Wendong Xu

Tunable three-dimensional intensity distribution by a pure phase-shifting apodizer

The three-dimensional distribution of light intensity that is modulated by a pure phase-shifting apodizer is studied. Results show that the Strehl ratio can be altered by the proposed apodizer and by the waist width of incident Gaussian beams. By changing geometrical parameters of the proposed apodizer, we can increase the focal depth to several times that of the original system. The proposed apodizer can also be used to realize focal splitting and local minimum of intensity, which may be advantageous for constructing an optical trap. Furthermore, the local minimum of intensity number is tunable by changing the parameters of the apodizer.

Tunable focal depth of an apodized focusing optical system

The axial intensity distribution and focal depth of an apoclized focusing optical system are theoretically investigated with two kinds of incident light fields: a uniform-intensity-distribution beam and a Gaussian beam. Both a low-numerical-aperture and a high-numerical-aperture optical system are considered. Numerical results show that the depth of focus can be adjusted by changing the geometrical parameters and transmissivity of the apodizer in the focusing optical system. When a Gaussian beam is employed as the incident beam, the waist width also affects the depth of focus. The tunable range of the focal depth is very considerable. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

Read-only memory disk with AgOx and AgInSbTe superresolution mask layer

Two novel read-only memory (ROM) disks, one with an AgOx mask layer and the other with an AgInSbTe mask layer, are proposed and studied. The AgOx and the AgInSbTe films sputtered on the premastered substrates with pit depths of 50 nm and pit lengths (space) of 380 nm are studied by atomic force microscopy. Disk readout measurement is carried out using a dynamic setup with a laser wavelength of 632.8 nm and an object lens numerical aperture (NA) of 0.40. Results show that the superresolution effect happens only at a suitable oxygen flow ratio for the AgOx ROM disk. The best superresolution readout effect is achieved at an oxygen flow ratio of 0.5 with the smoothest film surface. Compared with the AgOx ROM disk, the AgInSbTe ROM disk has a much smoother film surface and better superresolution effect. A carrier-to-noise ratio (CNR) of above 40 dB can be obtained at an appropriate readout power and readout velocity. The readout CNR of both the AgOx and AgInSbTe ROM disks have a nonlinear dependence on the readout power. The superresolution readout mechanisms for these ROM disks are analyzed and compared as well. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

Static Optical Recording Properties of Super-Resolution Near-Field Structure with Bismuth Mask Layer

Super-resolution near-field structure (super-RENS) with bismuth (Bi) mask layer (Bi-super-RENS) is reported for the first time in this paper. Bi thin films with various thicknesses were studied by atomic force microscopy and grazing incident X-ray diffraction. Static optical recording tests with and without super-RENS were carried out using 650 nm semiconductor laser at recording power of 14 mW and 7 mW with pulse duration of 100 ns. The recording marks were observed by scanning electron microscopy and high-resolution optical microscopy with a CCD camera. Results showed that the Bi mask layer can also concentrate energy into the center of a laser beam at low laser power similar to the traditional Sb mask layer. Moreover, a (ZnS)80(SiO2)20 protection layer performed better than the SiN protection layer in the Bi-super-RENS. The direct observation of laser-recording marks may help better understand the working mechanism of the super-RENS, super-resolution ablation, and other nonlinear switch phenomena.

Static recording characteristics of super-resolution near-field structure with bismuth mask layer

Static recording characteristics of super-resolution near-field structure with bismuth (Bi) mask layer and antimony (Sb) mask layer were investigated and compared. The experimental results show that Bi mask layer can also concentrate energy into the center of a laser beam at a low laser energy input similar to Sb, which may be because that Bi film exhibits giant nonlinearity at low laser intensity. The direct observation of laser-recording marks may help better understand the working mechanism of the super-RENS, super-resolution ablation, and other nonlinear switching phenomena.

Dynamic Testing System for Hybrid Magneto-Optical Recording

Hybrid Magneto-Optical Recording is a potential data storage technology in the future informational society. To construct a research platform for hybrid recording, a dynamic testing system is designed and built in this paper, in which 406.7nm blue laser is used for recording and 655nm red laser for focus servo. With high modularization, the computer serves as the control core for the laser external modulation, focus servo, and sample plate spinning. Each module and its function are discussed in detail in the paper. Experimental results are also given to verify the stable and smooth performance of the system, in which the key obstacle, vibration noise, is successfully surmounted.

Method for testing small light spot produced by optical systems of high NA

We report a method for testing small light spot produced by an optical system with high numerical-aperture (NA). A high NA objective was used to converge the incident linear polarized light, and a tapered optical fiber probe with an opening of 50-80 nm mounted in the near-field optical microscopy (SNOM) apparatus was used to measure light intensity. The small light spot can be measured with high spatial resolution. The results show that a resolution of 50~100 nm can be obtained.

Testing system for groove geometry of CD-R substrates

We introduce a homemade testing system for groove geometry of CD-R substrates by measuring diffraction orders. This testing is of particular importance in CD-R disc manufacture process because the results fed back from the testing can be used to help optimizing recording, developing, metalizing, electroplating and replicating processes. Even if the width and depth of groove are not accurately obtained by this system, it is also valuable in CD-R disc manufacturing process because the system is simple, sensitive, quick and non- destructive, and can be well-used to judge the quality of substrates. The results of the same sample tested by our system and an AFM microscope are presented.