Overview of published articles & reports
Title: Damping of superfluid flow by a thermal cloud
Authors: R. Meppelink, S.B. Koller, J.M. Vogels, H.T.C. Stoof, and P. van der Straten
Abstract: One of the principal signatures of superfluidity is the frictionless flow of a superfluid through another substance. Here we study the flow of a Bose-Einstein condensate (the superfluid) through a thermal cloud and study its damping for different harmonic confinements and temperatures. The measured damping rates close to the collisionless regime are found to be in good agreement with Landau damping and become smaller for more homogeneous systems. In the hydrodynamic regime we observe additional damping due to collisions and we discuss the implications of these findings for superfluidity in this system.
Published: Phys. Rev. Lett. 103, 265301 (2009)
Download: oop6.pdf
Archive: 0909.0886
Title: Phase contrast imaging of Bose condensed clouds
Authors: R. Meppelink, R.A. Rozendaal, S.B. Koller, J.M. Vogels and P. van der Straten
Abstract: Phase contrast imaging is used to observe Bose-Einstein condensates (BECs) at finite temperature \insitu. The imaging technique is used to accurately derive the absolute phase shift of a probe laser beam due to both the condensate and the thermal cloud. The accuracy of the method is enhanced by using the periodicity of the intensity signal as a function of the accumulated phase. The measured density profiles can be described using a two relevant parameter fit, in which only the chemical potential and the temperature are to be determined. This allows us to directly compare the measured density profiles to different mean-field models in which the interaction between the condensed and thermal atoms is taken into account to various degrees.
Published: Phys. Rev. A 81, 053632 (2010)
Download: pci.pdf
Archive: 0909.4429
Title: Observation of shock waves in a large Bose-Einstein condensate
Authors: R. Meppelink, S.B. Koller, J.M. Vogels, P. van der Straten, E.D. van Ooijen, N.R. Heckenberg, H. Rubinsztein-Dunlop, S.A. Haine, M.J. Davis
Abstract: We observe the formation of shock waves in a Bose-Einstein condensate containing a large number of sodium atoms. The shock wave is initiated with a repulsive, blue-detuned light barrier, intersecting the BEC, after which two shock fronts appear. We observe breaking of these waves when the size of these waves approaches the healing length of the condensate. At this time, the wave front splits into two parts and clear fringes appear. The experiment is modeled using an effective 1D Gross-Pitaevskii-like equation and gives excellent quantitative agreement with the experiment, even though matter waves with wavelengths two orders of magnitude smaller than the healing length are present. In these experiments, no significant heating or particle loss is observed.
Published: Phys. Rev. A 80, 043606 (2009)
Download: shockwave.pdf
Archive: 0907.3989
Title: Sound propagation in a Bose-Einstein condensate at finite temperatures
Authors: R. Meppelink, S.B. Koller, and P. van der Straten
Abstract: We study the propagation of a density wave in a magnetically trapped Bose-Einstein condensate at finite temperatures. The thermal cloud is in the hydrodynamic regime and the system is therefore described by the two-fluid model. A phase-contrast imaging technique is used to image the cloud of atoms and allows us to observe small density excitations. The propagation of the density wave is used to determine the speed of sound as a function of the temperature. We find the speed of sound to be in good agreement with calculations based on the Landau two-fluid model.
Published: Phys. Rev. A 80, 043605 (2009)
Download: sound3.pdf
Archive: 0909.3455
Title: Enhanced Heat Flow in the Hydrodynamic Collisionless Regime
Authors: Meppelink, R; van Rooij, R; Vogels, JM; van der Straten, P
Abstract: We study the heat conduction of a cold, thermal cloud in a highly asymmetric trap. The cloud is axially hydrodynamic, but due to the asymmetric trap radially collisionless. By locally heating the cloud we excite a thermal dipole mode and measure its oscillation frequency and damping rate. We find an unexpectedly large heat conduction compared to the homogeneous case. The enhanced heat conduction in this regime is partially caused by atoms with a high angular momentum spiraling in trajectories around the core of the cloud. Since atoms in these trajectories are almost collisionless they strongly contribute to the heat transfer. We observe a second, oscillating hydrodynamic mode, which we identify as a standing wave sound mode.
Published: Phys. Rev. Lett 103, 095301 (2009)
Download: thermal_conductivity2.pdf
Archive: 0908.1659
Title: Atom lithography without laser cooling
Authors: B. Smeets, P. van der Straten, T. Meijer, C.G.C.H.M. Fabrie, K.A.H. van Leeuwen
Abstract: Using direct-write atom lithography, Fe nanolines are deposited with a pitch of 186 nm, a full width at half maximum (FWHM) of 50 nm, and a height of up to 6 nm. These values are achieved by relying on geometrical collimation of the atomic beam, thus without using laser collimation techniques. This opens the way for applying direct-write atom lithography to a wide variety of elements.
Published: Appl. Phys. B 98, 697-705 (2009)
Download: atom_litho.pdf
Archive: 0908.2733
Title: Cruising through molecular bound-state manifolds with radiofrequency
Authors: F. Lang, P. v. d. Straten, B. Brandstatter, G. Thalhammer, K. Winkler, P.S. Julienne, R. Grimm and J. Hecker Denschlag
Abstract: The production of ultracold molecules with their rich internal structure is currently attracting considerable interest. For future experiments, it will be important to efficiently transfer these molecules from their initial internal quantum state at production to other quantum states of interest. Transfer tools such as optical Raman schemes, radiofrequency transitions or magnetic field ramping exist, but are either technically involved or limited in their applicability. Here, we demonstrate a simple, highly efficient hybrid transfer method that overcomes a number of the previous limitations. The scheme is based on magnetically tuned mixing of two neighbouring molecular levels, which enables otherwise forbidden radiofrequency transitions between them. By repeating this process at various magnetic fields, molecules can be successively transported through a large manifold of quantum states. Applying nine transfers, we convert very weakly bound Feshbach molecules to a much more deeply bound level with a binding energy corresponding to 3.6 GHz.As an important spin-off of our experiments, we demonstrate a high-precision spectroscopy method for investigating level crossings.
