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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,153 records · Page 64
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Characterization of Spurious Charge in SENSEI Skipper-CCDs

Skipper Charge-Coupled Devices (Skipper-CCDs) are a leading technology in the search for sub-GeV dark matter and coherent elastic neutrino-nucleus scattering. A key background for rare-event searches with these detectors arises from "spurious charge" -- single-electron events generated when charges are transferred through the active region to the serial register, and across the serial register to the readout stage. We present a characterization of spurious charge in both the active region and the serial register of SENSEI Skipper-CCDs, and show that, in a well-shielded low-background environment, the dominant contribution originates in the serial register during Skipper readout, when horizontal clocks are held at constant voltage between pixel transfers. Motivated by this finding, we develop a "tri-level" clocking scheme in which the held-low phase is raised to an intermediate voltage during readout to suppress trap-mediated charge generation. Using the SENSEI detector near the MINOS cavern, we measure a serial-register single-electron density of $(2.9 \pm 0.1) \times 10^{-5}$ electrons/pixel/image under standard SENSEI readout conditions, reduced to $(4.0 \pm 0.4) \times 10^{-6}$ electrons/pixel/image with tri-level clocking -- a factor of $\sim$7 improvement. This technique offers a promising path to lower backgrounds in current and future Skipper-CCD experiments.

Wu, Yikai [YITP, Stony Brook; SUNY, Stony Brook]↗
DOE OSTI2014

Quantum displacement receiver for M-ary phase-shift-keyed coherent states

We propose quantum receivers for 3- and 4-ary phase-shift-keyed (PSK) coherent state signals to overcome the standard quantum limit (SQL). Our receiver, consisting of a displacement operation and on-off detectors with or without feedforward, provides an error probability performance beyond the SQL. We show feedforward operations can tolerate the requirement for the detector specifications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Hyperspectral X-ray Imaging with TES Detectors for Nanoscale Chemical Speciation Mapping

We are developing an imaging capability (“Hyperspectral X-ray Imaging”) for mapping chemical information (molecular formula, phase, oxidation state, hydration) that is based on ultra-high-resolution X-ray emission spectroscopy with large transition-edge sensor microcalorimeter arrays in the scanning electron microscope. By combining microcalorimeter arrays with hundreds of pixels, high-bandwidth microwave frequency-division multiplexing, and fast digital electronics for near real-time data processing, our goal is to enable measurements using laboratory-scale instrumentation rather than synchrotron beamlines. Our application focus here is on mapping the chemical form of uranium compounds on the nanoscale. Furthermore, we will present our approach to developing the Hyperspectral X-ray Imaging capability, progress toward a 128-pixel microwave multiplexed X-ray fluorescence instrument at LANL, and the path to high-throughput nanoscale chemical mapping.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

The Phase-2 electronics upgrade of the ATLAS liquid argon calorimeter system

The LHC high-luminosity upgrade in 2024–2026 requires the associated detectors to operate at luminosities about 5–7 times larger than assumed in their original design. The pile-up is expected to increase to up to 200 events per proton bunch-crossing. The current readout of the ATLAS liquid argon calorimeters does not provide sufficient buffering and bandwidth capabilities to accommodate the hardware triggers requirements imposed by these harsh conditions. Furthermore, the expected total radiation doses are beyond the qualification range of the current front-end electronics. For these reasons an almost complete replacement of the front-end and off-detector readout system is foreseen for the 182,468 readout channels. Here, the new readout system will be based on a free-running architecture, where calorimeter signals are amplified, shaped and digitized by on-detector electronics, then sent at 40 MHz to the off-detector electronics for further processing. Results from the design studies on the performance of the components of the readout system are presented, as well as the results of the tests of the first prototypes.

