Status Report on the B820 CO2 Laser R&D

Status Report on the B820 CO2 Laser R&D

Status Report on the B820 CO2 Laser R&D Program Mikhail Polyanskiy Where we stand 2 CO2 laser R&D TW ! 2 of 25 Outline Introduction Picosecond long-wave infrared (LWIR) laser ATFs know-hows (CPA, mixed-isotope CO2) Steady progress since last ATF users meeting Pulse duration reduced (a lot) Puzzle of pulse extension at high energy Mystery solved, path for further improvement Pleasant surprise: high gain of rare-isotope CO2 molecules Technical details New optical layout of TW room New re-incarnation of CO2 freeze-out system

Reflection isolator Plasma shutter Vacuum beam transport Copper apodizing mirrors Non-linear pulse compressor: simplified design for sub-scale test Summary CO2 laser R&D 3 of 25 Introduction CO2 laser R&D 4 of 25 ATFs Long Wave Infra Red laser Solid state (OPA) 104 22 10-6 J 102-103

CO2 10 J -2 CO2 J++ Seed laser Produces a picosecond seed pulse Regenerative amplifier Provides most of amplification CO2 laser R&D 5 of 25 Final amplifier Main source of energy ATFs know-how Chirped

Pulse Amplification STRETCHER CO2 CO2 Mixed-isotope active medium CO2 laser R&D 6 of 25 COMPRESSOR Why mixed-isotope active medium? 1 ps 0.15 m 1 bar 10 bar 10 bar,

isotopes 2 ps @ 9.2 m CO2 laser R&D C16O2 : C16O18O : C18O2 25% : 50% : 25% Simulations: co2amp 7 of 25 Transition to full-scale CPA and isotopic active medium 2014: isotopes & CPA in regen only STRETCHER CO2 COMPRESSOR CO2

Polyanskiy, Pogorelsky,isotopes Yakimenko, Picosecond pulse amplification 2018: full-scale & CPA in isotopic CO2 active medium, Opt. Express 19, 7717-7725, 2011 Polyanskiy, Babzien, Pogorelsky, "Chirped-pulse amplification in a CO2 laser," Optica 2, 675-681, 2015 STRETCHER CO2 CO2 laser R&D CO2 8 of 25 COMPRESSOR Pulse duration improvement over last year CO2 laser R&D

9 of 25 Pulse duration Nov 2017 (20th ATF Users meeting) gy r e mm en . 3 of 0 1 % 30 in p -p t os u optimization s e

s l Dec 2017 mixed-isotope amplifiers Aug 2018 (AAC) optimization Nov 2018 (Now) new (denser) gratings [Mid-2019] 9.2 mm single pulse CO2 laser R&D 10 of 25 AGSe Our understanding of CPA as of 2017 pulse configuration 75 lines/mm 100 lines/mm

(present) (new gratings) 10.3 mm 4 ps 0.11 THz 20 ps 2 9.2 mm 2 ps 0.22 THz 40 ps (mixed-isotope CO2) 2 80 ps * calculated for 10-J pulse

CO2 laser R&D 11 of 25 Why 10% difference in wavelength is non-negligible? 10.3 mm 9.2 mm Grating pair Group delay dispersion (ps/THz) in dispersive elements of CPA 10.3 mm 75 lines/mm Stretcher (fixed length) 206.2 NaCl (1800 mm) -16.5 Compressor (optimized length) -189.7

CO2 laser R&D 9.2 mm 75 lines/mm 144.7 9.2 mm 100 lines/mm ~2 291.2 -11.5 -11.5 -133.2 -279.7 12 of 25 Accurate model pulse

configuration 75 lines/mm 100 lines/mm (present) (new gratings) 10.3 mm 4 ps 0.11 THz 21 ps 1.4 9.2 mm 2 ps 0.22 THz 29 ps 40 ps (mixed-isotope CO2)

2.1 62 ps 80 ps * calculated for 20-J pulse CO2 laser R&D 13 of 25 What stretching do we need? Old system (10.3 mm) 0.11 THz Mixed-isotope CO2 (9.2 mm) 75 -> 100 lines/mm gratings 0.1 J/cm2 0.5 J/cm2 1.0 J/cm2 1.5 J/cm2 2.0 J/cm2 2.5 J/cm2 0.22 THz 0.22 THz

2018 2017 2 ps 4 ps CO2 laser R&D 14 of 25 2019 2 ps Peak power Next milestone: 4 TW Now: 2 TW CO2 laser R&D 15 of 25 [5 TW] need compressor efficiency ~70%

(now 50%) Gain of isotopic CO2 active medium revisited 50% 46% 43% Sim ula tio n s Ex p eri me n t Oxygen-18: 54%

New constants: A(C16O2) same A(C16O18O) 1.5x A(C18O2) 2.25x Simulations: co2amp CO2 laser R&D Gain: 2.1 % / cm New constants, 43% 18O Old constants, 54% HITRAN 2008 > HITRAN 2016 1.4 % / cm A(C16O2) ~same A(C16O18O) ~same A(C18O2) 1.9x 16 of 25 18

O What else? CO2 laser R&D 17 of 25 Compressor re-configured, re-located to TW room 3m ter e m o r Spect gs n i t a r g ator l

e r r co Auto CO2 laser R&D p m A 18 of 25 r e i f li CO2 laser R&D v. re ~8 ge 20 ho n 08 ur

s rs v re . 2- ge 20 3 n ho 15 u er + + v fin . 2- al 2 3 am 0 ho ur plif 18 s i CO2 recovery (enabling technology!) N2

He CO2 N2 He 19 of 25 ~1:1:18 LN2 Plasma shutter T0 Shutter Open CO2 Pulse From Amplifier To Experiment Nd:YAG T0 + 20-25 ns Shutter Closed Switching Pulse

CO2 Pulse Retroreflected Amplifier Protected From Experiment CO2 laser R&D 20 of 25 Vacuum beam transport FEL Room Ion chamber, existing experimental chamber Laser shutter, 1x Mirror box, 10x Plasma

shutter Com Las presse er P d ulse Gate valve, 4x Experimental BL1 experimental Hall chambers (3x) CO2 laser R&D 21 of 25 Laser-machined apodizing Cu mirrors 01 R 1.0 0.8 0.6 0.4 0.2 0.0

-R R 0 sin2 CO2 laser R&D 22 of 25 Collaboration with Euclid Techlabs Non-linear pulse compressor: design of sub-scale proof-of-principle setup 50 mm NaCl 25 mm 12-m vacuum enclosure Brewster ZnSe 12 mm 5 mm dia. aperture 4.5 m

NaCl 60 mm 7.5 m ~1.5 TW ~0.5 - Input NaCl (vacuum window) minimum impact on the pulse 0.31 E=1 0.35 J J 0.92 - ZnSe (nonlinear component) self-phase modulation + self-focusing 160 fs FWHM = 2 ps - Aperture (spatial filter) performance stabilization = 15 mm - Output NaCl (dispersive compressor) pulse compression via linear dispersion CO2 laser R&D 23 of 25 Conclusion

CO2 laser R&D 24 of 25 Summary Next milestone: 4 TW 2.5 TW achieved (reliable operation @ 2 TW) [5 TW] need compressor efficiency ~70% (now 50%) Full-scale mixed-isotope, CPA operation 9.2 mm (!), 2 ps, 2 TW Now: 2 TW Better understanding of CPA, path to higher peak power (4-5 TW) Progress on spectroscopy/simulations front All-new beam delivery infrastructure (reflection isolation, vacuum) Simplified design of NLPC ===== THE END ===== CO2 laser R&D 25 of 25

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