The Fabrication of a Distributed-feedback Quantum Cascade Laser Emitting at Around 4.6 mm and its Application in Photoacoustic Detection of Trace CO Gas
S. Tan, J-C. Zhang, L-J. Wang, J-Y. Chen, J-Q. Liu, F-Q. Liu and Z-G. Wang
Photoacoustic (PA) detection of CO gas was demonstrated by using self-designed distributed-feedback quantum cascade laser (DFB-QCL) emitting at around 4.6 mm. Details of the laser fabrication and the PA detection system are described. Single-mode lasers were designed to cover the strong CO absorption lines by using a buried first-order grating. Though the grating period is 0.72 μm which is not the most appropriate period to get the highest performance lasers made from our epitaxial material, single-mode room temperature continuous wave (CW) operation (side-mode suppression ration (SMSR) above 25 dB) and pulsed operation at 70°C were achieved. By using a differential Helmholtz resonant PA cell with 11 cm path length, the PA spectra for different CO concentrations from 120 to 10 mmol/mol were obtained at room temperature.
Keywords: Quantum cascade laser, distributed-feedback, buried first-order grating, side-mode suppression ration (SMSR), photoacoustic spectroscopy, trace gas detection, carbon monoxide (CO)