-     Laser Model: Long-Wavelength Difference Frequency Generation laser system

-     Description: Custom-designed mid-infrared laser source based on the difference frequency generation (DFG) process between an external-cavity quantum-cascade-laser tunable over 5.49 - 5.71 μm (pump source) and a CO₂ gas laser tunable over 9.23 - 10.86 μm (signal source). The DFG process was realized in a nonlinear, orientation-patterned GaAs (OP-GaAs) crystal and results in an idler beam tunable in the range 12.7 – 15 μm, i.e., the fingerprint region.

-     Applications: The laser system targets the vibrational bending modes which are typically useful for selective measurements. The system is particularly important in selectively sensing the BTEX family (benzene, toluene, ethylbenzene and xylene) whose absorption spectra in the DFG range are distinguishable but otherwise overlapping in other IR ranges.

-     Brief description of previous studies: The DFG system has been used to measure forming benzene and HCN in reactive experiments in low-pressure shock tube.

-     Controlling/tuning method(s): Finely piezo-tuning the CO₂ gas laser or coarsely by grating, and/or tuning the QCL by a mechanically motorized diffraction-grating.

-     Specifications:  

-     DFG Setup:

OI: optical isolator, CM: concave mirror, BC: beam combiner, PM: parabolic mirror, M: mirror, LF: long-pass filter, BP: band-pass filter, D: detector