Resonant optothermoacoustic detection: technique for measuring weak optical absorption by gases and micro-objects

Area of Science:

• Laser Spectroscopy
• Optical Physics
• Materials Science

Background:

• Optical absorption measurements are crucial for gas analysis and micro-object characterization.
• Existing techniques may face limitations in sensitivity or sample handling.

Purpose of the Study:

• To develop and demonstrate a sensitive laser spectroscopy technique for detecting optical absorption.
• To evaluate the technique's performance for both gaseous samples and micro-objects.

Main Methods:

• Utilized laser spectroscopy coupled with thermal effects.
• Employed a sharp mechanical resonance in a quartz crystal as a transducer.
• Tested with near-infrared diode lasers, pure carbon dioxide (CO2), and acetylene (C2H2) in nitrogen.

Main Results:

• Achieved a noise-equivalent sensitivity of 7.3 × 10⁻⁸ cm⁻¹W/(Hz)¹/² for gas absorption.
• Estimated capability to detect 10⁻⁸ fractional absorption by micro-objects on a transparent fiber.

Conclusions:

• The developed laser spectroscopy technique offers high sensitivity for optical absorption detection.
• The method is versatile, applicable to both gases and micro-objects, paving the way for advanced sensing applications.