Jiaoling Zhao

Influence of film thickness and nanograting period on color-filter behaviors of plasmonic metal Ag films

The effects of film thickness and nanograting period on color filter behaviors of the device, fabricated by sub-micrometers patterning on plasmonic silver thin films, have been studied. It is found that color filter properties strongly correlate with film thickness and nanograting period. Based on obtained results, the relationship of the wavelength of transmission minima with film thickness and nanograting period was derived. This equation can predict the transmission minima for a given thickness and period in one-dimensional Ag metallic film nanograting on glass substrate, which could guide to design color filter device with desirable wavelength.

Morphology, structure and optical properties in TiO 2 nanostructured films annealed at various temperatures

Amorphous TiO2 nanostructured thin films (TNFs) were deposited by the glancing angle deposition technique (GLAD) with an electron gun. All of the prepared TNFs were composed of discrete nanoscale columns, characterized by scanning electron microscope. With the annealing treatment, the pure anatase phase was transformed from amorphous TNFs. The morphological, structural and optical properties of TNFs under the annealing treatment were measured, and the evolvement mechanism was further analyzed. The optimum annealing temperature for the pure anatase precipitation of TNFs is about 400°C. The variation of morphology, chemical state and crystallization of TNFs also resulted in the shift of the transmittance spectra. The results show that appropriate post-annealing treatment can build fine nanostructures and pure anatase precipitation, which can support the applications and researches about the anatase phase TNFs powerfully.

Defect analysis of UV high-reflective coatings used in the high power laser system.

By considering the rapid change of standing-wave electric-field and assuming the interface defect distribution, an improved model is developed to analyze the defect density distribution and assess the damage performance of high-reflective coatings. Two kinds of high-reflective coatings deposited by e-beam evaporation (EBE) and ion beam sputtering (IBS) techniques are analyzed with this method. The lower overall damage threshold is the major feature for the coatings deposited by IBS method according to the defect parameters extracted from the model. Typical damage morphologies of coatings are also measured and analyzed. The assumption of interface defects is supported by the damage behavior. The damage mechanisms of two high-reflective coatings are attributed to the formation of molten pool and mechanical ejection. The influence of the incident angle on the damage probability is also considered and numerically calculated. The defect analysis model improved here is suitable for high-reflective coatings.

Spontaneous emission properties of organic film in plane optical microcavity

The spontaneous emission properties of a single layer organic film in plane optical microcavities were studied. Optical microcavity was formed by a Tris(8-quinolinolato) aluminium (Alq) film sandwiched between a distributed Bragg reflector (DBR) and a Ag metallic reflector. Two kinds of microcavities were devised by using a different DBR structure. Compared with a Alq film, significantly spectral narrowing and intensity enhancement was observed in the two microcavities, which is attributed to the microcavity effect. The spectra characteristics of the two microcavities showed that the structure of DBR has much influence on the emission properties of a microcavity

Stimulated emission in the blue wavelength region from a copolymer containing PPV segment

The lasing properties of a soluble conjugated polymer, Poly[1,8-octanedioxy-2,6-dimethoxy-1,4-phenylene-1,2-ethenylene-1,2-phenylene-1,2-ethenylene-3,5-dimethoxy-1,4-phenylene] (CNMBC-Ph) in chloroform solution were investigated. The third harmonic radiation of a Nd:YAG laser was used as the pump light. The stimulated emission with a linewidth of 15 nm was observed in the blue wavelength region with the peak at 450 nm. The threshold pulse peak power was about 2.8 MW/cm(2). The energy conversion yield of the laser was estimated to be about 3.4%. The maximum peak power of the laser output pulse reached 40 kW

High-precision measurement of optical constants of ultra-thin coating using surface plasmon resonance spectroscopic ellipsometry in Otto-Bliokh configuration

