50 research outputs found
Hyperfine Spectroscopy of Optically Trapped Atoms
We perform spectroscopy on the hyperfine splitting of Rb atoms trapped
in far-off-resonance optical traps. The existence of a spatially dependent
shift in the energy levels is shown to induce an inherent dephasing effect,
which causes a broadening of the spectroscopic line and hence an inhomogeneous
loss of atomic coherence at a much faster rate than the homogeneous one caused
by spontaneous photon scattering. We present here a number of approaches for
reducing this inhomogeneous broadening, based on trap geometry, additional
laser fields, and novel microwave pulse sequences. We then show how hyperfine
spectroscopy can be used to study quantum dynamics of optically trapped atoms.Comment: Review/Tutoria
Ultrafast nano-focusing with full optical waveform control
The spatial confinement and temporal control of an optical excitation on
nanometer length scales and femtosecond time scales has been a long-standing
challenge in optics. It would provide spectroscopic access to the elementary
optical excitations in matter on their natural length and time scales and
enable applications from ultrafast nano-opto-electronics to single molecule
quantum coherent control. Previous approaches have largely focused on using
surface plasmon polariton (SPP) resonant nanostructures or SPP waveguides to
generate nanometer localized excitations. However, these implementations
generally suffer from mode mismatch between the far-field propagating light and
the near-field confinement. In addition, the spatial localization in itself may
depend on the spectral phase and amplitude of the driving laser pulse thus
limiting the degrees of freedom available to independently control the
nano-optical waveform. Here we utilize femtosecond broadband SPP coupling, by
laterally chirped fan gratings, onto the shaft of a monolithic noble metal tip,
leading to adiabatic SPP compression and localization at the tip apex. In
combination with spectral pulse shaping with feedback on the intrinsic
nonlinear response of the tip apex, we demonstrate the continuous micro- to
nano-scale self-similar mode matched transformation of the propagating
femtosecond SPP field into a 20 nm spatially and 16 fs temporally confined
light pulse at the tip apex. Furthermore, with the essentially wavelength and
phase independent 3D focusing mechanism we show the generation of arbitrary
optical waveforms nanofocused at the tip. This unique femtosecond nano-torch
with high nano-scale power delivery in free space and full spectral and
temporal control opens the door for the extension of the powerful nonlinear and
ultrafast vibrational and electronic spectroscopies to the nanoscale.Comment: Contains manuscript with 4 figures as well as supplementary material
with 2 figure
Effect of Embryo Thermal Stimulation on the Serum Levels of Immunoglobulins and Corticosterone, and Organ Histopathology of 1 day-old Broilers
Deciphering the stem cell machinery as a basis for understanding the molecular mechanism underlying reprogramming
Stem cells provide fascinating prospects for biomedical applications by combining the ability to renew themselves and to differentiate into specialized cell types. Since the first isolation of embryonic stem (ES) cells about 30 years ago, there has been a series of groundbreaking discoveries that have the potential to revolutionize modern life science. For a long time, embryos or germ cell-derived cells were thought to be the only source of pluripotency—a dogma that has been challenged during the last decade. Several findings revealed that cell differentiation from (stem) cells to mature cells is not in fact an irreversible process. The molecular mechanism underlying cellular reprogramming is poorly understood thus far. Identifying how pluripotency maintenance takes place in ES cells can help us to understand how pluripotency induction is regulated. Here, we review recent advances in the field of stem cell regulation focusing on key transcription factors and their functional interplay with non-coding RNAs
Double-helix enhanced axial localization in STED nanoscopy
Stimulated Emission Depletion (STED) microscopy enables subdiffraction resolution in the imaging plane. However, STED's lateral improvement in resolution is generally better than the enhancement in the axial direction. Here, we combine conventional STED superresolution imaging with Double Helix Point Spread Function (PSF) modulation for axial localization with a precision better than the classical Rayleigh limit. To demonstrate the capability of the method we resolve in a STED microscope sub-diffraction fluorescent bead assemblies, and localize them axially with better than 25nm precision. We also show that the same setup allows straightforward implementation of wide field phase contrast by imaging larger beads with spiral and dark field phase filtering. (C) 2013 Optical Society of Americ
3D interferometric optical tweezers using a single spatial light modulator
Hexagonal arrays of micron sized silica beads have been trapped in three-dimensions within an optical lattice formed by the interference of multiple plane-waves. The optical lattice design with sharply peaked intensity gradients produces a stronger trapping force than the traditionally sinusoidal intensity distributions of other interferometric systems. The plane waves were generated using a single, phase-only, spatial light modulator (SLM), sited near a Talbot image plane of the traps. Compared to conventional optical tweezers, where the traps are formed in the Fourier-plane of the SLM, this approach may offer an advantage in the creation of large periodic array structures. This method of pattern formation may also be applicable to trapping arrays of atoms
Improvement of cold resistance and performance of broilers by acute cold exposure during late embryogenesis
EXPRESSION OF MYCOBACTERIUM-LEPRAE 18-KDA ANTIGEN IN YEAST IN A GPI-ANCHORED FORM
The 18-kDa protein from Mycobacterium leprae is a major target for the immune response in leprosy. We have developed a system to express this antigen in yeast as a fusion protein with the C-terminal region of the yeast membrane protein GAS1, which would render the recombinant protein anchored to the plasma membrane by a glycosylphosphatidylinositol (GPI) anchor. Cells lacking the GAS1 gene and transformed with the hybrid 18-kDa-GAS1 construct express a polypeptide that reacts with an 18-kDa-specific monoclonal antibody. In addition, these cells react with an alpha-CRD antibody after GPI-PLC treatment. The non-transformed cells are negative. These data indicate that our system may be suitable for the expression of foreign proteins in yeast in a GPI-anchored form.ESCOLA PAULISTA MED,DEPT MICROBIOL IMMUNOL & PARASITOL,BR-04063900 SAO PAULO,SP,BRAZILUNIV CAMBRIDGE,DEPT BIOCHEM,CAMBRIDGE CB2 1QW,ENGLANDFREE UNIV BRUSSELS,B-1640 BRUSSELS,BELGIUMUNIV BASEL,BIOCTR,DEPT BIOCHEM,CH-4056 BASEL,SWITZERLANDESCOLA PAULISTA MED,DEPT MICROBIOL IMMUNOL & PARASITOL,BR-04063900 SAO PAULO,SP,BRAZILWeb of Scienc