Design Of Compact Optical System For Cold Atom Gravimeter Based On Fiber Lasers

Absolute gravimeter based on atomic interferometer has attracted more and more attention because of its high sensitivity and accuracy.It has many advantages,such as short measurement time,high accuracy and stable performance.Although there are great progresses in this gravimeter,it can only be used in a steady point due to its large size and complexity.It has not yet achieved for mobile measurement in field tasks.It is desirable to make gravimeter for achieving mobile measurement and field detection.Therefore,it is imperative to make the laser system of the gravimeter compact and environmentally adaptable.In this thesis,we designed a compact optical system based on fiber lasers.The system achieved is integrated into a box,the volume of the box is reduced to 1/3 of the original one.It can be moved and assembled by one person.In contrast,at least four persons are needed to move the previous one.After the miniaturization,based on the problems faced by the field exploration mission,we have done experiments on the influence of temperature change on the optical system.It is found that the temperature has a great influence on the coupling efficiency of the optical system.The efficiency variation can be changed from 10% to less than 1% if the temperature is controlled properly.Based on this,an insulation box is designed for the optical system.Temperature changes are controlled less than 0.1℃ inside the box.The main contents of each chapter are summarized as follows:In the first chapter,I introduce the historical background,development process and potential applications of cold atomic gravimeters,describe the development trend and application prospects of cold atomic gravimeters at home and abroad in recent years,emphasize the importance of miniaturized optical system design of cold atomic gravimeters,and briefly describes the focus of this paper.In the second chapter,I describe the advantages of NKT Photonics narrow linewidth fiber laser.I also describe the aspects to optimize our system.All the properties of the fiber laser including the stability of the fiber laser as the light source are described in details.In the third chapter,the laser system is designed.The optical system scheme and intensity distribution scheme of miniaturized system are introduced in detail.Additionally,the advantages of the laser scheme and optical scheme are described in detail.The components of the mechanical shutter light shielding system based on step motor are introduced,and the light shielding performance of the mechanical light shutter system is described.In the fourth chapter,the temperature-dependent characteristics of the compact laser system are studied.Firstly,we study the influence of temperature on the output optical power and output optical wavelength of the fiber laser.It is found that the two parameters do not change with temperature.The internal temperature control system of fiber laser can cope with the change of environmental temperature.Then the influence of temperature on optical system is studied.The experimental results show that the temperature will change the coupling efficiency of optical fiber.In the fifth chapter,by using various thermal insulation materials(heat insulation cotton,thermal insulation foam glue),a thermal insulation box is designed for the laser system and the optical path system.The thermal insulation characteristics of the heat preservation box are studied.In the sixth chapter,the main results of this paper are summarized and future research is prospected.