Optical Tweezers: Fundamentals and Some Biophysical Applications

Kamal R.Dhakal, Vasudevan Lakshminarayanan

Electromagnetic radiation changes its momentum when it interacts with small particles and a gradient force is experienced by the particle. This can be utilized to manipulate microscopic particles in an optical trap and is commonly referred to as optical tweezing. Optical tweezers are used as multifunctional tools in a myriad of applications such as micromanipulation, nanofabrication, biological studies of DNA, cells, biological micrometers, etc. This chapter will discuss the basic theory of optical tweezers (both wave theoretical and ray optics approximation) and provide examples from biomedical science and nanotechnology.

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Macroscopic Theory of Optical Momentum

Brandon A. Kemp

Light possesses energy and momentum within the propagating electromagnetic fields. When electromagnetic waves enter a material, the description of energy and momentum becomes ambiguous. In spite of more than a century of development, significant confusion still exists regarding the appropriate macroscopic theory of electrodynamics required to predict experimental outcomes and develop new applications. This confusion stems from the myriad of electromagnetic force equations and expressions for the momentum density and flux. In this review, the leading formulations of electrodynamics are compared with respect to how media are modeled. This view is applied to illustrate how the combination of electromagnetic fields and material responses contribute to the continuity of energy and momentum. A number of basic conclusions are deduced with the specific aim of modeling experiments where dielectric and magnetic media are submerged in media with a differing electromagnetic response. These conclusions are applied to demonstrate applicability to optical manipulation experiments.

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