共查询到20条相似文献,搜索用时 15 毫秒
1.
T. I. Karu O. A. Tiphlova Yu. A. Matveyets A. P. Yartsev V. S. Letokhov 《Journal of photochemistry and photobiology. B, Biology》1991,10(4)
To evaluate the contribution of local pulsed heating of light-absorbing microregions to biochemical activity, irradiation of Escherichia coli was carried out using femtosecond laser pulses (λ = 620 nm, τp=3 × 10−13 s, fp = 0.5 Hz, Ep = 1.1 × 10−3J cm−2, Iav = 5.5 × 10−4 W cm−2, Ip = 109 W cm−2) and continuous wave (CW) laser radiation (λ = 632.8 nm, I = 1.3 W cm−2). The irradiation dose required to produce a similar biological effect (a 160%–190% increase in the clonogenic activity of the irradiated cells compared with the non-irradiated controls) is a factor of about 103 lower for pulsed radiation than for CW radiation (3.3 × 10−1 and 7.8 × 102 J cm−2 respectively). The minimum size of the microregions transiently heated on irradiation with femtosecond laser pulses is estimated to be about 10 Å, which corresponds to the size of the chromophores of hypothetical primary photoacceptors—respiratory chain components. 相似文献
2.
The formation mechanism for multiply charged ions (Cq+ and Oq+ (q = 2–4)) were investigated using a dual polarity time-of-flight mass spectrometer when diethyl ether clusters interacted with nanosecond laser pulse. The signal intensity of multiply charged ions and electron energy was measured experimentally. It was shown that the intensity of multiply charged ions increased about 50 times when laser intensity increased from 7.6 × 109 to 7.0 × 1010 W/cm2, then saturated as laser intensity increased further. It is interesting that the evolution of the mean value of electron energy was same to that of multiply charged ions. The theoretical calculation showed the ionization potential of atomic ions could be significantly decreased due to the effect of Coulomb screening especially at low laser intensity. It indicated that the electron ionization combined with Coulomb screening effect could explain the production of multiply charged ions in nanosecond laser field. 相似文献
3.
Alexandr Zalessky Yuriy Fedotov Elizaveta Yashkina Viktor Nadtochenko Andreyan N. Osipov 《Molecules (Basel, Switzerland)》2021,26(13)
To assess the prospects for using intense femtosecond laser radiation in biomedicine, it is necessary to understand the mechanisms of its action on biological macromolecules, especially on the informational macromolecule—DNA. The aim of this work was to study the immunocytochemical localization of DNA repair protein foci (XRCC1 and γH2AX) induced by tightly focused femtosecond laser radiation in human cancer A549 cells. The results showed that no XRCC1 or γH2AX foci tracks were observed 30 min after cell irradiation with femtosecond pulses of 1011 W∙cm−2 peak power density. An increase in the pulse power density to 2 × 1011 W∙cm−2 led to the formation of linear tracks consisting both of XRCC1 and γH2AX protein foci localized in the places where the laser beam passed through the cell nuclei. A further increase in the pulse power density to 4 × 1011 W∙cm−2 led to the appearance of nuclei with total immunocytochemical staining for XRCC1 and γH2AX on the path of the laser beam. Thus, femtosecond laser radiation can be considered as a tool for local ionization of biological material, and this ionization will lead to similar effects obtained using ionizing radiation. 相似文献
4.
A. Lytkine J. Manne W. Jger J. Tulip 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,63(5):947
We have measured the output parameters of a 10.3-μm pulsed distributed-feedback (DFB) quantum cascade (QC) laser manufactured by Alpes Lasers and intended for high-sensitivity detection of ammonia and ethylene. The laser beam was collimated with an AR-coated aspheric ZnSe lens with focal length of 11.6 mm and clear aperture of 16.5 mm. Near- and far-field distributions of the laser emission were recorded with an infrared imaging camera. The fast-and slow-axis laser beam divergences were measured to be 1.2 and 1.4 mrad (FWHM), respectively. The divergence was found to be increasing with injection current. An air-spaced Fabry–Perot interferometer with free spectral range of 0.05 cm−1 was used to measure the frequency tuning rates of the laser. The laser was tuned by either heat sink temperature, injection current or pulse repetition rate with rates of −8 × 10−2 cm−1 K−1, −7 × 10−2 cm−1 A−1 and −9 × 10−4 cm−1 kHz−1, respectively. The laser frequency decreased linearly with a rate of 10−2 cm−1 ns−1 (300 MHz ns−1) for laser pulses varied from 10 to 50 ns, and the frequency chirp rate was found to decrease for longer laser pulses. 相似文献
5.
