Investigation of the acousto-optical effect of the amplitude and phase modulation of light diffracted at a standing ultrasonic wave
To determine the sound velocity in water, the 0th order of diffraction is aligned to a photodiode and a first maximum amplitude is searched for. Afterwards, the sound frequency is gradually increased and the frequencies of the following maximum amplitudes are determined. For the measuring points entered in the diagram, there arises a sound velocity in water of (1498 ± 7) m/s (T = 25 °C). The laser beam is splited with a beam splitter to determine the phase shift. The second partial beam is aligned to a second photodiode so that another diffraction maximum can be obtained with it. At the oscilloscope, the phase shift between the two different orders of diffraction can be determined.