Lasers slim down radiotherapy equipment

Hospitals could benefit from a new technique that uses ultra-short laser pulses to simplify radiotherapy equipment.

via www.optics.org

Researchers from Italy, France and Germany have shown that a tabletop laser can be used to accelerate a beam of electrons suitable for use in radiotherapy. The group, led by Antonio Giulietti of the Institute for Physical Chemistry Processes in Pisa, believes that such laser-based particle acceleration could considerably reduce the size and simplify the operation of radiotherapy facilities (Physical Review Letters 101 105002).

In radiotherapy beams of photons, electrons, protons, neutrons or ions are used to destroy tumours by ionizing the atoms within the tumours' DNA. Usually this involves irradiating the patient from a number of different directions in order to pinpoint the tumour, and in the case of deep tumours, using higher-energy particles. This inevitably leads to some damage of the healthy tissue surrounding the tumour.

Damage limitation

Damage can be limited using a technique known as intraoperatory radiotherapy (IORT), which involves irradiating the patient just once with electrons. This occurs in the operating theatre right after the tumour has been surgically removed. The idea is to destroy tumour cells that the surgery has missed. Because they do not have to penetrate deeply, the electrons can be fewer in number and have a lower energy, which means that the accelerators employed can be smaller.

However, as Giulietti points out, IORT, like ordinary radiotherapy, still uses radiofrequency electric fields to accelerate the electrons, which requires a machine more than two metres high and over half a tonne in weight. The machine must be shielded from the operating theatre and any maintenance requires the shut down of the theatre. "This therefore limits the energy of the electrons that can be used in the technique," he adds.

Giulietti and colleagues have shown that these problems can be overcome by using a laser rather than radiofrequency electric fields to accelerate the electrons.

At the SLIC laboratory in Saclay, France, the researchers fired ultra-short laser pulses onto a jet of gas, creating a plasma with a fluctuating electron density. The electric field generated by these fluctuations accelerated the free electrons within the plasma such that they had energies and spatial characteristics suitable for use in IORT. By then passing these electrons through a 2 mm–thick piece of tantalum (and therefore decelerating them rapidly) the researchers were able to create gamma–ray photons that could also be used in radiotherapy.

Just a small metal box

Because the laser beam can travel for several tens of metres without any appreciable loss, the laser itself can be located outside the operating theatre. According to Giulietti, the only thing that would need to be in the theatre is a metallic box perhaps 50 by 20 by 20 cm across that would convert the laser beam into the electron beam, and which would contain a roughly 10 cm–long device to generate the gas jet and focusing optics of a similar size.

Giulietti points out that scaling up the facility would allow IORT to be carried out at higher energies than is currently possible, which would render the technique more effective against certain kinds of tumours. He adds that more work is needed to design a laser–based system suitable for actual hospital use, in particular ensuring the stability of both the laser output and the acceleration process within the plasma.

Thin-disk laser yields energetic femtosecond pulses

Ursula Keller's group at ETH Zurich in Switzerland has built the first Yb:YAG thin-disk laser to deliver femtosecond pulses with energies above 10 µJ. The team believes that the design could yield a compact source of high-power ultrashort pulses for applications such as high-resolution imaging and precision micro- and nanomachining.

"Our motivation was to increase the pulse energy of femtosecond oscillators," team member Thomas Südmeyer told optics.org. "In this way, many experiments and applications that previously relied on complex and expensive amplifier systems are now within the reach of simple and cost-efficient diode-pumped solid-state lasers."

Generating high-energy femtosecond pulses is a crucial requirement for many scientific and industrial applications. The normal approach in these applications is to exploit a laser amplifier system, but the repetition rate is typically limited to the kilohertz regime – which in turn affects the signal-to-noise ratio and also restricts the throughput and precision of materials processing applications.

Other techniques are capable of delivering microjoule pulses at megahertz repetition rates, but these require complex amplifier systems with a seed laser and multiple amplification stages. In contrast, the new laser developed by Südmeyer and colleagues produces femtosecond pulses directly using a high-power oscillator, eliminating the need for any external amplification.

The laser delivers up to 45 W of average power at a repetition rate of 4 MHz. This yields 11.3 µJ pulses with a duration of 800 fs and a peak power of 12.5 MW, which Südmeyer says is sufficient for driving high-field experiments.

