DC-excited cw CO₂ metal waveguide laser

Abstract

A novel design for a DC excited cw C02 metal waveguide laser has been developed in which a slotted hollow-cathode in a transverse discharge also doubles as a metal waveguide. This design has been implemented in a compact design that produces up to 1 watt of cw, 10.6 µm radiation. The discharge characteristics, laser gain and laser output has been studied as functions of various discharge parameters. The advatages of the new transverse discharge of the slotted hollow 2 cathode geometry include low voltage, positive impedence and high optical gain.Overall efficiency is comparable with those of conventional longitudinal C02 lasers. The output laser modes were very clean low order Gaussian modes. DC-EXCITED CW INTRODUCTIONDemand for the development of infrared optical waveguides to deliver C02 laser beams to a target, has led researchers to investigate two types of waveguides, the flexible metal [l,2,3] and the infrared fiber-optical [4,5] waveguides. There are often clear advantages to using a fiber optic waveguide for low power application, but for high-power applications metallic waveguides have proved to be the best choice.A metallic waveguide could be a hollow tube [1] or a concave strip [2]. In order to efficiently couple laser beams into either type of waveguide, Marhic [3] proposed a laser whose output modes match the waveguide modes. This is done there are practical differences between the two schemes. The glass tube laser suffers from very inefficient use of the gain medium. The second laser is more efficient but is more expensive because it requires a RF power supply, which complicates matters because it requires impedance matching between the RF power supply and the laser discharge which is hard to obtain. These problems may be 2 simultaneously eliminated by carefully designing a new type of waveguide discharge that is able to generate a relatively high gain medium using DC excitation.The focus of this thesis is to develop a novel design of high gain transversely DC excited metal waveguide laser. This new type of waveguide laser has been constructed and investigated. The design of this waveguide laser device is described in the next section of this chapter.In chapter II, a brief discussion of the molecular spectra and the excitation processes is presented. Understanding these processes is a prerequisite for finding the right discharge conditions for laser gain which demands knowing the role of each gas and their interactions in an electrcal discharge. Chapter III will introduce the low pressure glow discharge and finally focuses on the discharge characteristics of our slotted hollow-cathode waveguide.In chapter IV, the gain measurement, which is a necessery step in assessing the suitability of our new waveguide discharge for laser excitation and in obtaining the optimum discharge conditions for laser action, is presented. Next, the above amplifier is turned into a laser medium by placing it inside an optical resonator. In chapter V, The operation of this laser is studied by observing the transverse o...