Instrumentation and techniques

Introduction Cathodoluminescence is generated when a suitable specimen, such as a polished thin section, is bombarded with a beam of high-energy electrons. Some of the earliest observations of cathodoluminescence were made in the early 1960s by using an electron probe microanalyzer (EPMA), commonly referred to as an electron probe or electron microprobe (e.g., Long, 1963; Long and Agrell, 1965; Stenstrom and Smith, 1964; Smith and Stenstrom, 1965). In spite of this early application to CL study, the EPMA has not subsequently been used extensively for this purpose. Although CL images can be viewed in an EPMA, the EPMA is used primarily for compositional analysis. As reported by Marshall (1988, p. 19), designs were also being developed in the early 1960s for a simpler electron excitation source that could be attached to the stage of a standard petrographic microscope to allow cathodoluminescence observations with an optical microscope. Long and Agrell (1965) discuss the design of a cathodoluminescence microscope attachment (CMA) that utilizes a heated filament gun, and Sippel (1965) designed a CMA that utilized a cold cathode gun. Subsequently, other designs for CMAs have been produced both for commercial use and for use by various research laboratories. For example, Herzog et al . (1970) described a commercial design for a CMA called the Luminoscope, an instrument still in use today. A major breakthrough in cathodoluminescence instrumentation came with the development of CL detectors that could be attached to a scanning electron microscope (SEM).