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

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

Mar 14, 2024 555 likes •756 views

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. Savelev

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SLIDE 1

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

  • f M.V.Lomonosov

Moscow State University

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SLIDE 2

ωs ΩR ∆ω ∼1/τ

L p

ωL

Concerned effects

laser pulse self-compression in noble gases influence of Raman scattering and four-wave mixing on laser pulse spectra and envelope in atomic gases Spectra broadening Pulse compression

  • Self-phase modulation
  • Self-steepening
  • Plasma blue wing

2

1 ( ) n ∆ = − ω

Negative dispersion in plasma for femtosecond pulses:

  • appearance of new components in

spectra of radiation

  • Raman soliton generation (plasma

in filament core can serve as a media with negative dispersion)

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SLIDE 3

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

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SLIDE 4

Experimental setup

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SLIDE 5

600 700 800 900 1000 0,0 0,2 0,4 0,6 0,8 1,0 amp. a.u.

λ, nm

Spectra peculiarities in noble and molecular gases

Argon (0.9 atm) blue wing Spectra is widened up to 300 nm from 30 nm in initial laser pulse

300 µm aperture

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SLIDE 6

Spectra peculiarities in noble and molecular gases

Argon (0.9atm) blue wing

600 700 800 900 1000 0,0 0,2 0,4 0,6 0,8 1,0 amp. a.u.

λ, nm

Air (1 atm) Raman spectral component is generated.

200 µm aperture

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SLIDE 7

Spectra peculiarities in noble and molecular gases

Argon (0.9atm) blue wing

600 700 800 900 1000 0,0 0,2 0,4 0,6 0,8 1,0 amp. a.u.

λ, nm

Air (1 atm)

AS A0 in filament core AS/A0~7

200 µm aperture

Raman spectral component is generated.

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SLIDE 8

Spectra peculiarities in noble and molecular gases

Argon (0.9atm) blue wing

600 700 800 900 1000 0.0 0.2 0.4 0.6 0.8 1.0 amp. a.u.

λ, nm

Nitrogen (1 atm)

200 µm aperture

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SLIDE 9

Laser pulse self-compression in argon

Argon (0.9atm) blue wing

  • 40
  • 20

20 40 0.0 0.2 0.4 0.6 0.8 1.0 A,a.u. t, fs

12 fs

Pulse energy ~ 1.5 mJ Essential suppression pre- and post- pulses Argon, P=0.9 atm, L = 285 cm

700 µm aperture

2.2 2.4 2.6 0.5 1.0 S,a.u

ω, PHz

  • 2

2 φ,rad

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SLIDE 10

Argon (0.9atm) blue wing

Laser pulse self-compression in argon

(*) O.Kosareva, N.Panov

Short pulse (tp~15+/-3 fs) is generated in about 90% of laser shorts.

20 40 60 80 100 10 20 30 40 50 60 experimental results (700 µm) numerical simulation (100µm)(*) Pulse duration, fs P, kPa

  • 40
  • 20

20 40 0.0 0.2 0.4 0.6 0.8 1.0 A,a.u. t, fs

12 fs

2.2 2.4 2.6 0.5 1.0 S,a.u

ω, PHz

  • 2

2 φ,rad

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SLIDE 11

Argon (0.9atm) blue wing

300 µm aperture

  • 40
  • 20

20 40 0.0 0.2 0.4 0.6 0.8 1.0 A,a.u. t, fs

8 fs

2.2 2.4 2.6 2.8 0.5 1.0 S,a.u.

ω,PHz

  • 150
  • 100
  • 50

φ,rad

Laser pulse self-compression in argon

Pulse energy ~ 250 µJ Argon, P=0.9 atm, L = 285 cm

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SLIDE 12

New spectral components generation due to Raman scattering and four-wave mixing

We investigate spectra peculiarities in dependence on:

  • gas type and pressure
  • distance along filament
  • laser pulse chirp
  • aperture size

In nitrogen spectra of radiation has the similar envelope The component appearance connected with Raman scattering

600 700 800 900 1000 0,0 0,2 0,4 0,6 0,8 1,0 amp. a.u.

λ, nm

Air (1 atm)

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SLIDE 13

New spectral components generation due to Raman scattering and four-wave mixing

We investigate spectra peculiarities in dependence on:

  • gas type and pressure
  • distance along filament
  • laser pulse chirp
  • aperture size

Raman spectral component propagates in the filament core

650 700 750 800 850 900 950 0.0 0.2 0.4 0.6 0.8 1.0 wavelength, nm amp. a.u.

without aperture, Air 1 atm

without aperture

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SLIDE 14

New spectral components generation due to Raman scattering and four-wave mixing

We investigate spectra peculiarities in dependence on:

  • gas type and pressure
  • distance along filament
  • laser pulse chirp
  • aperture size

Raman spectral component propagates in the filament core

650 700 750 800 850 900 950 0.0 0.2 0.4 0.6 0.8 1.0 wavelength, nm amp. a.u.

800µm, Air 1 atm

800 µm aperture

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SLIDE 15

New spectral components generation due to Raman scattering and four-wave mixing

We investigate spectra peculiarities in dependence on:

  • gas type and pressure
  • distance along filament
  • laser pulse chirp
  • aperture size

Raman spectral component propagates in the filament core

200 µm aperture

650 700 750 800 850 900 950 0.0 0.2 0.4 0.6 0.8 1.0 wavelength, nm amp. a.u.

200µm, Air 1 atm

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SLIDE 16

700 750 800 850 900 950 0,0 0,5 1,0 L110cm L140cm L170cm L200cm L280cm amp. a.u.

λ, nm

100 150 200 250 300 2,15 2,20 2,25 2,30

ω, PHz

length from telescope, cm

New spectral components generation due to Raman scattering and four-wave mixing

Central wavelength of Raman spectral component moves with distance along filament

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SLIDE 17

650 700 750 800 850 900 950 0.0 0.2 0.4 0.6 0.8 1.0 wavelength, nm amp. a.u.

New spectral components generation due to Raman scattering and four-wave mixing

100 150 200 250 300 720 750 780 810 840 870 900

λ0 λas

λ, nm

propagation length, cm

λs

In several experiments together with Raman component we

  • bserved generation of the symmetrical (anti-stokes) spectral

component stokes anti- stokes

anti-stokes can be generated in each point of filament due to the next process: k0 k0 ks kas

2ω0=ωs+ωas 2k0=ks+kas

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SLIDE 18

Argon (0.9atm) blue wing Air, P=1 atm, L = 285 cm

700 µm aperture

Pulse duration is not changed along filament

  • 100
  • 50

50 100 0.0 0.2 0.4 0.6 0.8 1.0 t, fs A, a.u.

~30fs 160 200 240 280 320 10 20 30 40 50 Pulse duration, fs length from telescope, cm

New spectral components generation due to Raman scattering and four-wave mixing

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SLIDE 19

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

  • f 55fs laser pulse was achieved in about 90% of laser shorts.
  • Diameter of extracting aperture substantially determines compressed

pulse duration. In aperture with diameter 700µm minimal pulse duration is 12fs, while in 300µm 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.