(Color online) AFM with two laser beams of different wavelengths. Schematic diagram for the optical system of the AFM. The linearly polarized beams from a red laser diode or an IR laser diode are collimated by the respective collimation lenses (i-1, i-2), passed through the respective polarization splitters (ii-1, ii-2), and circularly polarized by the respective wave plates (iii-1, iii-2); then, they enter an objective lens (v) after being reflected by or transmitted through a dichroic mirror (iv-1, iv-2). The beams reflected back by a small cantilever are separated by the same dichroic mirror (iv-1). The reflected red laser beam is guided into a split photodiode through the polarization splitter (ii-1), a band-pass filter (vi), and a spherical planoconvex lens (vii).
DC displacement of the cantilever as a function of the IR laser power.
(Color online) (a) Frequency spectra of the gain (upper) and phase (lower) for a small cantilever excited by the intensity-modulated IR laser (solid lines) and theoretical frequency spectra for harmonic oscillation (dotted lines). The cantilever amplitude was . (b) The time-domain response of the cantilever displacement driven by the laser modulated with a rectangular wave. The response shown with dots is fitted by a double-exponential-function curve (solid line), with time constants of and .
Block diagrams of delay compensation circuits with a single loop (a) and a double loop (b).
(Color online) Frequency spectra of the gain (upper) and phase (lower) for a small cantilever excited by the intensity-modulated IR laser with delay compensation and theoretical frequency spectra for harmonic oscillation (dotted lines).
(Color online) Frequency spectra of the closed-loop transfer function for the cantilever actuation. While the tip was intermittently contacted the surface and then the cantilever deflection was modulated by sinusoidal signals, the output signals from the PID circuit were monitored for the closed loop. The feedback bandwidth was defined at the frequency with the 45° phase delay.
(Color online) AFM images of actin filaments gliding on myosin V under the laser excitation. The images were acquired at /frame but showed every five frames (as shown by lower number). The scan area and pixel size are and , respectively. The ends of the actin filament gliding are indicated by open circles.
(Color) AFM images of myosin V on mica in a buffer solution obtained by photothermally driving the cantilever [(a) and (b)] or by using a piezoactuator-based scanner [(c) and (d)]. The scan area is . The frame rate was /frame for all the images. Images (a) and (c) are taken at the beginning of imaging and images (b) and (d) are taken at around 7 and , respectively.
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