Femtosecond laser-induced plasma has proved to be the powerful source of short pulses of incoherent soft X-rays with energy from 50 ev up to few keV and even harder [1,2]. Extremely short X-ray pulse duration down to 1 ps makes it possible to use this radiation in time-resolved X-ray diagnostics of ultrafast processes (X-ray diffraction, spectroscopy, microscopy). It is of special interest to design X-ray microscope in so-called “water window” region to investigate living cells. One more advantage here is as shorter X-ray pulses are used less information recorded is deteriorated by damaging of an investigated cell by X-rays. To generate X-rays above 200 eV intensities of 1015– 1016 W·cm−2 and even higher have to be used. As it was shown previously [3] large amount of X-ray energy emitted from femtosecond plasma consisting of light atomic elements (B,C etc.) is radiated from resonance transitions of highly stripped ions. In the case of carbon target the most bright lines of H- and He-like C ions lie in the “water window” region. The main goals of our research are to find “optimal” conditions for generating powerful few-picosecond X-ray pulses in the vicinity of “water window” region by femtosecond laser pulses with rather low intensities 1015– 1017 W·cm−2 and to investigate whether it is possible to increase electron temperature of the plasma and to generate few keV X-rays by using thin targets.
Abstract. The source of time-correlated photon-pairs at 1064 nm is described. The source consists of the spontaneous parametric down-conversion (SPDC) generator, pumped by cw laser operating at 532 nm, and the measuring and control appliances. One of the main parts of the electronic systems is the "time-to-digital converter" which is designed and built by our group. The system allows to create and detect correlation of photon pairs with resolution better than 1 ns. We adduce the results of a quantum key distribution through open air. The key length was about 5000 bits and the accuracy ~0.1%.
Keywords: quantum optics, spontaneous parametric down-conversionThe SPDC sources of correlated and entangled photons have taken its rightful place in modern quantum optical technologies [1,2]. In present work we report the time-correlated source of photons at 1064 nm and its applications on quantum key distribution via a novel time-algorithm with low error rate. The usage of this wavelength is motivated by potential possibility of applications of such sources as cryptographic sources implemented in existing fiber-based Internet connections with the future YAG:Nd 3+ point-to-point re-transmitters. For the same goal we use the quantum key distribution algorithm based on time-correlations. It should be noted that sources at 1064 nm previously were not widely used due to low quantum efficiency of existing avalanche-photodiodes. But now appropriate detectors for this spectral region have been invented and we may change our mind about this spectral region. Our source is based on the single-crystal SPDC scheme using a BBO crystal. The pump (0-300 mW) was the second harmonic of cw YAG:Nd 3+ diode-pumped laser. It has coherence length of ~ 3 mm. The SPDC crystal is the 3-mm length type-I cut (e-oo) BBO crystal. We use ID Quantique id400 SERIES avalanche photodiode having high quantum efficiency at 1064 nm, the multichannel time-to-digital converter IDQ's id800-TDC and the self-designed, developed as a part of the import substitution programm, time-to-digital converter "TDC-6" having the characteristics shown below:
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