In 1918 Albert Einstein wrote in a letter to Walter Dällenbach against his own theory of optical force: “It has long been known that the values I had derived with Laub at the time are wrong; Abraham, in particular, was the one who...
moreIn 1918 Albert Einstein wrote in a letter to Walter Dällenbach against his own theory of optical force: “It has long been known that the values I had derived with Laub at the time are wrong; Abraham, in particular, was the one who presented this in a thorough paper. The correct strain tensor has incidentally already been pointed out by Minkowski”. Unfortunately after almost 100 years, it is still not clear why Einstein wrote so regarding the theory of optical/electromagnetic force (the optical stress tensor (ST)) associated with Lorentz force. The electromagnetic force is one of the four fundamental interactions (other three: the strong interaction, the weak interaction and gravitation) in nature. In spite of experiencing much progress from 1970, research on optical/electromagnetic forces has so far revealed only the partial nature of light-matter interaction. For example, inside a material media an appropriate description of photon momenta (i.e. the Abraham-Minkowski dilemma) and an appropriate description of stress tensors along with Lorentz /volumetric forces (known as Minkowski, Abraham, Chu, Einstein-Laub and Ampere/Nelson forces) are still matters of great controversy. In this thesis, physics and applications of Lorentz force along with stress tensors and photon momenta have been investigated in details with special interest in tractor beam effect, plasmonic objects, chiral objects and the objects embedded in a generic material medium. At first, we have considered simpler case: application of Lorentz force for the objects placed in air. Specifically we demonstrate how the mechanism of Lorentz force can be used in a tractor beam-like effect for pulling multiple Rayleigh particles placed outside a dielectric hollow core waveguide and coupler. We also represent the Lorentz force analysis for plasmonic off-axis and on-axis spherical heterodimers and it is shown that the reversal of longitudinal binding force can be easily controlled by forced symmetry breaking. Though it is commonly believed that plasmonic forces mostly arise from the surface force and Fano resonance can be a promising way to achieve binding force reversal, our study based on Lorentz force dynamics suggests notably opposite proposals for the case of plasmonic spherical heterodimers. Next, we have also considered objects those are embedded in a material medium. The fundamental results/proposals of this thesis are presented afterwards. We have shown that the well-known Lorentz force leads to inconsistent result (pushing force) instead of the experimentally observed optical pulling force as observed in interfacial tractor beam experiments. As one of the major contributions of this thesis, we identify the ‘exact’ reasons why the well-known distinct Lorentz/volumetric forces fail not only for interfacial tractor beam experiment but also for several other major radiation pressure experiments performed up to date. Later, we demonstrate that it is still possible to establish different equivalent time-averaged Lorentz / volumetric force formulas based on the fulfilment of just two ‘consistency conditions’. Based on those proposed ‘consistency conditions’, finally, we demonstrate that by modifying the Einstein-Laub or Chu formulation; time-averaged STs and volume forces are obtainable, which can overcome the aforementioned inconsistencies. For example- these modified formulations can yield the ‘correct’ time averaged force similar to Minkowski’s force for almost all the previous real experiments. Specially, our proposed modified Einstein-Laub ST can be considered as an efficient mathematical toolkit, an alternative of time and memory consuming volumetric forces, to yield the internal bulk force of a chiral or achiral object embedded in complex material backgrounds (i.e. homogeneous, heterogeneous, bounded etc.). Later, we have also shown an interesting application of modified Lorentz force to control the reversal of optical binding force of plasmonic cubes placed over plasmonic substrate due to strong Fano resonance. Finally, based on our proposals throughout the thesis, at the end of this thesis we propose a new hypothesis named as the ‘existence domain’. ‘Existence domain’ is the region either outside of a scattering body taking only its exterior fields into account, or in its interior considering only the inside fields. Though almost all the time averaged distinct STs and volumetric force laws are restricted to the idea of ‘existence domain’, we demonstrate that the stress tensor, volumetric force and photon momentum of Minkowski are free from such and other restrictions both in instantaneous and time averaged situations. After almost 100 years of Einstein’s prediction, this thesis, most probably, finally answers why only Minkowski’s theory of optical force and photon momentum remains consistent in all circumstances. Proposals presented in this thesis can be very effective for resolving not only the dilemma of distinct stress tensors and optical Lorentz/ volumetric forces but also for settling the controversy of Abraham-Minkowski photon momenta. This thesis may also open a new window for optical pulling force/tractor beams along with the novel manipulation process of plasmonic dimers.