ATF CO2 LASER

back to basics present status research highlights

Igor Pogorelsky ATF block diagram

Nd:YAG LASER 81.6 MHz

x 35

RF GUN YAG: drives RF photocathode

slices ps CO2 pulse

CO2: used in laser/e-beam

New fs laser and laser/matter interaction experiments CO 2 LINAC LASER Coming soon: New 500 fs ……laser for sub- picosecond CO2 slicing

e- ATF laser personnel

z Igor Pogorelsky CO2 laser and experiments support

z Mikhail Poliansky LDRD Postdoc, simulations, CO2 diagnostics

z Marcus Babzien YAG laser, general optical diagnostics

z Daniil Stoliarov Post-doc, fs solid-state laser

z Karl Kusche laser safety, computer controls

z Vitaly Yakimenko global laser strategy

+ ATF computer engineer, electronic engineer, designers, technicians Industrial CO2 lasers

•Up to 100 kW average power •Operate at low pressure <<1 atm •Bandwidth ~P (10 atm supports a picosecond pulse)

4 Ultrafast gas lasers require high pressure

Inverse Fourier Transform for discrete spectrum results in a train of discrete pulses m n f ()t = ∑ fk (t0 + ∆t × k) f ()t = ∑ F j ()t exp[]i2π (ν 0 + ∆ν × j)t k=0 j=0 where τ k ≈ τ 0 , m≈1/τ0 δν, δν - rotational where n ≈ 1/τ0 ∆ν, τ0 is the initial pulse width. linewidth defined by pressure broadening.

∆t = 1 ∆ν ~20 ps

∆ν ~50 GHz

5 Commercially Available High-Pressure

CO2 Laser with UV-ionized discharge UV-preionized Pressure 10 atm Beam Size 13 x 13 mm2 Repetition Rate 20 -500 Hz Pulse Energy 1.5 J Average Power 750 W

6 Custom high-pressure x-ray ionized

CO2 amplifier operated at BNL/ATF

Optoel Co. St. Petersburg

Discharge 10x10x100 cm3 Stored energy hν x ∆N =10 mJ/cm3 Pressure 10 atm Small-signal gain σ x ∆N = 2%/cm Voltage 1 MV Saturation fluence hν/σ = 0.5 J/cm2 hν=0.1 eV=1.6x10-20 J, σ=3x10-20 cm2, ∆N= 1018 cm-3

7 High-pressure CO2 amplifiers operated at BNL/ATF

OPTOEL

SDI

8 Methods of short pulse generation Semiconductor optical switch

•Reflection by electron-hole super-critical plasma controlled by a short- wavelength laser.

Nd:YAG Reflected CO2

electron- hole plasma

Initial CO Reflectivity (%) 2

19 10 Transmitted CO2 Plasma Density (cm-3 ) •Reflection lasts for 200 ps defined by relaxation of free carriers.

•Two switches allow to slice CO2 pulse to the duration of a control pulse.

9 Methods of short pulse generation Kerr effect

ps GW YAG 45-deg polarized CS2 ps CO2 2 s-polarized

n io Polarizer ced t u za d ri in la o p

final E initial E

•A higher-power laser induces polarization in optically active CS2 liquid. •This rotates polarization of a portion of a CO2 pulse overlapped with YAG. •Relaxation of CS2 molecules in 1-2 ps.

10 Methods of short pulse generation Parametric generator

CO 2

ω2

CO2 YAG ω2=ω1−ω3 ω1 Two-step process: ω3=ω1−ω2 •Mixing two laser beams in a nonlinear crystal with production of differential frequency.

•Mixing ω3 and ω1 with production of a CO2 pulse at the duration of YAG or shorter. •Insignificant stretch in thin crystals, 1 ps is possible.

11 CO2 laser system delivers 0.5 TW, 6 ps pulses

CO oscillator 3-atm preamplifier 2 10 ns

10-atm regenerative amplifier

14 ps YAG 14 ps YAG Kerr cell 200 ps 6 ps Ge switch

9-atm final amplifier 6 ps SH-YAG Ge switch

12 ATF success story

3 TW LACARA Ion and proton source Thomson scattering Intra-cavity PASER Compton 300 GW source Nonlinear EUV source Thomson scattering

HGHG STELLA 30 GW Thomson X-ray source Inverse Cherenkov accelerator IFEL accelerator 3 GW 1995 2000 2005 2010 13 BenefitsBenefits fromfrom usingusing COCO22 laserlaser

ATF pioneers a picosecond CO2 gas laser for strong-field physics applications. This provides a new platform for exploring novel methods of particle acceleration and radiation sources.

CO2 (λ=10 µm) advantages as compared to solid-state lasers (λ~1 µm) : • 10 times more photons per Joule • favorable scaling of accelerating structures, better electron phasing into the field • stronger ponderomotive effects at the same laser intensity Long-wavelength benefits: better electron phasing into the field Long-wavelength benefits: stronger ponderomotive effects

Energy of the electron quiver motion in laser field E

mv2 v& eE Φ = v ~ v& ~ 2 ω m - e2 E 2 Φ ~ 2mω 2

I Φ ~ note the ω2 dependence ω 2

16 Proton accelerator

Production of fast electrons is the key.

•At the same power and energy, CO2 laser will provide the same ponderomotive action within ~λ2 (100 times ) bigger area or ~λ3 (1000 times) bigger volume. •Accordingly, we expect that the number of accelerated ions would grow with λ.

17 Demonstration of record yield and 2nd harmonic in relativistic Thomson scattering

With 5 J CO2 laser focused to σ = 35 µm, note that 10-µm laser produces 10 times we demonstrated record x- more photons per Joule than 1-mm laser ray yield Nx/Ne-~1 nd And 2 harmonic in N N relativistic Thomson x = L σ scattering 2 T Ne πw0

18 Spin-offs from earlier Thomson scattering experiments

Parametric studies Intra-cavity gamma-source

65 MeV 66 MeV

70 MeV 67 MeV

69 MeV 68 MeV

credits to UCLA Next laser talks

z Marcus Babzien “Experimental support and instrumentation“ z Mikhail Polyanskiy ”Simulation and diagnostic tools for better understanding and upgrade of

the CO2 laser“

z Daniil Stolyarov “A femtosecond CO2 front end based on frequency mixing with an Ytterbium laser“

z Igor Pogorelsky “CO2 laser: Near-term plans“