Sensitivity analysis of differential absorption lidar measurements in the mid-infrared region

Nonlinear upconverted thermal emission through difference frequency generation

Thermal radiation management is of critical importance in energy, sensing, and heat transfer. According to Planck's law, objects at room temperature predominantly emit thermal radiation within the mid- and far-infrared bands. Here, we demonstrated the upconversion of the mid- and far-infrared thermal radiation emitted by second-order nonlinear material to the easily-detectable visible band through a difference frequency process. This nonlinear broad-spectrum upconversion is facilitated by the random quasi-phase-matching technique in the nanoparticle system. Furthermore, we show the temperature measurement of thermal spots using such nonlinear thermal radiation. This scheme paves the way for applications in thermal management and sensing.

Simulation and analysis of the CO2 range-resolved differential absorption lidar system at 2 μm

The range-resolved differential absorption lidar is a high-precision device to measure the concentration of carbon dioxide. This paper provides a system-wide theoretical analysis method for the performance analysis and parameter optimization of the lidar system using the given parameter range. The scattered echo signal, signal-to-noise ratio, and detection sensitivity were simulated by setting assumed parameters with the HITRAN 2020 database and the US 1976 standard atmosphere model to analyze the detection distance and concentration resolution of the lidar system. The effects of the laser energy, repetition frequency, and photodetector noise were also discussed. The wavelength selection near the absorption line is critical because it controls the height region of the highest sensitivity and the demands on frequency stability. Recommendations for the selection of absorption lines are provided in this paper. A quantitative analysis of each error source provided reasonable error ranges.

All-fiber multifunction differential absorption CO2 lidar integrating single-photon and coherent detection

This study demonstrates a differential absorption lidar (DIAL) for CO2 that integrates both single-photon direct detection and coherent detection. Based on all-fiber 1572 nm wavelength devices, this compact lidar achieves detection of CO2 concentration, wind field, and single photon aerosol backscattering signal. First, by comparing DIAL with VAISALA-GMP343, the concentration deviation between the two devices is less than 5 ppm, proving the accuracy of the DIAL. Second, through the scanning detection experiment in Chaohu Lake, Hefei, not only the CO2 concentration between single-photon detection and coherent detection but also the wind field was obtained, proving the multifunctionality and stability of the DIAL. Benefiting from the advantages of combined the two detection methods, single photon detection offers 3-km CO2 and aerosol backscattering signals; coherent detection offers a 360-m shorter blind zone and wind field. This DIAL can achieve monitoring of CO2 flux and sudden emissions, which can effectively compensate for the shortages of in-situ sensors and spaceborne systems.

Effect of magnetic field-assisted fermentation on the in vitro protein digestibility and molecular structure of rapeseed meal

BACKGROUND

There has been a significant growth in demand for plant-derived protein, and this has been accompanied by an increasing need for sustainable animal-feed options. The aim of this study was to investigate the effect of magnetic field-assisted solid fermentation (MSSF) on the in vitro protein digestibility (IVPD) and functional and structural characteristics of rapeseed meal (RSM) with a mutant strain of Bacillus subtilis.

RESULTS

Our investigation demonstrated that the MSSF nitrogen release rate reached 86.3% after 96 h of fermentation. The soluble protein and peptide content in magnetic field feremented rapeseed meal reached 29.34 and 34.49 mg mL-1 after simulated gastric digestion, and the content of soluble protein and peptide in MF-FRSM reached 61.81 and 69.85 mg mL-1 after simulated gastrointestinal digestion, which significantly increased (p > 0.05) compared with the fermented rapeseed meal (FRSM). Studies of different microstructures - using scanning electron microscopy (SEM) and atomic force microscopy (AFM) - and protein secondary structures have shown that the decline in intermolecular or intramolecular cross-linking leads to the relative dispersion of proteins and improves the rate of nitrogen release. The smaller number of disulfide bonds and conformational alterations suggests that the IVPD of RSM was improved.

CONCLUSIONS

Magnetic field-assisted solid fermentation can be applied to enhance the nutritional and protein digestibility of FRSM. © 2024 Society of Chemical Industry.

