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1.
E. D. Aluker N. L. Aluker G. M. Belokurov A. G. Krechetov B. G. Loboiko D. R. Nurmukhametov A. V. Tupitsyn V. P. Filin 《Russian Journal of Physical Chemistry B, Focus on Physics》2010,4(1):63-65
A comparative study of the efficiency of the laser initiation of PETN by the first and second harmonics (1060 and 530 nm)
of a neodymium-doped phosphate glass laser was performed. A significant difference in the efficiency of PETN initiation by
the different harmonics was revealed: as the initial temperature of the sample increased from 373 to 450 K, the threshold
initiation fluence decreased from 3.0 to 0.5 J/cm2; at the same time, the second harmonic failed to initiate PETN even at a fluence of 10 J/cm2. The absorption spectrum of PETN was found to have a weak absorption band with a maximum at λ
m
= 1020 nm. It was assumed that the high efficiency of initiation by the first harmonic is associated with light absorption
(photo-initiation) by this band 相似文献
2.
E. D. Aluker A. G. Krechetov A. Yu. Mitrofanov D. R. Nurmukhametov 《Russian Journal of Physical Chemistry B, Focus on Physics》2011,5(4):658-660
The temperature dependence of the efficiency of laser initiation (λ = 1060 nm) of pure PETN with an open and closed surface
and PETN with a light-scattering additive (0.5% MgO) and an open surface was studied. It was found that the closing of the
surface and introduction of light-scattering additives leads to a change in the temperature dependence of the initiation threshold.
The observed effect is associated with the specificity of the photoinduced fragmentation of PETN molecules in defective areas
of the crystal lattice. 相似文献
3.
E. D. Aluker A. G. Krechetov B. G. Loboiko D. R. Nurmukhametov V. P. Filin E. A. Kazakova 《Russian Journal of Physical Chemistry B, Focus on Physics》2008,2(3):375-377
The temperature dependence of the probability of PETN explosion upon laser pulse initiation (1064 nm, 10 ns, 1–5 J) was examined. As the temperature increases from 393 K to 450 K, the initiation threshold lowers, with the initiation of open-surface samples occurring over the entire temperature range. It was concluded that the initiation mechanism involves thermal-and photoactivation steps. The activation energy for the thermal activation step was found to be 0.35 ± 0.05 eV. 相似文献
4.
5.
E. D. Aluker N. L. Aluker A. G. Krechetov A. Yu. Mitrofanov D. R. Nurmukhametov V. N. Shvaiko 《Russian Journal of Physical Chemistry B, Focus on Physics》2011,5(1):67-74
The effect of the initial temperature of the sample on the efficiency of laser initiation and on the duration of the preexplosion
stage (induction period) of PETN is studied. An analysis of the results leads to the conclusion that, in the initiation of
PETN with the first harmonic of a neodymium laser (1060 nm), a new selective resonant mode of photoinitiation is realized,
through the formation of active radicals providing the development of a chain reaction of explosive decomposition at the preexplosion
(solid-phase) stage of the process. For this mode, the threshold volume density of energy absorbed is much lower than that
typical of the traditional non-selective mechanisms of initiation. The mode of resonant photoinitiation is, however, difficult
to realize because of a low value of the absorption coefficient in the actual band. This difficulty can be easily overcome
by introducing light-scattering additives, a modification that opens prospects for practical use of resonant photoinitiation. 相似文献
6.
B. P. Aduev D. R. Nurmukhametov I. Yu. Liskov A. V. Kalenskii M. V. Anan’eva A. A. Zvekov 《Russian Journal of Physical Chemistry B, Focus on Physics》2015,9(6):915-920
The critical fluence of the initiation of the explosive decomposition of pentaerythritol tetranitrate (PETN) by the second harmonic of a neodymium laser (532 nm) is found to be 12.3 J/cm2. It is shown that, under these conditions, the nonlinear two-photon absorption of light takes place. The critical fluence of the initiation of PETN explosive decomposition in the two-photon absorption mode is calculated within the framework of the thermal explosion model (14.7 J/cm2), which indicates that the thermal mechanism of explosive decomposition is operative under these conditions. 相似文献
7.
8.
Time-resolved transmission and reflectivity of bulk GaAs and GaAs on sapphire have been studied at λ = 1152 and 633 nm following excitation by an ≈8 ns pulse at 485 nm. As in the case of silicon, the spectral dependence of the transient absorption coefficient, from 1.1 eV to 2.5 eV, is inconsistent with the existence of a metallic molten state during pulsed laser annealing. 相似文献
9.
