Refraction of a Laser Beam in Various Mediums Due to Ultrasound Waves

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Cabrera, Sierra
Clement, Jacob
Lenzi, Christiano
Sheahan, Mira
Withers, Tai
Gas-Coupled Laser Acoustic Devices (GCLADs) are systems used to detect sound using a laser [1]. If implemented in a bubble chamber (a type of experiment used for particle detection [2]), the sounds made by bubbles forming and popping could theoretically be detected with GCLADs [3]. If properly utilized, GCLADs could prove to be an improvement over traditional microphones in characterizing these bubbles. To set up our optoacoustic detector, we aligned a laser operating in the visible spectrum towards a bicell photodetector. We then observed the deflections in the laser beam caused by sound waves via the changing voltage measured by the oscilloscope. Sound waves are pressure waves which affect the density of the material through which they propagate and, thus, cause deflections in any light beam traveling through said medium [4]. As such, we collected voltage-time data using an oscilloscope with a sampling rate of 10000 samples per second as we were hoping to capture very high frequency sounds in the range of our 40kHz ultrasound transducer. Although sensitivity was our greatest issue, we showed that we could characterize the frequency of our system even with very small amplitudes. With ultrasonic emissions at 40kHz, we were able to characterize these oscillations in air at 42:7 ± 2:7 kHz and in water at 40:7 ± 2:4 kHz. This demonstrated that with increased sensitivity, this system could be an effective method to detect bubbles in bubble chambers. This experiment is inspired by previous research performed by John Caron (see references [5], [3], [6], [4]) where ultrasound waves were transmitted in air, water, and gelatin.
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