Nonlinear optical effects in nanomaterials

We studied experimentally interaction of pulsed laser light with different nanomaterials. In nanostructured materials Bragg diffraction results in the photonic band gaps existence and it may lead to the enhancement of the photonic states density resulting in the nonlinear effects efficiency enhancement, their thresholds reduction and appearing of the new, not known effects. In our laboratory we for the first time observed stimulated low-frequency Raman scattering (SLFRS) in nanomaterials. This scattering is a result of laser light interaction with acoustic vibrations of nanoparticles. Spontaneous analog of this scattering has been studied in many works, but to excite stimulated process of this type it is necessary to have strong laser source with narrow spectral line. We used for this purpose ruby laser nanosecond pulses and with this pump observed SLFRS in different nanomaterials, high-ordered (synthetic opal matrices), less ordered (nanostructured thin films) and  random (metal, dielectric and semi-conductor nanoparticles suspensions). SLFRS frequency shifts are situated in gigahertz and terahertz range.

In synthetic opal matrices and nanocomposites on their base we observed photonic flame effect: long luminescence (up to 12 s) in blue spectral range under red nanosecond laser pulses excitation. Effect was observed at liquid nitrogen temperature. In nanomaterials, illuminated by laser pulses, directed X-ray emission could be excited.

Photonic crystals can influence significantly nonlinear processes, occurring in the materials, inserted into their voids. We observed strong enhancement of stimulated Raman scattering in the liquids infiltrating pores of the opal matrix compare to the bulk material.