R. Shuker - Academia.edu (original) (raw)

Papers by R. Shuker

Synchrotron radiation sources have opened a new window on the century-old use of x rays as a scie... more Synchrotron radiation sources have opened a new window on the century-old use of x rays as a scientific tool. X-ray fluorescence, excited by the photoabsorption process, has been a part of this research picture almost since the day that x rays were first discovered. However, the investigation of multi-photon processes in gases and solids had to wait until the second half of the 20th century. The advent of intense synchrotron radiation sources based on the use of specialized insertion devices will provide many new scientific opportunities for the 21st century. This presentation will outline some of the recent exciting discoveries in soft x-ray fluorescence spectroscopy and discuss a new type of laser-synchrotron hybrid experimental technique based on the time structure of the synchrotron radiation.

arXiv: Quantum Physics, 2020

Enhancement of the sensitivities of optical magnetometers, atomic clocks and atom interferometers... more Enhancement of the sensitivities of optical magnetometers, atomic clocks and atom interferometers and other quantum metrology devices requires introducing new physical processes to improve on their present achievements. Many body collective correlations among the atoms, spins or, in general, quantum systems may prove to be a suitable method. As these correlations introduce interference terms in the intensity of the scattering amplitudes, they may enhance the signal as N(N−1)N(N-1)N(N−1) for N correlated quantum systems. These correlations enhance the signal to noise ratio by a factor of N2N^2N2 and contribute to better sensitivity in quantum metrology. Moreover atomic correlation may provide quantum noise limit, Heisenberg limit. In the present communication excitation exchange induced by photons in a cavity between two atoms is calculated and clearly exhibits correlation and collective effects. A novel operator is introduced that expresses photon-induced excitation exchange that takes in accou...

High Pressure Research, 2017

ABSTRACT La K-edge X-ray absorption spectroscopy has been used to elucidate the changes in the lo... more ABSTRACT La K-edge X-ray absorption spectroscopy has been used to elucidate the changes in the local electronic and lattice structure that occur in the A-site deficient double perovskite LaNbO up to 6 GPa. The pressure evolution of the oxygen dodecahedrum around the A-site has been examined. XANES (X-ray absorption near edge structure) data show modifications ascribed to the increase of bands overlapping as a consequence of the bond distance contraction, which has been directly probed by EXAFS (extended x-ray absorption fine structure) spectra. The La–O Debye Waller factors (DWFs) tend to increase whereas the La–Nb bond DWFs show only a tendency to decrease indicating the robustness of the crystal lattice structure, even in presence of the oxygen disordering. This permits the system to reverse back to its original conditions in this pressure range as evident from the measurements upon pressure release. The present results have been interpreted in the light of charge transfer related to the two-step reduction mechanism acting at the Nb site (with niobium ions passing from Nb to Nb) which also results in the elongation of the Nb–O bond distances in the octahedra, in agreement with the Nb K-edge results reported earlier.

Physical Review A, 1975

Following recent reports on strong uv and ir laser transitions in noble-gas mixtures, we attempte... more Following recent reports on strong uv and ir laser transitions in noble-gas mixtures, we attempted to determine the dominant precursor reactions leading to laser action. In this paper we present experimental results of time-dependent spectroscopy of the various species existing in He/Xe mixtures excited by fast transverse electrical discharges. We also present some parametric measurements of the He/Xe laser in the ir region. A plasma model is suggested for explaining the time behavior of the helium and xenon emissions. According to this model, which is justified by the experimental results, ir laser action in the He/Xe mixture is excited mainly by energy transfer from metastable helium atoms and molecules by Penning ionization of xenon atoms.

