Measurements In Spectral Range Research Articles

Design Approach for an Advanced Multi-Channel Pyrometer for Bulk Oven Processes

Industrial processes such as smelting and sintering require stable and precise temperature control of furnaces. To achieve this, accurate temperature measurements are required. Pyrometry allows for contact- less measurement of bulk materials and is particularly suitable for high temperature applications. One of the main influences on the accuracy of pyrometric measurements is the knowledge of the emissivity in the spectral measurement range. To reduce this dependence, two-color pyrometers or multi-color pyrometers can be used. With this in mind, the IRS is further developing their existing pyrometer technology by designing an advanced multi-channel pyrometer for bulk oven processes in a joint venture with Stange Elektronik GmbH and New Generation Kilns Grün GmbH. The design approach is explained here and the considered methods of achieving emissivity independent temperature measurements are examined.

Cryovacuum facilities for studying astrophysical ices

This work introduces a cryovacuum apparatus used to investigate substances under near-space conditions. This device allows one to study the refractive index, infrared spectra, and density of substances that are condensed from the vapor phase onto a cooled substrate at temperatures ranging from 11 K to 300 K. Concurrently, the ultimate pressure of 0.1 nTorr can be obtained in the vacuum chamber. The introduced setup utilizes FTIR spectroscopy with a spectral measurement range of 400–7800 cm−1 and laser interference needed to determine the important physical and optical parameters. Several experiments allow us to stress that the data acquired using this apparatus are quite similar to those obtained by other researchers. Because of the non-directional deposition of substances from the vapor phase, the ice formed closely resembles the ice formed in space. This makes the introduced setup particularly useful. It is possible to use the presented cryovacuum apparatus to interpret data acquired in the course of astrophysical observations, allowing a researcher to determine the properties of space objects.

Cryovacuum setup for optical studies of astrophysical ice

This paper presents a cryovacuum setup for the study of substances under near-space conditions. The setup makes it possible to study the infrared spectra, refractive index, and density of substances that are condensed from the vapor phase onto a cooled substrate in the temperature range from 11 to 300 K. At the same time, it is possible to obtain the ultimate pressure of 1 × 10–10 Torr in the vacuum chamber. The presented setup is based on FTIR spectroscopy (the spectral measurement range is 400–7800 cm–1) and laser interference, through which the important physical and optical parameters are determined. A number of experiments allow us to point out that the data obtained using this setup correlate well with the experiments of other authors. Due to the non-directional deposition of substances from the vapor phase, the ice formed resembles the one formed under cosmic conditions as closely as possible, which makes the presented setup particularly valuable. The presented cryovacuum setup can be used for the interpretation of data obtained during astrophysical observations, providing a means to determine the properties of cosmic objects.

Intracavity dynamics-based gain-assisted sensing with microtubule Raman microlaser

Microcavity lasers show excellent performance as a miniaturized microsensor in various applications. However, their relatively weak power may be easily submerged in system noises and disturbed by environmental fluctuations, rendering them ineffective at detecting small signals for precise sensing. To solve this problem, the laser differential frequency-shift feedback technique is demonstrated in a microtubule Raman laser to achieve the optical gain assistance. When the microlaser is frequency-shift-modulated and returns back to the resonator, the measurement signal can resonate with the laser relaxation oscillation and be significantly enhanced. The intracavity dynamics-based enhancement makes it effective for increasing intensity changes caused by analytes. Small signals that would otherwise be buried in system noises and go undetected can be more easily resolved. In addition, the microsensor reduces the spectral measurement range and offers a way to observe the fast dynamic response. Based on that, a measurement resolution of 50 nm nanoparticle detection limit and a refractive index noise-limited resolution of 8.18 × 10−7 refractive index unit (RIU) are demonstrated. The dynamic phase transition of thermosensitive hydrogel is further investigated as a validation of its rapid detection capability. Integrated with an inherent microfluidic channel, the proposed microsensor provides a direct interaction between analytes and probe light with ultrasmall sample consumption down to 50 pl. It is expected to boost the detection of weak signals in microlasers and enlighten the development of optofluidic microsensors in exploring diverse biochemical processes.

