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In recent years, the quasi-2D perovskite material ((PEA) 2 (CsPbBr3) n -1 PbBr 4 ) has exhibited outstanding optoelectronic performance and environmental stability due to its unique structure, presenting a broad range of potential applications. However, structural differences arising from varying values of " n " result in distinct nonlinear effects in perovskite materials, which have not been thoroughly investigated to date. We conducted a comparative analysis of the mode-locked characteristics of 2D and n = 3, 4, 5, and 6 quasi-2D perovskite materials within an Erbium-doped fiber laser (EDFL). All materials exhibited excellent saturable absorption effects. Besides, the superior performance of the n = 5 quasi-2D perovskite material, with an SNR of 72.59 dB, performed best in terms of the average power and single pulse energy. The five-layer quasi-2D perovskites offer a suitable bandgap, exciton binding energy, and moderate quantum confinement, leading to effective laser operation. Additionally, the optimal nonlinear absorption, refractive index, and thermal stability contribute to stable and high-power laser performance, while suppressing surface states and interface effects. Experimental results indicate that quasi-2D perovskite materials hold significant potential for applications in the realm of ultrafast optics.

DNP-NMR and EPR experiments that operate at or greater than L-band (i.e., ν 0 (e - ) = 1-2 GHz) are typically limited to maximum sample volumes of several hundred µL. These experiments rely on well-known resonator designs for DNP/EPR irradiation such as the loop-gap resonator and Alderman-Grant coil, where their maximum volumes limit further application to imaging experiments and high-throughput screening beyond L-band. Herein, we demonstrate a birdcage (BC) resonator design that can accommodate several mL of sample while operating around 1.5 GHz. The sample volume is maximized by using two identical BC resonators in a stacked configuration. Simulations are used to optimize the BC design and the performance is validated experimentally with liquid-state Overhauser-DNP-NMR experiments. This BC design exploits just the parasitic capacitance of conductive rings and features no fixed tuning capacitors. An enhancement of -77 is achieved on a 10 mM 4-Amino-TEMPO in H 2 O sample for a 5 mL sample volume. The associated sample heating is minimal due to the low-E-fields generated and the large sample mass with +3.4 K when driving 100 W for several seconds., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Published by Elsevier Inc.)

A rigorous TomoSAR imaging procedure is proposed to acquire high-resolution L-band images of a forest in a local area of interest. A focusing function is derived to relate the backscattered signals to the reflectivity function of the forest canopies without resorting to calibration. A forest voxel model is compiled to simulate different tree species, with the dielectric constant modeled with the Maxwell-Garnett mixing formula. Five different inverse methods are applied on two forest scenarios under three signal-to-noise ratios in the simulations to validate the efficacy of the proposed procedure. The dielectric-constant profile of trees can be used to monitor the moisture content of the forest. The use of a swarm of unmanned aerial vehicles (UAVs) is feasible to carry out TomoSAR imaging over a specific area to pinpoint potential spots of wildfire hazards.

The 3Cat-4 mission aims at demonstrating the capabilities of a CubeSat to perform Earth Observation (EO) by integrating a combined GNSS-R and Microwave Radiometer payload into a 1-Unit CubeSat. One of the greatest challenges is the design of an antenna that respects the 1-Unit CubeSat envelope while operating at the different frequency bands: Global Positioning System (GPS) L1 and Galileo E1 band (1575 MHz), GPS L2 band (1227 MHz), and the microwave radiometry band (1400-1427 MHz). Moreover, it requires between 8 and 12 dB of directivity depending on the band whilst providing at least 10 dB of front-to-back lobe ratio in L1 and L2 GPS bands. After a trade-off analysis on the type of antenna that could be used, a helix antenna was found to be the most suitable option to comply with the requirements, since it can be stowed during launch and deployed once in orbit. This article presents the antenna design from a radiation performance point of view starting with a theoretical analysis, then presenting the numerical simulations, the measurements in an Engineering Model (EM), and finally the final design and performance of the Flight Model (FM).

