16 March 2015

Lawrence Livermore commissions highest peak-power laser diode arrays

Lawrence Livermore National Laboratory (LLNL) has installed and commissioned what are said to be the world's the highest peak-power laser diode arrays.

With total peak power of 3.2MW, the diode arrays form a key component of the High-Repetition-Rate Advanced Petawatt Laser System (HAPLS, under construction at LLNL). When completed, the HAPLS laser system will be installed in the European Union's Extreme Light Infrastructure (ELI) Beamlines facility, under construction in the Czech Republic.

HAPLS is designed to be capable of generating peak powers greater than 1 petawatt (1 quadrillion watts, or 1015) at a repetition rate of 10Hz, with each pulse lasting 30 femtoseconds (30 quadrillionths of a second). This very high repetition rate represents an advance over existing petawatt system technologies, which rely on flashlamps as the primary pump source and can fire a maximum of once per second. In HAPLS, the diode arrays fire 10 times per second, delivering kilojoule laser pulses to the final power amplifier. The HAPLS is being built and commissioned at LLNL and then installed and integrated into the ELI Beamlines facility starting in 2017.

"The Extreme Light Infrastructure in Europe is building international scientific user facilities equipped with cutting-edge laser technology to explore fundamental science and applications," says HAPLS program director Constantin Haefner. "Livermore is one of the world leaders in high-energy, high-average-power laser systems, and ELI Beamlines in Prague has partnered with us to build HAPLS, a new-generation petawatt laser system, enabling new avenues of scientific research."

To meet the rigorous design specification for HAPLS, LLNL had to look past existing laser pump technology. Previously, high-energy scientific laser systems – such as LLNL's National Ignition Facility – used flashlamp technology, from which intense flashes of white light pump the laser-active atoms in large slabs of laser glass to a higher or more excited energy state. To reach the high repetition rate required by HAPLS, the team needed to devise technology that transfers less heat than flashlamps and removes it at faster rates, reducing the time between laser shots.

"Flashlamp technology for lasers has been around for more than 50 years, and we've pretty much pushed the limits of that technology and maxed out what we can do with them," says HAPLS systems architect Andy Bayramian. "We've closed the books on flashlamps and started a new one with these laser diode arrays, enabling a far more advanced class of high-energy laser systems," he adds. 

To develop these diode arrays, LLNL partnered with high-powered semiconductor laser pump module developer Lasertel Inc of Tucson, AZ, USA (a member of the Finmeccanica Group). Lasertel combined semiconductor laser technology with novel micro-optics to supply the megawatt-class pump modules in a reliable, integrated platform. "Our collaboration has enabled several new benchmarks for laser performance to be set in a remarkably short period of time," says the firm's president Mark McElhinney. "This is a validation of the significant progress that has been made toward the routine production of high-energy lasers for revolutionary commercial applications and groundbreaking scientific research."

In addition, to drive the diode arrays, LLNL needed to develop a completely new type of pulsed-power system that supplies the arrays with electrical power by drawing energy from the grid and converting it to extremely high-current, precisely shaped electrical pulses. Each power supply is capable of driving 40,000A. LLNL holds a patent on this technology. 

It is expected that high-average-power, high-energy laser systems enabled by these technologies will drive international scientific research in areas as diverse as advanced imaging, particle acceleration, biophysics, chemistry and quantum physics in addition to national security applications and industrial processes such as laser peening and laser fusion.

"Combining Lasertel's diode technology with Livermore's highly compact and efficient pulsed-power system is the enabling technology to drive high-energy lasers at rep rate," says Haefner. "This combination of expertise has created a robust, stable, laser driver platform with high reliability, cost efficiency and – most important for the scientific user community – long-term scalability to maintain competitiveness in the future."

Tags: Laser diode Lasertel

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Visit: www.lasertel.com