A common approach to detecting weak signals or minute quantities involves leveraging the localized spectral features of resonant modes, whose sharper lines (i.e., high Q-factors) enhance transduction sensitivity. However, maximizing the Q-factor often introduces technical challenges in fabrication and design. In this work, we propose an alternative strategy to achieve sharper spectral features by using interference and nonlinearity, all while maintaining a constant dissipation rate. Using far-infrared thermomechanical detectors as a test case, we demonstrate that signal transduction along an engineered response curve slope effectively reduces the detector's noise equivalent power (NEP), achieving ∼ 30 pW / Hz NEP for electrical read-out, sub-THz detectors with an optimized absorbing layer.

Time-resolved ultrafast phenomena with hard X-ray radiation are key research areas for applications like pump-and-probe spectroscopy. The demand for higher performance drives advancements in detector technologies and multichannel acquisition techniques. This motivates our proposal for an innovative fully digital 3D (x-y-time) imager for hard X-rays. Key challenges in detector design include improving time resolution, spatial resolution (limited by the multipixel approach), and quantum efficiency, which is low for silicon detectors in the hard X-ray range. We propose using a Separate Absorption and Multiplication Avalanche PhotoDiode (SAM-APD) based on III-V semiconductors. GaAs-based alloys, with higher atomic number and mobility, offer significantly better efficiency and speed for hard X-ray absorption compared to silicon. Regarding acquisition systems, the shift towards multichannel methods and the need to minimize power and area per channel has led to the transition from traditional pixelated voltage-mode electronics to time-based acquisition systems, where both spatial (x and y) and timing information are linked to the detection event's time. By coupling a large-area GaAs SAM-APD (several mm in diameter) to two Cross Delay Lines (CDLs) and a 4 -channel 15 -ps precision FPGA-based Time-to-Digital Converter (TDC), we aim to achieve temporal and spatial resolutions of tens of picoseconds and hundreds of micrometers. This approach offers a powerful alternative to pixelated systems, requiring neither aggressive lithography nor one readout channel per pixel, using only four channels.

Since third-generation synchrotron radiation facilities are highly brilliant sources, the scattering of a partially coherent beam gives rise to strong interference effects. We present and discuss in this contribution the comparison of simulated and experimental diffraction patterns collected with an optical device made by two identical flat Micro Channel Plates (MCPs) illuminated by synchrotron radiation at different energies. The experimental patterns clearly show the increase of the density of the main peak with respect to those collected with a single flat MCP. Data demonstrate that the use of a device based on two MCPs is an ideal optical system to condense the primary radiation in a narrow intense central peak.

Elettra 2.0 will be a fourth generation storage ring light source replacing the existing Elettra synchrotron. This article illustrates design strategies, physical investigations and technical choices to meet multiple and sometimes conflicting requirements. These include to make Elettra 2.0 a fully transversely coherent source up to 0.5 keV-photon energy, diversify the type of experiments through a very broad range of photon energies, from infrared to hard x-rays, maximize the number of photon beamlines in excess of 2-times the machine periodicity, and be able to produce picosecond-long light pulses at MHz repetition rate without interference to the standard multi-bunch operation. Most recent advancements in beam physics, technical systems and installation plan are reported with some detail.

The increasing accessibility of cutting-edge photon sources, such as the latest generation of FreeElectron Lasers (FELs) and synchrotron facilities, has substantially broadened research horizons, particularly in the investigation of chemical and physical dynamics like time-of-fligth mass spectrometry. Consequently, there is a need for a new generation of precise and flexible timeresolved acquisition systems. Two-dimensional particle detectors play a crucial role in this paradigm shift, evolving from mere pixelated imaging sensors to time-based devices capable of encoding the spatial coordinates of detected events into time delays, in addition to associating temporal information with each received event. In this sense, Cross Delay-Lines (CDLs) detectors play crucial roles. In addition to the information provided by the CDL, which can be obtained with a simple acquisition system based on 4-channel Time-to-Digital Converter (TDC), it becomes increasingly necessary to provide auxiliary measurement channels in order to acquire additional information to correlate with the CDL data. The acquisition electronics of these setups rely on TDCs based on Application-Specific Integrated Circuits (ASICs), followed by Field Programmable Gate Arrays (FPGAs) for data processing. However, the lack of adaptability and flexibility inherent in ASICs prompted us to explore a fully FPGA-based approach aimed at achieving outstanding precision at high measurement rate retaining the unparalleled flexibility that only an FPGA can offer. In the following work, we propose a system based on a 16-channel TDC with a precision of 12 ps r.m.s., 5 ns of dead-time, and 4 ps of integral non-linearity. In this regard, 4 channels of the TDC are connected to a CDL, achieving a spatial resolution up to $30 / 40 \ \mu \mathrm{m}$ FWHM, while the remaining 12 channels are used for detecting auxiliary events to be correlated with the spatial information.

