Flashlamp Pulse Research Articles

Sol–gel deposition of multiply doped thermographic phosphor coatings Al 2O 3:(Cr 3+, M 3+) (M = Dy, Tm) for wide range surface temperature measurement application

A promising method of measuring surface temperatures in harsh environments is the use of thermographic phosphor coatings. There, the surface temperature is evaluated from the phosphorescence decay lifetime following a pulsed laser or flash lamp light excitation. Depending on the used dopant, single doped M 3+:α-Al 2O 3 (M = Cr, Dy, Tm) emit at 694 nm (Cr 3+), 488 nm (Dy 3+), 584 nm (Dy 3+), and 459 nm (Tm 3+), respectively. However, the accessible temperature range with a single dopant is limited: for the Cr 3+-transition from 293 K up to 900 K, and for the Dy 3+ and Tm 3+-transitions both from 1073 K up to 1473 K. In the present study a new approach is followed to extend these limitations by co-doping two dopants using the sol–gel method and dip coating of α-Al 2O 3 thin films. For that application (Dy 3+ + Cr 3+) co-doped thin α-Al 2O 3 films and (Tm 3+ + Cr 3+) co-doped α-Al 2O 3 films with thicknesses of 4–6 μm were prepared, and the temperature-dependent luminescence properties (emission spectra and lifetimes) were analysed after pulsed laser excitation in the UV (355 nm). The phosphorescence lifetime as a function of temperature were measured between 293 K and 1473 K. A considerably extended range for surface temperature evaluation was established following this new approach by combining different dopants on the molecular level.

Sol–gel deposition of multiply doped thermographic phosphor coatings Al 2O 3:(Cr 3+, M 3+) (M = Dy, Tm) for wide range surface temperature measurement application

A promising method of measuring surface temperatures in harsh environments is the use of thermographic phosphor coatings. There, the surface temperature is evaluated from the phosphorescence decay lifetime following a pulsed laser or flash lamp light excitation. Depending on the used dopant, single doped M 3+:α-Al 2O 3 (M = Cr, Dy, Tm) emit at 694 nm (Cr 3+), 488 nm (Dy 3+), 584 nm (Dy 3+), and 459 nm (Tm 3+), respectively. However, the accessible temperature range with a single dopant is limited: for the Cr 3+-transition from 293 K up to 900 K, and for the Dy 3+ and Tm 3+-transitions both from 1073 K up to 1473 K. In the present study a new approach is followed to extend these limitations by co-doping two dopants using the sol–gel method and dip coating of α-Al 2O 3 thin films. For that application (Dy 3+ + Cr 3+) co-doped thin α-Al 2O 3 films and (Tm 3+ + Cr 3+) co-doped α-Al 2O 3 films with thicknesses of 4–6 μm were prepared, and the temperature-dependent luminescence properties (emission spectra and lifetimes) were analysed after pulsed laser excitation in the UV (355 nm). The phosphorescence lifetime as a function of temperature were measured between 293 K and 1473 K. A considerably extended range for surface temperature evaluation was established following this new approach by combining different dopants on the molecular level.

Épilation par laser ou par lampe polychromatique pulsée

The theory behind laser hair removal and pulsed flashlamps is briefly reviewed, as are the devices currently available for this indication. Today, the treatment procedure has been firmly established so that clear and precise information can be provided to patient on the results obtained with these techniques, both for medical and esthetic indications. The potential complications are discussed with respect to the treatment procedures and a thorough understanding of the theoretical foundations.

Heat generation by optically and thermally interacting aggregates of gold nanoparticlesunder illumination

The generation of heat by clusters and arrays of gold nanoparticles under illumination isinvestigated theoretically. The nanoparticles are embedded in a homogeneous dielectric medium,and the finite thermal resistance at the interface between the nanoparticle and the medium istaken into account. An analytic solution is derived for the case of a single nanoparticle. TheT-matrix method is used to calculate the energy absorption efficiency of groups ofnanoparticles, taking into account their optical interactions. Heat transfer equations aredeveloped that take into account thermal interactions between nanoparticles. Theequations are solved numerically using the finite element software COMSOL. Periodicboundary conditions are applied to treat the thermal interactions between thenanoparticles for arrays of nanoparticles. Results are presented for illumination by astandard xenon flash lamp. The thermal resistance at the nanoparticle–medium interface isfound to strongly influence the nanoparticle temperature, but to have negligible influenceon the temperature of the dielectric medium after a few tens of nanoseconds of exposure tothe flash lamp pulse. Optical interactions are found to be important if particle centres areseparated by about twice the particle diameter or less. Thermal interactions betweennanoparticles via the medium are found to be the dominant factor in determiningthe temperature increase in the dielectric medium. The maximum temperatureincrease is proportional to the volume fraction of the nanoparticles in the medium.

