Time-resolved Spectrometer Research Articles

Design and characterization of the time-resolved opacity spectrometer (OpSpecTR) for the NIF iron opacity campaign.

A new time-resolved opacity spectrometer (OpSpecTR) is currently under development for the National Ignition Facility (NIF) opacity campaign. The spectrometer utilizes Icarus version 2 (IV2) hybridized complementary metal-oxide-semiconductor sensors to collect gated data at the time of the opacity transmission signal, unlocking the ability to collect higher-temperature measurements on NIF. Experimental conditions to achieve higher temperatures are feasible; however, backgrounds will dominate the data collected by the current time-integrating opacity spectrometer. The shortest available OpSpecTR integration time of ∼2ns is predicted to reduce self-emission and other late-time backgrounds by up to 80%. Initially, three Icarus sensors will be used to collect data in the self-emission, backlighter, and absorption regions of the transmission spectrum, with plans to upgrade to five Daedalus sensors in future implementations with integration times of ∼1.3ns. We present the details of the diagnostic design along with recent characterization results of the IV2 sensors.

Time-Resolved Fluorescence Spectroscopy of Blood, Plasma and Albumin as a Potential Diagnostic Tool for Acute Inflammation in COVID-19 Pneumonia Patients.

Fluorescence lifetime measurements of blood or plasma offer valuable insights into the microenvironment and molecular interactions of fluorophores, particularly concerning albumin. Neutrophil- and hypoxia-induced oxidative stress in COVID-19 pneumonia patients leads to hyperinflammation, various oxidative modifications of blood proteins, and potential alterations in the fluorescence lifetime of tryptophan-containing proteins, especially albumin. The objective of this study was to investigate the efficacy of time-resolved fluorescence spectroscopy of blood and plasma as a prompt diagnostic tool for the early diagnosis and severity assessment of COVID-19-associated pneumonia. This study examined a cohort of sixty COVID-19 patients with respiratory symptoms. To investigate whether oxidative stress is the underlying cause of the change in fluorescence lifetime, human serum albumin was treated with chloramine T. The time-resolved spectrometer Life Spec II (Edinburgh Instruments Ltd., Livingston, UK), equipped with a sub-nanosecond pulsed 280 nm diode, was used to measure the fluorescence lifetime of blood and plasma. The findings revealed a significant reduction in the fluorescence lifetime of blood (diluted 200 times) and plasma (diluted 20 times) at 360 nm in COVID-19 pneumonia patients compared with their respective values recorded six months post-infection and those of healthy individuals. Significant negative correlations were observed between the mean fluorescence lifetime of blood and plasma at 360 nm and several severity biomarkers and advanced oxidation protein products, while a positive correlation was found with albumin and the albumin-globulin ratio. The time-resolved fluorescence spectroscopy method demonstrates the potential to be used as a preliminary screening technique for identifying patients who are at risk of developing severe complications. Furthermore, the small amount of blood required for the measurements has the potential to enable a rapid fingerstick blood test.

Direct Observation of Photon Induced Giant Band Renormalization in 2D PdSe2 Dichalcogenide by Transient Absorption Spectroscopy.

Insight into fundamental light-matter interaction as well as underlying photo-physical processes is crucial for the development of novel optoelectronic devices. Palladium diselenide (PdSe2 ), an important representative of emerging 2D noble metal dichalcogenides, has gain considerable attention owing to its unique optical, physical, and chemical properties. In this study, 2D PdSe2 nanosheets (NSs) are prepared using the liquid-phase exfoliation method. A broadband carrier relaxation dynamics from visible to near-infrared bands are revealed using a time-resolved transient absorption spectrometer, giving results that indicate band filling and bandgap renormalization (BGR) effects in the 2D PdSe2 NSs. The observed blue-shift of the transient absorption spectra at the primary stage and the subsequent red-shift can be ascribed to this BGR effect. These findings reveal the many-body character of the 2D TMDs material and may hold keys for applications in the field of optoelectronics and ultrafast photonics.

