Study On The Non-contact Photoacoustic Detecting And Imaging Using An Optical Interferometer

In recent years,photoacoustic imaging(PAI)technology emerged as a new type of biomedical imaging technology,which combines the high selectivity of pure optical tissue imaging and the high penetration depth of pure ultrasonic tissue imaging.So the photoacoustic imaging is a hybrid imaging mode with high resolution and high contrast.PAI is the light absorption imaging technology.PAI has its unique advantages which it can image the endogenous tissue components that absorb illuminated light in biological tissue.The hemoglobin in the blood(oxyhemoglobin,deoxidation hemoglobin)provides a kind of endogenous optical contrast for imaging the blood flow because they have a larger optical absorption coefficient.So,PAI can not only provide the structure of the biological tissue imaging but also realize the function imaging of biological tissue.It provides an important means for investigating the morphological structures of biological tissue and metabolic functions and so on.We demonstrate a noncontact photoacoustic imaging method using a homodyne interferometer with a long coherence length laser.The generated photoacoustic signal is detected by the system that is locked at its maximum sensitivity through the use of balanced detection and zero-crossing triggering.When the system reaches the maximum sensitivity.The synchronization approach is used to trigger the excitation and detection of the photoacoustic signal.The system is immune to ambient vibrations.A thin glycerin layer on the sample surface is used to reduce the effect of the rough tissue surface.In this paper,mainly includes the following parts.(1)In this paper,the basic theory of photoacoustic imaging was first introduced.We elaborate the existing non-contact photoacoustic system using an interferometer as detector.From the photoacoustic effect principle,the basic theory of the coherent optical interference and interference light intensity along with the change of phase analysis,we demonstrate the generation,transmission and acquisition of the photoacoustic signal.(2)We set up non-contact photoacoustic imaging system based on a high coherence interferometer.Based on the existing non-contact photoacoustic imaging system,we made some improvement on that system.We use long-coherence interferometer to detect photoacoustic signals to enhance the stability of the system.In addition,for improving the accuracy of the system,we design a balance adjustment device to optical path compensation.We used a galvanometer scanner and a motor-stage to achieve scan along the X-axis and the Y-axis of the imaging area.That greatly improved the imaging speed and provided the probable of real-time imaging.(3)In order to test the feasibility and stability of the system,four hairs and blood vessels in a mouse ear and head in vivo were imaged.The photoacoustic images were successfully obtained with high resolution.