Pulsed Raman Measurements of Phonon Populations: Time Reversal, Correction Factors, and All That

1983 ◽  
Vol 13 ◽  
Author(s):  
A. Compaan ◽  
H.W. Lo ◽  
A. Aydinli ◽  
M.C. Lee
Keyword(s):  
Energy Density ◽  
Time Reversal ◽  
Room Temperature ◽  
Laser Energy ◽  
Correction Factors ◽  
Experimental Conditions ◽  
Optic Phonon ◽  
Anti Stokes ◽  
Raman Probe ◽  
532 Nm

ABSTRACTTransient optic phonon populations are measured in crystalline Si as a function of 532 nm laser energy density. The use of a continuously tunable pulsed dye laser as the Raman probe allows us to obtain, under exact experimental conditions, all correction factors necessary to extract the phonon population without the necessity of relying on room temperature or oven-heated conditions. We find the shift of the 520 cm−1 Raman-line to be consistent with the observed Stokes/anti-Stokes ratios indicating a maximum optic phonon temperature of 450 ± 100°C. A discussion is also given of the errors in several recent criticisms of the Raman results.

Laser-Triggered Surface Flashover Characteristics of Al2O3 in Pulsed Voltage

2011 ◽  
Vol 354-355 ◽  
pp. 1224-1227
Author(s):  
Ru Zheng Pan ◽  
You Hua Wang ◽  
Min Tang Li ◽  
Ling Ling Pang ◽  
Jue Wang ◽  
...  
Keyword(s):  
Energy Density ◽  
Nd:Yag Laser ◽  
Delay Time ◽  
Laser Energy ◽  
Test System ◽  
Vacuum Condition ◽  
Surface Flashover ◽  
532 Nm ◽  
Time Decrease ◽  
Pulsed Voltage

Based on the platform of laser-triggered surface flashover in pulsed voltage, experiment of laser-triggered surface flashover is carried out in air and vacuum condition with pulsed voltage. A single/double harmonic, with wavelength of 1064/532 nm, Q-switched Nd:YAG laser is applied to trigger the surface flashover. The test system consists of flat electrodes and columned insulator. The material of electrode is copper and the material of insulator is Al2O3. Laser pulse’s wavelengths are 532nm and 1064nm, and laser is focused with rectangle. The results of experiment show that flashover delay time and jitter time decrease with increase of pulsed voltage or laser energy density, the delay time of 1064nm laser trigger is larger than that of 532nm laser trigger, and the delay time and jitter time in vacuum condition are less than the delay time and jitter time in air condition.

A Reinvestigation of the Deceptively Simple Reaction of Toluene with ●OH, and the Fate of the Benzyl Radical. I. a Combined Thermodynamic and Kinetic Study on the Competition Between ●OH Addition and Hydrogen Abstraction Reactions.

2019 ◽  
Author(s):  
Zoi Salta ◽  
Agnie M. Kosmas ◽  
Marc E. Segovia ◽  
Martina Kieninger ◽  
Oscar Ventura ◽  
...  
Keyword(s):  
Density Functional ◽  
Room Temperature ◽  
Hydrogen Abstraction ◽  
Reaction Rates ◽  
Composite Model ◽  
Alternative Mechanism ◽  
Radical Intermediate ◽  
Experimental Conditions ◽  
Methyl Group ◽  
Benzyl Radical

This work reports density functional and composite model chemistry calculations performed on the reactions of toluene with the hydroxyl radical. Both experimentally observed H-abstraction from the methyl group and possible additions to the phenyl ring were investigated. Reaction enthalpies and heights of the barriers suggest that H-abstraction is more favorable than ●OH addition to the ring. The calculated reaction rates at room temperature and the radical-intermediate product fractions support this view. This is somehow contradictory with the fact that, under most experimental conditions, cresols are observed in a larger concentration than benzaldehyde. Since the accepted mechanism for benzaldehyde formation involves H-abstraction, a contradiction arises that begs for an explanation. In this first part of our work we give the evidences that support the preference of hydrogen abstraction over ●OH addition and suggest an alternative mechanism which shows that cresols can actually arise also from the former reaction and not only from the latter.

