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Author

E. Zekou

Other affiliations: University of St Andrews
Bio: E. Zekou is an academic researcher from National Technical University of Athens. The author has contributed to research in topics: Electromagnetically induced transparency & Type (model theory). The author has an hindex of 3, co-authored 5 publications receiving 114 citations. Previous affiliations of E. Zekou include University of St Andrews.

Papers
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Journal ArticleDOI
TL;DR: In this article, the effects of mismatching wavelengths for the coupling and probe fields in Doppler-broadened media for the three basic energy level configurations commonly used to realize electromagnetically induced transparency (EIT) were considered.
Abstract: We present a theoretical study of the effects of mismatching wavelengths for the coupling and probe fields in Doppler-broadened media for the three basic energy level configurations commonly used to realize electromagnetically induced transparency (EIT). Three wavelength regimes are considered: mismatched wavelengths for which the coupling frequency is greater than the probe frequency, matched wavelengths for which the coupling and probe frequencies are equal, and mismatched wavelengths for which the probe frequency is greater than the coupling frequency. The transparency that may be induced in these regimes is compared for the cascade-, \ensuremath{\Lambda}-, and Vee-type systems. We show that in the first mismatched regime $({\ensuremath{\lambda}}_{c}l{\ensuremath{\lambda}}_{p})$ EIT is possible in all schemes and is in fact stronger than in the matched case. It is also demonstrated that for the second mismatched regime $({\ensuremath{\lambda}}_{c}g{\ensuremath{\lambda}}_{p})$ EIT can be realized most readily in the Vee-type configuration in the presence of Doppler broadening. These predictions are explained by considering the absorption as a function of both the probe field detuning and the atomic velocity.

51 citations

Journal ArticleDOI
TL;DR: In this paper, an experimental observation of transparency on a transition in the blue spectral region, induced by a continuous-wave infrared coupling field in a Doppler-broadened medium, is presented.
Abstract: An experimental observation of transparency on a transition in the blue spectral region, induced by a continuous-wave (cw) infrared coupling field in a Doppler-broadened medium, is presented. This experimental result is supported by extensive theoretical modeling of the system, a V-type scheme in atomic rubidium vapor. Transparency is observed by a 422-nm probe field on the transition between the hyperfine split ground state ${5S}_{1/2}$ and the excited state ${6P}_{1/2}.$ The coupling laser is employed on the linked transition ${5S}_{1/2}{\ensuremath{-}5P}_{3/2},$ inducing significant levels of transparency $(g70%)$ nondissipatively and in the absence of optical pumping effects.

46 citations

Journal ArticleDOI
TL;DR: In this article, the authors show that the presence of Doppler broadening does not preclude inversionless lasing for mismatched wavelengths; this is shown to hold even for Rabi splittings significantly less than the doppler width.
Abstract: Inversionless gain is predicted in a Doppler-broadened $V$ scheme for which the probe laser frequency is approximately twice that of the coupling laser. A comparison is made of inversionless gain achieved via electromagnetically induced transparency in Doppler-broadened matched and mismatched wavelength systems. We show that the presence of Doppler broadening does not preclude inversionless lasing for mismatched wavelengths; importantly, this is shown to hold even for Rabi splittings significantly less than the Doppler width. Our analysis demonstrates that inversionless gain is realizable in Doppler-broadened media, at modest continuous wave laser powers, for a probe frequency well in excess of the coupling field frequency. The presented theory is related to a practical mismatched system in atomic rubidium vapor. Approximately 8% gain is predicted in a 422 nm probe field coherently driven by a 780 nm coupling field, in the presence of a modest level of incoherent excitation.

18 citations

Proceedings ArticleDOI
05 Jan 2017
TL;DR: In this article, two types of paper are stained with fungi colonies, which grow on substrates of clean paper, as well as on paper with ink text, and they are treated by Nd:YAG laser light.
Abstract: Conservation of cultural heritage treasures is the most important issue for transferring knowledge to the public through the next generation of students, academics, and researchers. Although this century is authenticating e-books and information by means of electronic text, still historical manuscripts as content as well as objects are the main original recourses of keeping a record of this transformation. The current work focuses on cleaning paper samples by the application of pulsed light, which is interventional. Experiments carried out using paper samples that are artificially colonized with Ulocladium chartarum. Paper is treated by Nd:YAG laser light. The available wavelength is 1064 nm, at various fluences, repetition rates and number of pulses. Two types of paper are stained with fungi colonies, which grow on substrates of clean paper, as well as on paper with ink text. The first type of paper is Whatman No.1056, which is closer to pure cellulose. The second type of paper is a page of a cultural heritage book published in 1926. Cleaning is performed using laser irradiation, thus defining the damage threshold of each sample. The treatment on paper Watman showed a yellowing, especially on areas with high concentration of fungi. The second sample was more durable to the exposure, performing the best results at higher fluences. Eventually, the paper samples are characterized, with optical microscopy and SEM/EDX analyses, prior to and after cleaning.

