Research On 3D Reconstruction Technology Based On Photoacoustic Microscopy

The study of paleontological fossils can understand the process of earth evolution and the law of geological change,which is of great significance to mankind looking forward to the future.However,the three-dimensional morphological study of endophytic fossils has always been a difficult point in paleontological research,and previous studies generally obtain the morphological information of endophytic fossils through continuous sectioning of samples to complete the three-dimensional reconstruction of endophytic fossils,which is not only time-consuming and laborious,but also causes irreversible damage to fossils.The three-dimensional nondestructive reconstruction technology can quickly obtain the information of the appearance and internal structure of the specimen without destroying the fossil specimen,which has obvious advantages over the traditional visible light imaging method.In order to promote the development of fossil three-dimensional nondestructive reconstruction technology in the field of paleontology in China,thesis systematically introduces a new type of 3D reconstruction technology based on photoacoustic microscopy applied to the study of paleontological fossils.Photoacoustic microscopy imaging technology is based on the photoacoustic and photothermal effect of the material imaging technology,after periodic modulation of the laser interaction with the object to form a co-periodic heat source,and then produce sound waves,the amplitude of the sound wave can reflect the optical characteristics and structure of the sample surface,and the phase reflects the thermal diffusion characteristics of the sample.Photoacoustic microscopy imaging technology uses laser to scan the sample point by point,and the photoacoustic signal generated varies with the sample characteristics of each point,and the coordinates of the scanning point are drawn into a photoacoustic microscopic image.According to the principle of photoacoustic microscopy,a set of 3D reconstruction system of photoacoustic microscopy based on solid-state coupling is constructed.The system software is built based on the Lab VIEW platform,which is divided into lock-in amplifier control module,galvanometer control module and imaging module.First,the lock-in amplifier is used to control the laser to generate the corresponding frequency laser,the laser is reflected to the target point position through the galvanometer,and the acoustic signal is received through the self-made detector,and the software then uses the coordinates,phase and amplitude information of the acoustic signal for microscopic imaging.Through the test,the effective imaging area of the photoacoustic microscopy imaging system built in thesis is greater than 243mm^2,the lateral resolution is better than36μm,and the longitudinal resolution is better than 100μm.Using the above system,traditional photoacoustic imaging and 3D reconstruction imaging were carried out on molded fossils,micro-metamorphosis fossils and complete petrified fossils,respectively.It was found that molded fossils and complete petrified fossils were more sensitive to amplitude information,but the imaging quality of molded fossils decreased with the increase of harmonic level.Micro-metamorphosis fossils are more sensitive to phase during imaging due to the retention of some biological properties.Combined with the characteristics of different types of fossils,they should be reconstructed in three dimensions using different imaging methods.Through the research of thesis,the application of photoacoustic microscopy imaging technology in the field of paleontological research has been promoted,and it is believed that in the near future,with the study of more paleontological samples in three-dimensional photoacoustic reconstruction,the establishment of different types of paleontological fossil photoacoustic databases will greatly promote the development of paleontological fossil research.