Monday, February 26, 2007

Counterpropagating light opens door to tabletop X-ray laser

A team of researchers at the University of Colorado at Boulder has developed a new technique to generate laser-like X-ray beams, removing a major obstacle in the decades-long quest to build a tabletop X-ray laser that could be used for biological and medical imaging.

A paper on the subject by Murnane and Kapteyn, CU-Boulder graduate students Xiaoshi Zhang, Amy Lytle, Tenio Popmintchev, Xibin Zhou and Senior Research Associate Oren Cohen of JILA was published in the online version of the journal Nature Physics on Feb. 25.

Source: University of Colorado at Boulder

Wednesday, February 21, 2007

Terawatt Ultrafast High Field Facility: TUHFF

The Chemistry Division’s Terawatt Ultrafast High Field Facility (TUHFF) was built in order to provide a source of femtosecond electron pulses, femtosecond tunable x-rays (soft and hard), and femtosecond proton pulses. TUHFF will primarily be used for applications in the fields of chemistry and physics. A Titanium:Sapphire based laser system that produces 0.6 Joules of energy in a 50 femtosecond pulse was constructed. This system produces peak powers in excess of 10 terawatt! Because of these extremely high power levels, part of the laser system and the experimental areas (target chamber) are contained in vacuum chambers to prevent the dielectric breakdown of air. Currently, we are exploring the generation of femtosecond pulses of ionizing radiation (both protons and electrons) and of x-rays by focusing this intense beam (power density >10^19 W/cm2!) into either a metal target (hard x-rays and protons) or a supersonic gas jet (energetic electrons).
Source: Chemistry division, Argonne National Laboratory

Monday, February 19, 2007

Extreme Light Lab installs near-petawatt system

Laser science at the 100-terawatt (10^14 W) peak-power level has entered the commercial realm. An ultrafast Ti:sapphire laser system produced by Thales Laser (Orsay, France) and installed at the University of Nebraska, Lincoln (UNL; Lincoln, NE) reaches a 150 TW level and is upgradeable in the future to above the petawatt mark. Called Diocles, the laser, considered a fully commercial product, is enabling Donald Umdstadter’s group at UNL’s new Extreme Light Laboratory to perform day-to-day, stable, reproducible ultrafast experiments with an uptime much higher than that of pre-existing lasers of the same power scale. As such, it may usher in a new era of R&D with ultrapowerful lasers.

The Ti:sapphire oscillator is pumped with a continuous-wave green laser, the first amplifier is pumped with a 1 kHz diode-pumped Nd:YLF (yttrium lithium fluoride) frequency-doubled laser, and the three medium-to-high-power stages are pumped with 10 Hz frequency-doubled lamp-pumped Nd:YAG lasers. “The hybrid diode/lamp architecture is there to provide high beam quality and stability on the initial low-energy stages (diode pumped), and low-cost energy input for the high-energy stages (flashlamp pumped),” says Marquis. The pump lasers are all water-cooled via a water-water exchanger; the Ti:sapphire laser crystals are also water-cooled via a patent-pending technique that avoids the need for cryogenic cooling. The uncompressed output of the final amplifier exceeds 5 J at a 10 Hz pulse-repetition rate. The laser’s final output beam exceeds a Strehl ratio of 0.7.

Source: Laser Focus World

Wednesday, February 14, 2007

Plasma wakefield accelerator doubles particle energy in just one meter

Physicists in the US claim to have doubled the 42 GeV electron-beam energy of the three-kilometre-long Stanford Linear Accelerator Centre (SLAC) by simply adding a metre-long device on the end. The device, which uses a plasma wakefield to accelerate a small fraction of the electron beam, could allow conventional particle accelerators to reach higher energies (Nature 445 741).

Plasma acceleration is a technique for accelerating charged particles, such as electrons, positrons and ions, using an electric field associated with an electron plasma wave. The wave is created by the passage of a very brief laser or electron pulse through the plasma. The technique appears to offer a way to build high performance particle accelerators of much smaller size than conventional devices at the expense of coherency. Current experimental devices show accelerating gradients several orders of magnitude better than current particle accelerators. For example, one experimental device at the Lawrence Berkeley National Laboratory accelerates electrons to 1 GeV over about 3.3 cm, whereas the SLAC conventional accelerator requires 64 m to reach the same energy. (Via Wikipedia)