Published: Nature Physics 4, 223 (2008)
Download: nphys838.pdf
Title: Coherent Optical Transfer of Feshbach Molecules to a Lower Vibrational State
Authors: K. Winkler, F. Lang, G. Thalhammer, P. v. d. Straten, R. Grimm, and J. Hecker Denschlag
Abstract: Using the technique of stimulated Raman adiabatic passage (STIRAP) we have coherently transferred ultracold 87Rb2 Feshbach molecules into a more deeply bound vibrational quantum level. Our measurements indicate a high transfer efficiency of up to 87%. Because the molecules are held in an optical lattice with not more than a single molecule per lattice site, inelastic collisions between the molecules are suppressed and we observe long molecular lifetimes of about 1 s. Using STIRAP we have created quantum superpositions of the two molecular states and tested their coherence interferometrically. These results represent an important step towards Bose-Einstein condensation of molecules in the vibrational ground state.
Published: Phys. Rev. Lett. 98, 043201 (2007)
Download: stirap.pdf
Title: Resonant superradiant backward-scattering as a source for many-particle entanglement
Authors: K.M.R. van der Stam, R. Meppelink, J.M. Vogels, J.W. Thomsen, P. van der Straten
Published: Phys. Rev. Lett. (submitted)
Archive: 0707.1465
Title: Reaching the hydrodynamic regime in a Bose-Einstein condensate by suppression of avalanches
Authors: K. M. R. van der Stam, R. Meppelink, J. M. Vogels, and P. van der Straten
Abstract: We report the realization of a Bose-Einstein condensate (BEC) in the hydrodynamic regime. The
hydrodynamic regime is reached by evaporative cooling at a relatively low density suppressing the
effect of avalanches. With the suppression of avalanches a BEC containing more than 108 atoms
is produced. The collisional opacity can be tuned from the collisionless regime to a collisional
opacity of more than 2 by compressing the trap after condensation. In the collisional opaque regime
a significant heating of the cloud at time scales shorter than half of the radial trap period is measured, which is a direct proof that the BEC is hydrodynamic.
Published: Phys. Rev. A 75, 031602 (2007)
Download: Hydro.pdf
Archive: cond-mat/0609172
Title: On the role of Penning ionization in photoassociation spectroscopy
Authors: E van der Zwan, D van Oosten, D Nehari, P van der Straten and H T C Stoof
Abstract: We study the role of Penning ionization on the photoassociation spectra of
He(2 3^S_1)-He(2 ^3S_1). The experimental set-up is discussed and experimental
results for different intensities of the probe laser are shown. For modelling the
experimental results we consider coupled-channel calculations of the crossing
of the ground state with the excited state at the Condon point. The coupledchannel
calculations are first applied to model systems, where we consider two
coupled channels without ionization, two coupled channels with ionization,
and three coupled channels, for which only one of the excited states is
ionizing. Finally, coupled-channel calculations are applied to photoassociation
of He(2 ^3S_1)-He(2 ^3S_1) and good agreement is obtained between the model and
the experimental results.
Published: J. Phys. B 39, S825-S847 (2006)
Download: multi-chan.pdf
Archive: physics/0603268
Title: Large atom number Bose-Einstein condensate of sodium
Authors: K. M. R. van der Stam, E. D. van Ooijen, R. Meppelink, J. M. Vogels, and P. van der Straten
Abstract: We describe the setup to create a large Bose-Einstein condensate containing more than 120 10^6
atoms. In the experiment a thermal beam is slowed by a Zeeman slower and captured in a dark-spot
magneto-optical trap MOT. A typical dark-spot MOT in our experiments contains 2.0 10^10 atoms
with a temperature of 320 microK and a density of about 1.0 10^11 atoms/cm3. The sample is spin
polarized in a high magnetic field before the atoms are loaded in the magnetic trap. Spin polarizing
in a high magnetic field results in an increase in the transfer efficiency by a factor of 2 compared to
experiments without spin polarizing. In the magnetic trap the cloud is cooled to degeneracy in 50 s
by evaporative cooling. To suppress the three-body losses at the end of the evaporation, the
magnetic trap is decompressed in the axial direction.
Published: Rev. Sci. Instr. 78, 013102 (2007)
Download: LargeNbec.pdf
Archive: physics/0609028
Title: Spin-polarizing cold sodium atoms in a strong magnetic field
Authors: K. M. R. van der Stam, A. Kuijk, R. Meppelink, J. M. Vogels, and P. van der Straten
Abstract: The efficiency of evaporative cooling, which is used for the creation of a Bose-Einstein condensate, depends
strongly on the number of particles at the start of the evaporation. A high efficiency can be reached by filling
the magneto-optical trap with a large number of atoms and subsequently transferring these atoms to the
magnetic trap as efficiently as possible. In our case, for sodium, this efficiency is limited to 1/3, because the
magnetic substates of the F=1 state, which is used in the trapping process, are equally populated. This limit
can be overcome by spin-polarizing the sample before the transfer. For sodium atoms, however, the improvement
is very small when it is done in a small magnetic field due to the large number of optical transitions in
combination with the high optical density. In this paper, we describe spin-polarizing sodium atoms in a high
magnetic field. The transfer efficiency is increased by a factor of 2. The high magnetic field makes the process
also more robust against variations in the magnetic field, the laser frequency, and the polarization of the laser
beam.
Published: Phys. Rev. A 73, 063412 (2006)
Download: spinpol.pdf
Archive: physics/0603255
Title: Atom lithography of Fe
Authors: E. te Sligte, B. Smeets, K. M. R. van der Stam, R. W. Herfst, P. van der Straten, H. C. W. Beijerinck, and K. A. H. van Leeuwen
Abstract: Direct write atom lithography is a technique in which nearly resonant light is used to pattern an atom
beam. Nanostructures are formed when the patterned beam falls onto a substrate. We have applied
this lithography scheme to a ferromagnetic element, using a 372 nm laser light standing wave to
pattern a beam of iron atoms. In this proof-of-principle experiment, we have deposited a grid of
50-nm-wide lines 186 nm apart. These ultraregular, large-scale, ferromagnetic wire arrays may
generate exciting new developments in the fields of spintronics and nanomagnetics. © 2004
American Institute of Physics.
