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High-Spectral Resolution Lidar (HSRL) Instrument Handbook
High-spectral-resolution lidar (HSRL) systems provide vertical profiles of optical depth, backscatter cross-section, depolarization, and backscatter phase function. All HSRL measurements are calibrated by reference to molecular scattering, which is measured at each point in the lidar profile. Like the Raman lidar (RL), but unlike simple backscatter lidars such as the micropulse lidar (MPL), this enables the HSRL to measure backscatter cross-sections and optical depths without prior assumptions about the scattering properties of the atmosphere. The depolarization observations allow robust discrimination between ice and water clouds. Rigorous error estimates can be computed for all measurements. A very narrow angular field of view reduces multiple scattering contributions. The small field of view, coupled with a narrow optical bandwidth, nearly eliminates noise due to scattered sunlight. The laser transmitter is a diode-pumped, frequency-doubled Nd:YAG laser. Narrow-band, single-frequency operation is provided by injection seeding with a single-frequency, cw-diode-pumped diode laser. The main laser cavity is maintained in resonance with the seed laser by adjusting the cavity length to minimize the time between the Q-switch trigger and the emission of the laser pulse. The emission wavelength is tuned via temperature control of the seed laser crystal and is locked to line #1109 of the iodine absorption spectra. Locking is accomplished by minimizing the transmission through a 2-cm-long iodine absorption cell. Use of a high-repetition-rate laser and expansion of the transmitted beam through a 400-mm telescope reduces the transmitted energy density to eye-safe levels. It is possible to look directly into the output beam without hazard. The receiver and transmitter use the same afocal telescope, simplifying the maintenance of stable alignment of the transmitter and receiver although the angular FOV is only 100 μrad. The small FOV and the 4-kHz repetition rate also limit the near-field signal strength, making it possible to record continuous profiles that start at an altitude of ~100 m and extend to 30 km using photon counting detectors. The small FOV also suppresses multiple scattering contributions.
Instrument Control Software for Spectrophotometers
SRNL has developed instrument control software for diode array spectrophotometers that can be used for real time monitoring of dynamic systems. This software has evolved through several iterations as instruments have been developed for use in processing facilities at Savannah River Site. There are several noteworthy features of the software. The wavelength calibration is checked and updated in real time against reference emission lines that are designed into the instrument light source. Nonlinearities and offsets associated with the intensity response of the instruments are characterized, and absorbance spectra are appropriately corrected. These actions are necessary for accurate calculation of an absorbance spectrum from the intensity responses of two individual diode array detectors. The corrections also result in the spectra obtained for a particular sample by two (or more) different diode array detector pairs being nearly identical. This property assures consistent measurements at multiple locations with different instruments. It also permits the use of a single analyte calibration across many instruments without modification and without loss of accuracy
Achieving Higher Fidelity Pulsed-Power Simulations Using Advanced Gap Closure Modeling
This project has progressed several physics models in the EMPIRE plasma simulation code to achieve higher fidelity simulations of high-current diode operation in pulsed-power accelerators. In this report, we present details for the following major work products: (1) a set of verification problems covering all key processes involved in gap closure physics has been designed; this suite has facilitated feature vetting and overall model maturation, (2) a new EMPIRE exemplar has been developed: the Radiographic Integrated Test Stand 6 (RITS-6) diode, and (3) An exemplar for the Saturn accelerator exemplar was enabled by the models matured under this work to self-consistently simulate further into the diode pulse than previously possible (bipolar flow regime). These developments have lead to the highest confidence EMPIRE power flow predictions of the Saturn accelerator to date. Additionally, three modeling approaches for simulating electrode plasmas have been investigated. We report on these results and provide recommendations.
On-chip spectroscopic sensors with optical fringe suppression
An on-chip spectroscopic sensor includes a tunable diode laser. A laser driver for drives the tunable diode laser. An analyte test cavity receives a chemical sample and exposes the received chemical sample to light from the tunable diode laser. An optical detector detects light emerging from the analyte test cavity as a result of the laser exposure. A spectral analyzer determines a spectrum of the emerging light, matches and removes one or more known optical fringe patterns from the determined spectrum, and determines a composition or concentration of the chemical sample from the optical fringe pattern-removed spectrum.