Optimization of ultrasound-assisted cellulase degradation method on the extraction of mulberry leaf protein and its effect on the functional characteristics

The mulberry leaf protein extracted by ultrasound-assisted cellulase degradation (UACD) method was optimized with the protein dissolution amount (PDA) as the index. The Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy of extracted mulberry leaf protein were measured. The functional characteristics of protein extracted by the UACD method were evaluated. Results showed that the extraction condition was optimized and adjusted to the following parameters: pH value of 7.20, ultrasound temperature of 35.00 °C, enzyme dosage of 4.20% and ultrasound time of 10.00 min. Under these optimized conditions, the experimental verification value of PDA was 13.87 mg/mL, which was approaching to the predicted value of 13.54 mg/mL. The analysis results of FTIR showed that after extraction by the UACD method, the mulberry leaf protein with the vibrational peak of ester carbonyl (C = O) absorption peak (1734.66 cm-1) disappeared. The α-helix content of protein extracted by the UACD decreased by 8.13%, and the β-turn and random coil content of protein increased by 20.22% and 18.79%, respectively, compared to that of the blank. The microstructure of mulberry leaf protein showed that the UACD method could break the dense structure of protein raw materials, reduce the average size of proteins and increase the specific surface area and roughness of proteins. According to the results of functional characteristics, the mulberry leaf protein extracted by the UACD method presented the highest enzymolysis properties and solubility, which was beneficial for the application in the food industry. In conclusion, the UACD method was a very effective way to extract protein from mulberry leaf.

Performance evaluation of InGaAs/InP single-photon avalanche diodes based on fitting of dark current

We analyzed the dark current characteristics of InGaAs/InP single-photon avalanche diodes (SPADs) at different bias voltages and developed a method to evaluate SPAD material quality. We performed dark current and dark count experiments on two sample device groups. By sub-area fitting dark current experimental data, we obtained the material parameters for the two groups. The difference in the parameters between the two groups is attributed to the difference in the cavity temperatures used for epitaxial growth. Finally, we calculated the dark count probability of the two groups and validated the effectiveness of our method by comparing the calculated and experimental values. The evaluation method contributes to continuous improvements in the material quality of SPADs.

Photon-counting distributed free-space spectroscopy

Spectroscopy is a well-established nonintrusive tool that has played an important role in identifying and quantifying substances, from quantum descriptions to chemical and biomedical diagnostics. Challenges exist in accurate spectrum analysis in free space, which hinders us from understanding the composition of multiple gases and the chemical processes in the atmosphere. A photon-counting distributed free-space spectroscopy is proposed and demonstrated using lidar technique, incorporating a comb-referenced frequency-scanning laser and a superconducting nanowire single-photon detector. It is suitable for remote spectrum analysis with a range resolution over a wide band. As an example, a continuous field experiment is carried out over 72 h to obtain the spectra of carbon dioxide (CO2) and semi-heavy water (HDO, isotopic water vapor) in 6 km, with a range resolution of 60 m and a time resolution of 10 min. Compared to the methods that obtain only column-integrated spectra over kilometer-scale, the range resolution is improved by 2-3 orders of magnitude in this work. The CO2 and HDO concentrations are retrieved from the spectra acquired with uncertainties as low as ±1.2% and ±14.3%, respectively. This method holds much promise for increasing knowledge of atmospheric environment and chemistry researches, especially in terms of the evolution of complex molecular spectra in open areas.

Recent Advances in High Speed Photodetectors for eSWIR/MWIR/LWIR Applications

High speed photodetectors operating at a telecommunication band (from 1260 to 1625 nm) have been well studied with the development of an optical fiber communication system. Recent innovations of photonic systems have raised new requirements on the bandwidth of photodetectors with cutoff wavelengths from extended short wavelength infrared (eSWIR) to long wavelength infrared (LWIR). However, the frequency response performance of photodetectors in these longer wavelength bands is less studied, and the performances of the current high-speed photodetectors in these bands are still not comparable with those in the telecommunication band. In this paper, technical routes to achieve high response speed performance of photodetectors in the extended short wavelength infrared/mid wavelength infrared/long wavelength infrared (eSWIR/MWIR/LWIR) band are discussed, and the state-of-the-art performances are reviewed.

