Photoacoustic effect applied to sound speed measurement

Abstract

Keywords: Photoacoustic effect, homemade laser, speed of sound. ABSTRACT.We present a simple experiment to show the photoacoustic effect, a well established but not widely known effect which has many applications. The photoacoustic effect consists of the generation of acoustic waves by pulsed radiation incident on a sample. In our case, we used a homemade Nitrogen laser as a source of pulsed light for many samples in order to measure the speed of sound. The Nitrogen laser is easy to build by undergraduate students, it is a transversal discharge laser at atmospheric pressure (TEA), excited by a Blumlein circuit, emitting nanosecond pulses in the ultraviolet region of the spectrum (λ = 337.1 nm) and has been previously reported. The acoustic waves generated on the surface of the samples travel through the material and are detected with a piezoelectric sensor. The transducer is also easy to build using the piezoelectric of cigar lighters. The electric signals are registered by a 100 Mhz oscilloscope triggered by the light produced at the laser discharge. Knowing the thickness of the sample and the arrival time of the acoustic wave we can precisely measure the speed of sound. INTRODUCTION.

Hearing light from an incandescent bulb

“…So far, a number of studies have been done on a number of subjects such as imagination and diagnosis [2][3][4][5][6][7]. Applications in PAE are also reported in undergraduate subjects, such as the measurement of sound speed [8], the realization of low-cost imaging systems [9,10] and the basic study of nanomaterials [11]. Instead of a laser, in our experiment we construct a device using a 250 W incandescent bulb and we notice a novel phenomenon, i.e.…”

Music-of-light stethoscope: a demonstration of the photoacoustic effect

“…This observation led him to the invention of the ‘photophone’ for transmitting the human voice [ 1 ]. In the past the PA effect has been vastly explored in solids for spectroscopy [ 2 ] allowing measurement of properties of materials such as absorption [ 3 ] and the speed of sound [ 4 ].…”