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Laser schlieren microphone for optoacoustic spectroscopy
1Brown University, Chemistry Department, Providence, Rhode Island 02912, USA.
Applied Optics
|April 20, 2010
Summary
This study introduces a laser schlieren microphone for optoacoustic measurements. The device uses a laser beam and a diaphragm to detect pressure variations, significantly reducing noise for accurate signals.
Area of Science:
- Acoustics
- Optics
- Sensor Technology
Background:
- Optoacoustic spectroscopy requires sensitive microphones for detecting pressure variations.
- Traditional microphones can be limited by noise and frequency response.
- Laser-based sensing offers a non-contact and potentially high-frequency alternative.
Purpose of the Study:
- To describe the design and operation of a novel laser schlieren microphone.
- To analyze the mathematical model of the microphone's response.
- To experimentally determine the linear operating range of the device.
Main Methods:
- Utilizing a low-power He-Ne laser beam deflected by a diaphragm in an optoacoustic Helmholtz resonator.
- Converting diaphragm distortion due to pressure variations into amplitude modulation of the laser beam.
- Employing a photodiode detector and a lock-in amplifier for signal processing and noise reduction.
Main Results:
- The laser schlieren microphone effectively converts pressure variations into an amplitude-modulated laser signal.
- A mathematical model demonstrates a linear response for small optoacoustic signals.
- Experimental investigation characterized the microphone's linear response range for large amplitude signals.
Conclusions:
- The developed laser schlieren microphone is a viable tool for optoacoustic measurements.
- High-frequency modulation and lock-in amplification significantly improve signal-to-noise ratio.
- The system exhibits linear behavior within a defined range, suitable for various applications.