IEEE Transactions on Magnetics, 2009

We show that a single-cell spin-exchange relaxation-free (SERF) atomic magnetometer can be used f... more We show that a single-cell spin-exchange relaxation-free (SERF) atomic magnetometer can be used for 3-D field measurements. The 3-D operation is achieved by optically pumping the magnetometer cell in successive layers perpendicular to the laser probe beam and by collecting the signals with a photodiode array. The vapor cell is thus divided into voxels acting as local atomic magnetometers. Each voxel's contribution to the probe linear polarization rotation is proportional to the convolution of the local polarization and the magnetic field. The layers are pumped in sequence without waiting for the atomic polarization in the previously pumped layer to relax to zero, consequently, reducing the total measurement time. The photodiode signals are the sum of accumulated linear polarization rotation caused by all the layers. These signals are processed by a deconvolution algorithm that extracts the information originating from each individual voxel. Our theoretical analysis and experimental results show that the time of a single-layer pumping can be reduced below the atomic-cell relaxation time constant, with almost no loss of precision.

Physical Review A, 1983

Observations of Cooper minima in excited-state photoionization cross sections for the Ne 3s and A... more Observations of Cooper minima in excited-state photoionization cross sections for the Ne 3s and Ar4s levels are reported. Prebreakdown Ne and Ar discharges under irradiation by light in the 200-400-nm wavelength range yield spectral dependences of photoionization cross sections with minima at the ionization threshold of these states in Ne and slightly distant from them in Ar. They are in close agreement with certain theoretical predictions. Autoionization structure which exists between the two ionization limits p3/2 and p~~2 was not observed in any of the Ne or Ar photoionization spectra due to both low spectral resolution and the high density of levels in this spectral region. Application of these measurements to ultraviolet-radiation detection is examined. High detection sensitivity of ultraviolet light is indicated.

The conventional way of studying laser noise assumes analytic solution of the quantum problem for... more The conventional way of studying laser noise assumes analytic solution of the quantum problem for the laser field coupled to the active medium. A number of the laser schemes have been discussed, and predictions for noise reduction and for the squeezed state of field have been made.1 On the basis of first principies of the quantum mechanies, the conventional approach exhibits the relatively rare situation in which the quantum equations admit compact analytic solution. At the same time, the difficulty in interpreting the results seems to be unresolved. Specifically, it is very difficult lo determine the relative contribution of each physical source of noise to the final fluctuation result.

Technical Digest. Summaries of Papers Presented at the International Quantum Electronics Conference. Conference Edition. 1998 Technical Digest Series, Vol.7 (IEEE Cat. No.98CH36236), 1998

The behavior of a laser intensity as a function of a pump rate is studied. We consider a three-le... more The behavior of a laser intensity as a function of a pump rate is studied. We consider a three-level lasing scheme with two different types of pumping. In the first case, the lower lasing level is depleted to the ground state, and then the pumping is used to excite the atom from the ground state to the upper lasing level. In the second case the pumping is used to excite the atom directly from the lower lasing level to one of the excited states, which is then depleted to the upper lasing level. We refer these two types of pumping as type 1 and type 2, respectively. It is shown that although these two schemes are equivalent mathematically, i.e., they are formally described by the same set of equations, physically their dynamical properties are completely different. It is noted that the pumping of the type 1 does not affect either of lasing levels directly, whereas the pumping of the type 2 does connect the lower lasing level with one of the excited states. It is this difference of the two ways of pumping which is responsible for the crucial difference in the dynamic behavior of the lasing schemes of types 1 and 2

Conference on Lasers and Electro-Optics, 1986

Conical light emission is observed when an intense quasiresonant laser beam propagates in an atom... more Conical light emission is observed when an intense quasiresonant laser beam propagates in an atomic vapor.1-4 A parametric four-wave mixing process was suggested to explain this effect.1 However, this model is inconsistent with experiments both quantitatively in the value of the predicted cone angle and qualitatively due to the absence of the obligatory blue counterpart to the red-shifted cone photon.2-4 A model of Cherenkov radiation by a laser-induced moving polarization was proposed to account for the origin and angular/spectral dependencies of the conical emission.3

Journal of Physics B: Atomic and Molecular Physics, 1987

ABSTRACT The observations of anomalous emission near the D1 transition of a dense (>or=101... more ABSTRACT The observations of anomalous emission near the D1 transition of a dense (>or=1014 cm-3) sodium vapour illuminated by a laser detuned to the blue with respect to the D2 transition is studied and reported. A discussion of existing models is presented. The authors propose a type of parametric down-conversion process to explain this emission. This process involves a laser photon splitting into two photons by the three-level system of sodium, assisted by a magnetic dipole transition.

