Direct Interferometric Measurements Research Articles

The first interferometric survey of massive YSOs in the K-band

Context. Circumstellar discs are essential for the formation of high mass stars, while multiplicity, and in particular binarity, appears to be an inevitable outcome, as the vast majority of massive stars (>8 M⊙) are found in binaries (up to 100%). Our understanding of the innermost regions of accretion discs around massive stars and the binarity of high-mass young stars is sparse because of the high spatial resolution and sensitivity required to trace these rare and distant objects. Aims. We aim to spatially resolve and constrain the sizes of the dust and ionised gas emission from the innermost regions of a sample of massive young stellar objects (MYSOs) for the first time, and to provide high-mass binary statistics for young stars at 2–300 au scales using direct interferometric measurements. Methods. We observed six MYSOs using long-baseline near-infrared K-band interferometry on the VLTI (GRAVITY, AMBER) in order to resolve and characterise the 2.2 μm hot dust emission originating from the inner rim of circumstellar discs around MYSOs, and the associated Brγ emission from ionised gas. We fitted simple geometrical models to the interferometric observables, and determined the inner radius of the dust emission. We placed MYSOs with K-band measurements in a size–luminosity diagram for the first time, and compared our findings to their low- and intermediate-mass counterparts (T Tauris and Herbig AeBes). We also compared the observed K-band sizes (i.e. inner rim radius) to the sublimation radius predicted by three different disc scenarios: a classical thick flattened structure with oblique heating in action, and direct heating from the protostar via an optically thin cavity with and without backwarming effects. Lastly, we applied binary geometries to trace close binarity among MYSOs. Results. The characteristic size of the 2.2 μm continuum emission towards this sample of MYSOs shows a large scatter at the given luminosity range. When the inner sizes of MYSOs are compared to those of lower mass Herbig AeBe and T Tauri stars, they appear to follow a universal trend in that the sizes scale with the square-root of the stellar luminosity. The Brγ emission originates from a similar or somewhat smaller and co-planar area compared to the 2.2 μm continuum emission. We discuss this new finding with respect to a disc-wind or jet origin. Finally, we report an MYSO binary fraction of 17–25% at milli-arcsecond separations (2–300 au). Conclusions. The size–luminosity diagram indicates that the inner regions of discs around young stars scale with luminosity independently of the stellar mass. The observed fraction of MYSO binaries in K-band is almost ‘flat’ for a wide range of separations (2–10 000 au). At the targeted scales (2–300 au), the MYSO binary fraction is lower than what was previously reported for the more evolved main sequence massive stars, which, if further confirmed, could implicate predictions from massive binary formation theories. Lastly, with this study, we can finally spatially resolve the crucial star–disc interface in a sample of MYSOs, showing that au-scale discs are prominent in high-mass star formation and are similar to their low-mass equivalents, while the ionised gas can be linked to disc wind and disc accretion models similar to Herbig AeBes.

Precision Interferometry as a New Method for Studying the Conformational State of Protein and Its Interaction with a Solvent

A new method for studying the conformational state of a protein and its interaction with a solvent has been developed. The method is based on measuring the refractive index of a protein solution using a precision laser interferometer with an error of 10–7. The interferometer was calibrated on the basis of the known dependences of the refractive index change with a change in water temperature, and the refractive index change of a NaCl solution with a change in concentration. Using the interferometer, the refractive index changes were first recorded in the course of proteolysis (during pepsin-catalyzed hydrolysis, an increase in the refractive index of solutions of bovine serum albumin and egg lysozyme by 9 × 10–6 and 2.4 × 10–6, respectively) and denaturation (an increase in the refractive index by 4.5 × 10–5 during the reaction of egg lysozyme with guanidine hydrochloride and dithiothreitol). Based on direct interferometric measurements, we have disproved the widespread assumption that the refractive index of protein solutions is determined only by concentration of the protein and its amino acid composition and does not depend on the state of protein fragmentation. The increased accuracy of the interferometer makes it possible to study the refractive index increment (dn/dc) at low concentrations of dissolved compounds ( $$ \ll $$ 1%), as well as to examine the processes leading to changes in the conformation of macromolecules in solution.

