Optical Laser Interferometry Research Articles

Phase Equilibria and Interdiffusion in Bimodal High-Density Polyethylene (HDPE) and Linear Low-Density Polyethylene (LLDPE) Based Compositions.

The compositions based on bimodal high-density polyethylene (HDPE, copolymer of ethylene with hexene-1) and in mixture with monomodal tercopolymer of ethylene with butene-1/hexene-1 (LLDPE, low-density polyethylene) have been studied. Phase equilibrium, thermodynamic parameters of interdiffusion in a wide range of temperatures and ratios of co-components were identified by refractometry, differential scanning calorimetry, optical laser interferometry, X-ray phase analysis. The phase state diagrams of the HDPE—LLDPE systems were constructed. It has been established that they belong to the class of state diagrams of “solid crystal solutions with unrestricted mixing of components”. The paired parameters of the components interaction and their temperature dependences were calculated. Thermodynamic compatibility of α-olefins in the region of melts and crystallization of one of the components has been shown. The kinetics of formation of interphase boundaries during crystallization of α-olefins has been analyzed. The morphology of crystallized gradient diffusion zones has been analyzed by optical polarization microscopy. The sizes of spherulites in different areas of concentration profiles and values of interdiffusion coefficients were determined.

Opto-electrochemical Instruments; Detection of Crevise Corrosion

Background: Two techniques of laser optical interferometry have been reviewed for detection of crevice corrosion of low carbon steel samples in aqueous solutions. The first technique used an optical corrosion-meter to detect localized corrosion such as crevice corrosion, of the low carbon steel samples in seawater. The concept of the optical corrosion-meter was based on incorporating holographic interferometry and the cyclic polarization test. The second technique used a modified electrochemical noise technique based on holographic interferometry to detect crevice corrosion of the low carbon steel samples in 1 M of sodium hydroxide (NaOH) solution. Objective: Emphasis on the significant role of the optical techniques of detecting crevice corrosion of carbon steel in aqueous solutions alongside to the DC methods. Method: The optical corrosion-meter and the modified electrochemical noise technique were used in the present investigation. Results: Observations of crevice corrosion of the carbon steel samples in seawater by the optical corrosion-meter were found to be in agreement with the cyclic polarization test. In addition, the modified electrochemical noise technique was found to be very useful for quantitatively distinguishing of localized corrosion, passivation, and uniform corrosion of the carbon steel samples in 1 M NaOH solution. Conclusions: The optical techniques of detecting crevice corrosion of carbon steel in aqueous solutions were found efficient opto-electrochemical instruments for substantiating results of those DC methods. Keywords: Electronic instruments, electrochemical properties, electromagnetic field, optical corrosion-meter, holographic interferometry, electrochemical noise technique, and opto-electrochemistry.

Alignment of the aberration-free XUV Raman spectrometer at FLASH.

An extreme-ultraviolet (XUV) double-stage Raman spectrometer is permanently installed as an experimental end-station at the PG1 beamline of the soft X-ray/XUV free-electron laser in Hamburg, FLASH. The monochromator stages are designed according to the Czerny-Turner optical scheme, adapted for the XUV photon energy range, with optical elements installed at grazing-incidence angles. Such an optical scheme along with the usage of off-axis parabolic mirrors for light collimation and focusing allows for aberration-free spectral imaging on the optical axis. Combining the two monochromators in additive dispersion mode allows for reaching high resolution and superior stray light rejection, but puts high demands on the quality of the optical alignment. In order to align the instrument with the highest precision and to quantitatively characterize the instrument performance and thus the quality of the alignment, optical laser interferometry, Hartmann-Shack wavefront-sensing measurements as well as off-line soft X-ray measurements and extensive optical simulations were conducted. In this paper the concept of the alignment scheme and the procedure of the internal optical alignment are presented. Furthermore, results on the imaging quality and resolution of the first monochromator stage are shown.

Counterpropagating Radiative Shock Experiments on the Orion Laser.

We present new experiments to study the formation of radiative shocks and the interaction between two counterpropagating radiative shocks. The experiments are performed at the Orion laser facility, which is used to drive shocks in xenon inside large aspect ratio gas cells. The collision between the two shocks and their respective radiative precursors, combined with the formation of inherently three-dimensional shocks, provides a novel platform particularly suited for the benchmarking of numerical codes. The dynamics of the shocks before and after the collision are investigated using point-projection x-ray backlighting while, simultaneously, the electron density in the radiative precursor was measured via optical laser interferometry. Modeling of the experiments using the 2D radiation hydrodynamic codes nym and petra shows very good agreement with the experimental results.

