INFLPR

1. INFLPR Amplificarea pulsurilor laser ultrascurte. CPA in Ti:safir sau OPCPA? Solutii pentru laserul ELI-RO. (Partea I) R. Dabu Sectia Laseri, INFLPR

2. INFLPR • De ce aceasta prezentare? • Cunoasterea stadiului actual pe plan mondial in domeniul laserilor de mare putere in femtosecunde • Incercam sa dam un raspuns privind solutia tehnica potrivita pentru laserul ELI-RO • Ce putem face ca sa ne incadram in efortul stiintific necesar pentru realizarea acestui laser • Sa facem un pas mai departe in pregatirea unor specialisti in domeniul “laseri in femtosecunde de mare putere si directii de cercetare bazate pe acesti laseri” • Sa atragem in echipa de lucru tineri cu un background care sa le permita incadrarea rapida in acest domeniu

3. INFLPR • CUPRINS • 1. Amplificarea pulsurilor laser cu deriva de frecventa (“chirped pulse amplification” - CPA) in Ti:safir. • - Caractersiticile Ti:safir ca mediu amplificator laser. • - Probleme legate de amplificarea pulsurilor de femtosecunde de mare energie. • 2. Ce este amplificarea parametrica si, in particular, OPCPA. • - Oscilatia, generarea si amplificarea parametrica ca fenomene in optica neliniara. • - Relatiile care guverneaza fenomenele parametrice. • - Castigul unui amplificator parametric, banda de frecventa. • 3. Amplificare parametrica optica (OPA) de banda larga si de banda foarte larga. • - Conditiile de obtinere a amplificarii parametrice de banda larga sau foarte larga. • - Cum se calculeaza pentru un cristal dat parametrii de functionare in cele doua cazuri. • - Potentialul aplicarii pentru laserii cu pulsuri ultrascurte de mare putere. • - Amplificarea parametrica a pulsurilor largite cu deriva de frecventa – OPCPA. • - Metode de obtinere a amplificarii de banda larga: la degenerescenta, amplificare necoliniara, folosirea mai multor laseri de pompaj. Exemple. • - Metode de obtinere a amplificarii de banda foarte larga.Benzile de amplificare foarte larga in cristale BBO si DKDP pentru laserii din clasa PW. • 4.Prezentarea unor sisteme laser amplificatoare in domeniul PW: • - Laserul rusesc cu oscilator in fs la 1250 nm (Cr:forsterite) si amplificare in cristale DKDP. • Laserul englez (910 nm) cu amplificare de mare energie in DKDP. • - Laserul german cu amplificare pe ~ 900 nm. • - Laserul francez cu amplificare pe 800 nm in BBO si Ti:safir. • - Comparatie intre diferite sisteme de amplificare (China, Korea, Japonia, Rusia, Franta, Germania si Anglia). OPCPA versus amplificare in Ti-safir: avantaje si dezavantaje. • 5. Care ar fi cea mai buna solutie pentru laserul ELI-RO? Ce e de facut pentru realizarea la timp si la parametrii propusi a sistemului laser ELI-RO?

4. 2xFRONT END DPSSL-pumped OPCPA AMPLIFIERS Ti:Sapphire pumped by ns Nd:YAG & Nd:Glass lasers DIAGNOSTICS A3 +A4+ A5 POWER AMPLIFIERS >300 J A1 + A2 BOOSTERS > 4 J, 10Hz FE1: 10-20 mJ BW > 120 nm TCP = 50 ps 0.1-1 kHz C > 10^12 BEAM TRANSPORT IN VACUUM COMPRESSOR >200 J COMPRESSOR 200 J A3 +A4+ A5 POWER AMPLIFIERS >300 J A1 + A2 BOOSTERS > 4 J, 10Hz BEAM TRANSPORT IN VACUUM INFLPR COMPRESSOR 200 J COMPRESSOR >200 J TARGETS FE2: > 100 mJ BW > 80 nm TCP= 1-2 ns 10-100 Hz C > 10^12 A3 +A4+ A5 POWER AMPLIFIERS >300 J A1 + A2 BOOSTERS > 4 J, 10Hz BEAM TRANSPORT IN VACUUM COMPRESSOR 200 J COMPRESSOR >200 J Φ = 1-20 μm IΣ = 3 x 1023 -24W/cm2 TEST COMPRESSOR TARGETS DIAGNOSTICS BW – Spectral bandwidth, C – intensity contrast, TCP- chirped pulse duration, TC – re-compressed pulse duration, Φ – focused laser beam diameter, IΣ – intensity on target Nuclear Laser Facility Layout (as presented in the ELI Cz-Hu-Ro proposal)

