Showing papers on "Fourier transform spectroscopy published in 2020"

Oxygen vacancy engineering of self-doped SnO2−x nanocrystals for ultrasensitive NO2 detection

Abstract: It remains a great challenge to engineer oxygen vacancies in metal oxides and elucidate the interrelation between oxygen vacancy contents and gas sensing performance. Herein, we report the self-doping of SnO2−x nanocrystals (NCs) through a solvothermal reaction using Sn powder and SnCl4 as precursors. The effect of Sn2+ doping concentration in the SnO2−x lattice on the nanocrystal size, band structure, and oxygen vancancies was investigated in detail. Gas-sensing tests revealed that the SnO2−x NCs showed ultra-high sensitivity to NO2 with low optimal operating temperature (100 °C). The detection limit of the sensor was as low as 500 ppb. This phenomenon is attributed to the active role of oxygen vancancies during the surface reactions with NO2, which was substantiated by in situ reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). This work highlights the possibility of simultaneous engineering of surface energistics and electronic properties of SnO2 based materials and provides an effective strategy to achieve excellent gas sensing performance for NO2 gas sensors.

Fourier transform infrared spectroscopy with visible light

Abstract: Nonlinear interferometers allow spectroscopy in the mid-infrared range by detecting correlated visible light, for which non-cooled detectors with higher specific detectivity and lower dark count rates are available. We present a new approach for the registration of spectral information, which combines a nonlinear interferometer using non-degenerate spontaneous parametric down-conversion (SPDC) with a Fourier-transform spectroscopy concept. In order to increase the spectral coverage, we use broadband non-collinear SPDC in periodically poled LiNbO3. Without the need for spectrally selective detection, continuous spectra with a spectral bandwidth of more than 100 cm−1 are achieved. We demonstrate transmission spectra of a polypropylene sample measured with 6 cm−1 resolution in the spectral range between 3.2 µm to 3.9 µm.

Energy relaxation pathways between light-matter states revealed by coherent two-dimensional spectroscopy

Abstract: Coupling matter excitations to electromagnetic modes inside nano-scale optical resonators leads to the formation of hybrid light-matter states, so-called polaritons, allowing the controlled manipulation of material properties. Here, we investigate the photo-induced dynamics of a prototypical strongly-coupled molecular exciton-microcavity system using broadband two-dimensional Fourier transform spectroscopy and unravel the mechanistic details of its ultrafast photo-induced dynamics. We find evidence for a direct energy relaxation pathway from the upper to the lower polariton state that initially bypasses the excitonic manifold of states, which is often assumed to act as an intermediate energy reservoir, under certain experimental conditions. This observation provides new insight into polariton photophysics and could potentially aid the development of applications that rely on controlling the energy relaxation mechanism, such as in solar energy harvesting, manipulating chemical reactivity, the creation of Bose–Einstein condensates and quantum computing. Recent spectroscopic studies have elucidated light-matter interactions in exciton-polaritons at room temperature, yet their precise excited-state dynamics remain unclear. Here, broadband 2D Fourier transform spectroscopy reveals the relaxation between polaritonic states and the role of dark states.

Sensitivity of SWIFT spectroscopy

Abstract: SWIFT spectroscopy (Shifted Wave Interference Fourier Transform Spectroscopy) is a coherent beatnote technique that can be used to measure the temporal profiles of periodic optical signals. While it has been essential in understanding the physics of various mid-infrared and terahertz frequency combs, its ultimate limits have not been discussed. We show that the envelope of a SWIFTS interferogram is physically meaningful and is directly related to autocorrelation. We derive analytical expressions for the SWIFTS signals of two prototypical cases—chirped pulses from a mode-locked laser and a frequency-modulated comb—and derive scaling laws for the noise of these measurements, showing how it can be mitigated. Finally, we confirm this analysis by performing the first SWIFTS measurements of near-infrared pulses from femtosecond lasers, establishing the validity of the technique for highly-dispersed sub-picojoule pulses.

Effect of Humidity on Light-Activated NO and NO2 Gas Sensing by Hybrid Materials.

