Measurement of Broad Absorption Features Using a Tunable External Cavity Quantum Cascade Laser
We demonstrate the use of a tunable external cavity quantum cascade laser system for measurement of broad absorption features in the mid-infrared spectral region. The thermoelectrically cooled external cavity laser was tuned over a 65 cm-1 range centered at 8.7 microns using stepper motor control. Pulsing the laser at a high duty cycle provided 3-5 mW average output power over the tuning range, and enabled phase-sensitive detection of amplitude-modulated signals. We used the laser system to measure the absorption spectra of Freon-125 using a Herriott cell. In addition, the absorption spectrum of water in the laboratory air was measured. The measurements showed excellent agreement with reference spectra, in both wavelength and amplitude. The measured scan resolution of 0.14 cm-1 is suitable for measurement of the absorption features of complex molecules as well as simple molecules with atmospherically broadened lines. We discuss the limits to the scan resolution due to effects of spectral chirp and mode-hops during pulsed operation.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 928283
- Report Number(s):
- PNNL-SA-56621; NN2001000
- Country of Publication:
- United States
- Language:
- English
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ABSORPTION SPECTRA
DETECTION
FREONS
INTERMEDIATE INFRARED RADIATION
LASERS
OCIS codes
TUNING
WATER
infrared
optoacoustic and thermo-optic
tunable