Optical-resolution photoacoustic microscopy (OR-PAM) has rapidly developed and is capable of characterizing optical absorption properties of biological tissue with high contrast and high resolution (micrometer-scale lateral resolution). However, the conventional excitation source of rapidly diverging Gaussian beam imposes limitations on the depth of focus (DOF) in OR-PAM, which in turn affects the depth-resolving ability and detection sensitivity. Here, we proposed a flexible DOF, depth-invariant resolution photoacoustic microscopy (FDIR-PAM) with nondiffraction of Airy beams. The spatial light modulator was incorporated into the optical pathway of the excitation source with matched switching phase patterns, achieving the flexibly adjustable modulation parameters of the Airy beam. We conducted experiments on phantoms and intravital tissue to validate the effectiveness of the proposed approach for high sensitivity and high-resolution characterization of variable topology of tissue, offering a promising DOF of 926 μm with an invariant lateral resolution of 3.2 μm, which is more than 17-fold larger compared to the Gaussian beam. In addition, FDIR-PAM successfully revealed clear individual zebrafish larvae and the pigment pattern of adult zebrafishes, as well as fine morphology of cerebral vasculature in a large depth range with high resolution, which has reached an evident resolving capability improvement of 62% mean value compared with the Gaussian beam.
Coherent anti-Stokes Raman scattering (CARS) microscopy enables the analysis of the chemical composition and distribution within living cells, biomolecules, or living organisms in a label-free manner. Compared with the traditional spontaneous Raman imaging technology, its advantages of high imaging sensitivity and resolution, fast imaging speed and strong signal intensity make it more popular in multiple disciplines. The available CARS microscopes are most adopted advanced crystal solid-state lasers, which are expensive, bulky, and sensitive to the environmental changes. Supercontinuum fiber lasers with a wide spectral tuning range are increasingly used in biomedical applications due to their low cost, small size, and low environmental impact. Here, we homebuilt a CARS microscope based on a supercontinuum fiber laser, a specially tailored laser with a dual-channel time-synchronous outputs. The influence factors were investigated including the objective numerical aperture, laser power, and sample concentration, etc. The feasibility of CARS microscope was then verified by imaging the polystyrene microspheres (PS) and polymethyl methacrylate microspheres (PMMA). Finally, we imaged the lipid droplet distribution of EC109 cell, which revealed the application potential of the supercontinuum fiber laser-based CARS microscope in biomedical applications.
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