JEOS:RP - Journal of the European Optical Society Rapid publications
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Self calibration of sensorless adaptive optical microscopes
Get PDFWe present a self-calibrating scheme for microscopes using model-based wavefront sensorless adaptive optics. Unlike previous methods, this scheme permits the calibration of system aberration modes without the need for a separate wavefront sensor or interferometer. Basis modes are derived from the deformable mirror influence functions and an image cross-correlation method is used to remove image displacement effects from these modes. Image based measurements are used to derive an optimum modal representation from the displacement-free basis modes. These new modes are insensitive to system misalignments and the shape of the illumination profile. We demonstrate the effectiveness and robustness of these optimal modes in a third harmonic generation (THG) microscope
Optical forces and trapping potentials of a dual-waveguide trap based on multimode solid-core waveguides
Get PDFWe propose a novel design of the dual-waveguide trap for trapping and Raman identification of microscopic particles and biological objects in a fluid. The device is based on two embedded Si3N4 waveguides launching counterpropagating beams into the fluidic channel of a lab-on-chip. For waveguides with a square cross-section of 1 μm2, a 5 μm gap between them and a 785 nm operation wavelength, we perform finite-difference time-domain simulations of the beam profiles and the trapping forces acting on polystyrene beads (diameter 0.2-1.4 μm). The forces reach values up to 16 pN/W for a bead diameter of 1.4 μm, indicating that the trap is very suitable for trapping of particles in a fluidic environment. This is confirmed by the trapping potentials deduced from the force curves. The design of waveguides and chip is completely compatible with glass-based microfluidic technology, thus enabling mass production and widespead application, contrary to previous approaches
High pulse energy and symmetrical far field from an optical parametric oscillator in the red spectral range
Get PDFRed pulses with >30 mJ energy and <0.6 nm bandwidth have been demonstrated using a type 2 phase matched optical parametric oscillator pumped at 532 nm. A symmetrical signal beam with beam diameter-divergence product of ~3 mm•mrad was obtained by applying KTA and BBO crystals in the same resonato
Rubidium atomic beam clock based on lamp-pumping and fluorescence-detection scheme
Get PDFA compact, portable rubidium atomic beam clock based on lamp-pumping and fluorescence-detection scheme is proposed. The expected short-term frequency stability can be at least two orders of magnitude better than previous experimental results. The usages of lamp pumping, fluorescence detection and microwave slow-wave resonance structures make this design robust and compact
Optimal pulses for arbitrary dispersive media
Get PDFA variational procedure is given for finding the pulses for which the initial temporal rms width and the rate of increase of this width are jointly minimized for propagation in non-absorbing media with arbitrary dispersive properties. We show that, while in linearly dispersive media the optimal pulses are Gaussian, in other situations such as a hollow metallic waveguide or for purely cubic dispersion departures from Gaussian behavior become evident. An interpretation of the results in terms of suitable phase-space representations is also given
Neuronal chemotaxis by optically manipulated liposomes
Get PDFWe probe chemotaxis of single neurons, induced by signalling molecules which were optically delivered from liposomes in the neighbourhood of the cells. We implemented an optical tweezers setup combined with a micro-dissection system on an inverted microscope platform. Molecules of Netrin-1 protein were encapsulated into micron-sized liposomes and manipulated to micrometric distances from a specific growth cone of a hippocampal neuron by the IR optical tweezers. The molecules were then released broken the liposomes with UV laser pulses. Chemotaxis induced by the delivered molecules was confirmed by the migration of the growth cone toward the liposome position. Since the delivery can be manipulated with high temporal and spatial resolution and the number of molecules released can be controlled quite precisely by tuning the liposome size and the solution concentration, this technique opens new opportunities to investigate the effect of physiological active compounds as Netrin-1 to neuronal signalling and guidance, which represents an important issue in neurobiology
Characterization of the anamorphic and frequency dependent phenomenon in Liquid Crystal on Silicon displays
No full textThe diffractive efficiency of Liquid Crystal on Silicon (LCoS) displays can be greatly diminished by the appearance of temporal phase fluctuations in the reflected beam, depolarization effects and also because of phase modulation depths smaller than 2Ï€. In order to maximize the efficiency of the Diffractive Optical Elements (DOEs) implemented in the LCoS device, the Minimum Euclidean Distance principle can be applied. However, not all the diffractive elements can be corrected in the same way due to the anamorphic and frequency dependent phenomenon, which is related to the LCoS response, largely dependending on the period and the spatial orientation of the generated DOE. Experimental evidence for the anamorphic and frequency dependent phenomenon is provided in this paper, as well as a comparative study between the efficiency obtained for binary gratings of different period
Comparison of far field characterisation of DOEs with a goniometric DUV-scatterometer and a CCD-based system
Get PDFWe have measured far field diffraction patterns of different diffractive optical elements at an illumination wavelength of 193 nm using a new type of goniometric DUV (deep ultraviolet) scatterometer, which has been developed and set up recently at the PTB, the national metrology institute of Germany. This system offers both a high dynamic range and angular resolution. The scatterometer is especially suitable to analyse weak background light like stray light and local variations of the diffraction patterns over the DOEs (diffractive optical element). The measurement results are compared with measurements using a CCD (charge-coupled device)-based imaging DOE measurement system from Carl Zeiss SMT. An excellent agreement is demonstrated
Power smart in-door optical wireless link design
Get PDFPresented for the first time, to the best of the authors´ knowledge, is the design of a power smart in-door optical wireless link that provides lossless beam propagation between Transmitter (T) and Receiver (R) for changing link distances. Each T/R unit uses a combination of fixed and variable focal length optics to smartly adjust the laser beam propagation parameters of minimum beam waist size and its location to produce the optimal zero propagation loss coupling condition at the R for that link distance. An Electronically Controlled Variable Focus Lens (ECVFL) is used to form the wide field-of-view search beam and change the beam size at R to form a low loss beam. The T/R unit can also deploy camera optics and thermal energy harvesting electronics to improve link operational smartness and efficiency. To demonstrate the principles of the beam conditioned low loss indoor link, a visible 633 nm laser link using an electro-wetting technology liquid ECVFL is demonstrated for a variable 1 to 4 m link range. Measurements indicate a 53% improvement over an unconditioned laser link at 4 m. Applications for this power efficient wireless link includes mobile computer platform communications and agile server rack interconnections in data centres
Optical trapping at low numerical aperture
Get PDFA theory of optical trapping at low Numerical Aperture (NA) is presented. The theory offers an analytical description of the competition between the stabilizing gradient and destabilizing scattering force. The trade-off can be characterized by a single dimensionless trapping parameter, which increases with bead size to wavelength ratio and refractive index contrast and decreases with NA. The gradient force dominates for small trapping parameters, the scattering force for large trapping parameters. The potential well depth, maximum forces and trap stiffness as a function of the three parameters (, , NA) can be mapped onto universal functions of the trapping parameter. These functions do not depend on any free parameter. The universal well depth and maximum force curves match with numerical results based on the exact multipole expansion of the optical trapping force. The paraxial limit of low NA is relevant for compact optical tweezers based on Optical Pickup Units known from optical data storage