Matter in Extreme Conditions (MEC)

Overview

The Matter in Extreme Conditions (MEC) instrument of LCLS is provided part time to LaserNetUS users as a laser facility for optical-laser-only experiments using either or both of its long and short pulse lasers in the 2 m target chamber. The two laser systems may be used together or separately. The same expert staff that operates MEC as part of the LCLS national user facility is available to support LaserNetUS experiments.

Long pulse laser system

The long pulse laser at MEC is designed to provide up to 10s of Joule shapeable pulses at 527 nm to create high pressure states (typically ~ 0.1 to 4 Mbar), warm dense matter conditions, high strain rate material states, or the formation of a plasma environment. The maximum energy deliverable to target will depend greatly on pulse shape, with a reference point of >60 J deliverable in a 10 ns square pulse. This energy is split between four arms, which are polarization-multiplexed into two beamlines for delivery to target. The laser system features a diode pumped front end with exquisite pulse shaping capabilities and excellent stability. A variety of pulse shapes, from as short as 3 ns  to as long as 35 ns can be provided to users, tailored to create specific thermodynamic trajectories in a compression system. The shot rate of the main amplifiers is 1 per seven minutes.

The long pulse focus can be shaped by one of several phase plates available at MEC. These phase plates produce nominally 150 µm, 300 µm, and 600 µm spot sizes with the standard aspheric lens sets, and measured beam profiles can be provided on request. Uniaxial shocks above 3 Mbar have been demonstrated in plastic ablators using the 150  µm spot; higher pressures can be reached through impedance mismatch.

Short pulse laser system

MEC employs a Ti:Sapphire double CPA laser system to enable dense plasma studies and relativistic particle production. A CPA regenerative amplifier front end is delivered compressed to a pulse cleaner, the output of which is stretched to 180 ps and amplified in two bowtie amplifiers to up to 1.5 J, compressed to 1 J in 40 fs for delivery to target, at up to 5 Hz repetition rate.

A robust pulse cleaner based on a Topas-Prime colinear OPA allows the system to achieve a pulse contrast of better than 10^-8 at 4 ps, and better than 10^-11 at 30 ps. This is currently the measurement threshold for the full energy output; the front end contrast reaches the noise floor of 10^-12 at 5 ps.

The short pulse laser has been used in a number of specialized configurations:

• Frequency doubled to 400 nm for extreme contrast, with over 400 mJ to target at up to 5 Hz, or mJ level at up to 120 Hz
• A frequency doubling crystal and dichroic optics are available to deliver 400 nm light to target at even higher contrast.
• An uncompressed mode for over 1.5 J in 130 ps at up to 5 Hz 
• In specialized demonstration experiments, generation of betatron, HHG, or THz probes for interaction with matter heated and/or compressed either with part of the short pulse energy laser energy or the long pulse.

Target chamber and diagnostics

The MEC target chamber is a versatile 2 m vessel designed after the LLNL Titan and LANL Trident West target chambers. The target chamber has numerous ports on the sides, top and bottom, which can be fitted with windows, feedthrough ports, and target delivery systems. A standard target positioner with 5-axis motion and a large rastering target frame are used most frequently, but a number of custom target types have been fielded by users including rotating cylinder, gas jet and cryogenic liquid jets.

Commonly used diagnostics at MEC include dual line VISARs, a set of X-ray spectrometers covering photon energy ranges from 5 to 25 keV, a set of X-ray cameras including four large format vacuum pixel array detectors for diffraction measurements, and an X-ray imaging platform including compound refractive lenses and an Optique Peter X-ray microscope. Less commonly used diagnostics at MEC include a fourier domain interferometer and XUV spectrometer. Users should contact MEC with questions  regarding existing hardware and accommodation of user-provided hardware.

MEC User Support

MEC is an instrument of the LCLS user facility, which typically runs 10 months per year. MEC provides optical-laser-only beam time to LaserNetUS users as the LCLS schedule allows, typically 1-2 user experiments per year. A professional staff provides direct experimental support with each experiment dedicated points of contact for experiment setup, controls/data systems, detectors, lasers, and mechanical engineering. The LCLS facility provides a full-service user experience, from proposal development, through planning and experimental execution, to online data analysis.

Facility access

All members of an experimental team expecting to be present at MEC must be registered with LCLS through the SLAC User Portal and complete all required courses before arriving (some courses are only required for specific activities). The spokesperson for an accepted LaserNetUS proposal (e.g. they who submitted the proposal) will be asked to name a principal investigator (PI) for the experiment. An MEC Instrument Scientist Point Of Contact (POC) will be assigned, who will guide the PI through the steps of preparing for their laser time.

https://lcls.slac.stanford.edu/instruments/mec
Gilliss Dyer, Gilliss@slac.stanford.edu