45° double-drive photoelastic modulation

In this report, a new type of double-drive photoelastic modulation effect is studied. Two piezoelectric actuators are connected to a symmetric photoelastic crystal at an angle of 45°. The actuators and crystal have the same resonant frequency. By adjusting the amplitude and phase difference between the driving voltages of the two piezoelectric actuators, two special forms of photoelastic modulation can be realized, namely, a pure standing wave form and a pure traveling wave form. The retardation magnitude and the azimuth angle of the modulation fast axis can be regulated in the pure standing wave, and the modulation axis moves circumferentially in the pure traveling wave. We have experimentally observed the two special photoelastic modulation modes, and the test and calibration methods are also reported.