Standoff Chemical Detection Using Laser Absorption Spectroscopy: A Review

Remote chemical detection in the atmosphere or some specific space has always been of great interest in many applications for environmental protection and safety. Laser absorption spectroscopy (LAS) is a highly desirable technology, benefiting from high measurement sensitivity, improved spectral selectivity or resolution, fast response and capability of good spatial resolution, multi-species and standoff detection with a non-cooperative target. Numerous LAS-based standoff detection techniques have seen rapid development recently and are reviewed herein, including differential absorption LiDAR, tunable laser absorption spectroscopy, laser photoacoustic spectroscopy, dual comb spectroscopy, laser heterodyne radiometry and active coherent laser absorption spectroscopy. An update of the current status of these various methods is presented, covering their principles, system compositions, features, developments and applications for standoff chemical detection over the last decade. In addition, a performance comparison together with the challenges and opportunities analysis is presented that describes the broad LAS-based techniques within the framework of remote sensing research and their directions of development for meeting potential practical use.

Localized enzymolysis and sonochemically modified sunflower protein: Physical, functional and structure attributes

Impacts of localized enzymolysis and sonication on physical, techno-functional, and structure attributes of sunflower meal protein (SMP) and its hydrolysate (SMPH) were studied. SMP was subjected to enzymolysis (using alcalase) to prepare SMPH with various degrees of hydrolysis (6-24% DH). Enzymolysis decreased colour lightness, turbidity, and particle size of unsonicated and sonicated SMP, while it increased the absolute values of zeta potential (P < 0.05). Sonication improved oil absorption capacity and dispersibility over unsonicated samples. Contrarily, sonicated preparations showed a decrease in water holding capacity. Intrinsic fluorescence and FTIR spectral analyses suggested that SMPH had more movable/flexible secondary structures than SMP. Moreover, the changes in sulfhydryl clusters and disulfide linkages following sonication demonstrated limited unfolding of SMP and SMPH structure and decrease in intermolecular interactions. SDS-PAGE profile exhibited significant reduction in molecular weight (MW) of sonicated SMP, whereas did not display differences between unsonicated and sonicated SMPH. From further MW analysis, SMPH was categorized with high proportion of small-sized peptides ≤ 3 kDa fractions, which increased from 78.64 to 93.01% (control) and from 82.3 to 93.88% (sonication) with enzymolysis (6-24DH). Localized enzymolysis and sonication can be utilised to modify the physical and conformational attributes of SMP and SMPH, which could enhance their functionalities and broaden the utilisation area in food industry.

Narrowband, tunable, infrared radiation by parametric amplification of a chirped backward-wave OPO signal

The strict momentum conservation constraints for backward-wave optical parametric oscillators (BWOPOs) gives an inherently narrowband backward-generated wave, even with broadband pumping. Unfortunately, the limited tuning range of this wave restricts potential applications. Here we demonstrate a method to circumvent this restriction and increase the tuning range by more than one order of magnitude. A linearly chirped pump modulation is transferred to the forward-generated BWOPO wave, which is then mixed with an identically chirped pump in a conventional optical parametric amplifier to obtain narrowband (38 GHz), broadly tunable, infrared radiation around 1.86 µm, with an output energy of 19 µJ.

GeSn lateral p-i-n photodetector on insulating substrate

We report the first experimental demonstration of germanium-tin (GeSn) lateral p-i-n photodetector on a novel GeSn-on-insulator (GeSnOI) substrate. The GeSnOI is formed by direct wafer bonding and layer transfer technique, which is promising for large-scale integration of nano-electronics and photonics devices. The fabricated GeSnOI photodetector shows well-behaved diode characteristics with high I_on/I_off ratio of ~4 orders of magnitude (at ± 1 V) at room temperature. A cutoff detection beyond 2 µm with photo responsivity (R_op) of 0.016 A/W was achieved at the wavelength (λ) of 2004 nm.

Effects of ultrasound-assisted α-amylase degradation treatment with multiple modes on the extraction of rice protein