Published: App. Phys. Lett. 85, 4493 (2004)
Download: smeets.pdf
Title: Laser collimation of an Fe atomic beam on a leaky transition
Authors: B. Smeets, R.W. Herfst, L.P. Maguire, E. te Sligte, P. van der Straten, H.C.W. Beijerinck, and K.A.H. van Leeuwen
Abstract: We report results of the first laser collimation of a thermal beam of Fe atoms on the leaky 5D4 - 5F5 transition, with both parallel linear pxpx and crossed linear pxpy laser polarization configurations. The measured atomic beam divergence is compared to a rate-equation model and a quantum Monte Carlo model. The experimental values for the divergence are limited by the finite laser line width, which is comparable to the natural line width of the Fe atom. In general, flux decreases with higher intensities, showing the effect of the leaky transition. At the best beam collimation a RMS = 0.17 mrad, which is for a detuning of d = -gamma and a saturation parameter of s = 6, the flux decreased to approximately 70%. Highest flux was measured for a detuning of d = -2 gamma and s = 4, reaching 135% of the uncooled value. From our measurements we estimate the total leak rate to be 1/(240 ± 40), which is in good agreement with the literature value of 1/244. The crossed linear polarization configuration is the better choice, with a slightly better collimation but the same atomic beam flux. Plugging of the largest leak would increase the flux to at least 80% of the closed transition value, resulting in better contrast for atom lithography.
Published: Appl. Phys. B 80, 833-839 (2005)
Download: smeets2.pdf
Title: Barrier-limited surface diffusion in atom lithography
Authors: E. te Sligte, K. M. R. van der Stam, B. Smeets, P. van der Straten, R. E. Scholten, H. C. W. Beijerinck, and K. A. H. van Leeuwen
Abstract: Thermally activated surface diffusion has a strong influence on structure widths in atom lithography.
We investigate the effects of two barriers to thermally activated atomic diffusion on atom
lithography: a thermally activated Ehrlich-Schwoebel barrier, and pollution from the residual
gas in the vacuum system. We performed kinetic Monte Carlo simulations using a one-dimensional
surface grid. We find that the ES barrier fails to explain the lack of temperature dependence
observed experimentally [W. R. Anderson et al., Phys. Rev. A 59, 2476 1999]. The dependencies
of the structure width on temperature, vacuum conditions, and beam characteristics can be explained
using the pollutant adatom hypothesis. Only the variation of structure width with deposition
duration was not entirely reproduced by this model. We attribute this to the one-dimensional nature
of our simulations. These results demonstrate that barrier-limited diffusion can play an important
role in atom lithography, and that pollutant adatoms are a likely candidate barrier.
Published: J. App. Phys. 43, 41-44 (2005)
Download: sligte.pdf
Title: Bose-Einstein condensatie
Authors: E.D. van Ooijen, K.M.R. van der Stam, D. van Oosten, F. Ditewig, J. van der Weg, J.M. Vogels en P. van der Straten
Published: Nevac blad, Jaargang 43, nr. 2, p. 41-44 (2005)
Download: nevac.pdf
Title: Atomic Trapping and Cooling
Authors: P. van der Straten and H.J. Metcalf
Published: Wiley-VCH Encyclopedia of physics
Download: A29a.pdf
Title: Laser cooling simulation based on the semiclassical approach
Authors: B. Smeets, R.W. Herfst, E. te Sligte, P. van der Straten, H.C.W. Beijerinck, and K.A.H. van Leeuwen
Abstract: We investigate the region of validity of the semiclassical approach to simulating laser cooling. We conclude that for the commonly used pi_x-pi_y polarization-gradient configuration, the semiclassical approach is valid only for transitions with recoil parameters omega_r on the order of 10-4 or less. For the standard laser-cooling transitions only the transitions in Rb and Cs satisfy this condition. For the Doppler and sigma+-sigma- polarization-gradient configuration the semiclassical approach is valid for most of the commonly used transitions; however, the expected gain in execution speed compared with quantum Monte Carlo calculations has been realized only in part. A drastic reduction in calculation time is to be expected by implementing an analytical approach to the long-term contribution of the diffusion coefficient
Published: J. Opt. Soc. Am. B 22, 2372 (2005)
Download: simu.pdf
Title: Rotationally induced Penning ionization of ultracold photoassociated helium dimers
Authors: J. Leonard, A. P. Mosk, M. Walhout, M. Leduc, M. van Rijnbach, D. Nehari and P. van der Straten
Abstract: We have studied photoassociation of metastable 23S1 helium atoms near the 23S1-23P2
asymptote by both ion detection in a magneto-optical trap and trap-loss measurements in a
magnetic trap. A detailed comparison between the results of the two experiments gives insight
into the mechanism of the Penning ionization process. We have identified four series of
resonances corresponding to vibrational molecular levels belonging to different rotational states in
two potentials. The corresponding spin states become quasi-purely quintet at small interatomic
distance, and Penning ionization is inhibited by spin conservation rules. Only a weak rotational
coupling is responsible for the contamination by singlet spin states leading to a detectable ion
signal. However, for one of these series Bose statistics does not enable the rotational coupling
and the series detected through trap-loss does not give rise to su±cient ionization for detection.
Published: Eur. Phys. Lett. 70, 190-196 (2005)
Download: ensutrecht.pdf
Archive: cond-mat/0502401
Title: Inelastic light scattering from a Mott insulator
Authors: D. van Oosten, D. B. M. Dickerscheid, B. Farid, P. van der Straten, and H. T. C. Stoof
Abstract: We propose to use Bragg spectroscopy to measure the excitation
spectrum of the Mott in- sulator state of an atomic Bose gas in an
optical lattice. We calculate the structure factor of the Mott
insulator taking into account both the selfenergy corrections of the
atoms and the corresponding dressing of the atom-photon interaction.
We determine the scattering rate of photons in the stimulated Raman
transition and show that by measuring this scattering rate in an
experiment, in particular the excitation gap of the Mott insulator can
be determined.