5. INFLPR Time schedule for ELI-RO Laser HIGH ENERGY AMPLIFIERS, COMPRESSOR, BEAM TRANSPORT AND FOCUSING MEDIUM ENERGY AMPLIFIERS FRONT-END E ~ 200 mJ B ~ 100 nm (compressible down to 15 fs) Tstretched ~ 2 ns Ns & ps contrast > 1012 Rep rate ≥ 10 Hz E > 300 J Compressible to < 20 fs and > 200 J Ns & ps contrast > 1012 Rep rate 0.1- 0.02 Hz I FOCUSED ~ 1023-24 W/cm2 E > 4 J Compressible down to 15 fs Ns & ps contrast > 1012 Rep rate 10 Hz 2010- Middle of 2012 End of 2013 End of 2015 2010 2011 2012 2013 2014 2015

6. 10 PW laser, a very difficult task (high risk project): X 50 more powerful than any existing femtosecond commercial laser X 20 more powerful than any existing femtosecond laboratory laser system X 500 more powerful than femtosecond TEWALAS laser at INFLPR Factors of (high) risk: -high energy (200-300 J/pulse)laser amplifier - re-compression of stretched amplified pulses and laser beam focusing - expected results of nuclear physics experiments INFLPR Two possible solutions for high energy femtosecond pulses amplification:

7. INFLPR Selection criteria for ELI-RO laser system • 1. Able to fulfill required specifications: • Peak pulse power ~ 10 PW per one amplifier chain • Pulse-width of the re-compressed amplified pulse < 20 fs • Rep-rate 1/10 – 1/60 Hz • Ns & ps contrast > 1012 • Focused laser intensity 1023-24 W/cm2 (Laser beam focused near the diffraction limit) • 2. Existing techniques proved by the long term laser facilities operation(200 TW Ti:sapphire CPA laser systems) • 3. Existing laser components and devices necessary to reach 10 PW power (e.g. ~ 30 cm diameter DKDP crystals) • 4. Required laser components and devices that could be probably developed in the next years (20-cm diameter Ti:S rods; Nd:YAG, Yb:YAG, Nd:glass, diode pump lasers; diffraction gratings, etc.) • 5. Conditions of operation and expected laser system long-term stability • 6. Costs of the whole laser system • First target : 2012  Front-End able to satisfy the required laser specifications to be installed in Bucharest-Magurele.

8. INFLPR Oscillator Stretcher Compressor Amplification Principle of Chirped Pulse Amplification (CPA) for Gaussian temporal and spectral pulse profile - ultra-short pulse duration, - phase-locked spectral band-width CPA technique involves the temporal stretching of ultra-short pulses with a large spectral bandwidth delivered by an oscillator. This way, the laser intensity is significantly reduced in order o avoid the damage of the optical components of the amplifiers and the temporal and spatial profile distortion by non-linear optical effects during the pulse propagation. After amplification, the laser pulse is compressed back to a pulse duration very closed to its initial value

9. INFLPR Definitions related to the broad-band ultrashort pulses • Ultrashort laser pulse is characterized by: • Central frequency and corresponding wave-number • - Frequency spread arround and corresponding spread in wave-number • Evolution in time of the pulse is related to: Phase velocity Group velocity If second, third order terms are negligible, the laser pulse travels undistorted in shape with the goup velocity VG.

