# Lasing Conditions of Transverse Electromagnetic Modes in Metallic-Coated Micro- and Nanotubes

## TL;DR

This paper investigates the lasing conditions of TE modes in metallic-coated micro- and nanotubes, revealing size-dependent lasing capabilities and providing a simple model for cavity mode frequencies, with applications in micro-lasers and sensing.

## Contribution

It introduces a detailed analysis of TE mode lasing in metallic-coated tubes, identifying size-dependent lasing regimes and a simple model for cavity mode frequencies.

## Key findings

- WGM lasing occurs only in nanoscale tubes.
- Large number of cavity modes with low thresholds in micrometer tubes.
- Simple one-parameter model accurately predicts cavity mode frequencies.

## Abstract

In this work, we study the lasing conditions of the transverse electric (TE) modes of micro- and nanotubes coated internally with a thin metallic layer. This geometry may tackle some of the problems of nanolasers and spasers as it allows the recycling of the active medium while providing a tunable plasmonic cavity. The system presents two types of TE modes: cavity modes (CMs) and whispering-gallery modes (WGMs). On the one hand, we show that the lasing of WGM is only possible in nanoscale tubes. On the other hand, for tubes of some micrometers of diameter, we found that the system presents a large number of CMs with lasing frequencies within the visible and near-infrared spectrum and very low gain thresholds. Moreover, the lasing frequencies of CMs can be accurately described by a simple one-parameter model. Our results may be useful in the design of micro- and nanolasers for `lab-on-chip' devices, ultra-dense data storage, nanolithography, or sensing.