The Generation and Characterisation of Ultrashort Mid-Infrared Pulses

Abstract

Over the past decade, ultrashort pulsed light sources have become an indispensable tool both in the laboratory and over a wider range of applications in the medical, industrial and telecommunication sectors. The availability of energetic sub-100 fs pulses, combined with the stability and usability of solid-state laser amplifiers, has opened up entire new fields such as femtochemistry, laser micro-drilling and knife-less laser eye surgery. However, while current ultrashort pulse sources are highly developed, their central wavelengths almost exclusively lie in the near-infrared spectral range below 1000 nm. Specifically, coherent pulses of mid-infrared (mid-IR) radiation, i.e. at wavelengths longer than 3 microns, are intensely sought for a range of applications in the life sciences, spectroscopy and environmental sensing but have not readily been available due to various technical challenges. These challenges are related not only to detecting and handling mid-IR radiation but also to the scarcity of mid-IR sources. Much effort has been invested in developing appropriate sources and technology to enable reliable production of such sources, but, even 50 years after the invention of the laser, a large portion of the mid-IR spectrum remains inaccessible, especially if one is interested in ultrashort pulsed sources. It is just within the last years that optical technology has made a major step forward; recent advances in fiber technologies are becoming available and reliable nonlinear media are now accessible. However, the current generation of mid-IR sources is not yet nearly as advanced as those in the near-IR. The various approaches and techniques often cover very narrow spectral ranges, come with very low output power, or are unable to provide short pulses of radiation. The last point in particular is common to the majority of mid-IR sources commonly used to date. Another drawback is that these very specific sources are typically designed as a specialists tool for a particular application. Very few systems have been designed to offer a robust, all-round performance in a flexible, upgradeable format. Thus, mid-IR sources often lack flexibility, and, with each source optimised for a very narrow set of applications (or perhaps even just one application), mid-IR source development has fractured into different specialist areas, resulting in a lack of coherence across the field, and ultimately thwarting the advancement of mid-IR science and technology. In this chapter we will restrict ourselves to sources of ultrashort pulses in the mid-IR spectral range. We will begin by motivating the development of sources as well as some technical limitations, mention some available sources as well as describe our new platform