Interferometer In Order Research Articles

Interferometric Rayleigh Scattering for Flow Temperature and Velocity Analysis

A new processing method is developed to analyze images from a Fabry–Pérot interferometer in order to extract point measurements of temperature and velocity within a gas flow, using Rayleigh scattering. Two types of interferograms are generated from a Fabry–Pérot model combined with a simulated light source. The first type is obtained from a diffuse coherent light source, namely, a laser beam on a diffuser. The interferometer characteristics, defined by only two independent parameters, are retrieved within 0.1% accuracy. The knowledge of these parameters is mandatory to analyze interferograms from Rayleigh scattered light. The second type corresponds to Rayleigh scattered light from a small volume under flow conditions, lighted with a focused laser beam and captured with long exposure time. Several flow parameters are chosen to generate these interferograms. The relative errors on the temperature and velocity estimates are found to be weak. Noise is also added to assess the robustness of the processing method. The error induced by the estimates of the instrument function is found to be of second order compared to the error induced by the image analysis.

Large Interferometer For Exoplanets (LIFE)

Context.The Large Interferometer For Exoplanets (LIFE) initiative is developing the science and a technology road map for an ambitious space mission featuring a space-based mid-infrared (MIR) nulling interferometer in order to detect the thermal emission of hundreds of exoplanets and characterize their atmospheres.Aims.In order to quantify the science potential of such a mission, in particular in the context of technical trade-offs, an instrument simulator is required. In addition, signal extraction algorithms are needed to verify that exoplanet properties (e.g., angular separation and spectral flux) contained in simulated exoplanet data sets can be accurately retrieved.Methods.We present LIFEsim, a software tool developed for simulating observations of exoplanetary systems with an MIR space-based nulling interferometer. It includes astrophysical noise sources (i.e., stellar leakage and thermal emission from local zodiacal and exozodiacal dust) and offers the flexibility to include instrumental noise terms in the future. Here, we provide some first quantitative limits on instrumental effects that would allow the measurements to remain in the fundamental noise limited regime. We demonstrate updated signal extraction approaches to validating signal-to-noise ratio (S/N) estimates from the simulator. Monte Carlo simulations are used to generate a mock survey of nearby terrestrial exoplanets and determine to which accuracy fundamental planet properties can be retrieved.Results.LIFEsimprovides an accessible way to predict the expected S/N of future observations as a function of various key instrument and target parameters. The S/Ns of the extracted spectra are photon noise dominated, as expected from our current simulations. Signals from multi-planet systems can be reliably extracted. From single-epoch observations in our mock survey of small (R <1.5REarth) planets orbiting within the habitable zones of their stars, we find that typical uncertainties in the estimated effective temperature of the exoplanets are ≲10%, for the exoplanet radius ≲20%, and for the separation from the host star ≲2%. Signal-to-noise-ratio values obtained in the signal extraction process deviate by less than 10% from purely photon-counting statistics-based S/Ns.Conclusions.LIFEsimhas been sufficiently well validated so that it can be shared with a broader community interested in quantifying various exoplanet science cases that a future space-based MIR nulling interferometer could address. Reliable signal extraction algorithms exist, and our results underline the power of the MIR wavelength range for deriving fundamental exoplanet properties from single-epoch observations.

Adaptive hyperspectral imaging using structured illumination in a spatial light modulator-based interferometer.

We develop a novel hyperspectral imaging system using structured illumination in an SLM-based Michelson interferometer. In our design, we use a reflective SLM as a mirror in one of the arms of a Michelson interferometer and scan the interferometer by varying the phase across the SLM display. For achieving the latter, we apply a checkerboard phase mask on the SLM display where the gray value varies between 0-255, thereby imparting a dynamic phase of up to 262° to the incident light beam. We couple a supercontinuum source into the interferometer in order to mimic an astronomical object such as the Sun and choose a central wavelength of 637.4 nm akin to the strong emission line of Fe X present in the solar spectrum. We use a bandwidth of 30 nm and extract fringes corresponding to a spectral resolution of 3.8nm which is limited by the reflectivity of the SLM. We also demonstrate a maximum wavelength tunability of ∼8 nm by varying the phase over the phase mask with a spectral sampling of around 0.03 nm between intermediate fringes. The checkerboard phase mask can be adapted close to real time on time-scales of a few tens of milliseconds to obtain spectral information for other near-contiguous wavelengths. The compactness, potential low cost, low power requirements, real-time tunability and lack of moving mechanical parts in the setup implies that it can have very useful applications in settings that require near real-time, multi-wavelength spectroscopic applications and is especially relevant in space astronomy.