47 OTHER INSTRUMENTATION↗
DOE OSTI2017

Phase-Slip Phenomena in Proximitized NbN/NiCu Superconducting Nanostripes

Ultrathin superconducting/ferromagnet (S/F) nanostripes are very interesting systems to investigate both the physics involved on nanoscale size and as light sensitive elements for superconducting single photon detectors. The electrical transport properties of NbN(8 nm)/NiCu(10 nm) nanostripes are presented down to a temperature of 4.2 K. A number of voltage steps were observed on the current-voltage characteristics, and they were investigated at different temperatures. A possible explanation in terms of active phase-slip phenomena has been proposed on the basis of the time-dependent Ginzburg-Landau theory, leading to an estimation of the inelastic electron-phonon relaxation time around 0.8 ps. The latter value was found to be in good agreement with a relaxation time, independently measured by femtosecond transient optical reflectivity experiments performed on the same bilayer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Determination of the structure-processing-properties relationship of Fe-6.5wt%Si

The role of Fe-6.5wt%Si as a soft magnetic material in motor and power generation will continue to increase as power and efficiency demands keep increasing due to high silicon steel’s superior magnetic and electrical properties when operated at high frequencies. However, the presence of brittle phases creates challenges for mass production of the materials and for machining the materials into parts with demanding geometries. Understanding the processing parameters controlling the presence of the brittle phases is necessary to promote high silicon steels as the superior soft magnetic material. This research pioneers the use of in-situ cooling rate thermal imaging analysis and a 2D Laue x-ray detector to quantify the relationship among processing parameters, final microstructure of melt-spun ribbons and the associated physical properties. These techniques reveal the superlattice peaks of the ordered B2/D03 phases separating them from the background A2 phase. Utilizing a variety of techniques investigating mechanical, electrical, and magnetic properties’ correlation to crystal structure alongside processing parameters a time temperature transformation curve can be generated.

01 COAL, LIGNITE, AND PEAT↗
NASA NTRS2019

Validation of CERES Flight Model 5 In-Orbit Calibrations Using Lunar Observations

Scientific studies require radiation fluxes over the Earth to be accurate within 1% for shortwave fluxes and 0.5% for outgoing longwave fluxes. The validation of in-orbit instrument performance requires both stability in calibration source and also calibration corrections to compensate for instrument changes. The Moon offers an external source whose signal variance is predictable and non-degrading. CERES detectors register the signal output from the entire face of the Moon. Lunar observations performed by CERES Flight Models (FM) 1 through 4 have been successful in assisting validation of radiances to the required accuracy. CERES Flight Model 5 (FM-5) is on Suomi/NPP spacecraft, orbiting since October 2011. This paper uses lunar measurements to validate detector output of FM-5. These measurements are adjusted to remove orbital effects due to variations in distance between Moon and Sun, distance between the satellite and the Moon and lunar phase angle. These effects create a total variation in lunar irradiance of 20% in the total channel and 8% in the shortwave channel. The change in orientation of the Moon as seen by the detector is called libration and causes variations of about 1% of the irradiance. A consistent dataset spanning at least 2 years in length is required to remove variations due to libration. The major uncertainties remaining in the measurements are assumed to be due to changes of the spectral responses of the channels due to degradation of optical surfaces in orbit. The results demonstrate that lunar observations can be used to validate FM-5 measurements.

Clouds and Earth Radiant Energy System↗
DOE OSTI2022

A unique gravitational wave signal from phase transition during inflation

We study the properties of the gravitational wave (GW) signals produced by first-order phase transitions during the inflation era. We show that the power spectrum of the GW oscillates with its wave number. This signal can be observed directly by future terrestrial and spatial gravitational wave detectors and through the B-mode spectrum in CMB. This oscillatory feature of GW is generic for any approximately instantaneous sources occurring during inflation and is distinct from the GW from phase transitions after the inflation. The details of the GW spectrum contain information about the scale of the phase transition and the later evolution of the universe.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Measurement of the phase between strong and electromagnetic amplitudes in the decay J/ψ → ϕη

The first direct measurement of the relative phase between the strong and electromagnetic amplitudes for a J/ψ decaying into a vector-pseudoscalar final state is performed using 26 energy points of e + e − annihilation data between 3.00 GeV and 3.12 GeV. The data sets were collected by the BESIII detector with a total integrated luminosity of 452 pb −1 . By investigating the interference pattern in the cross section lineshape of e + e − → ϕη, the relative phase between the strong and electromagnetic amplitudes of J/ψ decay is determined to be within [133°, 228°] at 68% confidence level.

