Fast fluorescence dynamics in non-ratiometric calcium indicators

A fluorescence decay of high-affinity non-ratiometric Ca2+ indicator Oregon Green BAPTA-1 (OGB-1) is analyzed with unprecedented temporal resolution in the two-photon excitation regime. A triple exponential decay is shown to best fit the fluorescence dynamics of OGB-1. We provide a new model for accurate measurements of the free Ca2+ concentration and dissociation constants of non-ratiometric calcium indicators.Comment: 3 pages, 2 figures, figures revised, added chi-square goodness of fi

3D Imaging based on Single Photon Detectors

This paper introduces a mathematical model to evaluate fast and cost-effective 3D image sensors based on single photon detectors. The model will help engineers evaluate design parameters based on operating conditions and system performance. Ranging is based on the time-of-flight principle using TCSPC techniques. Two scenarios are discussed: (i) short-distance range indoors and (ii) medium-distance range outdoors. The model predicts an accuracy of 0.25cm at 5m with 0.5W of illumination and 1klux of background light. In the medium-range scenario, a precision of 0.5cm is predicted at 50m with 20W of illumination and 20klux of background light

On the Application of a Monolithic Array for Detecting Intensity-Correlated Photons Emitted by Different Source Types

It is not widely appreciated that many subtleties are involved in the accurate measurement of intensity-correlated photons; even for the original experiments of Hanbury Brown and Twiss (HBT). Using a monolithic 4x4 array of single-photon avalanche diodes (SPADs), together with an off-chip algorithm for processing streaming data, we investigate the difficulties of measuring second-order photon correlations g2 in a wide variety of light fields that exhibit dramatically different correlation statistics: a multimode He-Ne laser, an incoherent intensity-modulated lamp-light source and a thermal light source. Our off-chip algorithm treats multiple photon-arrivals at pixel-array pairs, in any observation interval, with photon fluxes limited by detector saturation, in such a way that a correctly normalized g2 function is guaranteed. The impact of detector background correlations between SPAD pixels and afterpulsing effects on second-order coherence measurements is discussed. These results demonstrate that our monolithic SPAD array enables access to effects that are otherwise impossible to measure with stand-alone detectors.Comment: 17 pages, 6 figure

3D Near-infrared Imaging based on a Single-photon Avalanche Diode Array Sensor

A new imager for 3D near-infrared imaging has been designed based on a single-photon avalanche diode (SPAD) imager with 128x128 pixels capable of performing time-resolved measurements with a resolution of 97ps. The imager linearity has been improved to make more accurate measurements. A new optical setup has been imple- mented in order to prove the suitability of this kind of sensors for this application

High-energy sub-nanosecond optical pulse generation with a semiconductor laser diode for pulsed TOF laser ranging utilizing the single photon detection approach

Bulk and quantum well laser diodes with a large equivalent spot size of da/Γa ≈ 3 µm and stripe width/cavity length of 30 µm/3 mm were realized and tested. They achieved a pulse energy and pulse length of the order of ~1 nJ and ~100 ps, respectively, with a peak pulse current of 6–8 A and a current pulse width of 1 ns. The 2D characteristics of the optical output power versus wavelength and time were also analyzed with a monochromator/streak camera set-up. The far-field characteristics were studied with respect to the time-homogeneity and energy distribution. The feasibility of a laser diode with a large equivalent spot size in single photon detection based laser ranging was demonstrated to a non-cooperative target at a distance of a few tens of meters

Particle Shadow Tracking - Combining Magnetic Particle Manipulation with In-Situ Optical Detection in a CMOS Microsystem

We present a hybrid CMOS based microsystem where magnetic actuation of microparticles is combined with integrated optical detection via Single Photon Avalanche Diodes (SPADs). The system’s configuration permits the manipulation and detection of single magnetic particles having diameters of 1, 3 and 5 µm. We are able to show a size sensitivity of the particle detection, with a clear distinction between different particle diameters