Development of electrical substitution Fourier transform spectrometry for absolute optical power measurements.

We have demonstrated the first continuous-scan electrical substitution Fourier transform spectrometer (ES-FTS), which serves initially as an apparatus for absolute spectral responsivity calibrations of detectors over the wavelength range from 1.5 µm to 11 µm. We present data on the realization of a spectral detector-comparator system with high accuracy, high dynamic range, high spectral resolution and fast measurement in the infrared region, which is tied directly to an absolute power scale through electrical substitution. The ES-FTS apparatus employs a commercial Fourier transform spectrometer and a custom electrical substitution bolometer detector to enable spectrally-resolved absolute optical power measurements. A generalization of electrical substitution techniques enables determination of the voltage waveform that must be applied to the bolometer's electrical heater to cancel the optical signal from a Michelson interferometer in order to quantify the time-dependent optical power incident on the bolometer. The noise floor of the electrical substitution bolometer is on the order of 10 pW/Hz½ and its response is expected to be linear from the noise floor to 1 mW. A direct comparison between a pyroelectric standard detector and the ES-FTS has been performed, and experimental results reported here show great potential for this technique.

Quantum Backaction on kg-Scale Mirrors: Observation of Radiation Pressure Noise in the Advanced Virgo Detector.

The quantum radiation pressure and the quantum shot noise in laser-interferometric gravitational wave detectors constitute a macroscopic manifestation of the Heisenberg inequality. If quantum shot noise can be easily observed, the observation of quantum radiation pressure noise has been elusive, so far, due to the technical noise competing with quantum effects. Here, we discuss the evidence of quantum radiation pressure noise in the Advanced Virgo gravitational wave detector. In our experiment, we inject squeezed vacuum states of light into the interferometer in order to manipulate the quantum backaction on the 42kg mirrors and observe the corresponding quantum noise driven displacement at frequencies between 30 and 70Hz. The experimental data, obtained in various interferometer configurations, is tested against the Advanced Virgo detector quantum noise model which confirmed the measured magnitude of quantum radiation pressure noise.

Laser ultrasonics inspection for defect evaluation on train wheel

Passengers’ safety and in-service life of wheelset axles play an important role in railway vehicles. For this reason, periodic inspections are necessary. Among non-destructive techniques, ultrasonic ones are widely applied in this field. The main disadvantage of conventional ultrasonic techniques is that the overall inspection of wheels requires the train to be put out-of-service and disassembly each part, which is time-consuming and expensive.In this paper, a non-conventional non-contact laser ultrasonic inspection for train wheels is proposed. The proposed method uses a laser interferometer to receive the ultrasonic wave without contact. The receiving system allows choosing the distance between the surface to be inspected and the interferometer, overcoming any encumbrance issue. The experimental investigation is carried out on standard-reproduced defects in order to evaluate the reliability and the accuracy of the technique and to verify its applicability for railway components, as wheels, which have a complex geometry. The experimental setup consists of a pulsed laser for the ultrasonic wave generation. The receiving unit combines a continuous-wave laser and an interferometer in order to acquire the surface out-of-plane displacements. Surface and internal standard defects are detected by collecting all the A-scans in a B-scan map. The results are promising for the application of the laser technique to detect both surface and internal defects on in-service components.

