BESTIA (Brookhaven Experimental Supra-Terawatt Infrared at ATF) Laser: A Status Report.‬

Outline ATF’s Terawatt CO2 laser overview BESTIA concept (as presented at AAC ’14) Progress since AAC ’14 Current vision of the roadmap to 100 TW

ATF’s Terawatt CO2 laser: Active medium “1 ps” 1 bar 10 bar 10 bar, isotopes 3 ps @ 10.2 µm 1.7 ps @ 9.2 µm

ATF’s Terawatt CO2 laser: Scheme 1 µJ 10 mJ 6 J СЩ2 CO2 CO2 “Master oscillator” Produces a picosecond seed pulse Regenerative amplifier Provides most of amplification Small active volume Isotopic Final amplifier Main source of energy Large active volume No isotopes (yet)

ATF’s Terawatt CO2 laser: Specs Two amplifiers Single amplifier Maximum achievable Routine operation Peak power 2 TW 0.5 – 1 TW 5 GW Pulse energy 6 J 2 – 4 J 10 mJ Pulse duration 3 ps 3.5 ps 1.7 ps Rep. rate 0.05 Hz 3 Hz Wavelength 10.2 µm 9.2 µm

100-TW concept (as of AAC ’14) OPA: fs seed Stretcher + compressor = Chirped pulse amplification High-pressure, isotopic amplifiers Nonlinear compressor Collection of innovations: Non-linear compressor 70 J 50 J 2 ps 25 TW OPA Ti:Al2O3 Amplifier 1 Stretcher 35 µJ 350 fs 10 µJ 100 ps 100 mJ Amplifier 2a Amplifier 2b Amplifier 2c 10 J 100 fs 100 TW

Progress: solid-state frontend In routine operation 0.35 ps 25 µJ 5 ps 0.1 µJ New system: OPA Old system: TEA CO2 laser with amplifier and multi-stage pulse slicing

Chirped-pulse amplification: what’s done In routine operation CPA in regenerative amplifier only Str. Amp. Cmp. 0.35 ps → 80 ps → 50 ps → 1.7 ps Compressor Stretcher YAG Coupler Semiconductor switch (Si) Amplifier vessel Pockels cell Polarizing splitter Photo- detector Osc. OPA Ti:Al2O3 (1.6 ps) Polyanskiy, Babzien, Pogorelsky, "Chirped-pulse amplification in a CO2 laser,"  Optica 2, 675-681, 2015

Chirped-pulse amplification: work in progress 75 mm Self-focusing of a 3.5-ps pulse in NaCl window 0.5 J 0.7 J 0.9 J 1.3 J 1.7 J 2.5 J Full-power compressor test stand Vacuum chamber for BESTIA’s compressor: 1.5 x 2.4 m2 165x220 mm2 75 lines/mm 1 TW (3.8 J, 3.5 ps) demonstrated

Non-linear compressor non-linear material aperture (spatial filter) Pair of small-density gratings (linear compressor) >1 ps <1 ps 2.5 J 20 mm 3.5 J Spectrum 2.5 J OUT IN Proof-of-principle test: simulations Pulse Polyanskiy, "Pulse compressor,” US Patent Application 20160013605 A1 (Jan. 14, 2016) OUT Polyanskiy, "co2amp: A software program for modeling the dynamics of ultrashort pulses in optical systems with CO2 amplifiers,"  Appl. Opt. 54, 5136-5142, 2015 IN

Optical materials considerations F=50 cm sample laser vacuum: <= 0.1 mbar Cu mirror 100 µm I0 = 8.0 J/cm2 “Replica” Cu grating I0 = 3.4 J/cm2 Damage threshold (J/cm2) 1.7 ps @ 9.2 µm Bare Grating (replica) Grating (master) Cu 5 1.5 ??? Al 0.5 Mo 2.5 - 100 µm

6 m Ø1 m New final amplifier Discharge 3 × (8.5×10×100 cm3) isotopic CO2 50% 18O BESTIA’s design energy: 70 J before compression Present system: demonstrated 18.5 J in chirped pulse

Roadmap Present system CPA Real-life test of full-power CPA at 0.5-1 TW More stretching, reach 100 mJ in regen Test master Cu grating Non-linear compressor: proof of principle (R&D) BESTIA Final amplifier Start with two amplifier sections Start without isotopes Demonstrate 30-35 J in chirped pulse In-vacuum compressor Demonstrate 15-20 J after compression (5 TW, 3.5 ps @ 10.2 µm) Isotopes Install and test CO2 freeze-out system for isotope recovery Add isotopes to main amplifier Demonstrate 15-20 J after compression (10 TW, 1.7 ps @ 9.2 µm) Non-linear compressor (R&D) Achieve 25 TW Future BESTIA R&D towards 100 TW