arXiv subjects

Klaas De Kinder

Publications and source records attributed to Klaas De Kinder.

10 recordsLinked to original sources

arXiv2026

Space-Time Event Scattering and Extension Method (STESEM): A Universal Framework for Scattering in Space-Time Metamaterials

Space-time metamaterials offer unprecedented control over electromagnetic waves by enabling simultaneous manipulation of spatial and temporal degrees of freedom. However, analytical descriptions of their scattering processes remain fragmented, with existing approaches typically requiring configuration-specific derivations or transformations to specialized reference frames that become impractical for accelerated or multi-interface structures. In this tutorial, we introduce the space-time event scattering and extension method (STESEM), a universal framework for electromagnetic scattering at arbitrary space-time interfaces. By decomposing the scattering process into a local interaction event and a subsequent extension along invariant traveling-wave coordinates, STESEM formulates space-time scattering directly in the laboratory frame without requiring coordinate transformations. The method provides a unified description of scattering amplitudes, frequency transitions and phase transformations for arbitrary incident waveforms and interface trajectories. We demonstrate the framework by deriving the complete scattering responses of canonical space-time structures, including stationary and instantaneous interfaces, space-time corners, uniformly moving interfaces, wedges and accelerated boundaries. Beyond providing analytical solutions, STESEM reveals the physical principles underlying these distinct phenomena and shows that complex space-time scattering processes can be constructed from elementary moving-interface interactions. This framework establishes a systematic foundation for analyzing and designing advanced space-time metamaterials, enabling extensions toward dispersive, bianisotropic and higher-dimensional systems.

physics.optics↗

arXiv2026

Space-Time Lensing by Accelerated Interfaces in Dispersive Media

We present space-time lensing by synthetic accelerated interfaces in dispersive media. Frequency-dependent group velocities map spectral components of a pulse onto distinct trajectories in the longitudinal space-time plane, while an accelerated interface reshapes their frequencies through time-dependent Doppler shifts. We develop an inverse-design procedure for the interface trajectory that focuses a quasi-monochromatic wave packet at a prescribed space-time event for an arbitrary dispersion relation, then extend the construction to polychromatic pulses. In its time-reversed form, the operation collimates a broadband pulse into a narrow-band wave. Moreover, cascading the forward and reverse operations enables a broadband pulse to propagate through an otherwise dispersive channel in a spectrally compressed state before being refocused. Full-wave simulations validate the focusing construction and demonstrate dispersion suppression.

physics.optics↗

arXiv2026

Scattering at Space-Time Interfaces between Dispersive Media

Dynamic modulation of material properties in space and time enables powerful control over wave propagation, yet existing theories largely rely on idealized, nondispersive models. In realistic media, frequency dispersion can strongly reshape wave dynamics, especially near resonances in highly dispersive platforms such as epsilon-near-zero materials. Here, we develop a general frequency transition theory for electromagnetic scattering at moving interfaces between dispersive media. From phase continuity, we derive nonlinear frequency transition relations and show that dispersion fundamentally reshapes the space-time scattering landscape, enabling additional propagating solutions with no counterpart in nondispersive systems. Applied to Drude, Lorentz and double-Drude media, the theory reveals how resonant dispersion, material loss and negative-index branches reorganize the scattering channels. For the two-wave scattering class, we further introduce a mixed-domain formulation that combines time-domain interface kinematics with frequency-domain constitutive relations, yielding closed-form scattering coefficients. These results establish a unified framework for dispersive space-time scattering and open opportunities for dispersion-based transition engineering in realistic materials.

physics.optics↗

arXiv2025

Scattering at Interluminal Interfaces

Scattering at interluminal modulation interfaces, where a sharp space-time perturbation moves at a velocity lying between the wave velocities of the two surrounding media, has remained an open problem for decades. This regime is somewhat reminiscent of the Cherenkov regime, in which the velocity of a charged particle exceeds the phase velocity of light in a medium. However, because it involves two media and a moving interface, it gives rise to richer and more complex scattering dynamics, with a single scattered wave when the incident wave propagates in the same direction as the interface and three scattered waves when they propagate in opposite directions. Existing studies address only limited non-magnetic configurations, and a general formulation has yet to be established. In this paper, we present a complete and general solution to scattering in the interluminal regime using a symmetric decomposition approach based on subluminal and superluminal limit interfaces, together with a space-time impulse response. This approach provides clear physical insight into the scattering features of the interluminal regime. Our results bridge the long-standing gap between the subluminal and superluminal regimes and elucidate the fundamental mechanisms underlying interluminal scattering.