B. Lang A. Vierheilig E. Wiedenmann H. Buchenau G. Gerber 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1997,40(1):1-4
We report on studies of multiple ionization and fragmentation of free Hgn (n ≤ 80) clusters in the femtosecond time domain at wavelengths ranging from 255 nm to 800 nm. After excitation by single laser pulses of an intensity of 5 * 1011 W/cm2 we observe prompt formation of multiply charged Hgn clusters. The Hgn cluster size distribution observed up to n ≈ 80 shows in additon to singly charged also doubly and triply charged clusters with a surprisingly high amount of doubly charged clusters. The measured cluster size distribution is nearly independent of laser wavelengths. For higher laser intensities (2 * 1012 W/cm2) we observe multiply charged mercury atoms up to Hg5+. At 1013 W/cm2 molecules and clusters eventually disappear due to Coulomb explosion and complete Fragmentation. Only atomic ions, singly and multiply charged, with high kinetic energies are then observed. 相似文献
6.
Ionization Suppression of Heteronuclear Diatomic and Triatomic Molecules in Strong Infrared Laser Fields
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Lei Zhao Rui Wang Shi-wen Zhang Tian-xiang Yang Yi Lian Hang Lv Hai-feng Xu 《化学物理学报(中文版)》2017,30(6):631-636
Ionization is the fundamental process in interaction of atoms/molecules with femtosecond strong laser fields. Comparing to atoms, molecules exhibit peculiar behaviors in strong-field ionization because of their diverse geometric structures, molecular electronic orbitals as well as extra nuclear degrees of freedom. In this study, we investigate strong field single and double ionization of carbon monoxide (CO) and carbon dioxide (CO2) in linearly polarized 50-fs, 800-nm laser fields with peak intensity in the range of 2×1013 W/cm2 to 2×1014 W/cm2 using time-of-flight mass spectrometer. By comparing the ionization yields with that of the companion atom krypton (Kr), which has similar ionization potential to the molecules, we investigate the effect of molecular electronic orbitals on the strong-field ionization. The results show that comparing to Kr, no significant suppression is observed in single ionization of both molecules and in non-sequential double ionization (NSDI) of CO, while the NSDI probability of CO2 is strongly suppressed. Based on our results and previous studies on homonuclear diatomic molecules (N2 and O2), the mechanism of different suppression effect is discussed. It is indicated that the different structure of the highest occupied molecular orbitals of CO and CO2 leads to distinct behaviors in two-center interference by the electronic wave-packet and angular distributions of the ionized electrons, resulting in different suppression effect in strong-field ionization. 相似文献
7.
Ionization and dissociation of nitrosyl chloride ClNO were studied using femtosecond laser mass spectra tech-nique.Strong fragmental ions NO~ and Cl~ were observed with the laser intensity varied from 3.2×10~(14) to 2.5×10~(15) W/cm~2.These fragmental ions were attributed to the direct dissociation of the parent ions.Electronic structurecalculations were also carried out with Hartree-Fock,density functional and correlated levels of theory to under-stand the possible fragmentation pathways.The very low N-Cl bond energy in the parent ion of nitrosyl chloride isa clear reason for the absence of ClNO~ and ClN~ ion peaks from the femtosecond laser mass spectrum. 相似文献
8.
9.
Nonlinear Optical Susceptibility of Fe2O3 Thin Film Synthesized by a Modified Sol-Gel Method 总被引:1,自引:0,他引:1
The homogeneous transition metal oxide Fe2O3 thin films are synthesized in a modified sol-gel process by spin coating. The third order nonlinear optical susceptibility of the film is about 2 × 10–9 esu at 488 nm wavelength by the z-scan method with a 180 femtosecond pulse laser beam. The film is expected to be useful for the application of nonlinear optical devices. 相似文献
10.
T. Bezrodna G. Puchkovska V. Shymanovska J. Baran H. Ratajczak 《Journal of Molecular Structure》2004,700(1-3):175
The surface state of optically pure polydisperse TiO2 (anatase and rutile) was determined by infra-red (IR) spectroscopy analysis in the temperature range of 100–453 K. Anatase A300 spectrum, contrary to rutile R300 one, has a broad three-component absorption band with peaks at 1048, 1137 and 1222 cm−1 in the spectral range of δ(Ti–O–H) deformation vibrations. For rutile R300 we observed a very weak band at 1047 cm−1, and for the thermal treated rutile R900 these bands were not appeared at all. The analysis of temperature dependencies for the mentioned absorption bands revealed the spectral shift of 1222 cm−1 band towards the high frequencies, when the temperature increased, but the spectral parameters of 1137 and 1048 cm−1 bands remained the same. The temperature of 1222 cm−1 band maximum shift was 373–393 K and correlated with DSC data. Obtained results allowed to assign 1222 cm−1 band to the deformation vibrations of OH-groups, bounded to the surface adsorbed water molecules by weak hydrogen bonds (5 kcal/mol). During the temperature growth these molecules desorbed, which also resulted in the intensity decreasing of stretching OH-groups vibration IR-bands at 3420 cm−1. The destruction and desorption of surface water complexes led to Ti–O–H bond strengthening. IR bands at 1137 and 1048 cm−1 were attributed to the stronger bounded adsorbed water molecules, which are also characterized with stretching OH-groups vibration bands at 3200 cm−1. These surface structure were additionally stabilized by hydrogen bonds with the neighbouring TiO2 lattice anions and other OH-groups, and desorbed at higher temperatures. 相似文献
11.
