Interference Bands Research Articles

Spectral confocal reflection microscopy using a white light source

We present a reflection confocal microscope incorporating a white light supercontinuum source and spectral detection. The microscope provides images resolved spatially in three-dimensions, in addition to spectral resolution covering the wavelength range 450-650 nm. Images and reflection spectra of artificial and natural specimens are presented, showing features that are not normally revealed in conventional microscopes or confocal microscopes using discrete-line lasers. The specimens include thin film structures on semiconductor chips, iridescent structures in Papilio blumei butterfly scales, nacre from abalone shells and opal gemstones. Quantitative size and refractive index measurements of transparent beads are derived from spectral interference bands.

Experimental comparison of two methods for the measurement of long gauge blocks

A comparison of two methods of measurement of long gauge blocks is performed. It is shown that the relative divergence of the measurement results obtained by a method involving counting of the interference bands between the centers of gravity of the achromatic bands and a method involving matching fractional parts of the orders of interference amounts to less than 10−8.

Interference of Saturated Fats in the Determination of Low Levels of trans Fats (below 0.5%) by Infrared Spectroscopy

AbstractThe mandate to label food products with the content of total trans fatty acids has led to an increase in demand for sensitive and accurate methodologies for the rapid quantitation of trans fats. Unfortunately, the latest official infrared (IR) spectroscopic method lacks the required sensitivity. A more sensitive IR procedure that requires the measurement of the height of the second derivative (2D) of the trans absorption band at 966 cm−1 was recently proposed; however, a reported inconsistency at low trans levels between GC (0% of total fat) and IR (1.2% of total fat) results for a fully hydrogenated vegetable oil could not be reconciled, and triggered further investigations. For the first time, we recognize and report the presence of weak interference bands (962–956 cm−1) attributed to saturated fats in the IR spectra of trans fats; these interference bands have an adverse impact on the sensitivity and accuracy of the IR determination at low trans levels (≤0.5% of total fat). Therefore, weak spectral features observed at energies below the one expected for trans bands (966 cm−1) in test samples high in saturated fat (coconut oil and cocoa butter) must not be mistaken for trans bands.

Diagnostics of highly doped czochralski-grown silicon crystals

It is shown that effective diagnostics of strongly doped Czochralski-grown silicon single crystals in the initial (as-grown) state is provided by methods based on the interference phenomena of dynamic x-ray diffraction: the Lang section topography and the Borrmann effect diffractometry. The conditions of a test for the structural perfection of as-grown crystals, based on the observation of interference bands on the section topographs, are refined.

Multicarrier reflectometry

A new reflectometry method called multicarrier reflectometry (MCR) for fault location in cables is proposed. MCR combines a weighted set of sinusoidal excitations into a signal that is sent down the wire. The reflected signal from the cable under test is analyzed in order to determine the length of the wire or possible location of a fault. In the frequency domain, the phase response of the reflected signal contains the desired information. This method provides a system with greater flexibility than conventional frequency domain reflectometry, better noise immunity than time domain reflectometry, and the ability to employ frequency agility to avoid certain interference bands. This method introduces an approach to the generation of test signals that allows more control over the bandwidth of the test signal. All the data analysis can be done in the digital domain after the reflected wave is sampled, thus enabling the use of more meticulous digital signal processing techniques. The major advantage of this method is the potential use in live cables carrying other signals such as power or data. The bandwidth over which the test signals are transmitted can be chosen specifically to avoid the bandwidth of the live wire signal.

Interference bands observable at a distance from a light source

Interference bands observable at a distance from a light source

Electroreflectance Spectra of InGaN/AlGaN/GaN p-n-Heterostructures

ABSTRACTElectroreflectance (ER) spectra of InGaN/AlGaN/GaN p-n- heterostructures with multiple quantum wells (MQW) are studied. Structures with MQW InGaN/GaN were grown for blue LEDs by MOCVD technology and “flip-chip” mounted. The ER spectral maxima correspond to the high energy side of electroluminescence spectral line. The ER spectra caused by Franz-Keldysh effect are approximated by Aspnes theory. The ER spectra in a range 400 ÷ 800 nm have interference bands caused by the change of refraction index in the structure.

