Technology For He-Ne Laser Feedback Nanoscale Displacement Measurement

The physical meaning of the laser feedback phenomena is extremely rich, which need more people to search and discover. The measurement system based on laser feedback has the advantages of high sensitivity and self-alignment. Comparing with the traditional laser interferometer, the laser feedback interferometer only has one arm to detect and amplify the signal at the same time, so it also has the advantages of simplicity, compactness and low cost. Recently, the phenomena of laser at weak feedback level are researched by many people, but the phenomena of laser at strong level have not been discovered well. When at strong level, the laser is more sensitivity to the signal from the environment, so it can be easily disturbed by noises, which will make troubles for signal detection and processing. In order to solve these problems, this dissertation will do some systematic research in the area of laser with strong feedback and the application of it in the displacement measurement. According to the research, we provide a single high-order laser feedback displacement measurement system which has a nanoscale resolution that can be traceable to light wavelength. At the same time, we will also provide the calibration method. In addition, we discovered a special method of frequency stabilization for the laser feedback system at strong feedback level.Firstly, we studied the phenomenon of the single-mode laser with high-order feedback, and have got the high-order feedback fringe of the laser with a tilt feedback cavity. We get the exact feedback order by the method of ray tracing and the calibration of measurement system with different feedback level, so the resolution of this system is also known. The displacement measurement resolution is at nanometer scale. On this basis, the phenomenon of polarization hopping of the laser with a tilt feedback cavity has been discovered. In order to use this phenomenon to discriminate the direction of displacement, we control the hopping point by adding stress on the laser cavity mirror or inserting a wave plate in the external feedback cavity and rotating it. We judge the direction of displacement by setting an intensity threshold in the electric cabinet.Secondly, a quartz crystal is inserted in the laser cavity. By changing the tilting angle of it, we can get the high-order feedback displacement measurement fringes with high density, good cosine property and phase-quadrature in polarization orthogonally dual frequency laser with a tilt feedback cavity under the condition of strong feedback level. This system can also get nanometer measurement resolution, and the intensity curve of it can be used to judge the direction of the displacement and to do the electric fringe subdivision. Finally this system can get a sub nanometer resolution.Thirdly, according to the characteristics of the He-Ne laser with high order feedback, we provide a method that can stable the frequency of the laser with strong external feedback by heating the resistance wire that is wrapped on the laser tube and using the external cavity modulation technology at the same time. This method can prove a good anti-jamming capability of our system and increase the accuracy of the displacement.Finally, in order to solve the problem that in the laser measurement system with a tilt concave feedback mirror, light points of different feedback order are mixed together and we can not get an exact displacement measurement resolution, we set up a laser high-order feedback system based on Fabry-Perot feedback cavity. In this system, we obtained single high-order weak feedback fringe that has a uniform amplitude and exact resolution for the first time. Then, we calibrate the resolution of this system by counting the fringe number of high-order feedback system in one half wavelength fringe. After that, we turn the tilting angle of the F-P feedback cavity carefully, and obtain the ratio of these two different feedback fringes, which can match with the theoretical value. This method can eliminate the Abbe error effectively, so the traceability of this system can be ensured. After the calibration, the optical resolution of this system is 10.9nm, which can be traceable to light wavelength. The final resolution of this system is 0.55nm. This system has the potential to be used as the nanometer displacement standard.