Backscattering Spectra Research Articles

Measurement Speed Improvement of OFDR Using Differential-Spectrum Dispersion Degree

Signal processing in optical frequency-domain reflectometry (OFDR) involves the cross correlation between the reference and the measured Rayleigh backscattering spectra (RBS), which is a time-consuming operation with a large data size. This work demonstrates a fast demodulation method to accelerate the data processing of OFDR in static strain measurement. The dispersion degree of the optical frequency-domain differential spectrum (OFDS) is analyzed to remove the strain-free RBS. Therefore, data demodulation can be accomplished based only on the local cross correlation (LCC) between the retained RBSs. The validity of the proposed method was verified by multiple sets of static strain experimental results. The time consumption of the proposed method is evaluated under the different sensing spatial resolutions and the number of padding zeros. Compared to the conventional method with the whole RBS, the proposed method decreases the time cost from 4575.7 to 637.1 ms when the fiber length is 40 m with 8-mm sensing spatial resolution and 6000 padding zeros.

Cross beam energy transfer and backward stimulated Brillouin scattering in double-cone ignition experiment

<sec>In the research of direct-drive laser fusion, laser irradiation of a target pellet can stimulate various laser plasma instabilities, such as stimulated Brillouin scattering (SBS) and cross-beam energy transfer (CBET), which significantly reduce the energy coupling efficiency between the laser and target pellet as well as the laser irradiation uniformity, leading the implosion quality to degrade. In the double-cone ignition (DCI) scheme of laser fusion scheme, the diagnosis of SBS and CBET is important owing to the different target configurations and oblique incident laser irradiation from the traditional spherically symmetric direct-drive central ignition scheme. In this paper, a simple and reliable backscattering diagnostic system is developed and applied to the diagnosis of the time-resolved backscattering spectrum at wavelength near 351 nm in a DCI experiment on the Shenguang-II upgrade (SG-IIU) facility. We use the system to carry out an experimental study of the SBS process and CBET process in DCI.</sec><sec>The backscattering diagnostic system collects the backscattered light signal through the scattered light by reflector mirror via an optical fiber. The signal is dispersed by a spectrometer and then recorded by a streak camera. The signal contains both the laser reference signal from the frequency doubling crystal and the backscattered light. With the help of the reference signal, the diagnostic system can reliably give the energy fraction of backscattered light. The experimental results show that the energy fraction of backscattered light around 351 nm is not higher than 3%, which is significantly lower than the experimental result of the spherically symmetric irradiation direct-drive central ignition scheme.</sec><sec>By analyzing the correlation between the backscattered signal and the laser irradiation conditions and combining the results of a set of comparative experiments, we determine that the backscattered signal contains both CBET and SBS. There is a significant difference in the CBET fraction between the backscattered signal of the #5 laser and the backscattered signal of the #7 laser. By combining the polarisation state of the laser beams, we confirm that this phenomenon is related to the polarisation angle between the laser beams. This finding provides a reference for designing subsequent large-scale laser fusion devices.</sec>

Elemental characterization of freeze dried domestic animals’ milk using ion beam analysis techniques

Particle induced X-ray emission (PIXE) and particle induced γ-ray emission (PIGE) techniques were employed to perform elemental analysis in four milk samples of local domestic animals, namely sheep, caw, camel and goat. Additionally, Rutherford backscattering (RBS) spectra were acquired simultaneously with PIXE and PIGE to determine matrix elements. Milk samples were prepared in a simple dried base following freeze drying process. Optimization of PIXE/PIGE/RBS experimental conditions as well as data acquisition and analysis procedures were carefully addressed. Verification study was performed relying on the analysis of both IAEA-11 and IAEA-153 reference materials. Accuracies of ±5–10% together with relative standard deviations of less than 15% were mostly reported. Chemical element concentrations of 11 elements were determined, namely Na, Mg, P, S, Cl, K, Ca, Zn, Br, Rb and Sr. Obtained element concentration values were mostly in the range 1000–10000 μg/g for major elements and 5–100 μg/g for trace elements. No significant changes in elemental concentration differences for both trace and major elements were noticed in the four different milk samples. The contribution of the elements in these milk samples to the dietary recommended intakes (DRI) has been evaluated. Advantages of applying multiple ion beam analysis techniques have been discussed.

Distributed pH sensing based on hydrogel coated single mode fibers and optical frequency domain reflectometry.

