[en] A Comment on the Letter by Sheng Feng and Prem Kumar, [Phys. Rev. Lett. 101, 163602 (2008)]. The authors of the Letter offer a Reply.

[en] Optical vortex beams have many potential applications in the particle trapping, quantum encoding, optical orbital angular momentum (OAM) communications and interconnects. However, the on-chip compact OAM detection is still a big challenge. Based on a holographic configuration and a spin-dependent structure design, we propose and demonstrate an on-chip spin-controlled OAM-mode directional coupler, which can couple the OAM signal to different directions due to its topological charge. While the directional coupling function can be switched on/off by altering the spin of incident beam. Both simulation and experimental measurements verify the validity of the proposed approach. This work would benefit the on-chip OAM devices for optical communications and high dimensional quantum coding/decoding in the future. (paper)

[en] Long term observations by Brook et al. reveal that the derivative of rotational frequency of PSR J0738-4042 changed abruptly in 2005. Originally, the spin-down rate was relatively stable, with the rotational frequency derivative being −1.14×10⁻¹⁴ s⁻². After September 2005, the derivative began to rise. About 1000 days later, it arrived at another relatively stable value of about −0.98 × 10⁻¹⁴ s⁻², indicating that the pulsar is spinning-down relatively slowly. To explain the observed change in spin-down rate, we resort to an asteroid disrupted by PSR J0738-4042. In our model, the orbital angular momentum of the asteroid is assumed to be parallel to that of the rotating pulsar, so that the pronounced reduction in the spin-down rate can be naturally explained as due to the transfer of angular momentum from the disrupted material to the central pulsar. The derived magnetospheric radius is about 7.0 × 10⁹ cm, which is smaller than the tidal disruption radius (8.7 × 10¹⁰ cm). Our model is self-consistent. It is shown that the variability in the spin-down rate of PSR J0738-4042 can be quantitatively accounted for by accretion from the asteroid disrupted by the central pulsar. (paper)

[en] We consider the behaviour of the orbital angular momentum of the light field as a superposition of Hermite – Gaussian beams upon astigmatic mode conversion. An analytical expression is obtained for the orbital angular momentum of such fields. Expressions are found for various linear combinations of Hermite – Gaussian beams. The astigmatic mode conversion of the initial light fields that are equivalent from the point of view of the orbital angular momentum is shown to lead to significantly different final results. (paper)

[en] Considering sum-frequency generation in an isotropic chiral nonlinear medium, we analyze the transfer of the spin angular momentum of fundamental elliptically polarized Gaussian light beams to the signal beam, which appears as the superposition of two Laguerre–Gaussian modes with both spin and orbital angular momentum. Only for the circular polarization of the fundamental radiation is its angular momentum fully transferred to the sum-frequency beam; otherwise, part of it can be transferred to the medium. Its value, as well as the ratio of spin and orbital contributions in the signal beam, depends on the fundamental frequency ratio and the polarization of the incident beams. Higher energy conversion efficiency in sum-frequency generation does not always correspond to higher angular momentum conversion efficiency. (letter)

[en] The characteristics of the output probe (OP) field is revisited in a compound system of two coupled cavities. Our model consists of two high Q Fabry-Pérot cavities in which one cavity is optomechanical. In the compound cavity system, one mirror has rotational motion that can generate Laguerre–Gaussian (twisted light) light having orbital angular momentum (OAM). In the presence of coupling strength J between the cavities and OAM l of the twisted light, we achieved a single and double optomechanical induced transparency (OMIT). It is found that the distance between the two transparency windows is dependent on the OAM of the twisted light. The double OMIT can be used to measure the OAM of the twisted light. Thus we suggested a model to measure the OAM of the twisted light with a transparency window. (paper)

[en] Mean values of total and specific orbital angular momenta are systematically analyzed for binary galaxies of various types. The angular momenta of the pairs which include irregular galaxy are considerably smaller than those for pairs of other types. The distribution of orbital angular momenta of the pairs which include Sb galaxy and the distribution of the pairs which do not include Sb galaxy are very different. Most pairs which include Sb galaxy have orbital angular momenta of the order of our Galaxy proper rotation momentum

[en] Total and specific orbital angular momenta of all physical pairs of galaxies from the catalogues of Karachentsev (1972) and Turner (1976) are estimated along with the ratios of the orbital momenta to the total spins. The majority of pairs have orbital momenta of the order of the spin of our Galaxy. Almost all the pairs have specific orbital angular momenta not larger than 4x10³⁰ cm²/s. The angular momentum for pairs of spiral galaxies is nearly uniformly distributed between spins and orbital momentum

[en] We derive analytical expressions of the probabilities for the signal and the crosstalk orbital angular momentum (OAM) states of a high order Bessel–Gaussian beam used in underwater optical communications. Our numerical results show that the probabilities of the signal and crosstalk OAM states are affected by the propagation distance and the parameters of the oceanic turbulence. The receiver aperture can be used to reduce the probabilities of the crosstalk OAM states and the probability of the detected signal OAM states keeps almost unchanged. Our results may improve the quality of optical communications systems. (paper)

[en] Optical vortex is a mode of light whose phase distribution varies as exp(iϕ), where l is called the topological charge of the vortex and ϕ is an azimuthal angle in the plane perpendicular to the propagating direction. The vortex beam of charge l carries an orbital angular momentum of lħ and has its application in manipulating micrometer-sized particles. A common method to detect topological charges of optical vortices is interference with a tilted Gaussian beam. In this work, we study the interference pattern of two obliquely-incident vortex beam with different topological charges, created by spatial light modulators (SLMs). We find fork-like fringes similar to those observed from the interference between a vortex and Gaussian beam. The fringe difference between the top and the bottom of the fork equals the difference the topological charges of the two vortices, as predicted by the theory. When the topological charges are the same and the fork pattern disappears. The tilted angle between the vortex beam affects the fringe spacing: the larger the tilt angle the smaller the fringe spacing. When the tilt angle radial from the defect canter. We suggest the result can be used to detect a topological charge of a vortex beam. (paper)