S. V. Zabotnov

Ultrashort excitations of surface polaritons and waveguide modes in semiconductors

Polarization-dependent structures have been formed on the silicon surface under the action of femtosecond laser pulses. Some model concepts are proposed to describe changes in the response of the semiconductor surface caused by the generation of a nonequilibrium electron-hole plasma and explain the excitation of surface polaritons and waveguide modes during a femtosecond laser pulse.

Generation of surface electromagnetic waves in semiconductors under the action of femtosecond laser pulses

It is demonstrated that intense photoexcitation of the surface of a semiconductor with femtosecond laser pulses can induce fundamental changes in its optical response and ensure conditions for the generation of surface electromagnetic waves of various types. The connection between electronic processes initiated in the surface layer by photoexcitation and the formation of periodic surface microstructures observed in experiments on irradiation of Si targets is considered. The importance of photoemission in the processes taking place under ultrashort excitation is confirmed.

Phase-matched third-harmonic generation in anisotropically nanostructured silicon

A frequency-tunable laser system based on an optical parametric oscillator is used to implement phase-matched third-harmonic generation in porous silicon films with a strong form birefringence. Phase matching, orientation dependences, and the behavior of the third harmonic as a function of the thickness of an absorbing film are confirmed by calculations and linear-optical measurements.

Second- and third-harmonic generation as a local probe for nanocrystal-doped polymer materials with a suppressed optical breakdown threshold

Abstract Second- and third-harmonic generation processes are shown to allow the detection of absorptive agglomerates of nanocrystals in transparent materials and the visualization of optical breakdown in nanocomposite materials. Correlations between laser-induced breakdown and the behavior of the second- and third-harmonic signals produced in SiC/PMMA nanocomposite films are studied. The potential of second- and third-harmonic generation for the on-line visualization of laser breakdown in nanocomposite polymer materials is revealed, with the ablative material removal being monitored by the decay of the second- and third-harmonic signals. The second and third harmonics generated around the optical breakdown threshold by 75-fs pulses of 1.25-μm Cr:forsterite laser radiation are respectively more than two and four orders of magnitude more intense than the second and third harmonics produced under identical conditions by 40-ps pulses of a Nd:YAG laser. The breakdown threshold for PMMA films doped with 10–20-nm SiC nanocrystals forming absorptive agglomerates are demonstrated to be more than an order of magnitude lower than the breakdown threshold for crystalline SiC and about an order of magnitude lower than that for nondoped PMMA films.

Structural properties of silicon nanoparticles formed by pulsed laser ablation in liquid media

Silicon nanoparticles have been formed as a result of the irradiation of single-crystal silicon targets in distilled water and liquid nitrogen, by, respectively, picosecond and femtosecond laser pulses. The main structural properties of these nanoparticles have been investigated by atomic force microscopy, transmission electron microscopy, electron diffraction, Raman scattering, and photoluminescence spectroscopy. These particles are found to be mainly spherical. The presence of crystalline and amorphous silicon phases under picosecond ablation in water is established experimentally. Irradiation by femtosecond pulses in liquid nitrogen can yield nanoparticles smaller than 5 nm in size, which are quantum dots with a characteristic photoluminescence peak near 750 nm.

Femtosecond nanostructuring of silicon surfaces

Nanostructures were formed upon the irradiation of single-crystal silicon surfaces with femtosecond laser pulses. These nanostructures were detected using scanning electron microscopy, Raman spectroscopy, and a photoluminescence technique.

Creation of silicon nanocrystals using the laser ablation in liquid

The method for the formation of silicon nanoparticles by picosecond laser pulses is studied upon the surface irradiation of the single-crystal silicon in various liquids. The ablation products are investigated using the atomic-force microscopy and Raman spectroscopy. The experimental results indicate the crystal-line structure of nanoparticles and the dependence of their size on the ablation medium.

Consideration for the dynamic depolarization in the effective-medium model for description of optical properties for anisotropic nanostructured semiconductors

The effective-medium model has been generalized within the dipole approximation, with allowance for the shape anisotropy and dynamic depolarization of semiconductor nanoparticles. The calculations revealed nonmonotonic dependences for the birefringence and dichroism on the nanoparticle size. Comparison of the measured and calculated refractive index dispersion of birefringent porous silicon layers in the near-IR region indicates that consideration for the dynamic depolarization gives a better description of the optical properties for this material in comparison with the generally used effective-medium electrostatic approximation.

Laser-ablated silicon nanoparticles: optical properties and perspectives in optical coherence tomography

Due to their biocompatibility silicon nanoparticles have high potential in biomedical applications, especially in optical diagnostics. In this paper we analyze properties of the silicon nanoparticles formed via laser ablation in water and study the possibility of their application as contrasting agents in optical coherence tomography (OCT). The nanoparticles suspension was produced by picosecond laser irradiation of monocrystalline silicon wafers in water. According to transmission electron microcopy analysis the silicon nanoparticles in the obtained suspension vary in size from 2 to 200 nm while concentration of the particles is estimated as 1013cm−3. The optical properties of the suspension in the range from 400 to 1000 nm were studied by spectrophotometry measurements revealing a scattering coefficient of about 0.1 mm−1 and a scattering anisotropy factor in the range of 0.2–0.4. In OCT study a system with a central wavelength of 910 nm was employed. Potential of the silicon nanoparticles as a contrasting agent for OCT is studied in experiments with agarose gel phantoms. Topical application of the nanoparticles suspension allowed the obtaining of the contrast of structural features of phantom up to 14 dB in the OCT image.

Methods for increasing the efficiency of nonlinear optical interactions in nanostructured semiconductors

Methods for increasing the efficiency of the optical second-and third-harmonic generation in gallium phosphide and silicon nanostructures formed by electrochemical etching of crystalline semiconductors are discussed. The efficiency of nonlinear optical interactions can be increased by using phase matching in anisotropic nanostructured semiconductors that exhibit form birefringence or by increasing the local field, as in scattering in macroporous semiconductors. The efficiencies of third-harmonic generation in porous silicon and of second-harmonic generation in porous gallium phosphide are found to increase by more than an order of magnitude.