QCD↗
DOE OSTI2013

Actively triggered 4d cone-beam CT acquisition

Purpose: 4d cone-beam computed tomography (CBCT) scans are usually reconstructed by extracting the motion information from the 2d projections or an external surrogate signal, and binning the individual projections into multiple respiratory phases. In this “after-the-fact” binning approach, however, projections are unevenly distributed over respiratory phases resulting in inefficient utilization of imaging dose. To avoid excess dose in certain respiratory phases, and poor image quality due to a lack of projections in others, the authors have developed a novel 4d CBCT acquisition framework which actively triggers 2d projections based on the forward-predicted position of the tumor.Methods: The forward-prediction of the tumor position was independently established using either (i) an electromagnetic (EM) tracking system based on implanted EM-transponders which act as a surrogate for the tumor position, or (ii) an external motion sensor measuring the chest-wall displacement and correlating this external motion to the phase-shifted diaphragm motion derived from the acquired images. In order to avoid EM-induced artifacts in the imaging detector, the authors devised a simple but effective “Faraday” shielding cage. The authors demonstrated the feasibility of their acquisition strategy by scanning an anthropomorphic lung phantom moving on 1d or 2d sinusoidal trajectories.Results: With both tumor position devices, the authors were able to acquire 4d CBCTs free of motion blurring. For scans based on the EM tracking system, reconstruction artifacts stemming from the presence of the EM-array and the EM-transponders were greatly reduced using newly developed correction algorithms. By tuning the imaging frequency independently for each respiratory phase prior to acquisition, it was possible to harmonize the number of projections over respiratory phases. Depending on the breathing period (3.5 or 5 s) and the gantry rotation time (4 or 5 min), between ∼90 and 145 projections were acquired per respiratory phase resulting in a dose of ∼1.7–2.6 mGy per respiratory phase. Further dose savings and decreases in the scanning time are possible by acquiring only a subset of all respiratory phases, for example, peak-exhale and peak-inhale only scans.Conclusions: This study is the first experimental demonstration of a new 4d CBCT acquisition paradigm in which imaging dose is efficiently utilized by actively triggering only those projections that are desired for the reconstruction process.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2017

Design of the protoDUNE raw data management infrastructure

The Deep Underground Neutrino Experiment (DUNE) will employ a set of Liquid Argon Time Projection Chambers (LArTPC) with a total mass of 40 kt as the main components of its Far Detector. In order to validate this technology and characterize the detector performance at full scale, an ambitious experimental program (called “protoDUNE”) has been initiated which includes a test of the large-scale prototypes for the single-phase and dual-phase LArTPC technologies, which will run in a beam at CERN. The total raw data volume that is slated to be collected during the scheduled 3-month beam run is estimated to be in excess of 2.5 PB for each detector. This data volume will require that the protoDUNE experiment carefully design the DAQ, data handling and data quality monitoring systems to be capable of dealing with challenges inherent with peta-scale data management while simultaneously fulfilling the requirements of disseminating the data to a worldwide collaboration and DUNE associated computing sites. Here in this paper, we present our approach to solving these problems by leveraging the design, expertise and components created for the LHC and Intensity Frontier experiments into a unified architecture that is capable of meeting the needs of protoDUNE.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Development of Diamond Membrane-Based X-Ray Optics: Fresnel Zone Plates, Beam Stops, and Grids

This project was proposed to develop the design and fabrication of zone plates for hard X-ray focusing up to 25 keV photon energies with 20 nm resolution (with zone doubling), based on diamond membranes. The benefits of using diamond are: improved mechanical robustness which among other advantages prevents collapse of high-aspect-ratio ring structures, a known high-aspect-ratio etch method, and excellent compatibility with other processes, excellent radiation hardness, extremely low X-ray absorption, and significantly improved thermal/dimensional stability as compared to alternative materials. The Phase I findings enable Phase II goals as well as significant progress in other diamond-membrane devices, such as diamond-supported X-ray optics (beam stops, apertures, phase shift disks for phase contrast X-ray microscopy, grids, resolution targets, coded apertures for coherence measurements, etc), X-ray windows and membrane–based detectors. Zone plates with outermost zones of 60 nm were written in 500 nm electron resist and transferred to a depth of up to 1.8 mm (exceeding the expectations) into a stack of engineered multilayer ultra-nano-crystalline diamond alternating non-conductive and conductive layers. The active material for focusing was added on top (Au and Ir). Several processes were investigated and validated to enable in Phase II the enhancement of the thickness of the structures, including polishing the over-plated zone plates and growing diamond on top of Ir-coated zone plates without the destruction of the nanostructures underneath. The zone plates were geometrically characterized.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2015

