Programmable Dual-Wavelength Switchable All-fiber Laser via Hybrid Optical Amplifier in the NIR-III Region for Multi-Contrast Photoacoustic Microscopy

Abstract

Photoacoustic microscopy (PAM) is a bond-selective imaging technique that provides optical resolution in deep tissues. Employing multi-contrast PAM expands the potential for non-destructive and label-free analysis of various substances. The efficiency of multi-contrast PAM largely depends on laser sources possessing high pulse switching rates. Recently, a dual-wavelength switchable fiber amplifier operating in the near-infrared-II (NIR) window is reported for multi-contrast PAM. Nevertheless, transitioning to the NIR-III region, which has higher absorption peaks, presents challenges due to the fixed Raman frequency shift and the absence of suitable pumps, complicating the search for a switchable source within this window. Herein, a unique dual-wavelength switchable all-fiber laser functioning within the NIR-III region is presented via a hybrid optical amplifier. Thanks to flexible optical parametric conversion, the laser produces 1.5 µJ pulses and realizes arbitrary pulse trains with 1725-nm and 1930-nm wavelengths. Simultaneously, utilizing programmable pulse shaping for two telecom lasers, the proposed source generates high power-spectral-density pulses with a flexible pulse width and a switching frequency of up to 100 kHz. Multi-contrast PAM using the proposed source distinguishes between the two types of microplastics in water, presenting a promising methodology for efficient microplastic detection in aqueous environments.