physics.optics↗

arXiv2025

Dispersion-Mediated Space-Time States

Space-time varying media enable unprecedented control over electromagnetic waves, yet most existing studies assume idealized, nondispersive materials and thus fail to capture the intrinsic frequency dispersion of realistic platforms. Here, we develop a general framework for dispersive space-time varying systems that rigorously identifies the physically allowed frequency transitions of waves scattered at moving interfaces. Unlike previous approaches, our method is valid for arbitrary dispersion profiles, including resonances, and does not rely on the commonly used frame hopping approach, allowing treatment of multiple-velocity and accelerated systems. Applying this framework to canonical Drude and Lorentz media, we uncover a family of dispersion-mediated space-time states that arise from the multiple frequency transitions permitted by material dispersion. These states extend beyond conventional nondispersive scattering, revealing qualitatively new regimes of space-time scattering behavior. Beyond the frequency transitions, we derive the scattering coefficients for dispersive moving interfaces and provide a Fourier-domain formulation that yields a complete electromagnetic scattering solution for both monochromatic waves and broadband pulses. Our results establish a rigorous foundation for the design of realistic space-time metamaterials, with immediate relevance to emerging experiments in epsilon-near-zero optical platforms and open pathways for dispersion-engineered wave manipulation.

physics.optics↗

arXiv2025

Scattering and Chirping at Accelerated Interfaces

Space-time varying media with moving interfaces unlock new ways to manipulate electromagnetic waves. Yet, analytical solutions have been mostly limited to interfaces moving at constant velocity or constant proper acceleration. Here, we present exact scattering solutions for an arbitrarily accelerating interface, derived directly in the laboratory frame through a suitable change of variables. We show that acceleration introduces rich effects that do not occur with uniform motion, including transitions between multiple velocity regimes, multiple scattering events and generalized frequency chirping. We also solve the inverse problem of designing an interface trajectory that produces a desired chirping profile, demonstrating how tailored acceleration can synthesize complex frequency modulations. These results provide a fundamental framework to understand and control wave interactions with accelerated boundaries, opening pathways for advanced applications in space-time signal processing and dynamic pulse shaping.

physics.optics↗

arXiv2025

Doppler Pulse Amplification

The ability to amplify ultrashort pulses has revolutionized modern laser science, driving advances in various fields such as ultrafast optics and spectroscopy. A pivotal development in this field is chirped pulse amplification (CPA), which stretches, amplifies and recompresses ultrashort optical pulses using dispersive elements to overcome amplification limits. However, CPA faces limitations due to gain narrowing, restricting the final pulse duration. Here, we propose Doppler pulse amplification (DoPA), a novel approach for amplifying ultrashort pulses. While DoPA shares similarities with CPA in that it also stretches, amplifies and recompresses pulses, it differs in how it achieves this temporal compansion. Unlike CPA, DoPA exploits Doppler shifts induced by space-time modulated interfaces through a space-time wedge implementation without chirping. We show that DoPA dynamically shifts the pulse spectrum, effectively mitigating the gain narrowing issue of CPA. Additionally, we show that DoPA enables more compact amplification systems via a space-time Fresnel implementation. This approach may pave the way for more efficient, high-intensity laser systems and expand the potential for applications in both laboratory research and practical environments.

physics.optics↗

arXiv2025

Space-Time Graded-Index Interfaces and Related Chirping

Space-time modulated systems have recently emerged as a powerful platform for dynamic electromagnetic processing in both space and time. Most of the related research so far has assumed abrupt parameter profiles. This paper extends the field to generalized graded-index (GRIN) interfaces, which are both more practical than ideal profiles and offer new avenues for wave manipulations. It presents an exact solution for wave propagation across arbitrary space-time modulated GRIN interfaces and describes versatile chirping effects. The solution is based on a generalization of the impulse response method from linear time-invariant to linear space-time-varying systems. The proposed framework shows that space-time GRIN systems represent a novel approach for generating a new form of chirping that is not inherently based on dispersion, with promising applications in pulse shaping and signal processing.

physics.optics↗

arXiv2024

Space-Time Wedges

Space-time-modulated systems have attracted significant interest over the past decade due to their ability to manipulate electromagnetic waves in unprecedented ways. Here, we introduce a new type of space-time-modulated structure, the space-time wedge, consisting of two interfaces moving at different velocities, which results in either closing or opening wedges. Using moving boundary conditions, we derive closed-form solutions for the scattering of electromagnetic waves in such a wedge and leverage these solutions to unveil the underlying physics, including multiple space-time scattering and Doppler shifting. The space-time wedge holds potential for various optical and photonic applications.

physics.optics↗

arXiv2024

Electromagnetic Scattering at an Arbitrarily Accelerated Interface

We present a general analytical solution to the problem of electromagnetic scattering at a one-dimensional arbitrarily accelerated space-time engineered-modulation (ASTEM) interface in the subluminal regime. We show that such an interface fundamentally produces chirping, whose profile can be designed according to specifications. This work represents an important step in the development of ASTEM crystals and holds significant potential for applications in microwave and optical devices reliant on chirp-based functionalities.

physics.optics↗