Registration Number
0211U005706,
0111U006688
, R & D reports
Title
Spatiotemporal dynamics of a femtosecond laser pulse filamentation in condensed media.
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Head
Kadan Viktor Mykolaiovych, Доктор фізико-математичних наук
Registration Date
22-12-2011
Organization
Institute of physics NASU
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In the first stage we were working on the development of the experimental base for measurement of spatial-temporal dynamics of the filamentation of femtosecond laser pulse. A gas cell for self-compression studies of filamented femtosecond laser pulse in rare gases is manufactured. Options for the probe pulse for femtosecond optical time-resolved polarigraphy, coinciding with the frequency of the pump, doubled frequency, and white supercontinuum are discussed. It is shown that the best time resolution of the "pump-probe" technique (~ 100 fs) is provided using the doubled frequency of the probe beam, while the duration of the white supercontinuum pulse is increased up to ~ 200 fs. The spectral and spatial characteristics of the white supercontinuum obtained by focusing the exciting beam in the water are studied. It is shown that the angular distribution of the wavelength of conical emission produced by femtosecond Bessel beam in water is determined by the condition of equality of the axial phase velocities of all its spectral components. Gain in the axial direction by four-wave mixing leads to the discreteness of conical emission rings. In the second stage spatio-temporal dynamics of filamentation of femtoscond laser pulses in fused silica has been studied. The method of time-resolved microscopy of transient absorption showed that relaxation of transient absorption (TA) after passing the filamented femtosecond pulse has a two-stage character in K-8 glass. It is described by the two exponents ?1 ~ 17 ? 17,5 ps and ?2>> 300 ps. These results indicate that, in spite of prolonged (>> 300 ps) presence of plasma in the core of the filament, after 0.45 ps after the excitation the TA is not dominated by the plasma mechanism, but due to non-stationary electronic states (NES). Analysis of energy and the kinetic parameters of the plasma and the NES suggests that the capture of carriers in the NEC state comes from the long-living plasma "reservoir", and excitation energy of the NES and the width of the corresponding transition responsible for the TA, are 2,6 ? 2 7 eV and 0,35 ? 0,45 eV, respectively. The first stage of relaxation of NP with ?1 ~ 17 ? 17,5 ps is determined by the thermalization of the plasma, while the second, with ?2>> 300 ps - by its life-time. Application area: fundamental research in femtooptiki; modification of properties of relevant materials optoelectronics.
Product Description
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Блонський Іван Васильович
Головченко Олена Миколаївна
Кадан Віктор Миколайович
Коренюк Петро Іванович
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2020-04-02