Abstract: Air humidity is one of the main factors affecting the characteristics of semiconductor gas sensors, especially at low measurement temperatures. In this work we analyzed the influence of relative humidity on sensor properties of the hybrid materials based on the nanocrystalline SnO2 and In2O3 and Ru (II) heterocyclic complex and verified the possibility of using such materials for NO (0.25-4.0 ppm) and NO2 (0.05-1.0 ppm) detection in high humidity conditions (relative humidity (RH) = 20%, 40%, 65%, 90%) at room temperature during periodic blue (λmax = 470 nm) illumination. To reveal the reasons for the different influence of humidity on the sensors' sensitivity when detecting NO and NO2, electron paramagnetic resonance (EPR) spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) investigations were undertaken. It was established that the substitution of adsorbed oxygen by water molecules causes the decrease in sensor response to NO in humid air. The influence of humidity on the interaction of sensitive materials with NO2 is determined by the following factors: the increase in charge carrier's concentration, the decrease in the number of active sites capable of interacting with gases, and possible substitution of chemisorbed oxygen with NO2- groups.

Fluorescence-detected Fourier transform electronic spectroscopy by phase-tagged photon counting.

Abstract: Fluorescence-detected Fourier transform (FT) spectroscopy is a technique in which the relative paths of an optical interferometer are controlled to excite a material sample, and the ensuing fluorescence is detected as a function of the interferometer path delay and relative phase. A common approach to enhance the signal-to-noise ratio in these experiments is to apply a continuous phase sweep to the relative optical path, and to detect the resulting modulated fluorescence using a phase-sensitive lock-in amplifier. In many important situations, the fluorescence signal is too weak to be measured using a lock-in amplifier, so that photon counting techniques are preferred. Here we introduce an approach to low-signal fluorescence-detected FT spectroscopy, in which individual photon counts are assigned to a modulated interferometer phase (‘phase-tagged photon counting,’ or PTPC), and the resulting data are processed to construct optical spectra. We studied the fluorescence signals of a molecular sample excited resonantly by a pulsed coherent laser over a range of photon flux and visibility levels. We compare the performance of PTPC to standard lock-in detection methods and establish the range of signal parameters over which meaningful measurements can be carried out. We find that PTPC generally outperforms the lock-in detection method, with the dominant source of measurement uncertainty being associated with the statistics of the finite number of samples of the photon detection rate.

High specific energy asymmetric supercapacitor based on alpha-manganese dioxide/activated expanded graphite composite and activated carbon-polyvinyl alcohol

Abstract: In this study, alpha-manganese dioxide/activated expanded graphite (α-MnO2/AEG) composite was successfully synthesized using simple hydrothermal method. Morphology, structure, elemental composition and specific surface area of the material were characterised by scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) spectroscopy, Raman spectroscopy, infrared Fourier transform spectroscopy (FTIR) and Brunauer-Emmett-Teller (BET) method. Electrochemical evaluations were achieved using three- and two-electrode configurations in 1 M Na2SO4 electrolyte. The maximum specific capacitance of 185.5 F g−1 at 1 A g−1 was recorded for three-electrode measurements. The half-cell retained an efficiency of 99.7% over 2000 cycles at 5 A g−1. The fabricated device using α-MnO2/AEG composite and activated carbon-polyvinyl alcohol (AC-PVA) as positive and negative electrodes, respectively, showed a remarkable capacitive property with a specific energy of 33 Wh kg−1 and specific power of 999 W kg−1 at 1 A g−1 within 2.0 V cell potential. Great stability of 97.8% was observed at a specific current of 5 A g−1 for over 10, 000 cycles. Further stability of the device was confirmed by performing a voltage holding of up to 70 h and retained 70% of its initial capacitance at 5 A g−1.

Vibrational Dynamics of Carbamazepine: Studies Based on Two-Dimensional Correlation Spectroscopy and X-ray Diffraction

Abstract: Fourier transform infrared spectroscopy as well as X-ray diffraction (XRD) were employed to thoroughly study phase transitions taking place during heating-cooling-heating cycle of carbamazepine (CBZ), a well known and commonly used antiepileptic drug. Both techniques revealed cold crystallization taking place during second heating. Moreover, XRD studies for the first time proved the coexistence of CBZ (form I) and iminostilbene (product of the degradation of CBZ) after a heating-cooling cycle. Moving window two-dimensional correlation (MW 2D-COS) spectroscopy and two-dimensional correlation spectroscopy were shown to be effective tools to reveal phase sequences and to provide information about the order of sequential changes of bands' intensities during each phase transition, respectively.