In this paper, a surface plasmon resonance (SPR) spectroscopic ellipsometry, based on Otto-Bliokh configuration, is developed for the measurement of thickness and optical constants of ultra-thin coatings. This technique combines sensitivity of surface plasmon with accessibility of optical constants and other advantages of ellipsometry. Surface plasmons (SP) are generated in the sample under test in total reflectance mode and SP geometric distribution over the sample surface is influenced by the coating thickness and optical properties on one hand, and by the air gap thickness on the other hand. Nanoscale control of the thickness of the air gap between a convex surface and the sample was assured using a micron-size beam spot irradiating the contact zone. The amplitude and phase change induced by SPR in the visible and near-infrared spectral range were obtained to determine the dispersion of optical constants and the thickness of the ultra-thin layer. The extracted optical constants were found to be in excellent agreement with the results obtained using TEM and XRR techniques. Both theoretical analysis and experimental results demonstrated high sensitivity and precision of the proposed technique for the analysis of coatings of both metals and dielectrics on metals.

Suppression of nano-absorbing precursors and damage mechanism in optical coatings for 3ω mirrors.

Damage precursors in the 3ω (351 nm) mirror for a high-power laser system are investigated as well as the relevant damage mechanisms. The precursors are classified into two ensembles according to the different laser resistance and damage features. The former is nano-absorbing precursors, which are sensitive to the standing wave electric field and vulnerable to the laser irradiation. The latter is submicrometer nodular defects, which have higher laser resistance and are sensitive to the adhesion strength between the fluoride coatings and oxide coatings. The damage due to nano-absorbing precursors is efficiently suppressed with the double stack design that screens the electric field in the oxides. Currently, the nodular seed is major originating from the Al2O3/SiO2 stack. Even for the same defect type and mirror, the final damage features are dependent on the local mechanical properties at the irradiation location. The investigations of the damage mechanisms provide a direction to further improve the laser-induced damage threshold of the 3ω mirror.

Diffusion of metal ions from a substrate into oxide coatings

Concentrations of metal ions from a substrate were found in coatings adjacent to the substrate by studying the coatings using X-ray photoelectron spectroscopy before and after annealing. Small metal ions easily diffused into the coating from the substrate, whereas larger metal ions had more difficulty doing so because of their large atomic radii. A higher annealing temperature and a lower packing density induced a faster diffusion rate and a higher concentration of metal ions in the coating. Smaller metal ions passed through a SiO2 layer and preferentially accumulated in the Ta2O5 layer due to the migration of oxygen vacancies. These results are relevant for selecting the coating temperature, annealing temperature, and the substrate.

Origin of the plasma scalds in dielectric coatings induced by 1ω laser

The plasma scalds initiated by a 1053 nm (1ω) nanosecond laser are separated from the defect-induced damage pits, which is verified as a result of the ionization wavefront with the subnanosecond laser. Considering the beam reflection from solid-state absorption fronts during the damage process, a theoretical scalding threshold about 6.84 J/cm2 (12 ns) based on the energy required to start an air avalanche is evaluated and agrees well with the experimental scalding threshold. The occurrence order of the initial explosion and subsequent ionization wavefront is verified to explain most of the damage morphologies caused by the 1ω laser. In addition to the significance in laser conditioning or cleaning for a high-power laser system, the results also indicate that through the occurrence of plasma scalds it is possible to mark the onset time of air plasma during laser-coating interaction.

Influence of thickness and annealing temperature on the structure properties of random mask deposited by magnetron sputtering

The structure properties of random mask of antireflective structure prepared by the thermal dewetting process are investigated. As a low-cost and large-scale technique, the mask obtained in our work has a great prospect in the field of solar cell and high power laser system. Ultrathin films of amorphous Ag are deposited on the fused silica by magnetron sputtering. By fast thermal annealing the structures in Ag film are agglomerated on the substrate and form mask. The influence of different thickness and annealing temperature on the structure properties of random mask are studied. The surface morphologies are characterized by scanning electronic microscopy. The suitable conditions to obtain excellent quality Ag nanomasks with the pebble particles are achieved.