Fringe Shift Research Articles

Chemical Sensor Based on Porous Silicon Dual Transducers

Novel porous Si exhibiting dual optical properties, both Fabry-Perot fringe (optical reflectivity) and photoluminescence, were developed and used as chemical sensors. Porous Si samples were prepared by an electrochemical etch of p-type silicon under the illumination with a 300 W tungsten filament bulb for the duration of etch. The surface of porous Si was characterized by FT-IR instrument. The porosity of samples was about 80%. Both reflectivity and photoluminescence were simultaneously measured under the exposure of organic vapors. The shift of Fabry-Perot fringe to the longer wavelength under the exposure of chloroform vapors was obtained. The steady-state photoluminescence spectra and quenching photoluminescence under the exposure of various organic vapors were obtained. A set of organic compounds were analyzed by both quenching photoluminescence and change of optical thickness.

Interference fringes ofm=0spin states under the Majorana transition caused by rapid half-rotation of a magnetic field

The phase shift and visibility of fringes in the Ramsey atom interferometer composed of the $|F=1$,${m}_{F}=0\ensuremath{\rangle}$ and $|F=2$,${m}_{F}=0\ensuremath{\rangle}$ states were examined systematically for rapid half-rotation of the magnetic field. It was verified that the phase shifts by $\ensuremath{\pi}$ rad in the adiabatic regime, but it does not shift from the original one in the nonadiabatic regime. These results support Robbins and Berry's claim [J. M. Robbins and M. V. Berry, J. Phys. A 27, L435 (1994)]. The fact that the interference fringes disappear in the intermediate regime and reappear in the nonadiabatic regime can be explained by the Majorana transition caused by a rapid reverse of the magnetic field.

High-precision technique for in-situ testing of the PZT scanner based on fringe analysis

A technique based on fringe analysis is presented for the in-situ testing of the PZT scanner, including the end rotation analysis and displacement measurement. With the interferograms acquired in the Twyman–Green interferometer, the testing can be carried out in real time. The end rotation of the PZT scanner and its spatial displacement deviation are analyzed by processing the fringe rotation and interval changes; displacement of the PZT scanner is determined by fringe shift according to the algorithm of template-matching, from which the relation between the driving voltage and displacement is measured to calibrate the nonlinearity of the PZT scanner. It is shown by computer simulation and experiments that the proposed technique for in-situ testing of the PZT scanner takes a short time, and achieves precise displacement measurement as well as the end rotation angle and displacement deviation measurement. The proposed method has high efficiency and precision, and is of great practicality for in-situ calibration of the PZT scanner.

Simple thin-film fiber optic temperature sensor based on Fabry-Perot interference

A simple fiber optic temperature sensor with a micro Fabry-Perot cavity constructed with a thin film coated on a fiber end is presented. Its operation principle is based on the temperature-dependent wavelength shift of the interference fringes formed by Fresnel reflections from both interfaces of the thin film. An analytical formula is derived from the theory of two-beam interference. Experimental temperature data agree with the theoretical result. A temperature resolution of 0.1 K within the range from 20 to 100 °C with good stability can be achieved. The proposed temperature sensor has a simple, solid, and compact structure.

Detection of volatile organic compounds by an interferometric sensor

In the present work the development of an interferometric gas sensor to detect volatile organic compounds (VOCs) is presented. A polydimethylsiloxane (PDMS) sensing film was deposited on a glass substrate. PDMS has the property of swelling and/or change its refractive index when it interacts with VOCs. This causes a fringe shift in a Pohl interferometric arrangement. Such fringe shift was measured by a conventional photodetector. The results showed that the sensor response was almost linear in the concentration range of 0–24,000 ppm for ethanol. The sensor responses for other VOCs were also measured. From measurements and calculations it was found that the sensor response characteristics are determined essentially by the swelling effect more than the refractive index change. Therefore it could be said that the sensor response is related to the volume of the VOC molecule.

