Flashlamp Research Articles

Past Forward: The Nobelist’s First Laser

When George Porter arrived at the University of Cambridge in 1945 as a Ph.D. student, he found the equipment remarkably primitive. Students had to build their own oscilloscopes! To conduct his research—detecting the short-lived molecules known as free radicals—Porter pieced together a setup that included a surplus army searchlight powered by a surplus diesel engine. After seeing flash lamps at a Siemens factory, he decided to modify his approach, replacing the continuous light source with short, intense pulses of light. With his flash photolysis technique, Porter was able to capture reactions lasting mere milliseconds. To study even faster reactions, though, he needed a faster light source, for which he’d have to wait. The ruby laser, invented in 1960, was the ideal solution. Porter used this one to record nanosecond-scale reactions. Flash photolysis is still used to study semiconductors, nanoparticles, and photosynthesis, among other things. For their work on high-speed, lightdriven chemical reactions, Porter; his Ph.D. adviser, Ronald G.W. Norrish; and Manfred Eigen shared the 1967 Nobel Prize in Chemistry.

100 Hz repetition-rate 2.794 μm Cr,Er:YSGG passively Q-switched laser with Fe2+:ZnSe saturable absorber

A concave-convex resonator was used to compensate for the thermal focal length, which obviously realizes the high energy output of Cr,Er:YSGG lasers at 100 Hz pumped by a flash lamp. The maximum output energy of the concave-convex cavity is 62.3 mJ, which is 2.9 times the maximum with a plane-parallel cavity when the same energy is injected in free-running operation. A passively Q-switched 2.794 μm laser using a Fe2+:ZnSe saturable absorber was demonstrated in this research. The device produced single pulses of 4.3 mJ energy with a 107.6 ns pulse width and multi-pulses (5 pulses) with 20 mJ total output energy at 100 Hz.

Non-destructive testing of delamination defects in GFRP patches using step heating thermography

Composite materials are extensively used for repairs in the different industries, where their quality is monitored by nondestructive testing. Through this work, the functional role of step-heating thermography on the detection of delamination defects in multi-layer GFRP composite patches are investigated. Specimens prepared for testing were GFRP patches of different thicknesses (4 and 8 layer laminates) which were mounted on to the aluminum plates. In order to create interlaminar separation, kepton sheets of miscellaneous sizes were incorporated between the laminas, during the patch manufacturing. The defects were arranged at the edge and center of different layers, simultaneously. After applying of step heating by using of flash lamps to the manufactured samples, the factors affecting the defect identification (thermal intensity and size difference percentage) were investigated. The results showed that all defects in both 4 and 8 layer laminates were identified in the thermal images were the dimensional accuracy of the defect size was 30% higher in 8 layer patch due to the lesser reflection of heat to the IR camera.

Crystallization of catalytic CVD hydrogenated n-a-Si films on textured glass substrates by flash lamp annealing

Flash lamp annealing (FLA) is a short-duration annealing technique that can crystallize amorphous silicon (a-Si) films for thin-film polycrystalline Si (poly-Si) solar cells. We investigated the crystallization of n-type hydrogenated a-Si (n-a-Si:H) films formed by catalytic chemical vapor deposition on Si nitride- (SiN x -) coated textured glass substrates. The n-a-Si:H films with a thickness of ∼2.7 μm were crystallized by FLA with no film peeling even without chromium adhesion layers. We also confirmed that the crystallization takes place through explosive crystallization (EC). The addition of phosphorous to the precursor a-Si:H slightly modifies the crystallization, resulting in different grain sizes and EC velocities compared to the case of EC of intrinsic a-Si:H.