Split-And-Delay Unit for FEL Interferometry in the XUV Spectral Range

In this work we present a reflective split-and-delay unit (SDU) developed for interferometric time-resolved experiments utilizing an (extreme ultraviolet) XUV pump–XUV probe scheme with focused free-electron laser beams. The developed SDU overcomes limitations for phase-resolved measurements inherent to conventional two-element split mirrors by a special design using two reflective lamellar gratings. The gratings produce a high-contrast interference signal controlled by the grating displacement in every diffraction order. The orders are separated in the focal plane of the focusing optics, which enables one to avoid phase averaging by spatially selective detection of a single interference state of the two light fields. Interferometry requires a precise relative phase control of the light fields, which presents a challenge at short wavelengths. In our setup the phase delay is determined by an in-vacuum white light interferometer (WLI) that monitors the surface profile of the SDU in real time and thus measures the delay for each laser shot. The precision of the WLI is 1 nm as determined by optical laser interferometry. In the presented experimental geometry it corresponds to a time delay accuracy of 3 as, which enables phase-resolved XUV pump–XUV probe experiments at free-electron laser (FEL) repetition rates up to 60 Hz.

Development and first experimental tests of Faraday cup array

A new type of Faraday cup, capable of detecting high energy charged particles produced in a high intensity laser-matter interaction environment, has recently been developed and demonstrated as a real-time detector based on the time-of-flight technique. An array of these Faraday cups was designed and constructed to cover different observation angles with respect to the target normal direction. Thus, it allows reconstruction of the spatial distribution of ion current density in the subcritical plasma region and the ability to visualise its time evolution through time-of-flight measurements, which cannot be achieved with standard laser optical interferometry. This is a unique method for two-dimensional visualisation of ion currents from laser-generated plasmas. A technical description of the new type of Faraday cup is introduced along with an ad hoc data analysis procedure. Experimental results obtained during campaigns at the Petawatt High-Energy Laser for Heavy Ion Experiments (GSI, Darmstadt) and at the Prague Asterix Laser System (AS CR) are presented. Advantages and limitations of the used diagnostic system are discussed.

Absolute distance sensing by two laser optical interferometry

We have developed a method for absolute distance sensing by two laser optical interferometry. A particularity of this technique is that a target distance is determined in absolute and is no longer limited to within an ambiguity range affecting usually multiple wavelength interferometers. We implemented the technique in a low-finesse Fabry-Pérot miniature fiber based interferometer. We used two diode lasers, both operating in the 1550 nm wavelength range. The wavelength difference is chosen to create a 25 μm long periodic beating interferometric pattern allowing a nanometer precise position measurement but limited to within an ambiguity range of 25 μm. The ambiguity is then eliminated by scanning one of the wavelengths over a small range (3.4 nm). We measured absolute distances in the sub-meter range and this with just few nanometer repeatability.

Holographic interferometry of oil films and droplets in water with a single-beam mirror-type scheme

Application of single-beam reflective laser optical interferometry for oil films and droplets in water detection and characterization is discussed. Oil films can be detected by the appearance of characteristic interference patterns. Analytical expressions describing intensity distribution in these interference patterns allow determination of oil film thickness, size of oil droplets, and distance to the oil film from the observation plane. Results from these analyses indicate that oil spill aging and breakup can be monitored in real time by analyzing time-dependent holographic fringe patterns. Interferometric methods of oil spill detection and characterization can be automated using digital holography with three-dimensional reconstruction of the time-changing oil spill topography. In this effort, the interferometric methods were applied to samples from Chevron oil and British Petroleum MC252 oil obtained during the Deep Water Horizon oil spill in the Gulf of Mexico.

Application of nonlinear laser photoacoustic technique to crack detection

Nonlinear acoustics is a promising method for non-destructive testing (NDT) as it allows to improve the sensitivity and contrast of defects detection. The application of contactless laser photoacoustic technique for the tasks of nonlinear acoustics looks very promising. Meanwhile, real examples of industrial systems using nonlinear photoacoustics are still absent. In this work nonlinear photoacoustic response of artificially prepared cracks has been studied. Acoustic vibrations have been excited through the loASAHGRcal heating caused by the absorption of a focused beam of visible or near-infrared laser radiation. Several methods have been applied for the detection of surface displacement including piezo-transducers, air-coupled transducers and optical laser interferometry. It has been shown, that nonlinear acoustic response increases drastically when both pump and probe points are localized near the crack. For this reason, the last two methods allowing local probing look very promising. Two dimensional scans of generation and detection points on the sample surface could be used to obtain the images of crack at new spectral components induced by crack nonlinearity. The goal of this work is to find optimal methods of the excitation and detection of nonlinear photoacoustic response of the crack. It should make the technique attractive for the industrial applications.