Two-dimensional (2D) materials have attracted extensive attention for use in fiber lasers for pulse generation due to their unique nonlinear optical properties. While 2D materials with tunable band gaps hold promise as versatile saturable absorber materials, their L-band (long-band) pulse generation capability remains challenging. Metal phosphorus trichalcogenides (MPX 3 ) have recently attracted the attention of researchers and shown potential for sub-band gap saturable absorption in the L-band due to their high diversity of chemical components and band structural complexity. Herein, high-quality MnPSe 3 is synthesized and exhibits broad-band linear and nonlinear absorption with the modulation depth and saturation intensity of 5.4% and 0.295 MW/cm 2 , respectively. Moreover, a stable passive pulse generation in the L-band is demonstrated in a fiber laser. The wavelengths of the passively pulsed laser at different pump powers are recorded, featuring a fixed central wavelength located at around 1602 nm with a maximum output power of 19.54 mW. This research promotes the realization of L-band pulsed lasers based on 2D materials, inspiring further exploration of the unique properties of the MPX 3 family.

This research proposes an inverted L-shaped patch antenna with a corner-truncated partial ground plane diagonally adjoined to a square branch for L-band applications. The adjoining square branch was used to perturb linear polarization for circular polarization, and the corner-truncated partial ground plane was utilized to enhance the axial ratio bandwidth (ARBW). Simulations were performed, an antenna prototype was fabricated, and experiments were carried out. The simulation and measured results were in good agreement. The proposed antenna could achieve an ARBW of 77.87% (1.09-2.48 GHz). The novelty of this research lies in the concurrent use of a square branch and a corner-truncated partial ground plane to realize wide ARBW in an L-band, rendering the technology suitable for satellite communication and navigation applications.

This article describes a novel digital L-band EPR spectrometer. The spectrometer uses direct digital detection with time-locked subsampling (TLSS). The device consists of a microwave bridge equipped with a microwave source based on direct digital synthesis (DDS) and a digital receiver. DDS technology combined with an ultra-low noise 1 GHz master clock allowed the development of a digitally controlled microwave source with exceptionally good phase noise characteristics. The obtained level of phase noise is as low as -140 dBc/Hz at 30.5 kHz from the carrier frequency of 1.15 GHz, which is important when registering the EPR dispersion signal. The receiver is equipped with a high-speed A/D converter that enables direct digitalization of the L-band microwave signal. The obtained discrete data are then buffered and averaged in a programmable logic FPGA device. Data packets from FPGA are transferred to a DSP microcontroller that correlates them with the appropriate reference signals. This detection algorithm requires time locking of the generator and the receiver, which is ensured by clocking both devices from the same reference source. This procedure allows the simultaneous detection of the absorption and dispersion signals at the magnetic field modulation frequency and at any of its harmonics. The software to control the spectrometer was designed in the LabView programming environment. The program also allows further data processing. To the best of our knowledge, the described spectrometer is one of the first full implementation of the direct digital detection technique which could replace conventional analog CW spectrometers that utilize magnetic field modulation. For an 11 µm aqueous TEMPOL solution, the new spectrometer obtained a S/N ratio greater than 160 for an EPR spectrum registered in 69 s., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Forest structure plays an important role in forest biomass inversion using synthetic aperture radar (SAR) backscatter. Synthetic aperture radar (SAR) sensors with long-wavelength have the potentiality to provide reliable and timely forest biomass inversion for their ability of deep penetration into the forest. L-band SAR backscatter shows useful for forest above-ground biomass (AGB) estimation. However, the way that forest structure mediating the biomass-backscatter affects the improvement of the related biomass estimation accuracy. In this paper, we have investigated L-band SAR backscatter sensitivity to forests with different mean canopy density, mean tree height and mean DBH (diameter at breast height) at the sub-compartment level. The forest species effects on their relationship were also considered in this study. The linear correlation coefficient R, non-linear correlation parameter, Maximal Information Coefficient (MIC), and the determination coefficient R 2 from linear function, Logarithmic function and Quadratic function were used in this study to analyze forest structural properties effects on L-band SAR backscatter. The HV channel, which is more sensitive than HH to forest structure parameters, was chosen as the representative of SAR backscatter. 6037 sub-compartment were involved in the analysis. Canopy density showed a great influence on L-band backscatter than mean forest height and DBH. All of the R between canopy density and L-band backscatter were greater than 0.7 during the forest growth cycle. The sensitivity of L-band backscatter to mean forest height depends on forest canopy density. When canopy density was lower than 0.4, R values between mean forest height are smaller than 0.5. In contrast, the values of R were greater than 0.8 if canopy density was higher than 0.4. The sensitivity SAR backscatter to DBH fluctuated with canopy density, but it only showed obvious sensitivity when canopy density equals to 0.6, where both the linear and non-liner correlation values are higher than others. However, their effects on L-bang HV backscatter are affected by forest species, the effects on three forest structural parameters depend on tree species., Competing Interests: The authors declare there are no competing interests., (©2020 Ji et al.)

