Abstract
We present the experimental results of diffraction-induced temporal splitting of chirped femtosecond optical pulses under the dynamical Bragg diffraction in the Laue geometry. For the experiments we made a transparent, high quality porous-quartz based 1D photonic crystal composed of 500 layers. We demonstrate that a selective compression of pulses is observed in this case, that is only one pulse from the pair is compressed, while the second one is broadened. This selective compression effect is determined by the sign and the value of the chirp parameter of the input pulse, in agreement with the theoretical description.
Highlights
Optical effects accompanying the dynamical Bragg diffraction in photonic crystals (PC) [1,2,3,4,5,6] are being intensively studied in the last years [7,8,9,10,11,12,13,14]
Following the formalism of the X-ray optics, the boundary problem of the Bragg diffraction in a PC can be divided into two groups, which correspond to the Bragg geometry or to the Laue one [15,16]
Strongly coupled waves that propagate within a PC in the Laue diffraction scheme (Fig. 1(a)) do not experience strong losses under the reflection from the interfaces within a PC structure
Summary
Optical effects accompanying the dynamical Bragg diffraction in photonic crystals (PC) [1,2,3,4,5,6] are being intensively studied in the last years [7,8,9,10,11,12,13,14]. No photonic band gap appears for both longitudinal and transversal propagation directions even for an exact fulfilment of the “transversal” Bragg diffraction condition These four waves in pairs form the two propagating modes, Borrmann and anti-Borrmann ones [15,16,17]. The first one is formed by the direct and diffracted waves with smaller values of the wave vector projection kz = kz(1) Such waves propagate with the same group velocity v(g1) along the normal to the corresponding dispersion curve (see Fig. 1(b)) and are spatially localized in the layers with smaller refractive index. The second, anti-Borrmann, mode is localized in the layers with higher refractive index and is formed by the waves with larger kz = kz(2) values Their group velocity v(g2) coincides with v(g1) only under the exact fulfilment of the Bragg diffraction condition. The experimental results are in a good agreement with the finite-difference time-domain (FDTD) numerical modelling and with the analytical description [10]
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