Broadly tunable external cavity quantum cascade laser for medical hyperspectral imaging at 11 μm wavelength region

Molecular vibrational spectroscopy within the mid-infrared part of the spectrum is an attractive analysis technique. The spectral region required for the analysis requires tens of cm
^-1
tunability centered somewhere typically between 3 to 15 μm, depending on the constituent molecular compound to be analyzed. An important application is medical hyperspectral imaging for early stage cancer diagnosis. For this application, a broadly and continuously tunable light source centered near 11 μm is required [1]. Further, for highly detailed images, the source should be much brighter than traditional glow-bar sources. The external-cavity quantum cascade laser (EC-QCL) meets these requirements and has further advantages in being compact, robust, and relatively inexpensive. We describe an EC-QCL system based on the InGaAs/InAlAs heterosystem with good average power and tunability; the system is implemented as a portable and rugged light source for hyperspectral imaging near 11 μm.