Ultrafast nonlinear optical response of photoconductive ZnO films with fluorine nanoparticles

Time-resolved photoconductivity distribution measurement by a synchronized double-scanning method

The lifetime and the distribution of photoconductivity generated in laser-illuminated semiconductors are critical to photoconductivity-based applications. We propose a synchronized double-scanning method to measure time-resolved diffusion in the form of an afterglow embedded in the distribution map. The method combines spatial scanning of a coaxial resonator with synchronized laser scanning to map the dynamically excited conductivity on a semiconductor wafer. Thus, the photoconductivity afterglow effects can be mapped and retrieved by images of dynamic photoconductivity distribution. The photoconductivity lifetimes of silicon wafers with different thicknesses and by different lasers were measured and evaluated, which were also validated by the microwave photoconductivity decay (μ-PCD) method. In addition, the behavior of photoconductivity diffusion around a structural defect was exhibited. The method is nondestructive and can be applied in the photoconductivity property diagnostic.

Two-photon and three-photon absorption in ZnO nanocrystals embedded in Al2O3 matrix influenced by defect states

The broadband nonlinear absorption in ZnO nanocrystals embedded in Al₂O₃ matrix was investigated by Z-scan and pump-probe techniques from 400 nm to 800 nm. The effective two-photon absorption and three-photon absorption coefficients were determined to be ∼1.1×10³  cm/GW at 400 nm and ∼1.1×10^-1  cm³/GW² at 800 nm, respectively, which are at least two orders of magnitude greater than that in ZnO bulk crystal. It may be attributed to the defect-states-mediated multiphoton absorption process, which was proofed by comparison experiments with different densities of interfacial defect states. The corresponding lifetimes for the intraband relaxation, defect-states trapping, and interband recombination processes were measured by femtosecond transient absorption measurements as τ1 ∼ 1  ps, τ2 ∼ 13  ps, and τ3 ∼ 350  ps, respectively.

Nonlocal nonlinear refractive index of gold nanoparticles synthesized by ascorbic acid reduction: comparison of fitting models

In this paper, the nonlinear refractive index of colloidal gold nanoparticles under continuous wave illumination is investigated with the z-scan technique. Gold nanoparticles were synthesized using ascorbic acid as reductant, phosphates as stabilizer and cetyltrimethylammonium chloride (CTAC) as surfactant agent. The nanoparticle size was controlled with the CTAC concentration. Experiments changing incident power and sample concentration were done. The experimental z-scan results were fitted with three models: thermal lens, aberrant thermal lens and the nonlocal model. It is shown that the nonlocal model reproduces with exceptionally good agreement; the obtained experimental behaviour.

Optoelectronic modulation by multi-wall carbon nanotubes

We report the observation of photoconduction and a strong nonlinear optical absorptive response exhibited by multi-wall carbon nanotubes. An aerosol pyrolysis method was employed for the preparation of the samples. Measurements of the optical transmittance with 7 ns pulses at 1064 nm wavelength allowed us to identify a two-photon absorption effect as the main mechanism of third-order nonlinearity. Photoconductive experiments at 445 nm wavelength seem to confirm the possibility for generating non-resonant multi-photonic absorption processes in the multi-wall carbon nanotubes. By the optical control of the conductivity in the nanotubes, we implement an optoelectronic amplitude modulator device with potential applications for sharp selective functionalities.