Single-pulse photoacoustic technique for measuring IR multiphoton absorption by polyatomic molecules

Area of Science:

• Physical Chemistry
• Spectroscopy
• Acoustics

Background:

• Infrared multiphoton absorption is crucial for understanding molecular interactions with intense laser light.
• Photoacoustic spectroscopy offers a sensitive method for detecting absorbed energy.
• Characterizing signal origins is vital for accurate measurements.

Purpose of the Study:

• To measure cross sections for infrared multiphoton absorption using a single-pulse photoacoustic technique.
• To elucidate the origins of acoustic signals generated in the photoacoustic cell.
• To define the operational pressure range for this technique.

Main Methods:

• Utilized the single-pulse photoacoustic technique.
• Employed infrared laser pulses to excite gas molecules.
• Analyzed microphone signals to identify distinct acoustic events and their sources.

Main Results:

• Successfully measured infrared multiphoton absorption cross sections.
• Identified the first acoustic peak as directly proportional to absorbed energy.
• Determined that subsequent signals result from a combination of volume contributions and cell/microphone ringing.

Conclusions:

• The single-pulse photoacoustic technique is effective for quantifying IR multiphoton absorption.
• Understanding signal components is critical for accurate interpretation of photoacoustic data.
• The technique's applicability is dependent on the pressure range and acoustic properties of the cell.