Experimental observation of the diffraction-induced femtosecond pulse splitting in a linear photonic crystal.

Sergey E. Svyakhovskiy*, Anton I. Maydykovskiy, Vladimir B. Novikov, Viktor O. Kompanets, Sergey V. Chekalin, Alexander A. Skorynin, Vladimir A. Bushuev, Boris I. Mantsyzov, Tatiana V. Murzina.

Lomonosov Moscow State University , Russia

Photonic crystals (PhC) - periodic structures with period of about the wavelength of a visible light - can reveal a lot of optical effects induced by its structure, e.g. photonic band gap, second harmonic generation etc. Some effects are inspired by x-ray optics: borrmann effect, pendular effect. In this work we present the results of analytical prediction of the dynamical Diffraction-Induced femtosecond laser Pulse Splitting (DIPS) in a linear 1d photonic crystal at the Laue geometric scheme and the experimental confirmation of the effect. When a short laser pulse comes into 1d PhC (array of alternating dielectric layers of two types) at the Laue scheme (crystal layers are parallel to normal direction of incident surface), the pulse undergoes two splittings: spatial and temporal. The spatial splitting occurs due to diffraction on the PhC volume grating: formation of two pulses propagating in two directions under the Bragg condition is observed. The temporal splitting is caused by formation of two spatial modes inside the crystal: borrmann and antiborrmann, each of them is spatially localized into PhC layers of its own type. Therefore two pulses with different group velocities are forming and the temporal splitting occurs. The experimental sample was made of porous fused silica [1] with length of 0.5...2.0 mm, a Ti:Sapphire laser (800 nm, 100 fs, 100 mW) was used as a pump, a conventional autocorrelometer (10 fs precision, 15 ps range) was used as detector. We experimentally observed the DIPS effect for p- polarization of the incident pulse [2]. The splitting value is 600 fs for sample of 2 mm and is proportional to the sample length in all observable range. The value of splitting is independent on the incident power which confirms the optical linearity of the effect. For s- polarization of incident pulse the splitting value is 1.4 times less (theory) and 1.64 times less (experiment). This difference can be explained by different birefringence of materials of PhC layers. The porosity of PhC material gives a possibility to fill layers of the crystal with nonlinear substance (e.g. NaNO2). Therefore nonlinear effects, such as selective focusing and compression can be observed in this structure. [1] S.E. Svyakhovskiy, A.I. Maydykovskiy, T.V. Murzina "Mesoporous silicon photonic structures with thousands of periods". J. Appl. Phys. 112, 013106 (2012). [2] S.E. Svyakhovskiy, V.O. Kompanets, A.I. Maydykovskiy, et al. "Observation of the temporal Bragg-diffraction-induced laser-pulse splitting in a linear photonic crystal". Phys. Rev. A. (accepted).