Temporal optics of recoil-free gamma radiation

A discussion is given of the time-behavior of recoil-free γ-radiation passing through a resonant medium. The classical dispersion theory of Hamermesh is extended to account for different linewidths in source or absorber so that a synchrotron-radiation source can be simulated. A result, essentially the same as that of Kagan et al., follows in the limit of large source width. A review is given of the quantum beats which result from the absorption of one line of a frequency-modulation spectrum. An example is given of the measurement of second-order Doppler shift in Fe−Be by the method of quantum beats. Finally, there is a discussion of the measurement by quantum beats of the very small energy shift in a⁵⁷Co−Cu source by a magnetic field.     

Generation of low energy resonant electrons during relaxation of57Fe

Collection of low energy electrons (<15 eV) duringConversionElectronMossbauerSpectroscopy (CEMS) provides enhanced surface sensitivity. Spectra collected from a 0.928⁵⁷Fe foil using retarding field energy analyzers in conjunction with spiraltron electron multipliers demonstrates both resonant and nonresonant count rates which decrease by as much as 50% at 10 eV bias potential. Spectra from samples with the topmost 1.0 nm chemically labeled had total spectral areas of 99.0%mm/sec. The area ratio of the resonant 1.0 nm overlayer to the resonant substrate was 1.43 at 0 eV bias potential while at 15 eV the ratio decreased to 0.72. By vacuum evaporating a 5.0 nm copper coating on the sample, near complete attenuation of the low energy electrons from the 1.0 nm overlayer was achieved. These results suggest that some low energy electrons below 15 eV are formed as primary products of electronic relaxation following nuclear decay and that they are not the result of straggling or other scattering phenomena.     

High-frequency magnetic modulation of recoilless gamma radiation of57Fe

Radio-frequency (rf) magnetic modulation has been used to generate sidebands in⁵⁷Fe Mössbauer spectra of Fe_0.18Ni_0.82 Permalloy foils which have the smallest constant of magnetostriction among Fe?Ni alloys. Sidebands in Mössbauer spectra were observed at 30 MHz and 55 MHz. In addition to the generation of sidebands, the external rf magnetic field was found to alter the line positions of the original six line spectrum. An attempt was made to study acoustic vibrations in the foil by means of X-ray diffraction. The rf magnetic field caused changes in diffraction peak intensities and positions. It was found that X-ray diffraction can be used to study the amplitude of acoustic vibrations in Permalloy foils.     

Theory of resonant acoustic transmission through subwavelength apertures

A complete landscape is presented of the acoustic transmission properties of subwavelength apertures (slits and holes). First, we study the emergence of Fabry-Perot resonances in single apertures. When these apertures are placed in a periodic fashion, a new type of transmission resonance appears in the spectrum. We demonstrate that this resonance stems from the excitation of an acoustic guided wave that runs along the plate, which hybridizes strongly with the Fabry-Perot resonances associated with waveguide modes in single apertures. A detailed discussion of the similarities and differences with the electromagnetic case is also given.     

Electric field gradient sign determination in low magnetic fields perpendicular to the gamma rays in57Fe Mössbauer spectroscopy

The determination, by Mössbauer⁵⁷Fe spectroscopy, of the sign and the asymmetry parameter of the electric field gradient (EFG), in a non-magnetic powder sample, needs the use of an external magnetic field. Usually a “parallel-magnetic-field-to-the-gamma-rays” configuration is employed. In the present work, theoretically generated spectra in both configurations, parallel an perpendicular, are compared. The result is that the spectra in the perpendicular configuration show always a larger asymmetry for the same fields intensitics. In consequence, the sign determination of the EFG, is possible with magnetic fields significantly smaller in the perpendicular case than in the parallel one. Furthermore, the practical consequences are important, because EFG studies with conventional electromagnets, allowing only fields lower than 25 kGauss are feasible. As an example. Mössbauer experimental results obtained at room temperature for natural pyrite (FeS₂) in perpendicular fields of 15 and 20 kGauss, created by a conventional electromagnet, are shown here.     

