Jeremy Junghans

Bio: Jeremy Junghans is an academic researcher from University of Arkansas. The author has contributed to research in topics: Laser diode & JFET. The author has an hindex of 8, co-authored 21 publications receiving 234 citations.

High-power QCW arrays for operation over wide temperature extremes

Abstract: A family of laser diode arrays has been developed for QCW operation in adverse environmental conditions. The arrays contain expansion-matched heatsinks, hard solder, and are built using a process that minimizes the packaging-induced strain on the laser diode bars. The arrays are rated for operation at 200 Watts/bar under normal operating conditions. This work contains test results for these arrays when run under a variety of harsh operating conditions. The conditions were chosen to mimic those required by many military and aerospace laser programs. Life test results are presented over a range of operating temperatures common to military specifications (-40 °C to + 70 °C) at a power level of approximately 215 Watts/bar. The arrays experienced no measurable degradation over the course of the life test. Operation at the temperature extremes did not introduce any additional detectable failure mechanisms. Also presented are results of characterization and reliability tests conducted at cryogenic temperatures. Diode arrays have been subjected to repeated cycles in rapid succession between room temperature and 77 K with temperature ramp rates up to 100 K/minute. Pre- and post- thermal cycle P-I-V data are compared. The results demonstrate the suitability of these arrays for operation at cryogenic temperatures.

Microchannel cooler for a single laser diode emitter based system

Abstract: A laser system that allows transverse arrangement of laser emitters around a laser medium. The system includes a laser medium with a coolant source such as a pump and electrical controls. A pump layer has a mounting surface, an opposite bottom surface and a center aperture through which the laser medium is inserted. A plurality of laser diode emitters are disposed on the mounting surface of the pump layer circumferentially around the laser medium. An intermediate layer has at least one radial channel in fluid communication with the coolant conduit of the pump layer. The intermediate layer is in contact with the bottom surface of the pump layer. A middle layer has a plurality of micro-channels formed therethrough and a center aperture. The micro-channels are radially arranged around the center aperture and the middle layer in contact with the intermediate layer. The coolant source is fluidly coupled to the micro-channels to allow coolant to be directed through the microchannels and the radial channel to impinge on the bottom surface of the pump layer.

Operating condition limitations of high density QCW arrays

Abstract: Northrop Grumman Cutting Edge Optronics (NGCEO) has developed a laser diode array package with minimal bar-to-bar spacing. These High Density Stack (HDS ) packages allow for a power density increase on the order of ~ 2.5x when compared to industry-standard arrays. Power densities as high as 15 kW/cm 2 can be achieved when operated at 200 W/bar. This work provides a detailed description of the duty factor, pulse width and power limitations of high density arrays. The absence of the interposing heatsinks requires that all of the heat generated by the interior bars must travel through the adjacent bars to the electrical contacts. This results in limitations to the allowable operating envelope of the HDS arrays. Thermal effects such as wavelength shif ts across large HDS arrays are discussed. An overview of recent HDS design and ma nufacturing improvements is also pres ented. These improvements result in reliable operation at higher power densities and increased duty f actors. A comparison of the effect of bar geometry on HDS performance is provided. Test data from arrays featuring these improvements based on both full 1 cm wide diode bars as well as 3 mm wide mini-bars is also presented. Keywords: QCW, laser diode, solid-state pumping, hard solder, diode array, power density, high density stack, spacing, pitch, duty factor

QCW diode array reliability at 80x and 88x nm

Abstract: Northrop Grumman Cutting Edge Optronics (NGCEO) has recently developed high-power laser diode arrays specifically for long-life operation in quasi-CW applications These arrays feature a new epitaxial wafer design that utilizes a large optical cavity and are packaged using AuSn solder and CTE-matched heat sinks This work focuses on life test matrix of multiple epitaxial structures, multiple wavelengths, and multiple drive currents Particular emphasis is given to the 80x and 88x wavelength bands running at 100-300 Watts per bar Reliable operating points are identified for various applications including range finding (product lifetimes less than 1 billion shots) and industrial machining (product lifetimes greater than 20 billion shots) In addition to life test data, a summary of performance data for each epitaxial structure and each bar design is also presented

