Design and analysis of all-dielectric broadband nonpolarizing parallel-plate beam splitters

Past research on the all-dielectric nonpolarizing beam splitter is reviewed. With the aid of the needle thin-film synthesis method and the conjugate graduate refine method, three different split ratio nonpolarizing parallel-plate beam splitters over a 200 nm spectral range centered at 550 nm with incidence angles of 45 degrees are designed. The chosen materials component and the initial stack are based on the Costich and Thelen theories. The results of design and analysis show that the designs maintain a very low polarization ratio in the working range of the spectrum and has a reasonable angular field.     

Design and manufacture of all-dielectric nonpolarizing beam splitters

Past research on all-dielectric nonpolarizing beam splitters is reviewed. It is shown that, for a 50-nm spectral region, it is possible to design and manufacture a two-material nonpolarizing plate beam splitter for use at an angle of 45 degrees (with a measured rms reflectance of 0.50 +/- 0.01 for both s- and p-polarized incident light).     

Designs of infrared nonpolarizing beam splitters with a Ag layer in a glass cube

A novel design of a nonpolarizing beam splitter with a Ag layer in a cube was proposed and optimized, based on the needle optimization. The digital simulations of the reflectance and reflection-induced retardance were presented. The simulation results showed that both the amplitude and the phase characteristics of the nonpolarizing beam splitter could realize the design targets. The difference between the simulated and the target reflectance of 50% is less than 0.4% and the simulated and the reflection-induced retardance is less than 0.62 degrees in the 1260 -1360 nm range for both p and s components.     

Design of a nonpolarizing beam splitter based on the form birefringence of a subwavelength grating inside a glass cube

We propose a design concept to design a nonpolarizing beam splitter with a compact sandwich structure that has a subwavelength grating. The design is based on effective-medium theory and rigorous coupled-wave analysis. The simulation shows that a subwavelength grating inside a glass cube can eliminate the polarization effect.     

Thermal emission from dielectric beam splitters in michelson interferometers: a schematic analysis

Thermal emission from beam splitters in Fourier transform infrared spectrometers causes spectral amplitudes that are in quadrature to those of radiation from the field of view or from the detector port. Beam-splitter emission is described as a superposition of radiation of electromagnetic dipoles with angular polarization correlation taken into account for the real refractive index. Surface emission shows characteristic differences compared with volume emission. Numerical data are given for experimental conditions adapted to those of the airborne limb sounder MIPAS-FT.     

Polarization properties and fractional-power analysis of coated and uncoated parallel-slab multireflection beam splitters

The polarization properties of coated and uncoated parallel-slab multireflection beam splitters are investigated. In a recent study [Opt. Lett. 21, 1709 (1996)] it was shown that the parallel-slab beam splitter is a basic optical component of the parallel-slab division-of-amplitude photopolarimeter. The ellipsometric parameters and the fractional powers for multireflected components generated by this system are analyzed. Interesting new observations with respect to the polarization properties at the Brewster angle of incidence and the distribution of powers among the multireflected components are presented.     

Characterization of symmetric, absorbing 50-50 beam splitters

The equality of the transmitted and reflected irradiances by a symmetric, absorbing beam splitter consisting of three media is considered. The condition of minimum absorptance and the phase difference between the transmitted and reflected fields are studied as well.     

Symmetrically coated pellicle beam splitters for dual quarter-wave retardation in reflection and transmission

A trilayer pellicle that consists of a high-index center layer that is symmetrically coated on both sides by a low-index film can be designed to produce differential reflection and transmission phase shifts of +/- 90 degrees at oblique incidence and equal throughput for the p and the s polarizations. Such a device splits a beam of incident linearly polarized light into two orthogonal circularly polarized components that travel in well-separated angular directions. Examples of infrared dual quarter-wave retarders that use a symmetrically coated Ge pellicle at 77 degrees angle of incidence are presented. A 50-50% splitter requires a symmetric pellicle with at least five layers. Error analysis shows that the thicknesses of the high-index layers must be tightly controlled. These circular polarization beam splitters are intended for operation with a well-collimated light source and can be used as the basis of a novel circular polarization Michelson interferometer.     

Theoretical analysis of fluorescence light shifts in optically pumped cesium beam frequency standards

Shirley's analysis (1985) is generalized to calculate the fluorescence light shifts in various optically pumped Cs beam standards, especially in the two-beam type frequency standard that enables a real-time correction of an end-to-end cavity phase shift. Using tables of light shift coefficients and mean fluorescence photon numbers per atom, fluorescence light shifts in one- and two-beam type optically pumped Cs beam frequency standards using noncycling detection and cycling detection, are evaluated. Results obtained are useful to correct the fluorescence light shifts in optically pumped Cs beam frequency standards.     