Generation of singlet oxygen in fullerene-containing media: 1. Photodesorption of singlet oxygen from fullerene-containing surfaces

It is shown that upon irradiation of fullerene-containing surfaces by laser or flashlamp pulses, oxygen adsorbed by these surfaces efficiently escapes to the gas phase. The observation of luminescence pulses in the spectral region of 762 and 1268 nm confirms the presence of oxygen molecules in the excited singlet state in the desorbed oxygen. The conditions for optimisation of the efficiency of singlet-oxygen production are studied. It is shown that singlet oxygen at the concentration sufficient for obtaining operation of a fullerene–oxygen–iodine laser can be produced in this way.

Épilation par laser ou par lampe polychromatique pulsée

The theory behind laser hair removal and pulsed flashlamps is briefly reviewed, as are the devices currently available for this indication. Today, the treatment procedure has been firmly established so that clear and precise information can be provided to patient on the results obtained with these techniques, both for medical and esthetic indications. The potential complications are discussed with respect to the treatment procedures and a thorough understanding of the theoretical foundations.

Investigation of Cu-doped Li2B4O7 single crystals by electron paramagnetic resonance and time-resolved optical spectroscopy

A low-temperature study of the thermoluminescent dosimeter material, lithium tetraborate(Li2B4O7) doped by Cu, has been carried out by the methods of electron paramagnetic resonance(EPR) and time-resolved polarization spectroscopy using 4–20 eV synchrotron radiation and1 µs Xe flash lamp pulses in the region 3–6 eV. The observed EPR spectra of an unpaired holewith strong d-character and characteristic hyperfine splittings can be ascribed toCu2+ substituted at a Li lattice site and displaced due to relaxation. The results on theCu+-related luminescence strongly support the conclusion about a low-symmetry position of copperimpurity ions in the lithium tetraborate lattice. The temperature dependence of the decay kinetics ofthe Cu+-related 3.35 eV emission indicates a triplet nature for the relaxed excited state of theCu+ centres. An off-centreposition of the Cu+ ion in the relaxed excited state is suggested.

Theodore Harold Maiman

Theodore Harold Maiman

Triplet Energy Studies of Thiophene and para-Phenylene Based Oligomers

A series of conjugated materials based on oligomers of the para-phenylene type and oligothiophenes was prepared, and their phosphorescence spectra were recorded at 77 K using a pulsed flash-lamp as a light source and gated detection. The triplet energies of the oligomers were estimated and correlated with their chemical structure. It was found that simple changes in the building block sequence in the thiophene-containing oligomers allowed for tuning the triplet energy from 1.86 to 2.35 eV (530-670 nm). Hypsochromic shifts and little variation of the triplet energy were obtained with increasing length of the pi-system for thiophene end-capped oligomers, contrary to the usual behavior of unsubstituted oligomers. The experimental results were supported with theoretical computations from density functional theory (B3LYP/6-31G*) calculations, which indicated that changes in the geometry and delocalization of the triplet excited state account for the trends in the triplet energy evolution.

Electronic transitions in Li2B4O7:Cu single crystals

AbstractA low‐temperature study of Li2B4O7:Cu crystals by methods of time‐resolved polarization spectroscopy using synchrotron radiation in the 4–20 eV region and microsecond Xe flash lamp pulses in the 3–6 eV region is reported. The results strongly support the conclusion about a low‐symmetry position of the Cu+ ion in its ground state. The temperature dependence of the decay kinetics of the Cu+‐related 3.35 eV emission indicates a triplet nature for the relaxed excited state of the Cu+ centres. A pseudo off‐centre position of the Cu+ ion in the relaxed excited state is suggested. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Single Crystal CVD Diamond Growth for Detection Device Fabrication

AbstractSingle crystal (SC) CVD diamond is known to exhibit superior electronic properties than polycrystalline ones for detection applications. In our study, tested samples were grown using CVD in an ASTEX type reactor, at various microwave powers and keeping all other parameters constant. The crystalline quality and purity of the samples were investigated using Raman spectroscopy and birefringence microscopy measurements.The diamonds layers were chemically cleaned and oxidized, towards ionization chamber fabrication using Ni and Au contacts for rectifying properties. The devices electronics and detection properties were then evaluated: leakage currents were probed from I(V) measurements and the contacts behavior were tested under 60Co source at various dose rates. Time Of Flight (TOF) and Charge Collection Efficiency (CCE) measurements were evaluated under an 241Am alpha source and enabled the measurement of the mobility, carrier diffusion lengths and lifetime as a function of the growth parameters. Moreover the response under a UV pulsed flash lamp was probed in order to appreciate the CCE as a function of the repetition rate. The measurements demonstrated the importance of the power density during growth on the detection properties.

