This Small Business Innovation Research (SBIR) Phase II project will demonstrate a prototype frequency tunable quantum cascade laser (TQCL) operating at terahertz frequencies (2-5 THz) for applications including gas spectroscopy and non-destructive imaging. This novel source is based on distributed feedback (DFB) terahertz QCL with a lateral waveguide dimension much smaller than the wavelength (wire laser). This optical mode extends outside the waveguide, allowing an external MEMS plunger to interact with the mode and affect tuning. A cryogenically operated motor is used to deflect the MEMS plunger allowing for electronic control of output frequency. A combination of mechanical electrical Stark shift tuning will allow frequency tuning range of >300 GHz with a resolution of 1 MHz. The output frequency of the TQCL will be coarsely calibrated allowing the output frequency to be selected in software. The TQCL will be housed in a small footprint cryocooler, and will have output powers greater than 100 µW.
The broader impact/commercial potential of this project will be in detection and characterization of narrow gas lines (MHz) or solid absorption features (GHz) in spectroscopy, remote sensing, astronomy and spectroscopic imaging. The innovation will be useful for academic, industrial and governmental research. The electrical operation of the MEMS tunable source and the turnkey nature of the cryogenic system will allow non-expert researcher access to the terahertz spectral region. Future uses include incorporation into a swept-source optical coherence tomography system for non-destructive evaluation (NDE). Terahertz frequency radiation is of particular interest for use in NDE because they are able to penetrate materials that are opaque at infrared and visible wavelengths such as structural foams, polymers and paints. Potential applications include the validation of the structural integrity of foams used in the aerospace industry, continuous monitoring of paint processes in the automotive industry, and the validation of pharmaceuticals tablet coatings used in controlled release formulations.