A capacitance and optical method for the static and dynamic characterization of micro electro mechanical systems (MEMS) devices

As the micro technology field expands, the need of simple and standardized procedures to precisely evaluate device functionality, realibility and quality of micro electro mechanical systems devices increases. In this paper the application of two empirical methods suitable for the static and the dynamic characterization of micrometersized structures is proposed. The first methodology is based on capacitance measurements and finds simple application in case of comb-finger actuated devices. The second one is based on the Doppler phenomenon combined with laser optical interferometry allowing the characterization of a wide range of structures. The methodologies are applied to a reliability test structure specifically designed at STMicroelectronics for studying the fatigue behaviour of the structural material involved in the fabrication of their commercial products. This case of study highlights how the techniques may be coupled to usual design approaches for completing and verifying the information given by theory and simulations; thus improving the entire development cycle.

Laser optical interferometry as NDT methods for cleaner and sustainable desalination plants: pitting and crevice corrosion

In the present investigation, an optical corrosion-meter has been developed for materials testing and evaluation of different corrosion phenomena. The idea of the optical corrosion-meter was established based on principles of 3D-holographic interferometry for measuring microsurface dissolution, i.e. mass loss, and on those of electrochemistry for measuring the bulk electronic current, i.e. corrosion current of metallic samples in aqueous solutions. In the present work, an early stage of pitting corrosion of pure aluminium, UNS No.304 stainless steel alloy and copper in seawater were monitored in situ by the optical corrosion-meter during the cyclic polarization test. Also, an early stage of pitting corrosion of pure copper and an aluminium-brass alloy in tap water were monitored in situ by the optical corrosion-meter during the cyclic polarization test. The observations of pitting were basically interferometric perturbations detected only on the surface of the aluminium in seawater, UNS No.304 stainless steel in seawater, pure copper in tap water. In addition, an early stage of crevice corrosion of a carbon steel alloy, a titanium alloy, UNS No.316 stainless steel, UNS No.304 stainless steel, pure aluminium, and an aluminium-brass alloy in seawater as well as pure copper in tap water were monitored in situ by the optical corrosion-meter during the cyclic polarization test. The observations of crevice corrosion were basically interferometric perturbations detected on the surface of most of the tested samples in solutions, except UNS No.304 stainless steel and the pure aluminium in seawater. The crevice corrosion was detected underneath a crevice assembly on the surface of the samples. The crevice assembly made of Teflon bolt, Teflon nut, and Teflon washer. The crevice assembly was used on all tested samples to create a differential aeration cell between the surface of the sample and areas underneath the crevice assembly in solutions. Each Teflon washer contained radial grooves and had 20 plateaus which formed crevices (shield areas) when pressed against the surface of the sample. The interferometic perturbations interpreted as a localized corrosion in a form of an early pitting corrosion or crevice corrosion of a depth ranged between 0.3 μm to several micrometers. Consequently, results of the present work indicate that holographic interferometry is very useful technique as a 3D-interferometric microscope for monitoring pitting corrosion and crevice corrosion at the initiation stage of the phenomena for different metallic samples commonly used in desalination plants.

Laser optical interferometry as a zero resistance ammeter: fundamental and applications

It is well known that electronics instrumentation, i.e. Ammeter, Potential-meter, have been used for years to measure electrochemical properties of metallic electrodes in aqueous solutions. One of the disadvantages of using electronic instruments for the measurement of electrochemical properties is the invasive nature of those instruments to the electrochemical systems of the metallic electrodes in aqueous solutions. In recent works published elsewhere [1–16], it has been shown that laser optical interferometry can be used as an optical transducer to characterize the electromagnetic field, i.e. phase and amplitude of the reflected light waves of a surface of a metallic electrode moving further away from the light source, which develops as a result of the electron conduction in metallic electrodes in aqueous solutions due to the anodic reaction, corrosion processes, between the electrodes and the aqueous solutions. The characterization of such electromagnetic field (phase and amplitude of the reflected light waves of a surface) and a mathematical correlation of the electromagnetic field to any electrochemical properties, i.e. corrosion current density, double layer capacitance, alternating current impedance, and so on, would lead to the measurement of the electrochemical properties by optical interferometry, by the non-invasive method. In the present work, the corrosion current density of a pure Copper (99.8% Cu), an Aluminum–Brass alloy (76% Cu, 22% Ni, and 2% Al), and a Stainless steel (UNS No.304 Stainless steel, 19% Cr, 9% Ni, 0.45% Mn, and rest Fe) were obtained in natural seawater, respectively. Also, the corrosion current density of the same Stainless steel (UNS No.304 stainless steel, 19% Cr, 9% Ni, 0.45% Mn, and rest Fe) was obtained in 1 M NaCl solution. The obtained corrosion data from the optical interferometry technique, as a zero resistance ammeter were compared with corrosion data obtained on the same alloys in the specified solutions from an electronic zero resistance ammeter as well as from the linear polarization method. The comparison among the three techniques indicates that there is contrast in the results among the investigated alloys. In general, the results of the optical interferometry were found in agreement with the electronic zero resistance ammeter as compared with the linear polarization method. As a result, the optical interferometry can be considered as a useful zero resistance Ammeter for measuring the corrosion current density of metallic electrodes in aqueous solutions at the open circuit potential of the electrodes in the aqueous solutions.