Прецизионная интерферометрия как новый метод исследования конформационного состояния белка и его взаимодействия с растворителем

A new method for studying the conformational state of a protein and its interaction with a solvent has been developed. The method is based on measuring the refractive index of a protein solution using a precision laser interferometer with an accuracy of 1 • 10–7. The interferometer was calibrated based on the known temperature dependence of water refractive index and concentration dependence of the refractive index of a NaCl solution. Using an interferometer, changes in the refractive index during proteolysis (an increase of 9 ∙ 10-6 and 2.4 ∙ 10-6 in the refractive index of bovine serum albumin and egg lysozyme solutions during pepsin-catalyzed hydrolysis) and denaturation (increase in the refractive index by 4.5 ∙ 10-5 during the reaction of egg lysozyme with guanidine hydrochloride and dithiothreitol) have been first recorded. Based on direct interferometric measurements, the widespread assumption has been refuted that the refractive index of protein solutions is determined only by the concentration of the protein and its amino acid composition and does not depend on the state of protein fragmentation. The increased accuracy of the interferometer allows one to study the increment of the refractive index (dn/dc) at low concentrations of dissolved compounds (<< 1%), as well as processes leading to a change in the conformation of macromolecules in solution.

A 3-mirror surface force balance for the investigation of fluids confined to nanoscale films between two ultra-smooth polarizable electrodes.

We present a new technique, based on the Surface Force Balance (SFB), for the direct measurement of surface forces between two ultra-smooth and polarizable gold electrode surfaces across thin fluid films. Combining the direct interferometric measurement of surface separation and contact geometry with smooth electrode surfaces has proved challenging in the past, and for this reason, previous measurements with the SFB typically involved two insulating mica surfaces, or one mica surface and one electrode surface, or an alternative less direct measure of the surface separation. Here, we demonstrate that a 3-mirror interferometer can overcome these difficulties: the setup involves two ultra-smooth electrode/mirror surfaces between which the fluid is confined and a third mirror to allow for interferometric detection of the liquid thickness with nanometer resolution and at thicknesses much smaller than the diffraction limit of the light. We conclude with a proof-of-concept measurement across dry nitrogen gas. The technique should prove useful for studying the properties of fluids confined at the nanoscale inside a slit-pore of controlled electrical potential or subject to applied electric fields.

Ultimate Limit in the Spectral Resolution of Extreme Ultraviolet Frequency Combs

We present the results of direct interferometric measurements on the pulse-to-pulse phase jitter of a metrological, fiber-based, infrared (IR) frequency comb. We show that the short-time evolution of such phase fluctuations, which cannot be actively controlled by any feedback system, imposes a stringent limit on the tooth linewidth of extreme ultraviolet (XUV) combs produced by high-order harmonic conversion, thus explaining the difference of 9 orders of magnitude between the coherence times of state-of-the-art IR and XUV frequency combs.

Performance evaluation of compact channels with surface modifications for heat transfer enhancement: An interferometric study in developing flow regime

Performance evaluation of surface roughened compact channels for heat transfer applications has been investigated using non-intrusive, real time laser-based interferometric technique with water as the coolant medium. The lower wall of the channel has been roughened by creating hemispherical inward dimples. Projection data of the temperature field has been recorded using a Mach Zehnder interferometer. In order to facilitate direct comparison, experiments have also been conducted in smooth channel of similar dimensions. Results have been presented in the form of thermal boundary layer profiles, whole field temperature distributions and local variations of heat transfer coefficients. Direct interferometric measurements clearly reveal the disruption of thermal boundary layer due to the presence of inward dimples. Near wall temperature gradients were seen to be stronger in the case of dimpled channel in comparison with that of the smooth one resulting into a clear enhancement in heat transfer rates. At low Reynolds numbers, variation of heat transfer coefficients along the length of the dimpled channel showed the presence of local maxima. On the other hand, the corresponding profiles for the smooth channels showed a monotonic decrease with respect to the axial direction. The dynamic measurements, that are purely non-intrusive, revealed an improved thermal performance of surface roughened compact channels.

A COMPREHENSIVE CHARACTERIZATION OF THE 70 VIRGINIS PLANETARY SYSTEM

An on-going effort in the characterization of exoplanetary systems is the accurate determination of host star properties. This effort extends to the relatively bright host stars of planets discovered with the radial velocity method. The Transit Ephemeris Refinement and Monitoring Survey (TERMS) is aiding in these efforts as part of its observational campaign for exoplanet host stars. One of the first known systems is that of 70 Virginis, which harbors a jovian planet in an eccentric orbit. Here we present a complete characterization of this system with a compilation of TERMS photometry, spectroscopy, and interferometry. We provide fundamental properties of the host star through direct interferometric measurements of the radius (1.5% uncertainty) and through spectroscopic analysis. We combined 59 new Keck HIRES radial velocity measurements with the 169 previously published from the ELODIE, Hamilton, and HIRES spectrographs, to calculate a refined orbital solution and construct a transit ephemeris for the planet. These newly determined system characteristics are used to describe the Habitable Zone of the system with a discussion of possible additional planets and related stability simulations. Finally, we present 19 years of precision robotic photometry that constrain stellar activity and rule out central planetary transits for a Jupiter-radius planet at the 5σ level, with reduced significance down to an impact parameter of b = 0.95.