Time-resolved investigation of nanometric cell membrane patches with a mid-infrared laser microscope

The proton pump Bacteriorhodopsin (BR) undergoes repeated photocycles including reversible conformational changes upon visible light illumination. Exploiting the sensitivity of infrared (IR) spectra to the conformation, we have determined the reaction kinetic parameters of the conductive intermediate M for the wild-type protein and for its slow mutant D96N during its photocycle. Time-resolved IR micro-spectroscopy using an in-house developed confocal laser microscope operating in the mid-IR is employed to record absorption changes of 10−4 at wavelengths λ1 = 6.08 μm and λ2 = 6.35 μm, assigned to backbone and retinal structural modifications, respectively. Protein samples were embedded in dried lipid bilayers deposited on ultraflat gold supports to enhance the surface field. The signals were analyzed according to a simplified photocycle model with only two dominant states: the dark-adapted state BR* and the intermediate M. We obtained the excitation and relaxation times of the intermediate M from exponential fits to the absorption change time traces. Our results constitute a first step towards future plasmonic-assisted nanoscale time-resolved mid-IR spectrometers for the characterization of bioelectronic and light-harvesting nanodevices based on BR.

3-D Raman Imaging Using Time-Resolving CMOS SPAD Line Sensor and 2-D Mapping

The capability of Raman imaging to produce 2D and 3D chemical presentations of samples has gained a lot of interest in different application fields. In this paper, we present a 3D chemical image reconstruction based on 2D scanning of a sample utilizing a time-resolved Raman spectrometer based on a CMOS single-photon avalanche diode (SPAD) line sensor. The 2D scanning data contains the lateral information (XY-plane) whereas the time-of-arrival data of the Raman photons measured by the sensor carries the axial information (i.e., depth information, Z-axis). The sensor is fabricated in 110-nm CMOS technology. It has 256-spectral channels and each channel has its own 7-bit on-chip time-to-digital converter (TDC) with an adjustable resolution from 25 ps to 65 ps. In addition to the 3D chemical reconstruction of the scanned sample, we have also shown the ability to retrieve depth profiling information of each scanned pixel such as the boundaries and middle points of any selected layer over the depth range of the scanned object by means of a single measurement for each scanned pixel. In addition, we have discussed the system components and the post-processing parameters that affect the depth profiling accuracy and the 3D reconstruction operation the most. Results showed that the instrument response function of the system and the time gate window width in a post-processing phase are playing the most important role in determining the axial (depth) accuracy. We believe that our system will enable a whole new class of Raman applications that will allow simultaneous 3D chemical geometric representation at the cm-level during Raman operations.

Highly Emissive Luminogens in Both Solution and Aggregate States

Highly Emissive Luminogens in Both Solution and Aggregate States

The Mortality Risk and Pulmonary Fibrosis Investigated by Time-Resolved Fluorescence Spectroscopy from Plasma in COVID-19 Patients.

A method of rapidly pointing out the risk of developing persistent pulmonary fibrosis from a sample of blood is extraordinarily needed for diagnosis, prediction of death, and post-infection prognosis assessment. Collagen scar formation has been found to play an important role in the lung remodeling following SARS-CoV-2 infection. For this reason, the concentration of collagen degradation products in plasma may reflect the process of lung remodeling and determine the extent of fibrosis. According to our previously published results of an in vitro study, an increase in the concentration of type III collagen degradation products in plasma resulted in a decrease in the fluorescence lifetime of plasma at a wavelength of 450 nm. The aim of this study was to use time-resolved fluorescence spectroscopy to assess pulmonary fibrosis, and to find out if the lifetime of plasma fluorescence is shortened in patients with COVID-19. The presented study is thus far the only one to explore the fluorescence lifetime of plasma in patients with COVID-19 and pulmonary fibrosis. The time-resolved spectrometer Life Spec II with the sub-nanosecond pulsed 360 nm EPLED® diode was used in order to measure the fluorescence lifetime of plasma. The survival analysis showed that COVID-19 mortality was associated with a decreased mean fluorescence lifetime of plasma. The AUC of mean fluorescence lifetime in predicting death was 0.853 (95% CI 0.735–0.972, p < 0.001) with a cut-off value of 7 ns, and with 62% sensitivity and 100% specificity. We observed a significant decrease in the mean fluorescence lifetime in COVID-19 non-survivors (p < 0.001), in bacterial pneumonia patients without COVID-19 (p < 0.001), and in patients diagnosed with idiopathic pulmonary fibrosis (p < 0.001), relative to healthy subjects. Furthermore, these results suggest that the development of pulmonary fibrosis may be a real and serious problem in former COVID-19 patients in the future. A reduction in the mean fluorescence lifetime of plasma was observed in many patients 6 months after discharge. On the basis of these data, it can be concluded that a decrease in the mean fluorescence lifetime of plasma at 450 nm may be a risk factor for mortality, and probably also for pulmonary fibrosis in hospitalized COVID-19 patients.

