A compact mid-
IR laser device utilizes an
external cavity to tune the
laser. The
external cavity may employ a Littrow or Littman cavity arrangement. In the Littrow cavity arrangement, a filter, such as a
grating, is rotated to provide
wavelength gain medium selectivity. In the Littman cavity arrangement, a reflector is rotated to provide tuning. A
quantum cascade laser gain medium provides mid-IR frequencies suitable for use in molecular detection by signature absorption spectra. The compact nature of the device is obtained owing to an efficient
heat transfer structure, the use of a small
diameter aspheric lens for both the output lens and the
external cavity lens and a monolithic
assembly structure to hold the optical elements in a
fixed position relative to one another. The compact housing size may be approximately 20 cm×20 cm×20 cm or less. Efficient
heat transfer is achieved using a thermoelectric cooler TEC combined with a high
thermal conductivity heat spreader onto which the
quantum cascade laser gain medium is thermally coupled. The
heat spreader not only serves to dissipate heat and conduct same to the TEC, but also serves as an optical platform to secure the optical elements within the housing in a fixed relationship relative on one another. The small
diameter aspheric output and external cavity lens each may have a
diameter of 10 mm or less and each lens is positioned to provided a collimated beam output from the
quantum cascade laser gain medium. The housing is hermetically sealed to provide a rugged, light weight portable MIR
laser source.