Investigation Of All-solid-state High Repetition Frequency Sub-nanosecond Dual-wavelength Pulsed Laser And All-optical-device Photoacoustic Imaging

Photoacoustic imaging is a new kind of non-invasive imaging method,which combines optical and acoustic effects together.It has the advantages of high resolution,non-invasive and so on.It can perform high-resolution functional imaging of the structure inside the sample,and it has important application value and development potential in the field of biomedical research and clinical diagnosis.Compared with optical coherence tomography,computer tomography and other medical imaging techniques,the key problem to limit the application of photoacoustic imaging in clinical,especially the real-time diagnosis and monitoring during the surgery,is that traditional photoacoustic imaging devices and techniques rely on direct acoustic contact measurement.In other words,this measurement method requires filling ultrasonic coupling agents between the piezoelectric ultrasonic transducer and the object to be imaged.A feasible method to solve this problem is to use the principle of optical vibration measurement to measure the tiny displacement caused by photoacoustic signal on the surface of the object.In order to realize rapid all-optical non-contact photoacoustic imaging,a series of studies are carried out in high repetition frequency,narrow pulse width excitation light source,low noise optical interferometer,photoacoustic signal acquisition and image reconstruction.A all-optical non-contact photoacoustic imaging system was established,and a high signal-to-noise ratio photoacoustic signal was obtained.The application of the system in imaging phantom and living animal tissues was demonstrated.In order to further reduce the noise of photoacoustic signal,a quantum enhanced all-optical optoacoustic signal detection device and method are proposed.The 1064 nm squeezed vacuum state with a squeezing level of 5 d B is prepared experimentally by a type-I optical parametric oscillator（OPO）.The main work contents are as follows:1、An all-solid-state high repetition rate sub-ns dual-wavelength Q-switched laser has been developed.In theory,a theoretical model of a dual-wavelength electro-optic Q-switched laser is established,and parameters such as the time-varying loss of the Q-switch,the transmittance of the output coupling mirror,and the doping concentration of the gain medium are optimized.In experiments,using a quasi-continuous 808 nm laser to pump YVO₄-Nd:YVO₄composite crystal,the fundamental frequency light is divided into two parts by controlling the time-varying loss of the electro-optic Q-switch,and an electro-optic Q-switched laser combined with external frequency doubling is constructed.When the high-level-voltage of the driving signal was set as 1.4 times as the quarter wave voltage of PC,the YVO₄-Nd:（1 at.%）YVO₄composite crystal and the OC with a transmission of 30%were used,1 k Hz,sub-ns 1064 nm and 532 nm single-longitudinal mode pulse lasers were obtained.At a pump energy of 3.7 m J,the PWs of the 1064 nm and 532 nm lasers were 0.97 ns and 0.61 ns,the SPEs of the two laser were 0.55 m J and0.29 m J.The beam quality factor,the energy fluctuation and the time jitter of the 1064 nm laser were 1.58,0.000063%and 2.18 ps;and that of the 532 nm laser were 1.35,0.000011%and 1.56 ps.2、The all-solid-state high frequency sub-ns dual-wavelength Q-switched laser is used as the excitation source of photoacoustic imaging,and an all-optical noncontact photoacoustic imaging system based on low-noise coherent Mach-zender interferometer is established.We use a mode cleaner to reduce the noise of probe light,use all solid-state optical amplification to improve the signal to noise ratio of the photoacoustic signal,and using wavelet denoised method to reduce the noise of the original photoacoustic signal.After testing,we know the system has a lateral resolution and a axial resolution of 21μm and 33μm,respectively.Using this photoacoustic imaging system,imaging experiments were conducted on hair embedded in a phantom and an ear of nude mice.The signal-to-noise ratios of the images were 26 d B and 23 d B,respectively.Then,the image processing method was used to obtain the mice ear vascular images with good contrast and resolution.Finally,we analyze the characteristics of noise in the imaging system,and the corresponding noise is reduced in the process of the experiment..3、Research on improving the measurement sensitivity of photoacoustic signal by using squeezed vacuum state light field.Firstly,the basic principle of using the squeezed vacuum state to improve the measurement sensitivity of photoacoustic signal is deduced theoretically.Then,we generated a squeezed vacuum state in experimentally.The 1064nm squeezed vacuum state is generated by using the type-I OPO operating below the threshold and the balanced homodyne detector（BHD）is used to detect it.Finally,a 1064nm squeezed vacuum state with a squeezed level of 5 d B is obtained at the analysis frequency of 10 MHz.Based on the generated squeezed state light field,a quantum enhanced all optical photoacoustic signal detection device and method are proposed.