Laser-induced refractive index changes in nanocrystalline diamond membranes

We have observed what we believe to be a new phenomenon in nanocrystalline diamond membranes. The optical thickness of the membrane is changed under laser irradiation, which leads to a spectral shift of interference fringes in the transmission and photoluminescence spectra of high-quality thin self-supporting nanocrystalline membranes. The direction of the spectral shift (red/blue) can be tuned by the ambient air pressure. The effect is reversible and is accompanied by changes in photoluminescence intensity. We interpret the results in terms of the changes in the index of refraction caused by the photoinduced adsorption/desorption of air molecules that subsequently affect the properties of subgap energy states related to the surface and the grain boundaries of the nanocrystals.

An interferometric method for determining the mean refractive indices of highly birefringent fibres

An interferometric method with its mathematical derivation is suggested to determine the mean refractive indices and birefringence of highly birefringent fibres using multiple-beam Fizeau fringes in transmission. The application of this method depends on measuring the cross-sectional area of the fibre and the area enclosed under the fringe shift. It is very difficult to measure the area enclosed under the fringe shift in case of highly birefringent fibres, as these fibres have a relatively large optical path difference and a bad connection with the surrounding medium fringe. This difficulty is solved using the suggested method. Poly(aryel ether ether ketone) (PEEK) and poly(ethylene 2,6-naphthalene-dicarboxylate) (PEN) were used as applied examples of highly birefringent fibres for the suggested method. The refractive indices and birefringence of polypropylene fibre with draw ratio 4 are determined using the suggested and conventional methods. The results of the two methods are compared and it is found to be in agreement with the previously published data. The diffraction of He–Ne laser beam was used to determine the mean value of cross-sectional areas of fibres. Microinterferograms and tables are given for illustrations.

On line interferometric investigation of the neck propagation phenomena of stretched polypropylene fibre

On line interferometric investigation of the neck propagation phenomenon of stretched fibre is carried out using an automatic multiple-beam Fizeau fringes technique. It was observed that under such a deformation condition, a neck deformation is formed and propagated steadily towards the gripped ends of the stretched sample. The neck propagation was recorded carefully during the course of the tests by means of a CCD camera. The fringe shift profile due to the neck formation was analyzed during the propagation stage. A polypropylene (PP) sample was stretched until a neck deformation is formed at room temperature. The 3D time-refractive index profile is investigated to clarify the fixed profile of propagation. The obtained microinterferograms are clarifying the fixed neck profile during the propagation of necking phenomena. The speed of neck propagation was calculated. The dependence of the propagation on the drawing speed and draw ratio was investigated.

电光相位体调制器驱动电路

A driving circuit was designed for the electro-optical phase modulator, according to its structural characteristics. The circuit consists of OP37 and PA84. It is simple, but stable. The peak-to-peak value of the circuit’s output voltage is up to 200 V within the frequency range of 0 to 280 kHz. Phase compensation was designed for the output signals, and then an optical phase modulation experiment was conducted. The shift of interference fringes caused by the change of driving voltage imposed on the electro-optical modulator was observed by a photodetector.

RETRACTED: Physical interpretation of the fringe shift measured on Michelson interferometer in optical media

This article has been retracted at the request of the Editors-in-Chief. Please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). Reason: Matters have been brought to the attenton of the editors warranting further review of this article. This further review has revealed that the theoretical and experimental claims made by the author cannot be supported and the article should not have been published. The Editors and Publisher apologize to readers of the journal that this was not detected during the submission process.

