Sensitive Spectroscopy of Acetone Using a Widely Tunable External-Cavity Quantum Cascade Laser

Area of Science:

• Spectroscopy
• Laser Technology
• Environmental Monitoring

Background:

• Acetone detection is crucial for environmental and industrial applications.
• Broadband spectroscopy requires tunable lasers with high resolution.
• Wavelength modulation spectroscopy enhances detection sensitivity.

Purpose of the Study:

• To utilize a tunable external-cavity quantum cascade laser for acetone spectroscopy.
• To demonstrate broadband direct absorption and wavelength modulation spectroscopy capabilities.
• To achieve high sensitivity and resolution for acetone detection.

Main Methods:

• Employed a widely tunable (~300 cm-1) external-cavity quantum cascade laser (EC-QCL) operating around 8 µm.
• Utilized a compact multipass cell for broadband direct absorption spectroscopy (DAS) and wavelength modulation spectroscopy (WMS).
• Performed second harmonic WMS (WMS-2f) with high modulation amplitudes (up to 10 GHz) at 50 kHz.

Main Results:

• Measured the entire molecular absorption band of acetone at ~7.4 µm with ~1 cm-1 spectral resolution.
• Achieved a minimum detection limit of 15 ppbv for acetone in under 10 seconds using WMS-2f.
• Demonstrated a noise equivalent absorption sensitivity of 1.9 × 10-8 cm-1 Hz-1/2.

Conclusions:

• The tunable EC-QCL is effective for broadband and high-resolution acetone spectroscopy.
• WMS-2f technique with the EC-QCL offers high sensitivity for trace gas detection.
• This system shows promise for sensitive acetone monitoring applications.