High-Speed Mid-Infrared Frequency Modulation Spectroscopy Based on Quantum Cascade Laser

Abstract

We demonstrated a high-speed mid-infrared frequency modulation spectroscopy scheme based on a distributed-feedback quantum cascade laser for application in trace gas sensing by means of all-optical frequency modulation. With this method, the modulation frequency spectrum of a gas sample can be obtained within the mid-infrared pulse duration of about 200 ns. A frequency modulation of the middle infrared lasing optical frequency was achieved in quantum cascade laser with a modulation frequency of 200 MHz by illuminating with a 1550 nm near-infrared laser. For CO gas, with 2-mW near-infrared illumination, the noise-equivalent sensitivity of the frequency modulation spectroscopy was estimated to be 0.12 ppmv for an absorption length of 6.1 meters, indicating an improvement by a factor of 7 compared with Voigt-fitted direct absorption spectroscopy (0.84 ppmv). The frequency modulation signal was found to be proportional to the incident near-infrared power, and therefore the noise-equivalent sensitivity is expected to be further improved by increasing the near-infrared illumination power. This high-speed frequency modulation spectroscopy based on the distributed-feedback quantum cascade laser has promising applications in high-speed and high-sensitivity gas sensing.Index Terms -frequency modulation spectroscopy, middle-infrared spectroscopy, quantum cascade laser, gas sensing.

Mid-Infrared Frequency Modulation Spectroscopy of NO Detection in a Hollow-Core Antiresonant Fiber

“…In addition to the current modulation at radio frequency, FMS has also been demonstrated by optical illumination. All-optical frequency modulation of a DFB-QCL at 200 MHz was demonstrated by illuminating the 4.67 µm QCL using a 1.55 µm near-infrared laser [18]. FMS was also applied for high-temperature measurement of hydrogen cyanide (HCN) using a single-tone MIR frequency modulation detection scheme [19].…”