Additional Cover

The cover image is based on the Special Issue – Research Article Development of a highly stable picosecond time-resolved Raman spectrometer near Fourier-transform limit with a femtosecond light source by Tsukasa Tokita et al., https://doi.org/10.1002/jrs.6232.

Compressed sensing time-resolved spectrometer for quantification of light absorbers in turbid media.

Time-resolved (TR) spectroscopy is well-suited to address the challenges of quantifying light absorbers in highly scattering media such as living tissue; however, current TR spectrometers are either based on expensive array detectors or rely on wavelength scanning. Here, we introduce a TR spectrometer architecture based on compressed sensing (CS) and time-correlated single-photon counting. Using both CS and basis scanning, we demonstrate that-in homogeneous and two-layer tissue-mimicking phantoms made of Intralipid and Indocyanine Green-the CS method agrees with or outperforms uncompressed approaches. Further, we illustrate the superior depth sensitivity of TR spectroscopy and highlight the potential of the device to quantify absorption changes in deeper (>1 cm) tissue layers.

OrganiCam: a lightweight time-resolved laser-induced luminescence imager and Raman spectrometer for planetary organic material characterization.

OrganiCam is a laser-induced luminescence imager and spectrometer designed for standoff organic and biosignature detection on planetary bodies. OrganiCam uses a diffused laser beam (12° cone) to cover a large area at several meters distance and records luminescence on half of its intensified detector. The diffuser can be removed to record Raman and fluorescence spectra from a small spot from 2 m standoff distance. OrganiCam's small size and light weight makes it ideal for surveying organics on planetary surfaces. We have designed and built a brassboard version of the OrganiCam instrument and performed initial tests of the system.

Personal and area exposure assessment at a stainless steel fabrication facility: an evaluation of inhalable, time-resolved PM10, and bioavailable airborne metals

This study describes a comprehensive exposure assessment in a stainless steel welding facility, measuring personal inhalable PM and metals, time-resolved PM10 area metals, and the bioavailable fraction of area inhalable metals. Eighteen participants wore personal inhalable samplers for two, nonconsecutive shifts. Area inhalable samplers and a time-resolved PM10 X-ray fluorescence spectrometer were used in different work areas each sampling day. Inhalable and bioavailable metals were analyzed using inductively coupled plasma mass spectrometry (ICP-MS). Median exposures to chromium, nickel, and manganese across all measured shifts were 66 (range: 13–300) μg/m3, 29 (5.7–132) μg/m3, and 22 (1.5–119) μg/m3, respectively. Most exposure variation was seen between workers ( although cobalt and inhalable PM showed most variation within workers. Manganese was the most bioavailable metal from the inhalable size fraction (16 ± 3%), and chromium and nickel were 1.2 ± 0.08% and 2.6 ± 1.2% bioavailable, respectively. This comprehensive approach to welding-fume exposure assessment can allow for targeted approaches to controlling exposures based not only on individual measurements, but also on metal-specific measures and assessments of bioavailability.

