8,831 research outputs found
Goldstone Theorem in the Gaussian Functional Approximation to the Scalar Theory
We verify the Goldstone theorem in the Gaussian functional approximation to
the theory with internal O(2) symmetry. We do so by reformulating
the Gaussian approximation in terms of Schwinger-Dyson equations from which an
explicit demonstration of the Goldstone theorem follows directly.Comment: 11 page
An EPROM-based function generator
A circuit is described to produce arbitrary time-dependent voltage functions derived from digital information stored in EPROMs. While this circuit is designed to be used as a modulator of the microwave pump source or a solid state low noise maser, it can be readily adapted for other applications
Four wave mixing with self-phase matching due to collective atomic recoil
We describe a method for non-degenerate four-wave mixing in a cold sample of
4-level atoms. An integral part of the four-wave mixing process is a
collective instability which spontaneously generates a periodic density
modulation in the cold atomic sample with a period equal to half of the
wavelength of the generated high-frequency optical field. Due to the generation
of this density modulation, phase-matching between the pump and scattered
fields is not a necessary initial condition for this wave-mixing process to
occur, rather the density modulation acts to "self phase-match" the fields
during the course of the wave-mixing process. We describe a one-dimensional
model of this process, and suggest a proof-of-principle experiment which would
involve pumping a sample of cold Cs atoms with three infra-red pump fields to
produce blue light.Comment: to appear in Physical Review Letter
Towards Zeptosecond-Scale Pulses from X-Ray Free-Electron Lasers
The short wavelength and high peak power of the present generation of
free-electron lasers (FELs) opens the possibility of ultra-short pulses even
surpassing the present (tens to hundreds of attoseconds) capabilities of other
light sources - but only if x-ray FELs can be made to generate pulses
consisting of just a few optical cycles. For hard x-ray operation (~0.1nm),
this corresponds to durations of approximately a single attosecond, and below
into the zeptosecond scale. This talk will describe a novel method to generate
trains of few-cycle pulses, at GW peak powers, from existing x-ray FEL
facilities by using a relatively short 'afterburner'. Such pulses would enhance
research opportunity in atomic dynamics and push capability towards the
investigation of electronic-nuclear and nuclear dynamics. The corresponding
multi-colour spectral output, with a bandwidth envelope increased by up to two
orders of magnitudes over SASE, also has potential applications.Comment: Submitted to 35th International Free Electron Laser Conference, New
York, 201
Start-to-end modelling of a mode-locked optical klystron free electron laser amplifier
A free electron laser (FEL) in a mode-locked optical klystron (MLOK) configuration is modelled using start-to-end simulations that simulate realistic electron beam acceleration and transport before input into a full three-dimensional FEL simulation code. These simulations demonstrate that the MLOK scheme is compatible with the present generation of radiofrequency accelerator designs. A train of few-optical cycle pulses is predicted with peak powers similar to those of the equivalent conventional FEL amplifier. The role of electron beam energy modulation in these results is explained and the limitations of some simulation codes discussed. It is shown how seeding the FEL interaction using a High Harmonic seed laser can improve the coherence properties of the output
Investigation of a 2-Colour Undulator FEL Using Puffin
Initial studies of a 2-colour FEL amplifier using one monoenergetic electron
beam are presented. The interaction is modelled using the unaveraged, broadband
FEL code Puffin. A series of undulator modules are tuned to generate two
resonant frequencies along the FEL interaction and a self-consistent 2-colour
FEL interaction at widely spaced non-harmonic wavelengths at 1nm and 2.4nm is
demonstrated.Comment: Submitted to The 35th International Free-Electron Laser Conference,
Manhattan, New York (2013
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