A Reinvestigation of the Deceptively Simple Reaction of Toluene with ●OH, and the Fate of the Benzyl Radical. I. a Combined Thermodynamic and Kinetic Study on the Competition Between ●OH Addition and Hydrogen Abstraction Reactions.

2019 ◽  
Author(s):  
Zoi Salta ◽  
Agnie M. Kosmas ◽  
Marc E. Segovia ◽  
Martina Kieninger ◽  
Oscar Ventura ◽  
...  
Keyword(s):  
Density Functional ◽  
Room Temperature ◽  
Hydrogen Abstraction ◽  
Reaction Rates ◽  
Composite Model ◽  
Alternative Mechanism ◽  
Radical Intermediate ◽  
Experimental Conditions ◽  
Methyl Group ◽  
Benzyl Radical

This work reports density functional and composite model chemistry calculations performed on the reactions of toluene with the hydroxyl radical. Both experimentally observed H-abstraction from the methyl group and possible additions to the phenyl ring were investigated. Reaction enthalpies and heights of the barriers suggest that H-abstraction is more favorable than ●OH addition to the ring. The calculated reaction rates at room temperature and the radical-intermediate product fractions support this view. This is somehow contradictory with the fact that, under most experimental conditions, cresols are observed in a larger concentration than benzaldehyde. Since the accepted mechanism for benzaldehyde formation involves H-abstraction, a contradiction arises that begs for an explanation. In this first part of our work we give the evidences that support the preference of hydrogen abstraction over ●OH addition and suggest an alternative mechanism which shows that cresols can actually arise also from the former reaction and not only from the latter.

scholarly journals Amplification by stimulated emission of nitrogen-vacancy centres in a diamond-loaded fibre cavity

Nanophotonics ◽  
2020 ◽  
Vol 9 (15) ◽  
pp. 4505-4518
Author(s):  
Sarath Raman Nair ◽  
Lachlan J. Rogers ◽  
Xavier Vidal ◽  
Reece P. Roberts ◽  
Hiroshi Abe ◽  
...  
Keyword(s):  
Room Temperature ◽  
Gain Medium ◽  
Stimulated Emission ◽  
Nitrogen Vacancy ◽  
Qualitative Model ◽  
Seed Laser ◽  
Laser Threshold ◽  
Cavity System ◽  
Emission Changes ◽  
532 Nm

AbstractLaser threshold magnetometry using the negatively charged nitrogen-vacancy (NV−) centre in diamond as a gain medium has been proposed as a technique to dramatically enhance the sensitivity of room-temperature magnetometry. We experimentally explore a diamond-loaded open tunable fibre-cavity system as a potential contender for the realisation of lasing with NV− centres. We observe amplification of the transmission of a cavity-resonant seed laser at 721 nm when the cavity is pumped at 532 nm and attribute this to stimulated emission. Changes in the intensity of spontaneously emitted photons accompany the amplification, and a qualitative model including stimulated emission and ionisation dynamics of the NV− centre captures the dynamics in the experiment very well. These results highlight important considerations in the realisation of an NV− laser in diamond.

X-Ray Diffraction Study of Hep Metals. I. Line Broadening in Polycrystalline Cd Powder

1974 ◽  
Vol 29 (12) ◽  
pp. 1771-1777 ◽  
Author(s):  
N. C. Haider ◽  
S. H. Hunter
Keyword(s):  
Room Temperature ◽  
Small Deformation ◽  
Correction Factors ◽  
Line Broadening ◽  
X Ray Diffraction ◽  
Fault Probability ◽  
Large Particle Size ◽  
X Ray ◽  
Melting Temperatures ◽  
Diffraction Patterns

Powder Cd of 99.999% purity was prepared at room temperature (25 °C) and x-ray diffraction patterns were obtained using CuKaα radiation with Ni-filter. The line broadening was analyzed after incorporating the appropriate correction factors. At room temperature Cd was found to have large particle size (653 A), small root mean square strain (.001), small deformation fault probability a (.003). and negligible growth fault probability β(0). Compared to other hep metals which have been studied earlier and which have higher melting temperatures, metal Cd is much less affected by mechanical deformation at room temperature.

