Analysis of thousands of spectra identifies localized modes in random lasers

Whether a wave traveling in a 3D random medium can exhibit localized modes with coherent feedback loops without additional setup remains a key question for researchers investigating the randomness of wave physics. Random lasers provide chaotic lasing behavior that could provide insight into these hypothesized coherent feedback loops, although combining the correct experimental parameters with methods for data analysis is a challenge.

Researchers have built a platform to systematically analyze random lasing profiles. Powered by data from tens of thousands of lasing spectra from lasers made from zinc oxide nanoparticles, the approach by Hsu et al. can compare lasing wavelength, intensity, linewidth, and peak distribution. The platform led the group to find fixed and stable laser spikes that suggest photon localization in random lasers, whose chaotic lasing comes from its absence of resonant cavities.

Author Yang-Fang Chen said the study is one of the first to directly address whether random lasers are truly random.

“The discovery of stable localized modes in a three-dimensional random laser medium has not been seen in previous studies,” said Chen. “This finding provides an additional fundamental aspect for a wave traveling in a random medium, which can pave a key step for the understanding of transport properties of many other quantum particles.”

Prior attempts to study the randomness of random lasers have been hampered by having too rigid, special experimental designs, such as photonic crystals and waveguides.

The group next looks to expand their search for localized modes outside the spectrum of visible light, which would suggest they exist universally across the electromagnetic spectrum in a random medium.

Source: “Are random lasers really random?” by Yun-Tzu Hsu, Yi-Zih Chen, Yen-Yu Lin, Yu-Ming Liao, Hsia-Yu Lin, Wei-Cheng Liao, Wei-Ju Lin, Cheng-Fu Hou, Hsu-Yen Lee, and Yang-Fang Chen, Journal of Applied Physics (2025). The article can be accessed at https://doi.org/10.1063/5.0256553 .

This paper is part of the Disordered Materials at the Atomic Scale Collection, learn more here .