Effect of the Crystallization Conditions on the Epitaxial Relationship of Si Deposited on 3C-SiC(100)

The epitaxial relationship of Si deposited on 3C-SiC was studied using both free standing 3C-SiC(100) material from Hoya and 3C-SiC thin layers deposited on Si(100) as substrates. The conditions of Si growth were varied depending on the substrate. When Si is deposited at 1000°C on (001) 3C-SiC, it is in perfect epitaxial relation with the SiC layer [100]Si//[100]SiC and [001]Si//[001]SiC. After a 20 ms flash lamp pulse on the same sample, which has the effect of fast melting of the Si top layer only, the defects in the Si are eliminated. Using free standing 3C-SiC, the deposition temperature was not limited by the Si melting point so that it was fixed at 1500°C in order to form a set of Si liquid droplets on the surface with diameters ranging from 5 to 20 μm. Surprisingly more than 60% of the Si droplets exhibit the epitaxial relation [110]Si//[001]SiC and [111]Si//[110]SiC after crystallization. The occurrence of this epitaxial relationship can be understood in terms of lattice mismatch reduction from 20% to 18.3%. The conditions of crystallization, most probably the cooling rate, seem to have a strong effect on Si orientation.

New multichannel kinetic spectrophotometer–fluorimeter with pulsed measuring beam for photosynthesis research

A multichannel kinetic spectrophotometer-fluorimeter with pulsed measuring beam and differential optics has been constructed for measurements of light-induced absorbance and fluorescence yield changes in isolated chlorophyll-proteins, thylakoids and intact cells including algae and photosynthetic bacteria. The measuring beam, provided by a short (2 micros) pulse from a xenon flash lamp, is divided into a sample and reference channel by a broad band beam splitter. The spectrum in each channel is analyzed separately by a photodiode array. The use of flash measuring beam and differential detection yields high signal-to-noise ratio (noise level of 2 x 10(-4) in absorbance units per single flash) with negligible actinic effect. The instrument covers a spectral range between 300 and 1050 nm with a spectral resolution of 2.1, 6.4 or 12.8 nm dependent on the type of grating used. The optical design of the instrument enables measuring of the difference spectra during an actinic irradiation of samples with continuous light and/or saturation flashes. The time resolution of the spectrophotometer is limited by the length of Xe flash lamp pulses to 2 micros.

Millisecond Annealing: Past, Present and Future

AbstractThe challenge of achieving maximal dopant activation with minimal diffusion has re-awakened interest in millisecond-duration annealing processes, almost two decades after the initial research in this field. Millisecond annealing with pulsed flash-lamps or scanned energy beams can create very shallow and abrupt junctions with high concentrations of electrically active carriers, but solutions for volume manufacturing must also meet formidable process control requirements and economic metrics. The repeatability and uniformity of the temperature cycle is the key for viable manufacturing technology, and the lessons from the development of commercial rapid thermal processing (RTP) tools are especially relevant. Advances in the process capability require a fuller understanding of the trade-off between dopant activation, defect annealing. diffusion and deactivation phenomena. There is a strong need for a significant expansion of materials science research into the fundamental physical processes that occur at the short time scales and high temperatures provided by millisecond annealing.

The removal of co-deposited hydrocarbon films from plasma facing components using high-power pulsed flashlamp irradiation

The use of carbon-based materials for first wall components in tokamaks results in the formation of hydrocarbon deposits on divertor components that could lead to a high level of tritium retention in future fusion devices. Experiments at UMIST have demonstrated that photonic cleaning using high power Xenon flashlamp sources is an efficient method for removing such films and represents a good candidate technology for international thermonuclear experimental reactor (ITER) operations. Studies have shown that effective film removal occurs at a fluence threshold of between 1.9 and 2.5J/cm2. The by-products of the cleaning process, both particulates and gases, have been characterised using particle sizing spectrometry and quadrupole mass spectrometry respectively. It is found that hydrogen, methane, acetylene, ethylene, ethane and carbon dioxide are the principal gaseous products produced during the cleaning process, which also produces a significant fraction of particulates in the size range 2–20μm.

The Design and Comparison of Continuous and Pulsed Ultraviolet Reactors for Microbial Inactivation in Water

The following article discusses the design of a pulsed flashlamp reactor system for inactivation of microorganisms in drinking water. The results of a mathematical model for calculation of the flashlamp lifetime are reported, and the final design of the prototype UV reactor is shown. Experimental test results for static and flowing tests are also reported with a discussion of the DNA repair mechanisms that appear to be present when polychromatic light is used for inactivation of E. coli in water.

