Joseph J. Talghader

University of Minnesota Duluth, Duluth, Minnesota, United States

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Publications (101)138.02 Total impact

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    ABSTRACT: Spatial modulation spectroscopy (SMS) is a powerful method for interrogating single nanoparticles. In these experiments optical extinction is measured by moving the particle in and out of a tightly focused laser beam. SMS is typically used for particles that are much smaller than the laser spot size. In this paper, we extend the analysis of the SMS signal to particles with sizes comparable to or larger than the laser spot, where the shape of the particle matters. These results are important for the analysis of polydisperse samples that have a wide range of sizes. The presented example images and analysis of a carbon microparticle sample show the utility of the derived expressions. In particular, we show that SMS can be used to generate extinction cross-section information about micrometer-sized particles with complex shapes.
    Full-text · Article · Feb 2016 · Applied Optics
  • Kyle D. Olson · Joseph J. Talghader
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    ABSTRACT: Solar selective coatings that absorb solar incident light but that inhibit emission of thermal light can have a dramatic impact on the performance of Direct Steam Generation (DSG) systems. In prior art, perfect coatings with instantaneous transitions between high absorption and low absorption have been modeled. In this paper non-ideal spectral, environmental, and material properties of solar selective coatings are shown to have significant effects on the efficiencies and optimum transition wavelengths of real systems. By introducing more real world parameters into the coating optimization it is desired that a more cost effective and efficient system can be built. It is shown that using ideal conditions the optimum transition wavelength for a DSG system is 1.4. μm with an efficiency of 55.7%. Whereas for a realistic non-ideal DSG system the optimum transition is at 3.4. μm resulting in an efficiency around 30% depending on the concentration factor used. It is then shown that an optimized selective coating will be outperformed by a simple non-selective black absorber with 95% absorption at concentration factors above 80 and above 130 when the AM1.5 spectrum is used.
    No preview · Article · Feb 2016
  • Lucas Taylor · Joseph Talghader
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    ABSTRACT: Thermal effects in optical substrates are vitally important in determining laser damage resistance in long-pulse and continuous-wave laser systems. Thermal deformation waves in a soda-lime-silica glass substrate have been measured using high-speed interferometry during a series of laser pulses incident on the surface. Two-dimensional images of the thermal waves were captured at a rate of up to six frames per thermal event using a quantitative phase measurement method. The system comprised a Mach-Zehnder interferometer, along with a high-speed camera capable of up to 20,000 frames-per-second. The sample was placed in the interferometer and irradiated with 100 ns, 2 kHz Q-switched pulses from a high-power Nd:YAG laser operating at 1064 nm. Phase measurements were converted to temperature using known values of thermal expansion and temperature-dependent refractive index for glass. The thermal decay at the center of the thermal wave was fit to a function derived from first principles with excellent agreement. Additionally, the spread of the thermal distribution over time was fit to the same function. Both the temporal decay fit and the spatial fit produced a thermal diffusivity of 5 x 10(-7) m(2)/s. (C) 2015 Optical Society of America
    No preview · Article · Oct 2015 · Applied Optics
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    ABSTRACT: The present work describes the procedures and results from the first temperature measurements in closed chamber detonations obtained using the thermoluminescence (TL) of particles specifically developed for temperature sensing. Li2B4O7:Ag,Cu (LBO), MgB4O7:Dy,Li (MBO) and CaSO4:Ce,Tb (CSO) were tested separately in a total of 12 independent detonations using a closed detonation chamber at the Naval Surface Warfare Center, Indian Head Explosive Ordnance Disposal Technology Division (NSWC IHEODTD). Detonations were carried out using two different explosives: a high temperature plastic bonded explosive (HPBX) and a low temperature plastic bonded explosive (LPBX). The LPBX and HPBX charges produced temperatures experienced by the TL particles to be between ~550–670 K and ~700–780 K, respectively, depending on the shot. The measured temperatures were reproducible and typically higher than the thermocouple temperatures. These tests demonstrate the survivability of the TL materials and the ability to obtain temperature estimates in realistic conditions, indicating that TL may represent a reliable way of estimating the temperature experienced by free-flowing particles inside an opaque post-detonation fireball.
