| http://www.w3.org/ns/prov#value | - The driving unit 156 can vary the deflection angle, by obtaining driving signals from a sweep oscillator which can vary the frequency of signals, applying the signals to, for example, a piezo element constituting the acoustically modifiable beam deflector 153, producing therewith a periodic distribution of refractive indices in a transparent medium such as air, and thus altering the pitch of diffr
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