Advanced Laser Diode Cooling Concepts

Abstract: A new, patent-pending method of cooling high-power laser diode arrays has been developed which leverages advances in several areas of materials science and manufacturing. This method utilizes multi-layer ceramic microchannel coolers with small (100’s of microns) integral water channels to cool the laser diode bar. This approach is similar to the current state-of-the-art method of cooling laser diode bars with copper microchannel coolers. However, the multi-layer ceramic coolers offer many advantages over the copper coolers, including reliability and manufacturing flexibility. The ceramic coolers do not require the use of deionized water as is mandatory of high-thermal-performance copper coolers. Experimental and modeled data is presented that demonstrates thermal performance equal to or better than copper microchannel coolers that are commercially available. Results of long-term, high-flow tests are also presented to demonstrate the resistance of the ceramic coolers to erosion. The materials selected for these coolers allow for the laser diode bars to be mounted using eutectic AuSn solder. This approach allows for maximum solder bond integrity over the life of the part.

Emerging Applications of Liquid Metals Featuring Surface Oxides

Abstract: Gallium and several of its alloys are liquid metals at or near room temperature. Gallium has low toxicity, essentially no vapor pressure, and a low viscosity. Despite these desirable properties, applications calling for liquid metal often use toxic mercury because gallium forms a thin oxide layer on its surface. The oxide interferes with electrochemical measurements, alters the physicochemical properties of the surface, and changes the fluid dynamic behavior of the metal in a way that has, until recently, been considered a nuisance. Here, we show that this solid oxide “skin” enables many new applications for liquid metals including soft electrodes and sensors, functional microcomponents for microfluidic devices, self-healing circuits, shape-reconfigurable conductors, and stretchable antennas, wires, and interconnects.

State of the art of high temperature power electronics

Abstract: High temperature power electronics has become possible with the recent availability of silicon carbide devices. This material, as other wide-bandgap semiconductors, can operate at temperatures above 500 °C, whereas silicon is limited to 150-200 °C. Applications such as transportation or a deep oil and gas wells drilling can benefit. A few converters operating above 200 °C have been demonstrated, but work is still ongoing to design and build a power system able to operate in harsh environment (high temperature and deep thermal cycling).

Methods to pattern liquid metals

Abstract: This highlight describes emerging methods to pattern metals that are liquid at room temperature. The ability to pattern liquid metals is important for fabricating metallic components that are soft, stretchable, conformal, and in some cases, shape-reconfigurable. Applications include electrodes, antennas, micro-mirrors, plasmonic structures, sensors, switches, and interconnects. Gallium (Ga) and its liquid metal alloys are attractive alternatives to toxic mercury. This family of alloys spontaneously forms a surface oxide that dominates the rheological and wetting properties of the metal. These properties pose challenges using conventional fabrication methods, but present new opportunities for patterning innovations. For example, Ga-based liquid metals may be injected, imprinted, or 3D printed on either soft or hard substrates. The use of a liquid metal also enables rapid and facile room temperature processing. The patterning techniques organize into four categories: (i) patterning enabled by lithography, (ii) injection, (iii) subtractive techniques, and (iv) additive techniques. Although many of these approaches take advantage of the surface oxide that forms on Ga and its alloys, some of the approaches may also be suitable for patterning other soft-conductors (e.g., conductive inks, pastes, elastomeric composites).

Different shades of oxide: from nanoscale wetting mechanisms to contact printing of gallium-based liquid metals.

Abstract: Gallium-based liquid metals are of interest for a variety of applications including flexible electronics, soft robotics, and biomedical devices. Still, nano- to microscale device fabrication with these materials is challenging because, despite having surface tension 10 times higher than water, they strongly adhere to a majority of substrates. This unusually high adhesion is attributed to the formation of a thin oxide shell; however, its role in the adhesion process has not yet been established. In this work, we demonstrate that, dependent on dynamics of formation and resulting morphology of the liquid metal–substrate interface, GaInSn adhesion can occur in two modes. The first mode occurs when the oxide shell is not ruptured as it makes contact with the substrate. Because of the nanoscale topology of the oxide surface, this mode results in minimal adhesion between the liquid metal and most solids, regardless of substrate’s surface energy or texture. In the second mode, the formation of the GaInSn–substrat...

Wide Bandgap Technologies and Their Implications on Miniaturizing Power Electronic Systems

Abstract: The current state of wide bandgap device technology is reviewed and its impact on power electronic system miniaturization for a wide variety of voltage levels is described. A synopsis of recent complementary technological developments in passives, integrated driver, and protection circuitry and electronic packaging are described, followed by an outline of the applications that stand to be impacted. A glimpse into the future based on the current technological trends is offered.