The size of two-body weakly bound objects : short versus long range potentials

The variation of the size of two-body objects is investigated, as the separation energy approaches zero, with both long range potentials and short range potentials having a repulsive core. It is shown that long range potentials can also give rise to very extended systems. The asymptotic laws derived for states with angular momentum l=1,2 differ from the ones obtained with short range potentials. The sensitivity of the asymptotic laws on the shape and length of short range potentials defined by two and three parameters is studied. These ideas as well as the transition from the short to the long range regime for the l=0 case are illustrated using the Kratzer potential.Comment: 5 pages, 3 figures, submitted to Physical Review Letter

The Three-Boson System with Short-Range Interactions

We discuss renormalization of the non-relativistic three-body problem with short-range forces. The problem is non-perturbative at momenta of the order of the inverse of the two-body scattering length. An infinite number of graphs must be summed, which leads to a cutoff dependence that does not appear in any order in perturbation theory. We argue that this cutoff dependence can be absorbed in one local three-body force counterterm and compute the running of the three-body force with the cutoff. This allows a calculation of the scattering of a particle and the two-particle bound state if the corresponding scattering length is used as input. We also obtain a model-independent relation between binding energy of a shallow three-body bound state and this scattering length. We comment on the power counting that organizes higher-order corrections and on relevance of this result for the effective field theory program in nuclear and molecular physics.Comment: 24 pages, RevTex, 15 PS figures included with epsf.st

Ultra-low energy scattering of a He atom off a He dimer

We present a new, mathematically rigorous, method suitable for bound state and scattering processes calculations for various three atomic or molecular systems where the underlying forces are of a hard-core nature. We employed this method to calculate the binding energies and the ultra-low energy scattering phase shifts below as well as above the break-up threshold for the three He-atom system. The method is proved to be highly successful and suitable for solving the three-body bound state and scattering problem in configuration space and thus it paves the way to study various three-atomic systems, and to calculate important quantities such as the cross-sections, recombination rates etc.Comment: LaTeX, RevTeX and amssymb styles, 7 pages (25 Kb), 3 table

The New IR FEL Facility at the Fritz-Haber-Institut in Berlin

A mid-infrared oscillator FEL has been commissioned at the Fritz-Haber-Institut. The accelerator consists of a thermionic gridded gun, a subharmonic buncher and two S-band standing-wave copper structures [1,2]. It provides a final electron energy adjustable from 15 to 50 MeV, low longitudinal (<50 keV-ps) and transverse emittance (<20 π mm-mrad), at more than 200 pC bunch charge with a micro-pulse repetition rate of 1 GHz and a macro-pulse length of up to 15 μs. Regular user operation started in Nov. 2013 with 6 user stations. Pulsed radiation with up to 100 mJ macro-pulse energy at about 0.5% FWHM bandwidth is routinely produced in the wavelength range from 4 to 48 μm. We will describe the FEL design and its performance as determined by IR power, bandwidth, and micro-pulse length measurements. Further, an overview of the new FHI FEL facility and first user results will be given. The latter include, for instance, spectroscopy of bio-molecules (peptides and small proteins) conformer selected or embedded in superfluid helium nano-droplets at 0.4 K, as well as vibrational spectroscopy of mass-selected metal-oxide clusters and protonated water clusters in the gas phase

Universality in the Three-Body Problem for 4He Atoms

The two-body scattering length a for 4He atoms is much larger than their effective range r_s. As a consequence, low-energy few-body observables have universal characteristics that are independent of the interaction potential. Universality implies that, up to corrections suppressed by r_s/a, all low-energy three-body observables are determined by a and a three-body parameter \Lambda_*. We give simple expressions in terms of a and \Lambda_* for the trimer binding energy equation, the atom-dimer scattering phase shifts, and the rate for three-body recombination at threshold. We determine \Lambda_* for several 4He potentials from the calculated binding energy of the excited state of the trimer and use it to obtain the universality predictions for the other low-energy observables. We also use the calculated values for one potential to estimate the effective range corrections for the other potentials.Comment: 23 pages, revtex4, 6 ps figures, references added, universal expressions update

First Lasing of the IR FEL at the Fritz-Haber-Institut Berlin

A new mid-infrared FEL has been commissioned at the Fritz-Haber-Institut in Berlin. The oscillator FEL operates with 15 – 50 MeV electrons from a normal-conducting Sband linac. Calculations of the FEL gain and IR-cavity losses predict that lasing will be possible in the wavelength range from less than 4 to more than 50 μm. First lasing was achieved at a wavelength of 16 μm with an electron energy of 28 MeV. At these conditions, lasing was observed over a cavity length scan range of 100 μm

Status of the Fritz Haber Institute THz FEL

The THz FEL at the Fritz Haber Institute (FHI) in Berlin is designed to deliver radiation from 4 to 400 microns. A single-plane-focusing undulator combined with a 5.4 m long cavity is used is the mid-IR (< 50 micron), while a two-plane-focusing undulator in combination with a 7.2 m long cavity with a 1-d waveguide for the optical mode is used for the far-IR. A key aspect of the accelerator performance is low longitudinal emittance, < 50 keV-psec, at 200 pC bunch charge and 50 MeV from a gridded thermionic electron source. We utilize twin accelerating structures separated by a chicane to deliver the required performance over the < 20 - 50 MeV energy range. The first structure operates at near fixed field while the second structure controls the output energy, which, under some conditions, requires running in a decelerating mode. "First Light" is targeted for the centennial of the FHI in October 2011 and we will describe progress in the commissioning of this device. Specifically, the measured performance of the accelerated electron beam will be compared to design simulations and the observed matching of the beam to the mid-IR wiggler will be described

Design and Performance of the Wedged Pole Hybrid Undulator for the Fritz-Haber-Institut IR FEL

An IR and THz FEL with a design wavelength range from 4 to 500 μm has been commissioned at the Fritz- Haber-Institut (FHI) in Berlin, Germany. Lasing at 28 MeV and a wavelength of 16 μm was achieved in February 2012 [1]. We describe the performance of the undulator built and installed at FHI by STI Optronics for use in the mid-IR range (<50 μm) and 15- to 50-MeV beam energy. The undulator was a high-field-strength wedged-pole hybrid (WPH) with 40-mm period, 2.0-m long, and minimum gap 16.5 mm. A new improvement was including radiation resistance in the magnetic design. We will discuss the measured magnetic and mechanical performance, central and zero steering/offset end-field magnetic designs, key features of the mechanical design and gap adjustment system, genetic shimming algorithms, and control system