HOST STAR PROPERTIES AND TRANSIT EXCLUSION FOR THE HD 38529 PLANETARY SYSTEM

The transit signature of exoplanets provides an avenue through which characterization of exoplanetary properties may be undertaken, such as studies of mean density, structure, and atmospheric composition. The Transit Ephemeris Refinement and Monitoring Survey (TERMS) is a program to expand the catalog of transiting planets around bright host stars by refining the orbits of known planets discovered with the radial velocity technique. Here we present results for the HD 38529 system. We determine fundamental properties of the host star through direct interferometric measurements of the radius and through spectroscopic analysis. We provide new radial velocity measurements that are used to improve the Keplerian solution for the two known planets, and we find no evidence for a previously postulated third planet. We also present 12 years of precision robotic photometry of HD 38529 that demonstrate the inner planet does not transit and the host star exhibits cyclic variations in seasonal mean brightness with a timescale of approximately six years.

Experimental evidence for the thermal origin of1/ffrequency noise in erbium-doped fiber lasers

We present experimental evidence in support of the recent theoretical proposal that intrinsic $1/f$ frequency noise in short cavity erbium-doped fiber lasers is of thermal origin. We demonstrate that the power spectral density of frequency noise in distributed-feedback fiber lasers (DFB FL) exhibits predicted ${T}^{2}$ temperature dependence across all frequencies over a temperature range of almost 200 K. This temperature dependence is observed both in direct interferometric measurements of frequency noise in a single mode DFB FL and noninterferometric measurements of polarization-beat-frequency noise in a dual frequency DFB FL. It is also shown that frequency noise of orthogonal polarization modes in the dual frequency DFB FL is substantially correlated providing a strong indication of a common origin.

VLTI near-IR interferometric observations of Vega-like stars

We report in this paper the direct interferometric measurement of the angular diameter of five nearby Vega-like stars: α PsA, β Leo, β Pic, � Eri and τ Cet. The near-infrared (K and H bands) observations were conducted at the VLTI during the commissioning period with the VINCI instrument and three different baselines ranging from 66 m to 140 m. The five stellar photospheres are resolved and we derive their angular diameters with a 1 to 2% accuracy, except for β Pic (14%). We discuss the detectability and the influence of a possible small amount of warm circumstellar dust on our measurements. In addition, we have used the stellar evolution code CESAM (Morel 1997) to compare the computed fundamental parameters to the observed values (linear diameter, luminosity, temperature and chemical abundance). As a result of the simulation, the age of the stars is inferred and found to be in good agreement with previous estimates from various other methods.

Measurement of micro-roughness using a metrological large range scanning force microscope

A new method for traceable measurement of micro-roughness by using a newly developed metrological large range scanning force microscope (LR-SFM) is described. The LR-SFM has an Abbe error free design and direct interferometric position measurement capability, and is capable of measuring samples in a volume of 25 mm × 25 mm × 5 mm along x, y and z axes. The instrumentation and several important design concepts are introduced in this paper. Measurement results of a plane glass and a micro-roughness standard have illustrated that the instrument has a low noise level of Ra = 0.58 nm and good measurement repeatability. Furthermore, a group of comparison measurements on a micro-roughness standard have been carried out between the LR-SFM and a stylus profiler. The obtained roughness values from both instruments are in excellent agreement with each other. This LR-SFM overcomes the difficulty that roughness values measured by conventional SFMs cannot be compared to stylus profilers or interference microscopes, mainly due to the fact that conventional SFMs do not have the required scanning range of ISO standardized evaluation methods.

Metrological large range scanning probe microscope

We describe a metrological large range scanning probe microscope (LR-SPM) with an Abbe error free design and direct interferometric position measurement capability, aimed at versatile traceable topographic measurements that require nanometer accuracy. A dual-stage positioning system was designed to achieve both a large measurement range and a high measurement speed. This dual-stage system consists of a commercially available stage, referred to as nanomeasuring machine (NMM), with a motion range of 25 mm×25 mm×5 mm along x, y, and z axes, and a compact z-axis piezoelectric positioning stage (compact z stage) with an extension range of 2 μm. The metrological LR-SPM described here senses the surface using a stationary fixed scanning force microscope (SFM) head working in contact mode. During operation, lateral scanning of the sample is performed solely by the NMM. Whereas the z motion, controlled by the SFM signal, is carried out by a combination of the NMM and the compact z stage. In this case the compact z stage, with its high mechanical resonance frequency (greater than 20 kHz), is responsible for the rapid motion while the NMM simultaneously makes slower movements over a larger motion range. To reduce the Abbe offset to a minimum the SFM tip is located at the intersection of three interferometer measurement beams orientated in x, y, and z directions. To improve real time performance two high-end digital signal processing (DSP) systems are used for NMM positioning and SFM servocontrol. Comprehensive DSP firmware and Windows XP-based software are implemented, providing a flexible and user-friendly interface. The instrument is able to perform large area imaging or profile scanning directly without stitching small scanned images. Several measurements on different samples such as flatness standards, nanostep height standards, roughness standards as well as sharp nanoedge samples and 1D gratings demonstrate the outstanding metrological capabilities of the instrument.

