Strong quantum confinement effects in thin zinc selenide films

Stable Q-switched and femtosecond mode-locked erbium-doped fiber laser based on a CuSe nanosheets saturable absorber

Stable Q-switched and femtosecond mode-locked erbium-doped fiber laser (EDFL) have been achieved using CuSe nanosheets as novel saturable absorber (SA), where the CuSe nanosheets were prepared by a hydrothermal method. The nonlinear optical properties of CuSe nanosheets were measured using an Z-scan setup, revealing nonlinear absorption coefficients of -3.67 ± 0.22 cm GW-1 at 1560 nm. The prepared CuSe nanosheets were mixed with polyvinyl alcohol (PVA) to obtain a CuSe-PVA SA with a modulation depth of 3.8 ± 0.13%, and it was utilized to realize a Q-switched EDFL, obtaining the narrowest pulse duration of 1.29 µs and the maximum output power of 5.96 mW, which corresponds to a pulse energy of up to 103.7 nJ. In addition, CuSe nanosheets were deposited on a D-shaped fiber (DSF) to fabricate a CuSe-DSF SA with a modulation depth of 5.6 ± 0.17%, and it was utilized to realize a mode-locked EDFL. The mode-locked EDFL demonstrated a low threshold of only 42 mW, a pulse duration of 740 fs, and a maximum output power of 9.7 mW. Meanwhile, it exhibited a high signal-to-noise ratio of 72 dB. To the best of our knowledge, this is the first time of CuSe nanosheets as SA in EDFL. The results demonstrate that CuSe nanosheets are a highly promising nonlinear optical material with great potential for applications in ultrafast photonics.

Quantum Confinement Effects of Thin Co3O4 Films

Thin Co films were deposited on quartz and Corning glass by radio frequency magnetron sputtering. The films were postannealed at 500 °C in a furnace in air atmosphere. The resulting samples were examined with X-ray diffraction experiments, which revealed that they consist of single-phase, polycrystalline Co3O4. The morphology of selected samples was recorded by atomic force microscopy. Ultraviolet-visible light absorption spectroscopy experiments probed the absorbance of the films in the wavelength range 200–1100 nm. Two types of transitions (energy gaps) were clearly identified. Both of them were found to be “blue shifted” with decreasing film thickness; this is interpreted as evidence of quantum confinement effects. For the case of the first gap value, this was corroborated by calculations based on a combination of the Potential Morphing Method and the effective mass approximation.

Nonlinear Optical Studies of Gold Nanoparticle Films

Gold films are widely used for different applications. We present the results of third- and high-order nonlinear optical studies of the thin films fabricated from Au nanoparticle solutions by spin-coating methods. These nanoparticles were synthesized by laser ablation of bulk gold in pure water using 200 ps, 800 nm pulses. The highest values of the nonlinear absorption coefficient (9 × 10-6 cm W-1), nonlinear refractive index (3 × 10-11 cm² W-1), and saturation intensity (1.3 × 1010 W cm-2) were achieved using 35 fs, 400 nm pulses. We also determined the relaxation time constants for transient absorption (220 fs and 1.6 ps) at 400 nm. The high-order harmonic generation was studied during propagation of 35 fs, 800 nm pulses through the plasma during the ablation of gold nanoparticle film and bulk gold. The highest harmonic cutoff (29th order) was observed in the plasma containing gold nanoparticles.

A Study of Quantum Confinement Effects in Ultrathin NiO Films Performed by Experiment and Theory

Ultrathin NiO films in the thickness range between 1 and 27 nm have been deposited on high-quality quartz substrates by direct magnetron sputtering under a rough vacuum with a base pressure of 2 × 10⁻² mbar. The sputtering target was metallic Ni; however, due to the rough vacuum a precursor material was grown in which most of Ni was already oxidized. Subsequent short annealing at temperatures of about 600 °C in a furnace in air resulted in NiO with high crystallinity quality, as atomic force microscopy revealed. The images of surface morphology showed that the NiO films were continuous and follow a normal grain growth mode. UV-Vis light absorption spectroscopy experiments have revealed a blue shift of the direct band gap of NiO. The band gap was determined either by Tauc plots (onset) or by the derivative method (highest rate of absorbance increase just after the onset). The experimental results are interpreted as evidences of quantum confinement effects. Theoretical calculations based on Hartree Fock approximation as applied for an electron-hole system, in the framework of effective mass approximation were carried out. The agreement between theory and experiment supports the quantum confinement interpretation.

Oscillation of absorption bands of Zn(1-x)Mn(x)S clusters: an experimental and theoretical study

Electroporation of synthetic vesicles is utilized for the preparation of molecular size uncapped Zn(1-x)Mn(x)S clusters. The absence of caps permits (i) continued growth of the Zn(1-x)Mn(x)S clusters formed, (ii) the assessment of their true absorption spectra unaltered by stabilizing ligands, and (iii) the previously inaccessible live observation of the growth of the clusters in the molecular size regime. Upon cluster growth, the UV spectra exhibit novel, time-dependent, oscillation of red and blue shifts of the characteristic absorption band. The structure and electronic properties of Zn(N-1)MnS(N) clusters with N = 1-9 are calculated using the first-principles DMol(3) package. On the basis of similarities between the oscillating trend of the experimentally observed absorption spectra and that of the calculated highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap of Zn(N-1)MnS(N) clusters with N = 1-9, the wavelengths of the sequential spectral peaks can be assigned to Zn(2)MnS(3), Zn(3)MnS(4), Zn(4)MnS(5), Zn(6)MnS(7), and Zn(8)MnS(9), respectively. Our results demonstrate that both the cluster size and the composition can be used to tune the optical properties.