A state of the art commercial detector, a PCO Edge 4.2 bi based on a back illuminated sCMOS sensor developed for applications in the visible light/ultra violet regime has been adapted for ultra-high vacuum operations and has been characterized using soft X-ray in the energy range from 30 eV to 1000 eV. The imager features 2048 x 2048 pixel with a pixel size of 6.5 mu m x 6.5 mu m and allows full frame acquisitions at 48 Hz with a dynamic range of 88 dB at a noise level of 1.9 e(-). Spatial resolution and quantum efficiency have been elucidated in the aforementioned energy range at a soft X-ray beam line at Elettra Sincrotrone Trieste. The handiness of the camera as well as its Python library package allows easy and fast integration into the beam line environments of synchrotron sources and free electron lasers.

III-V-compound semiconductors offer many advantages over silicon-based technolo-gies traditionally used in solid-state photodetectors, especially in hard X-ray applications that require high detection efficiency and short response times. Amongst them, gallium arsenide (GaAs) has very promising characteristics in terms of X-ray absorption and high carrier velocity. Furthermore, implementing charge-multiplication mechanisms within the sensor may become of critical importance in cases where the photogenerated signal needs an intrinsic amplification before being acquired by the front-end electronics. This work reports on the experimental characteriza-tion by means of lasers and synchrotron radiation of gain, noise, and charge collection efficiencies of GaAs avalanche photodiodes (APDs), realized by molecular beam epitaxy (MBE), featuring separate absorption and multiplication regions (SAM) and different absorption region thicknesses. These devices have been fabricated to investigate the role of the thickness of the absorption region and of possible traps or defects at the metal-semiconductor interfaces in the collection efficiency in order to lay the groundwork for the future development of thicker GaAs devices for detection of hard X-rays.

We report on a suite of modeling approaches for the optimization of Avalanche Photodiodes for X-rays detection. Gain and excess noise are computed efficiently using a non-local/history dependent model that has been validated against full-band Monte Carlo simulations. The (stochastic) response of the detector to photon pulses is computed using an improved Random-Path-Length algorithm. As case studies, we consider diodes consisting of AlGaAs/GaAs multi-layers with separated absorption and multiplication regions. A superlattice creating a staircase conduction band structure is employed in the multiplication region to keep the multiplication noise low. Gain and excess noise have been measured in devices fabricated with such structure and successfully compared with the developed models.

With the advancement of new X-ray sources, such as synchrotron radiation facilities and Free Electron Lasers (FELs), which can generate high-flux and ultrashort X-ray pulses, time-resolved techniques have become general and powerful tools for exploring structural dynamics of matter. Thus, a new generation of acquisition system is needed, where the ability to temporally solve each measurement with great precision and versatility is required. Among the instruments most involved in this direction there are undoubtedly the particle detectors, which can no longer limit themselves to providing images but must be able to associate temporal information to each event received, in addition to the spatial one. With this in mind, Cross Delay-Lines (CDLs) detectors are among the most suitable and promising solutions allowing both spatial and temporal data to be acquired simultaneously. Typical architectures underlying the acquisition electronics of these detectors rely on an Application Specific Integrated Circuit (ASIC) Time-to-Digital Converter (TDC) followed by a Field Programmable Gate Array (FPGA) for data processing. The lack of reconfigurability and the inadequacy of adapting to different applications given by the ASIC, has brought us to study a new solution. Our multi-year work proposes a fully FPGA-based architecture with the purpose of obtaining excellent time resolution and fast parallel computing while maintaining the full flexibility only an FPGA can achieve. The acquisition chain is comprised of two FPGA boards, one hosting a custom-made TDC while the other the necessary image reconstruction algorithm. Over the years we managed to design an 8-channel TDC with a precision of 12 ps r.m.s, 5 ns dead-time, and 4 ps of non-linearity reaching a spatial resolution of 30/40 μm FWHM on the CDL. Improvements to the connection between the TDC and the image processing board are been implemented allowing a transfer rate of tens Gb/s, which means hundreds of Mmeasures/s.