We propose a distributed pH sensor based on an optical frequency domain reflectometry using a PEGDA-based pH-sensitive hydrogel coated on a single mode fiber. The volume of hydrogel increased as pH value of the surrounding fluid decreased, which converts the pH value to the axial strain in the fiber. Taking capacity of distributed strain measurement with high spatial resolution in optical frequency domain reflectometry, the pH value of the external medium is distributed measured by the wavelength shifts of the local Rayleigh backscattering spectra. The basic hydrogel with different molecular weight was optimized to balance the sensitivity, the response time and also the stability. In the experiment, the range of the pH value from 2 to 6 was measured with a sampling resolution of 1.7 mm, a sensitivity of -199 pm/pH and a response time of 14 min when the hydrogel coating diameter is 2 mm. Such a distributed pH sensing system has a potential to detect and locate some chemical or biological substances in a large-scale environment.

Differential evolution optimization of Rutherford backscattering spectra

We investigate differential evolution optimization to fit Rutherford backscattering data. The algorithm helps to find, with very high precision, the sample composition profile that best fits the experimental spectra. The capabilities of the algorithm are first demonstrated with the analysis of synthetic Rutherford backscattering spectra. The use of synthetic spectra highlights the achievable precision, through which it becomes possible to differentiate between the counting statistical uncertainty of the spectra and the fitting error. Finally, the capability of the algorithm to analyze large sets of experimental spectra is demonstrated with the analysis of the position-dependent composition of a SrxTiyOz layer on a 200 mm silicon wafer. It is shown that the counting statistical uncertainty as well as the fitting error can be determined, and the reported total analysis uncertainty must cover both.

Coherent high-spectral-resolution lidar for the measurement of the atmospheric Mie-Rayleigh-Brillouin backscatter spectrum.

In this study, a 1550 nm coherent high-spectral-resolution lidar (CHSRL) is developed to measure the optical properties of aerosols and atmospheric wind profiles in the atmospheric boundary layer. To determine the optical properties, a coherent frequency discriminator based on the fast Fourier transform is designed in the CHSRL to separate the Mie and the Rayleigh-Brillouin backscatter spectra to fulfill the needs of high-spectral measurements. The atmospheric wind velocity is retrieved using the simultaneously measured Doppler shift. This non-optical frequency discriminator is a feasible and low-cost solution compared to a narrow-bandwidth optical filter, such as a Fabry-Perot interferometer or an atomic filter. However, shot, amplifier spontaneous emission, and detector noise interfere with the Rayleigh-Brillouin spectrum. Therefore, a spectrum correction algorithm is proposed to recover the interfered Rayleigh-Brillouin spectrum, and the measurement results of the spectral line agree well with those modeled with Tenti S6 at different central frequencies. Finally, field observations for comparison are conducted with the co-located CHSRL, Raman lidar, and coherent Doppler wind lidar. The comparison results indicate that the correlation coefficient of the aerosol backscatter coefficient is 0.84. The correlation coefficient and standard deviation of wind velocity are 0.98 and 0.13 m · s-1, respectively.

Developing an optical backscatter method for determining casein micelle particle size in heated milk

A plethora of different factors, such as heat treatment, pH, soluble calcium and phosphate concentrations, colloidal calcium phosphate, ionic strength, redox potential, etc., affect functionally of critical milk components such as casein micelles, fat globules and whey proteins. These physicochemical changes induce fat- or protein-protein interactions that would be associated to changes in particle size that might be revealed using light backscatter measurements. We hypothesized that inline, simple, low-cost light backscatter measurements might have the potential to provide functionally related information, representing an interesting opportunity for process control. Casein micelle particle size and near infrared light backscatter spectra were measured in milks heat treated at 80 and 90 °C and pH 6.3, 6.7 and 7.1 in order to obtain prediction models for estimating changes in casein micelle particle size during milk heat treatment. Light intensity was measured over a spectral range of 200–1100 nm using a simple optical backscatter sensor and was implemented into models for particle size predictions as a function of heat treatment temperature and pH. Models which included an exponential factor containing a ratio of two specific wavebands were found to improve R2 when compared to single wavelength models. The best model exhibited an R2 of 0.993 and SEP of 2.36 nm. The developed prediction models show promise for in-line monitoring of whey protein denaturation and casein micelle particle size.