    No preview · Article · Sep 2015 · Journal of Luminescence
  • Andrew Brown · Albert Ogloza · Lucas Taylor · Jeff Thomas · Joseph Talghader
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    ABSTRACT: This paper describes the physical processes that occur when high-power continuous-wave laser light interacts with absorbing particles on a low-absorption optical surface. When a particulate-contaminated surface is illuminated by high-power continuous-wave laser light, a short burst of light is emitted from the surface, and the particles rapidly heat over a period of milliseconds to thousands of degrees Celsius, migrating over and evaporating from the surface. The surviving particles tend to coalesce into larger ones and leave a relatively flat residue on the surface. The total volume of the material on the surface has decreased dramatically. The optical surface itself heats substantially during illumination, but the surface temperature can decrease as the material is evaporated. Optical surfaces that survive this process without catastrophic damage are found to be more resistant to laser damage than surfaces that have not undergone the process. The surface temperature of the conditioned surfaces under illumination is lower than that of unconditioned surfaces. These conditioning effects on particles occurred within the first 30 s of laser exposure, with subsequent laser shots not affecting particle distributions. High-speed photography showed the actual removal and agglomeration of individual particles to occur within about 0.7 ms. Elemental changes were measured using time-of-flight secondary ion mass spectroscopy, with conditioned residuals being higher in hydrocarbon content than pristine particles. The tests in this study were conducted on high-reflectivity distributed Bragg reflector coated optics with carbon microparticles in the size range of 20-50 μm, gold particles of size 250 nm, and silica 1 μm in size.
    No preview · Article · Jun 2015 · Applied Optics
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    ABSTRACT: A method has been devised and tested for measuring the c-axis orientation of crystal grains in thin sections of glacier ice. The crystal orientation and grain size of ice are of great interest to glaciologists since these parameters contain information on the prior thermal and flow history of the ice. The traditional method of determining c-axis orientation involves a transmission measurement through an ice sample, a process that is time-consuming and therefore impractical for obtaining a continuous record. A reflection- or backscatter-based method could potentially be used inside boreholes, with bubbles as reflectors to avoid such drawbacks. The concept demonstration of this paper is performed on ice slices, enabling a direct comparison of accuracy with traditional methods. Measurements of the crystal orientations (, ) in 11 grains showed an average error of ±0.8° in , with no grain error >1.4°. Measurements of  showed an average error of ±8.2° on ten grains, with unexplained disagreement on the remaining grain. Although the technique is applied specifically to glacier ice, it should be generally applicable to any transparent birefringent polycrystalline material.
    Full-text · Article · Nov 2014 · Journal of Glaciology
  • P.R. Armstrong · M.L. Mah · L. Taylor · J.J. Talghader
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    ABSTRACT: Infrared-transparent microheaters have been constructed to reduce the background blackbody radiation produced by the heater. Among other applications, such heaters allow one to probe the high temperature peaks of thermoluminescent(TL) materials. The microheater consists of peripheral platinum heating elements on a mid-infrared transparent alumina platform. Alumina has a relatively low blackbody signal at high temperature for wavelengths less than 8μm. To test the reduced blackbody emission, an aperture was placed over the heating coils and then the transparent center of the microheater. The amount of infrared light transmitted through the aperture was reduced by 90% as the aperture moved from the highly emissive heater coils at 450°C to the largely transparent center at the same temperature.