12.
A.R.W. McKellar 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,63(5):959
A 2.3 μm near-room temperature tunable diode laser was tested for applications in high-resolution laboratory spectroscopy. It was mounted using a simple adaptor in a spectrometer usually used with lead-salt diode lasers, and was found to be electrically and optically compatible with the system. Good output power (several milliwatts) was observed, and a tuning range of 4460–4150 cm−1 was achieved for laser temperatures of 210–310 K. Some spectra of N2O and NH3 were recorded in the 4300–4430 cm−1 region. However, the laser was not generally useful due to noisy and unstable output and high sensitivity to optical feedback. 相似文献
13.
Jinfeng Yang Koichi Kan Nobuyasu Naruse Yoichi Yoshida Katsumi Tanimura Junji Urakawa 《Radiation Physics and Chemistry》2009,78(12):1106-1111
A near-relativistic 100-fs MeV electron beam is developed by using a photocathode rf gun for revealing the hidden ultrafast dynamics of intricate molecular and atomic processes in materials through experimentation of ultrafast time-resolved electron diffraction (UED). The transverse and longitudinal dynamics of femtosecond electron beam in the rf gun were studied theoretically by particle simulation. The growths of the emittance, bunch length and energy spread due to the rf and space charge effects were investigated by changing the laser parameters, field gradient and electron charge. The theoretical studies indicate that a 100-fs MeV electron beam with the transverse emittance of 0.1 mm mrad and the relative energy spread of 10−3–10−4 at bunch charge of 0.1–2 pC (106–107 electrons per pulse) is achievable for UED, in which the intensity is three orders of magnitude higher than that produced by the conventional dc or pulsed guns. 相似文献
14.
Tunable Diode Laser Absorption Studies of Hydrocarbons in RF Plasmas Containing Hexamethyldisiloxane
Röpcke J. Revalde G. Osiac M. Li K. Meichsner J. 《Plasma Chemistry and Plasma Processing》2002,22(1):139-159
Tunable infrared diode laser absorption spectroscopy has been used to detect the methyl radical and three stable molecules, CH4, C2H2 and C2H6, in radio frequency plasmas (f=13.56 MHz) containing hexamethyldisiloxane (HMDSO). The methyl radical concentration and the concentration of the stable hydrocarbons, produced in the plasma, have been measured in pure HMDSO discharges and with admixtures of Ar, while discharge power (P=20–200 W), total gas pressure (p=0.08–0.6 mbar), gas mixture and total gas flow rate (=1–10 sccm) were varied. The methyl radical concentration was found to be in the range of 1013 molecules cm-3, while methane and ethane are the dominant hydrocarbons with concentrations of 1014–1015 mol cm-3. Conversion rates to the measured stable hydrocarbons (RC(CxHy): 2×1012–2×1016 molecules J-1 s-1) could be estimated in dependence on power, flow, mixture and pressure. Under the used experimental conditions a maximum deposition rate of polymer layers of about 400 nm min-1 has been found. 相似文献
15.
《Radiation Physics and Chemistry》2006,75(11):1799-1807
A time-resolved X-ray microprobe to study optical strong-field processes has been developed. Individual atoms or molecules located within the strong-field environment created by a focused ultrafast laser are probed by undulator-produced X-ray pulses to achieve spatial, temporal, spectral and polarization selectivity. Approximately 106 monochromatic X-rays per 100-ps pulse are focused into a ∼10 μm spot to selectively probe atoms in focal volumes where intensities up to 1015 W/cm2 can be present. In this paper, we describe the time-resolved X-ray microprobe and provide some illustrative examples from our work studying strong-field phenomena such as laser-modified absorption spectra, Coulomb explosion, transient laser-produced plasmas and molecular alignment. 相似文献
16.