According to Südmeyer, the latest results are the culmination of several years' work on thin-disk lasers, which enable high average powers to be achieved with good beam quality. The Swiss team use a multiple-pass cavity to extend the length of the resonator to 37 m, while stable femtosecond pulses are produced by passive modelocking using a semiconductor saturable absorber mirror (SESAM). "This results in a power-scalable solution for the generation of pulses with durations in the femtosecond regime," said Südmeyer.

Until now, however, the pulse energies that could be produced from this set-up were limited to a few microjoules. "Our initial effort to increase the pulse energy was limited by some excess nonlinearity, which initially was not identified," commented Südmeyer. "We found that the source of the additional instabilities was the nonlinearity of the air atmosphere inside the laser cavity."

The solution, says Südmeyer, is to flood the laser cavity with helium, which has a negligible nonlinearity compared with air. The repetition rate was reduced to 4 MHz in order to produce pulses with energies greater that 10 µJ.

The team now plans to increase the average power to beyond 500 W and the pulse energy towards 100 µJ. "We will also investigate in collaboration with Professor Huber from the University in Hamburg new thin disk materials, which will allow us to achieve shorter pulse durations," said Südmeyer.

The researchers reported their work in Optics Express.

New technique measures ultrashort laser pulses at focus

Lasers that emit ultrashort pulses of light are used for numerous applications including micromachining, microscopy, laser eye surgery, spectroscopy and controlling chemical reactions. But the quality of the results is limited by distortions caused by lenses and other optical components that are part of the experimental instrumentation.

To better understand the distortions, researchers at the Georgia Institute of Technology developed the first device to directly measure complex ultrashort light pulses in space and time at and near the focus. Measuring the pulse at the focus is important because that’s where the beam is most intense and where researchers typically utilize it. Knowing how the light is distorted allows researchers to correct for the aberrations by changing a lens or using a pulse shaper or compressor to manipulate the pulse into the desired form.

The device was described in a presentation at the Conference on Lasers and Electro-Optics on May 8. This research was funded by the National Science Foundation and published in the August 2007 issue of the journal Optics Express.

It is difficult to measure ultrashort pulses because they typically last between a few femtoseconds and a picosecond, which are 10-15 and 10-12 of a second, and faster than the response time of the fastest electronics. To achieve the highest possible intensity of the laser, the pulse must be as small as possible in space and as short as possible in time. However, focused pulses nearly always have distortions in time that vary significantly from point to point in space due to lens aberrations in focusing optics. To address those issues, the new device, called SEA TADPOLE (Spatial Encoded Arrangement for Temporal Analysis by Dispersing a Pair of Light E-fields), allows researchers to measure complicated ultrashort pulses simultaneously in space and time as they go through the focus.

The research team – which also included former graduate students Pablo Gabolde and Selcuk Akturk – used the concept of interferometry to measure a pulse in space and time. Two pulses, one reference and one unknown, were sent through optical fibers. The fibers were mounted on a scanning stage so that the pulses could be measured at many locations around the focus.

The pulses were crossed and an interference pattern was recorded for each color of the pulse at each location with a digital camera. The patterns were used to determine the shape of the unknown pulse in space and time and to create movies showing how the intensity and color of the pulse changed in space and time as it focused.

he researchers tested the device by measuring ultrashort pulses focused by various lenses, since each lens can cause different complex distortions. To validate the measurements, Bowlan performed simulations of pulses propagating through the experimental lenses. Results showed that a common plano-convex lens displayed chromatic and spherical aberrations, whereas more expensive aspheric and doublet lenses exhibited mostly chromatic aberrations.

Spherical aberrations occur when the light that strikes the edges of the lens gets focused to a different point than the light that strikes the center, creating a larger, inhomogeneous focused spot size. Chromatic aberrations occur because the many colors in the laser travel at different speeds and do not stay together in space and time as the pulse passes through glass components in the experimental setup, such as lenses. As a result, each color arrives at the focus at a different time, creating a rainbow of colors in the electric field images.

Aberrations can drastically increase the pulse length, which decreases the laser intensity. A lower intensity forces researchers to increase the power of the laser, increasing the possibility of damaging the sample. Aberrations can also yield odd pulse and beam shapes at the focus, which complicate the interpretation of the experiment or application.

World's shortest single photon pulse created

The world’s shortest light pulse containing just one photon has been produced by Oxford University scientists.