Cryogenic readout techniques for germanium detectors

High Purity Germanium detectors are used in many applications, from nuclear and astro-particle physics, to homeland security or environment protection. Although quite standard configurations are often used, with cryostats, charge sensitive amplifiers and analog or digital acquisition systems all commercially available, it might be the case that a few specific applications, e.g. satellites, portable devices, cryogenic physics experiments, etc. also require the development of a few additional or complementary techniques. An interesting case is for sure GERDA, the Germanium Detector Array experiment, searching for neutrino-less double beta decay of {sup 76}Ge at the Gran Sasso National Laboratory of INFN - Italy. In GERDA the entire detector array, composed of semi-coaxial and BEGe naked crystals, is operated suspended inside a cryostat filled with liquid argon, that acts not only as cooling medium and but also as an active shield, thanks to its scintillation properties. These peculiar circumstances, together with the additional requirement of a very low radioactive background from all the materials adjacent to the detectors, clearly introduce significant constraints on the design of the Ge front-end readout electronics. All the Ge readout solutions developed within the framework of the GERDA collaboration, for both Phase I and Phase II, will be briefly reviewed, with their relative strength and weakness compared together and with respect to ideal Ge readout. Finally, the digital processing techniques developed by the GERDA collaboration for energy estimation of Ge detector signals will be recalled. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1996

A measurement concept for hot-spot BRDFs from space

Several concepts for canopy hot-spot measurements from space have been investigated. The most promising involves active illumination and bistatic detection that would allow hot-spot angular distribution (BRDF) measurements from space in a search-light mode. The concept includes a pointable illumination source, such as a laser operating at an atmospheric window wavelength, coupled with a number of high spatial-resolution detectors that are clustered around the illumination source in space, receiving photons nearly coaxial with the reto-reflection direction. Microwave control and command among the satellite cluster would allow orienting the direction of the laser beam as well as the focusing detectors simultaneously so that the coupled system can function like a search light with almost unlimited pointing capabilities. The concept is called the Hot-Spot Search-Light (HSSL) satellite. A nominal satellite altitude of 600 km will allow hot-spot BRDF measurements out to about 18 degrees phase angle. The distributed are taking radiometric measurements of the intensity wings of the hot-spot angular distribution without the need for complex imaging detectors. The system can be operated at night for increased signal-to-noise ratio. This way the hot-spot angular signatures can be quantified and parameterized in sufficient detail to extract the biophysical information content of plant architectures.

Reflectivity↗
NASA NTRS2010

Observing Mergers of Non-Spinning Black-Hole Binaries

Advances in the field of numerical relativity now make it possible to calculate the final, most powerful merger phase of binary black-hole coalescence for generic binaries. The state of the art has advanced well beyond the equal-mass case into the unequal-mass and spinning regions of parameter space. We present a study of the nonspinning portion of parameter space, primarily using an analytic waveform model tuned to available numerical data, with an emphasis on observational implications. We investigate the impact of varied m8BS ratio on merger signal-to-noise ratios (SNR~) for several detectors, and compare our results with expectations from the test-mass limit. We note a striking similarity of the waveform phasing of the merger waveform across the available mass ratios. Motivated by this, we calculate the match between our equal-mass and 4:1 mass-ratio waveforms during the merger as a function of location on the source sky, using a new formalism for the match that accounts for higher harmonics. This is an indicator of the amount of degeneracy in mass ratio for mergers of moderate mass ratio systems.