High-Efficiency Silicon Photonic Modulator Using Coupled Bragg Grating Resonators

In this, we propose a novel design of a silicon photonic modulator that has a high modulation efficiency and that is tolerant to temperature variations. A series of phase-shifted Bragg gratings are placed in each arm of a Mach–Zehnder interferometer in order to provide enhanced phase modulation. The slow light effect in these ultra-compact coupled resonators improves phase modulation efficiency compared to conventional silicon phase shifters. These Bragg grating cavities are designed such that the optical bandwidth is increased compared to other coupled resonators, such as micro-rings. This improved bandwidth reduces the temperature sensitivity of the devices. We present in detail how to optimize these modulators considering properties, such as modulation efficiency ( Vπ × L ), optical modulation amplitude, and optical bandwidth ( $\Delta \lambda _{BW}$ ); the latter property determines the operating temperature range (Δ T ). As examples, we present two designs that meet different target specifications for short-reach or long-haul applications. We further provide a model, based on the coupled mode theory, to investigate the dynamic response of the proposed modulators. A large signal analysis is performed using finite-difference time domain in order to simulate on/off keying modulation and eye diagrams up to 110 Gb/s.

A Comparative Study on the Elastic Characteristics of an Aluminum Thin-Film Using Laser Optical Measurement Techniques

The increase of a surface area-to-volume ratio with the reduction of material dimensions significantly alters the characteristics of materials from their macroscopic status. Therefore, efforts have been made to establish evaluation techniques for nanoscale films. While contact mechanics-based techniques are conventionally available, non-contact and nondestructive methods would be preferable in case damages left on a sample after testing are not desirable, or an in situ assessment is required. In the present study, the Young’s modulus of an aluminum thin-film was evaluated using two different laser optical measurement techniques. First, microscale beam testing has been performed so that the resonant frequency change of a microfabricated cantilever beam induced by coating of a 153 nm thick aluminum layer on its top surface can be detected using a laser interferometer in order to evaluate the mechanical property through modal analysis using the finite element method. Second, picosecond ultrasonics were employed for cross-verification so that the mechanical characteristics can be evaluated through the investigation of the longitudinal bulk wave propagation behavior. Results show that the Young’s moduli from both measurements agree well with each other within 3.3% error, proving that the proposed techniques are highly effective for the study of nanoscale films.

Strain measurement at high temperature environment based on Fabry-Perot interferometer cascaded fiber regeneration grating

In this paper, a Fabry-Perot interferometer structure (FPIS) cascaded with a regenerated grating (RG) is proposed for strain measurement in a high temperature environment. The FPIS is fabricated by splicing a section of simplified hollow-core fiber (HCF) between two single-mode fibers (SMFs). Simple splicing and cleaving techniques are used to optimize the interferometer in order to produce the FPIS with the properties of lower temperature sensitivity and high strain sensitivity. The optimized FPIS is cascaded with a seed grating and then subjected to a thermal annealing process in order to activate the RG. Experimental results indicate that the proposed sensor can be used for simultaneous measurement of strain and temperature over ranges of 0μe to 600με and 19°C to 600°C, respectively, and consists of a matrix with a low condition number of 12.09.

Ultrasonic Vibration in Leadframe for the Bondability for Au Wedge Bond

The in-situ inspection of ultrasonic vibration of wire bonder capillary was carried out using laser interferometer in order to analyze the formation of Au wedge bond. It was observed that the changes in ultrasonic vibration can be used to describe process of bonding formation. The loss of ultrasonic energy was exhibited in ultrasonic vibration waveform of wire bonding on leadframe A. This observation is due to the low frictional energy and high deformation of Au wedge bond on leadframe A. The lower pull strength obtained by Au wedge bond further confirms the reduction of bond formation on leadframe A.

Measurement of particle motion in optical tweezers embedded in a Sagnac interferometer.

We have constructed a counterpropagating optical tweezers setup embedded in a Sagnac interferometer in order to increase the sensitivity of position tracking for particles in the geometrical optics regime. Enhanced position determination using a Sagnac interferometer has previously been described theoretically by Taylor et al. [Journal of Optics 13, 044014 (2011)] for Rayleigh-regime particles trapped in an antinode of a standing wave. We have extended their theory to a case of arbitrarily-sized particles trapped with orthogonally-polarized counter-propagating beams. The working distance of the setup was sufficiently long to optically induce particle oscillations orthogonally to the axis of the tweezers with an auxiliary laser beam. Using these oscillations as a reference, we have experimentally shown that Sagnac-enhanced back focal plane interferometry is capable of providing an improvement of more than 5 times in the signal-to-background ratio, corresponding to a more than 30-fold improvement of the signal-to-noise ratio. The experimental results obtained are consistent with our theoretical predictions. In the experimental setup, we used a method of optical levitator-assisted liquid droplet delivery in air based on commercial inkjet technology, with a novel method to precisely control the size of droplets.

