ABSTRACT
Recent works demonstrated that digital time-resolved holography is the prospective approach to study nonlinear light-matter interaction processes. In this Letter, we present a straightforward inline holographic approach for studying degenerate phase modulation induced by an inclined collimated pump beam in the isotropic sample. The method is based on a minimization of the difference between experimentally acquired data and simulated inline holograms obtained from a numerical model of pump-probe interaction in optical nonlinear media. A sophisticated experimental data processing algorithm is implemented to provide high sensitivity and a signal-to-noise ratio eligible for soft interaction with a collimated pump beam. The integral phase shift determined by our method can be used to estimate the nonlinear refractive index and the relaxation time for material with a low damage threshold. We validated our approach for the case of soda-lime and BK7 glasses.
ABSTRACT
In this paper, we demonstrate experimentally for the first time (to our knowledge) the generation of spectral supercontinuum (SC) of more than two octaves with high intensity in a water jet. The spectrum of the generated SC extends from 350 to 1400 nm, with intensities up to 1011 W/cm2, and its generation efficiency is more than 50%. For the pump intensity 3.0×1012 W/cm2 in the spectral range from 400 to 800 nm, the spectrum is nearly flat (less than 40% deviation), which is useful for many applications.
ABSTRACT
The advantage of metasurfaces and nanostructures with a high nonlinear response is that they do not require phase matching, and the generated pulses are short in the time domain without additional pulse compression. However, the fabrication of large-scale planar structures by lithography-based methods is expensive, time consuming, and requires complicated preliminary simulations to obtain the most optimized geometry. Here, we propose a novel strategy for the self-assembled fabrication of large-scale resonant metasurfaces, where incident femtosecond laser pulses adjust the initial silicon films via specific surface deformation to be as resonant as possible for a given wavelength. The self-adjusting approach eliminates the necessity of multistep lithography and designing, because interference between the incident and the scattered parts of each laser pulse "imprints" resonant field distribution within the film. The self-adjusted metasurfaces demonstrate a high damage threshold (≈1012 W cm-2) and efficient frequency conversion from near-IR to deep UV. The conversion efficiency is up to 30-fold higher compared with nonresonant smooth Si films. The resulting metasurfaces allow for the generation of UV femtosecond laser pulses at a wavelength of 270 nm with a high peak and average power (≈105 W and ≈1.5 µW, respectively). The results pave the way to the creation of ultrathin nonlinear metadevices working at high laser intensities for efficient deep UV generation at the nanoscale.
ABSTRACT
We propose a method for direct conversion of an ultrashort pulse into a monochromatic beam whose wave front either repeats or is related to the phase structure of the pulse or its spectrum. This can be done by sum-frequency generation of the spectrally resolved pulses. Experimentally, we projected two spectra of the same chirped pulse onto the nonlinear crystal so that the dispersions were opposite. After sum-frequency generation, a converging or diverging monochromatic beam was formed that was the analog of the pulse spectrum. We could determine the chirp value by the measurement of the wave-front radius.
ABSTRACT
Targets and problems of complex engineering and hygienic examination of railway facilities are presented along with the principles of its planning. The staff of specialists carrying out such examinations is described. The technique for assessing the state of sanitary service premises is set forth. The results of the proposed examination approval are given.
