Self-compression and four-wave mixing of femtosecond laser radiation - PowerPoint PPT Presentation

Self-compression and four-wave mixing of femtosecond laser radiation under filamentation of collimated beam in gases D.S. Uryupina M.V. Kurilova A.V. Mazhorova S.R. Gorgutsa R.V. Volkov N.A. Panov O.G. Kosareva A.B. Savel’ev International Laser Center and Physics Faculty of M.V.Lomonosov Moscow State University

Concerned effects � laser pulse self-compression in noble gases • Self-phase modulation Spectra broadening • Self-steepening • Plasma blue wing 1 ∆ = − ω n ( ) Negative dispersion in plasma Pulse compression 2 � influence of Raman scattering and four-wave mixing on laser pulse spectra and envelope in atomic gases for femtosecond pulses: • appearance of new components in spectra of radiation • Raman soliton generation (plasma ω L ω s in filament core can serve as a media Ω R ∆ω ∼1/τ p L with negative dispersion)

Collimated beam vs focused one • gentle self organized beam collapse helps to avoid inevitable instability caused by gas breakdown by the focused beam. This provides higher stability of the output parameters of the compressed pulse. • parameters of the compressed pulse in the collimated beam geometry slightly depend on fluctuations of the parameters of the initial pulse (energy, duration). • one can extract compressed pulse with optimal parameters placing an aperture at appropriate position. • longer interaction length permits to became apparent wave mixing processes

Experimental setup

Spectra peculiarities in noble and molecular gases 300 µ m aperture Argon (0.9 atm) 1,0 amp. a.u. 0,8 0,6 blue wing Spectra is 0,4 widened up to 0,2 300 nm from 30 nm in initial laser 0,0 pulse λ , nm 600 700 800 900 1000

Spectra peculiarities in noble and molecular gases 200 µ m aperture Air (1 atm) Argon (0.9atm) 1,0 Raman spectral amp. a.u. component is 0,8 generated. 0,6 blue wing 0,4 0,2 0,0 λ , nm 600 700 800 900 1000

Spectra peculiarities in noble and molecular gases 200 µ m aperture Air (1 atm) Argon (0.9atm) 1,0 Raman spectral amp. a.u. component is 0,8 generated. 0,6 blue wing A S 0,4 in filament core 0,2 A S /A 0 ~7 A 0 0,0 λ , nm 600 700 800 900 1000

Spectra peculiarities in noble and molecular gases 200 µ m aperture Nitrogen (1 atm) Argon (0.9atm) 1.0 amp. a.u. 0.8 0.6 blue wing 0.4 0.2 0.0 λ , nm 600 700 800 900 1000

Laser pulse self-compression in argon 700 µ m aperture Argon, P=0.9 atm, L = 285 cm 1.0 Argon (0.9atm) A,a.u. 0.8 12 fs 0.6 0.4 0.2 0.0 blue wing -40 -20 0 20 40 t, fs 1.0 2 φ ,rad S,a.u 0.5 0 Pulse energy ~ 1.5 mJ -2 Essential suppression pre- and 2.2 2.4 2.6 ω, PHz post- pulses

Laser pulse self-compression in argon 60 experimental results (700 µ m) numerical simulation (100 µ m)(*) 50 1.0 A,a.u. Argon (0.9atm) Pulse duration, fs 0.8 40 12 fs 0.6 30 0.4 20 0.2 0.0 10 -40 -20 0 20 40 t, fs blue wing 0 20 40 60 80 100 P, kPa 1.0 2 φ ,rad S,a.u (*) O.Kosareva, N.Panov 0.5 0 Short pulse (t p ~15+/-3 fs) is generated in about 90% of -2 2.2 2.4 2.6 laser shorts. ω, PHz