The Oxford team can create individual photons that are 65 femtoseconds in duration: that’s approximately fifty times shorter than any single photon previously produced.

And every photon this source produces is identical to the previous one. Such photons could be a major breakthrough in quantum computing: the harnessing of quantum effects to perform calculations that would take conventional computers thousands of years to resolve.

‘Creating single photons even under controlled conditions is extremely challenging,’ said Peter Mosley of Oxford’s Department of Physics. ‘Even the purest laser light beam consists of many photons all bunched together. Our approach enables us to generate individual photon replicas, identical packets of light of very short duration that are ideal for quantum computing.’

Peter Mosley, a member of Oxford’s Ultrafast Group, is a co-author of a report of the research in Physical Review Letters.

The most intense laser pulse in the universe

The people on HERCULES laser at the University of Michigan has claimed to have created the most intense laser pulse in the universe.

The record-setting beam measures 20 billion trillion watts per square centimeter. It contains 300 terawatts of power, about 300 times the capacity of the entire US electricity grid. The laser beam’s power is concentrated to a 1.3-µm speck about 100th the diameter of a human hair. To achieve this beam, the research team added another amplifier to HERCULES (high-energy repetitive CUOS laser system) laser system, which previously operated at 50 terawatts.

Solar laser or solar energy laser?

Based on the news from Optics.org, Japanese team revives solar lasers in quest for clean fuels.

The idea of using solar energy to power lasers is not new. Current designs work by using a system of mirrors to concentrate sunlight into an Nd:YAG crystal, but these lasers are not widely used because they require huge mirrors to collect the light – and even then achieve only low efficiency.

To address these issues, Takashi Yabe and colleagues at the Tokyo Institute of Technology experimented with using a Fresnel lens instead of mirrors as light collectors. They also found that doping the Nd:YAG crystal with small amounts of chromium significantly increases the power output of the laser.

The laser demonstrated by the team produces a power output of 24 W at 1064 nm. The design, which incorporates a 1.3 m2 Fresnel lens, offers an unprecedented slope efficiency of 12% above a threshold solar input of 500 W.

Femtosecond time-delay X-ray holography

Researchers have used the ultrafast X-ray pulses from a free-electron laser to image a nanoscale object in just a femtosecond. The technique, which is a new form of X-ray holography, has been pioneered by Henry Chapman from Lawrence Livermore National Laboratory and colleagues in the US, Switzerland and Germany. Being able to study materials so fast brings us one step closer to the holy grail of observing, at the same time, how all the atoms in a molecule move (Nature 448 676).

The incident FEL pulse from the left passes through a hole in a multilayer-coated detector mirror. The 'dusty mirror' consists of particles on a 20-nm-thick silicon nitride membrane backed by a multilayer-coated plane mirror. This returns the direct beam back through the hole in the detector mirror, which reflects the diffracted light onto a CCD detector. The prompt diffraction (blue, the reference wave) and delayed diffraction (red, the object wave) interfere to generate the hologram on the CCD detector.

Plasma mirrors generate high harmonics

For many researchers working with high-intensity lasers, plasma formation is often bad news. For others, it’s an enabling step for putting their laser systems to good use, in the form of so-called plasma mirrors. Now, collaborators at CEN Saclay (Gif-sur-Yvette, France), École Polytechnique (Palaiseau, France), and the University of Toronto (Toronto, Ont., Canada) have used a chain of plasma mirrors to create extreme-ultraviolet (EUV) pulses that they predict to be on the attosecond timescale, all with a tabletop laser.

In the highest intensity femtosecond-laser systems, a nanosecond-scale prepulse can be enough to ablate the surface of samples before most of the pulse energy arrives. Enter the plasma mirror, a simple but effective solution to increase the contrast between the prepulse and the main pulse. By placing a highly polished mirror blank in the beam at Brewster’s angle, the nanosecond-scale prepulse passes unchanged. The rising edge of the main pulse, however, converts the surface of the mirror into a highly reflective plasma, specularly reflecting only the main pulse. Once the prepulse is cleaned up by two plasma mirrors, a third forms the basis for high-order harmonic generation (HHG).

C. Thaury et al.,Nature Phys. doi:10.1038/nphys595 (2007).

Laser vision fuels energy future

Photonics.com reported:

The proposed European High Power laser Energy Research (HiPER) facility -- a device intended to demonstrate the feasibility of laser-driven fusion as an energy source -- is entering the preparation phase after completion of a two-year study by an international team of scientists.