10. INFLPR Definitions related to the broad-band ultrashort pulses Group velocity mismatch Group velocity dispersion Electric field of the laser pulse in the frequency domain: where Group delay L, medium length Group delay dispersion Third order dispersion

11. INFLPR Ti:sapphire amplification Polarized fluorescence spectra and calculated gain line for a optical c-axis normal cut Ti:sapphire rod; π– c-axis parallel polarized radiation; σ– c-axis normal polarization Stimulated emission cross section at 795 nm (c-axis parallel polarized radiation): P. F. Moulton, JOSA B, Vol. 3, 125 (1986)

12. INFLPR Pulse amplification in Ti:sapphire Energy gain: where Fin is the input pulse fluence, Foutis the output pulse fluence, is the saturation fluence of Ti:sapphire, , n is the inverted population, l is the medium length. Very low input signal, Fin/Fs << 1, small signal gain: High-level energy densities, Fin /Fs >> 1, saturated gain: Damage threshold fluence at 532 nm, 10 ns pulse duration, 5-10 J/cm2 Conservative fluence at 532 nm, 10 ns pulse duration, 1-1.5 J/cm2 W. Koechner, “Solid-State Laser Engineering”, Springer Verlag, Germany, 1996

13. INFLPR TEWALAS - schematic drawing of the laser system

14. INFLPR TEWALAS - Laser system layout

15. INFLPR Critical characteristics of Ti:sapphire amplifiers • Spectral band-width of the amplified pulses (re-compressed pulse duration) • Intensity contrast of femtosecond pulses versus amplified spontaneous emission (ASE) and nanosecond pre-pulses • Strehl ratio, focused spot

16. INFLPR Pulse spectrum narrowing during Ti:S amplification – TEWALAS_INFLPR (a) (b) TEWALAS laser spectra: (a) without active Mazzler; (b) optimized by Mazzler. Mauve line – FEMTOLASERS oscillator; yellow line – after first multi-pass amplifier; after second multi-pass amplifier.

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18. INFLPR TEWALAS beam profiles (a) MP1, (b) MP2

19. INFLPR (a) (b) (c) Pulse duration measurements using SPIDER. (a), (b) with Dazzler phase correction; (c) without phase correction. All cases: with spectrum correction by Mazzler.

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21. INFLPR ASE contrast improvement by cross-polarized wave (XPW) generation XPW generation – four-wave mixing process governed by the third–order nonlinearity: XPW generated wave has the same wavelength as the input pulse and a cubic dependence on the intensity 2 mm BaF2 Lens P1, P2 – crossed polarizers Energetic efficiency – 10-30% Contrast improvement – 3-5 orders of magnitude P1 Y P2 X Z β angle f Peak intensity level ~ 3 x 10^12 W/cm^2 Fs nJ Oscillator Ps Stretcher mJ Amplifier Fs compressor 1-2 ns Stretcher XPW Double CPA PW laser High-energy ten-hundred J amplifier chain PW fs pulses High-energy fs compressor A. Jullien et al, Opt. Lett. 30, 920 (2005); A. Jullien et al, Appl. Pys. B, 84, 409 (2006); L. Canova et al, Appl. Phys. B, 93, 443 (2008)

22. INFLPR Nanosecond Contrast Nanosecond Contrast @600mJ: 8x10-8

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24. INFLPR Problems of Ti:sapphire laser amplifiers for PW femtosecond laser facilities Gain narrowing due to the high factor amplification, 5 nJ → 250 J, M = 5 x 1010 Amplified pulse duration – expected not shorter than 15-20 fs Required nanosecond and picosecond intensity contrast for a 10 PW laser (1023-24 W/cm2 focused peak power density) > 1012-13 Thermal loading (532, 527 nm → 800 nm) Ti:sapphire rods, ~ 200 cm diameter required (currently available – 100 cm diameter) Transversal lasing in large diameter Ti:sapphire rods. Development of high energy, high repetition rate nanosecond green lasers, with smooth, uniform spatial intensity profile. Strehl ratio