arXiv subjects

F. Ömer Ilday

Publications and source records attributed to F. Ömer Ilday.

7 recordsLinked to original sources

arXiv2026

Programmable emergence through hierarchical self-organisation

Predictively steering self-organising systems with hierarchical structure toward intended outcomes across widely separated dynamical scales remains a fundamental challenge. Despite decades of progress, hierarchy remains a descriptive property rather than a mechanism for control. Here, we show how a high-dimensional stochastic system can be steered toward preselected target states by exploiting its internal hierarchy of timescales. Fast variables lock to slower collective variables; iterating this locking across scales progressively reduces the effective dynamics to a small set of externally controllable parameters. This enables directing the system while maintaining dynamical insulation from noise across scales, thereby turning hierarchy from an observation into a mechanism for programmable emergence. We experimentally demonstrate this approach in a fully tractable platform: a mode-locked laser, in which we assemble and stabilise more than 100 pulses into harmonic patterns over timescales spanning 10 orders of magnitude. Phenomena such as nucleation, quantum-noise-induced annihilation, long-range interactions and annealing-like ordering are predicted and exploited to transition the system to preselected states. Our results establish a route to programming emergent behaviour in driven-dissipative systems, with implications ranging from optics to materials.

physics.optics↗

arXiv2025

Controlling Competing Feedback Mechanisms for Programmable Patterns via Nonlinear Laser Lithography

Controlling laser-induced pattern formation remains a long-standing challenge. A key advance was recognising the pivotal role of intrinsic feedback mechanisms in self-organisation, which enabled self-similar patterns with long-range order through nonlinear laser lithography. This concept was recently leveraged to surpass the diffraction limit. However, demonstrated structures in laser-induced pattern formation have been relatively simple and material-specific, as they rely on a single assumed formation mechanism for each material. Here, we reveal the coexistence of competing feedback mechanisms that drive distinct chemical and ablative processes, resulting in patterns with different symmetries. We show that one mechanism can be selectively activated, while completely suppressing the other, by tuning the laser parameters independently of the material. The competing mechanisms break surface symmetries in distinct lateral and vertical directions, and the selection can be dynamically inverted in situ, leading to rich surface chemistries and morphologies. We demonstrate the potential for applications through the maskless and ambient-air fabrication of complex composite patterns on diverse materials and substrates. These include seamlessly stitched superhydrophilic and superhydrophobic domains, structural colour, and a holographic temperature sensor. Combining programmable mechanism selection with recent demonstrations of sub-10 nm features could enable the maskless fabrication of composite structures that rival the capabilities of nanofabrication techniques.

physics.optics↗

arXiv2025

Ultrafast laser synthesis of zeolites

Research has demonstrated that zeolite nucleation and growth can be controlled by fine-tuning chemical composition, temperature, and pressure, resulting in structures with diverse porosities and functionalities. Nevertheless, current energy delivery methods lack the finesse required to operate on the femto- and picosecond timescales of silica polymerisation and depolymerisation, limiting their ability to direct synthesis with high precision. To overcome this limitation, we introduce an ultrafast laser synthesis technique capable of delivering energy at these timescales with unprecedented spatiotemporal precision. Unlike conventional or emerging approaches, this method bypasses the need for specific temperature and pressure settings, as nucleation and growth are governed by dynamic phenomena arising from nonlinear light-matter interactions, such as convective flows, cavitation bubbles, plasma formation, and shock waves. These processes can be initiated, paused, and resumed within fractions of a second, effectively freezing structures at any stage of self-assembly. Using this approach, we traced the entire nucleation and growth pathway of laser-synthesized TPA-silicate-1 zeolites, from early oligomer formation to fully developed crystals. The unprecedented spatiotemporal control of this technique unlocks new avenues for manipulating reaction pathways and exploring the vast configurational space of zeolites.

