Development of a novel fiber laser based backward-mode photoacoustic microscopy system and image characterization

Abstract

Among all other imaging modalities, optical methods using non-ionizing radiation became popular due to safety concerns. However, pure optical methods have severe limitations for deep tissue imaging. On the other hand, photoacoustic imaging is a promising imaging modality for in vivo tissue monitoring due to its high optical contrast and high ultrasonic resolution. The parameters of the laser used in photoacoustics, namely pulse duration, pulse repetition frequency, beamwidth and output power has a quanti able impact on signal amplitude, imaging speed and resolution. In literature, Q-switched lasers, solid state lasers and ber lasers are used for the microscopic scale of photoacoustic imaging. Most of the lasers used in photoacoustic studies has a xed capacity and key parameters cannot be adjusted independently. In this study, we declare a novel all- ber mode-locked laser with adjustable pulse duration between 1 - 3 ns and selectable pulse repetition frequency between 50 kHz and 3.1 MHz. All ber integration makes our laser resistant to vibrational disturbances, yet increases its stability. Additionally, we utilized a photonic crystal ber at the output stage of the laser to generate a supercontinuum of a wavelength range of 600 - 1100 nm. We analytically reveal laser parameter dependencies of photoacoustic signals. We test our microscopy system with a phantom made of horse hair, and present resultant images with point spread function of width 500 m.|Keywords : Photoacoustics, photoacoustic microscopy, mode-locked, supercontiuum, fiber laser, pulse duration, beam width, pulse repetition frequency.