Reduction of Radiographic Spot Size with Dual Diameter Sub-mm Rods
Among the most dominant factors in x-ray radiographic image resolution is the radiographic spot size, which is primarily a function of the physical extent of the x-ray source, so the most marked improvements in image resolution come from modifying the pulse power driver’s diode configuration to reduce that extent. The smaller the size of the x-ray spot, the higher the image resolution potential. The U.S. Naval Research Laboratory’s Mercury pulsed power accelerator has been configured with a rod-pinch diode, and recent measurements were conducted to demonstrate the impact of anode rod geometry on x-ray spot size. The “standard” anode rod is a 0.75 mm diameter cylinder that is tapered down to 0.25 mm over a length of 5 mm, and, in this study, it was replaced by rods with a sharp step between their two diameters, rather than a taper. The effect on spot size was assessed by analyzing the edge and line spread functions calculated from high-mag rolled edge and pinhole camera images. For certain diameter pairs, a reduction in radiographic spot size is observed. In addition, the dual-diameter rods have provided unique insight into the electron-anode coupling dynamics that are at play in all diodes of this type.
Lighting fixture
A lighting fixture can comprise a substantially flat sheet of metal supporting a circuit that comprises one or more light emitting diodes with one or more associated optics for manipulating emitted light. The circuit can be attached to, mounted next to, or integrated with the sheet of metal. In some examples, a layer of dielectric material adheres to the sheet of metal, and circuit elements adhere to the layer of dielectric material. Such circuit elements may comprise electrical traces, light emitting diodes, and/or a light emitting diode driver. The sheet of metal can provide a substrate for the circuit or a support for a freestanding circuit board that may be rigid or flexible.
On-chip spectroscopic sensors with optical fringe suppression
An on-chip spectroscopic sensor includes a tunable diode laser. A laser driver for drives the tunable diode laser. An analyte test cavity receives a chemical sample and exposes the received chemical sample to light from the tunable diode laser. An optical detector detects light emerging from the analyte test cavity as a result of the laser exposure. A spectral analyzer determines a spectrum of the emerging light, matches and removes one or more known optical fringe patterns from the determined spectrum, and determines a composition or concentration of the chemical sample from the optical fringe pattern-removed spectrum.
Opto-thermal laser detonator
An opto-thermal laser detonator uses resonantly absorptive tuned nano-material associated with secondary explosives for optical absorption and initiation by an integral laser diode. The opto-thermal laser detonator includes main explosive material; resonantly absorptive tuned nano-material; secondary explosive material, wherein the resonantly absorptive tuned nano-material and the secondary explosive material are associated to form associated material made of the resonantly absorptive tuned nano-material and the secondary explosive material; and a laser diode operatively connected to the associated material, wherein the laser diode initiates the associated material which in turn initiates the main explosive material.
Optical device for in-line and real-time monitoring of microorganisms
A multi-wavelength laser diode based optical sensor system capable of monitoring the dynamics and physiological changes of a microorganism culture in real-time. The microorganism culture from a microorganism production chamber is pumped to a flow chamber. Laser diodes emit light at certain wavelengths through the flow chamber, which is sensed by photodiodes. A laser control circuitry is operatively connected to the laser diodes and a signal conditioning circuitry is operatively connected to the photodiodes. A microprocessor reads and records voltage signals corresponding to the wavelengths. A data acquisition system converts said voltage signals into measurements of biological parameters, which are displayed on a graphical user interface and allow a user to monitor the measurements in real time.
Non-circular optical fiber and mode shape converter and method
A class of fibers is described that have a non-circular cross section on one or both ends that can by optimized to capture the optical radiation from a laser diode or diode array and deliver the light in the same or different shape on the opposite end of the fiber. A large multimode rectangular waveguide may be provided which can accept the radiation from a high-power diode bar and transform it into a circular cross section on the opposite end, while preserving brightness.
