Scarlet Laser Facility

Overview

The Scarlet Laser Facility includes over 4,000 sq. ft. of contiguous laboratory space with laser and experimental bays, an experimental development room (with two large optical tables, dedicated 36” diameter vacuum chamber) and the control/preparation room. The laser bay houses the Scarlet laser system within 1000+ sq. ft. of class 1000 clean room. The Scarlet pulse parameters are listed in the table below. Notable aspects:

• Tight focus resulting in on-target intensities exceeding 5×10²¹ W/cm².
• Pulses focused inside a 76” diameter target chamber located in the experimental bay.
• Many ports and large rectangular doors for easy access; Interior breadboard.
• Also available: 10 Hz pulses with a peak power of 10 TW, producing on-target intensities exceeding 10²⁰ W/cm².
• New long focal length mode using an f/17 focus, focus located in auxiliary chamber off main chamber..
• Liquid crystal film target system available.
• Liquid crystal film plasma mirror system available.

Technical design: A detailed discussion of Scarlet is described in Poole, et al., Applied Optics 55, 4713 (2016), but note current pre-pulse contrast is significantly improved. Briefly, Scarlet is based on dual chirped pulse amplification using Titanium Sapphire gain media. The system begins with a Femtopower 9 fs, Kerr lens modelocked oscillator, which is stretched to 2 ps and amplified to 1 mJ at 1 kHz in a 9-pass amplifier. The laser pulses are then compressed to 25 fs, and sent through a non-linear cross polarization wave generation filter system, which enhances the pre- and post-pulse contrast ratio by ~104. The pulse length is then stretched to 800 ps in a striped-grating pulse stretcher based on the Perry-Banks schematic. The stretched laser pulses are amplified to 500 µJ energy/pulse before pulse-selecting to 10 Hz using a Pockels cell. A fast, kHz mechanical shutter prevents leakage light from propagating further downstream. The laser is further amplified in two multi-pass amplifiers to an energy of 1.4 J/pulse, providing the 10 TW operational mode. For >300 TW operational level, the repetition rate is further gated to 1 shot/min using a Pockels cell. The laser beam is image relayed and spatially filtered to the final amplifier to preserve mode quality. The 3-pass final amplifier uses a 70 mm diameter Ti:Sapphire crystal pumped symmetrically by 50 J of green light from two custom Nd:Glass lasers by  Continuum Lasers to amplify the uncompressed short pulse to >22 J/pulse. The amplified pulses are spatially expanded and vacuum relay imaged to the high vacuum pulse compression chamber, containing two large high efficiency, high damage threshold gratings which compress the laser pulse to 30 fs duration at 10 J/pulse. After compression, the pulses are delivered to a dedicated 76” diameter target chamber. To prevent contamination of the compressor gratings from debris generated during an experiment, a pellicle chamber is placed between the target chamber and the compressor chamber, isolating the two chambers using a 2 μm thick pellicle placed at Brewster’s angle. Within the target interaction chamber, the compressed laser pulse is incident onto a specially designed “leaky” mirror which directs the majority of the pulse energy to an F/2 off-axis parabolic mirror, bringing the light to a 2 μm FWHM focal spot, producing on-target intensities in excess of 5×10²¹ W/cm². The leaky mirror transmits ~1% of the incident light which propagates to a separate diagnostic table, providing sufficient laser energy for a number of on-shot laser diagnostics.

Laser Diagnostics

A number of on-shot and on-demand laser diagnostics are available to provide characterization of the Scarlet laser pulse, including:

• Vacuum autocorrelator and SHG FROG.
• Pulse contrast measurable on-demand to >10 orders dynamic range using a SEQUOIA scanning third-order cross correlator.
• Nanosecond contrast measurable on-demand using a saturated fast photodiode, providing up to 8 orders dynamic range.
• For compressed pulses, all other diagnostics are performed on a diagnostic table outside the target chamber. These include on-shot energy, spectrum, equivalent plane focal spot, jitter monitor, GRENOUILLE

Experimental Chamber and Diagnostics

The target room houses a dedicated 76” diameter interaction chamber with 38 ports for mounting experimental equipment. The chamber is a ¾-scale version of the Titan laser chamber (JLF, LLNL) with some enhancements. Experimental diagnostics are available for implementation on the target chamber, including:

• Thomson parabola ion spectrometer for ions up to 35 MeV/nucleon; image plates or MCP detector
• Magnetic spectrometer for up to 50 MeV electrons/positrons
• Radiochromic film stacks for spatial distributions of accelerated ions
• Two HOPG x-ray spectrometers to measure k-α and k-β from Cu
• Cu Ka imager
• QUESTAR long working distance microscope for precision transverse target alignment
• Confocal High Intensity Positioner for precise target alignment within focal depth
• Housings for user provided  neutron bubble detectors.
• XUV/X-ray Flat field spectrometer (5 – 70 nm wavelength)
• Typhoon FLA 7000 Image plate reader; high resolution photographic scanner

https://hedp.osu.edu/facilities/scarlet
Douglass Schumacher, schumacher.60@osu.edu