Imitation Of Biological Tissue In Water Laser Ultrasonic Testing And Mechanism Analysis

Photoacoustic Imaging of biological tissue is a new imaging method and techniquewith great expectation at home and abroad. However, this technology is still at thedeveloping stage and many problems need to be solved.This paper mainly works on the detection and mechanism of photoacoustic signalgenerated by a line focus laser excite on biological tissue in water.A photoacoustic detection system is established. Different objectives are excited by Nd:YAG laser with a wavelength of 1064 nm, then ultrasonic signal is detected by Michelsoninterferometer with photorefractive crystal modifying a variant of the wave front.The paper also discusses the use of Wavelet threshold method in laser ultrasonic signal.The different effects that engendered by the different wavelet and threshold selectioncriteria are compared. Based on the analysis and comparison of signal denoising and thestatistical characteristics, wavelet Sym6 is selected to complete the signal denoising.The photo-ultrasonic mechanism is theoretically studied in this paper. The ultrasonicwaveforms are compared in three aspects---first, different distances between the objectand detecting film, second, different characters of the objectives and finally, different laserenergy. And the relation of the waveforms and each aspect are also studied. A experimentaldenoising method is introduced. The mechanism of each peak and methods of improvesignal-to-noise ratio in the late experimental data processing had been analyzed.Better signal-to-noise ratio of ultrasonic is gained by using the denoising methoddescribed in this paper. And the ultrasonic sources of each peak in the waveform has beendiscussed more deeply.The results of this research will provide as reference of the study of mechanism aboutlaser-tissue interaction and photoacoustic imaging of biological tissue.