147 research outputs found
Interferometric measurement of arbitrary propagating vector beams that are tightly focused
In this work we demonstrate a simple setup to generate and measure arbitrary
vector beams that are tightly focused. The vector beams are created with a
spatial light modulator and focused with a microscope objective with an
effective numerical aperture of 1.2. The transverse polarization components
(, ) of the tightly focused vector beams are measured with 3 step
interferometry. The axial component is reconstructed using the transverse
fields with Gauss law. We measure beams with the following polarization states:
circular, radial, azimuthal, spiral, flower and spider web.Comment: 4 pages, 4 figure
Characterization of periodic cavitation in an optical tweezer
Microscopic vapor explosions or cavitation bubbles can be generated
periodically in an optical tweezer with a microparticle that partially absorbs
at the trapping laser wavelength. In this work we measure the size distribution
and the production rate of cavitation bubbles for microparticles with a
diameter of 3 m using high speed video recording and a fast photodiode. We
find that there is a lower bound for the maximum bubble radius m which can be explained in terms of the microparticle size. More than
of the measured are in the range between 2 and 6 m,
while the same percentage of the measured individual frequencies or
production rates are between 10 and 200 Hz. The photodiode signal yields an
upper bound for the lifetime of the bubbles, which is at most twice the value
predicted by the Rayleigh equation. We also report empirical relations between
, and the bubble lifetimes.Comment: 5 pages, 3 figure
Shaping the angular spectrum of a Bessel beam to enhance light transfer through dynamic strongly-scattering media
We prepare a quasi-non-diffracting Bessel beam defined within an annular
angular spectrum with a spatial light modulator. The beam propagates though a
strongly scattering media and the transmitted speckle pattern is measured at
one point with a Hadamard Walsh basis that divides the ring into segments
(). The phase of the transmitted beam is reconstructed with
3 step interferometry and the intensity of the transmitted beam is optimized by
projecting the conjugate phase at the SLM. We find that the optimum intensity
is attained for the condition that the transverse wave vector (of the
Bessel beam) matches the spatial azimuthal frequencies of the segmented ring
. Furthermore, compared with beams defined on a 2d grid (i.e. Gaussian)
a reasonable enhancement is achieved for all the sampled with only 64
elements. Finally, the measurements can be done while the scatterer is moving
as long as the total displacement during the measurement is smaller than the
speckle correlation distance.Comment: 5 pages, 4 figures, submitted to Optics Letter
Isotopic difference in the heteronuclear loss rate in a two-species surface trap
We have realized a two-species mirror-magneto-optical trap containing a
mixture of Rb (Rb) and Cs atoms. Using this trap, we have
measured the heteronuclear collisional loss rate due to
intra-species cold collisions. We find a distinct difference in the magnitude
and intensity dependence of for the two isotopes Rb and
Rb which we attribute to the different ground-state hyperfine splitting
energies of the two isotopes.Comment: 4 pages, 2 figure
Birth and growth of cavitation bubbles within water under tension confined in a simple synthetic tree
Water under tension, as can be found in several systems including tree
vessels, is metastable. Cavitation can spontaneously occur, nucleating a
bubble. We investigate the dynamics of spon- taneous or triggered cavitation
inside water filled microcavities of a hydrogel. Results show that a stable
bubble is created in only a microsecond timescale, after transient
oscillations. Then, a diffusion driven expansion leads to filling of the
cavity. Analysis reveals that the nucleation of a bubble releases a tension of
several tens of MPa, and a simple model captures the different time scales of
the expansion process
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