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Pre-excitation of Rb atoms by frequency chirped laser pulses for efficient plasma generation

Pre-excitation of Rb atoms by frequency chirped laser pulses for efficient plasma generation. G.P. Djotyan Wigner Centre for Physics of the Hungarian Academy of Sciences Contributors: D. Dzsotjan Zs. S örlei J. Bakos G. Demeter

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Pre-excitation of Rb atoms by frequency chirped laser pulses for efficient plasma generation

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  1. Pre-excitation of Rb atoms by frequency chirped laser pulses for efficient plasma generation G.P. Djotyan Wigner Centre for Physics of the Hungarian Academy of Sciences Contributors:D. Dzsotjan Zs. Sörlei J. Bakos G. Demeter N. Sandor

  2. Outline Frequency chirped laser pulses and their application in manipulation of inner and translational states of multilevel atoms: some results achieved in the field in the Wigner Centre Robust pre-excitation of Rb atoms by frequency chirped ultra-short laser pulses for efficient OBI or impact ionization

  3. Over-barrier and impact ionization of excited Rb atoms

  4. Action of a laser pulse with area A = ∫ Ω(t) dt = 5 π

  5. Action of a frequency-chirped laser pulse on a two-level atom

  6. Coherent Population Transfer to a Target State Without Excitation of the Atom:Interaction of a singlefrequency chirped laser pulse with L –atom

  7. Dynamics of the populations of the L-atom in the field of single “narrowband” frequency-chirped laser pulse n3 1 n1 0.8 S N O I T 0.6 A L U P O 0.4 P n1 n2 0.2 n3 n2 0 - - - 3 2 1 0 1 2 3 TIME G.P. Djotyan, J.S.Bakos, Zs. Sörlei, J.Szigeti, Phys.Rev.A, 70, 063406 (2004)

  8. Creation of superposition between a ground and excited state G.P. Djotyan, N. Sandor, J.S. Bakos, Zs. Sörlei, Opt. Express, 19, n. 18, 17493(2011)

  9. Electromagnetically self-induced transparency of a single narrowband frequency-chirped laser pulse The propagation distance X is measured in the units of the absorption length G. Demeter, D. Dzsotjan, and G. P. Djotyan. Phys.Rev.A, 76, 023827 (2007)

  10. Using frequency-chirped pulses in manipulation of translational states of atoms

  11. Experiment: Momentum transfer to Rb atoms by partially overlapping laser pulses J.S. Bakos, G.P. Djotyan, et al., Eur. Phys. J. D,  39, 59 (2006); Eur. Phys. J. D 44, 149 (2007)

  12. Population transitions in Rb85 atom (D2 line) induced by frequency-chirped laser pulses GP. Djotyan, JS. Bakos, G. Demeter, PN. Ignacz, MA. Kedves, Zs. Sorlei, J. Szigeti, Z.Toth,Phys.Rev A, 68,053409 (2003)

  13. Parameters of the MOT and of the trapped and cooled atomic cloud • Volume~ 1 mm3 • Number of atoms ~ 10 7 • Lifetime ~ 500 msec • Temperature ~ 10 -100 μK

  14. Rb transition lines and the ionization scheme

  15. Dynamics of the populations for positive and negative frequency chirp I5> I2> I3> I4> I1> I0>

  16. Final populations of the ground state 5s and first excited state 5p 5s

  17. Final populations of the excited states 5d and 7s 5d 7s

  18. Conclusions Frequency chirped laser pulses may be successfully applied for pre-excitation of Rb atoms before further one-photon or over the barrier ionization by a strong laser pulse, or by the impact ionization. The pre-excitation of a gas of Rb atoms will drastically diminish the threshold of the ionization. Advantages of using frequency chirped laser pulses: i. Robustness of the atomic population transfer against variation of parameters of the laser radiation ii. Applicability in both homogeneously and in-homogeneously broadened media, e.g. hot vapors (Doppler-broadening) or solid-state environment ii. Ability to select a target state even in the case of broadband (e.g. ultra-short) laser pulses in the case of spectrally non-resolved manifold of atomic (molecular) energy levels.

  19. Our plans in the field of the theory of laser plasma generation: • Atomic physics: numerical simulations of interaction of multilevel atoms with ultra-short and intense laser pulses, including ones with phase modulation. Analysis and simulation of different regimes of ionization, including resonance-enhanced multi-photon, tunneling, OBI and impact ionization. • Simulation of propagation and nonlinear interaction of intense laser pulses in highly nonlinear resonant multi-level atomic media, including pulses with frequency modulation, electromagnetically induced transparency regime, etc. • At special interest: Propagation and nonlinear self-action effects of intense ultra-short pulses in gaseous media under conditions of plasma generation.

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