The effects of ultrasound-assisted α-amylase degradation (UAD) treatment with multiple modes on the extraction of rice protein (RP) from rice dreg powder were studied. The results showed that UAD treatment increased protein extraction rate significantly (p<0.05) compared to that of α-amylase degradation treatment and control. Among all the ultrasound mode treatments researched in this paper, sequential frequency ultrasound treatment presented higher protein extraction rate compared to that of simultaneous or single frequency ultrasound treatment. The highest protein extraction rate was obtained under 20/35kHz of sequential frequency UAD treatment with the protein extraction rate of 89.58% and protein purity of 92.99%. The test and analysis of fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, starch content, non-protein nitrogen content, SH and SS content, surface hydrophobicity, amino acids content and proteins characteristics were studied to reveal the mechanism of UAD on the protein extraction effect. After treated with UAD, the starch-protein agglomerates disintegrated completely, moreover, protein advanced structure was changed to some extent and the disulfide bond was partially broken, but the main chain structure (peptide chain), specificity of protein and amino acid composition were not obviously changed. Consequently, the structure modified RP extracted by UAD treatment presented higher solubility, emulsifying activity and foaming capacity, which was beneficial for the application of RP. In conclusion, UAD treatment is an effective method for maximizing extraction rate, purity and modifying properties of extracted protein.

Evaluation of EDAR vehicle emissions remote sensing technology

Despite much work in recent years, vehicle emissions remain a significant contributor in many areas where air quality standards are under threat. Policy-makers are actively exploring options for next generation vehicle emission control and local fleet management policies, and new monitoring technologies to aid these activities. Therefore, we report here on findings from two separate but complementary blind evaluation studies of one new-to-market real-world monitoring option, HEAT LLC's Emission Detection And Reporting system or EDAR, an above-road open path instrument that uses Differential Absorption LIDAR to provide a highly sensitive and selective measure of passing vehicle emissions. The first study, by Colorado Department of Public Health and Environment and Eastern Research Group, was a simulated exhaust gas test exercise used to investigate the instrumental accuracy of the EDAR. Here, CO, NO, CH₄ and C₃H₈ measurements were found to exhibit high linearity, low bias, and low drift over a wide range of concentrations and vehicle speeds. Instrument accuracy was high (R² 0.996 for CO, 0.998 for NO; 0.983 for CH₄; and 0.976 for C₃H₈) and detection limits were 50 to 100ppm for CO, 10 to 30ppm for NO, 15 to 35ppmC for CH₄, and, depending on vehicle speed, 100 to 400ppmC₃ for C₃H₈. The second study, by the Universities of Birmingham and Leeds and King's College London, used the comparison of EDAR, on-board Portable Emissions Measurement System (PEMS) and car chaser (SNIFFER) system measurements collected under real-world conditions to investigate in situ EDAR performance. Given the analytical challenges associated with aligning these very different measurements, the observed agreements (e.g. EDAR versus PEMS R² 0.92 for CO/CO₂; 0.97 for NO/CO₂; ca. 0.82 for NO₂/CO₂; and, 0.94 for PM/CO₂) were all highly encouraging and indicate that EDAR also provides a representative measure of vehicle emissions under real-world conditions.

Evaluation of a HgCdTe e-APD based detector for 2 μm CO2 DIAL application

Benefiting from close to ideal amplification properties (high gain, low dark current, and low excess noise factor), HgCdTe electron initiated avalanche photodiode (e-APD) technology exhibits state of the art sensitivity, thus being especially relevant for applications relying on low light level detection, such as LIDAR (Light Detection And Ranging). In addition, the tunable gap of the Hg_1-xCd_xTe alloy enables coverage of the short wavelength infrared (SWIR) and especially the 2 μm spectral range. For these two reasons, a HgCdTe e-APD based detector is a promising candidate for future differential absorption LIDAR missions targeting greenhouse gas absorption bands in SWIR. In this study, we report on the design and evaluation of such a HgCdTe e-APD based detector. The first part focuses on detector architecture and performance. Key figures of merit are: 2.8 μm cutoff wavelength, 200 μm diameter almost circular sensitive area, 185 K operating temperature (thermo-electric cooling), 22 APD gain (at 12 V reverse bias), 360  kΩ transimpedance gain, and 60  fWHz^-0.5 noise equivalent power (at 12 V reverse bias). The second part presents an analysis of atmospheric LIDAR signals obtained by mounting the HgCdTe e-APD based detector on the 2 μm differential absorption LIDAR developed at the Laboratoire de Météorologie Dynamique and dedicated to CO₂ monitoring. Discussion emphasizes random and systematic errors in LIDAR measurements regarding breadboard detector characterization. In particular, we investigate the influence of parasitic tails in detector impulse response on short range DIAL measurements.

