Ultrafast X-ray study of dense-liquid-jet flow dynamics using structure-tracking velocimetry

Yujie Wang1, Xin Liu2, Kyoung-Su Im1, Wah-Keat Lee1, Jin Wang1, Kamel Fezzaa1, David L. S. Hung3 & James R. Winkelman3

1. X-Ray Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
2. Mayo Clinic, Rochester, Minnesota 55905, USA
3. Visteon Corporation, Van Buren Township, Michigan 48111, USA

Nature Physics. doi:10.1038/nphys840

High-speed liquid jets and sprays are complex multiphase flow phenomena with many important industrial applications. Great efforts have been devoted to understand their dynamics since the pioneering work of Rayleigh on low-speed jets. Attempts to use conventional laser optical techniques to provide information about the internal structure of high-speed jets have been unsuccessful owing to the multiple scattering by droplets and interfaces, and the high density of the jet near the nozzle exit. Focused-X-ray-beam absorption measurements could provide only average quantitative density distributions using repeated imaging. Here, we report a novel approach on the basis of ultrafast synchrotron-X-ray full-field phase-contrast imaging. As illustrated in our case study, this technique reveals, for the first time, instantaneous velocity and internal structure of optically dense sprays with a combined unprecedented spatial and time resolution. This technique has tremendous potential for the study of transient phenomenon dynamics.

The X-ray beam is generated from the electron storage ring. The fill pattern shown is the hybrid-singlet mode: a single electron bunch (150 ps long and carrying 15 mA of current) is separated from a longer train of electrons (472 ns long, 94 mA) by a 1.59 s gap on both sides. The fast shutter absorbs more than 99% of the beam power, and lets the beam through for a few milliseconds at 1 Hz. The sample image is formed on a fast scintillator crystal (LYSO:Ce) and read on a CCD (charge-coupled device) camera via a microscope objective and a mirror at 45^° angle. The inset shows the APS undulator-A energy spectrum at 31 mm gap on a logarithmic scale. The fundamental sharp peak at 13.3 keV is 100 times brighter than the harmonics.

The concepts of entrance pupil and exit pupil

The entrance pupil of a system is the image of the aperture stop as seen from an axial point on the object through those elements preceding the stop. In contrast, the exit pupil is the image of the aperture stop as seen from an axial point on the image plane through the interposed lenses, if there are any.

The definition of pupil can be found from any optics textbook, however it's still hard to imagine what difference between the exit and entrance pupils. After seeing the left picture, you may impress the pupil on the memory. It's a normal camera lens, the entrance pupil is the image of aperture from the front side, and the exit pupil is the image of the same aperture from the back side .

Hot attosecond pulse at 2007

Physics News Update listed Ten Top Physics Stories for 2007. There are 2 news about ultrafast laser:

• Electron tunneling in real time can be observed with the use of attosecond pulses (http://www.aip.org/pnu/2007/split/818-2.html);
• The shortest light pulse, a 130-attosecond burst of extreme ultraviolet light (http://www.aip.org/pnu/2007/split/823-1.html); I reported this on my blog before.

The other stories are:

• Light, slowed in one Bose Einstein condensate (BEC), is passed on to another BEC (http://www.aip.org/pnu/2007/split/812-1.html);
• Laser cooling of coin-sized object, at least in one dimension (http://www.aip.org/pnu/2007/split/818-1.html);
• The best test ever of Newton’s second law, using a tabletop torsion pendulum (http://www.aip.org/pnu/2007/split/819-1.html);
• First Gravity Probe B first results, the measurement of the geodetic effect---the warping of spacetime in the vicinity of and caused by Earth-to a precision of 1%, with better precision yet to come(http://www.aip.org/pnu/2007/split/820-2.html);
• The MiniBooNE experiment at Fermilab solves a neutrino mystery, apparently dismissing the possibility of a fourth species of neutrino (http://www.aip.org/pnu/2007/split/820-1.html);
• The Tevatron, in its quest to observe the Higgs boson, updated the top quark mass and observed several new types of collision events, such as those in which only a single top quark is made, and those in which a W and Z boson or two Z bosons are made simultaneously (http://www.aip.org/pnu/2007/split/821-1.html);
• Based on data recorded at the Auger Observatory, astronomers conclude that the highest energy cosmic rays come from active galactic nuclei (http://www.aip.org/pnu/2007/split/846-1.html);
• And the observation of Cooper pairs in insulators (http://www.aip.org/pnu/2007/split/849-1.html).