Advanced microstructure, morphology and CO gas sensor properties of Cu/Ni bilayers at nanoscale

In this study, we investigated the morphology of synthesized Cu/Ni nanoparticles in trace of carbon sources by the co-deposition process of RF sputtering and RF-PECVD methods and localized surface plasmon resonance of CO gas sensing of Cu/Ni nanoparticles. The surface morphology was studied by analyzing 3D micrographs of atomic force microscopy using image processing techniques and fractal/multifractal analyses. The MountainsMap® Premium software with the two-way ANOVA (Variance analysis) and least-significant differences tests were used for statistical analysis. The surface nano-patterns have a local and global particular distribution. Experimental and simulated Rutherford backscattering spectra confirm the quality of nanoparticles. Then, prepared samples were exposed to CO gas flue to study their gas sensor application using the localized surface plasmon resonance method. Increasing the Ni layer over Cu one shows an interesting result in both morphology and gas sensing sides. Advanced stereometric analyses for the surface topography of thin films in conjunction with Rutherford backscattering spectrometry and Spectroscopic analysis make a unique study in the field.

Spatial Resolution Enhancement of Coherent Doppler Lidar by Pseudo-Random Phase Coding

A high spatial resolution coherent Doppler wind lidar (CDWL) incorporating pseudo-random phase coding (PRPC) is proposed and demonstrated. Random phase coding of the transmitted lightwave spreads the atmospheric backscattered spectrum and the spatial resolution can be enhanced as only the signal with specific time delay could be despread during decoding. The narrow peak of the despread spectrum provides higher wind velocity retrieval accuracy compared with conventional pulsed CDWL with the same spatial resolution. Spectrum difference is applied to reduce the interference between the spread and despread spectra. The new method's performance is verified in a comparison experiment with a non-coding CDWL. Continuous radial wind profile measurement over 800 m is demonstrated with spatial/temporal resolution of 4.5 m/1 s, at laser peak power of 250 W.

A method to predict texture effect on ion beam channeling analysis of polycrystals and the application to study the mosaic spreading effect in highly oriented pyrolytic graphite

We propose a method to convert the channeling Rutherford backscattering spectrum yield map of a single crystal to a polycrystal through a matrix rotation technique. The rotation matrix is determined by the deviation of the crystal axial direction from the original z axis. The final yield map is created after averaging the rotated yields using the texture function as the weight factor. For highly oriented pyrolytic graphite (HOPG) exhibiting mosaic spread, the method leads to a Gaussian kernel averaging of the map obtained from a single crystal. The yield map of a single crystal is obtained by a simulation of ion trajectories in a potential field described by Moliere screened Coulomb potentials. Yield maps are calculated under variousσ values (standard deviations of mosaic spread). The simulated results are compared with experimental results obtained using 1.2 MeV alpha particle. σ is extracted through the best fitting, demonstrating that the method can be used to obtain texture details. The effects of mosaic spread on minimum yield χmin and the half-width at half maximum of angular scans ψ1/2 are systematically modeled and compared with previous theoretical equations. The study also shows that previous theoretical equations are valid only at small σ values. The proposed method can be applied to any type of polycrystal and is not limited to HOPG. It provides near-surface mosaic spread and crystallography information with a longitudinal depth resolution of tens of nanometers and is not influenced by grain shapes.

Surface Waves Prediction Based on Long-Range Acoustic Backscattering in a Mid-Frequency Range

Underwater acoustic echosounding for surface roughness parameters retrieval is studied in a frequency band that is relatively new for such purposes. During the described 2-weeks sea experiment, 1–3 kHz tonal pulses were emitted from an oceanographic platform, located on the northern Black Sea shelf. Doppler spectra of the resulting reverberation were studied. The frequency band of the acoustic system, selected for this study, is chosen due to the fact that the sound propagation range is large enough for remote sensing in a coastal zone, and the resolution cell size does not limit the research. Backscattering of acoustical signals was received for distances around two nautical miles. However, it turned to be quite difficult to interpret the obtained data since backscattering spectrum shape was influenced by a series of effects, resulting in a complicated link to wind waves and currents’ parameters. Significant wave height and dominant wave frequency were estimated as the result of such signals processed with the use of machine learning tools. A decision-tree-based mathematical regression model was trained to solve the inverse problem. Wind waves prediction is in a good agreement with direct measurements, made on the platform, and machine learning results allow physical interpretation.

An approach based on gamma backscattering technique to measuring the density of liquid using the low-intensity radioactive source

This work aims to develop a practical solution to measure the density of a liquid. Two purposes of this study: (1) using a low-activity source to measure the density of a liquid, and (2) simplifying the experimental arrangement to reduce the size and weight of the measuring system. The proposed solution is to develop a measurement technique without both detector and source collimators, while it considers an appropriate technique for analyzing the backscattering spectrum. To validate the proposed method, we used two groups of liquid: one group of liquids with a certified density and one group of liquids collected from the market. For the first group, the obtained results showed that the relative errors between the measured density and the reference one are below 6.8% and the uncertainties in density are below 4%, which confirms the feasibility of the proposed approach. For the second group, the liquids collected from the market include 70 percent alcohol, cooking oil, saltwater, fresh milk, diesel oil, dishwashing liquid, machine oil, and wine. The results obtained show that the relative errors between the densities determined by the proposed method and densities determined by the traditional method using density kit are less than 4.3%, the uncertainties in density when using the proposed method are below 3.2%. These results initially confirm that the proposed solution is completely applicable in measuring the density of a liquid.

