Institute of Laser Physics

We report direct single-laser excitation of the strictly forbidden (6s2)1S0 <--> (6s6p)3P0 clock transition in 174Yb atoms confined to a 1D optical lattice. A small (approximately 1.2 mT) static magnetic field was used to induce a nonzero electric dipole transition probability between the clock states at 578.42 nm. Narrow resonance linewidths of 20 Hz (FWHM) with high contrast were observed, demonstrating a resonance quality factor of 2.6 x 10(13). The previously unknown ac Stark shift-canceling (magic) wavelength was determined to be 759.35 +/- 0.02 nm. This method for using the metrologically superior even isotope can be easily implemented in current Yb and Sr lattice clocks and can create new clock possibilities in other alkaline-earth-like atoms such as Mg and Ca.

We develop a method of spectroscopy that uses a weak static magnetic field to enable direct optical excitation of forbidden electric-dipole transitions that are otherwise prohibitively weak. The power of this scheme is demonstrated using the important application of optical atomic clocks based on neutral atoms confined to an optical lattice. The simple experimental implementation of this method--a single clock laser combined with a dc magnetic field--relaxes stringent requirements in current lattice-based clocks (e.g., magnetic field shielding and light polarization), and could therefore expedite the realization of the extraordinary performance level predicted for these clocks. We estimate that a clock using alkaline-earth-like atoms such as Yb could achieve a fractional frequency uncertainty of well below 10(-17) for the metrologically preferred even isotopes.

Direct laser-reduction of graphene oxide (GO), as a lithography-free approach, has been proven effective in manufacturing in-plane micro-supercapacitors (MSCs) with fast ion diffusion.

Abstract Over the past few decades, significant attention has been paid to the biomedical applications of terahertz (THz) technology. Nowadays, THz spectroscopy and imaging have allowed numerous demanding problems in the biological, medical, food, plant and pharmaceutical sciences to be solved. Among the biomedical applications, the label-free diagnosis of malignant and benign neoplasms represents one of the most attractive branches of THz technology. Despite this attractiveness, THz diagnosis methods are still far from being ready for use in medical practice. In this review, we consider modern research results in the THz diagnosis of malignant and benign neoplasms, along with the topical research and engineering problems which restrain the translation of THz technology to clinics. We start by analyzing the common models of THz-wave–tissue interactions and the effects of tissue exposure to THz waves. Then, we discuss the existing modalities of THz spectroscopic and imaging systems, which have either already been applied in medical imaging, or hold strong potential. We summarize the earlier-reported and original results of the THz measurements of neoplasms with different nosology and localization. We pay attention to the origin of contrast between healthy and pathological tissues in the THz spectra and images, and discuss the prospects of THz technology in non-invasive, minimally invasive and intraoperative diagnosis, as well as in aiding histology. Finally, we review the challenging problems of THz diagnosis, as well as attempts to solve them, which should bring THz technology much closer to medical practice. This review allows one to objectively uncover the benefits and weaknesses of THz technology in the diagnosis of malignant and benign neoplasms.

SIGNIFICANCE: Terahertz (THz) radiation has demonstrated a great potential in biomedical applications over the past three decades, mainly due to its non-invasive and label-free nature. Among all biological specimens, skin tissue is an optimal sample for the application of THz-based methods because it allows for overcoming some intrinsic limitations of the technique, such as a small penetration depth (0.1 to 0.3 mm for the skin, on average). AIM: We summarize the modern research results achieved when THz technology was applied to the skin, considering applications in both imaging/detection and treatment/modulation of the skin constituents. APPROACH: We perform a review of literature and analyze the recent research achievements in THz applications for skin diagnosis and investigation. RESULTS: The reviewed results demonstrate the possibilities of THz spectroscopy and imaging, both pulsed and continuous, for diagnosis of skin melanoma and non-melanoma cancer, dysplasia, scars, and diabetic condition, mainly based on the analysis of THz optical properties. The possibility of modulating cell activity and treatment of various diseases by THz-wave exposure is shown as well. CONCLUSIONS: The rapid development of THz technologies and the obtained research results for skin tissue highlight the potential of THz waves as a research and therapeutic instrument. The perspectives on the use of THz radiation are related to both non-invasive diagnostics and stimulation and control of different processes in a living skin tissue for regeneration and cancer treatment.

