scholarly journals Pulsed Co2-Laser Excitation of 03/02 Mixtures at Pressures From 0.16 to 1.20 Bar

1990 ◽  
Vol 10 (4) ◽  
pp. 207-226 ◽  
Author(s):  
B. Raffel ◽  
J. Wolfrum
Keyword(s):  
Laser Excitation ◽  
Vibrational Temperature ◽  
Laser Energy ◽  
Vibrational Excitation ◽  
Double Resonance ◽  
Uv Absorbance ◽  
Relaxation Model ◽  
Laser Fluences ◽  
Pulsed Co2 Laser ◽  
Fluence Dependence

An investigation is presented of the transient vibrational excitation of O3 in the collision dominated regime initiated by pulsed CO2-laser radiation. IR-UV-double resonance experiments and measurements of the absorbance for the CO2-laser lines 9P18, 20, and 22 were carried out. Mixtures of O3 (p=17 mbar) with 02 were investigated at pressures of 160 mbar ≤Pmixt≤1200 mbar and laser fluences of 0.10 J/cm2≤Fin< 2 J/cm2 . The results are interpreted by numerical simulations in terms of a comprehensive excitation/relaxation model based upon SSH-theory. Concerning the evolution of the excitation, simulated transients of the UV-absorbance compare well with the corresponding observed signals. The saturation of the absorbing O3-transitions is demonstrated by the measured fluence dependence of the absorption coefficient at the laser wavelengths. The extent of the 03-excitation can be deduced according to the model from the maximum vibrational temperature Tm reached in the v1- and v3-oscillators. Tm accessible via the UV-transients and also via the absorbed laser energy in the case of slow relaxation at 160 160​mbar≤Pmixt≤340 mbar. In this range both techniques result in the same values for Tm. The experimental and the corresponding simulated Tm depend exponentially on the laser fluence (Tm =const . F¯in0.3) provided Tm>400​K being also confirmed up to Pmixt=1200 mbar by the observed UV-transients.

Altitude dependence of the vibrational distribution of in the nightglow and the possible effects of vibrational excitation in the formation of O(1S)

1984 ◽  
Vol 62 (8) ◽  
pp. 780-788 ◽  
Author(s):  
I. C. McDade ◽  
E. J. Llewellyn ◽  
R. G. H. Greer ◽  
G. Witt
Keyword(s):  
Vibrational Relaxation ◽  
Vibrational Excitation ◽  
Relaxation Model ◽  
Terrestrial Atmosphere ◽  
Transfer Step ◽  
Vibrational Distribution ◽  
Altitude Dependence ◽  
Vibrational Levels ◽  
The Individual

A simple vibrational relaxation model that reproduces the observed vibrational distribution of the [Formula: see text] Herzberg II bands in the terrestrial nightglow is used to derive the altitude profiles of the fractional populations in the individual vibrational levels. Through consideration of these profiles it is shown that if [Formula: see text] is the Barth precursor of O(1S) in the nightglow then, at least in the terrestrial atmosphere, the higher vibrational levels appear to be more effective in the Barth transfer step than the lower vibrational levels.

Experiment Research of Laser Induced Air Breakdown

2014 ◽  
Vol 599-601 ◽  
pp. 201-204
Author(s):  
Hai Dong Wu
Keyword(s):  
Energy Conversion ◽  
High Speed ◽  
Laser Excitation ◽  
Laser Energy ◽  
Ionization Process ◽  
High Speed Camera ◽  
Experiment Research ◽  
Sound Energy ◽  
Air Breakdown

The principle of laser induced air breakdown was introduced. The laser energy conversion in ionization process was studied. The phenomenon of laser induced air breakdown was observed by using high speed camera. It was found that a higher laser energy induced more laser energy to transfer into light and sound energy. The plasma reached maximum in shape in about 20 to 30 ns after laser excitation, and disappeared in about 16μs.

