We show that the concept of the Lorentz-invariant mass of groups of particles can be applied to light pulses consisting of very large but finite numbers of noncollinear photons. Explicit expressions are found for the invariant mass of this manifold of photons for the case of diverging Gaussian light pulses propagating in vacuum. As the found invariant mass is finite, the light pulses propagate in vacuum with a speed somewhat smaller than the light speed. A small difference between the light speed and the beam-propagation velocity is found to be directly related to the invariant mass of a pulse. Focusing and/or defocusing light pulses is shown to strengthen the effect in which the pulse slows down while the pulse invariant mass increases. A scheme for measuring these quantities experimentally is proposed and discussed
A brief overview of entanglement characterization is given in the cases of biphoton and multiphoton polarization states. The importance of the approach is stressed based on the Schmidt decomposition. This method is applied to the characterization of the quadrature entanglement in two-mode multiphoton states. The fruitfulness of this approach is illustrated by a series of examples.
In this work, we investigated the frequency stabilization method of a diode laser that operates on the excited state transition 5P→5D of Rb atoms. The described technique allows simple control of the diode laser frequency stabilization to be performed. The critial parameters of stabilization, such as laser intensity and the temperature of a reference cell, have been investigated and long-time laser stability has been demonstrated with frequency stability of about 1 MHz.
A theory of the photon echo is presented for excitation of the vibrational–rotational transitions in a polyatomic molecule followed by the process of intramolecular vibrational redistribution (IVR). A model is considered that includes a description of IVR using the general statistical properties of chaotic states rather than phenomenological. Special attention is paid to the echo signals at the delay times that are considerably larger than the characteristic times of IVR. It is shown that echo measurements for the far plateau of the IVR curve can provide, directly or indirectly, determination of the so-called dilution factors; their values are of primary importance for estimating effective density of the molecular states that participate in IVR. Differences between the echo and anti-Stokes Raman scattering, really used for the same purposes, are discussed.
It is demonstrated that the interaction of a two-level quantum emitter (atom, molecule, etc) with a plasmonic nanoparticle (prolate nanospheroid) in an external laser field features either an essential increase (up to a few orders of magnitude) or reduction (up to a few times) of the total decay rate of the emitter in specific areas around the nanoparticle in contrast to its decay rate in a vacuum. It is also shown that the resonance fluorescence spectrum of the emitter in close proximity to a plasmonic nanoparticle is very sensitive to both the location of the emitter around the nanoparticle and to polarization of the near-field, which depends in turn on the polarization of the incident laser field. This can be used in engineering potential quantum optics experiments with quantum emitters in the near-field, as well as for 3D nanoscopy of the near-field by registering the resonance fluorescence spectra of quantum emitters scattered in the vicinity of a plasmonic nanoparticle.
The influence of waveguide parameters (thicknesses and contrasts in both transverse and lateral directions) on optical mode compositions in narrow-ridge lasers is numerically investigated. The proposed numerical model explains our experimental results on the drastic difference in optical mode compositions in broad-area and narrow-ridge lasers processed from the same wafer based on a broadened GaAs/AlGaAs transverse-waveguide heterostructure. It is shown that in the broadened transverse waveguides the fundamental mode tends to have a much lower 2D optical confinement factor than high-order modes. We suppose that waveguides possessing no more than two transverse eigenmodes would provide more opportunities for designing narrow-ridge lasers with robust single-mode emission.