47 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
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
Examination of laser microbeam cell lysis in a PDMS microfluidic channel using time-resolved imaging
We use time-resolved imaging to examine the lysis dynamics of non-adherent BAF-3 cells within a microfluidic channel produced by the delivery of single highly-focused 540 ps duration laser pulses at λ = 532 nm. Time-resolved bright-field images reveal that the delivery of the pulsed laser microbeam results in the formation of a laser-induced plasma followed by shock wave emission and cavitation bubble formation. The confinement offered by the microfluidic channel constrains substantially the cavitation bubble expansion and results in significant deformation of the PDMS channel walls. To examine the cell lysis and dispersal of the cellular contents, we acquire time-resolved fluorescence images of the process in which the cells were loaded with a fluorescent dye. These fluorescence images reveal cell lysis to occur on the nanosecond to microsecond time scale by the plasma formation and cavitation bubble dynamics. Moreover, the time-resolved fluorescence images show that while the cellular contents are dispersed by the expansion of the laser-induced cavitation bubble, the flow associated with the bubble collapse subsequently re-localizes the cellular contents to a small region. This capacity of pulsed laser microbeam irradiation to achieve rapid cell lysis in microfluidic channels with minimal dilution of the cellular contents has important implications for their use in lab-on-a-chip applications
Nonresonant central exclusive production of charged-hadron pairs in proton-proton collisions at √s = 13 TeV
The central exclusive production of charged-hadron pairs in collisions at a center-of-mass energy of 13 TeV is examined, based on data collected in a special high-* run of the LHC. The nonresonant continuum processes are studied with the invariant mass of the centrally produced two-pion system in the resonance-free region, +−1.8 GeV. Differential cross sections as functions of the azimuthal angle between the surviving protons, squared exchanged four-momenta, and +− are measured in a wide region of scattered proton transverse momenta, between 0.2 and 0.8 GeV, and for pion rapidities ||<2. A rich structure of interactions related to double-pomeron exchange is observed. A parabolic minimum in the distribution of the two-proton azimuthal angle is observed for the first time. It can be interpreted as an effect of additional pomeron exchanges between the protons from the interference between the bare and the rescattered amplitudes. After model tuning, various physical quantities are determined that are related to the pomeron cross section, proton-pomeron and meson-pomeron form factors, pomeron trajectory and intercept, and coefficients of diffractive eigenstates of the proton