Quantum Microscopy of Biological Systems by Michael Taylor

Author:Michael Taylor
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

With this setup, 1 polystyrene particles were tracked in water with a sensitivity of m Hz (see Fig. 6.3). Then, the measurement scheme was tested to verify whether the measured signal corresponded to motion along the axis. A 1 kHz sinusoidal modulation with 5 V peak-to-peak amplitude was applied to the piezo drivers along the and axes of the positioning stage (Nanomax MAX302). The resulting power spectra for the measured signal are shown in Fig. 6.3. When the axis was modulated, the resulting measurement yields a strong signal at 1 kHz. By contrast, the response at 1 kHz is 40 times smaller for a modulation along the axis. This clearly demonstrates that the measurement predominantly samples the particle motion along the axis. Since the stage itself is imperfect, the observed cross-talk may have originated in either the positioning stage or imperfections in the detection.

Movement along the axis shifts the relative phase between the scattered field and local oscillator. This phase is compensated with the phase lock, and to first order the residual phase difference does not affect the measured signal. Modulation of the axis, however, introduced a large axial motion which the phase lock was unable to compensate. The feedback loop could not respond adequately to the driven motion, and the phase lock became unstable. This suggests that axial motion could produce more cross-talk than axis motion. Without a stable phase lock it is not possible to perform reliable measurements, and the exact level of this axial cross-talk was not characterized.

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