Investigation on optical path of laser detection of multiple thermal fluids and suppression of high-temperature stray radiation interference

The on-line detection of the component content of multiple thermal fluids (MTFs) has a crucial impact on heavy oil recovery. A long absorption path-length is an indispensable condition for on-line laser detection system (MTFs-OLDS). Therefore, an open-path reflectarray gas cell was presented based on multi-reflection absorption spectroscopy model. The off-axis optical receiver with extinction threads and spherical filter cavity was designed to suppress the thermal radiation emitted from high temperature injection tube internal wall. The effect of detecting deviations on receiving efficiency and the effectiveness of stray radiation suppression structure were analyzed by Monte Carlo ray tracing method. The results show that the proposed absorption path-length is enhanced 22 times, when the optical window material is fused silica and the reflector mirror coating is silver. The increases of beam divergence angle and alignment error have a reduction role of receiving efficiency. Extinction ratio of extinction threads is improved with base length and hemline length decrease. After adding the filter cavity in the dewar baffle, the point source transmittance (PST) of off-axis optical receiver can be reduced to 1.21 × 10−7 at the off-field angle 5° of incident stray light. The conclusion indicates the PST of the optical receiver of MTFs-OLDS is less than the maximum allowable value, and the level of stray radiation suppression is dramatically improved.