Optical Trapping

An optical trap, also known as "optical tweezers", is

formed when a single laser beam is sharply focused

to a near-diffraction limited spot. A laser induces

fluctuating dipoles in dielectric particles, and the

interaction of these dipoles with inhomogeneous

electric field of the laser gives rise to the

gradient trapping force.

optical tweezers and trapping  

Optical trapping/tweezers are tools whereby a piconewton force is exerted on microscopic dielectric objects and is used to physically hold, manipulate, and/or repulse the material in question by utilizing highly focused laser beams.  Mainly employed in the arena of bioresearch, dielectric objects are attracted along the strong electric field gradient to the region of the strongest electric field, which is located at the beam waist.  Once the particle is trapped in the beam waist, it can be translated to another location, as if it were picked up by tweezers.

Due to the ability to translate on the sub-nanometer scale, optical tweezers are used to study single molecules which have been attached to the dielectric particle. For example, biological research into the properties of DNA and associated proteins has been advanced significantly due to the advent of optical trapping and tweezing. To probe the biomolecules of interest, many of the optical trap setups utilize the fundamental wavelength of 1 μm continuous wave lasers. These single frequency, linear polarized lasers are essential because many biological samples, aqueous in nature, have a low absorption coefficient at this wavelength, which minimizes the damage to the biological material. Other wavelengths, such as green (0.51-0.55 μm) and near-IR (1.15-1.8 μm), are also used.

Although TEM00 Gaussian beams are the most common choice, other laser beam modes have found use, including Hermite Gaussian beams, Laguerre-Gaussian beams, and Bessel beams.  IPG's lasers are especially well-suited to applications in optical trapping due to nearly perfect  beam mode with the M2 values near unity, and a high degree of pointing stability. For this, IPG offers a suite of lasers and associated solutions to provide the wavelength, beam mode, and overall beam quality necessary to conduct advanced optical trapping experiments.   strand of DNA
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