Feasibility of Free-Space Transmission using L-Band Maser Signals in Organic Gain Media

TL;DR

This study demonstrates the feasibility of free-space transmission of organic L-band maser signals at room temperature, maintaining coherence and strong coupling under adverse atmospheric conditions, paving the way for secure microwave communication.

Contribution

It provides the first experimental proof-of-concept for room-temperature organic masers functioning as interference-resilient free-space microwave links in realistic conditions.

Findings

Coherent maser signals preserved over 25 cm distances.

Strong spin-photon coupling confirmed by Rabi oscillations.

Achieved peak output power of 4.29 mW with short pulse duration.

Abstract

Atmospheric conditions such as fog, humidity, and scattering by foliage routinely degrade optical free-space (FS) links, motivating alternatives that are robust in adverse conditions. Coherent microwave sources offer a compelling alternative for quantum-secure communication, yet their propagation outside enclosed resonators has remained untested. Here, we demonstrate room-temperature FS transmission of maser signals generated using organic L-band (1-2 GHz) gain media, pentacene doped p-terphenyl (Pc: PTP), and Diazapentacene-doped p-terphenyl (DAP:PTP). Spectral and temporal coherence is preserved over distances up to 25 cm, approximately one wavelength at the masing frequency. Tests included polarisation misalignment, high-humidity conditions, and partial occlusion by foliage to emulate realistic FS reception scenarios. Strong spin-photon coupling was maintained, as confirmed by persistent rabi oscillations and normal-mode splitting. An instantaneous peak output of 4.29 mW (+6.32 dBm) from a 0.01% DAP:PTP gain medium. with a pulse duration of ~4 {\mu}s, marks a performance benchmark for directly coupled masers. These findings demonstrate a proof-of-concept for masers as viable platforms for short-range, interference-resilient coherent microwave links, with future relevance to quantum sensing and secure communication technologies.