  With growing interest in the mid-infrared spectral region, dysprosium has
recently been revisited for efficient high-performance infrared source
development. Despite historically receiving less attention than other rare
earth ions, in recent years lasers utilizing the dysprosium ion as the laser
material have set record mid-infrared performance, including tunability from
2.8 to 3.4 um (in addition to 4.3 um lasing), continuous wave powers exceeding
10 W, greater than 73% slope efficiencies, and even ultrafast pulsed operation.
Herein, the unique energy level structure and spectroscopy of the dysprosium
ion are examined and the major developments that have led to this resurgence of
interest and subsequent record mid-infrared laser performance are surveyed.
Also mid-infrared applications of emerging dysprosium lasers are highlighted,
in addition to surveying the many opportunities that lie ahead.
