Photonic Crystals Demonstrate Strong Energy Dependent Transition Radiation at Brewster Angles

The behaviour of radiation emitted by fast-moving charged particles interacting with specially designed materials presents a long-standing challenge in physics, but new research offers a significant advance in understanding and controlling this phenomenon. V. Gareyan and Zh. Gevorkian, from Alikhanyan National Laboratory, alongside their colleagues, investigate how radiation changes when particles pass through alternating layers of materials, both in random and ordered arrangements. Their work reveals a strong relationship between the number of layers and the intensity of emitted radiation, leading to highly focused beams, and crucially, demonstrates a powerful energy dependence in certain periodic structures resembling photonic crystals. This discovery opens up exciting possibilities for developing novel detectors of high-energy particles, exploiting the unique way these materials respond to relativistic speeds.

Strong Energy Dependent Transition Radiation in a Photonic Crystal V. Gareyan and Zh. 2, Yerevan, Armenia Institute of Radiophysics and Electronics, Ashtarak-2, Armenia Radiation of a charged particle crossing an alternating stack of slabs in the optical region is considered. Both disordered and periodic stacks are investigated. It is shown that for a special type of alternating disordered and periodic stacks, the radiation problem can be solved exactly for backward and forward Brewster observation angles. Strong N2 dependence of radiation is demonstrated.

Photonic Crystals Control Transition and Cherenkov Radiation

This research explores how photonic crystals, periodic structures that manipulate light, can control transition and Cherenkov radiation. Scientists investigated how these structures interact with charged particles to generate and modify emitted radiation, focusing on isofrequency curves which describe the relationship between wave direction, wavelength, and frequency within the crystal. The research demonstrates the ability to control the angle of emitted radiation by carefully designing the photonic crystal. A saturation effect was observed, where radiation intensity plateaus at high particle energies due to the radiation becoming highly directional.

Importantly, slight imperfections in the photonic crystal materials can be compensated for by adjusting the observation angle, allowing for precise control over emitted radiation. Deviations from ideal material proportions within the photonic crystal can shift the peak intensity of emitted radiation to specific energy levels. Operating near the Brewster angle, where reflection is minimized, maximizes radiation intensity, providing a foundation for understanding and manipulating radiation emission in complex materials.

Photonic Crystals Enhance Transition Radiation Emission

This research presents a novel approach to enhancing transition radiation using carefully designed photonic crystals. Scientists demonstrated that constructing a photonic crystal from alternating layers of materials with specific properties allows precise control over radiation emitted by relativistic particles. The key breakthrough lies in tailoring the photonic crystal to mimic the band structure of Dirac cones, enabling strong interaction with the particle’s radiation field. Experiments revealed a strong relationship between radiation intensity and the number of layers within the photonic crystal.

By optimizing the ratio of layer thickness to the space between layers, the team significantly enhanced forward-propagating radiation at Brewster’s angle. The measured spectral-angular intensity exhibits a γ⁴ dependence at lower energies, where γ represents the particle’s Lorentz factor, indicating a powerful amplification of emitted radiation as particle energy increases. As particle energy increases, the integrated intensity eventually reaches a saturation point, proportional to Ns², where Ns is the number of layers. This saturation occurs without further change in emitted radiation, consistent with the principles of resonance transition radiation, establishing a new pathway for designing highly sensitive detectors of relativistic particles.

Brewster Angle Radiation in Dielectric Stacks

This research presents a detailed investigation into the radiation emitted by charged particles traversing alternating stacks of dielectric layers, both disordered and periodic arrangements. Scientists demonstrate that, for specific configurations of these stacks, an exact solution to the radiation problem is achievable at Brewster’s angles for both forward and backward observation. The team found a strong relationship between radiation intensity and the number of layers within disordered stacks, leading to pronounced directivity in either the forward or backward direction. Notably, the study reveals a strong energy dependence of radiation intensity observed at Brewster’s angle within certain periodic photonic crystals, particularly for relativistic particles. This dependence exhibits saturation at higher energies, linked to the band structure of the photonic crystal which shares similarities with Dirac cones, proposing the use of these specific photonic crystals as potential detectors for relativistic particles. The authors acknowledge that the efficiency of such detectors may be limited by the increasing radiation formation zone length at very high Lorentz factors, suggesting future work could focus on optimising the photonic crystal structure to mitigate this limitation and enhance detector performance.