$) currently inaccessible to magnetic-undulator FELs, with broad implications for ultrafast structural, electronic, and nuclear sciences.

physics.acc-ph↗

arXiv2025

Broadband coherent XUV light from $e^-/e^+$ microbunching in an intense laser pulse

Attosecond pulses of coherent extreme ultraviolet (XUV) light are instrumental for investigating subatomic dynamics and can be produced using a free-electron laser (FEL). It has been suggested that an optical FEL, which employs a laser pulse in place of a conventional undulator, could enable a dramatically more compact implementation of such a light source. Yet, the high electron density and subsequent high emittance implied by an optical FEL makes this concept challenging to realize with an electron beam. There has been impressive progress in recent years producing collimated dense and relativistic beams of electrons and positrons in the laboratory. As we demonstrate here, the inherent stability of a quasi-neutral electron-positron beam mitigates Coulomb expansion, and renders it a promising alternative source of coherent light. Specifically, we show via computer simulations that broadband coherent light in the XUV domain, which takes the form of 8-as pulses at 92-as intervals, can be generated by microbunching of relativistic electrons and positrons in a laser pulse. This process occurs over a sub-millimeter length scale, enabling the development of light sources which are orders-of-magnitude more compact than existing sources, with potential applications in physics, chemistry, biology, and industry.

physics.plasm-ph↗

arXiv2017

Treelogy: A Novel Tree Classifier Utilizing Deep and Hand-crafted Representations

We propose a novel tree classification system called Treelogy, that fuses deep representations with hand-crafted features obtained from leaf images to perform leaf-based plant classification. Key to this system are segmentation of the leaf from an untextured background, using convolutional neural networks (CNNs) for learning deep representations, extracting hand-crafted features with a number of image processing techniques, training a linear SVM with feature vectors, merging SVM and CNN results, and identifying the species from a dataset of 57 trees. Our classification results show that fusion of deep representations with hand-crafted features leads to the highest accuracy. The proposed algorithm is embedded in a smart-phone application, which is publicly available. Furthermore, our novel dataset comprised of 5408 leaf images is also made public for use of other researchers.

cs.CV↗