Decapitating the Duck: The (Non)Association of PSR B1757−24 and Supernova Remnant G5.4−1.2

We have made the first direct interferometric proper-motion measurements of the radio pulsar PSR B1757-24, which sits at the tip of the beak of the putative Duck supernova remnant. The peculiar morphology of this radio complex has been used to argue alternately that the pulsar's space motion was either surprisingly high or surprisingly low. In fact, we show that the pulsar's motion is so small that it and its associated nonthermal nebula G5.27-0.9 (the head) are almost certainly unrelated to the much larger G5.4-1.2 (the wings).

Optical flat surfaces: direct interferometric measurements of small‐scale irregularities

Some applications of optical surfaces place very stringent lim- its on small-scale surface irregularities, such as ripples. A method that can be used to make direct interferometric measurements of such small- scale irregularities is described. © 1996 Society of Photo-Optical Instrumentation Engineers.

Interferometric measurements of the photoinduced refractive index profiles in photorefractive Bi 12TiO 20 crystal

By direct interferometric measurement in Bi 12TiO 20 under external DC electric field, we demonstrate that the steady-state photorefractive lens produced by the laser beam with the initial circular cross-section is essentially anisotropic: its focusing strength along the direction of the applied electric field is remarkably higher. Experimental data are supported by computer simulations and analytical results.

Direct interferometric measurement of the holographic lens wave aberration

Classical interferometric methods for measurement of wave aberrations of holographic lenses have certain drawbacks. The limited diffraction efficiency of such lenses is the reason. To overcome this problem a new type of interferometer is suggested. The holographic lens under test is a basic element of the interferometer itself. The interference pattern is formed by adding the undiffracted and the diffracted waves.

Cascading of second-order processes in quadratic molecular media at the origin of very large cubic effects

We have shown that very large nonlinear shifts ranging from π/4 to π/2 observed at relatively modest input intensities in single-crystal cored fibers of 4-( N, N-dimethylamino)-3-acetamidonitrobenzene (DAN) have their origin in the cascading of two second-order nonlinear processes: second-harmonic generation followed by down-frequency conversion. The nonlinear shifts and corresponding n 2 values extracted from independent observationsof self-phase modulation and direct interferometric measurements are as large as 10 −12 cm 2/W at relatively modest input intensities from 30 to 60 MW/cm 2. The cascading origin of large n 2 values was fully confirmed by z-scan measurements performed on a single DAN crystal.

Direct interferometric measurements of quantum-confined Stark effect in InAs/GaAs short period strained-layer superlattice MQWs

The electrorefraction within and below the band edge of multiple (50) InAs/GaAs short period strained-layer superlattice quantum wells has been measured. An index change of 4×10−3 was measured near the excitonic resonance with an applied electric field of 27 kV/cm, corresponding to a quadratic electro-optic coefficient of −3×10−13 cm2/V2. These results agree with predictions from the Kramers-Kronig relations based on measurements of electroabsorption.

Direct interferometric measurement of nonlinear refractive index of optical fibres by crossphase modulation

We have computed the nonlinear refractive index of optical fibres from the phase shift resulting from crossphase modulation between a probe signal and a pulsed pump. This phase shift is obtained with a Mach-Zehnder interferometer. Values of 0.92 × 10-13esu for silica and 0.80 × 1013esu for fluorozirconate glasses have been measured.

The Michelson interferometer

The apparatus that Michelson brought to the BIPM in 1892 to “determine the value of the metre in luminous wavelengths” has generated a vast family of instruments typically used for length measurement. Looking at them from this point of view teaches us a lot about the characteristics of the Michelson interferometer that make it specially convenient for Fourier transform spectroscopy (FTS). Michelson himself used the principle of the FTS to check the monochromaticity of various spectral lines. He was looking for a good standard of length, hence he did not care so much about the general problem of spectroscopy. Furthermore, he was limited to the parameter that he called the visibility of the fringes, i.e. the modulus of the Fourier transform of the spectral distribution, in fact the only parameter that the naked eye can roughly estimate, besides the fringe spacing. As he counted only up to 1212 fringes, and thereafter used a stepping process by “optical addition”, he did not worry about the optical defects that impair direct interferometric measurement of long distances. A few technological improvements have made the fringe-counting technique the current way of measuring length. It is shown that the analysis required for accurate length measurements with a Michelson interferometer is similar to the one required to make accurate FTS.