Deep silicon grating as high-extinction-ratio polarizing beam splitter

A deep binary silicon grating as high-extinction-ratio reflective polarizing beam splitter (PBS) at the wavelength of 1550 nm is presented. The design is based on the phenomenon of total internal reflection (TIR) by using the rigorous coupled wave analysis (RCWA). The extinction ratio of the rectangular PBS grating can reach 2.5×105 with the optimum grating period of 397 nm and groove depth of 1.092 μm. The effciencies of TM-polarized wave in the 0th order and TE-polarized wave in the −1st order can both reach unity at the Littrow angle. Holographic recording technology and inductively coupled plasma (ICP) etching could be used to fabricate the silicon PBS grating.

Technique for diagnosing x-ray laser beam quality by use of the moire signal

We present what we believe is a novel technique based on the moire effect for fully diagnosing the beam quality of an x-ray laser. Using Fresnel diffraction theory, we investigated the intensity profile of the moire pattern when a general paraxial beam illuminates a pair of Ronchi gratings in the quasi-far field. Two formulas were derived to determine the beam quality factor M-2 and the effective radius of curvature R-e from the moire pattern. On the basis of the results, the far-field divergence, the waist location, and the radius can be calculated further. Finally, we verified the approach by use of numerical simulation. (C) 1999 Optical Society of America [S0740-3232(99)01502-1].

Analysis of beam-quality degradation in nonlinear frequency conversion

Based on the ripple transfers of electric-field amplitude and phase in frequency tripling, simple formulas are derived for the harmonic laser's beam-quality factor M-3omega(2), with an arbitrary fundamental incidence to ideal nonlinear crystals. Whereas the harmonic beam's quality is generally degraded, the beam's divergence is similar to that of the fundamental after nonlinear frequency conversion. For practical crystals with periodic surface ripples that are caused by their machining, a multiorder diffractive model is presented with which the focusing properties of harmonic beams can be studied. Predictions of the theories are shown to be in excellent agreement with full numerical simulations. (C) 2002 Optical Society of America.

Focusing properties of concentric piecewise cylindrical vector beam

The focusing properties of a concentric piecewise cylindrical vector beam is investigated theoretically in this paper. The beam consists of three portions with different and changeable phase retardation and polarization. Numerical simulations show that the evolution of the focal shape is very considerable by changing the radius and polarization rotation angle of each portion of the vector beam. And some interesting focal spots may occur, such as two- or three-peak focus, dark hollow focus, ring focus, and two-ring-peak focus. Corresponding gradient force patterns are also computed, and novel trap patterns, including cup shell shape trap with one trap at its each side along axis, rectangle shell shape trap with one trap at its each side, dumbbell optical trap, spherical shell optical trap, may occur, which shows that the concentric piecewise cylindrical vector beam can be used to construct controllable optical tweezers. (c) 2006 Elsevier GmbH. All rights reserved.

Beam quality improvement of laser diode array by using off-axis external cavity

A novel off-axis external cavity is designed for laser diode array to improve the beam quality. In this external cavity, a circle aperture with variable size is used as a spatial filter. The diameter of aperture is optimized to 1.2mm and the off-axis angle of external cavity is optimized at 2.6 deg. In the optimal case, the beam parameter product (BPP) of laser diode array is reduced to 121 mm. mrad from 1050 mm. mrad with external cavity optical efficiency of 81%. (C) 2007 Optical Society of America.

Layer uniformity of glancing angle deposition

Some results of an investigation on the layer thickness uniformity of glancing angle deposition are presented. A zirconia monolayer has been deposited by glancing angle deposition to analyze the layer thickness uniformity. The experimental results indicate that the thickness variation over the substrate is less than 0. 1%, which is considered as good uniformity. It is found that the non-uniformity of experimental results is larger than that of the theoretical results. (c) 2005 Elsevier Ltd. All rights reserved.

Structure and optical properties of ZnS thin films grown by glancing angle deposition

The glancing angle deposition (GLAD) technique was used to deposit ZnS films by electron beam evaporation method. The cross sectional scanning electron microscopy (SEM) image illustrated a highly orientated microstructure composed of slanted column. The atomic force microscopy (APM) analysis indicated that incident flux angle had significant effects on the nodule size and surface roughness. Under identical nominal thickness, the actual thickness of the GLAD films is related to the incident flux angle. The refractive index and in-plane birefringence of the GLAD ZnS films were discussed, and the maximum bireffingence Delta n = 0.036 was obtained at incident flux angle of alpha = 80 degrees. Therefore, the glancing angle deposition technique is a promising way to create a columnar structure with enhanced birefringent property. (c) 2005 Elsevier B.V. All rights reserved.

Structural and optical properties of nanostructured TiO2 thin films fabricated by glancing angle deposition

TiO2 films deposited by electron beam evaporation with glancing angle deposition (GLAD) technique were reported. The influence of flux angle on the surface morphology and the microstructure was investigated by scanning electron microscopy. The GLAD TiO2 films are anisotropy with highly orientated nanostructure of the slanted columns. With the increase of flux angle, refractive index and packing density decrease. This is caused by the shadowing effect dominating film growth. The anisotropic structure of TiO2 films results in optical birefringence, which reaches its maximum at the flux angle alpha = 65 degrees. The maximum birefringence of GLAD TiO2 films is higher than that of common bulk materials. It is suggested that glancing angle deposition may offer an effective method to obtain tailorable refractive index and birefringence in a large continuous range. (c) 2006 Elsevier B.V. All rights reserved.

