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For the first lab activity, you'll be using the optical tweezers (OT) as a standard inverted microscope. That is, you won't use it to "tweeze" anything.
The OT setup is shown to the left.
The important pieces to consider when using this as just a microscope are
- the LED -- this gets turned on by plugging together the two wires circled
- the camera -- this is a Thorlabs camera and plugs into the computer's USB port with a red cable
- the condenser lens -- illuminates the sample
- the objective lens -- images the sample onto the camera
- the xyz stage -- allows you to move the sample with respect to the lenses
You can also see that there's a white fiber going from the laser (see image below) to a port on the microscope. This fiber is very fragile. Do not put anything on top of it or move it.
When we use the OT for trapping particles, we will use a 100x oil-immersion objective lens. However, for just imaging microspheres, we will use a 40x air objective.
The slide should be placed on the stage as shown, with both clamps securing the slide. For the calibration slide, the writing on the slide should be placed facing down. For slides of suspensions of microspheres or other fluid samples, the slides should be placed coverlsip down.
When using the 40x air objective, there should be about 1-2 mm of space between the front of the objective and the slide. Be very careful to avoid crashing the objective into the slide.
The z-axis micrometer on the stage will move the stage up and down. Counterclockwise rotations will bring the stage downward, closer to the objective. After you finish imaging, always move the stage up, away from the objective. To do so, turn the z-axis micrometer clockwise.
Here, the z-axis micrometer is being turned counterclockwise to bring the sample into focus. Note that there is a fine and a course knob for the micrometers controlling x-, y- and z-motion of the stage. Be very careful when making adjustments as you do not want to crash the sample slide into any delicate components.
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