Low-frequency electron paramagnetic resonance (EPR) spectra were obtained for the Co complex of ethylene diamine tetraacetic acid (CoEDTA). It was found that the cobalt hyperfine at g eff -mid is better resolved at a low frequency, L-band (1.37 GHz), and not resolved at X-band (9.631 GHz), which is the conventional frequency used for most spectra for metal complexes. Resolved cobalt hyperfine lines lead to additional EPR parameters like A -mid for cobalt and a more-accurate determination of g -mid. Resolved hyperfine lines in the L-band, but not the S-band, spectra were obtained at a concentration of 1 mM. Knowing these additional EPR parameters provides a means to better determine the electron density in the ground state orbital for each cobalt complex, as well as to determine differences upon a change of ligation. If zinc sites can be replaced by cobalt, the cobalt spectra for these sites will enhance the characterization of the zinc sites.

Radiometers operating at L-band (1.4 GHz) are used to retrieve sea surface salinity over ice-free oceans and have been used recently to study the cryosphere. One hindrance of their use in the high latitudes is the preponderance of mixed scenes, where seawater and sea ice are both present in the sensor's field of view (FOV). Accurately characterizing the scene is crucial for oceanographic and cryospheric applications. To that end, a sea ice fraction model, composed of passive microwave sea ice concentration retrievals and an instrument simulator that integrates radiative power coming from all around the antenna, is used. We investigate the model currently used operationally to derive the ice fraction affecting the Aquarius observations and show that it can be significantly improved. On the one hand, the current model tends to overestimate sea ice fraction in the marginal ice zone where observations are used for salinity retrievals. On the other hand, the current model underestimates ice fraction within the ice pack where observations are used to derive sea ice properties. For the northern hemisphere, we also find evidence of the sea ice type impact on L-band radiometric observations. We present a model to derive sea ice fractions that are in better agreement with Aquarius radiometric observations using the Advanced Microwave Scanning Radiometer 2 Bootstrap algorithm for sea ice concentration and using high-resolution integration over the sensor's FOV.

Molecular processes involved in photosystem II adaptation of woody species to diurnal changes in light and temperature conditions are still not well understood. Regarding this, here we investigated differences between young and mature leaves of common fig (Ficus carica L.) in photosynthetic performance as well as accumulation of the main photosynthetic proteins: light harvesting complex II, D1 protein and Rubisco large subunit. Investigated leaf types revealed different adjustment mechanisms to keep effective photosynthesis. Rather stable diurnal accumulation of light harvesting complex II in mature leaves enabled efficient excitation energy utilization (negative L-band) what triggered faster D1 protein degradation at high light. However, after photoinhibition, greater accumulation of D1 during the night enabled them faster recovery. So, the most photosynthetic parameters, as the maximum quantum yield for primary photochemistry, electron transport and overall photosynthetic efficiency in mature leaves successfully restored to their initial values at 1a.m. Reduced connectivity of light harvesting complexes II to its reaction centers (positive L-band) in young leaves increased dissipation of excess light causing less pressure to D1 and its slower degradation. Decreased electron transport in young leaves, due to reduced transfer beyond primary acceptor Q A - most probably additionally induced degradation of Rubisco large subunit what consequently led to the stronger decrease of overall photosynthetic efficiency in young leaves at noon., (Copyright © 2016 Elsevier GmbH. All rights reserved.)

The use of the reflected Global Navigation Satellite Systems' (GNSS) signals in Earth observation applications, referred to as GNSS reflectometry (GNSS-R), has been already studied for more than two decades. However, the estimation precision that can be achieved by GNSS-R sensors in some particular scenarios is still not fully understood yet. In an effort to partially fill this gap, in this paper, we compute the Cramér-Rao bound (CRB) for the specific case of static ground-based GNSS-R receivers and scenarios where the coherent component of the reflected signal is dominant. We compute the CRB for GNSS signals with different modulations, GPS L1 C/A and GPS L5 I/Q, which use binary phase-shift keying, and Galileo E1 B/C and E5, using the binary offset carrier. The CRB for these signals is evaluated as a function of the receiver bandwidth and different scenario parameters, such as the height of the receiver or the properties of the reflection surface. The CRB computation presented considers observation times of up to several tens of seconds, in which the satellite elevation angle observed changes significantly. Finally, the results obtained show the theoretical benefit of using modern GNSS signals with GNSS-R techniques using long observation times, such as the interference pattern technique., Competing Interests: The authors declare no conflict of interest.