Laser pulse self-compression in argon 300 µ m aperture Argon, P=0.9 atm, L = 285 cm 1.0 A,a.u. Argon (0.9atm) 0.8 8 fs 0.6 0.4 0.2 0.0 -40 -20 0 20 40 t, fs blue wing φ ,rad 1.0 0 S,a.u. -50 0.5 -100 Pulse energy ~ 250 µ J -150 2.2 2.4 2.6 2.8 ω ,PHz

New spectral components generation due to Raman scattering and four-wave mixing Air (1 atm) 1,0 We investigate spectra amp. a.u. peculiarities in 0,8 dependence on: 0,6 • gas type and pressure 0,4 • distance along filament 0,2 • laser pulse chirp • aperture size 0,0 λ , nm 600 700 800 900 1000 In nitrogen spectra of radiation has the similar envelope The component appearance connected with Raman scattering

New spectral components generation due to Raman scattering and four-wave mixing without aperture without aperture, Air 1 atm 1.0 We investigate spectra amp. a.u. peculiarities in 0.8 dependence on: 0.6 • gas type and pressure 0.4 • distance along filament 0.2 • laser pulse chirp 0.0 650 700 750 800 850 900 950 • aperture size wavelength, nm Raman spectral component propagates in the filament core

New spectral components generation due to Raman scattering and four-wave mixing 800 µ m aperture 800 µ m, Air 1 atm 1.0 amp. We investigate spectra a.u. 0.8 peculiarities in dependence on: 0.6 • gas type and pressure 0.4 • distance along filament 0.2 • laser pulse chirp 0.0 650 700 750 800 850 900 950 • aperture size wavelength, nm Raman spectral component propagates in the filament core

New spectral components generation due to Raman scattering and four-wave mixing 200 µ m aperture 200 µ m, Air 1 atm 1.0 amp. We investigate spectra a.u. 0.8 peculiarities in dependence on: 0.6 • gas type and pressure 0.4 • distance along filament 0.2 • laser pulse chirp 0.0 650 700 750 800 850 900 950 wavelength, nm • aperture size Raman spectral component propagates in the filament core

New spectral components generation due to Raman scattering and four-wave mixing 1,0 amp. a.u. 0,5 0,0 L110cm L140cm L170cm 2,30 ω , PHz L200cm L280cm 2,25 700 750 800 850 900 950 λ , nm 2,20 Central wavelength of Raman spectral component moves with 2,15 100 150 200 250 300 distance along filament length from telescope, cm

New spectral components generation due to Raman scattering and four-wave mixing In several experiments together with Raman component we observed generation of the symmetrical (anti-stokes) spectral component 1.0 900 amp. λ, nm stokes λ s a.u. 870 0.8 840 0.6 810 anti- λ 0 0.4 780 stokes 750 0.2 λ as 720 0.0 650 700 750 800 850 900 950 100 150 200 250 300 wavelength, nm propagation length, cm anti-stokes can be generated in each point of filament due to the next process: 2ω 0 =ω s + ω as k 0 k s k as 2k 0 =k s +k as k 0

New spectral components generation due to Raman scattering and four-wave mixing 700 µ m aperture 1.0 A, a.u. Air, P=1 atm, L = 285 cm 0.8 Argon (0.9atm) ~30fs 0.6 0.4 0.2 0.0 -100 -50 0 50 100 t, fs blue wing 50 Pulse duration, fs 40 30 20 10 Pulse duration is not 0 160 200 240 280 320 changed along filament length from telescope, cm

Conclusions • Our study demonstrates that under filamentation of collimated beam in argon one can obtain very stable self-compressed laser pulse with essential suppression pre- and post- pulses. Nearly fivefold compression of 55fs laser pulse was achieved in about 90% of laser shorts. • Diameter of extracting aperture substantially determines compressed pulse duration. In aperture with diameter 700 µ m minimal pulse duration is 12fs, while in 300 µ m aperture pulse duration is 8fs. • Under filamentation in molecular gases (air, nitrogen) new bright spectral component appears due to Raman scattering. This component propagates in the filament core. Its duration is about 30fs and is not changed along filament. Central wavelength of this component moves with the distance along filament.