Preparation and characterization of nanostructured ZrO2 thin films by glancing angle deposition

ZrO2 films were prepared by electron beam evaporation with glancing angle deposition (GLAD) technique. The as-deposition and annealed ZrO2 films are all amorphous, different from that deposited at normal incidence. Due to the shadowing effect, a highly orientated structure composed of slanted columns formed, and the obtained films became the mixture of slanted columns and voids. The relationship among the effective refractive index, packing density and flux incident angle was investigated. The refractive index and packing density of ZrO2 films decrease with the increase of the incident angle. The in-plane birefringence of GLAD ZrO2 films was calculated. At the packing density of 0.576, the maximum birefringence is 0.037. (c) 2006 Elsevier B.V. All rights reserved.

Structure and optical properties of Nb2O5 sculptured thin films by glancing angle deposition

Nb2O5 sculptured thin. films deposited by electron beam evaporation with glancing angle deposition were prepared. Nb2O5 sculptured thin. films with tilted columns are optical anisotropy. XRD, SEM, UV-vis-NIR spectra are employed to characterize the microstructure and optical properties. The maximum of birefringence (Delta n) is up to 0.045 at alpha = 70 degrees with packing density of 0.487. With increasing the deposition angle, refractive index and packing density of Nb2O5 STF are decreasing. The relationship among deposition parameter, microstructure and optical properties was investigated in detail. (C) 2008 Elsevier B. V. All rights reserved.

High power laser with integrated lens using focused ion beam etching

In this study, a collimating lens is introduced at the output facet of a tapered waveguide laser to compensate for the divergence of the optical mode. The collimating lens is shown to enhance the laser efficiency while simultaneously reducing the far field divergence.

Angular distribution of field emitted electrons from vertically aligned carbon nanotube arrays

Angular field emission (FE) properties of vertically aligned carbon nanotube arrays have been measured on samples grown by plasma enhanced chemical vapor deposition and characterized by scanning electron microscope and I-V measurements. These properties determine the angular divergence of electron beams, a crucial parameter in order to obtain high brilliance FE based cathodes. From angular distributions of the electron beam transmitted through extraction grids of different mesh size and by using ray-tracing simulations, the maximum emission angle from carbon nanotube tips has been determined to be about ± 30 around the tube main axis. © 2012 American Institute of Physics.

Occurrence of particle debris field during focused Ga ion beam milling of glassy carbon

To explore the machining characteristics of glassy carbon by focused ion beam (FIB), particles induced by FIB milling on glassy carbon have been studied in the current work. Nano-sized particles in the range of tens of nanometers up to 400 nm can often be found around the area subject to FIB milling. Two ion beam scanning modes - slow single scan and fast repetitive scan - have been tested. Fewer particles are found in single patterns milled in fast repetitive scan mode. For a group of test patterns milled in a sequence, it was found that a greater number of particles were deposited around sites machined early in the sequence. In situ EDX analysis of the particles showed that they were composed of C and Ga. The formation of particles is related to the debris generated at the surrounding areas, the low melting point of gallium used as FIB ion source and the high contact angle of gallium on glassy carbon induces de-wetting of Ga and the subsequent formation of Ga particles. Ultrasonic cleaning can remove over 98% of visible particles. The surface roughness (Ra) of FIB milled areas after cleaning is less than 2 nm. © 2010.

Off-axis sonar beam pattern of free-ranging finless porpoises measured by a stereo pulse event data logger

The off-axis sonar beam patterns of eight free-ranging finless porpoises were measured using attached data logger systems. The transmitted sound pressure level at each beam angle was calculated from the animal's body angle, the water surface echo level, and the swimming depth. The beam pattern of the off-axis signals between 45 and 115 (where 0 corresponds to the on-axis direction) was nearly constant. The sound pressure level of the off-axis signals reached 162 dB re 1 mPa peak-to-peak. The surface echo level received at the animal was over 140 dB, much higher than the auditory threshold level of small odontocetes. Finless porpoises are estimated to be able to receive the surface echoes of off-axis signals even at 50-m depth. Shallow water systems (less than 50-m depth) are the dominant habitat of both oceanic and freshwater populations of this species. Surface echoes may provide porpoises not only with diving depth information but also with information about surface direction and location of obstacles (including prey items) outside the on-axis sector of the sonar beam. 2005 Acoustical Society of America.

Design of novel polarization beam splitter in two-dimensional photonic crystal

We present the design and the simulation of an ultracompact high efficiency polarization beam splitter (PBS) based on the properties of the light waves propagating in straight waveguide and composite structure photonic crystal. The splitting properties of the PBS are numerically simulated and analyzed by using the plane wave expansion (PWE) method and finite difference time domain (FDTD) method. The PBS consists of three parts, namely, input waveguide, beam structure and output waveguide. It is shown that a high efficiency and a large separating angle for TE mode and TM mode can be achieved. Owing to these excellent features, including small size and high rate, the PBS makes a promising candidate in the future photonic integrated circuits.