Multipass annular mirror system for spectroscopic studies in shock tubes

Abstract

A fundamentally new multipass reflecting mirror system for studies in shock tubes is designed. Conducting optical absorption measurements in shock tubes when modelling processes of controlled combustion is necessary. The results of these optical studies facilitate working out recommendations on efficient and non-polluting burning of natural fuels in industry. The basic component of the suggested multipass optical system is an annular reflector in the form of a spherical concave belt joined as a separate section to the shock tube. Radiation from a source directed inwards the annular reflector traverses the tube section many times reflecting from the mirror surface which thereby increases the thickness of the absorbing layer. Because of the absence of bulging edges inside the reflector, no perturbations appear in the flow. The system design allows simple control of the optical path length. Equations relating the angular aperture of an incident beam to the chosen parameters of the annular reflector are reported. A formula for the number of beam passes as a function of the incidence angle of the beam entering the reflector is derived.