Abstract Carbon nanotubes (CNTs) possess both remarkable optical properties and high potential for integration in various photonic devices. We overview, here, recent progress in CNT applications in fibre optics putting particular emphasis on fibre lasers. We discuss fabrication and characterisation of different CNTs, development of CNT‐based saturable absorbers (CNT‐SA), their integration and operation in fibre laser cavities putting emphasis on state‐of‐the‐art fibre lasers, mode locked using CNT‐SA. We discuss new design concepts of high‐performance ultrafast operation fibre lasers covering ytterbium (Yb), bismuth (Bi), erbium (Er), thulium (Tm) and holmium (Ho)‐doped fibre lasers.

We present nonstandard optical Ramsey schemes that use pulses individually tailored in duration, phase, and frequency to cancel spurious frequency shifts related to the excitation itself. In particular, the field shifts and their uncertainties can be radically suppressed (by two to four orders of magnitude) in comparison with the usual Ramsey method (using two equal pulses) as well as with single-pulse Rabi spectroscopy. Atom interferometers and optical clocks based on two-photon transitions, heavily forbidden transitions, or magnetically induced spectroscopy could significantly benefit from this method. In the latter case, these frequency shifts can be suppressed considerably below a fractional level of $10$${}^{\ensuremath{-}17}$. Moreover, our approach opens the door for high-precision optical clocks based on direct frequency comb spectroscopy.

The 1s-2s interval has been measured in the muonium (&mgr;(+)e(-)) atom by Doppler-free two-photon pulsed laser spectroscopy. The frequency separation of the states was determined to be 2 455 528 941.0(9.8) MHz, in good agreement with quantum electrodynamics. The result may be interpreted as a measurement of the muon-electron charge ratio as -1-1.1(2.1)x10(-9). We expect significantly higher accuracy at future high flux muon sources and from cw laser technology.

We develop a generalized principle of electromagnetically induced transparency (EIT) vector magnetometry based on high-contrast EIT resonances and the symmetry of atom-light interaction in the linearly polarized bichromatic fields. Operation of such vector magnetometer on the ${D}_{1}$ line of $^{87}\mathrm{Rb}$ has been demonstrated. The proposed compass-magnetometer has an increased immunity to shifts produced by quadratic Zeeman and ac-Stark effects, as well as by atom-buffer gas and atom-atom collisions. In our proof-of-principle experiment the detected angular sensitivity to magnetic field orientation is ${10}^{\ensuremath{-}3}$ deg/Hz${}^{1/2}$, which is limited by laser intensity fluctuations, light polarization quality, and magnitude of the magnetic field.

This is the second paper in a series where we build a self-consistent model to simulate the mass-loss process of a close-orbit magnetized giant exoplanet, so-called hot Jupiter (HJ). In this paper we generalize the hydrodynamic (HD) model of an HJ expanding hydrogen atmosphere, proposed in the first paper, to include the effects of intrinsic planetary magnetic field. The proposed self-consistent axisymmetric 2D magnetohydrodynamics model incorporates radiative heating and ionization of the atmospheric gas, basic hydrogen chemistry for the appropriate account of major species composing HJ's upper atmosphere and related radiative energy deposition, and H3+ and Ly{\alpha} cooling processes. The model also takes into account a realistic solar-type X-ray/EUV spectrum for calculation of intensity and column density distribution of the radiative energy input, as well as gravitational and rotational forces acting in a tidally locked planet-star system. An interaction between the expanding atmospheric plasma and an intrinsic planetary magnetic dipole field leads to the formation of a current-carrying magnetodisk that plays an important role for topology and scaling of the planetary magnetosphere. A cyclic character of the magnetodisk behavior, composed of consequent phases of the disk formation followed by the magnetic reconnection with the ejection of a ring-type plasmoid, has been discovered and investigated. We found that the mass-loss rate of an HD 209458b analog planet is weakly affected by the equatorial surface field <0.3 G, but is suppressed by an order of magnitude at the field of 1 G.