Opto-thermal laser detonator
An opto-thermal laser detonator uses resonantly absorptive tuned nano-material associated with secondary explosives for optical absorption and initiation by an integral laser diode. The opto-thermal laser detonator includes main explosive material; resonantly absorptive tuned nano-material; secondary explosive material, wherein the resonantly absorptive tuned nano-material and the secondary explosive material are associated to form associated material made of the resonantly absorptive tuned nano-material and the secondary explosive material; and a laser diode operatively connected to the associated material, wherein the laser diode initiates the associated material which in turn initiates the main explosive material.
Heterogenous Integration of Boron-Doped p -Diamond with Monolayer n -MoS 2 for PN Junctions Operating at Room Temperature
Diamond has tremendous potential for power electronics, due to its superior thermal conductivity, large electric field strength, and high carrier mobilities. However, the absence of a reliable room temperature n-type transport has impeded any advancements in diamond-based electronics. Here, we circumvent this bottleneck by integrating n-type two-dimensional (2D) monolayers of molybdenum disulfide (MoS 2 ) with boron doped p-type single crystal diamond and demonstrate 2D/3D heterostructure-based PN junction diodes that operate at room temperature with excellent rectification characteristics. Our diodes achieve a maximum forward current density (J D ) of ∼4000 A/cm 2 , an ideality factor (η) value of ∼3.7, and a rectification ratio (RR) of 10 6 . We find that the origin of current rectification stems from the interlayer recombination of majority carriers driven by direct tunnelling (DT) and Fowler Nordheim (FN) tunnelling mechanisms. In conclusion, our demonstration can open new avenues for diamond-based power electronics through its integration with 2D materials.
Electrically Pumped Epitaxially Regrown GaSb-Based Type-I Quantum-Well Surface-Emitting Lasers with Buried High-Index-Contrast Photonic Crystal Layer
Epitaxially regrown electrically pumped photonic crystal surface-emitting lasers (PCSELs) emitting near 2 and 2.6 μm are designed, fabricated, and characterized. A high-index-contrast photonic crystal layer is incorporated into the GaSb-based laser heterostructure by air-hole-retaining epitaxial regrowth. A square lattice of triangular holes is etched in the top waveguide core layer of the incomplete laser heterostructure. The nanopatterned surface is subsequently cleaned and regrown with AlGaAsSb p-cladding material. Transmission electron microscopy studies demonstrate uniform regrowth over the nanopatterned GaSb surface. The selected regrowth regimes yield a buried 2D array of elongated air-holes. The diode PCSELs based on moderately etched nanopatterns demonstrate band-edge lasing near 2 μm up to room temperatures. The cascade diode PCSELs operate near 2.6 μm with minimum threshold current densities of about 500 A cm -2 achieved at 180 K. The devices generate mW level output in narrow divergence beam emitted from the window in substrate contact. The angle-resolved electroluminescence measurements reveal a four-sub-band band structure with an apparent photonic bandgap corresponding to the buried high-index-contrast square photonic crystal layer. Finally, the PCSELs made of heterostructures supporting two modes in the vertical direction demonstrate two sets of sub-bands showing anti-crossing-like interaction.