Time-Resolved Raman Spectrometer With High Fluorescence Rejection Based on a CMOS SPAD Line Sensor and a 573-nm Pulsed Laser

A time-resolved Raman spectrometer is demonstrated based on a 256 × 8 single-photon avalanche diodes fabricated in CMOS technology (CMOS SPAD) line sensor and a 573-nm fiber-coupled diamond Raman laser delivering pulses with duration below 100-ps full-width at half-maximum (FWHM). The collected backscattered light from the sample is dispersed on the line sensor using a custom volume holographic grating having 1800 lines/mm. Efficient fluorescence rejection in the Raman measurements is achieved due to a combination of time gating on sub-100-ps time scale and a 573-nm excitation wavelength. To demonstrate the performance of the spectrometer, fluorescent oil samples were measured. For organic sesame seed oil having a continuous wave (CW) mode fluorescence-to-Raman ratio of 10.5 and a fluorescence lifetime of 2.7 ns, a signal-to-distortion value of 76.2 was achieved. For roasted sesame seed oil having a CW mode fluorescence-to-Raman ratio of 82 and a fluorescence lifetime of 2.2 ns, a signal-to-distortion value of 28.2 was achieved. In both cases, the fluorescence-to-Raman ratio was reduced by a factor of 24-25 owing to time gating. For organic oil, spectral distortion was dominated by dark counts, while for the more fluorescent roasted oil, the main source of spectral distortion was timing skew of the sensor. With the presented postprocessing techniques, the level of distortion could be reduced by 88%-89% for both samples. Compared with common 532-nm excitation, approximately 73% lower fluorescence-to-Raman ratio was observed for 573-nm excitation when analyzing the organic sesame seed oil.

A method for studying pico to microsecond time-resolved core-level spectroscopy used to investigate electron dynamics in quantum dots

Time-resolved photoelectron spectroscopy can give insights into carrier dynamics and offers the possibility of element and site-specific information through the measurements of core levels. In this paper, we demonstrate that this method can access electrons dynamics in PbS quantum dots over a wide time window spanning from pico- to microseconds in a single experiment carried out at the synchrotron facility BESSY II. The method is sensitive to small changes in core level positions. Fast measurements at low pump fluences are enabled by the use of a pump laser at a lower repetition frequency than the repetition frequency of the X-ray pulses used to probe the core level electrons: Through the use of a time-resolved spectrometer, time-dependent analysis of data from all synchrotron pulses is possible. Furthermore, by picosecond control of the pump laser arrival at the sample relative to the X-ray pulses, a time-resolution limited only by the length of the X-ray pulses is achieved. Using this method, we studied the charge dynamics in thin film samples of PbS quantum dots on n-type MgZnO substrates through time-resolved measurements of the Pb 5d core level. We found a time-resolved core level shift, which we could assign to electron injection and charge accumulation at the MgZnO/PbS quantum dots interface. This assignment was confirmed through the measurement of PbS films with different thicknesses. Our results therefore give insight into the magnitude of the photovoltage generated specifically at the MgZnO/PbS interface and into the timescale of charge transport and electron injection, as well as into the timescale of charge recombination at this interface. It is a unique feature of our method that the timescale of both these processes can be accessed in a single experiment and investigated for a specific interface.

Ground calibration and in-orbit performance of the time-resolved soft x-ray spectrometer on board XPNAV-1