Ballistic transmission through quasi-periodic shape barrier resonant tunneling structures

A theoretical model is proposed to study the ballistic electron transport for a quasi-periodic multibarrier structure where two different barrier shapes are arranged according to the Thue–Morse sequence. Important tunneling features are revealed form such arrangements. It is noted that the tunneling band spectrum could be fragmented by tailoring the shape of the barriers in the structure. Results for the transmission coefficients and the current densities are compared with the corresponding periodic and single shape barrier arrangements. The quasi-periodic structure consisting of the rectangular and triangular barrier shapes is suggested to be more suitable for the electronic and opto-electronic devices due to its high negative differential conducting effect.     

Families of bose rays in quantum optics

Having known classical wave optics and wave mechanics, can we reverse Schrödinger's path and extend the concept of families of rays of light to provide a new exact rendering of quantum optics including the Bose nature of photons? This question is answered in the affirmative, and the implications of the Bose symmetry for certain nonlocal correlations of the many-ray distribution functions are worked out. The similarities and the differences between classical and quantum wave optics are brought out. The ray-ray Bose correlation is analyzed. The generating functional for the many-ray distribution functions is formulated; and the notion of paraxial illumination for quantum optics is made precise.     

Compilation of low-energy gamma rays

A compilation of selected nuclear gamma rays has been prepared in order to identify the most attractive candidate nuclei for a gamma-ray laser. The compilation consists of two parts: (1) a listing of selected gamma rays emanating from an isomeric state and (2) a listing of selected gamma rays following the decay of an energy level close to the isomeric state. The compilation is based on the latest “Nuclear Data Sheets” (Ref. 1) for each A-chain available on 1 January 1987.     

Recoil-free resonant gamma-ray absorption in57Fe nuclei in the presence of a strong microwavefield

A calculation of the cross-section of resonant gamma-ray absorption in the presence of strong microwave fields has been performed. This calculation is based on papers published earlier [1-3], in which the possibility of nuclear recoil compensation at the absorption of gamma-rays, by means of optical photons, was considered. Preliminary experimental results concerning there coil-free gamma absorption in the presence of a 3 GHz strong microwave field are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Generalized pencils of rays in statistical wave optics

The recently introduced generalized pencil of Sudarshan which gives an exact ray picture of wave optics is analysed in some situations of interest to wave optics. A relationship between ray dispersion and statistical inhomogeneity of the field is obtained. A paraxial approximation which preserves the rectilinear propagation character of the generalized pencils is presented. Under this approximation the pencils can be computed directly from the field conditions on a plane, without the necessity to compute the cross-spectral density function in the entire space as an intermediate quantity. The paraxial results are illustrated with examples. The pencils are shown to exhibit an interesting scaling behaviour in the far-zone. This scaling leads to a natural generalization of the Fraunhofer range criterion and of the classical van Cittert-Zernike theorem to planar sources of arbitrary state of coherence. The recently derived results of radiometry with partially coherent sources are shown to be simple consequences of this scaling.     

Remarkable zeroth-order resonant transmission of microwaves through a single subwavelength metal slit

A slit in a thick metal plate that is extremely subwavelength will not transmit microwaves polarized parallel to it. It is shown here that cuts perpendicular to the slit allow parallel polarized radiation to resonantly transmit. Furthermore, a zero-order mode may be excited within the slit, the frequency of which, to first order, is independent of the plate depth. Remarkably, for this novel type of resonance, the field in the slit oscillates with a constant phase and little amplitude variation throughout the plate depth, while the resonant wavelength tends to infinity as the slit width approaches zero.     