Theoretical analysis of a multi-grating-based cross-dispersed spatial heterodyne spectrometer.

This paper presents a multi-grating-based cross-dispersed spatial heterodyne spectrometer (MGCDSHS). The principle of generation of two-dimensional interferograms for two cases, where the light beam is diffracted by one sub-grating or two sub-gratings, is given and equations for the interferogram parameters in these two cases are derived. An instrument design with numerical simulations is presented that demonstrates the spectrometer's ability to simultaneously record separate interferograms corresponding to different spectral features with high resolution over a broad spectral range. The design solves the mutual interference problem caused by overlapping of the interferograms, and also provides the high spectral resolution and broad spectral measurement range that cannot be achieved using conventional SHSs. Additionally, by introducing cylindrical lens groups, the MGCDSHS solves the throughput loss and light intensity reduction problems caused by direct use of multi-gratings. The MGCDSHS is compact, highly stable, and high-throughput. These advantages make the MGCDSHS suitable for high-sensitivity, high-resolution, and broadband spectral measurements.

Accuracy analysis of the refractive index measurements by modifed prism methods

Goniometric methods of measuring the refractive index of optically transparent materials based on the refraction of light by a triangular prism are considered. Modified method of the minimum deviation and 3 modified constant deviation methods are considered, which allows determining the refractive index of triangular prisms with unknown apex angles. According to modified methods, the angles of light deviation by a prism are measured with goniometer, and the refractive index of the material and the prism angles are determined from solving the systems of equations. Thus, there is no need for preliminary measurement of the prism angles, which requires the use of special autocollimation goniometers. In addition, the modified methods do not use radiation reflected from the faces of the prism, which makes it possible to extend the spectral range of measurement of the refractive index to the infrared and ultraviolet regions. A comparative accuracy analysis of the considered methods for a prism with a refractive index of 1.5 and an angle of 60° as example is carried out. It is shown that the modified methods can be used for high-precision measurements of the refractive index in cases if the apex angles of the prism are unknown or their measurement is associated with technical difficulties. The considered methods can be used to measure the refractive index of triangular prisms made of optically transparent materials, as well as liquids poured into hollow prisms with plane-parallel transparent windows. The practical implementation of such a methods can be useful in the optical, chemical and food industries to control the composition and properties of optically transparent substances.

Design Approach for an Advanced Multi-Channel Pyrometer for Bulk Oven Processes

Industrial processes such as smelting and sintering require stable and precise temperature control of furnaces. To achieve this, accurate temperature measurements are required. Pyrometry allows for contact-less measurement of bulk materials and is particularly suitable for high temperature applications. One of the main influences on the accuracy of pyrometric measurements is the knowledge of the emissivity in the spectral measurement range. To reduce this dependence, two-color pyrometers or multi-color pyrometers can be used. With this in mind, the IRS is further developing their existing pyrometer technology by designing an advanced multi-channel pyrometer for bulk oven processes in a joint venture with Stange Elektronik GmbH and New Generation Kilns Grün GmbH. The design process is explained here and the different methods of achieving emissivity independence are examined.

Sagnac interferometer-based optical fiber strain sensor with exceeding free spectral measurement range and high sensitivity

Sagnac interferometer-based sensors have shown high sensitivity, but limited measurement range due to the free spectral range (FSR) limitation especially the higher the sensitivity. In this paper, we designed an optical fiber Sagnac interferometer with a polarization maintaining fiber (PMF) and a fiber Bragg grating (FBG) in the loop. The strain sensing performance was experimentally conducted. The PMF in the Sagnac interferometer showed a high strain measurement sensitivity with a limited measurement range due to the FSR. On the contrary, FBG in the Sagnac interferometer showed a low strain sensitivity but a large measurement range. By combining the PMF and FBG in a Sagnac interferometer, a high strain sensitivity of about 17.08 pm/µε with a large measurement range of 0–5187 µε was experimentally achieved. The method used in this paper can also be utilized to expand the sensing range in other interferometers. The proposed PMF and FBG constructed Sagnac interferometer shows the merits of simple structure, high sensitivity, and large measurement range, which make it a competitive candidate in strain monitoring.

