122 research outputs found
Mathieu beams as versatile light moulds for 3D micro particle assemblies
We present tailoring of three dimensional light fields which act as light moulds for elaborate particle micro structures of variable shapes. Stereo microscopy is used for visualization of the 3D particle assemblies. The powerful method is demonstrated for the class of propagation invariant beams, where we introduce the use of Mathieu beams as light moulds with non-rotationally-symmetric structure. They offer multifarious field distributions and facilitate the creation of versatile particle structures. This general technique may find its application in micro fluidics, chemistry, biology, and medicine, to create highly efficient mixing tools, for hierarchical supramolecular organization or in 3D tissue engineering
Phase-conjugation of the isolated optical vortex using a flat surfaces
The robust method for obtaining the helical interference pattern due to the
phase-conjugation of an isolated optical vortex by means of the non-holographic
technique is proposed. It is shown that a perfect wavefront-reversal of the
vortex in a linear polarization state via even number of reflections is
achievable due to the turn of the photon's momentum with respect to the photon's orbital angular momentum projection . The
possible experimental realization is based upon like
reflections inside the confocal optical cavity. The alternative scheme
contains the Dove prism embedded in the optical with the odd number of
reflections from mirrors. This interferometric technique is
applicable to the optical tweezers, atomic traps, Sagnac laser loops and
metamaterials fabrication.Comment: 4 pages, 3 figures, submitted to referred journa
Rotational Doppler shift of the phase-conjugated photon
The rotational Doppler shift of a photon with orbital angular momentum is shown to be an even multiple of the angular frequency
of the reference frame rotation when photon is reflected from the
phase-conjugating mirror. We consider the one-arm phase-conjugating
interferometer which contains Dove prisms or other angular momentum
altering elements rotating in opposite directions. When such interferometer is
placed in the rotating vehicle the
rotational Doppler shift appears and rotation of the helical interference
pattern with angular frequency occurs. The
accumulation of angular Doppler shift via successive passage through the
image-inverting prisms is due to the phase conjugation, for conventional
parabolic retroreflector the accumulation is absent. The features of such a
vortex phase conjugating interferometry at the single photon level are
discussed.Comment: 6 pages, 3 figures, submitted to referred journa
Position clamping in a holographic counterpropagating optical trap
Optical traps consisting of two counterpropagating, divergent beams of light allow relatively high forces to be exerted along the optical axis by turning off one beam, however the axial stiffness of the trap is generally low due to the lower numerical apertures typically used. Using a high speed spatial light modulator and CMOS camera, we demonstrate 3D servocontrol of a trapped particle, increasing the stiffness from 0.004 to 1.5μNm<sup>−1</sup>. This is achieved in the “macro-tweezers” geometry [Thalhammer, J. Opt. 13, 044024 (2011); Pitzek, Opt. Express 17, 19414 (2009)], which has a much larger field of view and working distance than single-beam tweezers due to its lower numerical aperture requirements. Using a 10×, 0.2NA objective, active feedback produces a trap with similar effective stiffness to a conventional single-beam gradient trap, of order 1μNm<sup>−1</sup> in 3D. Our control loop has a round-trip latency of 10ms, leading to a resonance at 20Hz. This is sufficient bandwidth to reduce the position fluctuations of a 10μm bead due to Brownian motion by two orders of magnitude. This approach can be trivially extended to multiple particles, and we show three simultaneously position-clamped beads
Interferometric measurement of complex-field changes in transient detection imaging
We report an experimental method that combines nonlinear-crystal-based transient detection imaging (TDI) with interferometric complex-field retrieval. The system allows measuring both phase and amplitude of a dynamic scene while suppressing stationary background. Theoretical and experimental results prove the linear relation existing between input and output phases, as well as the benefits of phase analysis for both detection and measurement with high resolutions of λ/30, even under noisy conditions. Additionally, we present experimental evidence of the remarkable ability of the technique to detect phase sign changes in the scene what we call differential-phase TDI showing great detection sensitivity and no calibration requirements
Laser Singular Theta-Pinch
The interaction of the two counter-propagating ultrashort laser pulses with a
singular wavefronts in the thin slice of the underdense plasma is considered.
It is shown that ion-acoustic wave is excited via Brillouin three-wave
resonance by corkscrew interference pattern of a paraxial singular laser beams.
The orbital angular momentum carried by light is transferred to plasma
ion-acoustic vortex. The rotation of the density perturbations of electron
fluid is the cause of helical current which produce the kilogauss axial
quasi-static magnetic field. The exact analytical configurations are presented
for an ion-acoustic current field and magnetic induction. The range of
experimentally accessible parameters is evaluated.Comment: 6 pages, 2 figures, accepted to publication in Physics Letters
Superfluid rotation sensor with helical laser trap
The macroscopic quantum states of the dilute bosonic ensemble in helical
laser trap at the temperatures about are considered in the
framework of the Gross-Pitaevskii equation. The helical interference pattern is
composed of the two counter propagating Laguerre-Gaussian optical vortices with
opposite orbital angular momenta and this pattern is driven in
rotation via angular Doppler effect. Macroscopic observables including linear
momentum and angular momentum of the atomic cloud are evaluated explicitly. It
is shown that rotation of reference frame is transformed into translational
motion of the twisted matter wave. The speed of translation equals the group
velocity of twisted wavetrain and alternates with a sign
of the frame angular velocity and helical pattern handedness .
We address detection of this effect using currently accessible laboratory
equipment with emphasis on the difference between quantum and classical fluids.Comment: 8 pages, 3 figures, accepted to publication Journ.Low Temp.Phy
- …