Le rajeunissement du visage : techniques de complément ou de substitution à la chirurgie. Apport des lasers et systèmes à effets thermiques

The methods additional or substitution for the surgery of facial skin ageing are dramatically rising before 40 years. These methods are addressed more to the wrinkles and others signs of aging skin. They can constitute a door of entry in the aesthetic treatments and needs a professional approach. These noninvasive methods (within the meaning of the incision) can present complications this the more so as the tendency is with the vulgarizing and with under considerations of the initial diagnosis and the treatment itself. The devices of thermal effects consist of lasers, pulsed flashlamps and radiofrequency. The objective of this development is to consider the bonds, which link the initial diagnosis and the proposal for a treatment by considering side effects and complications of each method.

Tunable ultraviolet visible photoacoustic detection: Analysis of the sensitivity and selectivity provided by a xenon flash lamp

A fundamental understanding of the physical and chemical properties that dictate the absorption of pulsed light and subsequent release of heat to generate a transient pressure wave was used to test the concept of a multi-wavelength photoacoustic detector. Analysis of the wave equation predicts that with long-pulse excitation, i.e. microseconds FWHM, absorption by the solvent, and not electrostriction determines the limit of detection. Calculation of the mechanical to electrical conversion efficiencies of piezoelectric transducers shows that absorbed pulse energies of microjoules, typical of pulsed flash lamps, are sufficient to provide measurable photoacoustic signals. A pulsed xenon flash lamp (2 μs FWHM) which emits a broad spectrum over the UV and visible region is used as an excitation source to detect trace quantities of metals in aqueous solution using pulsed photoacoustic detection. In this work, dielectric mirrors were used to detect two analytes, CrO 4 2− (monitored at 355 nm) and Co 2+ (monitored at 532 nm), simultaneously. This approach increases both the flexibility and selectivity of pulsed photoacoustic methods. We obtained a detection limit of 2.6×10 −4 absorbance units per centimeter in aqueous samples. This work shows that pulsed lasers are not a necessity for ultra-sensitive photoacoustic spectroscopy.

Photophysics of the triple state of metal complexes of 9-anthracenecarboxylic acid

The triplet-triplet (T-T) absorption spectra and the T-T absorption decay kinetics are measured for solutions of 9-anthracenecarboxylic acid (ACA) and its complexes with metal ions (Cd3+ and Ln3+=Y3+, La3+, Ce3+, Eu3+, Gd3+, and Tb3+) in dimethylsulfoxide (DMSO) by the methods of flashlamp and laser pulse photolysis. The rate constants kT of intracomplex quenching of the triplet state are measured for ACA complexes with ions Gd3+, Ce3+, Tb3+, and Eu3+. Larger values of kT in complexes of ACA with paramagnetic ions Ce3+, Tb3+, and Eu3+, which have low-lying energy levels, compared to the values of kT for complexes with other ligands (pyrene-3-sulfonate, pyrene-1,3,6,8-tetrasulfonate, and benzo[ghi]perylene-1,2-dicarboxylate) were explained by the lower energy of the triplet state of ACA (14400 cm−1). For a complex with a paramagnetic ion Gd3+, which has no low-lying energy levels, the value of kT is close to that measured by us earlier for the inner-sphere complex of pyrene-1,3,6,8-tetrasulfonate with the same ion. These results confirm our earlier assumption about the inner-sphere complexing of ACA with Ln3+ ions in DMSO.

Wavelength-dependent measurements of optical-fiber transit time, material dispersion, and attenuation

A new, to our knowledge, method for measuring the wavelength dependence of the transit time, material dispersion, and attenuation of an optical fiber is described. We inject light from a 4-ns rise-time pulsed broadband flash lamp into fibers of various lengths and record the transmitted signals with a time-resolved spectrograph. Segments of data spanning a range of approximately 3000 A are recorded from a single flash-lamp pulse. Comparison of data acquired with short and long fibers enables the determination of the transit time and the material dispersion as functions of wavelength dependence for the entire recorded spectrum simultaneously. The wavelength-dependent attenuation is also determined from the signal intensities. The method is demonstrated with experiments using a step-index 200-mum-diameter SiO(2) fiber. The results agree with the transit time determined from the bulk glass refractive index to within ?0.035% for the visible (4000-7200-A) spectrum and 0.12% for the UV (2650-4000-A) spectrum and with the attenuation specified by the fiber manufacturer to within ?10%.