Soft X-ray absorption study of sputtered tin oxide films

The bonding structure of tin oxide (SnOx) films grown by reactive DC magnetron sputtering has been studied by the combination of X-ray diffraction (XRD) and soft X-ray absorption near-edge structure (XANES). The oxygen incorporation in the films has been controlled by the O2 partial pressure (PO2) in the O2/Ar discharge mixture. In addition, the impact of substrate heating and post-deposition flash lamp annealing (FLA) on crystal growth has been studied. In general, it has been stablished a transition from SnO to SnO2 arrangements by increasing PO2, where XRD and XANES provide complementary results about the formation of single- and mixed-phase films. In samples produced at room temperature, XANES gives unique information about such structural evolution, as well as related to defects like the incorporation of O2 molecules at high PO2. FLA on samples grown at room temperature promotes crystal growth and the phase evolution follows the initial structural selectivity. Finally, the optical properties and surface morphology of the films have been correlated with the structural identification.

A first quantitative approach for detecting volumetric defects in additive manufactured metal samples by using active thermographic technique

This work is focused on the quantitative analysis of defects produced in metal samples of AISI 316L with Laser Powder Bed Fusion (L-PBF) additive manufacturing (AM) process by means of active thermographic techniques. A simple and common set-up with 2 flash lamps and a cooled sensor has been used to analyse the differences between planar and volumetric defects. In particular, the presence of imprinted spheres containing inside non-sintered metallic powder has been compared with those of similar cylinders in size and depth, induced in similar samples. Furthermore, the differences in terms of thermal contrasts have been studied between the cylinder manufactured as an internal defect with powder inside, against the same geometry, but with a small channel for the discharge of the non-melted material. The analysis of the thermal signal and the application of post processing algorithms allowed us to identify the thermal features suitable for describing the behaviour of different kind of defects, typical of the process.

Sol-Gel Derived, Inkjet Printed, and Flash Lamp Annealed Ta2o5 on Flexible, Interdigitated Electrodes for Capacitive Ph Sensing at High Ionic Strength

Sol-Gel Derived, Inkjet Printed, and Flash Lamp Annealed Ta2o5 on Flexible, Interdigitated Electrodes for Capacitive Ph Sensing at High Ionic Strength

High-Frequency (MHz) Ignition of Commercial Flash Lamps for Solid State Lasers

High-Frequency (MHz) Ignition of Commercial Flash Lamps for Solid State Lasers

Aerosol Jet Printed and Photonic Cured Paper-Based Ammonia Sensor for Food Smart Packaging

In this work, we report the manufacturing and experimental analysis of low-cost and eco-friendly paper-based gas sensors for food smart packaging. The hygroscopic properties of paper help detecting the presence of water-soluble gases in an environment provided with relative humidity (RH) above a given threshold (RH > 75%) and discovering the presence of gaseous-markers of the food-spoilage process, like ammonia. Carbon interdigitated electrodes were printed by Aerosol Jet Printing and sintered by Flash Lamp Annealing on chromatographic paper, obtaining a mean resistance value of (231 ± 20) kΩ and (249 ± 28) kΩ for the left and the right electrode, respectively. After being tested at different RH values (75, 80, 90, 100%), and once stabilized, they were tested with different ammonia concentrations (3, 6, 9, and 12 ppm). A proportional resistance decrease was evidenced in increasing ammonia concentration. Considering the baseline at a constant value of RH=75%, the sensors showed a resistance variation of 12% in presence of the lowest concentration of 3 ppm. Three different temperatures were considered during the tests, 5 °C, 15 °C, and 25 °C, evidencing no primary influence of this parameter. Ethanol and acetone were investigated as representatives of interfering compounds such as alcohols and ketones that may be developed during food spoilage. Good selectivity was observed both by studying these compounds individually and together with ammonia. Experimental results showed that 48 ppm of acetone induced a resistance change lower than 3 ppm of ammonia, while 240 ppm of ethanol induced a resistance change comparable to 12 ppm of ammonia.

Dependence of the Xe flash lamps’ UV radiation efficiency on the volumetric power density of the discharge

The study results of the peak and average electrical volumetric power density influence on the radiation efficiency and brightness temperature in the 200–300 nm bactericidal spectrum range are presented. A linear dependence of the radiation efficiency change in the 5.1–8.4 % range was obtained with the average volumetric power density increase from 177 to 390 kW/cm3. The brightness temperature dependence in the specified spectral region on the peak volumetric power density is a logarithmic character with decreasing growth rate when approaching 9 kK. This effect can be associated with both radiation blocking by vaporized quartz fumes and with UV light shielding by outer plasma layers

Controlled Silicidation of Silicon Nanowires Using Flash Lamp Annealing.

