Optical Tweezers A highly focused laser beam creates a force attracting particles to the center of the beam. This electric field gradient, typically in the order of piconewtons, can be used to trap and manipulate microscopic particles and is particularly useful for biological single cell manipulation. The single cell can be held in the beam waist, the point which forms the center of the beam for further analysis such as IR or Raman spectroscopy. By trapping a number of particles in different laser beams inter molecular forces can be investigated.
The laser used for optical tweezing and trapping can be a range of different wavelengths, but it is common to use the Infrared region when working with biological samples to reduce absorption of light energy that can cause cell heating. The laser should however have a good beam quality with an M2 close to unity and a high pointing stability to maintain the position of the focus and beam waist.