Research on two-dimensional laser warning integrated detection technology

Laser weapons are playing an increasingly important role in modern warfare. To address the growing laser threat, it is necessary to study high-performance two-dimensional laser warning integrated detection technology to achieve simultaneous measurement of two-dimensional directional angle, wavelength and pulse width of incoming laser. This is of great importance for rapid response to security threats. To this end, the paper investigates a two-dimensional laser warning integrated detection system. The measurement principle of the system is as follows: under the condition that the optical system is known, the incidence angle and wavelength of the incoming laser can be judged by the position of the zero-level and first-level diffraction spots, and the mathematical relationship is theoretically derived, so that the principle of laser pulse width measurement based on time-to-digital conversion can be analyzed. For this purpose, firstly, the pulsed laser detection system was designed, the photoelectric conversion of the pulsed laser signal and the time interval measurement were completed, and the pulse width measurement and control unit were experimentally verified. Secondly, the imaging control system of the surface array detector was designed and the imaging effect was verified, and the spot images of lasers with different central wavelengths incident from different angles were collected and the extracted spot center coordinate data were analyzed. Thirdly, the assembly and testing of the two-dimensional laser warning integrated detection system were completed, and the measured wavelength, azimuth, pitch angle and pulse width multi-parameters were tested, and the measurement results were analyzed. The test results show that the system has an azimuth angle of 95°, a pitch angle of 75°, an angular measurement resolution of ≤ 0.5°, a spectral measurement range of 400–1700 nm, and a minimum measurement pulse width of 5 ns, and the two-dimensional laser warning integrated detection system can meet the practical application requirements.

Dynamic spectroscopic characterization for fast spectral variations based on dual asynchronous undersampling with triple optical frequency combs

A dynamic spectroscopic characterization scheme for fast spectral variations based on dual asynchronous undersampling with triple optical frequency combs is proposed and demonstrated here. The tri-comb scheme leverages two of the combs to simultaneously sample the fast spectral variations applied to the third comb. The repetition rate differences for both pairs of combs are relatively small, in order to maintain sufficiently large spectral measurement ranges. The corresponding sampling rates could be much slower than a fast time-varying spectral modulation to be measured. Nevertheless, despite of the frequency ambiguity in the undersampled dual-comb results, it is shown that it is possible to identify the original frequency of spectral variations based on the difference in the undersampled frequency domain information. Experimental results show that our scheme can increase the frequency demodulation range by at least two orders of magnitude while retaining the accuracy and spectral measurement range of similar DCS schemes. Demonstration based on a tri-comb mode-locked fiber laser is carried out to measure the dynamic spectral response from a fiber Bragg grating (FBG), to which up to 110 kHz of vibration is applied. This scheme could further extend the capability of dual-comb spectroscopic techniques, and it also illustrates the potential of the low-complexity multi-comb laser source for novel yet practical applications.

Колебательная спектроскопия тонких пленок конденсатов смеси этанола с инертным газом

It is known that by changing the concentration in an inert medium, it is possible to form clusters of various sizes of any substance by condensing them on a cold substrate from the gas phase. Traditionally, such systems are presented by molecular cryocrystals. This paper demonstrates the results of IR spectro­metric studies of cryovacuum condensates of ethanol mixture with nitrogen. The main task of this study is to explain the complex, most often, ambiguous behavior of thin films of ethanol cryovacuum conden­sates in the process of its co­condensation with nitrogen. For this purpose, vibrational spectroscopy of cryodeposited thin films of “ethanol in nitrogen” mixtures in various concentration ratios was performed. The objects of research are thin films of cryocondensates of ethanol mixture with inert gas (N2). The sam­ples were condensed at the temperature T = 16 K. The pressure of the gas phase of the mixture during cryocondensation was kept at P = 10­5 Torr. The range of ethanol concentrations in the mixtures varied from 3% to 90%. The spectral range of measurements was considered in 400­-4200 1/cm. It is assumed that the change in the concentration of ethanol in the mixture leads to the formation of various cluster compositions of ethanol molecules dissolved in an inert medium.

Influence of Atmosphere on Calibration of Radiation Thermometers.

