971 research outputs found
Nanolithography with metastable helium atoms in a high-power standing-wave light field
We have created periodic nanoscale structures in a gold substrate with a
lithography process using metastable triplet helium atoms that damage a
hydrofobic resist layer on top of the substrate. A beam of metastable helium
atoms is transversely cooled and guided through an intense standing-wave light
field. Compared to commonly used low-power optical masks, a high-power light
field (saturation parameter of 10E7) increases the confinement of the atoms in
the standing-wave considerably, and makes the alignment of the experimental
setup less critical. Due to the high internal energy of the metastable helium
atoms (20 eV), a dose of only one atom per resist molecule is required. With an
exposure time of only eight minutes, parallel lines with a separation of 542 nm
and a width of 100 nm (1/11th of the wavelength used for the optical mask) are
created.Comment: 5 pages, 5 figure
Efficient temporal compression of coherent nanosecond pulses in compact SBS generator-amplifier setup
Numerical simulations on the motion of atoms travelling through a standing-wave light field
The motion of metastable helium atoms travelling through a standing light
wave is investigated with a semi-classical numerical model. The results of a
calculation including the velocity dependence of the dipole force are compared
with those of the commonly used approach, which assumes a conservative dipole
force. The comparison is made for two atom guiding regimes that can be used for
the production of nanostructure arrays; a low power regime, where the atoms are
focused in a standing wave by the dipole force, and a higher power regime, in
which the atoms channel along the potential minima of the light field. In the
low power regime the differences between the two models are negligible and both
models show that, for lithography purposes, pattern widths of 150 nm can be
achieved. In the high power channelling regime the conservative force model,
predicting 100 nm features, is shown to break down. The model that incorporates
velocity dependence, resulting in a structure size of 40 nm, remains valid, as
demonstrated by a comparison with quantum Monte-Carlo wavefunction
calculations.Comment: 9 pages, 4 figure
XUV-laser spectrometer for direct absorption measurements; application to CO in the wavelength range 95-97 nm.
High-power parametric amplification of 11.8-fs laser pulses with carrier-envelope phase control
Phase-stable parametric chirped-pulse amplification of ultrashort pulses from a carrier-envelope phase-stabilized mode-locked Ti:sapphire oscillator (11.0 fs) to 0.25 mJ/pulse at 1 kHz is demonstrated. Compression with a grating compressor and a LCD shaper yields near-Fourier-limited 11.8-fs pulses with an energy of 0.12 mJ. The amplifier is pumped by 532-nm pulses from a synchronized mode-locked laser, Nd:YAG amplifier system. This approach is shown to be promising for the next generation of ultrafast amplifiers aimed at producing terawatt-level phase-controlled few-cycle laser pulses. (C) 2005 Optical Society of America
A Degenerate Bose-Fermi Mixture of Metastable Atoms
We report the observation of simultaneous quantum degeneracy in a dilute
gaseous Bose-Fermi mixture of metastable atoms. Sympathetic cooling of helium-3
(fermion) by helium-4 (boson), both in the lowest triplet state, allows us to
produce ensembles containing more than 10^6 atoms of each isotope at
temperatures below 1 micro-Kelvin, and achieve a fermionic degeneracy parameter
of T/Tf=0.45. Due to their high internal energy, the detection of individual
metastable atoms with sub-nanosecond time resolution is possible, permitting
the study of bosonic and fermionic quantum gases with unprecedented precision.
This may lead to metastable helium becoming the mainstay of quantum atom
optics.Comment: 4 pages, 3 figures submitted to PR
A Large Atom Number Metastable Helium Bose-Einstein Condensate
We have produced a Bose-Einstein condensate of metastable helium (4He*)
containing over 1.5x10^7 atoms, which is a factor of 25 higher than previously
achieved. The improved starting conditions for evaporative cooling are obtained
by applying one-dimensional Doppler cooling inside a magnetic trap. The same
technique is successfully used to cool the spin-polarized fermionic isotope
(3He*), for which thermalizing collisions are highly suppressed. Our detection
techniques include absorption imaging, time-of-flight measurements on a
microchannel plate detector and ion counting to monitor the formation and decay
of the condensate.Comment: 4 pages, 3 figures (changed content
Heteronuclear ionizing collisions between laser-cooled metastable helium atoms
We have investigated cold ionizing heteronuclear collisions in dilute
mixtures of metastable (2 3S1) 3He and 4He atoms, extending our previous work
on the analogous homonuclear collisions [R. J. W. Stas et al., PRA 73, 032713
(2006)]. A simple theoretical model of such collisions enables us to calculate
the heteronuclear ionization rate coefficient, for our quasi-unpolarized gas,
in the absence of resonant light (T = 1.2 mK): K34(th) = 2.4*10^-10 cm^3/s.
This calculation is supported by a measurement of K34 using magneto-optically
trapped mixtures containing about 1*10^8 atoms of each species, K34(exp) =
2.5(8)*10^-10 cm^3/s. Theory and experiment show good agreement.Comment: 8 pages, 6 figure
Third-harmonic generation of a continuous-wave Ti : Sapphire laser in external resonant cavities
An all-solid-state tunable continuous-wave (cw) laser operating near 272 nm with a bandwidth Gamma approximate to 3 MHz has been developed. The third harmonic of light from a single-cw Ti:Sapphire laser has been generated using two external enhancement cavities. An output power of 175 mW has been produced, corresponding to an overall conversion efficiency of 8%. (C) 2003 American Institute of Physics
Phase stability of terawatt-class ultrabroadband parametric amplification
The phase stability of broadband (280 nm bandwidth) terawatt-class parametric amplification was measured, for the first time to our knowledge, with a combination of spatial and spectral interferometry. Measurements at four different wavelengths from 750 to 900 nm were performed in combination with numerical modeling. The phase stability is better than 1/23 rms of an optical cycle for all the measured wavelengths, depending on the phase-matching conditions in the amplifier. (C) 2007 Optical Society of America
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