scholarly journals Ê-μ-V Correlation In One-Colour Photolysis/Ionization Of Tert-Butyl Nitrite

1990 ◽  
Vol 10 (3) ◽  
pp. 197-206 ◽  
Author(s):  
P. Marcus ◽  
I. Platzner ◽  
I. Bar ◽  
S. Rosenwaks
Keyword(s):  
Transition Dipole Moment ◽  
Laser Polarization ◽  
Experimental Conditions ◽  
Transition Dipole ◽  
Vector Correlation ◽  
Peak Splitting ◽  
Tert Butyl ◽  
Spatial Velocity ◽  
Fragment Peak ◽  
532 Nm

An anisotropic spatial velocity distribution was observed for NO+ produced following one-color photolysis/ionization of tert-butyl nitrite (TBN) by a pulsed polarized laser at 266, 355 and 532 nm in a time-of-flight mass spectrometer. The dependence of the NO+ fragment mass peak profile on the wavelength and on the polarization was monitored. The most striking feature is the varying fragment peak splitting obtained under the same experimental conditions by changing the laser polarization direction. This phenomenon is a result of the vector correlation between the laser polarization,Ê, at a given wavelength, the electronic transition dipole moment of TBN,μ, and the direction of the NO fragment velocity, v. The dynamics of the photodissociation process and, in particular, its directional properties are discussed in view of these results.

DLC Coated Textile Vascular Prostheses Tested in Sheep

2013 ◽  
Vol 647 ◽  
pp. 20-24
Author(s):  
Miroslav Jelínek ◽  
Jiří Podlaha ◽  
Tomáš Kocourek
Keyword(s):  
Energy Density ◽  
Carotid Artery ◽  
Layer Thickness ◽  
Laser Energy ◽  
Diamond Like Carbon ◽  
Vascular Prostheses ◽  
Merino Sheep ◽  
Preliminary Results ◽  
20 Nm ◽  
Deposition Conditions

Textile vascular prostheses ARTECOR were coated by laser with amorphous diamond-like carbon layers (DLC) with thickness up to 200 nm. Layers were created in 0.25 Pa of Argon at laser energy density of 8 or 22 Jcm-2. Depending on the deposition conditions, DLC properties moved from soft „graphitic“ to more „diamond“ (53 % of sp3 bonds). Coated prostheses of various DLC thickness and sp3 content were implanted into carotid artery of Merino sheep. The prostheses were extirpated after 100 days (~180 days). From preliminary results follows that prostheses coated with DLC layer thickness of 20 nm and higher sp3 content showed the best results.

scholarly journals Preliminary Laser Cleaning Studies of a Consolidated Prehistoric Basketry Coming from the Pile Building of Fiavè-Carera in the North-East of Italy

2006 ◽  
Vol 2006 ◽  
pp. 1-5 ◽  
Author(s):  
Romina Belli ◽  
Antonio Miotello ◽  
Paolo Mosaner ◽  
Laura Toniutti ◽  
Marta Bazzanella
Keyword(s):  
Energy Density ◽  
Material Removal ◽  
Laser Energy ◽  
Laser Cleaning ◽  
Original Surface ◽  
North East ◽  
The North ◽  
Cleaning Procedures ◽  
Krf Excimer Laser ◽  
Organic Deposits

In the archaeological field, some specific advantages are recognized to laser cleaning, like, for example, the absence of mechanical contacts with the sample. The cleaning procedures generally involve a multilayer structure (dust, dirty, organic deposits, and, in some cases, consolidant substances). In this work, prehistoric wood samples (found and consolidated in 1970s) have been laser irradiated (KrF excimer laser) in order to restore their original surface aspect. A certain amount of burned matter was also present. Samples came from a fragment of a prehistoric basketry found in the lake dwelling site of Fiavè-Carera, Trento, Italy (1500–1400 BC). It was observed that the laser cleaning effects are strictly dependent on the irradiation parameters (power density and number of pulses). Efficient material removal was possible by using appropriate energy density. Moreover, for lower laser energy density, special structures appeared on the surface of the consolidating substance that we attributed to heating-induced stresses on the consolidant surface.

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