Electrical pumping of color center lasers

This paper presents an assessment of the feasibility of using electrical pumping to achieve laser action in color centers in the alkali halides. We discuss mainly the self-trapped exciton in the alkali halides, which is a prime candidate for such a pumping scheme because it is known to produce strong electroluminescence. The theory of electrical contacts to insulating crystals is reviewed, as is the theory of space-charge-limited currents in insulators. It is shown that sufficient energy can be delivered to an alkali halide crystal by a space-charge-limited current to reach the threshold for laser action. We present experimental evidence which demonstrates that when ohmic contact is made to a KI single crystal, large space-charge-limited currents can flow. Finally, from the measured value of the electroluminescent intensity we infer the value of the population inversion achieved through electrical pumping of KI with blocking contacts.