Their conclusions have allowed the HiPER project to be selected as part of the European roadmap for future large-scale science facilities. The preparatory phase of the HiPER facility is expected to begin in January and to last for three years.

Achieving nuclear fusion using lasers is the goal of the National Ignition Facility, the latest in a series of high-power laser facilities used for research in inertial confinement fusion. Now under construction at the Lawrence Livermore National Laboratory, in Livermore, Calif., NIF is being built by the US Department of Energy as part of its Stockpile Stewardship program, and as such has a strong defense mission. "This is largely due to the fact that NIF converts its laser light to x-rays, and those x-rays are then used to implode the pellet (or perform other, classified experiments)," Dunne said. "This is meant to be analogous to the use of x-rays in thermonuclear weapons."

HiPER removes this link to defense science, Dunne said. "It uses the optical laser light directly to drive the implosion and initiate fusion. The physics associated with the interactions of lasers with matter have no relevance whatsoever to nuclear weapons, so we see this as very much a 'swords into ploughshares' undertaking."

Laser Fusion Facilities
LASER FACILITY	LOCATION	COMPRESSION ENERGY	IGNITION POWER	ESTIMATED START
National Ignition Facility	United States	1.8 MJ	NA	2009
Laser Mégajoule	France	2.0 MJ	NA	2011
FIREX-I + Gekko XII	Japan	10 kJ	1 PW (10 kJ)	2007
OMEGA EP	United States	30 kJ	2 PW (5 kJ)	2007
HiPER	Europe	200 kJ	10 PW (70 kJ)	proposed

For more information, visit: www.hiper-laser.org

Relativistic tennis with photons

Science daily news reported that a team from Advanced Photon Research Center at the Japan Atomic Energy Agency has demonstrated to generate an ultrashort and ultraintense x-ray pulse using the ordinary laser.

Sergei Bulanov of the Advanced Photon Research Center at the Japan Atomic Energy Agency in Kyoto and colleagues say they have a prototype that can generate pulses of x-ray laser light on the cheap. The researchers call their technique "relativistic tennis with photons," but a more violent analogy may better convey how it works. Suppose you throw a golf ball at a locomotive that is speeding toward you. The golf ball will bounce off it and come flying back at you with tremendous energy--just before you get run over.

The golf ball is a pulse of ordinary low-energy photons. With a tabletop setup, Bulanov and colleagues create the equivalent of a locomotive by firing a different laser into a cloud of plasma, where it creates a wake that travels at near-light speed. When the photons hit the wake, their energy increases 56-fold. They are also focused into an ultrashort, ultraintense blast by the wake, which is shaped like a miniature radar dish.

Laser-generated radiation for cancer therapy?

Will laser-generated radiation one day prove useful in cancer therapy? A UK collaboration aims to find out. Reported from oprtics.org:

A consortium of UK-based scientists has secured £5 million ($9.9 million) in research funding to turn the concept of laser-generated radiation into a robust, ready-to-go technology. The four-year project, involving researchers from nine separate institutions, could lead to cheaper, simpler solutions for proton and ion radiotherapy. Laser-energized radiation sources could also cut the cost of research into cosmic-radiation exposure from frequent air travel and manned space missions.

The project named LIBRA, which means Laser Induced Beams of Radiation and their Applications. Development of the technology will require access to a very high-powered laser with a rapid-fire repetition rate. One such system is the GEMINI laser, due to come on-line at the Rutherford Appleton Laboratory (RAL) near Oxford, UK, later this year. GEMINI is expected to deliver 1 PW (10^15 W) pulses every 20 seconds.

related links: LIBRA, GEMINI

Theodore Maiman -- Laser Inventor Dies at 79

Theodore Maiman, PhD, inventor of the first operable laser and twice nominated for a Nobel Prize, died May 5 in Vancouver, British Columbia. His death was confirmed by his wife, Kathleen.

He had been called “the father of the electro-optics industry,” according to a biography at the IEEE virtual Museum, but Maiman considered himself "a scientist and an engineer, with research interests in electro-optics, lasers, displays and aerodynamics."