cond-mat.mtrl-sci↗

arXiv2018

Intracavity Optical Trapping

Standard optical tweezers rely on optical forces that arise when a focused laser beam interacts with a microscopic particle: scattering forces, which push the particle along the beam direction, and gradient forces, which attract it towards the high-intensity focal spot. Importantly, the incoming laser beam is not affected by the particle position because the particle is \emph{outside} the laser cavity. Here, we demonstrate that \emph{intracavity nonlinear feedback forces} emerge when the particle is placed \emph{inside} the optical cavity, resulting in orders-of-magnitude higher confinement along the three axes per unit laser intensity on the sample. We present a toy model that intuitively explains how the microparticle position and the laser power become nonlinearly coupled: The loss of the laser cavity depends on the particle position due to scattering, so the laser intensity grows whenever the particle tries to escape. This scheme allows trapping at very low numerical apertures and reduces the laser intensity to which the particle is exposed by two orders of magnitude compared to a standard 3D optical tweezers. We experimentally realize this concept by optically trapping microscopic polystyrene and silica particles inside the ring cavity of a fiber laser. These results are highly relevant for many applications requiring manipulation of samples that are subject to photodamage, such as in biological systems and nanosciences.

physics.optics↗

arXiv2014

Efficient, high-speed ablation of soft tissue with few-microjoule, femtosecond pulse bursts

Femtosecond pulses hold great promise for high-precision tissue removal. However, ablation rates are severely limited by the need to keep average laser power low to avoid collateral damage due to heat accumulation. Furthermore, previously reported pulse energies preclude delivery in flexible fibers, hindering in vivo operation. Both of these problems can be addressed through use of groups of high-repetition-rate pulses, or bursts. Here, we report a novel fiber laser and demonstrate ultrafast burst-mode ablation of brain tissue at rates approaching 1 mm$^3$/min, an order of magnitude improvement over previous reports. Burst mode operation is shown to be superior in terms of energy required and avoidance of thermal effects, compared to uniform repetition rates. These results can pave the way to in vivo operation at medically relevant speeds, delivered via flexible fibers to surgically hard-to-reach targets, or with simultaneous magnetic resonance imaging.

physics.optics↗

arXiv2013

Si nano-VINe: Electrical Percolation in Quantum-Confined nc-Si:SiO2 Systems

Nanostructures, especially of silicon, are of paramount importance for new generation solar cell applications. The key material requirements for solar cells are good electrical conductivity, confinement of excitons, and a tunable band-gap that allows for tandem arrangements to absorb a maximally large portion of the solar spectrum. However, to date, existing Si-based nanostructures have addressed these requirements individually. The difficulty is that these requirements are entangled in complex ways, so an effort to improve one can lead to a major trade-offs in the others. In this study, we report on a novel silicon nanostructure, where the key advance is that we have managed to satisfy all the abovementioned requirements simultaneously: We demonstrate that the excitons are confined, the bandgap is tunable, and the electrons can freely travel along the nc-Si network.

cond-mat.mtrl-sci↗

arXiv2011

Semianalytic theory of self-similar optical propagation and mode locking using a shape-adaptive model pulse

A semianalytic theory for the pulse dynamics in similariton amplifiers and lasers is presented, based on a model pulse with adaptive shape. By changing a single parameter, this test function can be continuously tweaked between a pure Gaussian and a pure parabolic profile and can even represent sech-like pulses, the shape of a soliton. This approach allows us to describe the pulse evolution in the self-similar and other regimes of optical propagation. Employing the method of moments, the evolution equations for the characteristic pulse parameters are derived from the governing nonlinear Schrödinger or Ginzburg-Landau equation. Due to its greatly reduced complexity, this description allows for extensive parameter optimization, and can aid intuitive understanding of the dynamics. As an application of this approach, we model a soliton-similariton laser and validate the results against numerical simulations. This constitutes a semianalytic model of the soliton-similariton laser. Due to the versatility of the model pulse, it can also prove useful in other application areas.

physics.optics↗