Optical and Photoacoustic Properties of Laser-Ablated Silver Nanoparticles in a Carbon Dots Solution
Amir Reza Sadrolhosseini Ganesan Krishnan Suhaidi Shafie Suraya Abdul Rashid Sulaiman Wadi Harun 《Molecules (Basel, Switzerland)》2020,25(24)
This study used the carbon dots solution for the laser ablation technique to fabricate silver nanoparticles. The ablation time range was from 5 min to 20 min. Analytical methods, including Fourier transform infrared spectroscopy (FTIR), UV-visible spectroscopy, transmission electron microscopy, and Raman spectroscopy were used to categorize the prepared samples. The UV-visible and z-scan techniques provided optical parameters such as linear and nonlinear refractive indices in the range of 1.56759 to 1.81288 and 7.3769 × 10−10 cm2 W−1 to 9.5269 × 10−10 cm2 W−1 and the nonlinear susceptibility was measured in the range of 5.46 × 10−8 to 6.97 × 10−8 esu. The thermal effusivity of prepared samples, which were measured using the photoacoustic technique, were in the range of 0.0941 W s1/2 cm−2 K−1 to 0.8491 W s1/2 cm−2 K−1. The interaction of the prepared sample with fluoride was investigated using a Raman spectrometer. Consequently, the intensity of the Raman signal decreased with the increasing concentration of fluoride, and the detection limit is about 0.1 ppm. 相似文献
17.
Ram Kripal Pragya Singh Har Govind 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,74(2):357-362
EPR studies are carried out on Cr3+ ions doped in d-gluconic acid monohydrate (C6H12O7·H2O) single crystals at 77 K. From the observed EPR spectra, the spin Hamiltonian parameters g, |D| and |E| are measured to be 1.9919, 349 (×10−4) cm−1 and 113 (×10−4) cm−1, respectively. The optical absorption of the crystal is also studied at room temperature. From the observed band positions, the cubic crystal field splitting parameter Dq (2052 cm−1) and the Racah interelectronic repulsion parameter B (653 cm−1) are evaluated. From the correlation of EPR and optical data the nature of bonding of Cr3+ ion with its ligands is discussed. 相似文献
18.
Energetic H(2) (+) ions are formed as a result of intramolecular rearrangement during fragmentation of linear alcohols (methanol, ethanol, propanol, hexanol, and dodecanol) induced by intense, pulsed optical fields. The laser intensity regime that is accessed in these experiments (peak intensity of 8 x 10(15) W cm(-2)) ensures multiple ionization of the irradiated alcohol molecules such that Coulomb explosions would be expected to dominate the overall fragmentation dynamics. Polarization dependent measurements show, counterintuitively, that rearrangement is induced by the strong optical field within a single, 100 fs long laser pulse, and that it occurs before Coulomb explosion of the field-ionized multiply charged alcohols. 相似文献
19.
Mitsumasa Taguchi Grard Baldacchino Satoshi Kurashima Atsushi Kimura Yumi Sugo Yosuke Katsumura Koichi Hirota 《Radiation Physics and Chemistry》2009,78(12):1169-1174
This article reports a highly sensitive transient absorbance measurement system using pulsed energetic ions. The ions were pulsed by a beam chopper, which was synchronized with the cyclotron, and accelerated to the desired energy around 18 MeV/u. H, He, C and Ne ions can be used for the transient absorption measurement. The optical system can measure an absorbance smaller than 1.0×10−4 in the wavelength range of 400–740 nm. 相似文献
20.
Combining a temperature variable 22-pole ion trap with a cold effusive beam of neutrals, rate coefficients k(T) have been measured for reactions of CO2+ ions with H, H2 and deuterated analogues. The neutral beam which is cooled in an accommodator to TACC, penetrates the trapped ion cloud with a well-characterized velocity distribution. The temperature of the ions, T22PT, has been set to values between 15 and 300 K. Thermalization is accelerated by using helium buffer gas. For reference, some experiments have been performed with thermal target gas. For this purpose hydrogen is leaked directly into the box surrounding the trap. While collisions of CO2+ with H2 lead exclusively to the protonated product HCO2+, collisions with H atoms form mainly HCO+. The electron transfer channel H+ + CO2 could not be detected (<20%). Equivalent studies have been performed for deuterium. The rate coefficients for reactions with atoms are rather small. Within our relative errors of less than 15%, they do not depend on the temperature of the CO2+ ions nor on the velocity of the atoms (k(T) lays between 4.5 and 4.7 × 10−10 cm3 s−1 with H as target, and 2.2 × 10−10 cm3 s−1 with D). For collisions with molecules, the reactivity increases significantly with falling temperature, reaching the Langevin values at 15 K. These results are reported as k = α (T/300 K)β with α = 9.5 × 10−10 cm3 s−1 and β = −0.15 for H2 and α = 4.9 × 10−10 cm3 s−1 and β = −0.30 for D2. 相似文献