We produce Lissajous figures by modulating a laser beam along two perpendicular directions by means of two tuning forks. When the ratio of the resonant frequencies of the tuning forks is a small rational number, Lissajous figures are clearly resolved on a screen. Because the ratio of frequencies is never exactly a rational number, a phase drift of the Lissajous figures is observed as a function of time. If the period of this phase drift is measured, variations in the resonant frequencies as small as 0.01 Hz can be detected.
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Crystals were float-zone grown n-Si(111) (phosphorus doping, with a resistivity of and low oxygen content of ) and were double-sided polished with a native oxide surface. The crystals were provided by B. Surma (ITME, Warsaw).
© 2011 American Association of Physics Teachers.
2011
American Association of Physics Teachers
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