The deposition angle-dependent density of amorphous solid water films

The index of refraction and thickness of amorphous solid water (ASW) films are determined using laser optical interferometry. From the film thickness, the density of ASW can be calculated directly since the molecular beam flux and the H2O condensation coefficient are both known. From the index of refraction the ASW density can also be determined using the Lorentz–Lorenz relationship. The densities determined via both methods agree within experimental uncertainty. For films deposited at 22 K using a collimated molecular beam, the index of refraction and density decrease monotonically as the deposition angle is varied from normal to oblique incidence. At normal incidence the films have an index of refraction of 1.285 and are presumed to be fully dense (0.94 g/cm3). At glancing incidence (86°) the film has a refractive index of 1.05 and a density of 0.16 g/cm3, indicating a porosity exceeding 80%. The angle-dependent film density is in semiquantitative agreement with the results of ballistic deposition simulations of ASW film growth.

Optical in-situ measurement of the dissolution rate of a silica-Czochralski-crucible with silicon melt and comparison to ex-situ measurements

The dissolution of the silica crucible by the silicon melt acts as a source of oxygen doping in the growth of silicon single crystals by the Czochralski-method. Literature data on the dissolution rate of silica in silicon melts are available up to now only from ex-situ measurements. These data were obtained by measuring the decrease of the diameter of silica rods or plates dipped into a silicon melt. In the present work, the silica dissolution rate is measured for the first time by an in-situ technique. The decrease of the thickness of the wall of a silica crucible of a laboratory-scale Czochralski crucible containing silicon melt is measured by optical laser interferometry. The obtained results are compared quantitatively to literature data obtained by the above-mentioned ex-situ technique.

Quantitative optical in-situ measurement of the dissolution rate of the silica crucible in the silicon Czochralski process

The dissolution of the silica crucible by the silicon melt acts as a source of oxygen doping in the growth of silicon single crystals by the Czochralski-method. Literature data on the dissolution rate of silica in silicon melts are available up to now only from ex-situ measurements. In the present work, the silica dissolution rate is measured for the first time by an in-situ technique. The decrease of the thickness of the wall of a silica crucible of a laboratory-scale Czochralski-crucible containing silicon melt is measured quantitatively by optical laser interferometry. It is demonstrated that the influence of relevant growth parameters of the silicon Czochralski process like temperature of the silica crucible wall and pressure of the Argon gas can be detected and quantitatively related to the dissolution rate.

The improved performance of GaAs micromachined power sensor microsystem

Thermal effects in a 2-μm thick GaAs cantilever beam of the power sensor microsystem are investigated. The increased thermal sensitivity of the microsystem to the thermal conductance changes of the ambient atmosphere is evaluated by the experiment and simulation. A bimetallic effect in the microsystem cantilever beam is studied using both the microscopic laser optical interferometry and laser optical reflectance measurement. The cantilever beam deflections induced by the differential thermal expansion of the cantilever layers are found to be linear with the power dissipated in the microsystem MESFET-heater. The key microsystem transfer characteristics based on the bimetallic effect are obtained.

Inharmonic Overtone Spurious Mode Suppression by Partial Mass-Loading onto the Electrode for Energy-Trapped-Type Thickness-Extensional-Mode Piezoelectric Ceramic Resonators

Experimental studies have been performed on the suppression of the inharmonic overtone responses for realizing piezoelectric ceramic resonators with low resonance impedance compatible with a wide-area electrode(>φ15λ). The circumferential mass-loading onto the electrode is effective for the fabrication of an oscillator with a low oscillation startup voltage, without any jump to spurious frequencies. In addition, this technique results in a wide rejection bandwidth for TV/VCR adjacent-channel sound-carrier-signal traps. This effect (stepped energy-trapping) is observed to arise from the spatial vibration energy distribution dispersion by the additive weighting electrode using optical laser interferometry and finite- element-method analysis.