Acousto-optical effects (Ultrasound Experimental Set 8)

This set has been designed for some sophisticated experiments, which deal with the interactions between a mechanical wave and light – the acousto-optical effects (AOM, acousto-optical modulation). The experiments promote a knowledge and understanding of the propagation characteristics of mechanical as well as electromagnetic waves.It is shown that the changes in density that occur due to the compression and dilatation of an ultrasound wave cause a change in the diffraction index of the medium. The grating created causes the diffraction of laser light. In addition, the intensity modulation and wavelength alteration of laser light are demonstrated.In different experiments, the diffraction characteristics of light at standing and travelling ultrasonic waves are investigated and measured. The sound velocity of different liquids is determined by means of the variation of the interference maxima of the laser light at different ultrasound frequencies (resonance cell).The amplitude modulation and phase shifting of laser light at a standing wave can be represented with a photodiode and recorded with an oscilloscope. The frequency change of the sound wave influences the amplitude modulation and makes it possible to calculate the sound velocity of the medium.The difference of the diffraction at standing and travelling waves is demonstrated by means of an acoustic absorber, which prevents the formation of standing ultrasound waves in the sample reservoir.At the travelling ultrasonic wave, a frequency shift of the laser light, caused by the Doppler effect, can be measured. Buy using a beam splitter and reflectors, differently diffracted portions of light can be turned into interference. The resulting beats are displayed and measured with the oscilloscope.This experimental set is suitable both for the demonstration of the acousto-optical effects and their application in technology and for carrying out interesting experiments in advanced practical training for students in higher education of all natural scientific and technical fields.