4 citations

Proceedings ArticleDOI
08 Oct 2010
TL;DR: In this article, laser cleaning of ink was performed to a book of 1934, by choosing the best conditions and parameters from cleaning the test samples, like Nd:YAG laser operating at 532 nm.
Abstract: Lasers can provide a precious tool to conservation process due to their accuracy and the controlled energy they deliver, especially to fragile organic material such as paper. The current study concerns laser modification such as paper cleaning, initially of test papers artificially soiled and then of an original book of the early 20 th Century. The test objects were A4 copier paper, newspaper, and paper Whatman No.1056. During the experiments, ink of a pen, pencil and ink from a stamp was mechanically employed on each paper surface. Laser cleaning was applied using a Q-switched Nd:YAG operating at 532 nm and CO 2 laser at 10.6 μm for various fluences. The experimental results were presented by using optical microscopy. Eventually, laser cleaning of ink was performed to a book of 1934, by choosing the best conditions and parameters from cleaning the test samples, like Nd:YAG laser operating at 532 nm.

1 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the authors derived the analytical expressions of the space-time dependent probe field, the corresponding phase shift, absorption or amplification, group velocity, and group velocity dispersion for all three schemes.
Abstract: We analyze the electromagnetically induced transparency (EIT) in $V$-, $\ensuremath{\Lambda}$-, and cascade-type schemes in a time-dependent way via the Schr\"odinger-Maxwell formalism. We derive explicitly the analytical expressions of the space-time dependent probe field, the corresponding phase shift, absorption or amplification, group velocity, and group velocity dispersion for all the three schemes. These simple analytical expressions not only demonstrate explicitly the similarities and essential differences of the three schemes but also provide a convenient basis for investigating how the many-body effects in solids modify the magnitude, spectral shape, and space and time dependence of EIT and EIT-related quantum coherence phenomena.

503 citations

Journal ArticleDOI
TL;DR: In this article, the main motivation in inversionless lasing research was discussed, namely, the generation of short-wavelength laser light, and the basic physics of LWI in two-level and, eventually, in three-and multilevel atomic configurations.
Abstract: This review paper is devoted to amplification and lasing without population inversion involving atomic transitions in gas media. We start by discussing the main motivation in inversionless lasing research, namely, the generation of short-wavelength laser light. Then, we review the basic physics of inversionless lasing in two-level and, eventually, in three- and multilevel atomic configurations. Finally, we summarize the current state of the art of LWI experiments and indicate the main difficulties with respect to short-wavelength laser generation.

258 citations

Journal ArticleDOI
TL;DR: In this article, the principles of the electromagnetically induced transparency (EIT) in basic three-level schemes are sketched, and some applications of this phenomenon are described, and a presentation follows of a five-level EIT model of Bloch equations, which was developed to reconstruct multipeak cascade-EIT spectra registered in a sample of cold 85 Rb atoms in MOT.
Abstract: In the initial part of the paper, the principles of the electromagnetically induced transparency (EIT) in basic three-level schemes are sketched, and some applications of this phenomenon are described. Next a presentation follows of a five-level EIT model of Bloch equations, which was developed to reconstruct multipeak cascade-EIT spectra registered in a sample of cold 85 Rb atoms in MOT. The respective experiment is also described. The achieved good agreement between theory and performed experiment is documented and discussed.

78 citations

Journal ArticleDOI
TL;DR: In this paper, the properties of an electromagnetically induced grating formed in a Ξ-type three-level atomic system in the presence of a standing wave pump and travelling wave probe fields at resonant and off-resonant two-photon absorption were analyzed.
Abstract: We have analysed the properties of an electromagnetically induced grating formed in a Ξ-type three-level atomic system in the presence of a standing wave pump and travelling wave probe fields at resonant and off-resonant two-photon absorption. We have also shown the validity of this grating in an inhomogeneously broadened regime.

77 citations

Journal ArticleDOI
TL;DR: In this paper, the four-wave mixing in a double-V scheme via robust electron spin coherence in semiconductor quantum wells was analyzed, and the results demonstrated that the electromagnetically induced gain loss, the electromagnetic induced absorption and superluminal propagation phenomena may be realized in quantum quantum wells at room temperatures.

74 citations