McWilliams, Sean T.↗
DOE OSTI2014

MO-PIS-Exhibit Hall-01: Imaging: CT Dose Optimization Technologies I

Partners in Solutions is an exciting new program in which AAPM partners with our vendors to present practical “hands-on” information about the equipment and software systems that we use in our clinics. The imaging topic this year is CT scanner dose optimization capabilities. Note that the sessions are being held in a special purpose room built on the Exhibit Hall Floor, to encourage further interaction with the vendors. Dose Optimization Capabilities of GE Computed Tomography Scanners Presentation Time: 11:15 – 11:45 AM GE Healthcare is dedicated to the delivery of high quality clinical images through the development of technologies, which optimize the application of ionizing radiation. In computed tomography, dose management solutions fall into four categories: employs projection data and statistical modeling to decrease noise in the reconstructed image - creating an opportunity for mA reduction in the acquisition of diagnostic images. Veo represents true Model Based Iterative Reconstruction (MBiR). Using high-level algorithms in tandem with advanced computing power, Veo enables lower pixel noise standard deviation and improved spatial resolution within a single image. Advanced Adaptive Image Filters allow for maintenance of spatial resolution while reducing image noise. Examples of adaptive image space filters include Neuro 3-D filters and Cardiac Noise Reduction Filters. AutomA adjusts mA along the z-axis and is the CT equivalent of auto exposure control in conventional x-ray systems. Dynamic Z-axis Tracking offers an additional opportunity for dose reduction in helical acquisitions while SmartTrack Z-axis Tracking serves to ensure beam, collimator and detector alignment during tube rotation. SmartmA provides angular mA modulation. ECG Helical Modulation reduces mA during the systolic phase of the heart cycle. SmartBeam optimization uses bowtie beam-shaping hardware and software to filter off-axis x-rays - minimizing dose and reducing x-ray scatter. The DICOM Radiation Dose Structured Report (RDSR) generates a dose report at the conclusion of every examination. Dose Check preemptively notifies CT operators when scan parameters exceed user-defined dose thresholds. DoseWatch is an information technology application providing vendor-agnostic dose tracking and analysis for CT (and all other diagnostic x-ray modalities) SnapShot Pulse improves coronary CTA dose management. VolumeShuttle uses two acquisitions to increase coverage, decrease dose, and conserve on contrast administration. Color-Coding for Kids applies the Broselow-Luten Pediatric System to facilitate pediatric emergency care and reduce medical errors. FeatherLight achieves dose optimization through pediatric procedure-based protocols. Adventure Series scanners provide a child-friendly imaging environment promoting patient cooperation with resultant reduction in retakes and patient motion. Philips CT Dose Optimization Tools and Advanced Reconstruction Presentation Time: 11:45 ‘ 12:15 PM The first part of the talk will cover “Dose Reduction and Dose Optimization Technologies” present in Philips CT Scanners. The main Technologies to be presented include: DoseRight and tube current modulation (DoseRight, Z-DOM, 3D-DOM, DoseRight Cardiac) Special acquisition modes Beam filtration and beam shapers Eclipse collimator and ClearRay collimator NanoPanel detector DoseRight will cover automatic tube current selection that automatically adjusts the dose for the individual patient. The presentation will explore the modulation techniques currently employed in Philips CT scanners and will include the algorithmic concepts as well as illustrative examples. Modulation and current selection technologies to be covered include the Automatic Current Selection component of DoseRight, ZDOM longitudinal dose modulation, 3D-DOM (combination of longitudinal and rotational dose modulation), Cardiac Dose right (an ECG based dose modulation scheme), and the DoseRight Index (DRI) IQ index. The special acquisition modes covers acquisition techniques such as prospective gating that is designed to reduce exposure to the patient through the Cardiac Step and Shoot scan mode. This mode can substitute the much higher dose retrospective scan modes for certain types of cardiac imaging. The beam filtration and beam shaper portion will discuss the variety of filtration and beam shaping configurations available on Philips scanners. This topic includes the x-ray beam characteristics, tube filtration as well as dose compensator characteristics. The Eclipse collimator, ClearRay collimator and the NanoPanel detector portion will discuss additional technologies specific to wide coverage CT that address some of the unique challenges encountered and techniques employed to optimize image quality and optimize dose utilization. The Eclipse collimator reduces extraneous exposure by actively blocking the radiation tails at either end of helical scans that do not contribute to the image generation. The ClearRay collimator and the NanoPanel detector optimize the quality of the signal that reaches the detectors by addressing the increased scattered radiation present in wide coverage and the NanoPanel detector adds superior electronic noise characteristics valuable when imaging at a low dose level. The second part of the talk will present “Advanced Reconstruction Technologies” currently available on Philips CT Scanners. The talk will cover filtered back projection (FBP), iDose4 and Iterative Model Reconstruction (IMR). Each reconstruction method will include a discussion of the algorithm as well as similarities and differences between the algorithms. Examples illustrating the merits of each algorithm will be presented, and techniques and metrics to characterize the performance of each type of algorithm will be presented. The Filtered Back projection portion will discuss and provide a brief summary of relevant standard image reconstruction techniques in common use, and discuss the common tradeoffs when using the FBP algorithm. The iDose4 portion will present the algorithms used for iDose4 as well the different levels. The meaning of different levels of iDose4 available will be presented and quantified. Guidelines for selection iDose4 parameters based on the imaging need will be explained. The different image quality goals available with iDose4 and specifically how iDose4 enables noise reduction, spatial resolution improvement or both will be explained. The approaches to leveraging the benefits of iDose4 such as improved spatial resolution, decreased noise, and artifact prevention will be described and quantified; and measurements and metrics behind the improvements will be presented. The image quality benefits in specific imaging situations as well as how to best combine the technology with other dose reduction strategies to ensure the best image quality at a given dose level will be presented. Insight into the IMR algorithm as well as contrast to the iDose4 techniques and performance characteristics will be discussed. Metrics and techniques for characterizing this class of algorithm and IQ performance will be presented. The image quality benefits and the dose reduction capabilities of IMR will be explored. Illustrative examples of the noise reduction, spatial resolution improvement, and low contrast detectability improvements of the reconstruction method will be presented: clinical cases and phantom measurements demonstrating the benefits of IMR in the areas of low dose imaging, spatial resolution and low contrast resolution are discussed and the technical details behind the measurements will be presented compared to both iDose4 and traditional filtered back projection (FBP)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