Comparative Study of the Morphology, Aggregation, Adherence to Glass, and Surface-Enhanced Raman Scattering Activity of Silver Nanoparticles Prepared by Chemical Reduction of Ag+ Using Citrate and Hydroxylamine

Two different silver colloids were prepared by chemical reduction of silver nitrate with trisodium citrate and hydroxylamine hydrochloride to compare their characteristics in relation to their possible use in surface-enhanced Raman scattering (SERS) spectroscopy. The morphology and plasmon resonance of the single nanoparticles and aggregates integrating these colloids were characterized by means of UV-vis absortion spectroscopy and scanning electron microscopy, revealing important differences between each type of nanoparticle as concerns their physical properties. These metallic systems also manifested differences in the aggregation and the adherence to glass surfaces, revealing significant differences in the chemical surface properties of these nanoparticles. SERS and surface-enhanced IR also indicated the presence of interference bands which can overlap the spectra of the analyte, mainly in the case of the citrate colloid. All these differences have an important influence on the applicability of these nanostructured systems in SERS. In fact, the enhancement factor and spectral pattern of the SERS obtained by using alizarin as a molecule probe are different.

Anomalous scenario of the dynamic chaos onset in multimode laser diodes

Anomalous transition to the regime of dynamic chaos in a multimode quantum-well heterolaser (λ = 635 nm) is possible as a result of an injection-current-induced change in the gain. A stable multimode regime (featuring more than ten longitudinal modes) is established near the lasing threshold under conditions of weak nonlinear coupling. As the injection current increases, the competition of modes results in a partial suppression of weak laser modes. At a certain excess of the gain over losses, a regime with hard excitation of four modes is realized that is characterized by the onset of a dynamic chaos manifested by irregular amplitude pulsation of modes, broadening of the optical spectrum, and loss of coherence. The loss of coherence is revealed by a decrease in the visibility of interference bands and by their chaotic shifts. An increase in the overall nonlinear coupling and the corresponding competition of modes leads to a decrease in the dimension of the self-oscillatory system and to the onset of a stable single-mode lasing regime.

Formation of X-ray shift fringes and a new method for determination of the difference sign of interplanar distances

A detailed investigation of the conditions for the formation of X-ray shift fringes is carried out, aiming to apply these patterns to investigations of crystal imperfections. Expressions for the amplitudes and X-ray intensity distribution are obtained for a two-crystal interferometer, in which the interplanar distance between two reflecting planes, d, has a relative change Deltad/d approximately 10(-8) - 10(-5). It is theoretically proven and experimentally confirmed that the value of the period of interference bands essentially depends on the sign of Deltad.

Estimation of the Dispersion of Absorptance in the Region of Resonant Transitions Using the Reflection Spectra in a Fabry–Perot Interferometer

It is shown that in the region of resonant transitions the dependence of the area under the contour of the Fabry–Perot interference bands on the frequency minus the area under the envelope of the minima reflects the character of the dispersion of light absorptance.

A ‘‘Fresnel-transducer’’ for prostate hyperthermia treatment

Simulations and construction methods will be described for a novel ‘‘Fresnel-transducer.’’ The transducer is designed for transrectal hyperthermia treatment of prostate cancer as an adjuvant to radiotherapy or chemotherapy. Forty nine 6.3 mm diameter 1.5 MHz PZT elements are arranged in a 3 by 7 cm honeycomb-like pattern. They are individually aimed so that their beams partially converge behind the prostate. The increased beam density away from the transducer compensates for the loss of acoustic intensity due to attenuation. The aiming of the beams is additionally biased toward the periphery of the heated region to compensate for cooling from lateral heat conduction. The elements are divided into three interspersed sets, each driven at a slightly different frequency, to minimize stationary Moire interference bands between the beams. The combined effect is to uniformly raise the prostate temperature to 43<th>°C without overheating the rectal wall. [Research supported by the Department of Defense Congressionally Directed Medical Prostate Cancer Research Program.]

Plotting holographic interferograms for visualization of dynamic results from finite‐element calculations

AbstractProcedures for plotting computer generated interferograms from the results of finite‐element analysis based on the principles of optical holography can provide a realistic view of dynamic processes taking place in the analysed structures. Such visualization is based on a solid physical background, does not require animation for representing dynamic processes, and is also important from the point of view of interpretation of experimental holograms.The numerical method for obtaining time‐averaged digital interferograms for structural dynamics applications is presented. Intensity mapping as well as the methods of digital stroboscopic analysis are used for plotting clearer images due to the fact that the intensity of higher interference bands decreases rapidly with the growth of vibration amplitudes. The digital time averaging of intermediate states of the moving surface together with varying direction of incident laser beam and estimation of diffuse and specular reflection phenomena enables the generation of realistic interferograms. Such a procedure is scalable in parallel computations and applicable to a wide variety of problems. Copyright © 2003 John Wiley & Sons, Ltd.

