Developments in the Photonic Theory of Fluorescence

Conventional fluorescence commonly arises when excited molecules relax to their ground electronic state, and most of the surplus energy dissipates in the form of photon emission. The consolidation and full development of theory based on this concept has paved the way for the discovery of several mechanistic variants that can come into play with the involvement of laser input – most notably the phenomenon of multiphoton-induced fluorescence. However, other effects can become apparent when off-resonant laser input is applied during the lifetime of the initial excited state. Examples include a recently identified scheme for laser-controlled fluorescence. Other systems of interest are those in which fluorescence is emitted from a set of two or more coupled nanoemitters. This chapter develops a quantum theoretical outlook to identify and describe these processes, leading to a discussion of potential applications ranging from all-optical switching to the generation of optical vortices

Optical-Particle Trapping with Higher-Order Doughnut Beams Produced Using High-Efficiency Computer-Generated Holograms

Laser beams containing higher-order phase singularities can be produced with high efficiency computer generated holograms made with very simple equipment. Using such holograms in an optical tweezers experiment we have successfully trapped reflective and absorptive particles in the dark central spot of a focused charge 3 singularity beam. Angular momentum absorbed from the beam can set particles into rotation

Measurement of the Optical Force and Trapping Range of a Single-Beam Gradient Optical Trap for Micron-Sized Latex Spheres

A single-beam gradient optical trap was constructed using a 20 mW 632.8 nm He-Ne laser coupled to an optical microscope. Latex spheres were trapped in water at the focal point of a tightly-focused laser beam, which was generated using a 100 x objective. The efficiency of the trap was evaluated by determining the maximum speeds at which the trapped particles could be manipulated. Typical maximum speeds of tens of microns per second were recorded, at the maximum trapping power of 6.7 mW. The effective transverse trapping range for 1-7 mum diameter latex spheres was measured to be 1-3 mum, and the maximum transverse optical force on 1-12 mum diameter latex spheres varied in the range 0.4-4.5 pN

Transfer of angular momentum to absorbing particles from a laser beam with a phase singularity

Phase singularities in laser beams carry angular momentum due to the associated helical wavefront structure. This angular momentum can be transferred to absorbing particles trapped in the beam, setting them into rotation

Dual-beam interferometric laser trapping of Rayleigh and mesoscopic particles

There has been a significant amount of experimental work with counter-propagating, crossed-beam, and other interferometric laser trapping of neutral dielectric particles. Apart from the benefits of these configurations, such as the compensation or neutralization of scattering forces, there are a number of interesting applications. For example, the optical lattice resulting from interference can be used to sort particles of different refractive indices or sizes. The system can also be used to study thermal hopping between potential wells or to investigate Brownian motion subject to a quasi-periodic external potential

Laser-Beams with Phase Singularities

Phase singularities in an optical field appear as isolated dark spots and can be generated in active laser cavities or by computer generated holograms. Detection and categorization of these singularities can easily be achieved either by interferometry or Fourier transform pattern recognition using a computer generated hologram

Interferometric Measurements of Phase Singularities in the Output of a Visible Laser

We report the use of a simple interferometric technique which allows direct identification of phase singularities in laser fields. Phase singularities are observed in families of optical patterns formed via cooperative frequency mode locking in a continuous single longitudinal mode Na2 ring laser. The interferometric technique complements a previously reported astigmatic imaging method, and is superior in that it can be used to elucidate the structure of the higher order stationary patterns