Coherent sources of mid-infrared (mid-IR) radiation are of great
interest for a wide range of scienti?c and technological applications
from spectroscopy and frequency metrology to information technology,
industrial process control, pho- chemistry, photobiology and
photomedicine. The mid-IR spectrum, which may be de?ned as wavelengths
beyond ?2µm, covers important atmospheric windows, and numerous
molecular gases, toxic agents, air, water, and soil pollutants, c-
ponents of human breath, and several explosive agents have strong
absorption ?ngerprints in this region. The development of practical
coherent solid-state sources in the mid-IR can thus provide
indispensable tools for a variety of - plications in environmental
monitoring and pollution control, detection of water and soil
contaminants, food quality control, agriculture and life sciences, and
n- invasive disease diagnosis and therapy through breath analysis.
Coherent mid-IR sources also offer important technologies for
atmospheric chemistry, free-space communication, imaging, rapid
detection of explosives, chemical and biological agents, nuclear
material and narcotics, as well as applications in air- and sea-born
safety and security, amongst many. The timely advancement of coherent
mid-IR sources is, therefore, vital to future progress in many
application areas across a broad range of scienti?c, technological, and
industrial disciplines. On the other hand, more than 40 years after the
invention of laser, much of the mid-IR spectrum still remains
inaccessible to conventional lasers due to fun- mental limitations, most
notably a lack of suitable crystalline laser gain materials.
