A Dual-Mode Expansion Cloud Chamber for Reproducible Laboratory Studies of Laser Propagation in Fog and Clouds

In this paper, we present the development of a portable expansion cloud chamber designed to investigate the interaction of high-power laser radiation (≥ 3 kW) with fog and cloud structures under controlled and reproducible laboratory conditions. The main aspects of the facility design, operating principles, and achievable atmospheric parameter ranges are discussed, with particular emphasis on controlled cloud and fog generation and optical propagation experiments.
The chamber employs a dual-mode adiabatic expansion concept, allowing both gradual pressure reduction using vacuum pumps and rapid decompression via a secondary pressure reservoir. This approach enables precise control of supersaturation conditions and reproducible formation of fog and cloud fields through controlled decompression.
The main chamber consists of a double-walled cylindrical vacuum vessel with an internal diameter of 2 m and a length of 10 m, integrated into a 45-foot container structure. The system covers a wide operational parameter space, including temperatures from -50 °C to +40 °C, relative humidity from 0 % to 100 %, and pressures between 100 and 1100 mbar. Homogeneous air mixing is achieved using multiple fan configurations, while configurable heating elements allow the generation of turbulent flow regimes. A dense and redundant sensor network provides real-time monitoring of thermodynamic, microphysical, and optical parameters at multiple locations within the chamber.
This experimental setup enables fundamental investigations of laser propagation, attenuation, and scattering in realistic atmospheric conditions. The facility provides a controlled platform for advancing the understanding of laser-atmosphere interactions and supports the development and validation of optical propagation models, with direct relevance for free-space optical and satellite communication systems.