Collision‐Induced Absorption of CH4‐CO2 and H2‐CO2 Complexes and Their Effect on the Ancient Martian Atmosphere

Abstract: Experimental measurements of collision-induced absorption (CIA) cross-sections for CO2-H2 and CO2-CH4 complexes were performed using Fourier transform spectroscopy over a spectral range of 100-500 ...

Electrospun ZnO/Pd Nanofibers: CO Sensing and Humidity Effect.

Abstract: Variable air humidity affects the characteristics of semiconductor metal oxides, which complicates the reliable and reproducible determination of CO content in ambient air by resistive gas sensors. In this work, we determined the sensor properties of electrospun ZnO and ZnO/Pd nanofibers in the detection of CO in dry and humid air, and investigated the sensing mechanism. The microstructure of the samples, palladium content, and oxidation state, type, and concentration of surface groups were characterized using complementary techniques: X-ray fluorescent spectroscopy, XRD, high-resolution transmission electron microscopy (HRTEM), high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), energy-dispersive X-ray (EDX) mapping, XPS, and FTIR spectroscopy. The sensor properties of ZnO and ZnO/Pd nanofibers were studied at 100–450 °C in the concentration range of 5–15 ppm CO in dry (RH25 = 0%) and humid (RH25 = 60%) air. It was found that under humid conditions, ZnO completely loses its sensitivity to CO, while ZnO/Pd retains a high sensor response. On the basis of in situ diffuse reflectance IR Fourier transform spectroscopy (DRIFTS) results, it was concluded that high sensor response of ZnO/Pd nanofibers in dry and humid air was due to the electronic sensitization effect, which was not influenced by humidity change.

Identifying Thermal Decomposition Products of Nitrate Ester Explosives Using Gas Chromatography–Vacuum Ultraviolet Spectroscopy: An Experimental and Computational Study:

Abstract: Analysis of nitrate ester explosives (e.g., nitroglycerine) using gas chromatography-vacuum ultraviolet spectroscopy (GC-VUV) results in their thermal decomposition into nitric oxide, water, carbon monoxide, oxygen, and formaldehyde. These decomposition products exhibit highly structured spectra in the VUV that is not seen in larger molecules. Computational analysis using time-dependent density functional theory (TDDFT) was utilized to investigate the excited states and vibronic transitions of these decomposition products. The experimental and computational results are compared with those in previous literature using synchrotron spectroscopy, electron energy loss spectroscopy (EELS), photoabsorption spectroscopy, and other computational excited state methods. It was determined that a benchtop GC-VUV detector gives comparable results to those previously reported, and TDDFT could predict vibronic spacing and model molecular orbital diagrams.

The 14N16O γ system reviewed through Fourier transform spectroscopy

Abstract: In the present work a new analysis of the γ system (A 2 Σ + → X2Π) of the molecular radical NO through high resolution Fourier transform spectroscopy is presented. Through this analysis the band origin values of 14 bands were corrected in up to 0.7 cm − 1 in respect to the previously reported values. The p and q parameters of the Λ-doubling of the X2Π electronic state are here analyzed assuming van Vleck’s pure precession approximation, showing a good agreement between the theoretical and experimental values. Regarding the electronic state A 2 Σ + , new values of the ρ-doubling parameter γ were obtained for the first three vibrational levels, in particular for v′ = 2 where for the first time this parameter is obtained by direct fit with reasonable accuracy.

High-resolution FTIR spectroscopy of CHD279Br: ro-vibrational analysis of the v4 fundamental and determination of the ground state constants

Abstract: The first high-resolution infrared spectrum of CHD279Br has been investigated by Fourier transform spectroscopy in the range 940–1100 cm−1 at an unapodised resolution of 0.0025 cm−1. This spectral ...