Published: Phys. Rev. A, 71, 021601(R) (2005)
Download: inelastic.pdf
Archive: cond-mat/0405492
Title: Laser frequency stabilization using Doppler-free bichromatic spectroscopy
Authors: E.D. van Ooijen, G. Katgert, and P. van der Straten
Abstract: We report on a method of laser stabilization,
Doppler-free bichromatic lock (DFBL) in which we use the differential
signal of two Lamb-dips shifted in frequency by means
of an AOM. We show that this method provides us with a tool
for precision locking to a molecular or atomic transition and
is relatively simple to implement in a diode or dye laser system
without the use of a frequency modulation of the laser or
lock-in amplifier. A simple model description of this method is
presented and the experimental realization is shown for a dye
laser at the Na D1 and D2 line.
Published: App. Phys. B 79, 57-59 (2004)
Download: apb1522.pdf
Title: Analysis of photoassociation spectra for giant helium dimers
Authors: J. Léonard, A. P. Mosk, M. Walhout, P. van der Straten, M. Leduc, and C. Cohen-Tannoudji
Abstract: We perform a theoretical analysis to interpret the spectra of purely long-range helium dimers produced by
photoassociation (PA) in an ultracold gas of metastable helium atoms. The experimental spectrum obtained
with the PA laser tuned closed to the 2 3S12 3P0 atomic line has been reported in a previous paper. Here, we
first focus on the corrections to be applied to the measured resonance frequencies in order to infer the
molecular binding energies. We then present a calculation of the vibrational spectra for the purely long-range
molecular states, using adiabatic potentials obtained from perturbation theory. With retardation effects taken
into account, the agreement between experimental and theoretical determinations of the spectrum for the 0u+
purely long-range potential well is very good. The results yield a determination of the lifetime of the 2 3P
atomic state.
Published: Phys. Rev. A 69, 032702 (2004)
Download: longrangehelium.pdf
Archive: quant-ph/0310006
Title: Mott insulators in an optical lattice with high filling factors
Authors: D. van Oosten, P. van der Straten, and H.T.C. Stoof
Abstract: We discuss the superfluid to Mott insulator transition of an atomic Bose
gas in an optical lattice with high filling factors. We show that also in
this multi-band situation, the long-wavelength physics is described by a
single-band Bose-Hubbard model. We determine the many-body renormalization
of the tunneling and interaction parameters in the effective Bose-Hubbard
Hamiltonian, and consider the resulting model at nonzero temperatures. We
show that in particular for a one or two-dimensional optical lattice, the
Mott insulator phase is more difficult to realize than anticipated
previously.
Published: Phys. Rev. A 67, 033606 (2003)
Download: numberfluct.pdf
Archive: cond-mat/0205066
Title: Photoassociation of ultracold sodium atoms
Authors: A. Amelink and P. van der Straten
Abstract: Using ultra-cold atoms a new technique of
photoassociation spectroscopy has been developed. The technique has an
unprecedented resolution and can be used to obtain high-resolution data on
singly and doubly excited states of diatomic molecules. We describe the
principle of the technique and show results for one specific case, namely
the Na_2 molecule.
Published: Phys. Scr. 68, C82-89 (2003)
Download: camp.pdf
Title: Laser frequency stabilization using an Fe-Ar hollow cathode discharge cell
Authors: B. Smeets, R. C. M. Bosch, P. van der Straten, E. te Sligte, R.E. Scholten, H. C. W. Beijerinck and K.A.H. van Leeuwen
Abstract: Polarization spectroscopy of an Fe-Ar hollow cathode discharge cell was
used to lock a frequency doubled Ti:Sapphire laser to the 372 nm 5D4->5F5
transition of 56Fe. The discharge cell produced a density of 10^18 m^-3
ground state 56Fe atoms at a temperature of 650 K, a density comparable to
a conventional oven at 1500 K. Saturated absorption spectroscopy and two
schemes of polarization spectroscopy were compared with respect to
signal-to-background ratio and the ef- fect of velocity changing collisions.
The laser was locked within 0.2 MHz for hours by feedback of the dispersive
polarization spectroscopy signal.
Published: submitted to Appl. Phys. B (2003)
Download: hollow_cathode.pdf
Title: Laser cooling and trapping of atoms
Authors: H.J. Metcalf and P. van der Straten
Abstract: This article presents a review of some of the principal techniques
of laser cooling and trapping that have been developed during the
past 20 years. Its approach is primarily experimental, but its
quantitative descriptions are consistent in notation with most of
the theoretical literature.
Published: The Optics Encyclopedia, pg. 975-1014, eds. Brown, Creath, Kogelnik, Kriss,
Schmit, Weber, Wiley-VCH, Weinheim, Germany, 2004.
Download: vch.pdf
Title: Laser cooling and trapping of atoms
Authors: H.J. Metcalf and P. van der Straten
Abstract: This paper presents a review of some of the principal techniques of laser
cooling and trapping that have been developed during the past 20 years. Its
approach is primarily experimental, but its quantitative descriptions are
consistent in notation with most of the theoretical literature. It begins
with a simplified introduction to optical forces on atoms, including both
cooling and trapping. Then its three main sections discuss its three
selected features of 1) quantization of atomic motion, 2) effects of the
multilevel structure of atoms, and 3) the effects of polychromatic light.
Each of these features is an expansion in a different direction from the
simplest model of a classical, two level atom moving in a monochromatic
laser field.
Published: J. Opt. Soc. Am. B 20, 887 (2003)
Download: visby.pdf
Title: The Quest for BEC
Authors: Peter van der Straten and Harold Metcalf
Abstract: Laser cooling of atoms was suggested in the 1970's as a way to perform
better laser spectroscopy. Since it has been very successful in producing
cold, dense sample of atoms it is nowadays used in many atomic physics
experiments. In this lecture note we will concentrate on those techniques,
that are used to cool and trap atoms to phase space densities sufficient to
observe a phase transition of the atoms to a Bose-Einstein condensation.