A novel absolute displacement measurement technology based on wavenumber resolved low coherence interferometry

Abstract This paper proposed a novel absolute displacement measurement technology which is based on the wavenumber spectrum of low coherence interferometry. The signal from a Michelson interferometer, which is derived from a broadband light source, is dispersed by a bulk dispersing grating. The interferometric signal of each wavelength is detected by a linear array charge coupled device (CCD). By transforming the wavelength spectrum of the signal into wavenumber spectrum, absolute displacement can be measured precisely by measuring the wavenumber difference between two neighboring peaks of the wavenumber spectrum. Unlike the normal low coherence interferometric measurement systems (LCIMS) which have to scan the optical path difference (OPD) of the interferometer in order to demodulate the measurand, there is no need of scanning action during the measurement procedure, which not only simplifies the measurement system but also improves the measurement speed greatly. A fiber Bragg grating (FBG) is employed to produce a feedback signal which is used to stabilize the Michelson interferometer so as to obtain high measurement precision. A step height with the calibrated value of 50 μm that is configurated with two gauge blocks is measured by the system. The measurement resolution is 6.03 nm and the standard deviation of 10 times measurement results is 6.8 nm.

Thermal sensitivity of DASH interferometers: the role of thermal effects during the calibration of an Echelle DASH interferometer

The use of a Doppler asymmetric spatial heterodyne (DASH) interferometer with an Echelle grating provides the ability to simultaneously image the 558 and 630 nm emission lines (e.g., at grating orders of n=8 and n=7, respectively) of atomic oxygen in the thermosphere. By measuring the Doppler shifts of these lines (expected relative change in wavelength on the order of 10⁻⁸), we are able to determine the thermospheric winds. Because the expected wavelength changes due to the Doppler shift are so small, understanding, monitoring, and accounting for thermal effects is expected to be important. Previously, the thermal behavior of a temperature-compensated monolithic DASH interferometer was found to have a higher thermal sensitivity than predicted by a simple model [Opt. Express 18, 26430, 2010]. A follow-up study [Opt. Express 20, 9535, 2012] suggested that this is due to thermal distortion of the interferometer, which consists of materials with different coefficients of thermal expansion. In this work, we characterize the thermal drift of a nonmonolithic Echelle DASH interferometer and discuss the implications of these results on the use of only a single wavelength source during calibration. Furthermore, we perform a finite element analysis of the earlier monolithic interferometer in order to determine how distortion would affect the thermal sensitivity of that device. Incorporating that data into the model, we find good agreement between the modified model and the measured thermal sensitivities. These findings emphasize the fact that distortion needs to be considered for the design of thermally compensated, monolithic DASH interferometers.

The Possibility of Visualizing Temperature Fields Using Digital Holographic Interferometry

The presented paper compares results of measured temperature fields achieved by digital holographic interferometry (DHI) and hot wire anemometry. It shows the possibility of using holographic interferometry for the visualization of temperature fields in periodically moving fluids. The measurement of temperature fields in moving fluids has many inherent difficulties. The usage of point temperature measurement methods, such as Constant Current Anemometry (CCA), is limited to frequencies up to 3000 Hz. This frequency should be the limiting factor for using CCA in fluids when a rapid change of temperature occurs. This shortcoming of CCA measurements could be overcome through the use of optical methods such as digital holographic interferometry. It is necessary to employ a special holographic setup with double sensitivity instead of the commonly used Mach-Zehnder type of holographic interferometer in order to attain parameters sufficient for the studied case. This setup is not as light-efficient as the Mach-Zehnder type but has double sensitivity. The special technique of acquiring and phase averaging the results from holographic interferometry is presented. The paper also shows the first results of an evaluated 3D temperature field.