    No preview · Article · Oct 2014
  • K. Olson · A. Ogloza · J. Thomas · J. Talghader
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    ABSTRACT: A model is presented and confirmed experimentally that explains the anomalous behavior observed in continuous wave (CW) excitation of thermally isolated optics. Distributed Bragg Reflector (DBR) high reflective optical thin film coatings of HfO2 and SiO2 were prepared with a very low absorption, about 7 ppm, measured by photothermal common-path interferometry. When illuminated with a 17 kW CW laser for 30 s, the coatings survived peak irradiances of 13 MW/cm2, on 500 μm diameter spot cross sections. The temperature profile of the optical surfaces was measured using a calibrated thermal imaging camera for illuminated spot sizes ranging from 500 μm to 5 mm; about the same peak temperatures were recorded regardless of spot size. This phenomenon is explained by solving the heat equation for an optic of finite dimensions and taking into account the non-idealities of the experiment. An analytical result is also derived showing the relationship between millisecond pulse to CW laser operation where (1) the heating is proportional to the laser irradiance (W/m2) for millisecond pulses, (2) the heating is proportional to the beam radius (W/m) for CW, and (3) the heating is proportional to W/m⋅ tan−1(t/m) in the transition region between the two.
    No preview · Article · Sep 2014 · Journal of Applied Physics
  • Ryan Shea · Anand Gawarikar · Joseph Talghader
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    ABSTRACT: Incorporation of bismuth telluride/antimony telluride co-sputtered thermoelectric junctions into MEMS devices requires process developments for patterning and encapsulation as well as characterization of properties such as film stress and contact resistance. Test structures are presented for measuring important thermoelectric properties, resistivity, thermal conductivity, carrier concentration, and Seebeck coefficient. A fabrication process is presented that allows the junctions to be deposited, patterned, encapsulated, and etch released. Measurement of the thermoelectric junctions reveals a room temperature figure of merit, ZT, of 0.43 with a total Seebeck coefficient difference of 150 mu V/K, resistivities of 17.4 and 7.6 mu Omega-m, and thermal conductivity of 0.34 and 0.30 W/mK for antimony telluride and bismuth telluride, respectively. The junctions have been incorporated into state of the art uncooled thermopile infrared detectors with a peak detectivity of 3 x 109 cm*Hz(1/2)/W.
    No preview · Article · Jun 2014 · Journal of Microelectromechanical Systems
  • A.S. Gawarikar · R.P. Shea · Joseph J. Talghader
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    ABSTRACT: We have derived an expression for the effective absorbing area for thermal infrared detectors having non-zero absorption in the support legs, which is different from the geometric areas of the constituent detector elements. This technique is particularly applicable to devices where sensitivity is more important than fill-factor, as opposed to standard imaging arrays. The effective area can simply be substituted in standard equations to obtain a good estimate of the detector performance under uniform flood illumination conditions. The formalism can also be used for estimating the contributions of the individual signal generating elements to the total measured signal. This approximation has been tested for MEMS infrared detectors with thermoelectric readout operating under vacuum. The responsivity of the same device calculated using the effective area approximation and measured using a tightly constrained absorbing area are found to match very closely, within 5% over the most wavelengths and within 15% at the shortest thermal infrared wavelengths.
    No preview · Article · Jun 2014 · Journal of Microelectromechanical Systems
  • Philip R. Armstrong · Merlin L. Mah · Sangho S. Kim · Joseph J. Talghader
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    ABSTRACT: Most thermoluminescent materials are created using crystal growth techniques; however, it would be of great utility to identify those few thermoluminescent materials that can be deposited using simpler methods, for example to be compatible with the early portions of a silicon integrated circuit or microelectromechanical fabrication process. In this work, thin films of yttrium oxide with a terbium impurity (Y2O3:Tb) were deposited on silicon wafers by electron beam evaporation. The source for the Y2O3:Tb was made by combining Y2O3 and Tb4O7 powders. The approximate thicknesses of the deposited films were 350 nm. After deposition, the films were annealed at 1100 °C for 30 s to improve crystallinity. There is a strong correlation between the x-ray diffraction (XRD) peak intensity and the thermoluminescent glow curve intensity. The glow curve displays at least two peaks at 140 °C and 230 °C. The emission spectra was measured using successive runs with a monochromator set to a different wavelength for each run. There are two main emission peaks at 490 nm and 540 nm. The terbium impurity concentration of approximately 1 mol% was measured using Rutherford backscattering spectrometry (RBS). The Y2O3:Tb is sensitive to UV, x-ray, and gamma radiation. The luminescent intensity per unit mass of UV irradiated Y2O3:Tb was about 2 times that of x-ray irradiated TLD-100.
