Around the Lab

The OMEGA EP Laser System, operating at a base wavelength of 1053 nm (IR), consists of four beamlines of which two have picosecond pulse capability. For pulse widths of 10 ps or greater, the on-target energy can be as high as 2600 J. When the pulse width is between 1 and 10 ps, the on-target energy is reduced, scaling as a function of the pulse width. This is because of damage thresholds of the optical coatings at the output of the system. For pulse widths less than 1 ps, the system is capable of producing ~0.7 PW (500 J/0.7 ps) of optical power on target. The focal spot of the short-pulse beams encloses 80% of the energy in a 16-µm-radius spot, producing on-target intensities of greater than 7 × 10¹⁹ W/cm².

In addition to the short-pulse capability in two of the beamlines, all four OMEGA EP beamlines have a long-pulse capability with pulses ranging from 0.1 to 10 ns. These pulses are used to produce plasmas for interaction experiments with the short-pulse beams and for nanosecond, high-energy-density experiments in the OMEGA EP target chamber. The nanosecond pulses are generated and delivered in essentially the same manner as those on OMEGA, including wavelength conversion from the base wavelength to 351 nm (UV). The long-pulse, on-target UV energies are again limited by the damage thresholds of the optical coatings but can reach 1250 J per beam for 1-ns pulses and 5000 J per beam for 10-ns pulses.

Radiography and other extreme-field experiments drive the mission for OMEGA EP. This system provides ultrahigh intensities for advanced x-ray and proton-beam radiography of compressed targets. Radiography is an important technique used in inertial confinement fusion (ICF) experiments for capturing a snapshot of targets as they are being driven by the laser. An intense laser pulse illuminates a block of material located near the target and generates a short burst of x rays or protons which, like a dental x-ray, produces a radiograph of the target. OMEGA EP’s very high intensities produce x-ray sources that can overcome the radiation emitted by the target driven by the OMEGA laser. In addition, x rays with very high photon energies can be produced that permit backlighting targets compressed to high density. The pulse widths described earlier provide for a short duration of the x-ray burst that sets the temporal resolution of the images that are collected. This is very important in capturing clear (not blurry) images of objects moving at very high velocity. High-energy protons can be produced in addition to x rays, offering the opportunity to probe a compressed target’s ionization state and electromagnetic fields in and around the target.