Surface Modification and Ablation of Insulators Using a Tunable, Picosecond Mid-Infrared Laser

1998 ◽  
Vol 526 ◽  
Author(s):  
R. F. Haglund ◽  
D. R. Ermer ◽  
A. H. Lines ◽  
M. R. Papantonakis ◽  
H. K. Park ◽  
...  
Keyword(s):  
Surface Modification ◽  
Near Infrared ◽  
Energy Content ◽  
Laser Energy ◽  
Vibrational Excitation ◽  
Average Power ◽  
Surface Modifications ◽  
Fused Silica ◽  
Laser Source ◽  
Near Ultraviolet

AbstractUltrashort-pulse lasers with fundamental wavelengths ranging from near-infrared to near-ultraviolet are increasingly being used for laser-induced surface modification of non-metallic solids. The relaxation of the initial electronic excitation into vibrational relaxation modes can produce efficient ablation and other desirable surface modifications with little collateral damage because the laser energy is deposited on a time scale much shorter than thermal diffusion times. Little is known, however, about how ultrashort pulses interact with insulators at wavelengths in the vibrational infrared. This paper describes surface modifications achieved by picosecond laser irradiation in the 2-10 lim range. The laser source was a tunable, free-electron laser (FEL) with I-ps micro-pulses spaced 350 ps apart in a macropulse lasting up to 4 μs, with an average power of up to 3 W. This unusual pulse structure makes possible novel tests of the influences vs fluence and intensity, as well as the effects of resonant vibrational excitation. As model materials systems, we studied calcium carbonate, its isoelectronic cousin sodium nitrate, and fused silica. Particularly intriguing are surface modifications achieved by tuning the laser into vibrational resonances and overtones of the target materials, or by tailoring the energy content of the pulse. The mechanisms underlying these effects, and their implications for materials-modification strategies, are discussed.

Spectroscopic Study of Pulsed Laser Induced Plasma from Aluminum Surface

1998 ◽  
Vol 526 ◽  
Author(s):  
Y. F. Lu ◽  
Z. B. Tao ◽  
M. H. Hong ◽  
D.S.H. Chan ◽  
T.S. Low
Keyword(s):  
Spectroscopic Study ◽  
Laser Energy ◽  
Plasma Temperature ◽  
Optical Emission ◽  
Spectral Lines ◽  
Aluminum Surface ◽  
Spontaneous Radiation ◽  
Incident Laser ◽  
Optical Emission Spectrum ◽  
Laser Fluences

AbstractOptical emission spectrum of aluminum plasma induced by a 1064 nm Nd:YAG laser is investigated by an Optical Multichannel Analyzer (OMA). Spectroscopic study shows that more number of Al, Al+, and Al++ spectral lines can be observed with increasing the incident laser fluence. Al, Al+, Al++ spectral lines are also observed successively with high fluence. The atomic spontaneous radiation is analyzed to interpret the calibrated plasma spectrum. The laser energy threshold for the appearance of excited Al, Al+, and Al++ spectral lines are about 0.8, 1.0 and 1.5 J/cm2 respectively. Assuming LTE (Local Thermodynamic Equilibrium) conditions, the plasma density is derived to be in the range of 0.7×1017 to 2×1017 cm-3 from the profiles of Al+ (358.7 and 286.1 nm) spectral lines with different gated times and incident laser fluences. The plasma temperature is also estimated to be 4000 ~ 8000 K, from relative intensities of two different Al I spectral lines (309.2 and 396.2 nm) with different fluence.

Threshold Fluence UV Laser Ablation of Single Crystal Bi2Sr2Ca1Cu2O8: Product Population and Kinetic Energy Distributions of Ejected Ionic Species

1990 ◽  
Vol 201 ◽  
Author(s):  
Lawrence Wiedeman ◽  
Hyun Sook Kim ◽  
Henry Helvajian
Keyword(s):  
Mass Spectrum ◽  
Kinetic Energy ◽  
Single Crystal ◽  
Mass Spectra ◽  
Laser Excitation ◽  
Population Distribution ◽  
Wavelength Dependence ◽  
Ionic Species ◽  
Uv Laser ◽  
Laser Fluences

