I am conducting an experiment to measure the velocity of the axial swirler in the closed plexiglass chamber using LDV (TSI Ar-ion Innova 70C) in back-scattering mode, as shown in the picture, at a laser power of 1W. The probe axis is perpendicular to the chamber. A part of the beams is reflected by the plexiglass chamber into the probe, which causes the saturation of the photomultiplier tube. Also, I have a separate receiver for forward scatter mode, but it also faces problems due to the scattering of light from the walls. Please suggest the best way to acquire data.