Mid-IR Difference Frequency Generation

Abstract

The availability of continuously tunable narrow-band laser sourcesemitting in the mid-infrared region of the electromagnetic spectrumbetween 2.5 mum and 15 mum is important for a large variety of applications.One way to achieve both broad tunability and narrow linewidth isfrequency conversion in a nonlinear optical material, in particulardifference frequency generation (DFG). After a brief introductionto the requirements of tunable mid-infrared sources, we present anoverview of the theoretical background of frequency conversion processes.Emphasized are phase-matching issues, as well as. material and designconsiderations to be observed when implementing a DFG laser source.The variety of possible combinations of pump/signal sources and nonlinearcrystals is illustrated by numerous reports found in the literature.Finally, design issues are discussed for a practical example of aDFG laser source wherein the experimental arrangement and systemperformance, as well as tuning characteristics, are treated. Examplesof spectroscopic applications reflect the advantages such as broadand continuous tuning range, narrow linewidth, and compact set-upof a DFG source, but also the drawbacks such as relatively low outputpower and high costs. The chapter is completed by some concludingremarks and a short outlook.