Springer Series in Optical Sciences, 1987

The passage of a laser light detuned to the blue of a resonant atomic transition results in a con... more The passage of a laser light detuned to the blue of a resonant atomic transition results in a conical emission around the laser beam [1, 2]. This conical emission shell has a half-angle of a few degrees around the laser axis, is red detuned from the transition and is spectrally broad (~ 10 cm-1).

Atomic and Quantum Optics: High-Precision Measurements, 1996

The most important mechanism to occur in biological distributed sensory networks (DSNs) is called... more The most important mechanism to occur in biological distributed sensory networks (DSNs) is called lateral inhibition, (LI). LI relies on one simple principle. Each sensor strives to suppress its neighbors in proportion to its own excitation. In this study, LI mechanism is exploited to localize the unknown position of a light source that illuminated the photosensitive sensory network containing high and low quality sensors. Each photosensitive sensor was then calibrated to accurately read the distance to the light source. A series of experiments were conducted employing both quality sensors. Low quality array was allowed to take advantage of LI, whereas the high quality one was not. Results showed that the lateral inhibition mechanism increased the sensitivity of inferior quality sensors, giving the ability to make the localization as sensitive as high quality sensors do. This suggests that the networks with multitude of sensors could be made cost-effective, were these sensory networks equipped with LI.

Physics and Chemistry of Minerals, 2013

Abstract High-pressure X-ray diffraction measurements have demonstrated that the cation-deficient... more Abstract High-pressure X-ray diffraction measurements have demonstrated that the cation-deficient perovskites Pr1/3NbO3, Pr1/3TaO3, Nd1/3NbO3, and Nd1/3TaO3 undergo irreversible pressure-induced amorphization (PIA). This occurs near 14.5 GPa for the niobates and 18.5 GPa for the tantalates. The unit cell volumes of the four oxides show an almost linear decrease as the pressure is increased. It is concluded that the PIA transition occurs at higher pressures in the tantalates due to the lower MO6 initial tilting at ambient conditions, which is associated with the larger atomic mass of the tantalum. The behavior of these oxides is compared to that of CaTiO3, and the role of both the weakening of the M–O–M π-bonding and the cation vacancies on the observed structural changes is discussed.

Physical Review A, 2003

A scheme for obtaining laser in the deep x-ray regime is proposed based on the principle of gain ... more A scheme for obtaining laser in the deep x-ray regime is proposed based on the principle of gain without inversion. A ladder scheme is proposed in Ar ϩ8 system. In this system, conventional lasing with population inversion has been obtained in a neonlike fashion. This lasing field is proposed for the drive field on the higher transition of the ladder. A coherent field obtained in the high harmonics ultrashort laser provides the probe field to be amplified. This will be selected to best match the frequency needed for the transition from lower level of the present x-ray lasing to the ground state. Numerical calculations in the bare state picture exhibit possible gain at resonance, and at the Rabi side bands, for appropriate choice of system parameters, i.e., the strength of the driving field, the strength of the incoherent pump that provides the required energy needed for the inversionless amplification and the deexcitation rate. The latter rate is detrimental to lasing as it increases. It is quite interesting to note that the system exhibits surprisingly high stability for gain without inversion even for quite high rate of the incoherent deexcitation processes. Real and imaginary parts of the coherences were also obtained for detuned drive and probe fields. These provide insight into the role played by the quantum interference. The present theoretical calculations give high confidence in the quantum interference process as a candidate for realizing very short wavelength laser.