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The most basic optical tweezer setup will likely include the following components: a laser (usually Nd:YAG), a beam expander, some optics used to steer the beam location in the sample plane, a microscope objective and condenser to create the trap in the sample plane, a position detector (e.g. quadrant photodiode) to measure beam displacements ...
Laser power used for trapping the cell is 100 mW, for stretching 1200 mW per fibre. Phase contrast images, 63× objective; scale bar is 10 μm. The trapping of micrometre-sized particles by two laser beams was first demonstrated by Arthur Ashkin in 1970, [1] before he developed the single-beam trap now known as optical tweezers. An advantage of ...
The equipment is arranged as can be seen in the diagram. A lens focuses a laser to a certain point, and after this point the beam naturally defocuses. After a further distance an aperture is placed with a detector behind it. The aperture causes only the central region of the cone of light to reach the detector.
A laser normally produces a very narrow beam of light in a single wavelength, in this case, green. Photons, the quanta of electromagnetic radiation, are released and absorbed from energy levels in atoms and molecules. In a lightbulb or a star, the energy is emitted from many different levels giving photons with a broad range of energies.
For illumination, a laser light-sheet is used, i.e. a laser beam which is focused only in one direction (e.g. using a cylindrical lens). A second method uses a circular beam scanned in one direction to create the lightsheet. As only the actually observed section is illuminated, this method reduces the photodamage and stress induced on a living ...
The latter is called the output coupler, because it allows some of the light to leave the cavity to produce the laser's output beam. Light from the medium, produced by spontaneous emission, is reflected by the mirrors back into the medium, where it may be amplified by stimulated emission. The light may reflect from the mirrors and thus pass ...
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By observing and recording the beam pattern, for example, one can infer the spatial mode properties of the beam and whether or not the beam is being clipped by an obstruction; By focusing the laser beam with a lens and measuring the minimum spot size, the number of times diffraction limit or focusing quality can be computed.