Even-order harmonic generation from nonlinear Thomson backscatter in a tightly focused Gaussian laser pulse

The electron dynamics and the Thomson backscattering spectra for an electron accelerating in a tightly focused Gaussian laser pulse are first investigated in detail. It is found that for a tightly focused Gaussian laser pulse, the ponderomotive force introduced due to the non-uniform intensity distribution of the laser pulse has the tendency to push out the electron from the laser pulse, which leads to the trajectory symmetry-breaking of the electron and then the generation of the even-order harmonics at the same time. Further, for the tightly focused Gaussian laser pulse, changes in several laser parameters, such as the increase of the laser peak amplitude, lengthening of the pulse width, and decrease of the beam waist, lead earlier to the relative ejected position of the electron to the laser pulse, which causes the more obvious trajectory symmetry-breaking of the electron, and then the more intensive peak intensity of the even-order harmonics. It is different from the well-known results of the plane waves and the Gaussian laser pulse with uniform transverse intensity distribution and provides a possible way for the generation of the even-order harmonics in nonlinear Thomson backscattering.

Transmission and backscattering characteristics of electromagnetic waves in single layer combined plasma array

Manipulation of electromagnetic (EM) waves is essential for various microwave applications. This research studies the modulation of EM waves by using single-layer plasma arrays consisting of discharge tubes. We experimentally investigate the transmission spectra and backscattering attenuation characteristics of the plasma arrays, and numerical simulations further reveal the modulation mechanism and influences of the plasma arrays. The experimental and numerical results show that broadband tunable photonic bandgaps can be achieved in frequency ranges of 4–7.5 GHz and 7–9.5 GHz for the transmission spectrum and the backscattering spectrum, respectively. In addition, the proposed plasma array can achieve different modulation effects to satisfy the corresponding scenario requirements by adjusting the configuration and parameters such as the plasma frequency, spacing of the plasma tubes, and the discharge tube’s excitation or extinction of the plasma array. The wave manipulation of the combined plasma array creates opportunities for developing numerous applications, including large-area spatial filtering, radar stealth, and reconfigurable antennas.

Measurement of (p,p) elastic differential cross sections for 17O in the 0.6–2 MeV range at 165°

17O(p,p)17O elastic scattering cross sections were measured for the first time, on the INSP SAFIR platform in Paris, using thin silica films prepared by thermal oxidation of Si under 17O2. The 17O content of the film was determined by a combination of ellipsometry and IBA measurements.The yield of elastically scattered protons was determined from the corresponding peak in the Elastic Backscattering spectra, with the underlying Si signal reduced by channeling of the incident beam in the silicon substrate. The measured 17O(p,p)17O cross section was determined with a systematic uncertainty of about 14%. The cross section consists of resonant structures superimposed on a smoothly varying component that increases from about 1.2 times the Rutherford cross section at 600 keV to about 3 times Rutherford at 2 MeV. A resonance at 1230 keV shows promise for proton Elastic Backscattering depth profiling, especially at large backscattering angles. The cross section is available on IBANDL (www-nds.iaea.org/ibandl/).

The study of channeling parameters of protons along axial and planar directions of Si

In this work, the channeling parameters, the ratio of channeling to random stopping power, and the mean channeling distance, of protons along the 〈100〉, 〈110〉, {100} and {110} directions of Si were studied in terms of the atomic potential of channels. The channeling parameters were deduced using the simulation of the channeling Rutherford backscattering spectra based on the exponential dechanneling function. The best simulation parameters were set using the Levenberg- Marquardt algorithm. The RBS/C spectra were taken in energy interval 1400–2200 keV, using a Si wafer. Considering the deduced parameters along the 〈100〉, 〈110〉, {100} and {110} directions in terms of the atomic potential of channels and using the data along the 〈111〉 and {111} channels reported in the literature, the channeling behavior of protons along the 〈111〉 and {111} direction was explained concerning the shallow and deep potentials. Finally, the mean channeling distance along the {111} channel was estimated.

Expanding the range of the resolvable strain from distributed fiber optic sensors using a local adaptive reference approach.

