Slide Mount Apparatus
Microscope Slide Mount
For several reasons, the microscope slide mount is an important piece of the optical tweezers set up. First, it needs to be sturdy enough to damp vibrations that move through the table and the lab. Since the Brownian motion measurements are observing particle oscillations of fractions of micrometers, any instability in the slide mount will skew the data. Secondly, it needs to be adjustable in all three dimensions to focus the sample, and scan over the slide surface. Thirdly, the mount must be electronically controlled in the horizontal directions to perform Stokes measurements. Ideally it will be electronically controlled in the vertical direction to finely focus the objective, without having to touch the slide mount. Touching the mount actually alter the focus of the objective.
Slide Mount Apparatus Components
First a Newport 462 Series three dimensional translation stage was obtained as a starting point for our slide apparatus. The adjustment knobs on this particular mount are good for larger scale adjustments but lack fine tuning capability. Additionally this mount alone cannot be electronically controlled. The Newport stage is the large silver stage in image below.
Next, two Thorlabs NFL5DP20 5 mm piezo translation stages were obtained to modify the Newport stage and enable electronic control. Additionally, a Thorlabs 3-axis Piezo Controller, and several BNC cables are needed to drive the Thorlabs stages. Additionally a function generator will be needed to perform Stoke's drag force measurements.
The translational stages are then all mounted on a custom aluminum base.
The custom slide mount piece will need to be attached to the apparatus in order to actually mount the slide on the apparatus. This will be located on the lab bench, if the apparatus is not already set up.
Slide Mount Apparatus Construction
The apparatus may be constructed in several different manors, but suggested method will now be described.
First the translational stages are assembled. We first added the piezo stages to Newport stage. We suggest using the piezo stages as the z and x stages, and to orient the knobs up and to the right, respectively, so as not to impede adjustment. We attached the z stage first, as doing so allowed us to put the slide mount in a more advantageous position. Then attach the slide mount to the last piezo stage, as doing so after it is already screwed into the base is difficult. Then screw the aluminum base into the optics table, then screw the translational stages plus the slide mount into the base. We suggest having the manual y axis screwed all the way out before doing this, so as to minimize the chance of bumping into the objective.. You should be very careful during this part because the translational stages cannot balance on their own, and may tip into the objective, damaging it. We suggest having one lab partner hold the stage while the other screws it into the aluminum base.
Figure 1: Three-Dimensional Piezo-Controlled Microscope Slide Translation Mount
Using Slide Mount Apparatus
A few tips for using this apparatus effectively are: Use the Newport adjustment knobs for large adjustments, save the Thorlabs stages for finer tuning. Think about the starting position of each adjustment knob. Try not to max out either of the directions before adjusting the slide's position. Always have the vertical Thorlabs stage connected to the piezo controller. This will make focusing the laser on the cover slide, much easier as you won't have to touch the apparatus at all. Finally, BE CAREFUL when adjusting the slide vertically. If the slide is pressed too hard against the microscope objective, the cover-slip will crack, which is dangerous to the microscope objective.