Laser Differential Interferometer for Diagnostics of Gas-Puff $Z$-Pinch

Laser shearing interferometers (LSIs) are suitable for measuring the plasma-density profile on the condition that the spatial-frequency shift of the interference fringes induced by the plasma is less than the spatial-carrier frequency of the fringes. When it is applied to the diagnostics of plasmas with very large density gradient and Laplacian, such as a plasma shell produced by <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> -pinch, the fringe pattern obtained in the experiment seldom meets the requirement. A new type of laser differential interferometer has been developed on the basis of a cyclic LSI. By placing a ring interferometer between the two lenses of a 4-f imaging system, the interferometer has the ability to change the ratio of frequency shift to carrier frequency arbitrarily, and thus, it is applicable to the diagnostics of plasma with large density gradient and Laplacian. The principle of the 4-f differential interferometer was illustrated. Gas-puff experiments were conducted on a Yang accelerator. The high-definition interferograms of the imploding plasma shell were obtained. The electron-density profiles and the plasma-shell shape were calculated from the interferograms.

Mach–Zehnder Interferometer for Spatiotemporal Plasma-Density Measurement in “Dragon-I” Target Zone

In this paper, interferometric measurement is used to establish the spatial- and temporal-resolved plasma-density distribution. The Mach-Zehnder interferometer is established in Dragon-I target zone; the experiment with the interferometer was conducted, and interferograms were obtained by the high-speed multiframe CCD camera. By counting the fringe shift on the interferograms, the density of plasma was calculated to be at the order of 1022/m3.

Nonlinear magneto-optical rotation narrowing in vacuum gas cells due to interference between atomic dark states of two spatially separated laser beams

We present, experimentally and theoretically, nonlinear magneto-optical rotation (NMOR) using two spatially separated laser beams, the pump laser beam for creation and the probe laser beam for detection of the coherence between ground Zeeman sublevels. Both pump and probe lasers are tuned to ${F}_{g}=2\ensuremath{\rightarrow}{F}_{e}=1$ transition in $^{87}\text{R}\text{b}$. With the specially designed spatial configuration of the pump and the probe beams we were able to obtain dispersively shaped probe laser NMOR resonances in the Rb vacuum gas cell. The theory indicates that the obtained line shapes are due to the interference between prepared atomic states and the probe laser field. The interference nature of the resonances is supported by narrowing of NMOR resonances with increased separation between laser beams, and by the shift of the central fringe from the zero magnetic field with increased angle between initial orientation of electric vectors of linearly polarized pump and probe beams.

Precise displacement measurement for a local surface

An optical measurement method to get the in-plane and out-of-plane displacements of a local surface using a laser is proposed. The proposed method simultaneously derives the in-plane and out-of-plane displacements by measuring the shift of interference fringes formed by scattered beams. The average errors of the in-plane and out-of-plane displacement measurements are significantly smaller than 10 nm. Moreover, the proposed method uses only low-cost optical elements.

Twin core photonic crystal fiber for in-line Mach-Zehnder interferometric sensing applications

We will discuss fabrication of twin core photonic crystal fiber (TC-PCF) using the stack-and-draw method and its application for in-line Mach-Zehnder interferometers. The small difference in the effective indexes of the two core modes leads to interference fringes and the birefringence of the twin cores results in polarization-dependent fringe spacing. The strain sensitivity was negative and wavelength-dependent. A novel intensity-based bend sensor is also demonstrated with bend-induced spatial fringe shift. High air filling fraction of fabricated TC-PCF cladding provides immunity to bend-induced intensity fluctuation.

Minimum refractometrically detectable concentrations of single atmospheric gases and simple mixtures with a Sagnac interferometer

The minimum quantities of the nine most abundant, isolated, atmospheric gases that are detectable with a refractometer are calculated. An examination of the applicability of refractometric techniques for detecting and analyzing gaseous mixtures is discussed and a comparison made against other established techniques. Traditionally, most gas analysis performed with an interferometer is in determining the dispersion or refractivity of a known sample, presented here is the inverse approach, where refractivities are measured to determine the concentrations of particular species within a gas. The method, and experimental results for determining the minimum quantities of a particular species detectable in a mixture has been explored, as well as the complications, such as the indistinguishability of dynamic polarizabilities of different gases and the subsequent demands for accurate pressure and fringe measurements of using interferometric techniques. It is shown that the concentration of a single (isolated) gas, in units of number density, can be determined to within approximately 1-10 x 10(18) m(-3), and a mixture of the three most abundant gases, N2, O2 and Ar, to within 3.4 x 10(4) parts in 10(6) (ppm) when a minimum detectable fringe shift of lambda/100 is assumed.