AbstractWe have conducted an experiment which measures the product population and kinetic energy (KE) distributions from the UV laser induced decomposition of crystalline Bi2Sr2Ca1Cu2O8. We have measured these distributions at two laser wavelengths 248, 351. At a third wavelength (355 nm) we have measured the photoejected mass spectra from both a single crystal Bi2Sr2Ca1Cu2O8 sample and a polycrystalline Bi2Sr2Ca2Cu3O10 sample. For all the experiments, the laser fluence is maintained near the threshold for ion formation. The laser fluences are well below the level for instigating a laser induced above surface plasma. Our results show that the ejected products are not the consequence of a laser surface evaporation process. We measure a wavelength dependence in the ejected species population distribution and the ejected kinetic energy distribution (< KE > = 5 ± 1 eV.2eV FWHM) is indicative of an electronic excitation process. The measured ion mass spectra show atomic, diatomic (e.g. Sr2+), and oxide (e.g. SrO+, CaO+) species with lesser quantities of the complex oxides (e.g. S2O+). Distinctly absent from the mass spectra are the oxide compounds BiO+, CuO+, and the atomic species O+. Furthermore, the mass spectrum shows that at 248 nm laser excitation, the Bi+ species is the abundant photopro-duct. However, for both the 351 nm and 355 nm excitations, the Sr+ and SrO+ ions are measured as more abundant. Also, comparing the 355 nm laser excitation of the single and polycrystalline samples, there is very little difference in the photoejected species mass spectrum.

Extreme Phonon Softening in Laser-excited Bismuth – Towards an Inverse Peierls-transition

2009 ◽  
Vol 1230 ◽  
Author(s):  
Wei Lu ◽  
Matthieu Nicoul ◽  
Uladzimir Shymanovich ◽  
Alexander Tarsevitch ◽  
Martin Kammler ◽  
...  
Keyword(s):  
Laser Excitation ◽  
Equilibrium Structure ◽  
Oscillatory Behavior ◽  
Intense Laser ◽  
X Ray Diffraction ◽  
Phonon Softening ◽  
Time Resolved ◽  
X Ray ◽  
Laser Fluences ◽  
Peierls Distortion

AbstractLarge amplitude coherent optical phonons have been investigated in laser-excited Bismuth by means of femtosecond time-resolved X-ray diffraction. For absorbed laser fluences above 2 mJ/cm2, the experimental data reveal an extreme softening of the excited A1g-mode down to frequencies of about 1 THz, only 1/3 of the unperturbed A1g-frequency. At even stronger excitation the measured diffraction signals no longer exhibit an oscillatory behavior presenting strong indication that upon intense laser-excitation the Peierls-distortion, which defines the equilibrium structure of Bismuth, can be transiently reversed.

Anomalous lattice vibrations of monolayer MoS2 probed by ultraviolet Raman scattering

2015 ◽  
Vol 17 (22) ◽  
pp. 14561-14568 ◽  
Author(s):  
Hsiang-Lin Liu ◽  
Huaihong Guo ◽  
Teng Yang ◽  
Zhidong Zhang ◽  
Yasuaki Kumamoto ◽  
...  
Keyword(s):  
Raman Scattering ◽  
Laser Excitation ◽  
Double Resonance ◽  
Resonance Raman ◽  
Lattice Vibrations ◽  
Raman Scattering Spectrum ◽  
Monolayer Mos2 ◽  
Scattering Process ◽  
Resonance Raman Scattering ◽  
Scattering Spectrum

Raman scattering spectrum of monolayer MoS2 shows anomalous enhanced peaks from 500 to 900 cm−1 for the 354 nm laser excitation, which can be explained by the double resonance Raman scattering process.