Source: Photonics.com

Ultrashort laser pulse around 100 attoseconds

Working at Italy's National Laboratory for Ultrafast and Ultraintense Optical Science in Milan (as well as laboratories in Padua and Naples), the researchers believe that their current technique will allow them to create even shorter pulses well below 100 attoseconds. Results will be presented in Baltimore at CLEO/QELS, May 6 – May 11.

Creating a single isolated attosecond pulse, rather than a train of them, is more complex. To do this, the researchers employ their previously developed technique for delivering intense short (5 femtoseconds, or millionths of a billionth of a second) laser pulses to an argon gas target. They use additional optical techniques (including ones borrowed from the research that won the 2005 Nobel Prize in Physics) for creating and shaping a single attosecond pulse. Light pulses lasting just 130 attoseconds offer possibilities for unlocking secrets of atoms and molecules.

Related Link: National Laboratory for Ultrafast and Ultraintense Optical Science
Source: PhysOrg.com

The crystal melting movie?

As Phy Org web reported, Stanford Synchrotron Radiation Laboratory (SSRL) researchers
have observed the atomic events involved in rapid crystal melting using an intense laser and ultra-fast x-rays.

Sub-Picosecond Pulse Source (SPPS) provides short bursts of x-rays (2 x 10^6 photons in an 80 fs FWHM pulse at 8.9 keV with a 1.5% bandwidth into a 200 um by 400 um spot). The laser pulse (50fs FWHM, 20 mJ @ 800 nm) at the sample, which convolved with the x-ray pulse yields a Gaussian cross correlation of 100 fs FWHM.

The data, published recently in Physical Review Letters, revealed that when their bonds destabilized, the atoms moved apart from each other quickly, as if repelling each other. The semiconductor material had visible melting damage after being struck by the laser.

A 32TW laser beam sending into the atmosphere

Recent paper published on APL reported the ultrahigh power laser pulses have been sent vertically into the atmosphere. Scientists from Switzerland and France sent 26J, 32TW laser pulses delivered by the Alise beamline of the CEA-CESTA into the sky. They found more than 400 self-guided filaments. The white light was observed when the laser beam propagating up to the air, beyond 20km.

If you are interested this phenomena, you may download the full text paper from the APL website.

What Is an Energy Recovery Linac (ERL)?

An Energy Recovery Linac (ERL) x-ray source is a candidate next-generation x-ray source technology now under active development. ERLs are made possible by recent advances in superconducting linear accelerators and in high-brightness electron sources. ERLs have the potential to generate synchrotron radiation with brightness about 1000 times greater than that of today's storage rings, resulting in highly coherent x-radiation. ERL's are particularly well suited for the production of very fast x-ray pulses to examine the dynamics of materials on extremely rapid time scales and for intense x-ray nanoprobe beams to study nanoscopic matter. While both ERLs and XFELS will be able to produce very fast x-ray pulses, the two sources are quite distinct in the timing of these pulses: ERLs are being designed to produce pulses times up to a billion times a second whereas XFELs produce bigger pulses but at a far lower rate per second.

Image 1. Electrons are released from the injector at the lower left, and are accelerated in a long linear superconducting accelerator (main linac). After emerging from this linac, the electrons pass through undulators that wiggle the electron beam and produce the x-rays in the usual way. Electrons are continuously injected, make one trip around the ring, and return to the main linac where their energy is recovered. The spent beam is directed to the dump. (Courtesy: Cornell University)

PHOTONIC FRONTIERS: PETAWATT LASERS

Squeezing energetic laser pulses down to ultrashort durations can generate tremendous peak powers. A decade ago the Lawrence Livermore National Laboratory (LLNL; Livermore, CA) blazed the trail by modifying one arm of its Nova fusion laser to create the Petawatt Laser, which delivered pulses exceeding 1015 W (1 PW). Now some 20 petawatt lasers are in operation or development around the world, and European planners are aiming for an exowatt (1018 W) laser (see table).

