Propagation of long-distance Bessel beams and its application to optical imaging in turbid seawater

The underwater imaging quality is exponentially affected by the attenuation length, making it particularly crucial to deliver laser energy to distant targets as efficiently as possible. Compared to Gaussian beams, Bessel beams exhibit superior propagation capabilities in scattering media. Therefore, we generated a Bessel beam with a diameter of 20 mm using combined axicons, achieving a maximum non-diffracting distance of up to 80 m. This beam serves as an illumination source with high energy density and long range for range-gated imaging. By replacing the Gaussian beam with the Bessel beam, we experimentally achieved signal intensity enhancements by factors of 1.677 in a simulated water tank environment and 2.328 in real seawater. Imaging quality improved, with an average RMS contrast enhancement by a factor of 1.5725 for images captured at a distance of 3 m under various illumination power levels.