The time-resolved soft x-ray spectrometer (TSXS) aboard on the X-ray Pulsar Navigation Test Satellite is an x-ray timing spectrometer covering the energy range of 0.5 to 10 keV. It is China’s first focusing x-ray telescope launched into space orbit. The optical system of TSXS is an x-ray grazing incidence focusing system with a field of view 15 arc min, which is nested with 4 parabolic mirrors with a focal length of 1150 mm. The focal plane detector of TSXS uses a silicon drift detector. From April to June 2016, ground calibration was carried out on TSXS, including the optical axis determination, calibration of energy linearity and energy resolution, calibration of time resolution and photon arrival time accuracy, and calibration of mirrors’ reflectivity. After the launch on November 10, 2016, the in-orbit calibration and performance verification of the telescope was carried out, including the optical axis determination, the performance of energy response, the performance of time accuracy, the calibration of effective area, and the evaluation of telescope sensitivity. After calibration and verification on the ground and in orbit, the photon energy measurement error of the telescope is better than 0.5% at energies above 1.5 keV, the energy resolution is better than 156 eV at 6.4 keV, the time resolution is <1 μs, the photon arrival time measurement accuracy is <302 ns, and the telescope in-orbit background is <4.16 ± 1.42 × 10 − 3 photons / s (0.5 to 3 keV, 40°N to 40°S, not including South Atlantic Anomaly). The telescope has an in-orbit observation sensitivity of 2.09 × 10 − 3 photons / cm2 / s / keV (0.5 to 3 keV, T = 1000 s, and nσ = 5).

Hypersonic impact flash characteristics of a long-rod projectile collision with a thin plate target

Impact flash occurs when objects collide at supersonic speeds and can be used for real-time damage assessment when weapons rely on kinetic energy to destroy targets. However, the mechanism of impact flash remains unclear. A series of impact flash experiments of flat-head long-rod projectiles impacting thin target plates were performed with a two-stage light gas gun. The impact flash spectra for 6061 aluminum at 1.3–3.2 km/s collision speeds were recorded with a high-speed camera, a photoelectric sensor, and a time-resolved spectrometer. The intensity of the impact flash exhibited a pulse characteristic with time. The intensity (I) increased with impact velocity (V0) according to I∝V0n , where n = 4.41 for V0 > 2 km/s. However, for V0 < 2 km/s, n = 2.21, and the intense flash duration is an order of magnitude less than that of higher V0. When V0 > 2 km/s, a continuous spectrum (thermal radiation background) was observed and increased in intensity with V0. However, for V0 < 2 km/s, only atomic line spectra were detected. There was no aluminum spectral lines for V0 < 2 km/s, which indicated that it had not been vaporized. The initial intense flash was emission from excited and ionized ambient gases near the impact surface, and had little relationship with shock temperature rise, indicating a new mechanism of impact flash.

Time-Resolved Laser-Flash Photolysis Faraday Rotation Spectrometer: A New Tool for Total OH Reactivity Measurement and Free Radical Kinetics Research.

The total OH reactivity (kOH') is an important parameter for quantitative assessment of the atmospheric oxidation capacity. Although laboratory measurement of kOH' has been achieved 20 years ago, the instruments required are often costly and complex. Long-term atmospheric observations remain challenging and elusive. In this work, a novel instrument combining laser-flash photolysis with a mid-infrared Faraday rotation spectrometer (LFP-FRS) has been developed for the measurement of kOH' and for studying gas phase free radical kinetics. The reactor is composed of a Herriott-type optical multipass cell, and OH radicals were generated by flash photolysis of ozone with a 266 nm pulsed Nd:YAG laser. The decay of the OH signal was directly measured with a time-resolved FRS spectrometer at 2.8 μm. The overlapping path length between the pump beam and probe beam was 25 m. High performance was achieved by subtracting the signals before and after flash photolysis to eliminate interferences caused by H2O absorption and background drift. The optimum precisions (1σ) of OH concentration and kOH' measurement were 4 × 106 molecules cm-3 and 0.09 s-1 over data acquisition times of 56 and 112 s, respectively. The performance of the system was evaluated by the reaction of OH with CO and NO. The measured rate coefficients (kOH+CO and kOH+NO) were in good agreement with values reported in the literature. The developed LFP-FRS provides a new, high precision, and highly selective tool for atmospheric chemistry research of OH radicals and other transient paramagnetic free radicals such as HO2 radicals.

Evidence and evolution of Criegee intermediates, hydroperoxides and secondary organic aerosols formed via ozonolysis of α-pinene.

