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Dive into the research topics where Václav Michálek is active.

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Featured researches published by Václav Michálek.


Physical Review A | 2010

Transverse coherence of photon pairs generated in spontaneous parametric down-conversion

Martin Hamar; Jan Perina Jr; Ondrej Haderka; Václav Michálek

Coherence properties of the down-converted beams generated in spontaneous parametric down-conversion are investigated in detail using an iCCD camera. Experimental results are compared with those from a theoretical model developed for pulsed pumping with a Gaussian transverse profile. The results allow us to tailor the shape of correlation area of the signal and idler photons using pump-field and crystal parameters. As an example, splitting of a correlation area caused by a two-peak pump-field spectrum is experimentally studied.


Physical Review A | 2012

Photon-number distributions of twin beams generated in spontaneous parametric down-conversion and measured by an intensified CCD camera

Jan Peřina; Martin Hamar; Václav Michálek; Ondřej Haderka

The measurement of photon-number statistics of fields composed of photon pairs, generated in spontaneous parametric down-conversion and detected by an intensified CCD camera is described. Final quantum detection efficiencies, electronic noises, finite numbers of detector pixels, transverse intensity spatial profiles of the detected beams as well as losses of single photons from a pair are taken into account in a developed general theory of photon-number detection. The measured data provided by an iCCD camera with single-photon detection sensitivity are analyzed along the developed theory. Joint signal-idler photon-number distributions are recovered using the reconstruction method based on the principle of maximum likelihood. The range of applicability of the method is discussed. The reconstructed joint signal-idler photon-number distribution is compared with that obtained by a method that uses superposition of signal and noise and minimizes photoelectron entropy. Statistics of the reconstructed fields are identified to be multi-mode Gaussian. Elements of the measured as well as the reconstructed joint signal-idler photon-number distributions violate classical inequalities. Sub-shot-noise correlations in the difference of the signal and idler photon numbers as well as partial suppression of odd elements in the distribution of the sum of signal and idler photon numbers are observed.


Scientific Reports | 2016

Ultrashort pulse laser ablation of dielectrics: Thresholds, mechanisms, role of breakdown

Inam Mirza; Nadezhda M. Bulgakova; Jan Tomastik; Václav Michálek; Ondřej Haderka; Ladislav Fekete; Tomas Mocek

In this paper, we establish connections between the thresholds and mechanisms of the damage and white-light generation upon femtosecond laser irradiation of wide-bandgap transparent materials. On the example of Corning Willow glass, evolution of ablation craters, their quality, and white-light emission were studied experimentally for 130-fs, 800-nm laser pulses. The experimental results indicate co-existence of several ablation mechanisms which can be separated in time. Suppression of the phase explosion mechanism of ablation was revealed at the middle of the irradiation spots. At high laser fluences, air ionization was found to strongly influence ablation rate and quality and the main mechanisms of the influence are analysed. To gain insight into the processes triggered by laser radiation in glass, numerical simulations have been performed with accounting for the balance of laser energy absorption and its distribution/redistribution in the sample, including bremsstrahlung emission from excited free-electron plasma. The simulations have shown an insignificant role of avalanche ionization at such short durations of laser pulses while pointing to high average energy of electrons up to several dozens of eV. At multi-pulse ablation regimes, improvement of crater quality was found as compared to single/few pulses.


Physical Review A | 2013

State reconstruction of a multimode twin beam using photodetection

Jan Peřina; Ondřej Haderka; Václav Michálek; Martin Hamar

Robust and reliable method for reconstructing quasi-distributions of integrated intensities of twin beams generated in spontaneous parametric down-conversion and entangled in photon numbers is suggested. It utilizes the first and second photocount moments and minimizes the declination from experimental photocount histograms. Qualitatively different forms of quasi-distributions for quantum and classical states are suggested in the method. The transition from quantum to classical states caused by an increased detection noise is discussed. Momentum criterion for non-classicality of twin beams is suggested.


