Ultrashort infrared 25–11  μm pulses: spatiotemporal profiles and absolute nonlinear response of air constituents

Abstract

We measure the detailed spatiotemporal profiles of femtosecond laser pulses in the infrared wavelength range = . − , and the absolute nonlinear response of major air constituents (N2, O2, and Ar) over this range. The spatiotemporal measurements reveal wavelength-dependent pulse front tilt and temporal stretching in the infrared pulses.

Powerful terahertz waves from long-wavelength infrared laser filaments

“…Figure 5a shows that Eq. (6) provides a very good fit for the experimental data obtained by Zahedpour et al 62,63 and confirms the flat and featureless landscape of air n 2K dispersion at mid-infrared and farinfrared wavelengths. Additionally, Brown et al 64 found that over the wavelength range of 2-4 μm, the Kerr nonlinear index n 2K of air is insensitive to the laser intensity up to intensities as high as 10 14 W/cm 2 (though at shorter wavelengths, a weak intensity dependence, caused by nonnegligible ionization, was observed for intensities above 5 × 10 13 W/ cm 2 ).…”

“…While the values of the Kerr nonlinear index n 2K for air have been measured for various wavelengths, from the ultraviolet up to the near-infrared parts of the spectrum, until recently, there were no corresponding data for the midinfrared and far-infrared spectral range. Currently, the most comprehensive measurements of n 2K for different air constituents were made by Zahedpour et al 62,63 using the single-shot supercontinuum spectral interferometry technique. They presented the experimental values of the Kerr nonlinear index for nitrogen and oxygen in a very wide range of wavelengths from 0.4 to 11 μm.…”

“…In addition to the n 2K values, Zahedpour et al 62,63 also measured the Raman nonlinear index n 2R for nitrogen and oxygen in the same wavelength range from 0.4 to 11 μm. According to the obtained results, the value of n 2R for air (calculated through the corresponding weighted sum) is constant over the considered wavelength range and equal to approximately 3 × 10 −20 cm 2 /W.…”

“…Parameters of Kerr and Raman contributions to the nonlinear index of air. a Dependence of the Kerr nonlinear index for air on the laser wavelength: experimental data obtained by Zahedpour et al62,63 (points) and theory developed by Brown et al64 according to Eq. (6) (line).…”

Resonant nonlinear refraction of 4.3-μm light in CO2 gas

“…We have found that the rovibrational nonlinearity of CO 2 is dominated by the resonant ac-Stark or power broadening effect and that the sign of the nonlinearity is opposite to that predicted by the commonly used two-level system model that describes the resonant nonlinear optics of both atoms and molecules in the gas phase [14]. We determine that the nonlinear refractive index of low-pressure CO 2 is ~ 10 -12 cm 2 /W suggesting that the 400 ppm CO 2 concentration can act to increase the nonlinear refractive index of ambient air by four orders of magnitude as compared to the non-resonant values measured in the midand LWIR [15][16][17][18].…”