Waclaw Bala

Third harmonic generation in undoped and X doped ZnO films (X: Ce, F, Er, Al, Sn) deposited by spray pyrolysis

There is a current interest in research of wide band gap semiconductor materials for the purposes of third order nonlinear optical properties in view of optoelectronics applications. Materials for nonlinear optics should present important changes of nonlinear intensity, dependence on changes of nonlinear refractive index, short response time, and weak absorption losses. We report the results of the third order nonlinear optical susceptibilities of undoped and doped (cerium, fluorine, erbium, aluminum, and tin) zinc oxide films using the third harmonic generation technique at 1064 nm wavelength region in picoseconds regime. Thin films were grown on glass substrate by the spray pyrolysis technique at different temperatures of substrates and characterized by using the x-ray diffraction, scanning electron microscope, transmission, and photoluminescence. A strong third harmonic signal was obtained from the studied films with a good crystallinity and roughness. We have found that at high conductivity, there is ...

Influence of different peripheral substituents on the nonlinear optical properties of cobalt phthalocyanine core

In this article, we show how the substituting different peripheral substituents around the cobalt phthalocyanine core correlate with nonlinear optical properties. We present the results on nonlinear optical properties of solution of cobalt phthalocyanine (CoPc), cobalt phthalocyanine with DNA-CTMA surfactant complex (CoPc-DNA-CTMA), and cobalt phthalocyanine with liquid crystal (CoPc-LC) measured by degenerate four-wave mixing (DFWM) method at the 532 nm wavelength region. We found that the values of third-order nonlinear optical susceptibility (χ⟨3⟩) of CoPc-LC and CoPc-DNA-CTMA increase in comparison with the value of the third-order nonlinear optical susceptibilities of CoPc. We supposed that this is caused by increase of the charge-transfer effects and of the dipole moments of the molecule with the increase of the chain length.

Stationary and modulated absorption spectroscopy of copper phthalocyanine (CuPc) layers grown on transparent substrate

Copper phthalocyanine thin films grown on glass and quartz substrates by the thermal evaporation method were investigated using stationary and modulated photoabsorption as well as photoreflectance spectroscopy. The stationary and modulated studies at room temperature were performed in the wavelength range 200–1200 nm and 400–1200 nm, respectively. The absorption coefficient of investigated layers was determined directly from the transmission spectrum and fitted in terms of the mixed Lorentz–Lorenz model, which assumed five oscillator components. Sensitive modulated spectroscopy, which enabled us to emphasize weakly visible transitions in the Q-band spectral region, was also performed to estimate the electronic structure of metallophthalocyanine layers. The complex nature of excited states of the metallophthalocyanine layers gave us abundant modulated spectra. These spectra were fitted using the third derivative line shape given by the Aspnes formula. Modulated photoabsorption and photoreflectance spectra for CuPc thin layers are presented for the first time in this paper.

Influence of free carrier concentration on absorption and third‐order susceptibilities of n‐type ZnSe crystals

This study analyzes the dependence of third‐order susceptibilities at 532 nm of n‐type ZnSe crystals in relation to free carrier concentration and annealing temperatures. The nonlinear optical absorption and the efficiency of degenerate four‐wave mixing of ZnSe are investigated. We find that the magnitude of the nonlinear absorption decreases with the electron concentration and annealing temperature increase, while the nonlinear refractive index increases slightly.

Dependence of the Third Order Nonlinear Optical Susceptibility on Concentration and Peripheral Substituent of Metallophthalocyanines

Third order nonlinear optical properties of metallophthalocyanines (MPcs) were investigated using degenerate four wave mixing (DFWM) method. We also studied how the replacement of peripheral substituent around the MPcs cores correlates with nonlinear optical properties. Therefore third order nonlinear optical susceptibilities (χ<3>) of MPcs with liquid crystal (MPcs-LC) were investigated. We found that the χ<3> values of MPcs-LC increase in comparison with the corresponding values of MPcs. We supposed that this is caused by the increase of the charge transfer effects and change of the dipole moments of the molecule with the increase of molecules dimension.

Optical Properties of Vacuum Sublimed Cobalt Phthalocyanine (CoPc) Thin Layers

In this article the temperature dependence of absorption spectra of vacuum sublimed cobalt phthalocyanine (CoPc) thin layer is presented. For comparison the optical properties of CoPc solution were also investigated. Absorption measurements revealed strong intermolecular interaction in the solid form as well as the presence of intramolecular charge transfer excitation below the B exciton band. Spectral distribution of complex refractive index (n) and extinction coefficient (k) as well as thickness of the layer were found basing on reflection and transmission measurements by minimization appropriately defined error function. Corresponding values of dielectric constants were also calculated.

Third-order nonlinear optical properties of CuPc: influence of thickness and concentration

The concentration dependence of third order nonlinear optical susceptibility ( χ<3> ) of copper phthalocyanine (CuPc) dissolved in tetrahydrofuran (THF) using the degenerate four wave mixing (DFWM) method at 532 nm was investigated. We present the linear dependence of the third order nonlinear optical susceptibility ( χ<3> ) as a function of different concentration for CuPc dissolved in THF. We also calculated the second order hyperpolarizability ( γ) of CuPc solutions. Third harmonic generation (THG) measurements at the 1064 nm performed on CuPc thin films are also presented. We found that the χ<3>DFWM values are larger than the χ<3>THG ones. This variation observed in χ<3> values, occurs probably due to the different resonance contributions in solution and solid state of CuPc. We show that in the case of DFWM measurements the one and two-photon resonant contributions at the Q and C-band increase χ<3>DFWM value of CuPc. In THG measurements, the three-photon resonance contribution at the Soret band gives rise to higher χ<3>THG value.

Kinetics of photoluminescence of porous silicon studied by photo-luminescence excitation spectroscopy and time-resolved spectroscopy

Photoluminescence (PL) spectra and excitation spectra (PLE) (under steady-state conditions), time resolved spectra (PL-TRS) and decay curves of photoluminescence (PL-DC) in micro- and nanosecond range (under pulsed operation) at different temperatures (10 K-room) on anodically etched boron-doped silicon are presented. PLE shows that visible PL is excited by light from UV region. PL and PL-TRS exhibit multiband structure and can be decomposed as a sum of few Gaussians. PL-DCs have multiexponential shape. Relaxation times depend on wavelength of the observation. To explain our results we assumed a model in which the multibarrier structure is formed by larger Si crystallites or wires (quantum well) surrounded by Si crystallites with diameters in the nanometer range (barrier region). The visible photoluminescence originates from radiative recombination between discrete energy levels in a quantum well.

Study of photoadmittance and admittance of porous silicon layers

In this work, we investigated electrical properties of Al/PS/p-Si structures. Admittance spectroscopy is one of the major semiconductor diagnostic techniques. Frequency, voltage and wavelengths dependencies of admittance will be analyzed in detail. It will be useful for better understanding of fundamental electrical properties of porous silicon.

DC and AC conductivity of PbSe/Si structures grown by pulsed laser ablation methods

In this paper we report the result of investigation of the electrical transport in PLD grown n-PbSe/n-Si heterojunction by DC and AC current measurement techniques. This characterization method is a well-suited and simple technique to study the interface between two semiconductors. The Si substrates are highly doped (ρ = 0.45 Ωcm), and consequently most of the heterojunction depletion layer falls in the PbSe epilayer. Fabrication of PbSe thin films on Si substrates by the pulsed laser deposition(PLD) method has been demonstrated. The films were characterized by X-ray diffraction analysis.