α-Pinene, the most abundant monoterpene in the atmosphere, accounts for more than 50% of global monoterpene emission. Though its reaction with ozone has been generally perceived as a major source of secondary organic aerosols (SOAs), direct evidence of its reaction intermediates (RI) and their evolution remain lacking. Here we study the ozonolysis of α-pinene between 180 and 298 K using a long-path, temperature-variable aerosol cooling chamber coupled to a rapid-scan time-resolved Fourier transform infrared spectrometer. The spectroscopic signatures of large Criegee intermediates (CIs) and hydroperoxides (HPs) were found for the first time. The aerosol size evolution during the reaction was also measured. In contrast to a previous perception, we show that temperature plays a determinant role in the ozonolysis kinetics. Finally, we show that the formation of HPs is an energetically favorable pathway to dissipate CIs. This study provides new insights into the ozonolysis of α-pinene and its contribution to SOA formation.

Investigation of photo- and thermal isomerization pathways of azobenzene derivative in photostationary state generated by two-color excitation

The reaction pathways for photo- and thermal isomerization in the photostationary state of Sudan red 7B (SR7B), which has two azo groups in its molecule, were examined by a laboratory-designed two-dimensional millisecond time-resolved transient absorption spectrometer that utilizes two-color cw lasers (532 nm and 650 nm) as pump and a white light as probe. The temporal population behavior of four isomeric forms after the two-color pump lasers were simultaneously switched off was monitored in terms of transient absorption change with the time resolution of 50 ms. It was found that, in the photostationary state generated by the two-color pump scheme, the two-color two-step photoisomerization process and the multistep thermal isomerization processes occurred. The reaction rates of the thermal isomerization processes were also determined. Based on the results, we constructed a framework for the reaction pathway network in the photostationary state of SR7B under two-color cw excitation.

Pulsar-based navigation results: data processing of the x-ray pulsar navigation-I telescope

Pulsar-based navigation for spacecraft is a revolutionary technology that has been researched for several decades. To validate it, China launched a small experimental satellite, the x-ray pulsar navigation-I (XPNAV-1), whose main payload was the first Chinese on-orbit grazing incidence focusing x-ray telescope, called the time-resolved soft x-ray spectrometer (TSXS). XPNAV-1/TSXS observes the x-ray pulsar at the 0.5- to 10-keV band. Based on 85-day observation data of the pulsar B0531+21 (Crab), a ground pulsar-based navigation experiment is conducted. The pulsar timing is performed to determine Crab’s spin parameters at the x-ray band. A pulse phase estimation method is designed that eliminates the influence of the Doppler effect and generates ranging measurements from 25 observations. The ranging measurements are introduced as control points into the orbit propagation of XPNAV-1. The result indicates that, in nearly three months, by observing Crab only, XPNAV-1 can locate itself with an average navigation error of 38.4 km at the control points.

Optimising passivation shell thickness of single upconversion nanoparticles using a time-resolved spectrometer

Lanthanide-doped upconversion nanoparticles (UCNPs) are the most efficient multi-photon probe that can be used for deep tissue bio-imaging, fluorescence microscopy, and single molecule sensing applications. Passivating UCNPs with inert shell has been demonstrated to be an effective method to significantly enhance their brightness. However, this method also increases the overall size of the nanoparticles, which limited their cellular applications. Current reports to optimise the thickness of the shell are based on the spectrum measurement of ensembles of UCNPs, which are less quantitative. The characterisation of single UCNPs would be desirable, but is limited by the sensitivity of conventional spectrometers. We developed an optical filter-based spectrometer coupled to a laser scanning microscopy system and achieved a high degree of sensitivity—seven times more than the traditional amount. Through highly controlled syntheses of a range Yb3+ and Tm3+ doped UCNPs with different shell thickness, quantitative characterization of the emission intensity and lifetime on single UCNPs were comprehensively studied using a home-made optical system. We found that the optimal shell thickness was 6.3 nm. We further demonstrated that the system was sensitive enough to measure the time-resolved spectrum from a single UCNP, which is significantly useful for a comprehensive study of the energy transfer process of UCNPs.