Line positions and intensities of the ν4 band of methyl iodide using mid-infrared optical frequency comb Fourier transform spectroscopy

Abstract: We use optical frequency comb Fourier transform spectroscopy to measure high-resolution spectra of iodomethane, CH3I, in the C H stretch region from 2800 to 3160 cm-1. The fast-scanning Fourier transform spectrometer with auto-balanced detection is based on a difference frequency generation comb with repetition rate, frep, of 125 MHz. A series of spectra with sample point spacing equal to frep are measured at different frep settings and interleaved to yield sampling point spacing of 11 MHz. Iodomethane is introduced into a 76 m long multipass absorption cell by its vapor pressure at room temperature. The measured spectrum contains three main ro-vibrational features: the parallel vibrational overtone and combination bands centered around 2850 cm-1, the symmetric stretch ν1 band centered at 2971 cm-1, and the asymmetric stretch ν4 band centered at 3060 cm-1. The spectra of the ν4 band and the nearby ν3+ν4-ν3 hot band are simulated using PGOPHER and a new assignment of these bands is presented. The resolved ro-vibrational structures are used in a least square fit together with the microwave data to provide the upper state parameters. We assign 2603 transitions to the ν4 band with a standard deviation (observed – calculated) of 0.00034 cm-1, and 831 transitions to the ν3+ν4-ν3 hot band with a standard deviation of 0.00084 cm-1. For comparison, in the earlier work using standard FT-IR with 162 MHz resolution [Anttila, et al., J. Mol. Spectrosc. 1986; 119:190–200] 1830 transition were assigned to the ν4 band, and 380 transitions to the ν3+ν4-ν3 hot band, with standard deviations of 0.00083 cm-1 and 0.0013 cm-1, respectively. The hyperfine splittings due to the 127I nuclear quadrupole moment are observed for transitions with J ≤ 2 × K. Finally, intensities of 157 isolated transitions in the ν4 band are reported for the first time using the Voigt line shape as a model in multispectral fitting.

On-chip polarization-insensitive Fourier transform spectrometer.

Abstract: Chip-scale monolithic Fourier transform spectrometers (FTSs) offer great potential for inexpensive, high-resolution, and robust spectroscopic applications in a wide variety of scenarios. Having attracted considerable attention, spatial heterodyne FTSs (SH-FTSs) are featured with a simple and stable configuration composed of an array of Mach–Zehnder interferometers (MZIs) with linearly increasing optical path differences. Owing to the strong waveguide birefringence, MZIs on the popular silicon-on-insulator platform are polarization-sensitive, raising the challenge of polarization control of incident light. We propose and demonstrate a polarization-insensitive SH-FTS using a two-dimensional grating coupler to split an arbitrary state of polarization into two orthogonal polarization components that are both coupled into the TE mode but propagate in opposite directions in the arrayed MZIs. The two orthogonal polarization components are finally recombined in photodetection without polarization-dependent losses. An edge-coupling configuration using a polarization splitter-rotator is also proposed.

Micro-Electro-Mechanical System Fourier Transform Infrared (MEMS FT-IR) Spectrometer Under Modulated–Pulsed Light Source Excitation:

Abstract: Miniaturized Fourier transform infrared (FT-IR) spectrometers suffer from limited optical throughput due to their tiny aperture size. Therefore, coherent wideband sources with high brightness can provide an advantage over the wideband thermal radiation sources. However, the former ones are available based on pulsed operation. In this work, we present and study a miniaturized FT-IR spectrometer with pulsed light sources including chopped thermal source, semiconductor optical amplifier, Q-switched and femtosecond mode-locked laser sources. A system model for the FT-IR spectrometer system under a modulated input light source is presented. The model accounts for the relatively high scanning speed of the micro-electro-mechanical system (MEMS) interferometer. The signal-to-noise ratio of the spectrometer, due to the light source modulation, is calculated at different values of modulation repetition rate ranging from 20 Hz to 2 MHz, and duty cycle values ranging from 1% to 50%. An analytical expression for the worst-case repetition rate for the spectrometer system is derived. The model results are verified by experimental measurements showing good agreement with the theoretical expectations. Spectroscopic measurements for CO2 gas with pressure ranging from 300 mbar to 700 mbar are also performed using a high-repetition rate source, and the measured spectra agree with the simulation results demonstrating the utility of the spectrometer.