S. Sinha A.K. Ray S. Kundu S. Sasikumar S.K.S. Nair K. Dasgupta 《Applied physics. B, Lasers and optics》2001,72(5):617-621
The photo-stability of laser dyes, Rhodamine-6G, Rhodamine-B, and Kiton-Red, under high repetition rate (6.3 kHz) Copper-vapour-laser
(CVL) irradiation has been investigated. Exhaustive photo-bleaching of these dyes in different solvents has been carried out
to study the extent to which the dye photo-degraded products would interfere with the lasing process in high-power CVL-pumped
dye lasers. Our results indicate that the photo-degradation of dyes occurs predominantly through excited-state intermolecular
reactions, involving the singlet state, rather than the process of nonlinear optical absorption in individual molecules.
Received: 13 March 2000 / Revised version: 2 August 2000 / Published online: 21 March 2001 相似文献
10.
11.
The method of quantum beat spectroscopy is extended to the study of pure electric field splittings. As an example Stark splittings of the 6s6p 1P1 term of Ba I are investigated by observing quantum beats after excitation by a short resonant dye-laser pulse. The derived value for the tensorial polarizability is in good agreement with previous work. Occurence and shapes of Stark quantum beat signals under different experimental conditions are discussed. 相似文献
12.
The effect of the design features of the gas-discharge tube on the processes proceeding in the discharge circuit of a metal-vapor
laser has been investigated. The position of electrodes in the gas-discharge tube has been found to significantly affect the
processes at work in the discharge circuit and the energy characteristics of the laser. For instance, gas-discharge tubes
with electrodes placed in the hot region of the discharge channel are typified by high metastable-population rates at the
leading edge of the excitation pulse, whereas with electrodes positioned in cold buffer regions, the leading edge of the voltage
pulse across the resistive component of the tube impedance is seen to peak. Conditions for running-wave generation in the
active media of lasers on self-terminated transitions of metal atoms and the running-wave use efficiency for laser pumping
are discussed, considering a strontium-vapor laser as an illustration. It is shown that the running wave is generated as the
result of the breakdown in the anode end of the gas-discharge tube and is maintained by the energy stored in the capacitive
component of the impedance of the gas-discharge tube. The lasing pulse duration under running-wave excitation corresponds
to the time it takes an ionization wave to propagate from the anode to the cathode of the gas-discharge tube, with pumping
efficiency being ~6–8% for a strontium-vapor laser. The average lasing power varies within 10–15% depending on whether the
totally reflecting cavity mirror is placed near the anode or the cathode of the tube.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 79–87, December, 2008. 相似文献
13.
The experiment on water molecule adsorption on the surface of nanoporous polymeric adsorbent in the Knudsenmode under conditions of selective action of IR radiation is described. Resonant excitation of the vibrational-rotational transition of the ortho-modification of H2O molecules at a wavelength of 1.85 µm is used. The applicability of this method to the production of water vapor with nonequilibrium concentration ratios of ortho and para modifications of water molecules is shown. 相似文献
14.
The structural luminescence spectra of protoporphyrin IX solid solutions in ethanol and hydrochloric acid were obtained under selective laser excitation in the region of the inhomogeneouly broadened pure electronic and vibronic bands at T = 3.8 K. The dependence of the excitation selectivity on the excitation frequency was investigated. The vibrational frequencies of protoporphyrin IX were obtained in the ground and excited electronic states when the excitation frequency has been scanned in the region of pure electronic and vibronic bands, respectively. A universal apparatus is described for the investigation of the absorption and luminescence spectra of polyatomic molecules in the temperature range from 3.5 to 300 K under the dye laser excitation tunable in the spectral region 265–365 nm, 435–730 nm, detection of spectra in the region 300–900 nm with a polychromator and silicon intensified image detector and processing of the spectral information with an optical spectrum analyser controlled with a microcomputer. 相似文献
15.
16.
