Photoacoustic effect in a flowing liquid

Area of Science:

• Photoacoustics
• Fluid Dynamics
• Spectroscopy

Background:

• Photoacoustic spectroscopy (PAS) is a sensitive analytical technique.
• Understanding factors affecting PAS signal intensity is crucial for accurate measurements.
• The influence of sample flow on photoacoustic signals in gas microphone cells is not fully understood.

Purpose of the Study:

• To experimentally investigate the effect of flowing liquid sample velocity on photoacoustic signals.
• To develop a theoretical model explaining the observed velocity dependence.
• To explore the implications for in vivo photoacoustic measurements.

Main Methods:

• Utilized a gas microphone photoacoustic cell with a flowing liquid sample.
• Varied liquid sample velocity, modulation frequency, and incident beam position.
• Developed a theoretical model incorporating temperature dependence and cell boundaries.

Main Results:

• Photoacoustic signal remained constant up to a threshold velocity.
• Above the threshold, a characteristic oscillatory behavior in the signal was observed.
• Threshold velocity and oscillation patterns systematically varied with modulation frequency and beam position.
• A simple theory accounting for temperature dependence and cell boundaries explained the observed phenomena.

Conclusions:

• Liquid sample velocity significantly impacts photoacoustic signals in gas microphone cells.
• Cell boundaries play a critical role in the observed velocity-dependent signal structure.
• The findings provide a basis for improving in vivo photoacoustic measurements of flowing biological fluids, such as blood.