Livermore Pushes Beyond Flashlamps to Boost Laser Repetition Rates

The world’s highest-peak-power laser diode arrays are now online at Lawrence Livermore National Laboratory.

Representing a total peak power of 3.2 MW, the arrays are destined to become part of the High-Repetition-Rate Advanced Petawatt Laser System (HAPLS) in 2017. Livermore has been developing the arrays for integration into the European Union’s Extreme Light Infrastructure (ELI) Beamlines facility under construction in Prague.

The facility is meant to support international research in 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.

To drive the diode arrays, Livermore needed to develop a completely new type of pulsed-power system. Images courtesy of Damien Jemison/ Lawrence Livermore National Laboratory.

HAPLS is designed to generate 30-fs pulses with peak powers >1 petawatt at a repetition rate of 10 Hz.

The repetition rate will be a major advancement over current 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.

To meet the rigorous design specification for HAPLS, Livermore had to look past current laser pump technology. Existing high-energy scientific laser systems like Livermore’s National Ignition Facility use flashlamp technology to pump atoms in large slabs of laser glass.

In order to get to the high repetition rate required by HAPLS, the team needed to come up with technologies that transfer less heat than flashlamps and remove it at faster rates, which lessens 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,” said HALPS systems architect Dr. 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.”

The diode arrays represent total peak power of 3.2 MW, making them the highest peak-power diode arrays in the world. Courtesy of Damien Jemison/Lawrence Livermore National Laboratory.

To develop these diode arrays, Livermore partnered with Lasertel Inc., a member of the Finmeccanica Group and a developer of high-powered semiconductor laser pump modules. Lasertel combined advanced 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,” said Lasertel 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, Livermore needed to develop a completely new type of pulsed-power system in order to drive the diode arrays. The pulsed-power system 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 40,000 A. Livermore holds a patent on this technology.

Meanwhile, Northrop Grumman Cutting Edge Optronics recently installed another HAPLS component at Livermore. The joule-class, injection-seeded, diode-pumped solid-state (DPSS) laser system will serve as the pump source for one of the HAPLS high-energy Ti:sapphire amplifier stages.

The Gigashot-HE consists of four PowerPulse laser modules — an oscillator, a pre-amplifier and two power amplifiers — radially side pumped Nd:YAG rods ranging in diameter from 3 to 18 mm. The system outputs 2 J of 532-nm energy in each sub-10-ns pulse at 10 Hz with a near-field flat-top beam profile.

For more information, visit www.llnl.gov.