Investigation Of Solar-Pumped Single Crystal Fiber Lasers

Since the 60s of the 20th century,the ruby laser invented by American physicist Maiman has achieved laser output,opening a new era of laser development.Solar-pumped laser uses solar energy as the pump source to realize the conversion of solar-to-laser,which is a way to effectively use solar energy.Solar-pumped lasers have a wide range of application prospects in the fields of wireless energy transmission,space communication,space laser weapons and so on.Single crystal fiber(SCF)can be considered as hybrid structures of bulk laser crystal and traditional rare-earth doped fiber,which has the advantages of bulk laser crystal and rare-earth doped fiber.Solar-pumped SCF laser can not only effectively use solar energy,but also give full play to the advantages of the SCF,which is a very promising solar-pumped laser.Owing to the relevant research of the solar-pumped SCF lasers has not been reported.Therefore,this paper proposes several concentrating system of solar-pumped SCF laser,to provide ideas for the solar-pumped SCF lasers,and analyzes the laser output and temperature field distribution of solar-pumped SCF lasers in theory.At the same time,the idea of high-power solar-pumped SCF laser was also proposed,and theoretical analysis was carried out.This paper mainly includes the following three aspects of research:(1)A concentrating system for solar side-pumping SCF laser media was designed.The concentrating system is based on a parabolic mirror,3D-CPC and a hollow cylindrical reflector,with a SCF placed in the center of the hollow cylindrical reflector.This chapter discusses the effects of hollow cylindrical reflectors with different cross-sectional shapes,the focal lengths of parabolic mirrors,and SCF laser media with different diameters on the absorption of solar power by SCFs.The system can collect solar power with an area of 1.3 m~2.The SCF can absorb the maximum solar power of 149 W on the pump band.By solving the rate equation and the power transmission equation,the SCF laser can obtain the maximum laser output power and the solar-to-laser conversion efficiency are 60 W and 4.64%,respectively.(2)In order to achieve the high power laser output of solar-pumped SCF lasers,a new tree-shaped solar concentrating system is designed,which is composed of 6 off-axis parabolic mirrors,6 3D-CPCs and a hollow cylindrical reflector.SCF is located inside a tree-shaped hollow reflector.With Trace Pro ray tracing and optimized design of tree-shaped hollow reflectors,SCF can achieve 453.43 W of solar power absorption.Through theoretical calculation,it is concluded that the SCF has a maximum laser output power of 183.76 W,and the solar-to-laser conversion efficiency is 2.52%.(3)Aiming at the absorption of the solar power of solar-pumped SCF laser,the thermal effect of SCF is analyzed in detail.Taking the solar absorption power of SCF under hollow cylindrical reflector and tree-shaped hollow reflector concentrating system as the main factors generating heat source,the axial and radial temperature distribution,thermal stress distribution on cross-sectional section and thermal lens focal length(radial and tangential)of SCF are theoretically obtained.The calculation shows that the maximum temperature,maximum thermal stress on the cross-section,and radial and tangential thermal lens focal lengths of the SCF are 41.96℃,14.03 MPa,240.2 mm and 136.21 mm respectively in a hollow cylindrical reflector and without water cooling.The maximum temperature,maximum thermal stress on cross-section,and radial and tangential thermal lens focal lengths of the SCF are 33.05℃,28.09 MPa,18.8 mm and 33.16 mm,respectively,when placed in a tree-shaped hollow reflector and water cooling.These researches can provide certain new design ideas for the designs of solar-pumped SCF lasers,and have certain reference value.