Experimental consideration of two-dimensional Fourier transform spectroscopy

Abstract: Two-dimensional Fourier transform (2D FT) spectroscopy is an important technology that developed in recent decades and has many advantages over other ultrafast spectroscopy methods. Although 2D FT spectroscopy provides great opportunities for studying various complex systems, the experimental implementation and theoretical description of 2D FT spectroscopy measurement still face many challenges, which limits their wide application. Recently, the 2D FT spectroscopy reaches maturity due to many new developments which greatly reduces the technical barrier in the experimental implementation of the 2D FT spectrometer. There have been several different approaches developed for the optical design of the 2D FT spectrometer, each with its own advantages and limitations. Thus, a procedure to help an experimentalist to build a 2D FT spectroscopy experimental apparatus is needed. This tutorial review is intending to provide an accessible introduction for a beginner to build a 2D FT spectrometer.

Direct infrared spectroscopy for the size-independent identification and quantification of respirable particles relative mass in mine dusts

Abstract: Due to the global need for energy and resources, many workers are involved in underground and surface mining operations where they can be exposed to potentially hazardous crystalline dust particles. Besides commonly known alpha quartz, a variety of other materials may be inhaled when a worker is exposed to airborne dust. To date, the challenge of rapid in-field monitoring, identification, differentiation, and quantification of those particles has not been solved satisfactorily, in part because conventional analytical techniques require laboratory environments, complex method handling, and tedious sample preparation procedures and are in part limited by the effects of particle size. Using a set of the three most abundant minerals in limestone mine dust (i.e., calcite, dolomite, and quartz) and real-world dust samples, we demonstrate that Fourier transform infrared (FTIR) spectroscopy in combination with appropriate multivariate data analysis strategies provides a versatile tool for the identification and quantification of the mineral composition in relative complex matrices. An innovative analytical method with the potential of in-field application for quantifying the relative mass of crystalline particles in mine dust has been developed using transmission and diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) within a unified multivariate model. This proof-of-principle study shows how direct on-site quantification of crystalline particles in ambient air may be accomplished based on a direct-on-filter measurement, after mine dust particles are collected directly onto PVC filters by the worker using body-mounted devices. Without any further sample preparation, these loaded filters may be analyzed via transmission infrared (IR) spectroscopy and/or DRIFTS, and the mineral content is immediately quantified via a partial least squares regression (PLSR) algorithm that enables the combining of the spectral data of both methods into a single robust model. Furthermore, it was also demonstrated that the size regime of dust particles may be classified into groups of hazardous and less hazardous size regimes. Thus, this technique may provide additional essential information for controlling air quality in surface and underground mining operations. Graphical Abstract.

Fourier transform CO spectra near 1.6 μm

Abstract: The absorption spectra of carbon monoxide have been recorded in the 6000–6450 cm−1 wavenumber regions using the Bruker IFS 125 HR Fourier transform spectrometer and a 30 m multipass cell with the White-type optical system. The spectra were recorded at spectral resolution of 0.008–0.012 cm−1, path length up to 1058 m, and at pressure range from 30 to 320 mbar. The temperature was about 301 K. The lines of the 3-0 bands of six isotopologues 12C16O, 13C16O, 12C18O, 12C17O, 13C18O, 13C17O and the lines of the hot 4-1 band of 12C16O were assigned in the spectra. The line intensities and the self-broadening coefficients were measured. In the case of the principal isotopologue the line intensities were determined for the lines with the angular momentum quantum number J up to 41. The effective dipole moment parameters describing the line intensities of the observed bands were fitted to the observed values of the line intensities. The uncertainty of the line intensity measurements for the strong unsaturated and unblended lines of the principal isotopologue varies between 2% and 2.5%. The comparison of our measured line intensities to those of other authors and of the HITRAN2016 database is given.

