Liquid crystal-based temperature-controlled recirculating flat jet system

In this paper, the design and implementation of a temperature-controlled recirculating flat jet system for liquid crystals (LCs)-based experiments are presented. In these experiments, the target liquid is usually exposed to medium to high laser fluences, possibly resonant with specific excitation, thus resulting in a change of local temperature and sudden degradation. To overcome this problem, each laser pulse must interact with a new volume of liquid, preferably with flat surfaces, while avoiding the use of substrates. A well-established solution consists of impinging two identical laminar jets that force the liquid into a radial expansion perpendicular to the plane formed by the jets, resulting in a consecutive chain of flat sheets bound by thick rims. In this context, LCs pose several challenges considering their viscosity, non-Newtonian behavior, and mesophase nature. Here, a precise control of temperature, thus mesophase, and pressure is demonstrated enabling the use of LCs in an impinging jet system. In particular, the system presented here delivers stable fluid chains of different sizes and thicknesses. The viscosity and non-Newtonian behavior of the LCs have a significant impact on the thickness of the chains as a function of the nozzle inner diameter, impinging angle, and radial distance from the impinging point. The flow rate, on the other hand, primarily affects the width and length of the liquid sheet.