    No preview · Article · Apr 2014 · Journal of Luminescence
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    ABSTRACT: 3D Meta-Optics are optical components that are based on the engineering of the electromagnetic fields in 3D dielectric structures. The results of which will provide a class of transformational optical components that can be integrated at all levels throughout a High Energy Laser system. This paper will address a number of optical components based on 2D and 3D micro and nano-scale structures and their performance when exposed to high power lasers. Specifically, results will be presented for 1550 nm and 2000 nm spectral bands and power densities greater than100 kW/cm 2 .
    Full-text · Conference Paper · Nov 2013
  • Lucas N Taylor · Andrew K Brown · Aaron J Pung · Eric G Johnson · Joseph J Talghader
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    ABSTRACT: The laser-damage thresholds of single material and nanolaminate thin films were compared under continuous-wave (CW) illumination conditions. Nanolaminate films consist of uniform material interrupted by the periodic insertion of one or more atomic layers of an alternative material. Hafnia and titania were used as the base materials, and the films were deposited using atomic-layer deposition. The nanolaminates were less polycrystalline than the uniform films, as quantified using x-ray diffraction. It was found that the nanolaminate films had reduced laser-damage thresholds on smooth and patterned substrates as compared to uniform single-material films. This behavior is unusual as prior art indicates that amorphous (less polycrystalline) materials have higher laser-damage thresholds under short-pulse excitation. It is speculated that this may indicate that local thermal conduction affects breakdown more strongly under CW excitation than the dielectric properties that are important for short-pulse excitation.
    No preview · Article · Nov 2013 · Optics Letters
  • Sangho S. Kim · Philip R. Armstrong · Merlin L. Mah · Joseph J. Talghader
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    ABSTRACT: It is well known that thermal gradients penetrating deep into a material can preserve a memory of the temperature history of the surface. To date, this concept has been largely applied in the earth sciences, but there are many applications where a memory of rapid thermal events would be useful. For example, multiple layers of thermoluminescent films could serve as temperature sensors that indicate temperature versus depth in a microfabricated structure. As an advance toward this goal, this paper examines the effect of nonuniform temperature profiles on the thermoluminescence of heterogeneous multilayers. A Nd:YAG laser is used to create a known thermal event and apply pulses of heat energy of varying duration to a metalized thermoluminescent multilayer composed of LiF:Mg,Ti and CaF2:Dy. The thermoluminescence of the system is measured before and after the applied laser pulse. To model the process, a finite-difference time-domain method is used to calculate the dynamic heat transfer, and the temperature distribution is plugged into a first order kinetics model of the thermoluminescence of each film to get a final luminescent intensity. A thermal contact conductance between the critical layers is also introduced. Dynamic temperatures in durations of hundreds of milliseconds are resolved with the technique, and simulation curves match experimental measurements to within 6% at 250 ms.
    No preview · Article · Aug 2013 · Journal of Applied Physics
  • A.S. Gawarikar · R.P. Shea · Joseph J. Talghader
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    ABSTRACT: We describe uncooled thermal detectors with a peak detectivity of at least 3 ×109 cm √{Hz}/W with spectrally selective absorption in the long-wave infrared. The spectral selectivity in absorption is achieved through resonant cavity coupling of a thin metal film with a low-order air-gap optical cavity. The electrical readout uses thermoelectric thin films with a Johnson noise limited performance. The detectors are of multiple sizes but those with 100- μm2 area have time constants of 58 ms and thermal conductances of 2.3 ×10-7 W/K.