Optical frequency domain reflectometry (OFDR) is a spectral measurement technique in which shifts in the local Rayleigh backscatter spectra can be used to perform distributed temperature or strain measurements relative to a reference measurement using ordinary single-mode optical fibers. This work demonstrates a data processing methodology for improving the resolvable range of temperature and strain by adaptively varying the reference measurement position by position, based on the time evolution of the local optical intensities and the correlation between the reference and active measurements. These methods nearly double the resolvable range of temperature and strain compared with that achieved using the traditional static reference approach.

Spectrally Resolved Raman Lidar to Measure Backscatter Spectra of Atmospheric Three-Phase Water and Fluorescent Aerosols Simultaneously: Instrument, Methodology, and Preliminary Results

This work presents a spectrally resolved Raman lidar (SRRL) for simultaneous measurement of volume backscattering coefficient spectra (backscatter spectra for short) of atmospheric three-phase water and fluorescent aerosols. The SRRL emits 354.8-nm laser light and records both N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Raman echoes around 386.7 nm and spectral signals in a specially modified spectral range of ~393–424 nm. By defining normalized spectra, a unique spectra decomposition approach is developed for successive retrieval of normalized spectra components of fluorescent aerosols, water vapor, ice water, and liquid water. Furthermore, the backscatter spectra of each component are obtained by referencing the N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Raman signals. Three typical measurement cases are provided. For the clear-day case, the lidar-measured normalized water vapor Raman spectra are found to be nearly invariant in shape and can serve as background spectra reference for decomposition of mixed-phase water Raman spectra. Besides, fluorescence backscatter intensities are usually weak enough to be neglected in clear areas. For the fluorescence case, the fluorescence backscatter intensities become much stronger to prevent accurate measurements of water vapor. For the mixed-phase water virga case, the decomposed backscatter spectra of condensed ice and liquid water indicate the coexistence of ice water and less amount of liquid water in the falling water virga. In conclusion, this kind of SRRL is believed to have provided the potential for simultaneous and accurate profiling of atmospheric water vapor and cloud liquid/ice water and opened up new perspectives for studies of cloud–aerosol interaction.

Synthesis of bimetallic AuAg nanoparticles by sequential ion implantation for modifying surface-plasmon-resonance properties

Bimetallic AuAg (Au (80%) and Ag (20%)) nanoparticles (NPs) have been synthesized in fused quartz matrix using sequential ion implantation and post-annealing in air at 600 °C, 700 °C, 800 °C and 900 °C. X-ray diffraction (XRD) results confirm the formation of crystalline Au80Ag20 bimetallic NPs after annealing. Transmission electron microscopy (TEM) investigations have confirmed presence of spherical AuAg alloyed and few AuAg alloy core- Ag shell/satellite NPs. Rutherford backscattering spectra, along with fittings, revealed the mixing of Au and Ag atoms after annealing and movement of elements towards the surface. The peak position of the surface plasmon resonance (SPR) feature of Au has been shifted towards higher energy after sequential Ag implantation. The SPR peak position and intensity is further modified after annealing of Au80Ag20 NPs. The mechanism of modified SPR properties is mechanistically discussed by considering the diffusion, alloying, segregation and redistribution of Au/Ag in the host matrix.

The quantitative 6H-SiC crystal damage depth profiling

The hexagonal silicon carbide (6H-SiC) is one of materials used in nuclear applications, and as such is exposed to crystal damage inducing by variety of energetic particles like neutrons. In this article the 6H-SiC crystal lattice damage was introduced by the 4 MeV C3+ and 4 MeV Si3+ channelling ion implantation at the room temperature. The implantation of C and Si ions (so called self-ions) to the set of different fluences, achieves a 6H-SiC crystal lattice damage more similar to what the exposure to neutrons would produce. The 6H-SiC crystal damage has been investigated by the Elastic Backscattering spectra taken in the channeling orientation (EBS/C). EBS/C spectra of the implanted 6H-SiC samples were taken with 1.725 MeV and 1.860 MeV protons. By fitting the EBS/C spectra, the quantitative 6H-SiC crystal damage depth profiles were obtained. Further, the cross section of crystal's implanted region has been scanned with the micro-Raman (μR) technique for a comparison. In this way, the qualitative analysis of a non-crystalline phase as a function of the crystal depth was independently determined. Additionally, a scanning electron microscopy (SEM) image was taken of the implanted crystal cross sections. The comparison of the crystal damage profiles obtained by fitting EBS/C spectra with the corresponding ones obtained with the μR and SEM techniques shows very good consistency between them.