Laser-induced breakdown spectroscopy (LIBS) was applied for parametric studies of titanium (Ti) plasma using single and double
pulsed laser excitation scheme. Here a pulsed Nd:YAG laser was employed for generation of laser produced plasma from solid
Ti target at ambient pressure. Several ionized titanium lines were recorded in the 312–334 nm UV region. The temporal evolution
of plasma parameters such as excitation temperature and electron number density was evaluated. The effect of incident laser
irradiance, position of the laser beam focal point with respect to the surface of illumination, single and double laser pulse
effect on plasma parameters were also investigated. This study contributes to a better understanding of the LIBS plasma dynamics
of the double laser pulse effect on the temporal evolution of various Ti emission lines, the detection sensitivity and the
optimal dynamics of plasma for ionized states of Ti. The results demonstrate a faster decay of the continuum and spectral
lines and a shorter plasma life time for the double pulse excitation scheme as compared with single laser pulse excitation.
For double pulse excitation technique, the emissions of Ti lines intensities are enhanced by a factor of five which could
help in the improvement of analytical performance of LIBS technique. In addition, this study proved that to avoid inhomogeneous
effects in the laser produced plasma under high laser intensities, short delay times between the incident laser pulse and
ICCD gate are required. 相似文献
17.
B. P. Aduev D. R. Nurmukhametov R. I. Furega A. A. Zvekov A. V. Kalenskii 《Russian Journal of Physical Chemistry B, Focus on Physics》2013,7(4):453-456
The results of measurements of the threshold of explosive decomposition of PETN with 0.1 wt % additives of aluminum nanoparticles under the action of the first and second harmonics of a YAG:Nd3+ laser with a pulse duration of 12 ns are presented. A comparison of experimental and theoretical results is performed. It is concluded that the absorption of radiation heats the nanoparticles to form chemical decomposition kernels in the vicinity of the hotspot, so that the initiation of explosive decomposition is not associated with optical breakdown of the sample. 相似文献
18.
B. P. Aduev D. R. Nurmukhametov A. V. Puzynin 《Russian Journal of Physical Chemistry B, Focus on Physics》2010,4(3):452-456
The temperature dependence of the probability of the explosion of pentaerythritol tetranitrate (PETN) with an admixture of
NiC particles (0.3 wt %) initiated by laser pulses (1064 nm, 20 ns) was studied over the temperature range 295–450 K. At 295–350
K, a weak temperature dependence was observed. The determining contribution to explosion initiation was made by the absorption
of laser radiation by nanoparticles. The threshold of explosive decomposition at 295 K decreased by ∼40 times compared with
samples free of NiC nanoparticles. Over the temperature range 400–450 K, the threshold of the explosive decomposition of samples
containing NiC nanoparticles decreased with the activation energy ∼0.4 eV. A decrease in the threshold of explosive decomposition
with a ∼0.4 eV activation energy over the temperature range 340–440 K was also observed for laser action on PETN samples not
containing NiC. A hypothesis was suggested according to which the absorption of a light quantum caused the transfer of an
electron from the valence band of the crystal to a level in the forbidden band with subsequent thermal positive ion dissociation
to the carbocation and NO3 radical. 相似文献
19.
A new theoretical model describing the emission and absorption dynamics in an ensemble of molecules under intense coherent pulsed pumping is developed on the basis of the concepts of cooperative light-induced luminescence (CLIL). The CLIL development is described within the framework of formalism of the system density matrix in the space of photon wave functions. It is shown that the fast growth of CLIL relates to the development of coherent states of the quantum field in the area of efficient cooperative interactions of molecules (coherence volume). A system of equations for the calculation of CLIL energy, population of excited states, and optical absorption of the system in dependence on the laser pump energy density is solved. The theoretical results obtained are in good agreement with the experimental data. 相似文献
20.
A.V. Papoyan M. Auzinsh K. Bergmann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(1):63-71
We report results of a theoretical and experimental study of the ground state nonlinear Hanle effect under strong laser excitation.
It is shown that besides the well-known zero-magnetic field suppression of absorption on F
g = F→F
e = F - 1 transitions caused by population trapping, an optical pumping induced enhanced absorption occurs on F
g = F→F
e = F + 1 transitions for small B-fields. The latter effect becomes more pronounced for high F values. The experiment with atomic vapor of Cs (D2 line, F
g = 4) confirms an increase of the spectrally unresolved fluorescence yield at zero magnetic field and 600 mW/cm2 laser intensity by 9% or 42%, when excitation occurs with linearly or circularly polarized light, respectively. The results
of the experiment agree with numerical simulation studies using equations of motion for a density matrix.
Received 24 November 2001 / Received in final form 25 March 2002 Published online 24 September 2002 相似文献