Evaluation of a Spatial Heterodyne Spectrometer for Raman Spectroscopy of Minerals

Abstract: Spatial heterodyne spectroscopy (SHS) is a novel spectral analysis technique that is being applied for Raman spectroscopy of minerals. This paper presents the theoretical basis of SHS and its application for Raman measurements of calcite, quartz and forsterite in marble, copper ore and nickel ore, respectively. The SHS measurements are done using a broadband (518–686 nm) and resolving power R ≈ 3000 instrument. The spectra obtained using SHS are compared to those obtained by benchtop and modular dispersive spectrometers. It is found that SHRS performance in terms of resolution is comparable to that of the benchtop spectrometer and better than the modular dispersive spectrometer, while the sensitivity of SHRS is worse than that of a benchtop spectrometer, but better than that of a modular dispersive spectrometer. When considered that SHS components are small and can be packaged into a handheld device, there is interest in developing an SHS-based instrument for mobile Raman spectroscopy. This paper evaluates the possibility of such an application.

Near infrared absorption cross sections for ethane broadened by hydrogen and nitrogen

Abstract: Near infrared absorption spectra of ethane (C2H6) were recorded in the 1800–6200 cm−1 region by high resolution Fourier transform spectroscopy (Bruker IFS 125 HR) at the Canadian Light Source (CLS). Absorption cross sections were obtained for pure samples and with nitrogen or hydrogen as broadening gases as appropriate for astronomical environments. Corrections to the cross sections were made using data from the Pacific Northwest National Laboratory (PNNL) infrared database.

Graphene aerogel-coated MoO 3 nanoparticle/polypyrrole ternary composites for high-performance supercapacitor

Abstract: A graphene aerogel-coated molybdenum trioxide/polypyrrole (MoO3/GA@PPy) composite was synthesized via hydrothermal and in site polymerization reactions. The character of PPy, MoO3/GA, and MoO3/GA@PPy were investigated by X-ray diffraction, Fourier transform spectroscopy, Raman spectroscopy, photoluminescence spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. The results of the morphological and structural analysis clearly revealed the formation of ternary nanocomposites. The electrochemical properties, such as capacitance, specific capacitance retention at different current loads, cycling stability, and impedance, were discussed as well. Improvement of electrochemical performances of the ternary nanocomposites was observed. The MoO3/GA@PPy showed a maximum specific capacitance of 1788 F/g at current density of 1 A/g.

Time-stretch spectroscopy for fast infrared absorption spectra of acetylene and hydroxyl radicals during combustion.

Abstract: We have developed a diagnostic that uses time-domain spectroscopy to measure transient infrared absorption spectra in gases. Using a time-stretch Fourier transform approach, we can determine pressure, temperature, and gas concentrations with sub-microsecond time resolution for over two milliseconds. We demonstrate high-resolution (0.015 nm), time-resolved spectral measurements in an acetylene-oxygen gas mixture undergoing combustion. Within a 5 µs period during the reaction, the acetylene line intensities decrease substantially, and new spectra appear that are consistent with the hydroxyl (OH) radical, a common by-product in the combustion, deflagration, and detonation of fuels and explosives. Post-reaction pressures and temperatures were estimated from the OH spectra. The technique measures spectra from 1520 to 1620 nm using fiber optics, photodetectors, and digitizers. No cameras or spectrometers are required.

Fourier transforms CO spectra near 1.19 µm

Abstract: The absorption spectra of carbon monoxide have been recorded in the 8150–8466 cm−1 wavenumber regions using the IFS 125 HR Fourier transform spectrometer and a 30 m multipass cell with the White-type optical system. The spectra were recorded at spectral resolution of 0.012–0.014 cm−1, path length up to 1058 m, and at pressure range from 196 to 492 mbar. The temperature of the recordings was about 302 K. The lines of the 4–0 band of three isotopologues 12C16O, 13C16O and 12C18O were assigned. The effective dipole moment parameters describing the line intensities of the 4–0 band of 12C16O were fitted to the observed values of the line intensities. Then using the isotopic substitution equations they were recalculated to those of the minor isotopologues including the radioactive ones. The accuracy of the line intensity measurements varies between 2% and 3% for the strong unblended lines. The comparison of our measured line intensities to those of other authors and to HITRAN2016 database is given.

