Theoretical and computational feasibility of femtosecond laser multifilament transverse structures reconstruction via circular-scanning-based photoacoustic tomography

Abstract We theoretically investigate the feasibility of reconstructing the transverse structures of femtosecond laser filaments in air by photoacoustic tomography. To simulate the emission and transmission of filament-induced ultrasonic signals more truly, a series of experimentally recorded cross-sectional images are used to simulate the initial pressure rise from multiple filaments (MFs). The aperture size and sensitivity of the detector was incorporated into the reconstruction algorithm. The results show that frequency of acoustic signals induced by MFs with maximum volumetric energy density ∼ 100 kJ/m 3 is about 2 MHz below. The initial spatial distribution of optical filaments can be clearly reconstructed with the back projection based algorithm. We recommend a PAT system with transducers of a lower central frequency and a stronger apodization working at a longer scanning radius can be used in photoacoustic image reconstruction of femtosecond laser multifilaments. This study demonstrates the feasibility of using photoacoustic tomography to reconstruct femtosecond multifilament images, which is helpful for studying the complex dynamic processes of multifilament and multifilament manipulation and is also valuable for the remote applications of laser filaments.