Unveiling the influence of selective-area-regrowth interfaces on local electronic properties of GaN p-n junctions for efficient power devices
Here, we report correlated nanoscale mapping of the structure, composition, and properties of regrown GaN p-n junctions to identify how etching and non-planar regrowth processes limit diode performance via the introduction of unintentional dopants and defect states. p-GaN was selectively regrown in n-GaN trenches with SiO 2 masks of variable mask-to-trench-width ratio. Dilute Al layers were periodically introduced during regrowth as markers of the growth interface. Correlated nanoscale mapping of doping, conductivity, and dopant complexes was achieved with atom probe tomography (APT), scanning spreading resistance microscopy (SSRM), and cathodoluminescence (CL) spectroscopy, respectively. The Al marker layers, detected by APT, enabled reconstruction of the faceted growth interface and correlation of the dopant concentration with position and time. The p-GaN growth rate is proportional to the mask-to-trench width ratio while the dopant incorporation rate is invariant. At trench edges, magnesium incorporation is suppressed, and oxygen incorporation enhanced, due to preferential incorporation on the semi-polar growth surface, leading to compensation and less abrupt p-n junctions; the SiO 2 mask is a source of oxygen. Residual etch damage below the regrowth interface induces n-type and p-type conductivity, creating leakage pathways. The non-uniform Mg incorporation is driven by crystal anisotropy and is thus inherent to non-planar regrowth, but can be mitigated by engineering the regrowth interface and process parameters. The unprecedented integration of spatially resolved mapping of dopants, impurities, conductivity, and carrier type is a powerful approach to discriminating distinct factors that limit the performance of regrown diodes, enabling the rational optimization of process and device design.
Plasmon-enhanced ultralow-threshold solid-state triplet fusion upconversion
Triplet fusion upconversion has potential applications in solar cells, photoredox catalysis, additive manufacturing and bioimaging. However, solid-state upconversion systems have struggled to measure up to their solution-phase counterparts, often requiring enormous optical power densities to operate at the maximum efficiency. Here we substantially improve the performance of upconversion films through excitation with surface plasmons that propagate along a planar silver-film interface, leading to an absorption enhancement that reduces the intensity threshold I th by a factor of 19 and enhances the external quantum efficiency by a factor of 17. From this, we achieve I th values as low as 3.4 mW cm −2 and an external quantum efficiency up to 0.094%. To demonstrate real-world viability, we couple the upconversion film to plasmons generated by the near-field of excitons in an organic light-emitting diode. As a result, this scheme is then used to fabricate a white-emitting organic light-emitting diode where blue emission sources from plasmon-excited upconversion, achieving a high colour rendering index of 86.2 and setting precedent for blue emission in the absence of high-energy polarons or triplets.
Electrically driven amplified spontaneous emission from colloidal quantum dots
Colloidal quantum dots (QDs) are attractive materials for realizing solution-processable laser diodes that could benefit from size-controlled emission wavelengths, low optical-gain thresholds and ease of integration with photonic and electronic circuits. However, the implementation of such devices has been hampered by fast Auger recombination of gain-active multicarrier states, poor stability of QD films at high current densities and the difficulty to obtain net optical gain in a complex device stack wherein a thin electroluminescent QD layer is combined with optically lossy charge-conducting layers. Here we resolve these challenges and achieve amplified spontaneous emission (ASE) from electrically pumped colloidal QDs. The developed devices use compact, continuously graded QDs with suppressed Auger recombination incorporated into a pulsed, high-current-density charge-injection structure supplemented by a low-loss photonic waveguide. These colloidal QD ASE diodes exhibit strong, broadband optical gain and demonstrate bright edge emission with instantaneous power of up to 170 μW.
Numerical simulation of a relativistic magnetron using a fluid electron model
An approach to numerically modeling relativistic magnetrons, in which the electrons are represented with a relativistic fluid, is described. A principal effect in the operation of a magnetron is space-charge-limited (SCL) emission of electrons from the cathode. We have developed an approximate SCL emission boundary condition for the fluid electron model. This boundary condition prescribes the flux of electrons as a function of the normal component of the electric field on the boundary. Here we show the results of a benchmarking activity that applies the fluid SCL boundary condition to the one-dimensional Child–Langmuir diode problem and a canonical two-dimensional diode problem. Simulation results for a two-dimensional A6 magnetron are then presented. Computed bunching of the electron cloud occurs and coincides with significant microwave power generation. Numerical convergence of the solution is considered. Sharp gradients in the solution quantities at the diocotron resonance, spanning an interval of three to four grid cells in the most well-resolved case, are present and likely affect convergence.