Published: Interaction in Ultracold Gases, ed. M. Weidemuller and C. Zimmerman, pg. 1-63, Wiley-VCH, Germany, 2003
Download: heidelberg.pdf
Title: Energy distributions of He^+ and He_2^+ ions formed in ultracold He(2
^3S_1)+He(2 ^3P_2) collisions
Authors: M. Pieksma, M. Cizek, J. W. Thomsen, P. van der Straten, and A. Niehaus
Abstract: Energy distributions of He^+ and He_2^+ ions produced in ultracold He(2
^3S_1)+He(2 ^3P_2) collisions are presented. These helium metastable atoms are
trapped and cooled in a magneto-optical trap, and have a temperature of
1.160.2 mK. Initial kinetic energies of the product He^+ and He_2^+ ions are
analyzed in energy, using a weak electrostatic extraction field in
combination with a time-of-flight technique. A pronounced structure is
observed in the He1 ion distribution, which can be well explained by a
theoretical model that considers the avoided crossings between only three
metastable ^3\Sigma_g^+ states of the transient He_2 molecule. The measured
He_2^+ distribution has a width that is consistent with the maximum recoil
energy of 1.1 meV.
Published: Phys. Rev. A 66, 022703 (2002)
Download: he_ion.pdf
Title: Magnetic nanodots from atomic Fe: Can it be done?
Authors: E. te Sligte, R.C.M. Bosch, B. Smeets, P. van der Straten, H.C.W. Beijerinck, and K.A.H. van Leeuwen
Abstract: Laser focusing of Fe atoms offers the possibility of creating separate
magnetic structures on a scale of 10 nm with exact periodicity. This can be
done by using the parabolic minima of the potential generated by a standing
light wave as focusing lenses. To achieve the desired 10-nm resolution, we
need to suppress chromatic and spherical aberrations, as well as prevent
structure broadening caused by the divergence of the incoming beam.
Chromatic aberrations are suppressed by the development of a supersonic Fe
beam source with speed ratio S=11+-1. This beam has an intensity of 3 x
10^15 sr-1 s-1. The spherical aberrations of the standing light wave will be
suppressed by aperturing with beam masks containing 100-nm slits at 744-nm
intervals. The beam divergence can be reduced by application of laser
cooling to reduce the transverse velocity. We have constructed a laser
system capable of delivering over 500 mW of laser light at 372 nm, the
wavelength of the ^5D_4->^5F_5 atomic transition of ^56Fe we intend to use
for laser cooling. Application of polarization spectroscopy to a hollow
cathode discharge results in a locking system holding the laser continuously
within 2 MHz of the desired frequency.
Published: Proc. Nat. Acad. Sci. 99, 6509 (2002)
Download: nanodots.pdf
Title: Supersonic Fe beam source for chromatic aberration-free laser
focusing of atoms
Authors: R.C.M. Bosch, H.C.W. Beijerinck, P. van der Straten, and K.A.H. van Leeuwen
Abstract: A monochromatic Fe beam is generated by heated supersonic expansion of
argon seeded with Fe vapor. At a nozzle temperature of 1930 K and 800 torr
argon inlet pressure the Fe beam has an axial velocity spread of 8% and
intensity of 3 x 10^15 sr-1 s-1, corresponding to a deposition rate of 10
nm/h at 150 mm from the nozzle. The two-chamber alumina crucibles are
chemically stable for liquid Fe. With 400 mm3 Fe we have operated for more
than 200 hours without reloading. The power consumption at 1930 K is 750 W.
Temperature stability at constant power (without feedback) is better than 30
K. The source is intended for deposition of nanostructures by laser focusing
of the Fe beam. The small axial velocity spread virtually eliminates the
increase in focal spot size due to chromatic aberration.
Published: Eur. Phys. J. Appl. Phys., 18, 221 (2002)
Download: Fe_source.pdf
Title: Laser cooling and trapping
Authors: H.J. Metcalf and P. van der Straten
Published: In Handbook of Optics III, ed. M. Bass, J.M. Enoch, E. van Strykland, and
B. Wolfe, McGraw-Hill, New York, 2002
Download: handpubl.pdf
Title: Polarization in Collisions between Ultra-cold Sodium Atoms
Authors: H.G.M. Heideman, P. van der Straten and A. Amelink
Abstract: We have studied polarization effects in the photoassociation
of two colliding ultra-cold Na-atoms. In a first step the two colliding
atoms absorb a laser photon to associate to a singly excited molecule in a
bound state of the 0_g^- or 1_g potential. In a second step the excited
molecule absorbs a second photon and is further excited to a bound level in
a doubly excited potential (0_u^- or 1_u which are autoionizing). By
measuring the produced ions with parallel and perpendicular polarizations of
the two laser beams used possible polarization effects can be studied. We
find strong polarization effects if a 0_g^- state is used as the
intermediate state and very little or no effects at all if a 1_g state is
used.
Published: To be published in Phys. Rev. Lett.
Download: pol_afh_pas.pdf
Title: Quantum phases in an optical lattice
Authors: D. van Oosten, P. van der Straten, and H. T. C. Stoof
Abstract: We present the zero-temperature
phase diagram of bosonic atoms in an optical lattice, using two different
mean-field approaches. The phase diagram consists of various insulating
phases and a superfluid phase. We explore the nature of the insulating phase
by calculating both the quasiparticle and quasihole dispersion relation. We
also determine the parameters of our single band Bose-Hubbard model in terms
of the microscopic parameters of the atoms in the optical lattice.
Published: Phys. Rev. A 63, 053601 (2001)
Download: hubbard.pdf
Archive: cond-mat/0011108
Title: Construction of a low velocity metastable Helium atomic beam
Authors: G.R. Woestenenk, J.W. Thomsen, M. van Rijnbach, P. van der Straten, and A. Niehaus
Abstract: We have constructed an atomic beam of metastable helium atoms
\Hetts\ with a mean velocity of 300 m/s (15 K) and a yield of
3\times10^12 atoms/s sr. The metastable atoms are produced in a
DC-discharge in a cryogenic environment cooled by liquid helium. Using a
hexapole magnetic lens we have increased further the beam intensity by
focusing the metastable atoms. Initial studies show a factor of 2.5 increase
in the beam flux but more is expected when the hexapole is constructed from
permanent hexapole magnets. The \Hetts\ atoms are subsequently loaded into a
magneto-optical trap (MOT).
