Zhengxiu Fan

Far-field intensity distribution and M 2 factor of hollow Gaussian beams

The far-field intensity distribution of hollow Gaussian beams was investigated based on scalar diffraction theory. An analytical expression of the M2 factor of the beams was derived on the basis of the second-order moments. Moreover, numerical examples to illustrate our analytical results are given.

Nonparaxial propagation of vectorial hollow Gaussian beams

Based on the vectorial Raleigh-Sommerfeld diffraction integral, the nonparaxial. propagation of vectorial hollow Gaussian beams (HGBs) in free space is studied. The far-field and paraxial cases can be treated as special cases of our general results. The typical numerical examples are given to illustrate our analytical results and comparisons between the different approximations present that the f parameter still plays an important role in determining the nonparaxiality of vectorial diffracted HGBs. (c) 2007 Optical Society of America.

Nonpolarizing guided-mode resonance filter

A normal-incidence nonpolarizing guided-mode resonance filter is designed. There are two waveguide layers and one grating layer in the filter. By adjusting the distance between the two waveguide layers, the same resonance wavelength for both TE and TM polarization can be achieved. An antireflection design method is also used to decrease the sideband reflection of the filter. The results show that the filter has high reflection, more than 99.9% at 500 nm, and the FWHMs of TE- and TM-polarized light are 2.16 and 0.15 nm, respectively.

Electric field enhancement in guided-mode resonance filters

Electric fields inside guided-mode resonance filters (GMRFs) may be intensified by resonance effects. The electric field enhancement is investigated in two GMRFs: one is resonant at normal incidence, the other at oblique incidence. It is shown that the two GMRFs exhibit different behaviors in their electric enhancement. Differences between the electric field distributions of the two GMRFs arise because coupling between counterpropagating modes occurs in the first case. It is also shown that the order of the electric field of maximum amplitude can be controlled by modulation of the dielectric constant of the grating.

Employing oxygen-plasma posttreatment to improve the laser-induced damage threshold of ZrO 2 films prepared by the electron-beam evaporation method

ZrO2 films are deposited by the electron-beam evaporation method. Parts of the prepared samples are post-treated with oxygen plasma at the environment temperature. The laser-induced damage threshold (LIDT) of the films increases from 15.9 to 23.1 J/cm2 after treatment with oxygen plasma. Compared with that of the as-grown samples, significant reduction of the average microdefect density and absorption are found after oxygen-plasma posttreatment. These results indicate that the oxygen-plasma posttreatment technique is an effective and simple method for reducing the microdefect density and absorption to improve the LIDT.

Optimization design of an ultrabroadband, high-efficiency, all-dielectric grating.

More than 97% flat-top diffraction efficiency in the -1st-order TE polarization over a 110 nm wavelength range around 800 nm in an all-dielectric grating is designed by a simulated annealing algorithm and the Fourier mode method. Its band is near to the maximum bandwidth provided by a dielectric high-reflectivity mirror under the match layer. This result will provide a way for high-efficiency chirped-pulse amplification to be used in an ultrashort high-power pulse laser system based on all-dielectric gratings. Furthermore, an effective method for broadband high-efficiency all-dielectric grating design is presented in this Letter.

Comparison of femtosecond and nanosecond laser-induced damage in HfO2 single-layer film and HfO2-SiO2 high reflector

HfO2 single layers, 800 run high-reflective (HR) coating, and 1064 ran HR coating were prepared by electron-beam evaporation. The laser-induced damage thresholds (LIDTs) and damage morphologies of these samples were investigated with single-pulse femtosecond and nanosecond lasers. It is found that the LIDT of the HfO2 single layer is higher than the HfO2-SiO2 HR coating in the femtosecond regime, while the situation is opposite in the nanosecond regime. Different damage mechanisms are applied to study this phenomenon. Damage morphologies of all samples due to different laser irradiations are displayed. (c) 2007 Optical Society of America.

Laser-induced damage of a 1064-nm ZnS/MgF 2 narrow-band interference filter

The laser-induced damage thresholds, absorptances, and damage morphologies of ZnS/MgF(2) interference filters that were designed to allow radiation at wavelengths near 1064 nm to pass through them have been examined. The damage morphologies as well as their laser behaviors suggest that the initial damage is located not at the surface layers but near the interface of the spacer layer where ZnS is sublimed to form many little bubbles. The electric field distribution and the temperature rise in the multilayer was calculated to model this interesting phenomenon. Various explanations for the thermodynamic coupling are presented.

Roughness evolution of ZrO2 thin films grown by reactive ion beam sputtering

A series of zirconium dioxide films were grown on rough borosilicate crown glass substrates with reactive ion beam sputtering technique. The evolution of the surface roughness was studied in the smoothing and roughening growth regimes using atomic force microscopy. By quantitative analysis of surface morphology, the interface width of the growth fronts was found to have a minimum during the deposition process. Dynamic scaling was observed for thicker films; the roughness exponent was found to be in the range of 0.7–0.9 and the growth exponent at approximately 0.4.

Nonpolarizing and polarizing filter design.

We describe a nonpolarizing filter design at oblique incidence and a polarizing filter design at normal incidence that use a uniaxially anisotropic layer. The phase thicknesses and the optical admittances of the layers are compensated for by the birefringent properties of a thin film at oblique incidence. This concept can be applied to the design of nonpolarizing bandpass and edge filters at oblique incidence and of polarizing beam splitters at normal incidence. Besides, the dependence of narrow-bandpass filters on normal incidence is discussed.