High-power infrared laser waveguide with two curved surfaces

Abstract

ABSTRACT The transmitting efficiency and light intensity of the hollow waveguide with two curved surfaces was analyzed with a rayoptics approach. The eigenmode of the waveguide was analyzed with Helmholtz equation. The hollow waveguide wasfabricated and the experiment of laser propagation in it was carried out. The CO2 laser power of 1 123 W was deliveredthrough the waveguide.Keywords: High power, laser, two curved surfaces, waveguide 1.INTRODUCTION In industry and medical application, it is difficult to transmit laser from source to target. Traditional method includesseveral mirrors, which reflect laser beam and are heavy and inflexible. So far, several kinds of waveguides have beenproposed or fabricated for infrared transmission in various 2 For relatively low power transmission, infrared solid-core fibers have been studied for use in thermal sensing or laser surgery. A dielectric-coated metallic circular hollowwaveguide has been developed by Akihito Hongo3.Hollow waveguide is promising for kilowatt-class CO2 laser transmission,because the reflective losses at the input and output ends are small. But, it is difficult to fabricate this kind of waveguide.Improving the smooth degree of inside surface is not easy. We have fabricated a new system, called the waveguide with twocurved surfaces. It can transmit kilowau-class infrared laser. Its fabrication is easier than above waveguide.In this paper, the behavior of the beam propagation along the waveguide is analyzed by using ray optics approach. Thetheoretical solution ofthe metal reflectivity is given when the incident angle is near 900. According to Fourier optics theory,a three-dimension ray model is given to simulate the laser beam by a ray bundle. The transmission curves of the waveguidewith different parameters are obtained by using this model.The solvability of Helmholtz equation of different coordinate is discussed. The eigenmode ofthe waveguide is calculated byusing finite element-method.The infrared waveguide transmission system has been fabricated. The laser power that transmits through waveguide is1 123w. The transmission efficiency is 80.7%/rn. The experiment results show that this hollow infrared waveguide ispromising for high-power CO2 laser bean transmission.