26 J. Eur. Opt. Society-Rapid Publ. 21, 32( 2025)
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Table
2. Experimental condition.
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EOM and HSC conditions |
Value |
EOM |
Modulation frequency |
5 kHz |
Modulation index |
3.14 rad |
HSC |
HSC frame rate |
60 kfps |
HSC pixel area |
128 128 pixels( Figs. 6 and 10) |
256 256 pixels( Fig. 7) |
HSC intensity resolution |
12 bits |
HSC pixel size |
20 lm, 20 lm |
Measurement time |
0.4 ~ 0.5 s |
Figure 6. Triangular displacement with 400 nm and 5 Hz,( a) Lissajous diagram at( 60, 60) pixel,( b) demodulated displacement at( 60, 60) pixel,( c) 2-D in-plane demodulated displacement.
2 nm and the frequency of 10 Hz are shown in Figure 8. The results without and with pre-filter are shown in Figures 8a and 8b, respectively. Without pre-filter, the noise amplitude is approximately as same as the displacement step. With pre-filter, the noise width is reduced to less than 0.5 nm. The intensity resolution of the HSC is 12 bits, so if the wavelength k is 633 nm, the displacement resolution is k = 2ð2 12 � 1Þ 77 pm. However, the resolution measured in Figure 8 is considerably worse than this. Resolution improvement is a future challenge.
The interferometer noise floor was measured with the PM stationary. The noise floor with frequency range from 0.5 Hz to 2.5 kHz is shown in Figure 9. Inthefigure, the black and gray lines show the noise floor results without and with the pre-filter, respectively. In the frequency range from 100 Hz to 2.5 kHz, the noise shape without pre-filter