    No preview · Article · Aug 2013 · IEEE Transactions on Electron Devices
  • Ryan P. Shea · Anand S. Gawarikar · Joseph J. Talghader
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    ABSTRACT: On extremely small scales, traditional microcooler performance estimates must be corrected to include losses due to radiation. We present a method for analysis of microcoolers having a significant radiative contribution to their thermal conductance. We have fabricated ultrasmall microcoolers from sputtered Bi2Te3/Sb2Te3 thermoelectric junctions with cooling volumes of 200 μm × 200 μm × 65 nm, which we believe to be the smallest microcoolers ever made. The devices are highly thermally isolated with total thermal conductance under 5 × 10−7 W/K in vacuum at room temperature. By fitting the temperature response to input power of the devices in vacuum, we have quantified the nonlinearity of the response to calculate the radiative and film contributions to the total thermal conductance of the device. Three device geometries are presented, with radiative contributions to thermal conductance of 15%, 26%, and 100% depending on their emissive area and support structure. The cooling capabilities of these devices are also measured with maximum cooling of 3.1 K for the 15% radiation-limited device and 2.6 K for the 26% radiation-limited device, with power consumptions below 5 μW.
    No preview · Article · Jul 2013 · Journal of Electronic Materials
  • Wing S. Chan · Mika J. Saarinen · Joseph J. Talghader
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    ABSTRACT: Vertical electrostatic wedge actuators are described that control nanometer-scale gaps between surfaces. Standard parallel-plate electrostatic actuators become difficult to stabilize across extremely small gaps because the nature of the forces and the force laws that describe them often deviate from a Coulomb's law dependence. In this work, a nanometer-scale air gap between a collapsed cantilever structure formed by two facing In0.53Ga0.47As surfaces, with areas of tens of microns, was controlled by a wedge electrostatic actuator. Upon actuation, the gap spacing between the surfaces was tuned over a maximum range of 55 nm with an applied voltage of 60 V.
    No preview · Article · Jun 2013 · Applied Physics Letters
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    ABSTRACT: We compared the laser damage performance of uniform versus nanolaminate thin films for hafnia and titania-based coatings. Our experiments showed that the films with higher crystallinity appeared to have better performance for CW systems.
    No preview · Conference Paper · Jun 2013
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    ABSTRACT: Thermoluminescent LiF:Mg, Ti (TLD-100) micro- particle sensors are demonstrated to record the thermal history of the environment around a high-explosive detonation. Microparticles are gamma-irradiated to fill their charge-carrier traps and then exposed to the detonation of 20 g of a plastic bonded HMX and Al explosive formulation at a test distance of approximately 22 cm from the center of the detonation. The thermal history of the microparticles is reconstructed by iteratively matching the degree of trap depopulation, derived from luminescence measurements, with that projected by theoretical simulations using appropriate models. Measurements and modeling indicate that the particles experienced a maximum temperature of 240°C, then cooled to 1°C above ambient temperature within 0.4 seconds. The resulting glow curve intensity is calculated to match the observed post-detonation signal to 3% averaged over the comparison values used for reconstruction.
    No preview · Article · May 2013 · IEEE Sensors Journal
  • A.S. Gawarikar · R.P. Shea · J.J. Talghader
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    ABSTRACT: Fabrication and characterization of high detectivity thermopile infrared detectors with spectrally selective absorption operating at room temperature is described. The detector architecture consists of a Johnson noise limited thermoelectric readout scheme integrated with a resonant cavity coupled absorber and a low thermal conductance support structure. A resonant responsivity enhancement of 4.3 and a peak detectivity of 1.3×109 cm Hz1/2 Watt-1 at 10.5 μm wavelength are demonstrated.
    No preview · Conference Paper · Jan 2013

Publication Stats

398 Citations
138.02 Total Impact Points

Institutions

  • 2000-2015
    • University of Minnesota Duluth
      • Department of Electrical Engineering
      Duluth, Minnesota, United States
  • 2007-2013
    • University of Minnesota Twin Cities
      • Department of Electrical and Computer Engineering
      Minneapolis, Minnesota, United States
    • Stanford University
      • Department of Electrical Engineering
      Palo Alto, California, United States