Multiple Interference Fringes Research Articles

Compact Michelson Interferometers with Subpicometer Sensitivity

The network of interferometric gravitational-wave observatories has successfully detected tens of astrophysical signals since 2015. In this paper, we experimentally investigate compact sensors that have the potential to improve the sensitivity of gravitational-wave detectors to intermediate-mass black holes. We use only commercial components, such as sensing heads and lasers, to assemble the setup and demonstrate its subpicometer precision. The setup consists of a pair of Michelson interferferometers that use deep frequency modulation techniques to obtain a linear, relative displacement readout over multiple interference fringes. We implement a laser-frequency stabilisation scheme to achieve a sensitivity of 0.3\,$\text{pm} / \sqrt{\text{Hz}}$ above 0.1\,Hz. The device has also the potential to improve other experiments, such as torsion balances and commercial seismometers.

Effect of Cu doping on the structural, optical and electrical properties of ZnO thin films grown by RF magnetron sputtering: application to solar photocatalysis

RF sputtered undoped and Cu doped ZnO (CZO) thin films were deposited on unheated glass substrates using a mixed Cu2O and ZnO powders target at different Cu concentrations of 0, 1, 2, 3 and 4 wt%. The effects of copper concentration on the structural, electrical, optical and photocatalytic properties of CZO films have been studied. From XRD and Raman spectroscopy studies, it was found that the deposited films were polycrystalline with a predominant hexagonal wurtzite structure along the c-axis perpendicular to the substrate surface. The presence of multiple interference fringes in the transmittance and reflectance spectra shows the good homogeneity of the films. All the films are highly transparent with transparency reaching 80% indicating the possibility to use these films as an optical window. The absorption tail gradually shifted towards a higher wavelength side, which resulted in the decrease of bandgap energy from 3.35 to 3.26 eV. All the sputtered films are highly conductive with a conductivity reaching 104 S.cm−1.The effect of Cu-doping on the photocatalytic activity of ZnO thin films for the degradation of methylene blue (MB) dye was studied under sunlight irradiation and the results showed that the Cudoping provokes appreciable degradation of MB and reached a maximum for the 1 wt% Cu doped ZnO film.

Optomechanical generation of a mechanical catlike state by phonon subtraction

We propose a scheme to prepare a macroscopic mechanical oscillator in a catlike state, close to a coherent state superposition. The mechanical oscillator, coupled by radiation-pressure interaction to a field in an optical cavity, is first prepared close to a squeezed vacuum state using a reservoir engineering technique. The system is then probed using a short optical pulse tuned to the lower motional sideband of the cavity resonance, realizing a photon-phonon swap interaction. A photon number measurement of the photons emerging from the cavity then conditions a phonon-subtracted catlike state with a negative Wigner distribution exhibiting separated peaks and multiple interference fringes. We show that this scheme is feasible using state-of-the-art photonic crystal optomechanical system.

Formation mechanisms of multiple holographic gratings in spirooxazine-doped polymer films

Multiple holographic gratings were stored in the same location of spirooxazine doped polymer films using peristrophic multiplexing techniques. Accompanied by UV irradiation, three sets of holographic gratings with different directions were recorded and readout by the He–Ne laser (632.8nm) and the Nd:YAG laser (532nm), respectively. Diffraction efficiency of each grating was controlled almost uniform by adjusting recording time. It was found that the growth rate of the holographic grating recorded later was lower than that of the earlier one, resulting from the weakened anisotropic distribution and the decreased population of photomerocyanine molecules. A kinetics description of isomerization gratings, competing with orientation gratings, agrees well with experimental results. Due to the thermal stability of the isomerization grating, multiple interference fringes in the photochromic film were reserved and observed by Confocal Laser Scanning Microscope.

Theoretical Analysis of Length Measurement Using Interference of Multiple Pulse Trains of a Femtosecond Optical Frequency Comb

As an alternative to the conventional method of measuring length as a function of the wavelength of a monochromatic laser source, we investigated the possibility of arbitrary distance estimation using the repetition interval of a femtosecond optical frequency comb (FOFC). The investigation is based on an analysis of the formation of the interference fringes of multiple pulse trains. It is found that distance can be measured as a function of the repetition interval between pulses by determining two values from the interference fringes of multiple pulse trains. One is the distance between temporal coherence peaks, and the other is the phase relation between the multiple interference fringes. Theoretical analysis and numerical investigations pave the way for the development of a new length traceability system directly linked to a stable FOFC for both scientific and industrial uses.

