Showing papers by "Richard E. Russo published in 2005"

Experimental investigation of ablation efficiency and plasma expansion during femtosecond and nanosecond laser ablation of silicon

Abstract: Femtosecond laser (Ti:sapphire, 100 fs pulse duration) ablation of silicon in air was compared with nanosecond laser (Nd:YAG, 3 ns pulse duration) ablation at ultraviolet wavelength (266 nm) Laser ablation efficiency was studied by measuring crater depth as a function of pulse number For the same number of laser pulses, the fs-ablated crater was about two times deeper than the ns-crater The temperature and electron number density of the laser-induced plasma were determined from spectroscopic measurements The electron number density and temperature of fs-induced plasmas decreased faster than ns-induced plasmas due to different energy deposition mechanisms Images of the laser-induced plasma were obtained with femtosecond time-resolved laser shadowgraph imaging Plasma expansion in both the perpendicular and the lateral directions were compared

Quantum efficiency of ZnO nanowire nanolasers

Abstract: Crystalline ZnO nanowires were grown on sapphire and silicon substrates using pulsed-laser deposition. The optical properties of nanowire nanolasers, including their absolute light emission intensity and external and internal quantum efficiencies were experimentally determined. The external differential quantum efficiency was measured to be as high as 60% for lasing ZnO nanowires of 7.5μm in length, compared to a value of approximately 10% for photoluminescence. The absolute light emission intensity for individual nanowires was found to be in the vicinity of 0.1mW. By measuring the dependence of external differential quantum efficiency on the cavity length, the internal quantum efficiency of ZnO nanowire nanolasers was determined to be about 85%.

Femtosecond laser assisted growth of ZnO nanowires

Abstract: Crystalline ZnO nanowires were grown by the pulsed laser deposition (PLD) approach using a femtosecond laser as the ablation source. As determined by electron microscopy, the femtosecond PLD grown ZnO nanowires showed good crystalline characteristics and reasonably uniform diameters, which can be attributed to the homogeneity of femtosecond laser produced precursor vapor in which micron sized particulates are minimal. Photoluminescence spectroscopy measurements indicated a low threshold for lasing at room temperature. In addition, we examined the influence of oxygen partial pressure during the PLD growth process on the morphology and photoluminescence property of ZnO nanowires.

Particle size dependent chemistry from laser ablation of brass.

Abstract: The proportion of zinc and copper in particles formed by laser ablation of brass was found to vary with the particle diameter. Energy-dispersive X-ray analysis showed that smaller particles were zinc enhanced while larger particles were composed mostly of copper. A model based on condensation of vapor onto large droplets ejected from a melted liquid layer is proposed to describe the change in particle composition versus size.

Study of particle size influence on laser ablation inductively coupled plasma mass spectrometry using an in-line cascade impactor

Abstract: An in-line cascade impactor was used as a low pass filter to study the effects of particles on inductively coupled plasma mass spectrometry (ICP-MS) performance. The temporal relative standard deviation (TRSD), which represents the short term internal precision during repetitive ablation, was improved from 20% to 4% by removing large particles ablated from brass alloys. External precision for spot to spot measurements on a bulk sample was improved to approximately 2%. The ablated aerosol chemistry was particle size dependent: smaller particles were zinc rich while larger particles were copper rich.

A Sensor for Laser Ultrasonic Measurement of Elastic Properties of Moving Paper

Abstract: An automated, non‐contact, non‐destructive sensor has been developed for measurement of sheet flexural and shear rigidity in paper manufacturing. It was tested on a pilot web handler at web speeds up to 25.4 m/s. A model equation was fitted to the frequency dependence of the phase velocity of Ao mode Lamb waves. Ultrasound was generated in paper with a pulsed Nd:YAG laser and detected with a Mach‐Zehnder interferometer coupled with a scanning mirror/timing system to compensate for paper motion.

Final Technical Report of project: "Contactless Real-Time Monitoring of Paper Mechanical Behavior During Papermaking"

