The SKED: speckle knife edge detector

3rd International Symposium on Laser Ultrasonics and Advanced Sensing

Sharpies, S.D.^1 ; Light, R.A.^1 ; Achamfuo-Yeboah, S.O.^1 ; Clark, M.^1 ; Somekh, M.G.^1

Electical Systems and Optics Research Division, Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom^1

关键词: High-frequency surfaces;    Lateral movement;    Optical beam deflection;    Optical speckles;    Optically rough surfaces;    Prototype devices;    Specular reflections;    Ultrasonic signals;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/520/1/012004/pdf
DOI  :  10.1088/1742-6596/520/1/012004

来源: IOP

【 摘 要 】

The knife edge detector - also known as optical beam deflection - is a simple and robust method of detecting ultrasonic waves using a laser. It is particularly suitable for detection of high frequency surface acoustic waves as the response is proportional to variation of the local tilt of the surface. In the case of a specular reflection of the incident laser beam from a smooth surface, any lateral movement of the reflected beam caused by the ultrasonic waves is easily detected by a pair of photodiodes. The major disadvantage of the knife edge detector is that it does not cope well with optically rough surfaces, those that give a speckled reflection. The optical speckles from a rough surface adversely affect the efficiency of the knife edge detector, because 'dark' speckles move synchronously with 'bright' speckles, and their contributions to the ultrasonic signal cancel each other out. We have developed a new self-adapting sensor which can cope with the optical speckles reflected from a rough surface. It is inelegantly called the SKED - speckle knife edge detector - and like its smooth surface namesake it is simple, cheap, compact, and robust. We describe the theory of its operation, and present preliminary experimental results validating the overall concept and the operation of the prototype device.