Acoplamento de dois feixes com lasers de femtossegundos em vapor de Rb

AUTOR(ES)

Bruno Gomes da Costa

DATA DE PUBLICAÇÃO

2007

RESUMO

Femtosecond lasers operating in the mode-locked regime have a repetition rate determined by the round trip time of the pulse inside the laser cavity (TR = 2L/c). For Ti:sapphire lasers the repetition rate is typically of the order of 100 MHz, with TR  10 ns. Under this condition TR may be smaller then the population relaxation time (T1) and the coherence relaxation time (T2) in atomic systems, which may be of the order of several tens of nanoseconds in Rb, for example. The result is that the interaction of a pulse with an atom happens before the modification produced in the system by the previous pulse has completely decayed, resulting in new interesting effects. In this work we present theoretical and experimental results of two-beam coupling in Rb vapor, where the modifications produced in a probe beam by its coupling with a pump beam. The experiment is made in a cell containing Rb atoms with densities which vary between 1012 and 1014 atoms/cm3. In our experiments we have focused in two distinct atomic transitions: 5Sâ5P1/2 e 5Sâ5P3/2â5D, the first corresponding to a one-photon transition while the second involves a two-photon transition. For the 5Sâ5P3/2â5D transition, the effect of population accumulation in a three level system produces 2.11 THz beatings in the signals for fluorescence and two-beam coupling, as observed in the experimental results. Linear propagation effects are also observed, and produce beatings in the observed signals on a picosecond time scale. We also study the 5Sâ5P1/2 transition, which is simpler to analyze because the 2.11 THz beating is not present. Numerical simulations were performed based on third order perturbation theory for a two-level system, including linear propagation of the pulses until the interaction region of the two beams, without considering accumulation. Through this theory it is possible to explain and understand better some of the essential characteristics present in the experimental results.

ASSUNTO(S)

propagaÃÃo linear de pulsos curtos propagation linear of short pulses acoplamento de dois feixes two-beam coupling femtosecond lasers nonlinear optics Ãptica nÃo-linear fÃsica atÃmica fisica atomica e molecular lasers de femtossegundos atomic physics

Documentos Relacionados

• Efeitos coerentes no acoplamento dos lasers de fentosegundo e de diodo em vapor de rubÃdio
• CaracterizaÃÃo de lasers de femtossegundos para metrologia Ãptica
• Estudo da estabilidade do acoplamento de modos de um laser a fibra dopada com érbio com pulsos de femtossegundos e taxa de 10 GHz
• Desenvolvimento de um modelo teÃrico para osciladores com catodo virtual com dois feixes de elÃtrons em contra fluxo.
• Estudo teÃrico de propagaÃÃo de feixes de lasers em guias planares utilizando a teoria escalar de difraÃÃo em uma dimensÃo.