Among other new device concepts, nickel silicide (NiSix)-based Schottky barrier nanowire transistors are projected to supplement down-scaling of the complementary metal-oxide semiconductor (CMOS) technology as its physical limits are reached. Control over the NiSix phase and its intrusions into the nanowire is essential for superior performance and down-scaling of these devices. Several works have shown control over the phase, but control over the intrusion lengths has remained a challenge. To overcome this, we report a novel millisecond-range flash lamp annealing (FLA)-based silicidation process. Nanowires are fabricated on silicon-on-insulator substrates using a top-down approach. Subsequently, Ni silicidation experiments are carried out using FLA. It is demonstrated that this silicidation process gives unprecedented control over the silicide intrusions. Scanning electron microscopy and high-resolution transmission electron microscopy are performed for structural characterization of the silicide. FLA temperatures are estimated with the help of simulations.

Comparing Bactericidal Effect of Pulsed Flash Lamp and Continuous Sterilization UV Lamps with a Cold Atmospheric Pressure Plasma Jet on E. Coli Solid Growth Medium

Comparing Bactericidal Effect of Pulsed Flash Lamp and Continuous Sterilization UV Lamps with a Cold Atmospheric Pressure Plasma Jet on E. Coli Solid Growth Medium

The dynamics of the formation of a plasma channel after the ignition of a discharge in cesium-mercury-xenon pulsed lamps

The paper deals with the spectral characteristics of the radiation of a pulsed discharge into a cesium – mercury – xenon mixture during the formation of a plasma channel from the moment of ignition until reaching the nominal operating mode of the flash lamp. It is shown that as the electric power of the discharge increases, the spectral emission lines of mercury vapors change their intensity, and the cesium lines self-reversal. It is revealed that the intensity of spectral lines in different regions of the plasma channel differs due to the presence of longitudinal temperature gradients.

Rapid photodegradation of organic micro-pollutants in water using high-intensity pulsed light

The rising concentration of organic micro-pollutants (OMPs) in water resources has become a major concern for aquatic ecosystems and human health. Advanced oxidation processes (AOPs), based on ultraviolet (UV) photolysis and photochemical reactions, have been suggested for the degradation of various micropollutants present in water and wastewater. However, the application of these methods on large scale is limited due to the long treatment times. Here we evaluate the efficiency of high-intensity pulsed light treatment (HIPL) for the degradation of organic compounds in aqueous conditions. A solution containing 11 OMPs was treated with short (<2 ms) and high-intensity light pulses produced by a Xenon flash lamp. It was observed that the HIPL parameters, such as the number of pulses and optical energy dose, have a significant impact on the efficiency of the treatment. The main advantage of HIPL is the fast kinetics that allows efficient photodegradation of OMPs from the aqueous solution rapidly and within milliseconds. The present work showcases the potential of HIPL technique for the post-treatment of contaminated water containing pharmaceuticals and endocrine disruptor compounds.

Toward low-temperature processing of lead zirconate titanate thin films: Advances, strategies, and applications

Lead zirconate titanate (PZT) thin films stand for a prominent technological brick in the field of microsystems. The recent improvements of their manufacturability combined with excellent piezoelectric properties have enabled their introduction in industrial clean rooms all around the world. These films require annealing temperatures beyond 600 °C to crystallize in the desired perovskite phase, which exhibits outstanding piezoelectric coefficients. This temperature requirement forbids large application fields such as flexible electronics, smart glass but also system-on-chip approaches. Decreasing the annealing temperature of PZT films would therefore spread further their potential usage to other applications. The purpose of this paper is to provide the reader with a comprehensive review of the different techniques available in the literature to process piezoelectric PZT thin films at temperatures compatible with semiconductors (450 °C), smart glass (400 °C), or flexible electronics (350 °C). We first present the typical ferroelectric and piezoelectric properties of PZT films. The different deposition techniques and growth mechanisms of these films are then reviewed with a focus on thermodynamics. Then, all the low temperature processes are detailed, such as seeding effects, the modification of deposition parameters in vapor-phase deposition, special annealing technologies assisted with UV, lasers, flash lamps, microwave radiations or high-pressure, a focus on the hydrothermal method, and finally what is called solution chemistry design with notably combustion synthesis. Transfer processing is also detailed, as an alternative way to this low temperature approach. An outlook of future applications enabled by these innovative techniques is finally provided.

