Data-volume reduction of optical vortex laser absorption spectroscopy by coarse-graining using a quadrant photodiode

We developed optical vortex laser absorption spectroscopy (OVLAS) to measure the transverse flow velocity relative to the probe beam. In our previous OVLAS setups, a camera is used in the measurement system. This approach constrained the time resolution by image data transfer time and required large computational resources due to the considerable amount of image data. In this paper, we discuss the coarse-graining of OVLAS as a method to improve time resolution and reduce computational resources achieved by replacing the camera with a quadrant photodiode (QPD). Measurement image data obtained from a camera was numerically coarse-grained to evaluate the feasibility of measurements using a QPD. Subsequently, the transverse flow velocity was measured by QPD. Measured transverse flow velocity had a mean absolute percentage error of 18%, confirming the practical validity of coarse-graining OVLAS. The data volume required to determine the flow velocity was reduced to 1/120 from the original OVLAS.