The utilization of time-based approaches in modern physics experiments, has seen continuous growth thanks to the increasing performance of modern time–interval–meters (TIMs). In this context, Time–to–Digital Converters (TDCs), that are fully–digital TIMs, play a fundamental role. The digital approach makes the integration into measurement setups easier, while giving the possibility to investigate time–events with picosecond resolution over extended dynamic–ranges. Cross Delay-Lines (CDL) detectors are remarkably valuable, due to the fact that the position of the event can be detected by measuring the time of arrival, obtaining both information at once. With the purpose of achieving both fast parallel computing and time precision, the conventional acquisition systems usually count on 4-channel Application Specific Integrated Circuit (ASIC) Time-to-Digital Converters (TDCs) preceding a Field Programmable Logic Array (FPGA), reaching state-of-the-art performance in time resolved experiments. In this kind of architecture, the lack of reconfigurability, given by the ASIC, is a tightly limiting factor when customization of the setup is required, even more so at present day, where state-of-the-art TDCs with performance similar to ASICs can be fully implemented on FPGAs; for this reason, we propose a fully-FPGA based approach to this problem, in order to obtain a complete real-time system that can be completely reconfigured in function of the experimental setup. With the aim of improving the accuracy of the experiments, the time correlation between the CDL and the arrival time of other events occurring in conjunction is essential. For this reason, auxiliary TDC channels are needed. In this contribution, we present a compact, powerful and fully–configurable FPGA-based solution, where an 8–channel TDC with a precision of 12 ps r.m.s. and the related real–time image reconstruction algorithm are performed on two different FPGA devices. In this sense, a spatial resolution on the CDL of 50/60 µm FWHM is achieved.

Time resolved experiments are among the most powerful tools in physic for exploring photoelectron spectroscopy phenomena over time scales from milliseconds to picoseconds Moreover, acquisition systems with versatility and real-time computing are needed. Cross Delay-Lines detectors (CDL) are extremely suitable for these applications, since arrival time measurement is exploited to perform position detection, allowing to provide both information together. Typical architectures for acquisition systems are based on Aplication Specific Integrated Circuit (ASIC) Time-to-Digital Converters (TDCs) followed by a Field Programmable Logic Array (FPGA); fast parallel computing is combined with time precision, allowing to perform state-of-the-art time resolved experiments. Nevertheless, the limiting factor of this architecture is the absence of reconfigurability of the ASIC that strongly limits the customization respect to the requests of a specific set-up. Especially today, where the state-of-the-art TDCs implemented in FPGA, is comparable to the ASIC solutions. In 2019 Nuclear Science Symposium, we presented a fully-reconfigurable FPGA-based solution, where the TDC and the image reconstruction algorithm were hosted in two FPGAs. In particular, we focused on the 4-channel TDC that, guarantees high-performance in terms of resolution (1 ps), Full-Scale Range (200 µs), Integral Non Linearity, (4 ps over 500 ns), In this contribution, we give significant improvements in order to satisfy the aforementioned experimental experimental requests. In fact, the “pulse-to-pulse” dead-time of the TDC has been reduced from 20 ns to 7 ns, and the transmission rate between the FPGAs has been incremented from 10 to 100 Msps. Furthermore, we have increased the number of channels of the TDC from 4 to 8. This makes possible to correlate the CDL events with signals coming from other sources that can be as well Time-of-Fight or laser pulses as other CDL signals.

Beat-by-beat \( \dot{Q} \) aO2 and breath-by-breath \( \dot{V} \)O2 were assessed in ten male subjects (24 ± 3.5 years; 78 ± 7.7 kg; 182 ± 5.6 cm) during cycling exercise at 50 W before and after a 14-day period of head-down tilt-bed rest (HDTBR). O2 deficit (DefO2) was calculated as the difference between the volume of O2 that would have been consumed if a steady state had been immediately attained minus that actually taken up during exercise. \( \dot{Q} \) aO2 kinetics was described fitting the data with a non-linear mono-exponential model with time delay. Mean response times (MRT) of \( \dot{V} \)O2 and \( \dot{Q} \) aO2 kinetics were then calculated. DefO2 and MRT of \( \dot{V} \)O2 response did not change after HDTBR, whereas MRT of \( \dot{Q} \) aO2 kinetics increased. The invariance of \( \dot{V} \)O2 kinetics after HDTBR suggests that, although \( \dot{Q} \) aO2 response became slower after HDTBR, it did not affect the kinetics of peripheral gas exchange, which probably remained under the control of local muscular mechanisms.

