Photoacoustic Microscopy Based On Multiplexed Fiber-Optic Ultrasound Sensors

Photoacoustic microscopy images the target tissue by detecting the ultrasonic waves excited by the focused pulsed laser in the living body,which provides an important imaging basis for medical research and disease diagnosis.Traditional photoacoustic microscopes use focused piezoelectric ultrasonic sensors to detect photo-induced ultrasonic signals,which cannot take into account the sensitivity and field of view area.In order to solve this problem,this paper proposes to use the fiber sensor array to detect photoacoustic signals and realize photoacoustic microscopy imaging with a large field of view.This paper starts with two aspects of improving the detection sensitivity and expanding the field of view.The main research contents are as follows:1.The noise characteristics of the fiber optic ultrasonic sensor are studied,and the contribution mechanism of the ultrasonic sensitive components,such as orthogonal dual-frequency fiber lasers,optical amplifiers,optical detectors and data acquisition modules,to the system noise is analyzed.The relationship between noise intensity and beat frequency signal power,signal optical power(or photocurrent).Studies have shown that the signal-to-noise ratio of the optical fiber sensing system can be significantly improved by increasing the optical power of the input photodetector.When the optical power injected into the photodetector reaches more than 10 m W,the mean square value of the frequency jitter of the beat frequency signal is reduced from 74 k Hz to 44 k Hz,and the noise equivalent sound pressure provided in the 50 MHz bandwidth is reduced from 32.9 Pa to 19.5 Pa.Furthermore,a fiber-optic photoacoustic microscope was constructed based on a fiber-optic ultrasonic sensor to image blood vessels in the ear of mice in vivo,and it was found that the signal-to-noise ratio of the image could be significantly enhanced by increasing the signal optical power.2.The wavelength division/time division multiplexing technology is proposed,and a 4-way multiplexed fiber optic ultrasonic sensor is realized.The signal light of each sensor is loaded on different wavelengths,and the signal light of each wavelength is injected into the photodetector in turn after different delays.A set of photoelectric acquisition system can obtain the information collected by multiple sensors at the same time.Using the sensor array as the ultrasonic detection unit,a photoacoustic microscope was built and the blood vessels in the cortical layer of the mouse brain were imaged in vivo,and the field of view was expanded to 8.6×3.5mm~2...