Abstract: The early precursors of laser ultrasonics on paper were Prof. Y. Berthelot from the Georgia Institute of Technology/Mechanical Engineering department, and Prof. P. Brodeur from the Institute of Paper Science and Technology, both located in Atlanta, Georgia. The first Ph.D. thesis that shed quite some light on the topic, but also left some questions unanswered, was completed by Mont A. Johnson in 1996. Mont Johnson was Prof. Berthelot's student at Georgia Tech. In 1997 P. Brodeur proposed a project involving himself, Y. Berthelot, Dr. Ken Telschow and Mr. Vance Deason from INL, Honeywell-Measurex and Dr. Rick Russo from LBNL. The first time the proposal was not accepted and P. Brodeur decided to re-propose it without the involvement from LBNL. Rick Russo proposed a separate project on the same topic on his side. Both proposals were finally accepted and work started in the fall of 1997 on the two projects. Early on, the biggest challenge was to find an optical detection method which could detect laser-induced displacements of the web surface that are of the order of .1 micron in the ultrasonic range. This was to be done while the web was having an out-of-plane amplitude of motion in the mm range due to web flutter; while moving at 10 m/s to 30 m/s in the plane of the web, on the paper machine. Both teams grappled with the same problems and tried similar methods in some cases, but came up with two similar but different solutions one year later. The IPST, GT, INL team found that an interferometer made by Lasson Technologies Inc. using the photo-induced electro-motive force in Gallium Arsenide was able to detect ultrasonic waves up to 12-15 m/s. It also developed in house an interferometer using the Two-Wave Mixing effect in photorefractive crystals that showed good promises for on-line applications, and experimented with a scanning mirror to reduce motion-induced texture noise from the web and improve signal to noise ratio. On its side, LBNL had the idea to combine a commercial Mach-Zehnder interferometer to a spinning mirror synchronized to the web speed, in order to make almost stationary measurements. The method was demonstrated at up to 10 m/s. Both teams developed their own version of a web simulator that was driving a web of paper at 10 m/s or higher. The Department of Energy and members of the Agenda 2020 started to make a push for merging the two projects. This made sense because their topics were really identical but this was not well received by Prof. Brodeur. Finally IPST decided to reassign the direction of the IPST-INL-GT project in the spring of 1999 to Prof. Chuck Habeger so that the two teams could work together. Also at this time, Honeywell-Measurex dropped as a member of the team. It was replaced by ABB Industrial Systems whose engineers had extensive previous experience of working with ultrasonic sensors on paperboard. INL also finished its work on the project as its competencies were partly redundant with LBNL. From the summer of 1999, the IPST-GT and LBNL teams were working together and helped each other often by collaborating and visiting either laboratory when was necessary. Around the beginning of 2000, began an effort at IPST to create an off-line laser-ultrasonics instrument that could perform automated measurements of paper and paperboard's bending stiffness. It was widely known that the mechanical bending tests of paper used for years by the paper industry were very inaccurate and exhibited poor reproducibility; therefore the team needed a new instrument of reference to validate its future on-line results. In 1999-2000, the focus of the on-line instrument was on a pre-industrial demonstration on a pilot coater while reducing the damage to the web caused by the generation laser, below the threshold where it could be visible by the naked eye. During the spring of 2000 Paul Ridgway traveled to IPST and brought with him a redesigned system still using the same Mach-Zehnder interferometer as before, but this time employing an electric motor-driven spinning mirror instead of the previously belt-driven mechanical spinning mirror. For testing we chose to use a 1 foot-wide paper loop running on IPST's large scale web handler which could reach a web speed of 2,000 feet/min (10.16 m/s). This was more representative of the conditions encountered of a pilot coater, than on a table-top scale web simulator.

Rapid ion-beam-induced Ostwald ripening in two dimensions

Abstract: Ion-beam-induced grain coarsening in initially amorphous (Zr,Y)Ox layers is observed by atomic force microscopy. The films were bombarded at room temperature. Grain-boundary grooves indicate that the larger grains have a diameter of about 83nm at 2min, and 131nm at 5min. Up to 5min, the grain size evolves with time as tβ, with β=0.5±0.2. Based on a new parametrization of ion-induced grain-boundary translation, we derive a theoretical estimate of β=3∕7, consistent with our measurement. By 7.5min, many of the grain-boundary grooves are shallow and indistinct, suggesting that the surviving grains are mutually well aligned. Such rapid grain growth at room temperature is unusual and is enabled by the ion bombardment. Similar grain growth processes are expected during ion-beam-assisted deposition film growth. The status of ion-textured yttria stabilized zirconia films as buffer layers for high-current high-temperature superconducting films is briefly summarized.

Laser Ultrasonics at 20 m/s in the production environment and on a budget: from dream to reality

Abstract: A laser-based ultrasonic system for non-contact and non-destructive measurement of the elastic properties of paper was demonstrated on a paper manufacturing machine during commercial operation with paper moving around 20 m/s. We believe this to be the highest sample traveling speed reported to date for a commercial application of laser ultrasonics. Ultrasonic waves were generated in the paper with a pulsed Nd:YAG laser at 1064 nm wavelength and detected with a Mach-Zehnder interferometer coupled with a scanning mirror/timing system to compensate for paper motion. Measurements of the flexural rigidity (FR) and out-of-plane shear rigidity (SR) of the paper web were done automatically by fitting the frequency dependence of the phase velocity of Ao mode Lamb waves to a model wave propagation equation. Variation in FR and SR across the width of the paper sheet (cross-direction profiles), effects of changes in paper manufacturing process variables on measured FR and SR, comparisons with traditional mechanical stiffness tests are presented. The sensor head is fully optical and thus measures the web properties without any contact. This laser-ultrasonics system combines a very reasonable cost with a relatively small footprint and low power consumption due to the low power output of the lasers that are used. Finally, laboratory data indicate that this technology is directly transferable to measurements on sheet metals and possibly other opaque web materials