Moving interference patterns created using the angular Doppler-effect

Optical counterpart of a Foucault pendulum

The twin beam vortex interferometer with a phase-conjugating mirror in a rotating reference frame is analyzed. The circular motion of the interference pattern occurs due to the exchange of angular momenta between photons and the interferometer. Using the concept of the ideal phase-conjugating mirror, it is shown that the motion of the helical interference pattern of interacting vortex photons with topological charge ℓ may be used for detection of slow rotations. The higher density of interference fringes may improve sensitivity by a factor containing 2ℓ compared to conventional Michelson interferometry.

Manipulation of continuous variable orbital angular momentum squeezing and entanglement by pump shaping

Spatially structured quantum states, such as orbital angular momentum (OAM) squeezing and entanglement, is currently a popular topic in quantum optics. The method of generating and manipulating spatial quantum states on demand needs to be explored. In this paper, we generated OAM mode squeezed states of -5.4 dB for the L G0+1 mode and -5.3 dB for the L G0-1 mode directly by an optical parametric oscillator (OPO) for the first time. Additionally, we demonstrated that the OAM mode squeezed and entangled states were respectively generated by manipulating the nonlinear process of the OPO by controlling the relative phase of two beams of different modes, thus making two different spatial multimode pump beams. We characterized the Laguerre-Gaussian (LG) entangled states by indirectly measuring the squeezing for the H G _10(45^∘) mode and H G _10(135^∘) mode, and directly measuring the entanglement between the L G0+1 and L G0-1 modes. The effective manipulation of the OAM quantum state provides a novel insight into the continuous variable quantum state generation and construction on demand for high-dimensional quantum information and quantum metrology.

Rotation dynamics of particles trapped in a rotating beam

The rotation dynamics of particles trapped in a rotating beam is theoretically investigated. We find that there is a critical angular speed for the rotating beam. If the angular speed of the rotating beam is smaller than the critical value, the angular velocity of the trapped particle is nearly the same as that of the rotating beam, which is in accord with existing experimental observation. Otherwise, the angular velocity of the trapped particles will become periodic or quasi-periodic with time, depending on the beam polarization, which, to the best of our knowledge, has not been previously reported. Moreover, we also propose some methods to determine the ratio between the beam power and the maximal angular speed of the trapped particle, which can be used to estimate the minimum power required to rotate the particle at a given angular speed.

Optical angular momentum in a rotating frame

It is well established that light carrying orbital angular momentum (OAM) can be used to induce a mechanical torque causing an object to spin. We consider the complementary scenario: will an observer spinning relative to the beam axis measure a change in OAM as a result of their rotational velocity? Remarkably, although a linear Doppler shift changes the linear momentum of a photon, the angular Doppler shift induces no change in the angular momentum. Further, we examine the rotational Doppler shift in frequency imparted to the incident light due to the relative motion of the beam with respect to the observer and consider what must happen to the measured wavelength if the speed of light c is to remain constant. We show specifically that the OAM of the incident beam is not affected by the rotating observer and that the measured wavelength is shifted by a factor equal and opposite to that of the frequency shift induced by the rotational Doppler effect.

Rotational Doppler-effect due to selective excitation of vector-vortex field in optical fiber

Experimental demonstration of rotational Doppler-effect due to direct and simultaneous excitation of orthogonal elliptically-polarized fundamental and vortex modes in a two-mode optical fiber is presented here. The rotation frequency and the trajectory of the zero-intensity point in the two-mode fiber output beam measured as a function of analyzer rotation matches with the S-contour of polarization singularity in the beam, identified via Stokes parameter measurement. The characteristics of the S-contour around the C-point in the output beam is also measured as a function of rotating Dove prism and half-wave plate - Dove prism combination to highlight the role of polarization modifying components on the observed rotational Doppler-effect of vector-vortex beams.

Optical ferris wheel for ultracold atoms

We propose a versatile optical ring lattice suitable for trapping cold and quantum degenerate atomic samples. We demonstrate the realisation of intensity patterns from pairs of Laguerre-Gauss (exp(i??) modes with different ? indices. These patterns can be rotated by introducing a frequency shift between the modes. We can generate bright ring lattices for trapping atoms in red-detuned light, and dark ring lattices suitable for trapping atoms with minimal heating in the optical vortices of blue-detuned light. The lattice sites can be joined to form a uniform ring trap, making it ideal for studying persistent currents and the Mott insulator transition in a ring geometry.

Rotational frequency shifts in partially coherent optical fields

We study the frequency shifts taking place when a random, stationary optical field rotates with respect to an observer. The field is expanded in terms of fully coherent Laguerre-Gaussian basis modes, for which the rotational frequency shifts have been studied previously. We demonstrate the formalism by considering the spectrum of a Gaussian Schell-model field, and show that for a spatially highly incoherent field, significant spectral changes can be expected.

Entangled double-helix phase

We present a novel phase with an entangled double-helix structure. Beams with this phase have the same transverse patterns as those of interference between two doughnut beams. This proposed method allows a complete set of the superpositions of the doughnut modes or the orbital angular momentum states with different topological orders to be obtained. Furthermore, it introduces a simple continuous and controlled rotation of the transverse patterns by use of a spatial light modulator. It can be used to form a three-dimensional structure by three-dimensional trapping in an optical tweezers setup or to study the quantum characteristics of an optical vortex.

Optical doughnut for optical tweezers

We describe novel optical doughnuts for optical tweezers. With new phase functions, the proposed doughnut beams have dark cores in specified shapes. The technique can offer a simple method for creating a variety of beam shapes to match the trapped objects. One can rotate the beams directly by revolving their phase structures about their axes on the initial plane. The technique for generating the traditional Laguerre-Gaussian beam can be used to create these novel beams.