Global Navigation Satellite System-Reflectometry (GNSS-R) has emerged as a remote sensing tool, which is complementary to traditional monostatic radars, for the retrieval of geophysical parameters related to surface properties. In the present paper, we describe a new polarimetric GNSS-R system, referred to as the GLObal navigation satellite system Reflectometry Instrument (GLORI), dedicated to the study of land surfaces (soil moisture, vegetation water content, forest biomass) and inland water bodies. This system was installed as a permanent payload on a French ATR42 research aircraft, from which simultaneous measurements can be carried out using other instruments, when required. Following initial laboratory qualifications, two airborne campaigns involving nine flights were performed in 2014 and 2015 in the Southwest of France, over various types of land cover, including agricultural fields and forests. Some of these flights were made concurrently with in situ ground truth campaigns. Various preliminary applications for the characterisation of agricultural and forest areas are presented. Initial analysis of the data shows that the performance of the GLORI instrument is well within specifications, with a cross-polarization isolation better than -15 dB at all elevations above 45°, a relative polarimetric calibration accuracy better than 0.5 dB, and an apparent reflectivity sensitivity better than -30 dB, thus demonstrating its strong potential for the retrieval of land surface characteristics.

The radicals in six 60 Co γ-irradiated solids: malonic acid, glycylglycine, 2,6 di-t-butyl 4-methyl phenol, L-alanine, dimethyl malonic acid, and 2-amino isobutyric acid, were studied by rapid scan electron paramagnetic resonance at L-band (1.04 GHz) using a customized Bruker Elexsys spectrometer and a locally-designed dielectric resonator. Sinusoidal scans with widths up to 18.2 mT were generated with the recently described coil driver and Litz wire coils. Power saturation curves showed that the rapid scan signals saturated at higher powers than did conventional continuous wave signals. The rapid scan data were deconvolved and background subtracted to obtain absorption spectra. For the same data acquisition time the signal-to-noise for the absorption spectra obtained in rapid scans were 23 to 37 times higher than for first-derivative spectra obtained by conventional continuous wave electron paramagnetic resonance.

Copper has many roles in biology that involve the change of coordination sphere and/or oxidation state of the copper ion. Consequently, the study of copper in heterogeneous environments is an important area in biophysics. EPR is a primary technique for the investigation of paramagnetic copper, which is usually the isolated Cu(II) ion, but sometimes as Cu(II) in different oxidation states of multitransition ion clusters. The gross geometry of the coordination environment of Cu(II) can often be determined from a simple inspection of the EPR spectrum, recorded in the traditional X-band frequency range (9-10 GHz). Identification and quantitation of the coordinating ligand atoms, however, is not so straightforward. In particular, analysis of the superhyperfine structure on the EPR spectrum, to determine the number of coordinated nitrogen atoms, is fraught with difficulty at X-band, despite the observation that the overwhelming number of EPR studies of Cu(II) in the literature have been carried out at X-band. Greater reliability has been demonstrated at S-band (3-4 GHz), using the low-field parallel (gz) features. However, analysis relies on clear identification of the outermost superhyperfine line, which has the lowest intensity of all the spectral features. Computer simulations have subsequently indicated that the much more intense perpendicular region of the spectrum can be reliably interpreted at L-band (2 GHz). The present work describes the development of L-band EPR of Cu(II) into a routine method that is applicable to biological samples., (© 2015 Elsevier Inc. All rights reserved.)

A method to identify and mitigate radio frequency interference (RFI) in microwave radiometry based on the use of a spectrum analyzer has been developed. This method has been tested with CAROLS L-band airborne radiometer data that are strongly corrupted by RFI. RFI is a major limiting factor in passive microwave remote sensing interpretation. Although the 1.400-1.427 GHz bandwidth is protected, RFI sources close to these frequencies are still capable of corrupting radiometric measurements. In order to reduce the detrimental effects of RFI on brightness temperature measurements, a new spectrum analyzer has been added to the CAROLS radiometer system. A post processing algorithm is proposed, based on selective filters within the useful bandwidth divided into sub-bands. Two discriminant analyses based on the computation of kurtosis and Euclidian distances have been compared evaluated and validated in order to accurately separate the RF interference from natural signals.