Automated spectrophotometric platform for the quantification of multiple nucleic acid samples

A novel automated spectrophotometric platform was developed to upgrade a conventional prototype instrument platform for commercial use. A pulsed xenon flash lamp was chosen as the light source to improve the light output and a microsampling system was employed to precisely and rapidly aspirate micro-volume sample solutions. In addition, a three-axis positioning system was devised to increase the measurement capacity. All electrical components of the developed platform were linked and controlled with an integrated system. To verify the measurement performance and automated operation, a series of experiments were carried out. Double-stranded DNA samples at seven concentrations were automatically quantified. The concentrations were estimated with high linearity (R 2 ≒ 0.9998), repeatability (relative standard deviation ≤10.3%), and accuracy (>87.5%) across the concentration range from 0.25 to 10 ng/μL. In addition, this platform can be used in many different ways by changing a few parts or a sub-system and will be most useful in laboratories that handle a large number of samples. It is expected that the developed platform will be utilized for measuring circulating cell-free DNA and for quality control of next-generation sequencing, forensic medicine, noninvasive prenatal tests, and liquid biopsies.

Transient behaviour of the energy release after the discharge of flash lamps – A consideration of the afterglow

The knowledge about energy release and transient behaviour of flash lamps, used as short-term energy source in flash thermography investigations, is essential for a quantitative analysis of the results as well as for simulations regarding such experiments. Usually, only a rectangular pulse shape of a typical duration of a few milliseconds is regarded when flash lamps pulses are described. This note considers the afterglow period of a flash lamp explicitly and shows that negligence of this afterglow effect leads to a systematic underestimation of the pulse length and the related total energy release. In the reported case, the intensity transient recorded by a silicon photo diode was transformed into a temperature transient, allowing the study of the real energy release. It turns out that approximately only 50% of the entire pulse energy were released during the usually regarded period of 2.8 ms, while the other half was released within a period of 20 ms with an exponential decay.

Photo-Sintered Silver Thin Films by a High-Power UV-LED Module for Flexible Electronic Applications.

In recent printed electronics technology, a photo-sintering technique using intense pulsed light (IPL) source has attracted attention, instead of conventional a thermal sintering process with long time and high temperature. The key principle of the photo-sintering process is the selective heating of a thin film with large light absorption coefficients, while a transparent substrate does not heat by the IPL source. Most research on photo-sintering has used a xenon flash lamp as a light source. However, the xenon flash lamp requires instantaneous high power and is unsuitable for large area applications. In this work, we developed a new photo-sintering system using a high-power ultraviolet light emitting diode (UV-LED) module. A LED light source has many merits such as low power consumption and potential large-scale application. The silver nanoparticles ink was inkjet-printed on a polyethylene terephthalate (PET) and photo-sintered by the UV-LED module with the wavelength of 365 and 385 nm. The electrical resistivity as low as 5.44 × 10−6 Ω·cm (just about three times compared to value of bulk silver) was achieved at optimized photo-sintering conditions (wavelength of 365 nm and light intensity of 300 mW/cm2).