Published: Rev. Sci. Instr. 72, 3842 (2001)
Download: source.pdf
Title: Penning Ionization in Optical Collisions
Authors: G. Woestenenk, P. van der Straten, and A. Niehaus
Abstract: We have studied binary collisions of cold He (2^3S_1) atoms under the
influence of nearly-resonant light. The light is tuned below the atomic
\sptrans\ transition. A semi-classical model is developed, calculating the
absolute ionization rate as a function of the detuning of the light. The
calculated ionization rate is compared with measurements and with values
that have appeared in the literature. Good agreement is found between theory
and measurements.
Published: To be published in Phys. Rev. A (2001)
Download: optcol.pdf
Title: Spectroscopy of autoionizing doubly excited states in ultracold Na_2
molecules produced by photoassociation
Authors: A. Amelink, K.M. Jones, P.D. Lett, P. van der Straten and H.G.M. Heideman
Abstract: We have performed photoassociation spectroscopy to study the doubly
excited states of Na2 involved in the associative ionization of colliding
Na(3P) atoms. Rovibrational levels of two doubly excited potentials
connected to the P3/2+P3/2 asymptote, one of 0u+ and one of 1u symmetry,
have been identified. These two doubly excited potentials dominate the route
to ionization used in photoassociation experiments of cold Na. Binding
energies and rotational constants for all the vibrational levels with
binding energies <50 GHz have been measured. The asymptotic potentials and
short-range ionization probabilities are extracted from the data.
Published: Phys. Rev. A 61, 042707 (2000)
Download: pseudo2col.pdf
Title: Photo-association spectroscopy of cold He(2~^3S) atoms
Authors: N. Herschbach, P. J. J. Tol, W. Vassen, W. Hogervorst, G. Woestenenk, J. W. Thomsen, P. van der Straten, and A. Niehaus
Abstract: We observe vibrational states by photo-association spectroscopy of cold
He(2~^3S) atoms. Photo-association resonances are detected as peaks in the
Penning ionization rate over a frequency range of 20~GHz below the atomic
2~^3S_1~-- 2~^3P_2 transition frequency. We have observed three
vibrational series, of which two can be identified. A possible mechanism to
explain the observed increase of the Penning ionization rate is discussed.
Published: Phys. Rev. Lett. 84, 1874 (2000)
Download: pashe.pdf
Title: Single-color photoassociative ionization of ultracold sodium: the region between -5 and 0 GHz
Authors: A. Amelink, K.M. Jones, P.D. Lett, P. van der Straten and H.G.M. Heideman
Abstract: We have measured the rate of production of
Na_2^+ ions in collisions of ultracold Na atoms held in a
magneto-optical trap (MOT) as a function of probe laser detuning using a
single-color probe beam. The ion rate is measured with the atoms mainly in
the 3S(f=2) level (``bright MOT'') or the 3S(f=1) level (``dark MOT'').
Using recent experimental information about the doubly-excited autoionizing
states of Na_2 we find that the large structures in the first 5 GHz red of
the atomic transition frequency are due to a doubly-resonant excitation
process with levels in the 0_g^- potential (asymptotically connected to
3S_1/2+3P_3/2) as the intermediate states, and levels in the 0_u^-
and 1_u potentials (asymptotically connected to 3P_3/2+3P_3/2) as
the final autoionizing states. We can account for nearly all of the observed
structure in this region of the spectra for both the bright and dark MOT.
Published: Phys. Rev. A 62, 013408 (2000)
Download: 5GHz.pdf
Title: Laser cooling and trapping
Authors: H.J. Metcalf and P. van der Straten
Abstract: The Book on Laser Cooling and Trapping
Published: Springer Verlag, New York, 1999
Title: Collisions between ultracold metastable He atoms
Authors: G. Woestenenk, H.C. Mastwijk, J.W. Thomsen, P. van der Straten, M. Pieksma, M. van Rijnbach, A. Niehaus
Abstract: We present experimental data on collisions between excited He-atoms
occurring in a magneto-optical trap (MOT) at a temperature of 1.1 mK.
He(23S)-atoms produced in a discharge are pre-cooled and trapped using the
He(23S)-He(23P2) transition for laser manipulation. Measurements of the
Penning ionization rate as a function of the MOT-laser frequency are
presented and theoretically analyzed. The analysis, based on a model which
is presented in detail for the first time, leads to a good understanding of
the complex nature of optical collisions. Further, first and preliminary
measurements of the kinetic energy distributions of He_2^+- and He^+-ions
formed by Penning ionization in optical collisions are presented.
Published: Nucl. Instr. and Meth. in Phys. Res. B 154, 194-203 (1999)
Download: woestenenk-nimb.pdf
Title: Photo Associative Reactions of Laser Cooled Sodium
Authors: P. van der Straten
Abstract: We describe the novel technique of dynamical spectroscopy
of transient molecules. We apply this technique to the study of ultra-cold
collisions of Na atoms at 200 muK. By careful choice of laser intensities
and detunings we can unravel the dynamics of these collisions and obtain
information on interactions taking place at internuclear distances of
100-1000 a_0 and interaction energies below 1 mu-eV.
Published: In Photonic, electronic and atomic collisions, ed. F. Aumayr and H.
Winter, World Scientific, Singapore, 1998
Download: icpeac97.pdf
Title: Optical collisions of cold, metastable helium atoms
Authors: H.C. Mastwijk, J.W. Thomsen, P. van der Straten and A. Niehaus
Abstract: We have studied the optical collisions
of cold, metastable helium atoms in a magneto-optical trap. We have detected
the rate of Penning and associative ionization of two metastable helium
atoms at a temperature of 1 mK with and without nearly resonant light. We
find that the associative ionization rate is increased with more than a
factor 20 due to the presence of the light field. The absolute ionization
rate near resonance of \EE{(1.9\pm0.8)}{-9} \ccps\ for the optical
collision differs two orders of magnitude with the rate reported by Bardou
\etal\ (\Journal{Europhys. Lett.}{20}{681}{1992}). Our experimental findings
are in good agreement with theory. We present a simple, semi-classical
model, which accounts for all the observed features.
