32 S. Yoshida et al. Fig. 5.5 Intensity profile of the reference and signal beams Fig. 5.6 Interference intensity obtained at frame # 2 and #12 the negative side. It is impossible to determine if this difference comes from the cosıo or J0(ı) term. The frame rate is not synchronized with the oscillation frequency and the interference intensity profile can vary at each time frame. Third, careful comparison of the profiles at frame #2 and 12 indicates that the shapes of the bulge of the two are different; the interference in frame #12 appears to be closer tox D0 than frame #2. This indicates that the way the reference and signal beams overlap each other is different between the two frames. Figure 5.7a plots the time trends of the peak position of the interference intensity along one row (along a line a parallel to the x-axis near the y center in Fig. 5.6) when the specimen is driven at various frequencies. It is seen that the peak locations fluctuate when the transducer is turned on. The three driving frequencies, i.e., 11.0 kHz, 11.2 kHz and 11.3 kHz show different
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