Current process of calibrating radiation thermometers, including thermal imagers, relies on measurement comparison with the temperature of a black body at a set distance. Over time, errors have been detected in calibrations of some radiation thermometers, which were correlated with moisture levels. In this study, effects of atmospheric air on thermal transmission were evaluated by the means of simulations using best available resources of the corresponding datasets. Sources of spectral transmissivity of air were listed, and transmissivity data was obtained from the HITRAN molecular absorption database. Transmissivity data of molecular species was compiled for usual atmospheric composition, including naturally occurring isotopologs. Final influence of spectral transmissivity was evaluated for spectral sensitivities of radiation thermometers in use, and total transmissivity and expected errors were presented for variable humidity and measured temperature. Results reveal that spectral range of measurements greatly influences susceptibility of instruments to atmospheric interference. In particular, great influence on measurements is evident for the high-temperature radiation pyrometer in the spectral range of 2–2.7 µm, which is in use in our laboratory as a traceable reference for high-temperature calibrations. Regarding the calibration process, a requirement arose for matching the humidity parameters during the temperature reference transfer to the lower tiers in the chain of traceability. Narrowing of the permitted range of humidity during the calibration, monitoring, and listing of atmospheric parameters in calibration certificates is necessary, for at least this thermometer and possibly for other thermometers as well.

Design of a multi-analyte resonant photonic platform for label-free biosensing

We have designed a multi-analyte biosensing platform based on a hybrid whispering gallery mode resonator to detect protein biomarkers, e.g. those allowing the early diagnosis of Alzheimer’s disease. Our proposed biosensor dependent on the hybrid mode naturally extends the capabilities of both plasmonic sensor and photonic sensor and thus performs better interrogation sensitivity. A multi-resonance of the hybrid mode could occur and the field intensity achieved its maximum value, thereby enabling a very strong light–matter interaction. The detection limit for bulk sensing reached a value of 2 × 10−5 RIU and that for surface sensing was at 0.6 pg mm−2. Our novel configuration has an advantage over the conventional plasmonic-waveguide resonator with a similar cavity size (Q-factor < 500) because a wide range of spectral measurements (56 nm) and a high Q-factor (1300) could be achieved simultaneously. Thus, large refractive index shifts in the medium could be detected with high sensitivity. This biosensor, with a footprint of 625 μm2 for each resonator, is a good candidate for integration into lab-on-chip microsystems for large-scale screening of a wide range of protein biomarkers in high risk of developing disease.

Broadband dynamic spectrum characterization based on gating-assisted electro-optic time lens

A broadband real-time optical spectrum characterization technique is proposed based on a gating-assisted electro-optic time lens. Operating at the repetition rate of 10-MHz, a 10-dB spectral measurement range of more than 70-nm is achieved with a resolution of up to 42.5-pm in the near-infrared regime. To demonstrate its performance in applications, real-time spectral observation of broadband wavelength sweeping of a Fourier domain mode-locked laser and a 32.4-GHz optical frequency comb is presented. Furthermore, a detailed comparison between dispersive Fourier transform and the time lens based spectral analysis technique for frequency comb measurements is made from both simulation and experiment. With its broadband performance, this technique can provide widespread applications requiring real-time spectral analysis.

Spectral characterization of laser-accelerated protons with CR-39 nuclear track detector.

CR-39 nuclear track material is frequently used for the detection of protons accelerated in laser-plasma interactions. The measurement of track densities allows for determination of particle angular distributions, and information on the kinetic energy can be obtained by the use of passive absorbers. We present a precise method of measuring spectral distributions of laser-accelerated protons in a single etching and analysis process. We make use of a one-to-one relation between proton energy and track size and present a precise calibration based on monoenergetic particle beams. While this relation is limited to proton energies below 1 MeV, we show that the range of spectral measurements can be significantly extended by simultaneous use of absorbers of suitable thicknesses. Examples from laser-plasma interactions are presented, and quantitative results on proton energies and particle numbers are compared to those obtained from a time-of-flight detector. The spectrum end points of continuous energy distributions have been determined with both detector types and coincide within 50-100 keV.

