Intensity enhancement in off-axis integrated cavity output spectroscopy

Area of Science:

• Laser-based absorption spectroscopy
• Optical physics
• Cavity-enhanced techniques

Background:

• Off-axis integrated cavity output spectroscopy (OA-ICOS) offers sensitivity and robustness with a simple optical design.
• A key limitation of OA-ICOS with highly reflective mirrors is low output intensity.
• Non-mode-matched cavities further exacerbate this low output intensity issue.

Purpose of the Study:

• To systematically investigate methods for increasing cavity output intensity in OA-ICOS.
• To develop an optical design that enhances transmission power while maintaining a long effective path length.
• To improve the sensitivity of laser absorption spectroscopy techniques.

Main Methods:

• Implementation of a third re-injection mirror placed before the absorption cavity.
• Systematic investigation of cavity output intensity enhancement.
• Utilizing a CO2 absorption line at 6240.10 cm-1 in the near-infrared region for testing.
• Comparison of experimental results with a simulation model.

Main Results:

• Achieved an intensity enhancement factor of 38, validating the simulation model.
• Demonstrated high transmission power and retained a long effective path length.
• Reached a noise equivalent absorption sensitivity of 1.6x10^-8 cm^-1 Hz^-1/2.
• Sensitivity was no longer limited by detector detectivity.

Conclusions:

• The addition of a re-injection mirror effectively increases cavity output intensity in OA-ICOS.
• This enhanced optical design significantly improves the sensitivity of laser absorption spectroscopy.
• The method offers a pathway to overcome detector limitations and achieve ultra-high sensitivity measurements.