Two-micron-wavelength germanium-tin photodiodes with low dark current and gigahertz bandwidth

We report the demonstration of a germanium-tin (Ge_0.9Sn_0.1) multiple-quantum-well p-i-n photodiode on silicon (Si) substrate for 2 μm-wavelength light detection. Characterization of the photodetector in both direct current (DC) and radio frequency (RF) regimes was performed. At the bias voltage of -1 V, a dark current density of 0.031 A/cm² is realized at room-temperature, which is among the lowest reported values for Ge_1-xSnx-on-Si p-i-n photodiodes. In addition, for the first time, a 3 dB bandwidth (f3dB) of around 1.2 GHz is achieved in Ge_1-xSnx photodetectors operating at 2 μm. It is anticipated that further device optimization would extend the f3dB to above 10 GHz.

1.9 octave supercontinuum generation in a As₂S₃ step-index fiber driven by mid-IR OPCPA

Using a 3.1-μm optical parametric chirped-pulse amplifier (OPCPA), we generate a supercontinuum in a step-index chalcogenide fiber that spans from 1.6 to 5.9 μm at the -20  dB points. The rugged step-index geometry allows for long-term operation, while the spectral bandwidth is limited by the transmission of the As2S3 fiber.

Time-dependent photon number discrimination of InGaAs/InP avalanche photodiode single-photon detector

We investigated the photon-number-resolving (PNR) performance of the InGaAs/InP avalanche photodiode (APD) as a function of the electric gate width and the photon arrival time. The optimal electric gate width was around 1 ns for PNR measurements in our experiment, which provided a PNR capability up to three photons per pulse when the detection efficiency was ~20%. And the dependence of the PNR performance on the arrival time of the photons showed that the photon number could be better resolved if the photons arrived on the rising edge of the electric gate than on the falling edge. In addition, we found that with the increase of the electric gate width, PNR performance got worse. The observation would be helpful for improving the PNR performance of the InGaAs/InP APD in the gated mode.

Lidar backscatter signal recovery from phototransistor systematic effect by deconvolution

Backscatter lidar detection systems have been designed and integrated at NASA Langley Research Center using IR heterojunction phototransistors. The design focused on maximizing the system signal-to-noise ratio rather than noise minimization. The detection systems have been validated using the Raman-shifted eye-safe aerosol lidar (REAL) at the National Center for Atmospheric Research. Incorporating such devices introduces some systematic effects in the form of blurring to the backscattered signals. Characterization of the detection system transfer function aided in recovering such effects by deconvolution. The transfer function was obtained by measuring and fitting the system impulse response using single-pole approximation. An iterative deconvolution algorithm was implemented in order to recover the system resolution, while maintaining high signal-to-noise ratio. Results indicated a full recovery of the lidar signal, with resolution matching avalanche photodiodes. Application of such a technique to atmospheric boundary and cloud layers data restores the range resolution, up to 60 m, and overcomes the blurring effects.

Photon-number-resolving detection at a telecommunications wavelength with a charge-integration photon detector

We demonstrate multiphoton discrimination at a telecommunications wavelength with the readout frequency of 40 Hz by a charge-integration photon detector (CIPD). The CIPD consists of an InGaAs pin photodiode and a GaAs junction field effect transistor as a preamplifier in a charge-integration circuit, which is cooled to 4.2 K to reduce thermal noise. The quantum efficiency of the CIPD (the detector itself) is 80% for 1530 nm light, and the readout noise is measured as 0.26 electrons at 40 Hz. We can construct Poisson distributions of photocarrier numbers with distinct peaks at each photocarrier number, corresponding to a signal-to-noise ratio of about 3.

Sensitivity studies for space-based measurement of atmospheric total column carbon dioxide by reflected sunlight

The feasibility of making space-based carbon dioxide (CO2) measurements for global and regional carbon-cycle studies is explored. With the proposed detection method, we use absorption of reflected sunlight near 1.58 microm. The results indicate that the small (degrees 1%) changes in CO2 near the Earth's surface are detectable provided that an adequate sensor signal-to-noise ratio and spectral resolution are achievable. Modification of the sunlight path by scattering of aerosols and cirrus clouds could, however, lead to systematic errors in the CO2 column retrieval; therefore ancillary aerosol and cloud data are important to reduce errors. Precise measurement of surface pressure and good knowledge of the atmospheric temperature profile are also required.