title: Role of condenser iris in optical tweezer detection system.
abstract: Optical tweezers have proven to be very useful in various scientific fields, from biology to nanotechnology. In this Letter we show, both by theory and experiment, that the interference intensity pattern at the back focal plane of the condenser consists of two distinguishable areas with anticorrelated intensity changes when the bead is moved in the axial direction. We show that the space angle defining the border of two areas linearly depends on the NA of the objective. We also propose a new octant photodiode, which could significantly improve the axial resolution compared to the commonly used quadrant photodiode technique.
authors: Department of Physics, Institute for Advanced Studies in Basic Sciences, Zanjan, Iran.
authors: Akbar
authors: A
authors: Samadi
authors: S Nader S
authors: SN
authors: Reihani
mesh_terms: D000465:Algorithms; D004867:Equipment Design; D007368:Interferometry / Q000379:methods; D007834:Lasers; D008853:Microscopy / Q000379:methods*; D055096:Optical Devices; D052898:Optical Tweezers; D055095:Optics and Photonics