Coupling effect of multi-wavelength lasers in damage performance of beam splitters at 355 nm and 1064 nm

The coupling effect between a 355 nm laser and a 1064 nm laser in damage initiation and morphology formation was investigated on beam splitters. When extra 1064 nm pulse energy was low, 355 nm laser-induced damage thresholds (LIDTs) increased because of laser conditioning, and when 1064 nm pulse energy was high enough, 355 nm LIDTs decreased. Damage morphologies were also studied to explore the damage mechanism at respective wavelengths. For the entirely different electric field intensity distributions, 355 nm laser-induced damages were mainly from nanometer-sized absorbers at upper interfaces, while initiators for the 1064 nm laser were located at substrate-coating interface or substrate subsurface. Under simultaneous illumination, the sensitive defects were still the precursors, and damages also showed the representative damage characteristics induced by a single laser, namely, 355 nm laser-induced small pits and 1064 nm laser-induced large delamination. Further studies also showed that, although the 1064 nm laser fluence was kept unchanged, delamination area grew with the increase of pits, which were induced by the 355 nm laser. A possible mechanism was proposed to interpret the delamination area growth phenomenon.     

Taper array in silica glass for beam splitting

We proposed taper array in silica glass for beam splitting which was fabricated by water-assisted femtosecond laser direct writing technology and the subsequent heat treatment. We divided the array into many fabricating cells which were executed automatically in sequences as specified by the program that contained the information for the three-dimensional stage movements. Each cell could fabricated a rectangular cylinder. The size and distribution of the rectangular cylinder could be controlled by adjusting the position of the fabricating cells. Then the heat treatment should be used to reshape the rectangular cylinders into taper array. The experimental results show that the taper periodic microstructures in silica glass are uniform and smooth, and the tapers can divide the incident light into beam array. The results demonstrated that the combination of the water-assisted femtosecond laser direct writing technology and the heat treatment is accessible and practical for the high quality micro-optical elements. These micro-optical elements will have potential applications in fluorescence detection and beam splitter.     

Electron beam induced synthesis of CdSe nanomaterials: Tuning of shapes from rods to cubes

Cadmium selenide (CdSe) nanomaterials of different shapes have been synthesized in the water pool of the water-in-oil microemulsions through 7 MeV electron beam irradiation. The rod shaped CdSe nanomaterials of lengths and breadths up to 1 μm and 200 nm, respectively with aspect ratios from 3 to 5 were grown in the case of microemulsions containing lower water content, water to surfactant concentrations ratio, w₀ = 10. In contrast, the cubic shaped CdSe nanomaterials of dimensions about 100 nm were formed in the microemulsions with higher water contents, w₀ values from 20 to 40. Such a transformation of shape from rod to cube was attributed to the change in the hydrophobicity and hydrophilicity of the micro-environment in the microemulsions. The as-grown CdSe nanomaterials were stable at ambient conditions and thus expected to be very useful in the device applications.     

Reflection coefficients of p- and s-polarized light by a quarter-wave layer: explicit expressions and application to beam splitters

The complex-amplitude reflection coefficients of p- and s-polarized light by a transparent freestanding, embedded, or deposited quarter-wave layer (QWL) are derived as explicit functions of the angle of incidence and layer refractive index. This provides the basis for the design of 50%-50% beam splitters for incident s-polarized or unpolarized light that use a high-index (e.g., TiO2 or Ge) QWL embedded in a glass cube in the visible and near infrared spectral range. These simple devices have good angular and spectral response and are insensitive to small film thickness errors to the first order.     

Theoretical study of optical absorption in cadmium sulphoselenide doped silicate glass

The optical absorption spectra of CdS_xSe_{1 − x} (x = 0.3) doped silicate glass is theoretically simulated. The optical extinction coefficients and hence the optical density are calculated taking into consideration surface effects on the dielectric constants of the microcrystallites (nm). The simulated spectra shows a good resemblence to the experimental spectra.     

Interaction of cracks between two adjacent indents in glass

Experimental observations of the interaction behaviour of cracks between two adjacent indents were made using an indentation technique in soda-lime glass. It was specifically demonstrated how one indent crack initiates and propagates in the vicinity of another indent crack. Several types of crack interactions were examined by changing the orientation and distance of one indent relative to the other. It was found that the residual stress field produced by elastic/plastic indentation has a significant influence on controlling the mode of crack interaction. The interaction of an indent crack with a free surface was also investigated for glass and ceramic specimens.NASA Resident Research Associate     

高应变率加载下玻璃板碎片尺寸的理论模型

基于材料损伤理论和损伤断裂机理,分析了普通平板玻璃在高应变率下的损伤破碎规律。根据玻璃碎片破坏损伤应变能和断裂表面能之间的平衡关系,推导了不同应变率下预测玻璃碎片大小的计算公式。该模型能够直接、定量地给出玻璃板中由于裂缝间的贯通形成的平均碎片大小,同时能够求出玻璃碎片的数量。对于该模型,讨论了玻璃板尺寸及临界应变等因素对玻璃碎片大小的影响。     

Growth and coalescence of two collinear indentation cracks in glass

Subcritical growth and coalescence of two collinear cracks of different lengths were investigated using small Knoop indentation cracks in glass. Indentation cracks subjected to bending in water showed anomalous crack growth in terms of the stress intensity factor, K_I. The crack growth velocity, dc/dt, was initially high, decreased and thereafter increased with increasing K_I. The effective stress intensity factor, K_I,eff, was calculated by adding a term describing the state of residual stress to explain this anomalous growth. Before crack coalescence, a large crack showed a crack velocity higher than expected from the coalescent crack. The coalescent crack velocity increased with K_I,eff and the slope of dc/dt−K_I,eff curves differed from that for a single crack, depending on the crack length.