共查询到20条相似文献,搜索用时 31 毫秒
1.
近年来,高速发展的激光技术已经广泛应用于医疗领域,比如眼科手术和光学相干层析成像。尤为特殊的是,飞秒激光更可专用于对活体细胞的基础研究。飞秒激光具有别种激光无法获得的特殊性质。它对于细胞的伤害很小,因为它的线性吸收和热效应远远低于连续光。此外,由于飞秒光的超高峰值功率,它可以对细胞形成多光子电离而在细胞膜上开孔,因此可以转基因和融合细胞,同时不会太过于伤害细胞。在这个报告里,将阐述我们的以下研究:飞秒光致转基因、细胞融合以及细胞在凋亡中的动态过程。在单细胞水平上提出了一些凋亡过程的可能机制,如活性氧化合物、核管和细胞内自由钙离子的产生。 相似文献
2.
Š. Vajda P. Rosendo-Francisco C. Kaposta M. Krenz C. Lupulescu L. Wöste 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):161-164
In this paper we characterize the ultrafast fragmentation in electronically excited Fe(CO)2(NO)2 and CpMn(CO)3 by means of femtosecond time-resolved spectroscopy combined with mass spectrometry. From the transient two-color multi-photon
ionization data, it was possible to record the transients of the parent molecule ions and their photofragment ions. The experimentally
observed decay times indicated an ultrafast loss of the first ligands (sub-100 fs decay times). Further we performed a feedback
control experiment on the photofragmenting CpMn(CO)3 molecular system in order to maximize the yield of desired ionic products through pulse modulation. The shape of the pulses
obtained from optimization reflect well the intrinsic molecular dynamics during photofragmentation and the change of the CpMn(CO)+/CpMn(CO)3
+ ratio shows a clear evidence for the capability of the optimization method to find tailor-made system-specific pulses.
Received 9 January 2001 相似文献
3.
Haiyi Sun Tianqing Jia Chengbin Li Shizhen Xu Xiaofeng Wang Zhizhan Xu 《Solid State Communications》2007,141(3):127-131
We studied the single-shot damage in magnesium fluoride irradiated by 800 nm femtosecond (fs) laser. The dependence of damage thresholds on the laser pulse durations from 60 to 750 fs was measured. The pump-probe measurements were carried out to investigate the time-resolved electronic excitation processes. A coupled dynamic model was applied to study the microprocesses in the interaction between fs laser and magnesium fluoride. The results indicate that both multiphoton ionization and avalanche ionization play important roles in the femtosecond laser-induced damage in MgF2. 相似文献
4.
K. Thomson M. Ziskind C. Mihesan E. Therssen C. Focsa 《Applied Surface Science》2007,253(15):6435-6441
Characterization of polycyclic aromatic hydrocarbons (PAHs) samples has been performed by laser desorption combined with multi-photon ionization technique using two different geometries of the ionization laser beam. This comparative study evidences the strong influence of ionization laser fluence on PAH fragmentation. Through a ∼103 enlargement of the ionization probe volume and 104 reduction of laser fluence over previous studies, fragment free mass spectra are obtained with higher sensitivity and selectivity. The ability to measure fragment free PAH mass spectra is a very important step in the end goal of measuring complex unknown mixtures of PAH desorbed from solid surface such as soot samples. 相似文献
5.
The photoelectron spectra of C60 ionized using a 790 nm laser with pulse durations varying from 25 fs to 5 ps have been determined. For 25 fs pulses, in the absence of fragmentation, the ionization mechanism is direct multiphoton ionization with clear observation of above threshold ionization. As the pulse duration is increased, this becomes dominated by a statistical ionization due to equilibration among the electronic degrees of freedom. For pulse durations on the order of a ps coupling to the vibrational degrees of freedom occurs and the well-known phenomenon of delayed (&mgr;s) ionization is observed. 相似文献
6.
利用飞秒光电子影像技术研究了碘甲烷分子在飞秒强激光场作用下的多光子电离动力学,在实验上实现了运用飞秒强场多光子电离技术对多原子分子离子的振动量子态进行光学操控.提高了飞秒激光的强度,从1.6×1013W/cm2提高到2.5×1013W/cm2.在增大的激光强度范围内,发现了新的能量组分,并对此进行归属.通过采集光电离的光电子影像可以得到强场电离后光电子的动能分布和角度分布两方面的信息,前期的研究主要侧重于讨论光电子动能随光强的变化,重点讨论了光电子角度分布随光强的变化,通过观察光电子角度分布的变化趋势对振动量子态调控机理进一步认识. 相似文献
7.
