Fiber-optic push-pull sensor systems

Fiber-optic push-pull sensors are those which exploit the intrinsically differential nature of an interferometer with concommitant benefits in common-mode rejection of undesired effects. Several fiber-optic accelerometer and hydrophone designs are described. Additionally, the recent development at the Naval Postgraduate School of a passive low-cost interferometric signal demodulator permits the development of economical fiber-optic sensor systems

Nonlinear energy pooling in nanophotonic materials

Recently there has been considerable interest in the construction of photoactive organic materials designed to exhibit novel forms of optical nonlinearity. By exploiting the unique properties of these nanomaterials at high levels of photon flux, new possibilities emerge for applications in energy harvesting, low-threshold lasing, quantum logic devices, photodynamic therapy, etc. In particular, a detailed appraisal of the theory spotlights novel mechanisms for directed energy transfer and energy pooling in nanophotonic dendrimers. Characterized by a nonlinear dependence on the optical irradiance, these mechanisms fall into two classes: (a) those where two-photon absorption by individual donors is followed by transfer of the sum energy to the acceptor; (b) where the excitation of two electronically distinct but neighbouring donor groups is followed by a collective migration of their energy to a suitable acceptor. In each case these transfer processes are subject to minor dissipative losses, associated with intramolecular vibrational relaxation in the donor species. In this paper we describe in detail the balance of factors and the constraints that determines the favored mechanism, which include the excitation statistics, structure of the energy levels, selection rules, molecular architecture, the distribution of donors and acceptors, spectral overlap and coherence factors. Knowledge of these factors and the means for their optimization offers fresh insights into nanophotonic characteristics, and informs strategies for the design of new photoactive materials

Near-field manipulation of interparticle forces through resonant absorption, optical binding, and dispersion forces

The relative motions of two or more neutral particles, subject to optical trapping forces within a beam, are influenced by intrinsic inter-particle forces. The fundamental character of such forces is well-known and usually derives from dispersion interactions. However, the throughput of moderately intense (off-resonant) laser light can significantly modify the form and magnitude of these intrinsic forces. This optical binding effect is distinct from the optomechanical interactions involved in optical tweezers, and corresponds to a stimulated (pairwise) forward-scattering mechanism. In recent years, attention has begun to focus on optical binding effects at sub-micron and molecular dimensions. At this nanoscale, further manipulation of the interparticle forces is conceivable on the promotion of optically bound molecules to an electronic excited state. It is determined that such excitation may influence the intrinsic dispersion interaction without continued throughput of the laser beam, i.e. independent of any optical binding. Nevertheless, the forwardscattering mechanism is also affected by the initial excitation, so that both the optical binding and dispersion forces can be manipulated on input of the electromagnetic radiation. In addition, the rate of initial excitation of either molecule (or any energy transfer between them) may be influenced by an off-resonant input beam which, thus, acts as an additional actor in the modification of the interparticle force. A possible experimental set-up is proposed to enable the measurement of such changes in the interparticle coupling. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE)