The Groove Profile Formation of Holographic Gratings

Models for predicting the groove profile of metal coated holographic gratings, fabricated in positive photoresist, are studied. Development is assumed to be an etching process, where the etching is directed perpendicularly to the resist-developer interface. Two methods for metal coating are considered; vacuum evaporation and sputtering, and models that describe the profile formation for these cases are presented. It is noted that even a thin coating has a considerable effect on the profile. The theoretical groove profiles are found to be in good agreement with experimental profiles, obtained from SEM photographs of fabricated gratings.     

Longitudinal-mode leaky SAW resonator filters on 64° Y-Xlithium niobate

Y-parameter modeling is applied to obtain the frequency response of a first/third dual-mode longitudinally-coupled leaky-SAW (LSAW) resonator-filter on 64°C Y-X LiNbO₃. Conventional driving-point and transfer admittance relationships for SAW filters are modified to incorporate the effects of LSAW reflection and bulk-wave scattering in the interdigital transducers and are expanded to include reflection gratings with shorted-metal strips. As inferred from experiment, the grating parameters incorporate a phase-shift term to relate the anomalous dispersion of shorted gratings, as well as a modified phase-slope parameter between input and output interdigital transducers (IDT's). Good agreement is obtained with experimental results published for 836.5 MHz two- and four-pole structures in the maximum-bandwidth configuration     

Broadband Poly(vinylidene fluoride-trifluoroethylene) Ultrasound Focusing Transducers for Determining Elastic Constants of Coating Materials

This paper develops broadband Poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] focusing transducers and its surface wave measurement system for determining the elastic constants of coating layers. The measurement is based on a defocussing measurement method and V(f,z) analysis of the focusing transducers. Few P(VDF-TrFE) focusing transducers are successfully fabricated in laboratory and the wave measurements can cover a wide frequency range of 4–120 MHz with great accuracy. Brass and glass substrates electroplated with nickel coating layer with thickness ranging from 15 to 60 μm are tested in this work. Dispersion curves sensitivity analysis is carried out to decide the best approach for inversely determination of coating elastic properties. A searching method based on the downhill simplex algorithm and numerical calculation on waves in a layered half-space model is used for inversely determining the elastic constants of coating layer. The results show good agreement with reported data. Measurement accuracy and potential applications for other types of nondestructive evaluation of the focusing transducers and measurement system are addressed.     

Dual layer matching (20 MHz) piezoelectric transducers with glassand parylene

This study describes a method of applying very thin broadband matching layers to 2 mm diameter 20 MHz transducers. Dual layer acoustic matching between the ceramic and the medium at the front face of the transducer was accomplished by selecting 1/4 wavelength glass layers from a commercial source, epoxying them to the ceramic, and vapor depositing parylene to 1/4 wavelength thickness on the glass. A 8 dB fractional bandwidth of 0.75 and insertion loss of -10 dB was found on the average for these transducers. This method allowed fabricating probes that performed well, were reproducible, provided both a matching and protection coating, and could be fabricated in a practical manner     

Effects of Gap Width on Vacuum-Ultraviolet Transmission Through Submicrometer-Period, FreeStanding Transmission Gratings

The effects of gap width on the transmission coefficient of vacuum-ultraviolet light through submicrometer-period, freestanding transmission gratings are reported. Results from computations and an analytical waveguide model are shown to be consistent with experimental measurements. These results show that thin gratings with narrow gaps and thick gratings with wide gaps are equally effective at eliminating 121.6-nm radiation. The thin gratings with the narrow gaps have the advantage of better attenuation of shorter-wavelength radiation than the thick gratings with the larger gaps.     

Acoustic wave-based sensors using mode conversion in periodic gratings

Using periodic gratings etched into the surface of a piezoelectric plate, surface acoustic waves (SAW) can be converted into bulk waves and vice versa with high efficiency. If parallel grating structures are fabricated on opposite surfaces of a piezoelectric plate, a SAW also can be directed from one surface to the other. Using such structures, acoustic wave-based sensors can be designed that utilize SAW for the detection of chemical analytes on an electrode-free surface, i.e., the back surface. As a result, spurious sensor response and electrode aging that may occur when a chemical analyte comes in contact with the transducers are minimized. The design principles of these grating-based SAW sensors are explained, and the mass sensitivity is investigated using chemical vapor deposited thin polymer films, a type of material used in many practical chemical sensor applications. Experimental results are presented for the detection of nitrogen dioxide (NO(2 )) in sub-ppm concentrations.     