8.
利用激光质谱法,采用355 nm及532 nm激光作为光源对丁酮分子进行了多光子电离解离研究,得到了2种波长下丁酮的多光子电离飞行时间质谱图主要有质荷比为1(H ),15(CH3 ),43(CH3CO )的质谱峰.532 nm质谱比较丰富,有较强的质荷比为45的信号,可以认为这是丁酮异构体电离解离得到的产物;同时探测到了质荷比为4,6,8的信号,可能是高价离子.355 nm质谱图相对简单.根据信号比例随激光能量的变化及主要的离子信号,得出了2种波长下主要的解离电离通道. 相似文献
9.
利用激光质谱法,采用355 nm及532 nm激光作为光源对丁酮分子进行了多光子电离解离研究,得到了2种波长下丁酮的多光子电离飞行时间质谱图主要有质荷比为1(H ),15(CH3 ),43(CH3CO )的质谱峰.532 nm质谱比较丰富,有较强的质荷比为45的信号,可以认为这是丁酮异构体电离解离得到的产物;同时探测到了质荷比为4,6,8的信号,可能是高价离子.355 nm质谱图相对简单.根据信号比例随激光能量的变化及主要的离子信号,得出了2种波长下主要的解离电离通道. 相似文献
10.
Single-shot laser damage threshold of MgO for 40-986 fs, 800 nm laser pulses is reported. The pump-probe measurements with femtosecond pulses were carried out to investigate the time-resolved electronic excitation processes. A theoretical model including conduction band electrons (CBE) production and laser energy deposition was applied to discuss the roles of multiphoton ionization (MPI) and avalanche ionization in femtosecond laser-induced dielectric breakdown. The results indicate that avalanche ionization plays the dominant role in the femtosecond laser-induced breakdown in MgO near the damage threshold. 相似文献
11.
A novel one-color Xe+-N laser induced collisional charge transfer system is proposed, and preparation of the initial state of the system, i.e., Xe+ is experimentally implemented through resonance enhanced multi-photon ionization (REMPI) by ~440 nm dye laser. The REMPI of Xe is experimentally investigated through time-of-flight (TOF) mass spectrometry and the intensity dependence of Xe+ is obtained, aiming at the preparation of Xe+. The resonant ionization spectra of Xe at ~440 nm under several different conditions are measured, showing the impacts of mode purification and source pressure on the resonant ionization spectrum. The results indicate the feasibility of preparing the initial state of the Xe+-N system by ~440 nm multi-photon resonant ionization, which prepares for a further experiment of laser-induced collisional charge transfer. 相似文献
12.
In this article, the effect of ionization on the energy spectrum of electrons within the interaction of a laser pulse with hydrogen atoms is investigated using particle-in-cell simulation codes. The results show that the behaviour of electrons' energy distribution function in the field-ionized plasma, which occurred due to the field ionization, compared with that in the pre-plasma strongly depends on the pulse shape. For short rise-time pulses (here 30 fs), due to the rapid enhancement of laser electric field, ionization occurs quickly, and as a result, there is not much difference in the electron energy in both the media. However, for pulses with rise time of 40 fs, in the pre-plasma state, the electron population reaches higher energies compared with the field-ionized plasma state. The main reason for this difference is the nonlinear wave breaking that happens earlier due to density inhomogeneity in the field-ionized plasma. On the other hand, at longer rise-time pulses (here 60 and 70 fs), electrons achieve higher energies in the field-ionized plasma than those in the case of pre-plasma. In this case, because of density fluctuations in the field-ionized plasma, the Raman backscattered radiations are seeded by a strong initial noise at the earlier times and the Mendonca condition for chaos threshold is met sooner. Therefore, the electrons gain more energy through the stochastic mechanism that is in agreement with chaotic nature of the motion. 相似文献
13.
14.
J. Ihlemann A. Scholl H. Schmidt B. Wolff-Rottke 《Applied Physics A: Materials Science & Processing》1995,60(4):411-417
The uv laser-ablation behavior of various oxide ceramics (Al2O3, MgO, ZrO2) has been studied using different wavelengths (248 nm, 308 nm) and pulse durations (30 ns, 500 fs). Time-resolved absorption measurements of the sample and the ablation plume during ablation were performed.Using sub-ps pulses the ablation threshold fluence is generally lower than for ns pulses; the ablation rate is higher in the whole investigated fluence range up to 20 J/cm2.The study of the morphology of the ablation structures and the results of the absorption experiments lead to the conclusion that different ablation mechanisms are involved. Using ns pulses plasma mediated ablation is dominating, whereas in the fs case the process is controlled by multi-photon absorption enabling microstructuring of the material. 相似文献
15.