Complementarity and post-selection in an atomic double-slit interferometer

AbstractThis paper analyzes, theoretically, an atomic double-slit interferometer in order to probe the extent to which complementary properties affect quantum interference. It is shown that if the energy eigenstates of a two-level atom are one-to-one correlated with its particle and wave behaviors, complementary phenomena can be measured simultaneously, indicating a reinterpretation of the complementarity principle. We also demonstrate that these complementary properties can be further distinguished by using a post-selection process.

Topography Mapping With a Portable Real-Aperture Radar Interferometer

In this letter, the requirements to derive topography from a portable terrestrial radar interferometer are introduced, the instrument design and the relationship between interferometric phase shift and surface topography are explained, and two examples of topographic maps from measurements at the Rhone glacier and Grabengufer rock glacier in Switzerland are presented. In the first case, an external digital elevation model was used to assess the error of topography mapping with the portable radar interferometer and to analyze ice surface changes of the glacier in the last 14 years. We found that the height error standard deviation is about 3 m within a distance of 2 km from the sensor and observed massive thinning of the Rhone glacier. In the second case, we used the terrestrial radar interferometer in order to measure the height difference between August 2009 and March 2010 over the rock glacier as a consequence of its destabilization.

J113031 空気圧ベローズを用いた静圧案内微動ステージの超精密位置決め

The demand for ultra precise positioning of nanometer-order is increasing with the progress of nanotechnology in biotechnology industry and especially semiconductor industry. Previously we developed the elastic hinge guide stage driven by pneumatic bellows for such a demand, and realized ultra precise positioning with accuracy of 0.02±3.9 [nm]. Then, positioning accuracy was limited by the vibration from a floor with the resonance frequency which is decided by the mass of a stage and the spring of elastic hinges. On the other hand, the measurement of exact stage position by the laser interferometer is difficult because fluctuation of air influences to the measurement. In this research, guide was changed into the air bearing from the elastic hinge, and positioning measurement was changed into the laser scale from the laser interferometer in order to solve these problems. The purpose of this research is investigated the positioning accuracy the changed stage. As a result, the positioning accuracy is improved to 0.01 ±0.9 [nm] with the positioning resolution of l [nm] and the good positioning repeatability.

Digital holografic interferometry used for identification of 2D temperature field

The presented paper shows the possibility of digital holographic interferometry application in measurement of unsteady 2D temperature field generated by pulsatile flow which is impinging heated surface. Special holographic setup with double sensitivity was developed instead of the commonly used MachZehnder type of holographic interferometer in order to attain the parameters sufficient for the studied case. This setup is not light efficient like the MachZehnder type but has double sensitivity. The results from the digital holographic interferometry experiments are perfected by measurement of the velocity field achieved by methods of hot-wire anemometry.

Influence of the collimation of the reference wave in off-axis digital holography

In digital holography, the novel concept of the digital reference wave has opened in numerous opportunities for various fields to which digital holography may be applied. Oftentimes, a plane wave is utilized in digital holography experiments to operate as the reference wave; thus, the simulation of the plane wave is necessary for performing a numerical reconstruction. Conventionally, perfect collimation producing a perfect plane wave impinging on the reference should be carefully adjusted with a shear interferometer in order to obtain acceptable results. In this paper, we claim that it is not necessary to use a perfect plane wave in digital holography experiments. We experimentally proved that by using the Michelson interferometer, no influence of imperfect collimation of the reference wave in an off-axis digital holography exists, as has been previously claimed. Our deductions were verified by applying perfect and imperfect collimations to three different surfaces (flat, spherical and step) for height inspection and the results were almost consistent. The consistencies of the measured height values for the three tested surfaces at both perfect and imperfect collimations prove that there is no influence of imperfect collimations in off-axis digital holography.

Coherent control of semiconductor quantum wire by high‐resolution and stable Michelson interferometer

AbstractWe developed a high‐resolution Michelson interferometer in order to stabilize the relative phase of double pulses by using a He‐Ne two‐frequency laser positioning system. A very stable phase‐locked pulse pair whose phase difference was only 4° at 900 nm was realized. Using a high‐resolution Michelson interferometer, we demonstrated coherent control of an exciton in a GaAs/AlGaAs crescent‐shaped quantum wire. The dephasing time of the single quantum wire was 400 fs. © 2011 Wiley Periodicals, Inc. Electron Comm Jpn, 94(5): 25–32, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10238