We introduce a new image cytometer design for detection of very small particulate and demonstrate its capability in water analysis. The device is a compact microscope composed of off the shelf components, such as a light emitting diode (LED) source,
a complementary metal oxide semiconductor (CMOS) image sensor, and a specific combination of optical lenses that allow, through an appropriate software, Fourier transform processing of the sample volume. Waterborne microorganisms, such as Escherichia coli (E. coli), Legionella pneumophila (L. pneumophila) and Phytoplankton, are detected by interrogating the volume sample either in a fluorescent or label-free mode, i.e. with or without fluorescein isothiocyanate (FITC) molecules attached to the micro-organisms, respectively. We achieve a sensitivity of 50 cells/ml, which can be further increased to 0.2 cells/ml by preconcentrating an initial sample volume of 500 ml with an adhoc fluidic system. We also prove the capability of the proposed image cytometer of differentiating microbiological populations by size with a resolution of 3 um and of operating in real contaminated water.
We demonstrate a compact, robust, and highly efficient source of polarization-entangled photons, based on linear bi-directional down-conversion in a novel folded sandwich configuration. Bi-directionally pumping a single periodically poled KTiOPO$_4$
(ppKTP) crystal with a 405-nm laser diode, we generate entangled photon pairs at the non-degenerate wavelengths 784 nm (signal) and 839 nm (idler), and achieve an unprecedented detection rate of 11.8 kcps for 10.4 $mu$W of pump power (1.1 million pairs / mW), in a 2.9-nm bandwidth, while maintaining a very high two-photon entanglement quality, with a Bell-state fidelity of $99.3pm0.3$%.
We present a simple but highly efficient source of polarization-entangled photons based on spontaneous parametric down-conversion (SPDC) in bulk periodically poled potassium titanyl phosphate crystals (PPKTP) pumped by a 405 nm laser diode. Utilizing
one of the highest available nonlinear coefficients in a non-degenerate, collinear type-0 phase-matching configuration, we generate polarization entanglement via the crossed-crystal scheme and detect 0.64 million photon pair events/s/mW, while maintaining an overlap fidelity with the ideal Bell state of 0.98 at a pump power of 0.025 mW.
Signal state preparation in quantum key distribution schemes can be realized using either an active or a passive source. Passive sources might be valuable in some scenarios; for instance, in those experimental setups operating at high transmission ra
tes, since no externally driven element is required. Typical passive transmitters involve parametric down-conversion. More recently, it has been shown that phase-randomized coherent pulses also allow passive generation of decoy states and Bennett-Brassard 1984 (BB84) polarization signals, though the combination of both setups in a single passive source is cumbersome. In this paper, we present a complete passive transmitter that prepares decoy-state BB84 signals using coherent light. Our method employs sum-frequency generation together with linear optical components and classical photodetectors. In the asymptotic limit of an infinite long experiment, the resulting secret key rate (per pulse) is comparable to the one delivered by an active decoy-state BB84 setup with an infinite number of decoy settings.
We study the optical properties of a two-axis galvanometric optical scanner constituted by a pair of rotating planar mirrors, focusing our attention on the transformation induced on the polarization state of the input beam. We obtain the matrix that
defines the transformation of the propagation direction of the beam and the Jones matrix that defines the transformation of the polarization state. Both matrices are expressed in terms of the rotation angles of two mirrors. Finally, we calculate the parameters of the general rotation in the Poincare sphere that describes the change of polarization state for each mutual orientation of the mirrors.
