Research On High Sensitivity Photoacoustic Detection Technology Based On Surface Wave Sensor

Optical methods for detecting photoacoustic signals to achieve photoacoustic microscopy have become one of the most important means of photoacoustic microscopy imaging.Traditional transducers based on ultrasonic transducers were used to convert photoacoustic signals into electrical signals.Due to the characteristics of piezoelectric ceramics,the bandwidth of collecting ultrasonic signals is limited and the sensitivity is low.Thereby destroying the longitudinal resolution of photoacoustic imaging and destroying the image quality.The difference from the traditional photoacoustic signal detection method is that the photoacoustic signal detected by the surface wave sensor can provide a larger detection bandwidth and higher sensitivity,which can greatly improve the image quality of photoacoustic imaging.The photoacoustic signal mainly depends on the photoacoustic effect,but the ultrasonic signal generated by the photoacoustic effect has a low sound pressure,and the pulse is short,which is difficult to directly measure.Therefore,the surface acoustic wave sensing high sensitivity and the ultra-fast time corresponding characteristics are used to detect the sound.A change in ambient refractive index caused by the pressure to reconstruct the photoacoustic signal.This paper theoretically compares the sensing characteristics of surface waves of three different mechanisms,and the detection capabilities of these three kinds of surface waves to photoacoustic signals,and selects the most suitable mechanism for application in photoacoustic signals.In the chapter 1,this paper mainly introduces the basic principle of photoacoustic imaging from the photoacoustic effect,and analyzes the disadvantages of traditional photoacoustic signal detection due to the saturation absorption effect and bandwidth limitation of ultrasonic transducer devices.Finally,the photoacoustic signal detection method of the new optical method is introduced,and the new mechanism of surface wave detection researched in this paper is proposed.In the first part of Chapter 2,we mainly focus on three different surface wave mechanisms:surface plasmon surface wave,total internal reflection evanescent field surface wave and cavity waveguide local surface wave.The way of excitation.In this paper,three surface wave models are constructed and their physical parameters are optimized.The field distribution and reflectivity curves of three surface waves are analyzed by finite time domain difference method,and the differences and similarities of the three are compared.In the second part of chapter 2,the signal detection is performed by the difference between the TE wave and the TM wave.In order to obtain the minimum resolution limit,we analyze the detector noise,and calculate the minimum light intensity resolution limit of the detector by using the scattered noise as the main noise source.The sensing characteristics of different surface wave mechanisms are used to calculate the respective sensing limits.In the experiment,we select the 150MHz detector to obtain the signal.Therefore,the minimum resolution limit of the detector obtained is9.7x10^-6 intensity change.Therefore,the refractive index resolution limits of the three surface waves are calculated to be 6.8x10^-8/RIU,2.1x10^-8/RIU,1.2x10^-8/RIU,respectively,and it can be known that the three sensing limit resolutions are sequentially increased,but The required angle of incidence is also more stringent.In the chapter 3,different experimental systems are built for different surface wave sensing mechanisms.For the SPR surface wave,we built a system with tight focus excitation and prism type excitation to compare the ability of different excitation forms for signal detection.For the surface waves of the TIR evanescent field and the surface wave of the cavity waveguide,it is mainly a suitable experiment on the glass substrate.By comparing the reconstructed sound waves,it is known that the sound pressure resolution obtained by the three kinds of three sensors is sequentially increased.Basically consistent with theoretical simulations.The last chapter summarizes the main work of this paper.By comparing and selecting the most advantageous one,it provides theoretical guidance and basis for further realization of photoacoustic imaging or mechanical wave perturbation weak measurement.