Novel II-IV semiconductor nanocrystal gain media : from amplified spontaneous emission to lasing

Abstract

This thesis details efforts in using cadmium selenide (CdSe) nanocrystallites (NCs) as a novel lasing media. We begin with the synthesis of polymer/NC composites, in which the NCs are stabilized within a long-chain methacrylate polymer. This chapter serves to highlight the processing flexibility afforded by the NCs as well as some of the salient linear optical properties of NCs. The wide range of colors that are accessible using these NCs and the ability to excite them simultaneously are emphasized and provide an incentive to use them as a gain medium. Chapter 3 summarizes work done in developing a NC-based gain media and lists the stringent requirements for observing amplified spontaneous emission (ASE), a signature manifestation of gain. Then the synthesis of a robust NCs-titania, sol-gel matrix is described which satisfies these requirements. We exploit the stability and processability of these matrices to study the optical properties of the NC gain media.

(cont.) True temperature independent gain and ASE thresholds are shown to present, thus confirming early theoretical predictions of strongly-confined, zero dimensional gain media. Chapter 4 considers the incorporation of such structures with a suitable feedback structure and presents evidence for the first NC based distributed feedback laser. Room-temperature operation of such devices is shown to follow naturally from the unique gain features of the constituent NCs. Chapter 5 emphasizes the flexibility inherent in using these NCs as a gain media. We combine the processability of NC-titania films with soft-lithographic techniques to construct more complicated lasing structures. Simultaneous, mixed-colored lasing is shown to be possible, which might allow for new devices that operate within a wide gain window.