Published: Phys. Rev. Lett. 80, 5516 (1998)
Download: optical.pdf
Title: Photo induced collisions with laser cooled He* atoms
Authors: H.C. Mastwijk, M. van Rijnbach, J.W. Thomsen, P. van der Straten and A. Niehaus
Abstract: This paper presents an experimental
investigation of cold collisions between metastable Helium atoms in an
optical trap at 1mK. Penning (PI) and associative (AI) ionization reactions
are distinguished using a mass spectrometer and studied under influence of
near resonant laser light. Sensitive behavior of the ion rate is observed
when the laser is tuned close to resonance. Experimental findings are well
described, on an absolute scale, by a semi-classical model we have developed
for optical collisions and by a modified Julienne-Vigue model.
Published: Eur. Phys. J. D 4, 131-137 (1998)
Download: phid.pdf
Title: Vibrational state distribution of Na_2^+-ions created in ultracold collisions
Authors: J.J. Blange, J.M. Zijlstra, A. Amelink, X. Urbain, H. Rudolph, P. van
der Straten, H.C.W. Beijerinck, and H.G.M. Heideman
Abstract: The vibrational distribution P(v) of Na_2^+ ions
created in ultracold collisions in a magneto-optical trap has been
determined. Only two vibrational states with v = 2 and 3 are populated and
we find P(2)=0.29\pm0.02 and P(3)=0.71\pm0.02. The results provide
conclusive evidence that the ionization mechanism is photo-associative
autoionization, and not photo-associative photoionization and will form a
fundamental test for the theoretical description of the process.
Published: Phys. Rev. Lett. 78, 3089 (1997)
Download: vibratie.pdf
Title: Diagnostic technique for Zeeman-compensated atomic beam slowing: Technique and results
Authors: P.A. Molenaar, P. van der Straten, H.G.M. Heideman and H. Metcalf
Abstract: We have developed a new diagnostic tool for the study of Zeeman-compensated slowing
of an alkali atomic beam. Our time-of-flight technique measures the
longitudinal velocity distribution of the slowed atoms with a resolution
below the Doppler limit of 30 cm/s. Furthermore it can map the position and
velocity distribution of atoms in either ground hyperfine level inside the
solenoid without any devices inside the solenoid. The technique reveals the
optical pumping effects interfering with the slowing process and shows in
detail how the slowing within the solenoid proceeds.
Published: Phys. Rev. A 55, 605 (1997)
Download: vspace.pdf
Title: Koud, kouder, koudst
Authors: Peter van der Straten
Abstract: In november 1997 maakte de Nobel commissie bekend, dat de
Nobelprijs voor de natuurkunde voor 1997 uitgereikt zal worden aan Bill
Phillips, Steven Chu en Claude Cohen-Tannoudji. Zij krijgen de prijs
voor het werk, dat ze verricht hebben op het gebied van de laserkoeling van
atomen. Hoewel de Nobelprijs zoals elk
jaar aan personen wordt uitgereikt, wordt de prijs van dit jaar vooral
beschouwd als een prijs voor het gehele gebied.
Published: De vakidioot
Download: vakidioot.pdf
Title: Dynamische spectroscopie van kortlevende moleculen
Authors: Arjen Amelink, Peter van der Straten en Henk Heideman
Abstract: De afgelopen 10 jaar hebben laserkoelings-technieken een geweldige
ontwikkeling doorgemaakt. In laboratoria over de hele wereld worden nu
routinematig atomen geproduceerd met temperaturen in het mK-regime en
dichtheden van 10^12/cm^3. Het werkpaard in de laserkoeling is de
magnetisch-optische val (magneto-optical trap, oftewel MOT), waarbij
zes laserbundels op ingenieuze wijze gecombineerd met een niet homogeen
magneetveld de atomen tegelijkertijd koelen en vangen. De lage temperatuur
en de voldoende hoge dichtheid zorgen ervoor, dat in de MOT interacties
kunnen worden bestudeerd in een nieuw regime, het regime van de ultra-koude
botsingen.
Published: Van A tot Q 11, 20, (1997)
Download: vatq.pdf
Title: Long-Range Predissociation in Two-Color Photoassociation of Ultracold Na Atoms
Authors: P.A. Molenaar, P. van der Straten and H.G.M. Heideman
Abstract: We report
two-color photo-associative ionization of sodium in a Magneto-Optical Trap.
The experimental results yield information on both singly and doubly excited
states. For the singly-excited states we find that the purely long range
0_g^- state can sustain up to 20 bound states. Higher bound states
predissociate into the 3^2P_3/2 + 3^2S_1/2(F_g=1) dissociation
continuum due to avoided crossings of the constituting hyperfine components
of this potential with those of other molecular symmetries. Based on
symmetry and energy considerations we argue that the doubly-excited 1_u
state ( adiabatically connected to 2^3\Delta_u) remains autoionizing even
when excited only a few GHz above the dissociation continuum.\\
Published: Phys. Rev. Lett. 77, 1460 (1996).
Download: twocolor.pdf
Title: Force, diffusion and channeling in sub-Doppler laser cooling
Authors: M.D. Hoogerland, H.F.P. de Bie, H.C.W. Beijerinck, E.J.D. Vredenbregt,
K.A.H. van Leeuwen, P. van der Straten and H.J. Metcalf
Abstract: We present an extensive
set of measurements on one-dimensional sub-Doppler cooling and channeling in
counterpropagating light beams. The experimental method consists of the
measurement of the profile of an initially sub-recoil collimated atomic
beam, which is deflected by the interaction with the light field. The
initial velocity of the atoms in the direction of the laser beams is varied
in the range -1 \leq v_{\perp} (ms^-1) \leq 1 by changing the
angle between atomic and laser beams. For the orthogonal circular
polarization (\sigma^+ \sigma^-) sub-Doppler cooling configuration, the
force and the diffusion coefficient characterizing the cooling process have
been determined as a function of the initial velocity v_{\perp} from the
average deflection and broadening of the atomic beam profile. We observe
transient effects due to the slow evolution of the distribution over the
magnetic sublevels to an equilibrium. The experimental results agree very
well with Quantum Monte-Carlo simulations and semiclassical calculations.
