Equal Thickness Interference Research Articles

Synergistic interference effect of femtosecond laser direct writing

With the increasing functional applications of periodic micro/nanostructures, it is necessary to provide simple and fast micromachining methods. It is very common to fabricate one-dimensional periodic structures based on one-step machining. However, it is difficult to rapidly process two- dimensional (2D) structures with multiple periods in one step. In this letter, we proposed a processing method based on laser-induced backward transfer (LIBT) technique, in which the sample is placed in a bound state, resulting in equal-thickness interference. Therefore, laser direct writing (LDW) ablation and interference effect are combined to induce 2D biperiodic microstructures. The effects of laser power and interference pattern on the 2D microstructures are studied. This is a promising method for fabricating 2D multiperiodic micro/nanostructures.

Interference fringes in a nonlinear Michelson interferometer based on spontaneous parametric down-conversion.

Quantum nonlinear interferometers (QNIs) can measure the infrared physical quantities of a sample by detecting visible photons. A QNI with Michelson geometry based on the spontaneous parametric down-conversion in a second-order nonlinear crystal is studied systematically. A simplified theoretical model of the QNI is presented. The interference visibility, coherence length, equal-inclination interference, and equal-thickness interference for the QNI are demonstrated theoretically and experimentally. As an application example of the QNI, the refractive index and the angle between two surfaces of a BBO crystal are measured using equal-inclination interference and equal-thickness interference.

Zygo interferometer for the precious measurement of tiny refractive index change of two laser crystals

An application of the Zygo system for measuring the refractive index change between two crystals such as 1at%Yb3+: YAG and YAG, was introduced in this paper, having a high accuracy at an order of 10−7. In this method, the tiny refractive index change of two crystals was obtained by measuring the difference in optical path distance of equal thickness interference between two crystals. The mean value of refractive index change of the crystals measured by the Zygo interferometer is 1.10×10−4 for a wavelength of 632.8nm. And a high accuracy of 3.2×10−6 was achieved.

Time- and space-modulated Raman signals in graphene-based optical cavities

We present fabrication and optical characterization of micro-cavities made of multilayer graphene (MLG) cantilevers clamped by metallic electrodes and suspended over Si/SiO2 substrates. Graphene cantilevers act as semi-transparent mirrors closing air wedge optical cavities. This simple geometry implements a standing-wave optical resonator along with a mechanical one. Equal thickness interference fringes are observed in both Raman and Rayleigh backscattered signals, with interfringe given by their specific wavelength. Chromatic dispersion within the cavity makes possible the spatial modulation of graphene Raman lines and selective rejection of the silicon background signal. Electrostatic actuation of the multilayer graphene cantilever by a gate voltage tunes the cavity length and induces space and time modulation of the backscattered light, including the Raman lines. We demonstrate the potential of these systems for high-sensitivity Raman measurements of generic molecular species grafted on a multilayer graphene surface. The Raman signal of the molecular layer can be modulated both in time and space in a similar fashion and shows enhancement with respect to a collapsed membrane.

A method for probing the refractive index change in photorefractive crystals

A method for probing refractive index changes in photorefractive crystals using an interferometric technique and digital image processing was proposed. Based on equal thickness interference in LiNbO 3 crystal and Fourier transform profilometry, we obtained phase value changes in interferograms induced by a photorefractive effect, and further calculated refractive index changes. The maximal values for extraordinary light (e-light) and ordinary light (o-light) are 6.6×10 –4 and 1.2×10 –4 , respectively.

A method of gap control based on the principle of equal thickness interference for HARNS fabrication

The gap, which affects pattern resolution, especially during the nanofabrication process by X-ray lithography, is a very notable problem researchers pay much attention to. Until now, there still has not been a simple, economical method to control a small and uniform gap. In this paper, a method based on the principle of equal-thickness interference has been proposed. Firstly, an accessorial structure with the height of the gap is fabricated on the mask support to achieve a small gap. Then the principle of equal-thickness interference is applied to adjust the parallelism to ensure a uniform gap between the mask and the wafer. This method is not only simple and low cost, but also can control a small and uniform gap accurately, so that the quality of pattern replication during X-ray lithography can be improved and the mask can also be protected. Based on this method, a small and uniform gap is realized and high aspect ratio nanostructures (HARNS) are fabricated.

HRTEM and X-ray diffraction analysis of Au wire bonding interface in microelectronics packaging

Interfacial microstructures of thermosonic Au wire bonding to an Al pad of die were investigated firstly by high-resolution transmission electron microscopy (HRTEM) and X-ray micro-diffractometer. The equal-thickness interference structures were observed by HRTEM due to diffusion and reaction activated by ultrasonic and thermal at the Au/Al bond interface. And X-ray diffraction results showed that three different interplanar crystal spacings (‘d’ value) of the interfacial microstructures were 2.2257 Å, 2.2645 Å, and 2.1806 Å respectively from the high intensity of diffraction to the low intensity of diffraction. These indicated that the intermetallic phase AlAu 2 formed within a very short time. It would be helpful to further research wire bonding technology.

Pits with coloured halos formed on 1Cr18Ni9Ti stainless steel surface after ennoblement in seawater

Micropits surrounded by coloured halos were observed under incident-light microscope on 1Cr18Ni9Ti stainless steel surface after “ennoblemen t” in seawater. Ennoblement has been attributed to biofilm formation on stainless steel surface in seawater. In this study, the environment in biofilm for ennoblement was simulated by adding H 2O 2 into seawater at concentrations that were reported to detect in marine biofilm [N. Washizu, Y. Katada, T. Kodama, Corros. Sci .46 (2004)1291.]. H 2O 2 increased the passivity of stainless steel in seawater, but this passivation was not uniform. The probability of pitting corrosion was increased after ennoblement. Equal thickness interference on the deposition film around the pits was believed to be the reason for the coloured fringes. It is conceivable that haloed pits on the stainless steel surface are the characteristic morphological indications for pitting corrosion formed under ennoblement condition in seawater. Examinations on the microbial and structural effects of the biofilm were not included in this study.

Profile of a laser crack in polymethyl methacrylate

The profile of a laser crack in a transparent dielectric, polymethyl methacrylate (in the free-generation procedure), has been studied by the equal-thickness interference band method. It has been established that zones of changed material, a zone of slow change of profile, and a zone of rapidly changing profile (center of the crack) exist in the cross section of the crack. Values of thickness of the crack are given. Suggestions are expressed as to a possible mechanism of laser damage.

Equal-Thickness Interference Fringes in the Bragg-case Diffraction of X-rays

Equal-Thickness Interference Fringes in the Bragg-case Diffraction of X-rays

Study on Precipitation Phenomena during Aging of Aluminium-Silver Alloy in Thin Evaporated Films

Precipitation phenomena during aging have been observed on aluminium-20 wt. per cent silver alloy in thin evaporated films by electron micryscopy and electron diffraction. A super-saturated solid solution has successfully been obtained in thin films by a new quenching method. In a preprecipitation stage aggregates composed of random clusters have been found in electron micrographs, no appreciable diffraction effect having been perceived. In a true precipitation stage precipitates have been found in electron micrographs to change from a needle-like to a three dimensional shape with increasing aging, the axial ratio obtained from diffraction patterns changing from 1.63 3 to 1.59 passing 1.61 2 . It is a merit of the present study that a hexagonal precipitate with the ideal axial ratio has been detected in the course of aging. Except this point, the results obtained confirm generally those reported by X-ray studies. So called “equal-thickness interference fringes” have been found in images of precipitates aged at 250°C.