Flash-Lamp Enabled Atomic Layer Deposition of Titanium Oxide

Atomic layer deposition (ALD) processes are widely used in research and development as well as in various production environments. Nowadays, a variety of materials can be deposited using thermal and energy enhanced atomic layer deposition but there are limits that are mainly set by the properties of available precursors and the related processes. Besides the necessity of suitable precursors and chemical reactions to deposit a specific material, there are two major limitations: the thermal self-decomposition of precursor molecules which can be in conflict with the required process temperatures enabling desired film properties, and the typical temperature-related reactivity of precursors and co-reactants with substrate materials. These can affect the initial film growth and can lead to adhesion issues and unwanted interface layers, such as oxides formed by oxidizing agents used during the ALD process.The thermal stability of precursors can be improved by optimizing precursor molecules but this is often related to reduced volatility and reactivity. Additionally, increased process temperatures might be incompatible with the tolerable thermal budget. Hence, processes with precursors chemisorbing at sufficiently low temperatures to avoid self-decomposition in combination with a second,preferably short process step at elevated temperatures to enable the required film properties is desirable.We developed a novel flash lamp enabled atomic layer deposition (FLE-ALD) process to address these limitations of common ALD processes. The process combines the self-limiting chemisorption of precursor molecules in the first half-reaction with a millisecond flash lamp anneal (FLA) during the second half-reaction. The applied heat during the second process step can even enable single-source ALD processes by inducing a thermal decomposition of chemisorbed molecules that form the desired film material.This paper demonstrates the FLE-ALD approach for the deposition of titanium oxide in a single-source process combining titanium tetraisopropoxide (TTIP) precursor exposures with flashes of optical light with a duration in the millisecond range to heat a surface for a very short time and to decompose the chemisorbed TTIP molecules. The heat induced by the short FLA step is distributed into the substrate’s bulk and the process chamber during the subsequent purging step, resulting in a constant substrate temperature and maintaining the self-limiting behavior of the TTIP chemisorption.A process was developed to confirm the self-limiting film growth typical for ALD process as well as the constant growth per cycle by varying and characterizing process parameters like precursor dose, purge times, flash lamp energy, substrate temperature, and cycle numbers. The FLA energy variation confirmed the need for the induced heat to decompose the TTIP molecules. Below an applied voltage of 1 kV, the flash lamps weren’t ignited and no film growth could be observed. This behavior was even confirmed for temperatures up to 300 °C as shown in figure 1, which compares the film growth with and without an FLA step for a wide range of process temperatures. Spectroscopic ellipsometry was used to measure the thicknesses and to investigate the optical properties of the deposited films. The obtained data was successfully described by a model using the optical properties of titanium oxide from literature enabling reliable and reproducible film thickness measurements. This result matches the film composition measured by X-ray photoelectron spectroscopy, showing only titanium and oxygen without noteworthy carbon or hydrocarbon impurities with less than 1 at.%. Figure 1

Pulsed Ultraviolet Light Decontamination of Meat Conveyor Surfaces.

Contact with continuous belt conveyors during processing results in opportunities for pathogenic and spoilage microorganisms to contaminate meat products. The objective of this project is to investigate the germicidal response on the surface of food-grade conveyor belt materials treated with pulsed ultraviolet (PUV) light. Four conveyor belt types including: a stainless-steel chain-link belt, a polytetrafluoroethylene (PTFE)-coated fabric belt, a solid pliable polymer belt, and a rigid-linked polymer belt, were evaluated for the inactivation of Escherichia coli K12-NSR strain and lactic acid bacteria (LAB). Prior to bacterial inoculation, samples were classified as soiled or unsoiled, based on the presence or absence of pork intramuscular fluid on the surfaces of the conveyor samples. Using a variable speed conveyor, equipped with a Xenon flashlamp positioned 10-cm above the surface, each belt sample was exposed to PUV light at three fixed conveyor speeds: 3.05, 15.24, and 30.48 cm/sec, resulting in a total energy exposure of 3.31, 0.66 and 0.33 J/cm2, respectively. For samples inoculated with E. coli K12-NSR, the surface condition (soiled or unsoiled) by treatment interaction was significant for microbial inactivation on the surface of the rigid polymer linked belt (P < 0.05). For samples inoculated with the LAB cocktail, the same interaction was significant for the PTFE-coated fabric belt and the solid pliable polymer belt (P < 0.05). Microbial reduction ranged from 0.74 to 5.04 log10 CFU/cm2 for E. coli K12-NSR and 0.63 to 4.61 Log10 CFU/cm2 for LAB for the evaluated treatment parameters. The results of this project demonstrate that PUV light is an effective means of decontamination for conveyor belts during food processing.