Comparación de los productos de TSM L3 generados a partir de los sensores AVHRR y MODIS frente al Golfo San Jorge, Argentina

&lt;p&gt;Since the early 1980s, the AVHRR sensor on board the NOAA satellites has provided SST estimates to the scientific community in general. Towards the end of the 1990s, a new generation of radiometers was added, combining a wider range of spectral measurements with improvements in technology, such as the MODIS sensor on board the Terra and Aqua satellites. The development of this last sensor was based on the years of NOAA/AVHRR series. Understanding the relationship between products derived from different sensors is critical to the continuous long-term monitoring of any variable and the construction of continuous time series. The objective of this work was to make a comparison of the monthly SST values for the 2003-2006 period calculated from data from the NOAA/ AVHRR series versus Aqua-MODIS on a sector of the middle Argentina Continental shelf off the San Jorge Gulf. For both sensors, the isotherms show a similar distribution pattern in all months. Pearson’s correlation coefficient was high, both in the seasonal (&amp;gt; 0.9) and monthly (&amp;gt; 0.8) analyzes. The comparative analysis of the temperature estimated by both sensors shows that SST products are similar and can be used to analyze large and continuous time series.&lt;/p&gt;

Retrieval of microstructure parameters of coarse-mode aerosol using their regression relationships with spectral extinction of light in the IR

We explore how the microstructure parameters of atmospheric aerosol can be estimated from regression equations that describe their relationships with spectral measurements of the aerosol optical depth (AOD). Special attention is paid to the problem of estimating the volume concentration, total cross section, and mean radius of coarse aerosol particles. This problem is topical because of large errors arising when an insufficiently wide spectral range of measurements is available to retrieve these parameters using directly the AOD inversion. Estimates of the coefficients of simple and multiple linear regressions are presented together with the results of their use to retrieve the parameters of coarse-mode aerosol from data of sun photometer measurements in Tomsk.

Expanding the Dynamic Range of Digital Spectral Measurements

Solutions of the problem of expanding the dynamic range of spectral measurements of the parameters of low-level signals by means of artificial noising of the signals are found and evaluated.

Optical pyrometry measurement on oxidized Zircaloy-4 cladding

In order to improve the safety of nuclear power plant, loss-of-coolant accident experiments are implemented in research reactor. In this framework, we develop an optical pyrometry device to measure surface temperature (700-1200°C) of Zircaloy cladding without contact. The whole set-up of the simplified device (under air, without radiation) and the measurement procedure including data treatment based on bichromatic pyrometry are presented, as well as results for various temperature levels. Temperature retrieval based on the hypothesis of emissivity ratio equal to a constant, is scanned over a large wavelength range. A rather constant surface temperature is obtained on the spectral range of measurement, confirming the relevancy of emissivity hypothesis. Differences between this non-contact temperature measurement and a complementary thermocouple temperature measurement are also discussed.

Ultrahigh-Resolution Optical Vector Analysis Based on Optical Single-Sideband Modulation

Knowing magnitude, phase, and polarization responses is of great importance for fabrication and application of optical devices. A large variety of parameters such as insertion loss, dispersion, group delay, polarization-dependent loss, and polarization mode dispersion can be obtained based on these responses. Conventional approaches achieve the optical spectral responses by sweeping the wavelength of a laser source. Restricted by the low-wavelength accuracy and poor wavelength stability of the wavelength-swept laser source, the resolution of the optical vector analyzers (OVAs) are usually poor (>1.6 pm). To achieve ultrahigh resolution measurement, an OVA based on optical single-sideband (OSSB) modulation has been proposed and developed, which potentially has a sub-Hz resolution. However, electrical-to-optical and optical-to-electrical conversions are required to implement the electrical frequency sweeping and to detect the phase and magnitude information in the electrical domain, which limits the spectral measurement range, accuracy, and dynamic range. In the past decade, great efforts have been devoted to deal with these problems. In this paper, techniques for constructing high-performance OSSB-based OVAs are discussed with an emphasis on the system architectures and operation principles for improving the spectral measurement range, accuracy, and dynamic range of the measurement system. Possible future research directions are also discussed.