Evaluation of planar silicon pixel sensors with the RD53A readout chip for the Phase-2 Upgrade of the CMS Inner Tracker

The Large Hadron Collider at CERN will undergo an upgrade inorder to increase its luminosity to7.5 × 10$^{34}$ cm$^{-2}$s$^{-1}$. The increased luminosityduring this High-Luminosity running phase, starting around 2029,means a higher rate of proton-proton interactions, hence a largerionizing dose and particle fluence for the detectors. The currenttracking system of the CMS experiment will be fully replaced inorder to cope with the new operating conditions. Prototype planarpixel sensors for the CMS Inner Tracker with square50 μm × 50 μm and rectangular100 μm × 25 μm pixels read out by theRD53A chip were characterized in the lab and at the DESY-II testbeamfacility in order to identify designs that meet the requirements ofCMS during the High-Luminosity running phase. A spatial resolutionof approximately 3.4 μm (2 μm) is obtained using themodules with 50 μm × 50 μm(100 μm × 25 μm) pixels at the optimalangle of incidence before irradiation. After irradiation to a 1 MeVneutron equivalent fluence ofΦ$_{eq}$ = 5.3 × 10$^{15}$ cm$^{-2}$, a resolution of9.4 μm is achieved at a bias voltage of 800 V using a modulewith 50 μm × 50 μm pixel size. All modulesretain a hit efficiency in excess of 99% after irradiation tofluences up to 2.1 × 10$^{16}$ cm$^{-2}$. Further studies ofthe electrical properties of the modules, especially crosstalk, arealso presented in this paper.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

A cylindrical quadrupole ion trap in combination with an electrospray ion source for gas-phase luminescence and absorption spectroscopy

A relatively simple setup for collection and detection of light emitted from isolated photo-excited molecular ions has been constructed. It benefits from a high collection efficiency of photons, which is accomplished by using a cylindrical ion trap where one end-cap electrode is a mesh grid combined with an aspheric condenser lens. The geometry permits nearly 10% of the emitted light to be collected and, after transmission losses, approximately 5% to be delivered to the entrance of a grating spectrometer equipped with a detector array. The high collection efficiency enables the use of pulsed tunable lasers with low repetition rates (e.g., 20 Hz) instead of continuous wave (cw) lasers or very high repetition rate (e.g., MHz) lasers that are typically used as light sources for gas-phase fluorescence experiments on molecular ions. A hole has been drilled in the cylinder electrode so that a light pulse can interact with the ion cloud in the center of the trap. Simulations indicate that these modifications to the trap do not significantly affect the storage capability and the overall shape of the ion cloud. The overlap between the ion cloud and the laser light is basically 100%, and experimentally >50% of negatively charged chromophore ions are routinely photodepleted. The performance of the setup is illustrated based on fluorescence spectra of several laser dyes, and the quality of these spectra is comparable to those reported by other groups. Finally, by replacing the optical system with a channeltron detector, we demonstrate that the setup can also be used for gas-phase action spectroscopy where either depletion or fragmentation is monitored to provide an indirect measurement on the absorption spectrum of the ion.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