Orthogonal microlens raster for two-coordinate displacement transducers

A study is made of the special features of using optical fibers (as microlens elements) in order to construct orthogonal gratings for two-coordinate displacement transducers. The fundamental analytical expressions are given for calculating the spacing of the interference fringes. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 22–25, July, 1997.     

Metal Gratings with Dielectric Coating of Variable Thickness within a Period

Abstract

The rigorous theory of diffraction is applied to metallic gratings with dielectric coating. The modulation depth of the profile between coating and air is assumed to be lower than the modulation depth of the profile between metal and coating. We call this levelling. For monochromator mounting together with a special coating thickness levelled single-coated gratings with blaze show a marked increase of the efficiencies for wavelengths greater than the blaze maximum wavelength. Optimal improvements run over two octaves of the wavelength.     

Brewster-Linsen und Ihre Verwendung in Optischen Resonatoren

The Rayleigh-Fourier method and the method of Chandezon et al. for the calculation of diffraction efficiency of sinusoidal metal, dielectric and coated dielectric gratings are compared with respect to the threshold truncation value and the thickness of the coating layer. For shallow gratings the convergence of the two methods is practically one and the same. However, for deeper gratings the method of Chandezon et al. is more powerful. It is shown that for coated dielectric gratings the thickness of the layer imposes a limit on the truncation value, the limitations being weaker for the method of Chandezon et al.     

Fabrication of chirped gratings on GaAs optical waveguides

After a brief review of the applications and fabrication techniques of gratings in integrated and guided wave optics, a new method of fabricating chirped gratings is presented. The method is based on the interference of two spherical laser beams after spatial filtering by pinholes. The experimental conditions required for fabricating antisymmetric linearly chirped gratings, symmetric quadratically chirped gratings and uniform gratings are presented by way of example. By this method chirped gratings with small variations in the period can be fabricated on GaAs thin film optical waveguides. Profiles and patterns of chemically etched corrugations are quite uniform, mainly because of the direct interference of beams immediately after spatial filtering.     

Modified Ultrasonic Technique to Study Gd-Doped ZnO Films

Normal ultrasonic transducers of 0.5, 1, and 2 MHz are modified using delay lines which are made of Quartz. Such modification is to ameliorate the capability of the transducer to investigate Gd-doped ZnO thin films whose thickness is too thin. The normal transducers cannot test materials that have too thin thickness due to the near fields of these transducers. The near field is considered as blind area of the transducer. Therefore, the specimen under test must have thickness bigger than the near field of the used transducer, or instead delay lines can be used. Samples of Gd-doped ZnO thin films are prepared using sol gel technique. The ultrasonic pulse echo method is used at room temperature. Flaws are found in different prepared specimens. Results show that such delay lines are suitable to ameliorate the ultrasonic transducer to test Gd-doped ZnO thin films.     

80-MHz intravascular ultrasound transducer using PMN-PT free-standing film

[Pb(Mg(1/3)Nb(2/3))O(3)](0.63)[PbTiO(3)](0.37) (PMN-PT) free-standing film of comparable piezoelectric properties to bulk material with thickness of 30 μm has been fabricated using a modified precursor coating approach. At 1 kHz, the dielectric permittivity and loss were 4364 and 0.033, respectively. The remnant polarization and coercive field were 28 μC/cm(2) and 18.43 kV/cm. The electromechanical coupling coefficient k(t) was measured to be 0.55, which was close to that of bulk PMN-PT single-crystal material. Based on this film, high-frequency (82 MHz) miniature ultrasonic transducers were fabricated with 65% bandwidth and 23 dB insertion loss. Axial and lateral resolutions were determined to be as high as 35 and 176 μm. In vitro intravascular imaging on healthy rabbit aorta was performed using the thin film transducers. In comparison with a 35-MHz IVUS transducer, the 80-MHz transducer showed superior resolution and contrast with satisfactory penetration depth. The imaging results suggest that PMN-PT free-standing thin film technology is a feasible and efficient way to fabricate very-high-frequency ultrasonic transducers.     

Groove profile modification of blazed gratings by dip coating with hardenable liquids

We modify groove profile of various blazed gratings with groove densities as great as 3600 lines/mm by dip coating with hardenable liquids with the aim of reducing the blaze angle. The groove profiles resulting from coatings with different layer thickness are measured by atomic force microscopy. A highly reproducible blaze angle reduction to as high as a factor of 6 is achieved with mechanically ruled as well as ion-beam-etched holographic blazed gratings. Blaze angles, to as small as 0.7 deg, which are required for vacuum-UV and soft-x-ray applications but can hardly be formed with sufficient groove profile accuracy by direct ruling, are realized with this coating technique.     

