The electronic nonlinear refractive index in Cs Vapor at 1.06μ is shown to be negative and to consist of two distinct contributions. One of these arises from a two-photon resonance in the susceptibility, and can be made comparable in magnitude to the positive n2in laser glass. The other term arises from population redistribution between the ground and the first excited state. We present preliminary measurements of self defocusing of a single pulse from a Nd:YAG mode locked laser which are in agreement with the theoretical predictions.
We outline a complete theory of the nonlinear susceptibility of cesium around 1.06 \ensuremath{\mu}m, and present the first measurements of the negative nonlinear refractive index
n2 primarily responsible for the self-defocusing that is observed. For linearly polarized light, our measured value of
n2 is $\ensuremath{-}(1.4\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}30}N$ esu, where
N is the atomic density. This is in reasonable agreement with our calculated value of $\ensuremath{-}2.62\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}30}N$. The main portion of
n2 comes from a two-photon resonance between the
6s and
7s levels, and an additional negative term arises from induced population changes between
6s and
6p. For circular polarization,
n2 arises mainly from the induced population changes, giving the measured and calculated values of $\ensuremath{-}(0.26\ifmmode\pm\else\textpm\fi{}0.03)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}30}N$ and $\ensuremath{-}0.525\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}30}N$, respectively. In our experiments where the 35-psec pulses were shorter than the $6s\ensuremath{-}6p$ inverse linewidth, the nonlinear susceptibility depends mainly on the instantaneous intensity; however, for longer pulses, one would obtain additional contributions proportional to time integrals over the intensity. Since the useful output power from large Nd laser systems is limited by self-focusing due to the laser glass, our results suggest the possibility of increasing this power by using Cs vapor for compensation.
Atomic vapors are systems well suited for nonlinear optics studies but very few direct measurements of their nonlinear refractive index have been reported. Here we use the
z-scan technique to measure the Kerr coefficient,
n2, for a Cs vapor. Our results are analyzed through a four-level model, and we show that coherence between excited levels as well as cross-population effects contribute to the Kerr nonlinearity.
We present measurements of the nonlinear refraction coefficients for the D1 line of cesium vapor. A variant of the z-scan technique is applied for which we scan the laser frequency across resonance for different sample positions and detect the transmission after an aperture in the far field. From the spectra for different positions we reconstruct the position-dependent transmission z-scan curve for a given laser detuning. This technique allows obtaining the vapor Kerr coefficient over a large and continuous range of frequencies. From the saturation of the Kerr coefficient, n2, with beam power we obtain n4, the next term in the refraction index expansion. A theoretical model is used to calculate n2 and n4 giving values consistent with experimental ones.
We report the measurement of the Kerr nonlinear refractive index of the rubidium vapor via the high sensitivity z-scan method by using an optical frequency comb. The novel self-focusing and self-defocusing effects of the vapor are presented with red and blue detunings of the laser frequency. The optical nonlinear characteristics of the rubidium vapor are clearly interpreted under different experimental parameters. Furthermore, the Kerr nonlinear refractive index n2 is obtained from the measured dispersion curve, and it basically occurs on the order of 10−6 cm2/W. The evolutions of the Kerr nonlinear coefficient n2 with the laser power and frequency detuning, respectively, are studied. To the best of our knowledge, the use of pulsed lasers to measure the Kerr nonlinear refractive index n2 of atomic vapor has not been reported yet. The direct measurement of the Kerr nonlinear coefficient will greatly help us understand and optimize nonlinear optical processes and find its more potential applications in quantum optics.