Spectral characteristics in long-period fiber gratings with nonuniform symmetrically ring shaped coatings

In this work, the spectral characteristics of nonuniform symmetrically ring shaped coatings deposited on long-period fiber gratings have been theoretically and experimentally investigated. Electrostatic self-assembling technique was used to deposit with fine control uniform azimuthally symmetric coatings at nanoscale level. UV laser micromachining operating at 193nm was applied to selectively remove the coating with high spatial resolution on ring shaped geometry. Phase shift effects and multiple interference fringes have been observed for all the attenuation bands, strongly depending on the length of the uncoated region and the coating features (thickness and optical properties). The ability of the proposed structure to exhibit wavelength selective operation, combined with the effects of high refractive index coatings on the cladding modes distribution, provides a valid technological platform for the development of advanced photonic devices for sensing and telecommunication applications.

Focus on spectroscopy

Focus on spectroscopy

Fringe generation with non-uniformly coated long-period fiber gratings

In this work, the spectral characteristics of non-uniform symmetrically ring shaped coatings deposited on long-period fiber gratings (LPFGs) have been theoretically and experimentally investigated. To optimize the structure performances, the device was designed with a simulation tool based on vectorial analysis of modes in a multilayer cylindrical waveguide and coupled mode theory. Electrostatic self-assembling technique was selected to deposit with fine control uniform azimuthally symmetric coatings on the cladding of the LPFG. UV laser micromachining operating at 193nm was used to selectively remove the coating with high spatial resolution and with azimuthal symmetry. By locally and selectively removing portions of the overlay surrounding the LPFG from the middle of the grating, strong modifications of its spectral characteristics were observed. Phase-shift effects and multiple interference fringes have been observed for all the attenuation bands, strongly depending on the length of the uncoated region and the overlay features (thickness and optical properties). This provides a valid technological platform for the development of advanced photonic devices for sensing and telecommunication applications.

Simultaneous measurement of three orthogonal components of displacement by electronic speckle-pattern interferometry and the Fourier transform method

The measurement of three-dimensional displacement by electronic speckle-pattern interferometry with three object beams and one reference beam is presented. Multiple interference fringes corresponding to different sensitivity vectors are recorded in a single interferogram and separated by means of the Fourier transform method to give three components of displacement. The relationship between the ratio of the speckle size to the pixel size of a TV camera and the measurement error is investigated experimentally and compared with the research of others. The optimum condition leading to a minimum measurement error occurs when the speckle size is approximately equal to the pixel size. With this condition satisfied, the measurement error varies from 1.5% to 6.0%.

Realization of phase Fresnel lenses by multiple beam interferometry

Multiple interference fringes generated by a Fabry-Perot interferometer are used for realizing phase Fresnel lenses. The authors deal with a parallelism between the decomposition of a spherical wavefront in Fresnel zones and a multiple interference pattern obtained with a FP cavity with specially designed mirrors. In the first section, the authors show that the phase profile of a Fresnel lens can be described as the superposition of pseudo-sinusoidal functions whose amplitude and phase are given by a Fourier decomposition. Synthesis of the Fresnel lens profile can be carried out by multiple interference fringes formed by a FP cavity observed in reflection. The reflection coefficients of the mirrors of the cavity make the amplitude and the phase of multiple waves proportional to the Fourier terms. Experimental results are reported in the second section. Multiple fringe patterns are recorded on bleached holographic plates. The diffraction efficiency of Fresnel lenses thus obtained is 65%.

Optical properties of SiAs single crystals

Single crystals of silicon arsenide have been grown by the Bridgman technique. SiAs was found to have an optical energy gap of 2.18±0.05 eV at room temperature and seemed to exhibit a direct optical transition. The temperature coefficient of the energy gap was about −(2.8±0.5)×10−4 eV/K. From the multiple interference fringes of some SiAs samples, the refractive index was calculated. Over a wavelength equal to infinity, it had a value of 3.1±0.1, thus leading to a value of 9.6±0.6 for the high-frequency dielectric constant. The extinction coefficient near the absorption edge has also been deduced.

Multiple Interference Fringes in Electron Micrographs of Wedge-Shaped Single Crystals

Multiple interference fringes have been observed in electron micrographs of wedge-shaped single crystals of poly-L-proline II. The interference fringes which occur when strong Bragg reflection is possible have been observed to split into two components as a result of secondary electron scattering and double refraction within the crystals. The separation of the fringe components is a function of the deviation of the incident electron beam from the exact Bragg condition for the reflection. The fringe contours are qualitatively interpreted using the dynamical theory of electron scattering.