Breath-by-breath (BbB) oxygen uptake rate (V˙O2) was measured at the mouth (MO) and at the alveolar level, at the onset of square wave cycling exercise of moderate intensity in six healthy male subjects. Alveolar BbB V˙O2 values were calculated correcting MO V˙O2 values by (i) estimating (GR); and (ii) measuring (opto-electronic plethysmography, OEP) BbB lung O2 store changes. V˙O2 kinetics was then described by a bi-exponential model. GR yielded larger values of the time constants (τ2) of the primary phase of V˙O2 kinetics. The mean response times (MRTs) calculated by analysing GR BbB V˙O2 values were larger than (i) those obtained by using MO and OEP at 90W; and (ii) that by using MO at 120W. OEP corrected V˙O2 yielded the highest normalised amplitude of the cardiodynamic phase of the V˙O2 on-response. Correction of BbB V˙O2 for actual BbB changes of lung O2 stores by OEP thus seems more appropriate for the study of the early cardiodynamic phase of V˙O2 kinetics than GR.

\( {{\dot{V}O}}_{2} , \) f H, \( \dot{Q}, \) SV, [Hb], CaO2, \( {{\dot{Q}}}_{\text{a}} \)O2, MAP and R P were measured in 10 young subjects at rest and during exercise at 50, 100 and 150 W before and after 14 days of head-down tilt bed rest (HDTBR) and of ambulatory (AMB) control period. f H was 18 and 8% higher after HDTBR and AMB, respectively. SV dropped by 15% both after HDTBR and AMB, whereas \( \dot{Q} \) did not change. After HDTBR, CaO2 decreased at rest (−8%) and at 50 W (−5%), whereas \( {{\dot{Q}}}_{\text{a}} \)O2 did not change; MAP was 14 and 6% lower at rest and at 100 W and R P decreased by 23% only at rest. Changes in f H and SV were larger after HDTBR than after AMB. These results show that, notwhistanding the drop of SV, moderate-intensity dynamic exercise elicited a normal pressure response after 14 days of HDTBR.

The cardio-vascular (CV) deconditioning observed in CV diseases or in weightlessness conditions can be reproduced by experimental maneuvers such as head down tilt bed rest (HDTBR) study. This maneuver can elicit CV regulation and control mechanisms. Three healthy subjects were studied during an exercise session before and after a sustained bed rest study. The CV, baroreflex response, and identification of the components of diastolic arterial pressure (DAP) and sources of variability were studied. Tachycardia and hypotension were observed after HDTBR. Changes were noticed in the baroreflex control of heart rate (HR) after HDTBR, whereas no clear difference in the diastolic time constant was found. Spectral power of DAP and of its tachogram-dependent component were lower after HDTBR.. The present work suggested the feasibility of the multiparametric analysis and gave preliminary indications of reflex mechanisms reset.

A detailed comparison of the surface sensitivity of x-ray photoemission spectroscopy for hard and soft x rays is presented and discussed. Electron scattering parameters and their energy dependence are given for Si and two Si spectra are analyzed: a Mg K alpha (h nu=1253.6 eV) excited spectrum of the Si 2p and 2s lines and a hard x-ray excited spectrum (h nu=5925 eV) of the Si 1s line. The differential inelastic scattering characteristics for Si are extracted from reflection electron energy loss spectra taken at energies of 1500 and 4000 eV. Using these scattering characteristics and electron mean free paths from the literature, simulated spectra are compared with experiment. The experimental spectra are deconvoluted to give the true intrinsic line shape corresponding to the theoretical collision statistics when interference effects between intrinsic and extrinsic scattering are neglected. The magnitude of interference effects cannot be assessed by our analysis. Within the (unknown) uncertainty introduced by neglecting interference effects, it is possible to determine the relative intensity of intrinsic and extrinsic excitations. In this way, it is found that in the case of the soft x-ray excited photoelectron spectrum of the shallower electronic shells (2p and 2s), intrinsic plasmon creation is rather weak, and the apparent asymmetric line shape of the spectrum might be interpreted as the fact that electron-hole pair creation dominates the intrinsic loss spectrum, while an alternative explanation in terms of surface core level shifted components is also proposed. For the deeper core electronic shell, probed with hard x rays, the opposite situation is observed: while intrinsic electron-hole pair creation was not observed, a strong contribution of intrinsic plasmon losses of about 30% was seen.