A BOXCARS investigation of the V–V energy transfer from highly excited SF6 to CS2 and the sensitized photodissociation of CS2

1994 ◽  
Vol 72 (11-12) ◽  
pp. 845-850 ◽  
Author(s):  
L. Wang ◽  
W. E. Jones
Keyword(s):  
Energy Transfer ◽  
Partial Pressure ◽  
Energy Exchange ◽  
Laser Excitation ◽  
Vibrational Energy ◽  
Vibrational Temperature ◽  
Excitation Intensity ◽  
Excitation Energies ◽  
Ir Laser ◽  
Partial Pressures

The BOXCARS technique was used to investigate the vibrational energy transfer between highly excited SF6 and CS2, and for the sensitized photodissociation of CS2. The analysis of data, as reported in our previous studies, to extract vibrational temperature from the CARS signal has been revised in the present work to adjust for the fact that the ground-state population may not be constant. The current investigation suggests that IR laser excitation of SF6 and the energy exchange between excited SF6 and CS2 create a high-lying vibrational energy reservoir in the CS2 vibrational manifold. The rate of energy transfer depends on the partial pressures of SF6 and CS2, and the excitation intensity. The transfer rate shows greater dependence on the partial pressure of SF6 than on the partial pressure of CS2. At higher excitation energies, the energy reservoir leads to photofragmentation products.

Laser-Induced Double Resonance Ionic Fluorescence of Rare Earths in the Inductively Coupled Plasma

1988 ◽  
Vol 42 (2) ◽  
pp. 281-285 ◽  
Author(s):  
M. E. Tremblay ◽  
J. B. Simeonsson ◽  
B. W. Smith ◽  
J. D. Winefordner
Keyword(s):  
Rare Earths ◽  
Inductively Coupled Plasma ◽  
Laser Excitation ◽  
Double Resonance ◽  
Emission Spectrometry ◽  
Inductively Coupled ◽  
Linear Dynamic ◽  
Partial Energy ◽  
Ionic Emission ◽  
First Time

Laser excitation of ionic fluorescence overcomes the problem of spectral interferences encountered when trace analysis of the rare earths is performed by atomic/ionic emission spectrometry in the inductively coupled plasma. Two pulsed, excimer pumped, tunable dye lasers are used to excite ionic fluorescence of rare earths in an inductively coupled plasma. Since several fluorescence lines have been observed after laser excitation, it is possible to draw partial energy level diagrams for lanthanum, ytterbium, europium, and lutetium. Detection limits, linear dynamic ranges, and sensitivities are also reported. This is the first time that two-step excited fluorescence has been observed for any rare earths in an inductively coupled plasma.

scholarly journals A Comparative Study of Laser-Induced Graphene by CO2 Infrared Laser and 355 nm Ultraviolet (UV) Laser

Micromachines ◽  
2020 ◽  
Vol 11 (12) ◽  
pp. 1094
Author(s):  
Liyong Wang ◽  
Zhiwen Wang ◽  
Ali Naderi Bakhtiyari ◽  
Hongyu Zheng
Keyword(s):  
Co2 Laser ◽  
Laser Energy ◽  
Three Dimensional ◽  
Infrared Laser ◽  
Photothermal Effect ◽  
Experimental Investigations ◽  
Uv Laser ◽  
Laser Fluences ◽  
Few Layer Graphene ◽  
Surface Morphologies

Laser-induced graphene (LIG) is an emerging technique for producing few-layer graphene or graphene-like material that has recently received increasing attention, due to its unique advantages. Subsequently, a variety of lasers and materials have been used to fabricate LIG using this technique. However, there is a lack of understanding of how different lasers (wavelengths) perform differently in the LIG conversion process. In this study, the produced LIG on polyimide (PI) under a locally water-cooled condition using a 10.6 μm CO2 infrared laser and a 355 nm ultraviolet (UV) laser are compared. The experimental investigations reveal that under the same UV and CO2 laser fluence, the ablation of PI show different results. Surface morphologies with micron-sized and nanometer pores were formed by the UV laser under different laser fluences, whereas micron-sized pores and sheet structure with fewer pores were produced by the CO2 laser. Energy dispersive spectrometry and three-dimensional topography characterization indicate that the photochemical effects were also involved in the LIG conversion with UV laser irradiation. It is also observed through experiments that the photothermal effect contributed to the formation of LIG under both lasers, and the LIG formed on PI substrates by the CO2 laser showed better quality and fewer layers.

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