Sub-wavelength convertible Bessel-beam and Gaussian-beam photoacoustic microscope in reflection-mode for in-vivo application

Abstract

A sub-wavelength convertible Bessel-beam (BB) and Gaussian-beam (GB) photoacoustic microscope (PAM) in reflection-mode has been developed. A miniature ultrasonic transducer was placed in front of the objective with a high numerical aperture and a working distance of a few millimeters to achieve the reflection-mode and sub-wavelength resolution. For BB-PAM system, a conical lens and an achromatic doublet lens were used to achieve extended depth of field (DoF). In particular, it was designed to easily convert the system from BB to GB by removing the two lenses described above, so that the DoF of BB-and GB-PAM can be compared accurately. The 532 nm pulsed laser used in this system was coupled to a single mode fiber. The sample was scanned using X-Y direction motors and the system was controlled using Labview software. The lateral resolution of the focus regions of BB-and GB-PAM obtained were 300 and 260 nm, respectively. As a result of measuring the DoF of BB-PAM, it was about 250 similar to 300 mu m, which was about 7 similar to 8 times better than the DoF of GB-PAM. In-vivo vascular structure of a mouse ear was successfully visualized using BB-and GB-PAM to compare the DoF of the two systems. Thus, the system developed in this study confirmed that BB-PAM enabled high-resolution imaging at extended DoF than GB-PAM, and further believed that this system could be useful for a variety of biomedical research.