Evolution of the electrically exploding wire observed with a Mach–Zehnder interferometer

The evolution of an exploding titanium wire embedded in 10 kPa air was studied with Mach–Zehnder interferometry. The exploding wire is characterized by a central dense core as well as the surrounding plasma and a rapidly expanding gas shell. Based on the fringe shifts, the electron density of the plasma and the increased density in the gas shell were calculated to be about 1.94×1018/cm3 and 4.78×10−4 g/cm3, respectively. The expanding speed of the gas shell is about 2.28 km/s. A thermal expansion lag of the dense vapor core and two-phase vaporization of the wire were observed. Due to the wire exploding in “under heat” mode, the first phase of the vaporization is by the Joule heating and the second one by the plasma heating.

Analysis on the laser beam pointing instability induced fringe shift and contrast dilution from different interferometers used for writing fiber Bragg grating

This paper presents an analysis on the effect of laser beam pointing instability on the fringe shift and hence the contrast dilution of superposed fringes from two beam interferometers. The interferometers analyzed are those commonly used in writing fiber Bragg grating (FBG) such as phase mask, bi-prism and phase mask based Talbot/Holographic type. The beam pointing instability is incorporated as slight change in the angle between two interfering beams. The relative immunity of different interferometers to laser beam pointing is discussed vs location of FBG writing plane from the beam splitter. The effect of the beam pointing was minimum in proximity FBG writing by phase mask. The effect, in terms of fringes contrast dilution, was worst in case of large length interferometers e.g. phase mask based-Talbot interferometer. For intermediate length prism interferometers, the effect was moderate. For a given length interferometer, the fringe shift was directly proportional to beam pointing angle and inversely proportional to fringe separation. Theoretical analysis is verified experimentally by studying the fringe instability of interference pattern formed by a bi-prism of angle 2o with the copper vapour laser (CVL, λ=510nm) beams of different beam pointing instabilities.

Anisotropic optical feedback of single frequency intra-cavity He–Ne laser

This paper presents the anisotropic optical feedback of a single frequency intra-cavity He–Ne laser. A novel phenomenon was discovered that the laser output an elliptical polarized frequency instead of the initial linear polarized one. Two intensities with a phase difference were detected, both of which were modulated in the form of cosine wave and a fringe shift corresponds to a λ/2 movement of the feedback mirror. The phase difference can be continuously modulated by the wave plate in the external cavity. Frequency stabilization was used to stabilize the laser frequency so as to enlarge the measuring range and improve the measurement precision. This anisotropic optical feedback system offers a potential displacement measurement technology with the function of subdivision of λ/2 and in-time direction judgment. The three-mirror Fabry–Perot cavity model is used to present the experimental results. Given the lack of need of lasing adjustment, this full intra-cavity laser can significantly improve the simplicity and stability of the optical feedback system.

Momentum-space interferometry with trapped ultracold atoms

Quantum interferometers are generally set so that phase differences between paths in coordinate space combine constructively or destructively. Indeed, the interfering paths can also meet in momentum space leading to momentum-space fringes. We propose and analyze a method to produce interference in momentum space by phase imprinting part of a trapped atomic cloud with a detuned laser. For one-particle wave functions analytical expressions are found for the fringe width and shift versus the phase imprinted. The effects of unsharpness or displacement of the phase jump are also studied, as well as many-body effects, to determine the potential applicability of momentum-space interferometry. For a broad range of parameters and conditions it is found that a ``dark notch'' in the momentum distribution depends linearly on the phase imprinted, with maximal sensitivity for noninteracting atoms in the ground state of tight traps.