Huynh Vinh Phuc Nguyen Thi Thu Thao Le Dinh Tran Cong Phong 《Journal of Physics and Chemistry of Solids》2014
Phonon-assisted cyclotron resonance (PACR) in GaAs quantum well (QW) structure is investigated via multi-photon absorption process when electrons interact with the confined acoustic phonon through deformation potential. The additional peaks in the absorption spectrum due to transitions between Landau levels accompanied with the emission and absorption of phonons are indicated. The dependence of absorption power on the temperature, magnetic field and well width is presented. Using profile method, we obtain PACR-linewidth as profiles of the curves. The temperature, magnetic field and well width dependences of the PACR-linewidth are investigated. The results are compared with those in the case of mono-photon absorption process, as well as in the electron-bulk acoustic phonon interaction. The results show that the multi-photon absorption process is strong enough to be detected in PACR. 相似文献
16.
M. Tscherneck J. Kleinert C. Haimberger M. E. Holmes N. P. Bigelow 《Applied physics. B, Lasers and optics》2005,80(6):639-643
Ultracold molecules have been produced by photoassociation of Cs atoms trapped in a mirror magneto-optical trap. The molecules
were detected by resonantly enhanced multi-photon ionization followed by time-of-flight mass spectroscopy. The time-of-flight
ofatomic and molecular ions was investigated in the presence of a dc bias voltageapplied to the conducting mirror. This technique
provides a new tool for determining the distance between the cold molecules and the mirror surface.
This revised version was published online in August 2005 with a corrected cover date. 相似文献
17.
In this contribution the first measurements of a single-shot femtosecond laser pump–probe technique are reported. The technique
is based on counter-propagating femtosecond laser pulses in a supersonic beam of a low density of sample molecules and simultaneous
probe detection by ion or fragment-ion formation through a reflectron time-of-flight mass spectrometer. It will be shown that
the range of the pump–probe delays covers the time span between 100 fs and 10 ps depending on the pulse width of the laser
used and the stability of the volt ages of the mass spectrometer. The application of this technique to organometallic compounds
as well as to medium-sized organic molecules reveals some insight into the electron-transfer process during ionization through
a 1+1 multi-photon absorption procedure. Furthermore it is demonstrated that this technique is also applicable to the investigation
of ultra-fast isomerization and fragmentation processes. As an example the results of the processes within iron pentacarbonyl
and substituted benzalacetones are reported.
Received: 22 October 1999 / Published online: 24 July 2000 相似文献
18.
J. Mertz 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,3(1):53-66
We present a simple model for calculating the fluorescence generated by the multi-photon excitation (MPE) of molecules in
solution. The model takes into account internal molecular dynamics such as ground-state depletion due to inter-system crossing
(ISC), as well as external molecular dynamics associated with diffusion into and out of an excitation volume confined in 3-dimensions.
Internal and external molecular dynamics are combined by using a technique of linearization of a modified diffusion equation
which takes into account the possibility of concentration depletion due to photobleaching. In addition, we discuss the phenomenon
of pulse saturation which effectively limits the molecular excitation rate constant in the case of short pulsed excitation.
Our results are specifically applied in the context of fluorescence autocorrelation functions and single-molecule detection.
In the latter case, we discuss some consequences of high-order multi-photon photobleaching. Finally, we include three appendices
to rigorously define the temporal and spatial profiles of an arbitrary excitation beam, and also to discuss some properties
of an exact evaluation of concentration depletion due to photobleaching.
Received: 9 March 1998 / Accepted: 20 April 1998 相似文献
19.
Ergler T Feuerstein B Rudenko A Zrost K Schröter CD Moshammer R Ullrich J 《Physical review letters》2006,97(10):103004
Applying 7 fs pump-probe pulses (780 nm, 4 x 10(14) W/cm2) we observe electronic ground-state vibrational wave packets in neutral D2 with a period of T=11.101(70) fs by following the internuclear separation (R-)dependent ionization with a sensitivity of Delta相似文献
20.
通过数值求解非Born-Oppenheimer近似条件下的一维含时薛定谔方程,理论模拟了H2+在不同核初始振动态条件下(=0到=7)的库仑爆炸核初始动能释放谱。模拟结果表明:强激光场中氢分子离子的电离通道主要包括直接多光子电离、电荷共振增强电离及有中间过程的电荷共振增强电离,并且可以通过选取不同的初始振动态实现对氢分子离子电离通道的控制。 相似文献