Some major petawatt laser projects

Name	Site	Timetable	Parameters	Web site Link
Advanced Radiographic Capability	Livermore	2009	10 kJ, 10 ps
Extreme Light Infrastructure	Laboratoire d’Optique Appliquée, France	Proposal	10 kJ, 10 fs	ELI
Firex-1	ILE, Osaka, Japan	Under construction	10 kJ, 10 ps
GEKKO Petawatt Module	ILE, Osaka, Japan	In operation	500 J, 500 fs
Laser Megajoule	University of Bordeaux	Proposal	2 MJ, 300 ps-10 ns	lmj
LULI 2000	LULI, Paris	Under construction; completion 2006	200 J, 400 fs
Omega EP	University of Rochester	2007	2.6 kJ, 1 ps	omegaep
Petawatt Laser (original)	Livermore	1996-1999	1.3 kJ, 800 fs	MPerry
Phelix	GSI Darmstadt, Germany	Under construction, with heavy-ion beam	500 J, <500 fs	phelix
Polaris	University of Jena, Germany	Development	120 J, 120 fs	ultraphotonics
Texas Petawatt Laser	University of Texas, Austin	Late 2007	130 J, 150 fs	petawatt
Titan	Livermore	In operation	400 J, 400 fs or long-pulse	JLF
Vulcan Petawatt	Rutherford Appleton Lab, UK	In operation	400 J, 400 fs	vulcan
Z-beamlet	Sandia National Laboratory	Under construction	2 kJ, 1-10 ps ultimately	z-beamlet

The first petawatt laser

Livermore’s Petawatt Laser used a chain of Nd:glass lasers from one beam of the Nova fusion laser to amplify nanosecond pulses to the kilojoule range. Pulses were expanded and compressed with high-efficiency 75 cm gratings. Amplifier output of 1.3 kJ in an 800 ps pulse could be compressed down to a 430 fs pulse with peak power of 1.3 PW, which in turn could produce power density approaching 1021 W/cm2. The system generated its first petawatt pulse on May 23, 1996, and ran for three years until Nova was dissembled in 1999.

The Livermore experiments demonstrated the potential of petawatt lasers to concentrate tremendous energies into small volumes, opening a new regime of high-temperature and high-pressure matter for study. The intense fields could accelerate both electrons and positive ions to high velocities over short distances (see www.laserfocusworld.com/articles/252490). Experiments generated bright beams of high-energy x-rays and gamma rays. And Livermore also showed that firing petawatt lasers into a laser-heated fusion target produced a powerful shock wave that helped ignite the fusion fuel.

Second-generation petawatt lasers

The second generation of petawatt lasers is already operating. The Rutherford Appleton Laboratory (Didcot, England) uses a Ti:sapphire oscillator and an optical parametric amplifier to preamplify pulses which then pass through a beam of the lab’s Vulcan Nd:glass laser, and three additional 208 mm Nd:glass disks salvaged from Nova (see Fig. 2). Commissioned in 2002, it initially produced 800 fs pulses with peak power of 500 TW. Further refinements ramped up power, which reached the petawatt level in October 2004, delivering 423 J onto the target in a 410 fs pulse.

Livermore has built a second-generation petawatt laser called Titan around the old two-beam Janus Nd:glass laser used in fusion target experiments back in 1975, says Andrew Ng of Lawrence Livermore National Laboratory (LLNL). Overhauled with better glass, the system has two independent beam lines for chirped-pulse amplification and a new generation of pulse-compression gratings. The first experiments in June 2005 generated 400 J in 400 fs to reach petawatt peak power focusable onto an 8 µm spot. It also can operate in long-pulse mode, generating 1 kJ in less than 3 ns or 140 J in 250 ps. Titan can fire long and short pulses simultaneously from its two arms. Ng says that firing long pulses to create a plasma and short pulses to probe the plasma is a very effective way to study high-energy states.

Livermore is also planning a big step up in energy with a second long-pulse system for use with the National Ignition Facility. Called the Advanced Radiographic Capability, it initially will fire 1 kJ pulses to record multiframe x-ray movies of NIF targets, says lead scientist Chris Barty of LLNL. By combining four NIF beams, he hopes to generate 13.2 kJ in a 10 ps pulse. The first beamline is to be commissioned in spring 2009.

Most other systems in operation, construction, or planning stages are either long-pulse systems based on Nd:glass or Ti:sapphire systems generating pulses as short as 20 fs. The main exception is the $15 million Texas Petawatt Laser, which will use parametric amplification to raise the 1 J output of a Ti:sapphire oscillator to 250 J, which they hope to deliver in 150 fs pulses. Project director Todd Ditmire hopes to produce his first petawatt pulses late in 2007.

Laser Focus World August, 2006
Author: Jeff Hecht

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

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

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)