Application of Nomarski interference contrast microscopy as a thickness monitor in the preparation of transparent, SiC-based, cross-sectional TEM samples

Reflected light optical microscopy using a Nomarski prism and a differential interference contrast filter have been employed in concert to achieve a technique that provides an accurate color reference for thickness during the dimpling and ion milling of transparent transmission electron microscopy samples of 6H-SiC(0 0 0 1) wafers. The samples had thin films of AlN, GaN, and Au deposited on the SiC substrate. A sequence of variously colored primary and secondary interference bands was observed when the SiC was thinner than 20 μm using an optical microscope. The color bands were correlated with the TEM sample thickness as measured via scanning electron microscopy. The interference contrast was used to provide an indication of the dimpling rate, the ion milling rate, and also the most probable location of perforation, which are useful to reduce sample breakage. The application of pressure during the initial cross-sectional preparation reduced the separation of the two halves of the sample sandwich and resulted in increased shielding of the film surface from ion milling damage.

A simple method of measuring and applying the dispersion of thin films

The position and the separation of the adjacent maxima and minima of the interference bands of an amorphous hydrogenated silicon film doped with aluminum are used to determine the order value unambiguously, the optical thickness to accuracy ranging from eight parts in 10 5 to one part in 10 3, and the refractive index accurately to ±0.03 across a wide spectral interval 0.5–2.5 μm. The dependence of the film dispersion on the doping concentration is expressed in terms of a polynomial dispersion function whose coefficients vary with the doping concentration.

Effects of Bandwidth and Overlap on Multivariate Calibration Models Based on Simulated Fourier Transform Infrared Interferogram Data

Simulated Fourier transform infrared (FT-IR) interferograms and spectra of mixture samples are used to investigate the effects of bandwidth and overlap on a quantitative analysis in which multivariate calibration models are constructed from short segments of digitally filtered interferogram data. By a comparison of calibration models constructed with interferogram data to similar models built with spectral data of varying instrumental resolution, the concepts of spectral resolution are explored in the context of an interferogram-based analysis. In this work, nominal spectral point spacings of 1, 2, 4, 8, and 16 cm−1 are explored. Five data sets are constructed in which the width and overlap of an analyte and interference band are varied. Calibration models based on partial least-squares (PLS) regression are optimized for both interferogram and spectral data. Even in cases of extreme spectral overlap between the analyte and interference bands, interferogram-based calibration models constructed from segments of 151 points or less are observed to perform as well as or better than all models computed with absorbance and single-beam spectral data, regardless of instrumental resolution. These results suggest that an interferogram-based analysis is a viable option for applications in which an FT-IR spectrometer is used in a dedicated monitoring application.

A method for continuous control of the refractive index of liquids in capillaries

An interference method for controlling the refractive index of liquids pumped through a capillary is considered. The liquid is sounded by two systems of interference bands, the period of which differs by an insignificant value prescribed by the condition of nonius coincidence. An analytical expression is obtained to calculate the refractive index of the liquid controlled in automatic reading of the interference patterns.

Polarization sensitive lensless Lau interferometer

We describe an interferometer based on the Lau effect, at finite distances, for producing interference bands sensitive to birefringent variations. Experimental resultants that verify our proposal are included.

Measurement of the components of the gas flow behind a shock front by streak photography of the spectrum of interference bands

This article is the first of several in a continuing series on opticophysical methods for the investigation of inhomogeneities, begun in the preceding issue and in the journal Metrologiya, No. 4 (1994). Here a method is proposed for determining the composition of an ionized gas from data obtained in streak photography of interference fringes produced by oblique transmission of the sensing light beam across a shock front. The author gives a comparative estimation of the errors of the results in normal and oblique transmission of a monatomic gas flow containing singly charged ions.

Optically Active Fabry-Perot Etalon

Abstract The paper studies multibeam interference in the case of multiple reflection of an electromagnetic wave (EMW) from a plane-parallel, isotropic, optically active and non-absorbing plate (Fabry-Perot etalon). Due to the optical activity the two refracted EMW in the plate are left- and right-circularly polarized and have unequal refractive indices. During their propagation through the plate the two waves accumulate a phase difference which modulates the multibeam interferogram. Both in the reflected and in the transmitted beams a polarization perpendicular to the polarization of the incident EMW appears (whose intensity is up to several tens of per cent of the incident beam intensity). Due to the gyrotropy of the plate at large angles of incidence the interference bands split. Thus the optical activity of the etalon may affect its precision as an optical element. The multibeam interference may be used as a source of spectroscopic information about the optical activity of the plate.