Igor Ozerov

Efficient third-harmonic generation in a thin nanocrystalline film of ZnO

Nonlinear optical conversion is studied in thin films of wide-bandgap materials. Very high conversion efficiency to the third-harmonic radiation is achieved for an unamplified femtosecond Cr4+:forsterite laser in a submicron-thick film of a nanocrystalline ZnO pulsed-laser-deposited on a fused silica substrate.

Two-photon pumped random laser in nanocrystalline ZnO

Thin film of ZnO nanoparticles with dimension of about 5–10nm were fabricated by the pulsed laser ablation method. By using a femtosecond laser beam at 700nm to pump micrometer-thick films the authors observed two-photon-induced lasing at 385nm. Experimentally obtained dependence of the threshold on the excitation spot radius r0 is closer to (1∕r02) than to (1∕r0), thus suggesting efficiency of the feedback by scattering-random lasing. The experimental data on nonlinear transmission of the film at the wavelength of pumping are presented.

Synthesis and laser processing of ZnO nanocrystalline thin films

Abstract We present the results of experiments on synthesis of ZnO nanoclusters by reactive pulsed laser deposition (PLD). The nanoclusters were formed and crystallised in the gas phase and deposited on SiO2 substrates. The nanostructured films were characterised by conventional photoluminescence (PL). The PL spectra consist of a narrow UV excitonic band and a broad visible band related to defects in the film. The film preparation conditions such as the substrate temperature, ambient gas nature and pressure, were optimised in order to increase the intensity of excitonic emission and prevent the formation of defects. A post-growth annealing by UV laser radiation improved the optical quality of the deposited films. The photoluminescence intensity was found to be dependent significantly on the laser fluence and on the number of shots per site. The nature of the defects responsible for the observed luminescence in a visible range is discussed.

Enhancement of exciton emission from ZnO nanocrystalline films by pulsed laser annealing

Pulsed ArF laser annealing in air and in hydrogen atmosphere improves the optical properties of ZnO nanostructured films. Independently on the ambient atmosphere, laser annealing produces two major effects on the photoluminescence (PL) spectra: first, the efficiency of the exciton PL increases due to the decrease of the number of non-radiative recombination centers; second, the intensity of the defect-related orange band decreases because of the removing of excessive oxygen trapped into the films during deposition. However, annealing in the ambient air also increases the intensity of the green band related to oxygen vacancies. We show that the combination of laser annealing and passivation of oxygen vacancies by hydrogen results in films free of defect-related emission and keeps intact their nanostructural character.

Production of Gas Phase Zinc Oxide Nanoclusters by Pulsed Laser Ablation

We present experimental results on the photoluminescence (PL) of gas-suspended zinc oxide nanoclusters prepared during ablation of sintered ZnO targets by a pulsed ArF laser in the presence of oxygen ambient gas. The PL spectra in the UV spectral region correspond to the exciton recombination in the nanoclusters which are crystallized and cooled down to the temperature of the ambient gas in the ablation chamber. The time evolution of the spectra as well as their dependence on the ambient gas pressure are discussed.

Phosphorus clusters: Synthesis in the gas-phase and possible cagelike and chain structures

Experimental results on the gas-phase formation of neutral and cationic phosphorus clusters are presented. The clusters were synthesized by visible (532 nm) or UV (193 nm) laser ablation of crystalline red phosphorus under high vacuum conditions and were analyzed using TOF mass spectrometry. Neutral Pn clusters produced by 532-nm ablation are found to be even-numbered while Pn+ cations are mainly odd-numbered, with P7+ and P21+ being the most abundant ions. For UV laser ablation, stable compound clusters, neutral P7H3 and P23H5, and cations P23H6+ were synthesized for the first time. The formation of Pn clusters by thermal vaporization of red phosphorus into a cold He gas was also investigated and only small clusters (n<6) were found. Possible structures of the observed phosphorus clusters, as well as their formation mechanisms under different conditions, are discussed.

Insight into electronic mechanisms of nanosecond-laser ablation of silicon

We present experimental and theoretical studies of nanosecond ArF excimer laser desorption and ablation of silicon with insight into material removal mechanisms. The experimental studies involve a comprehensive analysis of the laser-induced plume dynamics and measurements of the charge gained by the target during irradiation time. At low laser fluences, well below the melting threshold, high-energy ions with a narrow energy distribution are observed. When the fluence is increased, a thermal component of the plume is formed superimposing on the nonthermal ions, which are still abundant. The origin of these ions is discussed on the basis of two modeling approaches, thermal and electronic, and we analyze the dynamics of silicon target excitation, heating, melting, and ablation. An electronic model is developed that provides insight into the charge-carrier transport in the target. We demonstrate that, contrary to a commonly accepted opinion, a complete thermalization between the electron and lattice subsystems is not reached during the nanosecond-laser pulse action. Moreover, the charging effects can retard the melting process and have an effect on the overall target behavior and laser-induced plume dynamics.

Cluster Generation Under Pulsed Laser Ablation Of Compound Semiconductors

A comparative experimental study of pulsed laser ablation in vacuum of two binary semiconductors, zinc oxide and indium phosphide, has been performed using IR‐ and visible laser pulses with particular attention to cluster generation. Neutral and cationic ZnnOm and InnPm particles of various stoichiometry have been produced and investigated by time‐of‐flight mass spectrometry. At ZnO ablation, large cationic (n>9) and all neutral clusters are mainly stoichiometric in the ablation plume. In contrast, indium phosphide clusters are strongly indium‐rich with In4P being a magic cluster. Analysis of the plume composition upon laser exposure has revealed congruent vaporization of ZnO and a disproportionate loss of phosphorus by the irradiated InP surface. Plume expansion conditions under ZnO ablation are shown to be favorable for stoichiometric cluster formation. A delayed vaporization of phosphorus under InP ablation has been observed that results in generation of off‐stoichiometric clusters.

Extremely efficient direct third harmonic generation in thin nanostructured films of ZnO

We report a very efficient nonlinear optical conversion in thin films of wide band-gap materials. Very high conversion efficiency to the third harmonic radiation is achieved for an unamplified femtosecond Cr4+:forsterite laser in a sub-micron-thick film of a nanocrystalline ZnO pulsed-laser deposited on a fused silica substrate. Both the nonlinear optical coefficient and the coherence length are measured for film composed of 10-nm nanoclusters.

Very efficient direct third harmonic generation in nanostructured ZnO films

This study presents the very strong third-order nonlinear optical coefficient of nanostructured ZnO thin films. Hence, it is possible to directly generate third harmonic of ultrashort pulses with efficiency of several percent.