Actively coupled cavity ringdown spectroscopy with low-power broadband sources.

Area of Science:

• Spectroscopy
• Optical Physics
• Analytical Chemistry

Background:

• Cavity enhanced absorption spectroscopy (CEAS) traditionally requires high-power laser sources.
• Broadband light sources offer advantages in spectral coverage but are limited by low spectral power densities.
• Cavity ringdown spectroscopy (CRDS) is a sensitive technique for measuring low absorptions.

Purpose of the Study:

• To demonstrate a novel coupling scheme for CEAS using an intracavity acousto-optical modulator.
• To enable CRDS measurements with broadband, low-power light sources.
• To achieve high dynamic range absorption measurements, particularly in lossy environments.

Main Methods:

• Utilizing an intracavity acousto-optical modulator to actively switch light into and out of an optical resonator.
• Employing a broadband, low-coherence continuous-wave superluminescent diode as the light source.
• Configuring the setup to measure absorption losses over a wide dynamic range.

Main Results:

• Successfully implemented CRDS with a broadband light source having spectral power densities below 30μW/nm.
• Demonstrated high dynamic range absorption measurements, from 1.8×10^-8 cm^-1 to 7.5% per roundtrip.
• Measured absorption for the forbidden transition of gaseous oxygen in air at ~760nm.

Conclusions:

• The developed acousto-optical modulator coupling scheme effectively enables CRDS with low-power broadband light sources.
• Despite introducing additional losses, the method provides a high dynamic range suitable for lossy environments and process analytical applications.
• This technique expands the applicability of CRDS to a broader range of light sources and measurement scenarios.