1. Locate the problems in "Testing Basic Optical Tweezers (Part 1)"(2025/03/16)
I used a starter kit of a microscope to capture a particle, but it was difficult:
The particle was always deposited, firmly attached to the bottom of the slide, due to the density difference and electrostatic force, which made it difficult to catch and move it.
=> My solution involves adding salt to allow the Monodisperse Polystyrene Microspheres to float. Ensure that the density of the solution is slightly higher than that of the Microspheres.
Absence of the various optical filters, dichroic mirrors, caused severe interference fringes. And most importantly, the cover slip and its slide probably formed an F-P cavity. It steals the energy from the optical tweezers. It is necessary to distinguish which type of fringes your images belong to: Airy disk, Equal inclination interference, or F-P interference? Mine is unlikely to be an Airy disk, because the intensity doesn't seem to decline along the radius. And if you move away the cover slip, it still exists, then it must be Equal inclination interference, vice versa. Until now, I probably wrongly recognised it as an F-P interference fringe, but it still needs confirmation.
=> Choose appropriate 1. optical filters; 2. dichroic mirrors; 3. reflectors.
The sample evaporated too fast. Although the temperature was not too high, the volume was too small and the laser was too powerful for such small samples, it evaporated fast.
=> Choose concave slides, and seal your samples with epoxy resin for repeatable experiments.
2. Design a new modular optical tweezer(2025/07/23)
There're some testing videos on YouTube.
3. New stepper motor (2025/08/03)
The motors often get stalled. There are three TMC2209s on the board. So I guess it's because of insufficient current. Then I bought a single TMC2208 module, and the motor rotated smoothly.
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