Upgrade of the MTW Laser Facility

July 2013

The new 1430-sq-ft laboratory constructed to develop the MTW-OPAL System

A multi-year upgrade to the Multi-Terawatt (MTW) Laser Facility is underway that will advance high-energy-density plasma physics and ultrafast laser science at the Laboratory for Laser Energetics (LLE). A new ultrafast beamline, based on optical parametric chirped-pulse–amplification (OPCPA), is being added to the facility. This optical parametric amplifier line (MTW-OPAL) will generate 15-fs, 150-mJ pulses at 5 Hz synchronously with the current picosecond pulses. The upgrade also includes modifications to the MTW laser for pumping the final OPCPA amplifier to increase the energy in a single shot to 7.5 J for a peak power of 0.5 PW. This upgrade in a new 1430-sq-ft laboratory adjacent to the Laser Development Laboratory (LDL) enhances current MTW research capabilities and secures the foundation for a broad range of new optical physics and ultrahigh-intensity laser research.

Current research spurred by the MTW laser includes laser–matter interactions, ultrafast laser science, laser and radiation diagnostic development, and materials research. Experimental regimes are achieved that are inaccessible with conventional table-top laser systems and without the cost and schedule overhead associated with large-scale facilities. University of Rochester faculty, LLE staff, visiting scientists and students from external institutions, as well as graduate, undergraduate, and local high school students have performed research facilitated by the MTW laser.

The ultra-broadband front end is being reactivated after it was moved into the new laboratory

The MTW laser currently provides picosecond-scale laser pulses at energies greater than 10 J and will be ramped up to 100 J. Intense laser–solid interactions generate a unique, high-current electron source with relativistic energies. Uncertainties exist in how this hot-electron source is generated and how it couples to overdense plasmas. Important applications rely on a detailed knowledge of these processes, including rapid heating for fast-ignition fusion and energy deposition in solid material for flash radiography, isochoric heating, and x-ray scattering experiments. The aim of the research performed at this facility will be to characterize and optimize the hot-electron source generated with the MTW laser and to understand the underlying energy-coupling mechanisms.

Upgrades to the MTW laser will significantly scale up the peak THz electric field of pulsed THz radiations that can be achieved with conventional laser systems that deliver only pulse energies of the order of a few mJ. Currently, laser-based THz sources can reach a peak THz electric field of the order of 1 MV/cm pumped by laser pulses of ~30 fs and a few mJ. Such a peak electric field can be marginally used to investigate nonlinear interactions between pulsed THz waves and various materials. The peak electric field of laser-based THz radiations generated from laser-induced gas plasmas is mainly limited by the optical pulse energy and pulse duration of the pump laser. With the upgraded laser system, we expect an improvement of 3 or 4 orders of magnitude in the THz peak electric field. THz electric fields as high as 1 GV/cm can push electrons or other charged particles in novel materials (such as metamaterials and graphenes) into highly nonlinear regimes, which will open a new avenue toward nonlinear THz optics and optoelectronics.

The MTW laser system was upgraded in 2012 to boost output pulse energies up to 100 J for broadband (picosecond) or narrowband (nanosecond) operation. The upgrade added a Nd-doped glass rod amplifier (far left) and a programmable spatial light modulator (inset), along with new vacuum image relays, to improve energy extraction from the existing 150-mm disk amplifier.

The MTW laser has played a critical role over the last ten years in developing laser and target diagnostic technologies used for ultra-intense lasers and high-field science because of its high shot rate and flexible experimental platform. Diagnostic development on the MTW has included time-integrated K-photon spectroscopy, high-resolution x-ray crystal imaging, time-resolved x-ray spectroscopy, high-energy ion-emission analysis, and optical transition radiation diagnosis. Each diagnostic has provided a successful platform for diagnostic development in MTW experiments and deployment in larger research facilities such as OMEGA EP.

Extending the MTW laser with a femtosecond OPAL with 10-TW pulses at a 5-Hz repetition rate and 0.5 PW in a single shot will increase its utility as a facility for basic high-energy-density (HED) science and generate secondary radiation for numerous applications. It will also transform the MTW into an internationally competitive laser facility with the strong potential for new discoveries in intense laser–plasma interactions. Potential advances include high-energy particle acceleration, novel high-fluence radiation sources, proton radiography, laser-induced nuclear physics, and pair-plasma production. These areas represent an exciting opportunity with minimal overhead costs to upgrade an existing university-scale facility and for attracting the next generation of graduate-level HED plasma physicists.