We present a joint theoretical and experimental characterization of the coherent population trapping (CPT) resonance excited on the ${D}_{1}$ line of $^{87}\mathrm{Rb}$ atoms by bichromatic linearly polarized laser light. We observe high-contrast transmission resonances (up to $\ensuremath{\approx}25%$), which makes this excitation scheme promising for miniature all-optical atomic clock applications. We also demonstrate cancellation of the first-order light shift by proper choice of the frequencies and relative intensities of the two laser-field components. Our theoretical predictions are in good agreement with the experimental results.

We applied terahertz (THz)-pulsed spectroscopy to study ex vivo the refractive index and absorption coefficient of human brain gliomas featuring different grades, as well as perifocal regions containing both intact and edematous tissues. Glioma samples from 26 patients were considered and analyzed according to further histological examination. In order to fix tissues for the THz measurements, we applied gelatin embedding, which allows for sustaining their THz response unaltered, as compared to that of the freshly excised tissues. We observed a statistical difference between the THz optical constants of intact tissues and gliomas of grades I to IV, while the response of edema was similar to that of tumor. The results of this paper justify a potential of THz technology in the intraoperative label-free diagnosis of human brain gliomas for ensuring the gross-total resection.

New laser data on orthorhombic YAlO3:Er3+ crystals are obtained. Stimulated emission in the 4S3/2 →5I15/2 channel and cascase lasing of the sequential intermanifold 4S3/2 → 4I11/2 → 4I13/2 transitions are excited at ≈︁ 110 K with Xe-flashlamp pumping. Intensity absorption and luminescence characteristics of Er3+ ions in the YAlO3 crystal are experimentally determined and quantitatively analyzed in terms of the known semiempirical method. The intensity spectroscopic parameters Ωt obtained (Ω2 = 0.95, Ω4 = 0.58, and Ω6 = 0.55 (in 10−20 cm2)) nicely describe band-area intensities in the absorption spectrum of the YAlO3:Er3+ crystal in the spectral region below 30000 cm−1. A full set of reduced-matrix elements for the Er3+ ions is calculated involving all 41 J-manifolds of the 4f11 configuration lying in energy up to 97000 cm−1. Using these data, the earlier reported intensity parameter Ωt for the YAlO3:Er3+ crystal are revised and it is shown that involving highly excited levels of Er3+ ions into intensity spectroscopic analysis leads to an overestimation of the parameters Ωt because of the possible presence of some additional absorption sources in the YAlO3 host.

The experimental results on deposition of superconducting, semiconducting, quantum size and magnetic films by pulsed laser deposition technique are presented. The possible applications of pulsed laser deposition technique are discussed.

The results of studies of fast-proton generation from foil targets irradiated by 1-ps laser pulse at ${10}^{17}\phantom{\rule{0ex}{0ex}}\mathrm{W}/\mathrm{cm}{}^{2}$ are presented. It is shown that a considerable increase in proton energy and current is possible when a double-layer foil target containing a high- $Z$ layer and a low- $Z$ hydrogen-rich layer is used instead of a single-layer target. Proton energies and current increase with the $Z$ of the high- $Z$ layer and depend essentially on the target and the layer thicknesses. Above ${10}^{9}$ forward-emitted protons of energy $&gt;100\phantom{\rule{0ex}{0ex}}\mathrm{keV}$ have been recorded within a cone angle $&lt;3\ifmmode^\circ\else\textdegree\fi{}$.

