[Paper Review] Low-velocity-favored transition radiation

Jialin Chen, Ruoxi Chen+9 more|arXiv (Cornell University)|Dec 26, 2022

Strong Light-Matter Interactions4 citations

TL;DR

This paper discovers that transition radiation from ultra-low-velocity charged particles (v/c < 0.001) can exhibit radiation intensity comparable to that from relativistic particles (v/c ≈ 0.999), defying the conventional rule that radiation decreases with velocity. This phenomenon arises from the excitation of Ferrell-Berreman modes in epsilon-near-zero materials, enabling photon extraction efficiencies up to eight orders of magnitude higher than for high-energy particles.

ABSTRACT

When a charged particle penetrates through an optical interface, photon emissions emerge - a phenomenon known as transition radiation. Being paramount to fundamental physics, transition radiation has enabled many applications from high-energy particle identification to novel light sources. A rule of thumb in transition radiation is that the radiation intensity generally decreases with the particle velocity v; as a result, low-energy particles are not favored in practice. Here we find that there exist situations where transition radiation from particles with extremely low velocities (e.g. v/c&lt;0.001) exhibits comparable intensity as that from high-energy particles (e.g. v/c=0.999), where c is light speed in free space. The comparable radiation intensity implies an extremely high photon extraction efficiency from low-energy particles, up to eight orders of magnitude larger than that from high-energy particles. This exotic phenomenon of low-velocity-favored transition radiation originates from the excitation of Ferrell-Berreman modes in epsilon-near-zero materials. Our findings may provide a promising route towards the design of integrated light sources based on low-energy electrons and specialized detectors for beyond-standard-model particles.

Motivation & Objective

• To investigate the conditions under which transition radiation intensity from low-velocity charged particles exceeds that of high-velocity particles.
• To identify the physical mechanism enabling strong radiation from ultra-relativistic and non-relativistic particles alike.
• To explore the potential of epsilon-near-zero materials in enhancing transition radiation for integrated light sources and particle detection.
• To challenge the conventional assumption that low-energy particles are ineffective in transition radiation applications.

Proposed method

• Theoretical analysis of transition radiation from charged particles crossing an interface between vacuum and an epsilon-near-zero (ENZ) material.
• Modeling the excitation of surface modes, specifically Ferrell-Berreman modes, at the ENZ interface.
• Numerical simulation of radiation intensity as a function of particle velocity, showing non-monotonic behavior with peak intensity at low velocities.
• Use of Maxwell’s equations and boundary conditions to derive the radiation spectrum and power emission.
• Comparison of radiation efficiency between low-velocity (v/c < 0.001) and high-velocity (v/c ≈ 0.999) particles in ENZ media.
• Analysis of the role of the dielectric function near zero in enhancing near-field coupling and radiation efficiency.

Experimental results

Research questions

• RQ1 Can transition radiation from ultra-low-velocity particles (v/c < 0.001) achieve radiation intensity comparable to that from highly relativistic particles (v/c ≈ 0.999)?
• RQ2 What physical mechanism enables strong radiation emission from low-velocity particles in epsilon-near-zero materials?
• RQ3 Why does radiation intensity not monotonically decrease with decreasing particle velocity in ENZ media, contrary to conventional expectations?
• RQ4 How does the excitation of Ferrell-Berreman modes influence the photon extraction efficiency in transition radiation?
• RQ5 What are the practical implications of this phenomenon for integrated light sources and low-energy particle detectors?

Key findings

• Transition radiation intensity from ultra-low-velocity particles (v/c < 0.001) can be comparable to that from highly relativistic particles (v/c ≈ 0.999), defying the standard velocity dependence.
• The phenomenon is enabled by the excitation of Ferrell-Berreman modes at the interface of vacuum and epsilon-near-zero materials.
• Photon extraction efficiency from low-energy particles is up to eight orders of magnitude higher than from high-energy particles in the same medium.
• The radiation spectrum exhibits a non-monotonic dependence on particle velocity, with a peak intensity at very low velocities.
• The effect is robust in materials with epsilon near zero, where surface modes strongly enhance near-field coupling and radiation emission.
• This mechanism opens new pathways for designing compact, efficient light sources and ultrasensitive detectors for weakly interacting particles.