Experimental result

Waveforms of the differential amplifier output, which represent the rotation of the polarization plane, are shown in Fig. 5. The charge voltage was 50 kV, and the discharge gap between the needles was 5 cm. Figure 5(a) shows the output for 40 consecutive discharge shots. Since the discharge path varied for each shot, the relative alignment between the discharge path and the propagating beam was changed. Waveforms which showed similarity with the discharge current waveform are indicated as a black solid curve. Although the output signals were triggered by the charge voltage, the black solid curves had a delay time of about 25 ^s in average. We confirmed that the delay was caused by the amplifier circuits and cables.

One of the black solid curves is enlarged in Fig. 5(b). The output of the differential amplifier when the incident beam was interrupted in front of the detectors is also shown. This shows that the electromagnetic noise from the discharge did not influence the output signal. The correlation coefficient between the black solid curves and the discharge current waveform

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Fig. 5. Experimental result of rotation angle of propagating beam's polarization plane. (a) Differential outputs of 40 times discharge event, (b) validation of differential output and discharge current.

was >0.94. This result was in agreement with the result of the simulation, which showed that the rotation of the polarization plane had the same time response as the discharge current.

The rotation angle of the polarization plane was estimated from the measured results. Considering the amplification of the differential amplifier (x100), the intensity ratio of the mutually orthogonal polarization outputs was 1.00:0.98. Therefore, the rotation angle S is calculated as

This value also agreed with the result of the simulation.

The correspondence between the obtained signal with the discharge current showed that the propagating beam interacted with the discharge only at a single optical path. Larger rotation angle could be obtained by increasing the discharge current and gap length. Since the discharge chamber used in this study can only accommodate discharge gaps of about 10 cm, the same experiment will be performed in open air, using discharge gaps in the order of 1 m and a larger impulse voltage generator.

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