For the orthogonal linear polarization (\pi^x\pi^y) configuration, we
demonstrate the validity of the well-known Sisyphus picture for the cooling
mechanism by comparing the experimental data to the results of a simple
semiclassical Monte-Carlo model incorporating only the dipole force and
optical pumping. In weak standing waves of either circular or linear
polarization, we demonstrate the characteristic features of channeling.
Published: Phys. Rev. A 54, 3206 (1996)
Download: neon_force.pdf
Title: Sideband generation using a Fiber-Optical Modulator (FOM)
Authors: P.A. Molenaar, M.D. Steenbergen and P. van der Straten
Abstract: We have constructed a Fiber Optical
Modulator (FOM), which produces on the incoming laser frequency shifts of
the order of 30 GHz. The modulator consist of a fiber of sufficient length,
where the transmission is saturated by stimulated Brillouin scattering
(SBS). The frequency shift is determined by the parameters of the fiber and
is fixed. The ratio of intensity of the shifted frequency and the incoming
frequency can be varied over a large range by varying the incoming intensity
with respect to the threshold intensity for SBS.
Download: sbs.pdf
Title: Quantum trajectory pictures of laser cooling
Authors: G. Nienhuis, J. de Kloe and P. van der Straten
Abstract: We have applied the method of single
atom trajectories to study the mechanism behind some cooling schemes in
laser cooling. In several cases we recognize the cooling mechanism as being
due to a ``Sisyphus'' process, where the atoms move in a spatially varying
light shift potential and are optically pumped towards the most light
shifted states. In other cases we identify a ``Sisyphus'' process in time,
where the light shift is constant and the force on the atom alternates
between positive and negative. This process is interrupted by quantum jumps
at random instants and in each case we depict the mechanism leading to a
cooling force on the atom. In the special case of sub-Doppler laser cooling
in a strong magnetic field we obtain 12 jump operators and identify the jump
operators responsible for the cooling. The versatility of the single atom
trajectory method allows it to be applied to any cooling process and is
therefore a very valuable tool in unraveling the physical mechanisms behind
cooling processes.
Published: J. Opt. Soc. Am 12, 520 (1995)
Download: mcwf.pdf
Title: Force measurements on sub-Doppler cooling processes
Authors: M.D. Hoogerland, H.F.P. de Bie, H.C.W. Beijerinck, K.A.H. van Leeuwen, P. v.d. Straten, E. Vredenbregt, and H.J. Metcalf
Abstract: We present the first direct measurements of the velocity dependence of
the average force and diffusion constant for the metastable neon atoms in a
one-dimensional sigma + sigma - laser cooling configuration. Force and
diffusion are determined, respectively, from the deflection and broadening
of a highly collimated atomic beam by its interaction with a pair of
counter-running laser beams. The interaction time is much shorter than the
characteristic damping time of the cooling process. The resulted force and
diffusion measurements are compared with the results of both semiclassical
and quantum Monte Carlo calculations.
Published: Phys. Rev. Lett. 72, 3332 (1994)
Download: neon_prl.pdf
Title: Cooling and Trapping of Neutral Particles
Authors: H.J. Metcalf and P. v.d. Straten
Abstract: This article describes recent experiments that are directed at reduction
and control of thermal motion. There are many applications for a collection
of slowly moving and/or monovelocity atoms. We can expect new and
exquisitely more sensitive atomic beam experiments to probe the electrical
neutrality of matter, the effects of parity violating interactions,
gravitation, quantum statistics in optical absorption and emission, and
other fundamental interactions. Such atoms could serve as an ideal target
or beam for a variety of low energy and/or high energy-resolution scattering
experiments, chemical reaction studies, or surface studies.
Published: Phys. Rep. 244, 203 (1994)
Download: phsrp.pdf
Title: Laser Cooling at Low Intensity in a Strong Magnetic Field
Authors: P. van der Straten, S-Q. Shang, B. Sheehy, H. Metcalf and G. Nienhuis
Abstract: We have studied theoretically and experimentally the effect of a relatively
strong magnetic field on sub-Doppler laser cooling in a one-dimensional
optical molasses. We used the operator description of laser cooling with
the Larmor precession frequency \omega_Z much stronger then the optical
pumping rate. We found velocity selective resonances (VSR) in the force at
velocities v_r=n \omega_Z, with n=0,\pm 1, \pm 2 for both the
scattering and redistribution force operators. These depend on the relative
direction of the magnetic field and the polarization vectors of the light
beams. Analytical results for the force on the atom are obtained in two
cases that illustrate the effect of the VSR on the force. These formulas
are compared with numerical calculations of the force. We also discovered a
new redistribution mechanism that relies on the gradient of the eigenstates
of the light shift operator, with eigenvalues that are independent of
position so that a `Sisyphus' picture does not apply. The theory is compared
with many experimental results and excellent agreement is found. We believe
that all essential features of laser cooling at low intensity are well
described by this operator theory.
Published: Phys. Rev. A 47, 4160 (1993)
Download: magcool.pdf
Title: Magnetically Induced Laser Cooling for Ne*: Approaching the Recoil Limit
Authors: M.D. Hoogerland, H.C.W. Beijerinck, K.A.H. van Leeuwen, P. v.d. Straten, and H.J. Metcalf,
Abstract: Magnetically induced laser cooling to temperatures close to the recoil
limit is investigated in one dimension. For a metastable neon beam, we
present high precision measurements investigating the actual temperature
limit in this cooling process. Using time-of-flight techniques to reduce the
effect of the longitudinal velocity spread, we observe cooling at small
magnetic field toward v=0 with an rms width of the distribution of 5.4
cm/s, well below the Doppler limit. At a larger magnetic field (0.4 Gauss)
the velocity-selective resonances are extremely sharp. Here we find the rms
width of the distribution to be 3.4 cm/s, only 1.1 times the recoil speed
hbar k/M, corresponding to a temperature T=2.7 muK.
Published: Eur. Phys. Lett. 19, 669, (1992)
Download: neon_recoil_paper.pdf
Comments can be mailed to:
P.vanderStraten@phys.uu.nl