Optical setupThe optical setup used in the
experiments is shown in figures 1, 2 and 3. An Nd:YVO4 infrared laser
(1064 nm) is located on an auxiliary shelf below the optical table to
avoid noise from its cooling fans. The beam is brought to the desired
traveling height by means of a periscope system (P). A half-wave plate
(HWP) provides the right polarization to the beam incident on the
spatial light modulator (SLM, Hamamatsu X10468-03), which generates
steerable holographic traps. Two sets of telescopes (lenses L1 and L2,
and L3 and L4) allow us to adjust the beam width to the size of the SLM
display and to overfill the entrance pupil of the objective in which we
generate the image of the modulator. We take advantage of the objective
lens (Nikon Plan Apo 60x 1.2 NA, water-immersion and Nikon Plan Fluor
100x 1.3 NA, oil-immersion, phase contrast, Fig. 1) of the microscope
(Nikon, Eclipse TE-2000E) to tightly focus the laser beam on the sample
and to simultaneously observe the cells with a CCD camera (QImaging,
QICAM). A dichroic mirror inserted in between, before the objective
lens, redirects the beam so the same path can be used for both the laser
and the illumination light coming from the condenser. The light passes
through the mirror and reaches the CCD camera at the bottom of the
microscope. Finally, the objective focuses the laser on a tiny spot at
the specimen plane to generate the optical trap. By means of a
user-friendly software we can dynamically create, move and remove traps
to perform the experiments conveniently.
 Figure 1. High numerical aperture objectives used to create optical traps
Figure
2. General view of the optical setup used in the experiments. (P:
periscope, M: mirror, HWP: half-wave plate, L1-L4: lenses, SLM: spatial
light modulator)
Figure 3. Detailed laser pathway inside the microscope |