Journal of The Optical Society of America B-optical Physics | 2014

Optimal sub-Poissonian light generation from twin beams by photon-number resolving detectors

Marco Lamperti; Alessia Allevi; Maria Bondani; Radek Machulka; Václav Michálek; Ondřej Haderka; Jan Peřina

We generate nonclassical conditional states by exploiting the quantum correlations of multimode twin-beam states endowed with a sizeable number of photons. A strong relation between the sub-shot-noise correlations exhibited by twin beams and the sub-Poissonian character of the conditional states is experimentally revealed, determining the optimal conditions for sub-Poissonian light generation.


Physical Review A | 2013

Characterizing the nonclassicality of mesoscopic optical twin-beam states

Alessia Allevi; Marco Lamperti; Maria Bondani; Jan Peřina; Václav Michálek; Ondřej Haderka; Radek Machulka

We present a robust tool to analyze nonclassical properties of multimode twin-beam states in the mesoscopic photon-number domain. The measurements are performed by direct detection. The analysis exploits three different non-classicality criteria for detected photons exhibiting complementary behavior in the explored intensity regime. Joint signal-idler photon-number distributions and quasi-distributions of integrated intensities are determined and compared with the corresponding distributions of detected photons. Experimental conditions optimal for nonclassical properties of twin-beam states are identified.


Optics Letters | 2012

Absolute detector calibration using twin beams

Jan Peřina; Ondřej Haderka; Václav Michálek; Martin Hamar

A method for the determination of absolute quantum detection efficiency is suggested based on the measurement of photocount statistics of twin beams. The measured histograms of joint signal-idler photocount statistics allow us to eliminate an additional noise superimposed on an ideal calibration field composed of only photon pairs. This makes the method superior above other approaches presently used. Twin beams are described using a paired variant of quantum superposition of signal and noise.


Optics Express | 2013

Sub-Poissonian-light generation by postselection from twin beams.

Jan Peřina; Ondřej Haderka; Václav Michálek

States with sub-Poissonian photon-number statistics obtained by post-selection from twin beams are experimentally generated. States with Fano factors down to 0.62 and mean photon numbers around 12 are reached. Their quasi-distributions of integrated intensities attaining negative values are reconstructed. An intensified CCD camera with a quantum detection efficiency exceeding 20% is utilized both for post-selection and beam characterization. Experimental results are compared with theory that provides the optimum experimental conditions.


Physical Review A | 2017

Nonclassicality and entanglement criteria for bipartite optical fields characterized by quadratic detectors

Jan Peřina; Ievgen I. Arkhipov; Václav Michálek; Ondřej Haderka

Numerous inequalities involving moments of integrated intensities and revealing nonclassicality and entanglement in bipartite optical fields are derived using the majorization theory, non-negative polynomials, the matrix approach, as well as the Cauchy-Schwarz inequality. Different approaches for deriving these inequalities are compared. Using the experimental photocount histogram generated by a weak noisy twin beam monitored by a photon-number-resolving iCCD camera the performance of the derived inequalities is compared. A basic set of ten inequalities suitable for monitoring the entanglement of a twin beam is suggested. Inequalities involving moments of photocounts (photon numbers) as well as those containing directly the elements of photocount (photon-number) distributions are also discussed as a tool for revealing nonclassicality.


Physical Review A | 2017

Higher-order sub-Poissonian-like nonclassical fields: Theoretical and experimental comparison

Jan Peřina; Václav Michálek; Ondřej Haderka

Criteria defining higher-order sub-Poissonian-like fields are given using five different quantities: moments of (I) integrated intensity, (II) photon number, (III) integrated-intensity fluctuation, (IV) photon-number fluctuation, and (V) elements of photocount and photon-number distributions. Relations among the moment criteria are revealed. Performance of the criteria is experimentally investigated using a set of potentially sub-Poissonian fields obtained by post-selection from a twin beam. The criteria based on moments of integrated intensity and photon number and those using the elements of photocount distribution are found as the most powerful. States nonclassical up to the fifth order are experimentally reached in the former case, even the ninth-order non-classicality is observed in the latter case.

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Ondřej Haderka

Academy of Sciences of the Czech Republic

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Martin Hamar

Academy of Sciences of the Czech Republic

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Radek Machulka

Academy of Sciences of the Czech Republic

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Antonín Černoch

Academy of Sciences of the Czech Republic

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Jan Soubusta

Academy of Sciences of the Czech Republic

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Jan Tomastik

Academy of Sciences of the Czech Republic

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