26405621
Coherence effects in long-wavelength infrared synchrotron radiation emission.
We report measurements of synchrotron radiation emission in the wavelength region from 30 to 400 ..mu..m where coherent enhancement was predicted. The power ratio relative to a blackbody source exhibits no such enhancement and can be accounted for by the incoherent emission theory. This discrepancy is explained by showing that the coherent enhancement is reduced when proper account is taken of the relative phases of all emitting particles.
111253318
A synchronized FEL-synchrotron radiation facility at Jefferson Lab
Jefferson Lab is planning a facility for studying ultrafast dynamical processes using a 1 kW average power IR/UV FEL, and a mode-locked Ti-sapphire femtosecond laser in the visible, combined with a 1 nm critical wavelength electron storage ring. Light pulses from the three sources will be synchronized at 125 MHz for pump-probe studies (including pump-pump-probe and pump-probe-probe options) in chemistry, physics, materials science, medicine and biology. The FEL operates with pulses as short as 300 femtoseconds (/spl sigma/), which will provide the narrow bandwidth pump at high peak as well as average power. The FEL is currently operating and will soon be upgraded to operate at up to 10 kilowatt average power at an extended wavelength range from 300 nm to 10,000 nm. A compact superconducting storage ring, Helios-1, has recently been donated to Jefferson Lab that has a critical wavelength of 10 /spl Aring/ and is capable of storing currents up to 800 mA. In addition to providing spectroscopy capabilities, the storage ring will also support exploratory X-ray lithography R&D, including a precision stepper-aligner for training purposes. The facility, which is expected to become available in 2004, will be described and the capabilities detailed.
123627605
Intense, broadband, pulsed I-R source at the national synchrotron light source
We describe a broadband (1 μm−1 mm) synchrotron radiation infrared source, pulsed each 20–180 nseconds and delivering about 1015 photons/sec/1% bandpass into f10 optics. The source size is diffraction limited. This source is thus 100–1000 times brighter than a 2000°K black body, very stable and capable of being used for calibration.
45418780
Multiparticle coherence calculations for synchrotron-radiation emission.
We have used Monte Carlo calculations to verify the classical electrodynamics result describing the multiparticle coherent enhancement at long wavelengths for synchrotron-radiation emission. In addition we show the derivation of the result that, for a bunch of electrons in a storage ring, the synchrotron-radiation emission has a multiparticle coherent enhancement that is given by the square of the Fourier transform of the longitudinal spatial distribution function of the electrons. The result has been verified for Gaussian and sinusoidal distributions. For a Gaussian distribution of particles in a bunch, this is seen to have an effect only at wavelengths close to the bunch length. For a sinusoidal distribution as in the transverse optical klystron, the enhancement can easily be seen to occur at one specific wavelength.
55360891
Longitudinal Space Charge Effects in the JLAB IR FEL SRF LINAC
Observations of energy spread asymmetry when operating the Linac on either side of crest and longitudinal emittance growth have been confirmed by extending PARMELA simulations from the injector to the end of the first SRF Linac module. The asymmetry can be explained by the interaction of the accelerating electric field with that from longitudinal space charge effects within the electron bunch. This can be a major limitation to performance in FEL accelerators.
115765910
A SYNCHRONIZED FIR/VUV LIGHT SOURCE AT JEFFERSON LAB
We describe a dual free-electron laser (FEL) configuration on the UV Demo FEL at Jefferson Lab that allows simultaneous lasing at FIR/THz and UV wavelengths. The FIR/THz source would be an FEL oscillator with a short wiggler providing nearly diffraction-limited pulses with pulse energy exceeding 50 microJoules. The FIR source would use the exhaust beam from a UVFEL. The coherent harmonics in the VUV from the UVFEL are out-coupled through a hole. The FIR source uses a shorter resonator with either hole or edge coupling to provide very high power FIR pulses. Simulations indicate excel-lent spectral brightness in the FIR region with over 100 W/cm-1 output.
18461760
Solving the Bethe-Salpeter equation for scalar theories in Minkowski space.
The Bethe-Salpeter (BS) equation for scalar-scalar bound states in scalar theories without a derivative coupling is formulated and solved in Minkowski space. This is achieved using the perturbation theory integral representation, which allows these amplitudes to be expressed as integrals over weight functions and known singularity structures and hence allows us to convert the BS equation into an integral equation involving weight functions. We obtain numerical solutions using this formalism for anumber of scattering kernels to illustrate the generality of the approach. It applies even when the naive Wick rotation is invalid. As a check we verify, for example, that this method applied to the special case of the massive ladder exchange kernel reproduces the same results as are obtained by Wick rotation.
14542071
Study of exclusive radiative B meson decays
We have studied exclusive, radiative B meson decays to charmless mesons in 9.7x10(6) B&Bmacr; decays accumulated with the CLEO detector. We measure B(B0-->K(*0)(892)gamma) = (4.55(+0.72)(-0. 68)+/-0.34)x10(-5) and B(B+-->K(*+)(892)gamma) = (3.76(+0.89)(-0. 83)+/-0.28)x10(-5). We have searched for CP asymmetry in B-->K(*)(892)gamma decays and measure A(CP) = +0.08+/-0.13+/-0.03. We report the first observation of B-->K(*)(2)(1430)gamma decays with a branching fraction of (1.66(+0.59)(-0.53)+/-0.13)x10(-5). No evidence for the decays B-->rhogamma and B0-->omegagamma is found and we limit B(B-->(rho/omega)gamma)/B(B-->K(*)(892)gamma)<0.32 at 90% C.L.
16586082
Momentum dependence of the rho - omega mixing amplitude in a hadronic model.
We calculate the momentum dependence of the [rho]-[omega] mixing amplitude in a purely hadronic model. The basic assumption of the model is that the mixing amplitude is generated by [ital N[bar N]] loops and thus driven entirely by the neutron-proton mass difference. The value of the amplitude at the [omega]-meson point is expressed in terms of only the [ital NN][omega] and [ital NN][rho] coupling constants. Using values for these couplings constrained by empirical two-nucleon data we obtain a value for the mixing amplitude in agreement with experiment. Extending these results to the spacelike region, we find a [rho]-[omega] contribution to the [ital NN] interaction that is strongly suppressed and opposite in sign relative to the conventional contribution obtained from using the constant on-shell value for the mixing amplitude.