Biomedical subjects

W Hogervorst

Publications and source records attributed to W Hogervorst.

At least 19 recordsLinked to original sources

PubMed2006

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 microK, and achieve a fermionic degeneracy parameter of T/TF = 0.45. Because of their high internal energy, the detection of individual metastable atoms with subnanosecond 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.

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PubMed2005

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.

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PubMed2004

Simultaneous magneto-optical trapping of a boson-fermion mixture of metastable helium atoms.

We simultaneously confine fermionic metastable 3He atoms and bosonic metastable 4He atoms in a magneto-optical trap. The trapped clouds, containing up to 1.5 x 10(8) atoms of each isotope, are characterized by measuring ions and metastable helium atoms escaping from the trap. Optical pumping of 3He atoms to a nontrapped hyperfine state is investigated and it is shown that large atom numbers can be confined without additional repumping lasers. Unique possibilities for quantum degeneracy experiments with mixtures of spin-polarized metastable 3He and 4He atoms are indicated.

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PubMed2001

Double-well states of ungerade symmetry in H2: first observation and comparison with Ab initio calculations.

The observation of a new class of long-lived outer well states of ungerade symmetry (B"B1Sigma+u) in molecular hydrogen, lying above the ionization threshold, is reported. Rovibrational levels within a potential extended over internuclear separations of R = 7-25 a.u. are experimentally investigated in a triple resonance scheme. Good agreement ( <0.5 cm(-1)) with updated ab initio calculations is found for vibrational levels up to v = 26, demonstrating that such calculations can now be extended to this energetic range above ionization, as long as interaction with the Rydberg manifolds is shielded by a barrier. The dynamical behavior (predissociation and autoionization) of this class of " u" symmetry states is remarkably different from similar outer well states of " g" symmetry; this phenomenon can be understood from the structure of doubly excited electronic states.

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PubMed2000

A Dense Grid of Reference Iodine Lines for Optical Frequency Calibration in the Range 595-655 nm.

A dense grid of reference lines in the hyperfine structure of the B-X transitions of molecular iodine ((127)I(2)) is presented. Frequencies of 481 "t"-hyperfine components in 15 vibrational bands covering the wavelength range 595-655 nm were determined with an absolute accuracy of 1.0 MHz (1varsigma uncertainty). Spectra were obtained by Doppler-free saturation spectroscopy using a cw ring-dye laser of 1-MHz bandwidth. Center-of-gravity frequencies of rovibronic lines, determined by correcting for the calculated hyperfine shift, are included separately in a least-squares parametrization for each band. From the obtained molecular constants a prediction is made for all t-hyperfine components of the 15 bands covering 595-655 nm. Hence a dense grid of reference lines of 1 MHz (1varsigma) absolute accuracy is created, with a line in each interval of 1 cm(-1) in the entire range. This spectral atlas of about 3400 lines may provide a useful calibration tool in many laboratories. Copyright 2000 Academic Press.

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PubMed1998

A Dense Grid of Reference Iodine Lines for Optical Frequency Calibration in the Range 571-596 nm

A high precision dense grid of reference lines in the hyperfine structure of the B-X system of molecular iodine (127I2) is presented. A simple parametrization has been derived, predicting the hyperfine line positions of the "t" components for vibrational bands (13-1) up to (18-1) and rotational quantum numbers J = (9-140). The analysis in this paper is based on Doppler-free saturation spectroscopy spectra used for calibration of more than 100 new components in the hyperfine structure of 127I2. The data presented contains a prediction (with 2 MHz accuracy) for the positions of 1584 "t" components in the rotational structure of iodine, covering the wavelength interval 571-596 nm. Copyright 1998 Academic Press. Copyright 1998Academic Press

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PubMed1997