Fiber Bragg grating strain measurements in comparison with additional techniques for rock mechanical testing

Fiber Bragg gratings (FBGs) have been used as strain transducers for deformation measurements on two types of granite in uniaxial compression (UC) tests. A comparison of the strain results is given for mechanical extensometers based on cross-flexure strain gages, surface-mounted FBG sensors, and a noncontacting laser extensometer measuring system as additional optical reference.     

Photopolarimeter based on two gratings recorded in thin organic films

A photopolarimeter based on two different kinds of diffraction gratings (a two-grating photopolarimeter) has been developed for real-time measurements of the four elements of the Stokes vector. The main elements of the device are a pure polarization grating and an ordinary transmission grating, both recorded by means of holographic techniques in thin films of organic materials. The first one consists of a diffraction grating recorded by two interfering opposite circularly polarized beams in a Langmuir-Blodgett film of an azo-compound material. The second component is a grating recorded by two interfering parallel circularly polarized beams in a thin film of a photosensitive polymer. Both gratings offer long time stability and good diffraction efficiency. Four photodiodes collect the first-order diffracted beams from these gratings, the output signals of which are read through an analog-to-digital converter by a PC. The optical alignment of the device is easy and the calibration is realized in a one-step procedure.     

Weak anchoring of nematic liquid crystals on photo-induced surface relief gratings of organic polysilane

Surface relief gratings on organic polysilane thin films are fabricated by holographic exposure of ultra-violet light, and Au gratings are subsequently prepared on polysilane gratings by vapor deposition of Au. The anchoring energies of 4-pentyl-4′-cyanobiphenyl (5CB) nematic liquid crystal on the fabricated gratings are determined with a saturation voltage method. The anchoring energies of Au gratings are weaker than those of organic polysilane gratings because of suppression of π–π interaction between the liquid crystal and the alignment layer. The polar anchoring energies of Au gratings are also weaker than those reported in literature.     

The Finite-conjugate Self-imaging and the Generalized Lau Effect Due to Complex Gratings

Abstract

Laser induced gratings in nonlinear optical media, which are complex or phase gratings, are the key structures in many applications involving laser beam-nonlinear material interactions. The concept of coded imaging of self-imaging structures, developed elsewhere, has been utilized to make a comprehensive study of the self-imaging properties, at finite conjugates, of model complex or phase gratings. The same approach has been used to extend our previous work on the generalized Lau effect. An interesting application of the self-imaging process has been made to visualize, at a certain primary magnification, laser induced thin photorefractive grating in a BSO crystal. Possible applications of this technique include visualization of dynamic or developed laser induced gratings in thin nonlinear optical materials.     

基于布局优化的压电分流阻尼抑振实验研究

建立了带压电分流阻尼系统的四边固支正方形弹性薄板振动控制的实验模型。针对其前五阶模态振动响应的抑制问题,以压电元件存储的电能最大化为优化目标,对采用多个压电元件的压电分流阻尼系统进行了布局优化分析。将压电元件布局优化后的压电分流阻尼系统应用于弹性薄板的多阶模态振动响应的抑制实验,分别研究了不同压电元件数量和布局对抑振效果的影响。在压电分流阻尼抑振实验中,与分流电路开路时相比,电路闭路后弹性薄板的频响函数在对应的模态频率处的幅值分别降低了11.90dB、16.94dB、16.94dB、19.91dB和16.77dB,说明经过布局优化后的压电分流阻尼系统使弹性薄板的前五阶稳态响应都得到了很好的抑制。同时也进行了非优化布局的压电分流阻尼抑振实验,实验结果对比表明,对压电元件进行布局优化可以明显提高压电分流阻尼系统的抑振效果。     

Measurement of the Complex Compliance of Coatings of Elastic Materials

A procedure for measuring the compliance of viscoelastic coatings that are used to reduce the hydrodynamic friction has been developed (the frequency range of measurements is from 400 Hz to 2 kHz). The set of force transducers differing by the diameter of the surface of contact with a coating has been manufactured. The frequency and amplitude characteristics of the transducers have been given. It has been shown that the dynamic compliance is independent of the static deformation if >3%. The diameter of the coating sample for which the edge effects are of little importance has been selected. It has been shown that with a twofold increase in the coating thickness the measured resonant frequency of the coating decreases twofold as well.