Lensless hyperspectral phase imaging in a self-reference setup based on Fourier transform spectroscopy and noise suppression.

Abstract: A novel phase retrieval algorithm for broadband hyperspectral phase imaging from noisy intensity observations is proposed. It utilizes advantages of the Fourier transform spectroscopy in the self-referencing optical setup and provides additional, beyond spectral intensity distribution, reconstruction of the investigated object's phase. The noise amplification Fellgett's disadvantage is relaxed by the application of a sparse wavefront noise filtering embedded in the proposed algorithm. The algorithm reliability is proved by simulation tests and by results of physical experiments for transparent objects. These tests demonstrate precise phase imaging and object depth (profile) reconstruction.

Static Fourier transform mid-infrared spectrometer with increased spectral resolution using a stepped mirror

Abstract: Due to their high light throughput, static single-mirror Fourier transform spectrometers (sSMFTS) are well suited for spectral analysis in the mid-infrared range, and at the same time feature a more robust and compact design than conventional scanning instruments One major drawback, however, is the comparably low spectral resolution, which is mainly limited by the number of detector pixels Therefore, in this article, we propose a cost-effective design that almost doubles the spectral resolution of an sSMFTS by integrating a stepped mirror in one of the interferometer arms The calibration process is described and a proof of principle is given by measuring a CO2 laser The design works in a spectral range from about 2800 cm−1 to 600 cm−1 at a spectral resolution of 7 cm−1 and offers the potential to improve resolution even further

Silicon nanoparticles: a new and enhanced operational material for nitrophenol sensing

Abstract: The environmental problem is a big issue in the current scenario because the human beings are affected via natural or manmade sources. Over a range of industrial pollutents, the nitrophenol (referred to as 4-NP) known as harmful industrial chemical for the environment and listed as a carcinogenic compound for human health. To keep this view the present manuscript describes the formation of highly crystalline silicon nanoparticles (Si-NPs) and applied for the electrochemical sensing of 4-NP. The Si-NPs exhibit numerous applications in various directions such as catalyst, solar cells, LEDs, batteries etc. The Si-NPs were formed from the physical approach with using argon-silane mixture in a gas chamber with impregnation of microwave plasma. The processed material was examined through various techniques such as X-ray diffraction pattern (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Fourier transform spectroscopy (FTIR). It reveals from the acquired analysis that the size of each NP is ~ 4 nm with good structural and chemical characteristics and applied as a film form against to check the sensing of 4-NP with three electrode system. The electrochemical studies were conducted through cyclic voltammetry (CV) in terms of their low to high concentration (7.8, 15.62, 31. 25, 62.25, 250, 500, 1000 μM in PBS), scan rate at variable potential was accessed from 5 to 100 mV with Si-NPs based electrode. The sustainability, reproducibility and efficacy of the formed sensor (Si-NPs/GCE) was examined in occurrence with 4-NP (62.25 μM) for seven consecutive cycles. Including to this, chronoamperometry (0 to 1500 s) and electrochemical impedance spectra (7.8–1000 μM in PBS) were also analyzed. On the basis of acquired results and discussion a probable mechanism was also described.

Ubiquity of Fourier transformation in optical sciences.

Abstract: Fourier transformation is an important conceptual as well as computational tool in the arsenal of every practitioner of physical and mathematical sciences. I discuss some of its applications in optical science and engineering to provide a broad perspective on the intimate relation between the physical and mathematical concepts that are elegantly interwoven within the theory of Fourier transforms.

Continuous phase-shifting holography.

Abstract: A scanning full-field interferometer is a key device in the optical scheme of digital hyperspectral hologram registration. Behind the theory of hyperspectral holography is Fourier transform spectroscopy, wherein the set of spectrally resolved complex amplitudes of the object’s hyperspectral field is obtained via the Fourier transform of a series of interferograms registered in incoherent radiation. Several established approaches in digital holography, based on discrete phase-shifting techniques as well as continuous phase modulation of the reference signal by a scanning mirror, are special cases of Fourier transform spectroscopy, where a coherent light source is used for hologram registration. The proposed algorithm was found to apply to processing holograms registered by various phase-shifting techniques and can give a greater signal-to-noise ratio.