Two-photon resonantly-enhanced negative nonlinear refractive index in xenon at 248 nm

Effect of nonlinear dispersion on pulse self-compression in a defocusing noble gas

“…Nevertheless, it can be shown, that the length scales on which specific orders act can be estimated by |L P (3) /L P (5) | ≃ |P (5) /P (3) | ≃ |E/E at | 2 where E is the laser field and E at = 5×10 10 V/m [16]. We used field strengths E ≃ 0.4 × 10 9 V/m, giving |L P (3) /L P (5) | ≃ 2 × 10 −4 , so P (5) is negligible. Furthermore, the pulses launched at ω 00 do have a spectral width, thus experiencing, e.g., a n 2 ≈ 2.7 × 10 −23 m 2 /W at the halfmaximum frequency due to dispersion of the nonlinearity, which is already comparable to usual values of n 2 ∼ 1.0 × 10 −23 m 2 /W.…”

“…Indeed, negative values for the Kerr response can be found, e.g., in the UV near two photon resonances in Xe (Ref. [5]). However, the strong dispersion of the nonlinearity near these resonances questions the compression mechanism which is based on a constant nonlinearity.…”

Multiple filamentation of supercritical UV laser beam in atmospheric air

“…The filamentation pattern was well reproducible for repetitive USPs in time scales from nanoseconds to several minutes. There are two ways to avoid UV laser beam filamentation -to use the CPA scheme [25,26] or to explore a large negative two-photon resonantly-enhanced nonlinear refraction index in Xe [27], which could compensate a nonlinear phase shift acquired in long propagation tract in air and in amplifier windows.…”

A unified materials approach to mitigating optical nonlinearities in optical fiber. I. Thermodynamics of optical scattering

“…However, for highly covalent bonds, whose wave‐functions can extend over longer ranges, n 2 < 0 values might be possible; such as has been proposed to arise in uncoupled organic dimer bonds . While this sounds rather esoteric, negative n 2 values have been observed in gases under certain excitation conditions, in polymer composites containing TiO 2 nanoparticles, and in a variety of semiconductors …”