The complex crystallographic, spectroscopic, and laser properties of ${\mathrm{Dy}}^{3+}$ ions in $\ensuremath{\alpha}\ensuremath{-}\mathrm{KY}({\mathrm{WO}}_{4}{)}_{2}$ and $\ensuremath{\alpha}\ensuremath{-}\mathrm{KGd}({\mathrm{WO}}_{4}{)}_{2}$ single crystals are investigated. Individual Stark levels for many of the ${}^{2S+1}{L}_{J}$ manifolds of ${\mathrm{Dy}}^{3+}$ ${(4f}^{9})$ ions in these monoclinic tungstates are obtained from luminescence and absorption spectra up to \ensuremath{\approx}28 000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ at \ensuremath{\approx}15 K. A crystal-field splitting analysis for the majority of these manifolds is performed. The rms deviation between 73 experimental and calculated ${\mathrm{Dy}}^{3+}$ Stark levels for both crystals was \ensuremath{\approx}10 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. Theoretical calculations of intermanifold intensity parameters are carried out by methods using the Judd-Ofelt approach with regard to interconfiguration interaction. All luminescence channels originating from levels of the metstable ${}^{4}{F(3)}_{9/2}$ state are compared with measured data. Pulsed stimulated emission in the visible range at the wavelengths of two lasing channels ${}^{4}{\stackrel{\ensuremath{\rightarrow}}{{F(3)}_{9/2}}}^{6}{H}_{13/2}$ and ${}^{4}{\stackrel{\ensuremath{\rightarrow}}{{F(3)}_{9/2}}}^{6}{H}_{11/2}$ of ${\mathrm{Dy}}^{3+}$ ions are excited and identified. On the basis of observed spectroscopic data we determine the peak cross section for all observed induced transitions as well. We conclude that ${\mathrm{Dy}}^{3+}$-doped monoclinic tungstates $\ensuremath{\alpha}\ensuremath{-}\mathrm{KGd}({\mathrm{WO}}_{4}{)}_{2}$ and $\ensuremath{\alpha}\ensuremath{-}\mathrm{KY}({\mathrm{WO}}_{4}{)}_{2}$ are very attractive crystalline materials for generating visible laser light.

tree leaves and pork muscles. The developed experimental terahertz time-domain spectroscopy system operates both in transmission and reflection modes. The Landau-Looyenga-Lifshitz-based model is used for the calculation of the water concentration within the samples. The results of the water concentration measurements are compared with the results of the gravimetric measurements. The obtained results show that the water content in biological samples can be measured non-invasively, with a high accuracy, utilizing terahertz waves in transmission and reflection modes.

Possibilities of laboratory simulation of various explosive phenomena in space and cosmic plasmas with magnetic fields are analyzed on the bases of similarity criteria, properties of collisionless interactions, and parameters of laser-produced plasmas. It is shown how the physics of such widely different phenomena as barium releases in Earth's magnetosphere, collisionless deceleration of supernova remnants, and related shock-wave generation in interstellar medium or possible near-Earth anti-asteroid explosions could be reproduced in the laboratory. This review of worldwide efforts tries to reveal the problems and perspectives of modern collisionless laboratory astrophysics with high-power lasers.

SIGNIFICANCE: An increasing interest in the area of biological effects at exposure of tissues and cells to the terahertz (THz) radiation is driven by a rapid progress in THz biophotonics, observed during the past decades. Despite the attractiveness of THz technology for medical diagnosis and therapy, there is still quite limited knowledge about safe limits of THz exposure. Different modes of THz exposure of tissues and cells, including continuous-wave versus pulsed radiation, various powers, and number and duration of exposure cycles, ought to be systematically studied. AIM: We provide an overview of recent research results in the area of biological effects at exposure of tissues and cells to THz waves. APPROACH: We start with a brief overview of general features of the THz-wave-tissue interactions, as well as modern THz emitters, with an emphasis on those that are reliable for studying the biological effects of THz waves. Then, we consider three levels of biological system organization, at which the exposure effects are considered: (i) solutions of biological molecules; (ii) cultures of cells, individual cells, and cell structures; and (iii) entire organs or organisms; special attention is devoted to the cellular level. We distinguish thermal and nonthermal mechanisms of THz-wave-cell interactions and discuss a problem of adequate estimation of the THz biological effects' specificity. The problem of experimental data reproducibility, caused by rareness of the THz experimental setups and an absence of unitary protocols, is also considered. RESULTS: The summarized data demonstrate the current stage of the research activity and knowledge about the THz exposure on living objects. CONCLUSIONS: This review helps the biomedical optics community to summarize up-to-date knowledge in the area of cell exposure to THz radiation, and paves the ways for the development of THz safety standards and THz therapeutic applications.

We study the dependence of electromagnetically induced transparency (EIT) resonance amplitudes on the external magnetic field direction in a linearly polarized bichromatic light ($\mathit{lin}||\mathit{lin}$) configuration in $^{87}\mathrm{Rb}$ vapor. We demonstrate that all seven resolvable EIT resonances exhibit maxima or minima at certain orientations of the laser polarization relative to the wave vector and magnetic field. This effect can be used for the development of a high-precision EIT vector magnetometer.