Measurements of sound transmission through panels of locally resonant materials between impedance tubes

We present a method for the measurements of complex transmission coefficient through high transmission loss samples using three-sensors, two impedance tubes, monotonic wave excitation, and phase sensitive detection. Having demonstrated the effectiveness of the method on perforated plates measurements have been made on locally resonant sonic materials (LRSMs). The transmission losses of perforated plates are found to decrease with decreasing frequency down to 120 Hz, following the mass law. For the LRSM’s panels with the same area mass density but different compositions, the local resonance frequency (at which the transmission loss is maximum) is found to vary according to the predesigned value. Transmission losses as high as 96.5 dB at 630 Hz and 87 dB at 250 Hz can be measured with good accuracy, with corresponding phase spectra that match the theoretical prediction of LRSMs, confirming the reliability of the transmission data.     

Polarimetry of short-pulse gamma rays produced through inverse Compton scattering of circularly polarized laser beams

We have developed a polarimetry of ultrashort pulse gamma rays based on the fact that gamma rays penetrating in the forward direction through a magnetized iron carry information on the helicity of the original gamma rays. Polarized, short-pulse gamma rays of (1.1+/-0.2)x10(6)/bunch with a time duration of 31 ps and a maximum energy of 55.9 MeV were produced via Compton scattering of a circularly polarized laser beam of 532 nm off an electron beam of 1.28 GeV. The first demonstration of asymmetry measurements of short-pulse gamma rays was conducted using longitudinally magnetized iron of 15 cm length. It is found that the gamma-ray intensity is in good agreement with the simulated value of 1.0x10(6). Varying the degree of laser polarization, the asymmetry for 100% laser polarization was derived to be (1.29+/-0.12)%, which is also consistent with the expected value of 1.3%.     

Emission of gamma rays by electron-nuclear doubletransitions

In this paper we discuss the relevance of electron-nuclear double transitions for the problem of the amplification of gamma rays. We consider the electron-nuclear coupled system of ¹⁵¹Eu in a CaF₂ lattice, in the presence of a strong static magnetic field. We analyze the possibility of pumping this electron-nuclear coupled system from the ground atomic electron Zeeman level to a higher electron level with the aid of a microwave magnetic field, while the nucleus is simultaneously undergoing a gamma-ray transition to the nuclear ground state. It is shown that an overall inversion condition can be satisfied even in the absence of inversion of the nuclear populations, provided that the ratio of the electron populations in the excited and ground electron Zeeman states has a sufficiently small value. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of gamma rays on PADC detectors

The effect of Gamma radiation in Polyallydiglycol carbonate (PADC) detectorrs has been studied in the dose range of 10⁰–10⁶ Gy. Some of the properties like bulk-etch rate, track-etch rate, activation energy for bulk and track-etching have been found out for different gamma doses from ⁶⁰Co Source in PADC. The experimental results are presented and discussed.     

Predicted intensity of gamma rays from photonium

We have shown in a previous paper that stable electron-positron resonances (photonium) can account for the dark matter in the universe. In this paper we show that photonium in the galaxy will be dissociated by cosmic rays. We predict the intensity of the resulting 511 keV gamma rays as a test of the model. We find that the predictions exceed observations from the galactic center for model where the photonium has a similar distribution to the baryons. The predicted intensity is consistent with observations if the photonium is distributed in a large halo.One of us (JPV) acknowledges support from the U.S. Department of Energy under Grant DE-FG02-87ER40371, Division of High Energy and Nuclear Physics     

Observation of non-phase-matched parametric amplification in resonant nonlinear optics

The coupling between a resonant excitation and a nonresonant parametric process in a nonlinear system is studied experimentally under non-phase-matched conditions. Our study performed in the context of anti-Stokes stimulated Raman scattering provides a clear observation of the self-induced phase matching of a parametric process. A close agreement with theoretical predictions is observed.     

Proper motion of gamma rays from microhalo sources

I discuss the prospects of detecting the smallest dark matter bound structures present in the Milky Way by searching for the proper motion of gamma-ray sources in the upcoming Gamma Ray Large Area Space Telescope all sky map. I show that for dark matter particle candidates that couple to photons the detection of at least one gamma-ray microhalo source with proper motion places a constraint on the couplings and mass of the dark matter particle.