A mathematical simulation of intramolecular proton phototransfer

A system of equations for the matrix elements of the density operator of a seven-level model molecule interacting with a light pulse was solved numerically to determine the time dependences of the populations of molecule states at various radiation pulse parameters and parameters characterizing radiative and nonradiative spontaneous molecule transitions and reversible transitions between some of its states. The results were used to characterize the photoisomerization of molecules between states with different positions of the proton of the intramolecular H-bond (the keto and enol forms). Examples of oscillating molecular state population modulation in isomer-isomer tunnel proton shifts are given. Changes in the development of photoionization in time as molecular parameters and radiation pulse width and intensity changed were considered. An analysis of the results obtained is an example of the use of mathematical simulation of intramolecular dynamics for increasing the effectiveness of using spectral-time data in the determination of the mechanism of proton phototransfer in molecules with intramolecular H-bonds     

Quantum-classical simulation of the photoisomerization during the transformation of ultrashort light pulses by a molecule

The dynamics of photoisomerization of a model molecule during its transformation of ultrashort (with a duration much shorter than the lifetime of the resonant excited electronic state) light pulses is simulated numerically. The two-level electronic subsystem of the molecule is described using the quantum theory, while the nuclear subsystem (taking into account the two isomeric states of the molecule) and the radiation field are described using the classical theory. The ranges of the carrier frequency, the peak intensity, and the durations of nπ sinusoidal pulses (n = 1–10) irradiation with which results in the photoisomerization of molecules of the type under study (for example, cyanine dyes) are determined from the analysis of solutions to self-consistent equations that describe the motion of the “isomerization oscillator” and the time evolution of the population amplitude of the resonant electronic state of the molecule. Each of these non-overlapping ranges corresponds to a particular value of n. Bifurcation values of the above parameters of the light pulse are boundaries of these ranges.     

4H-SiC NMOS电子、质子辐照数值模拟

 分析了高能电子、质子对4H-SiC的损伤机理,建立了4H-SiC NMOS器件物理模型。电子、质子辐照效应模型。应用ISE-TCAD软件进行数值模拟计算,得出在能量为2.5 MeV、注量为5×10¹³ cm^-2的电子辐照及能量为6.5 MeV、注量为2×10¹⁴ cm^-2的质子辐照下,4H-SiC NMOS转移特性曲线和亚阈值漏电流曲线变化的初步规律。数值模拟结果与相同条件下Si NMOS实验结果吻合较好。     

4H-SiC NMOS电子、质子辐照数值模拟

分析了高能电子、质子对4H-SiC的损伤机理,建立了4H-SiC NMOS器件物理模型。电子、质子辐照效应模型。应用ISE-TCAD软件进行数值模拟计算,得出在能量为2.5 MeV、注量为5×1013 cm-2的电子辐照及能量为6.5 MeV、注量为2×1014 cm-2的质子辐照下,4H-SiC NMOS转移特性曲线和亚阈值漏电流曲线变化的初步规律。数值模拟结果与相同条件下Si NMOS实验结果吻合较好。     

Dose-controlled irradiation of cancer cells with laser-accelerated proton pulses

Proton beams are a promising tool for the improvement of radiotherapy of cancer, and compact laser-driven proton radiation (LDPR) is discussed as an alternative to established large-scale technology facilitating wider clinical use. Yet, clinical use of LDPR requires substantial development in reliable beam generation and transport, but also in dosimetric protocols as well as validation in radiobiological studies. Here, we present the first dose-controlled direct comparison of the radiobiological effectiveness of intense proton pulses from a laser-driven accelerator with conventionally generated continuous proton beams, demonstrating a first milestone in translational research. Controlled dose delivery, precisely online and offline monitored for each out of ～4,000 pulses, resulted in an unprecedented relative dose uncertainty of below 10 %, using approaches scalable to the next translational step toward radiotherapy application.     

Intense two-cycle laser pulses induce time-dependent bond hardening in a polyatomic molecule

A time-dependent bond-hardening process is discovered in a polyatomic molecule (tetramethyl silane, TMS) using few-cycle pulses of intense 800 nm light. In conventional mass spectrometry, symmetrical molecules such as TMS do not exhibit a prominent molecular ion (TMS(+)) as unimolecular dissociation into [Si(CH(3))(3)](+) proceeds very fast. Under a strong field and few-cycle conditions, this dissociation channel is defeated by time-dependent bond hardening: a field-induced potential well is created in the TMS(+) potential energy curve that effectively traps a wave packet. The time dependence of this bond-hardening process is verified using longer-duration (≥100 fs) pulses; the relatively slower falloff of optical field in such pulses allows the initially trapped wave packet to leak out, thereby rendering TMS(+) unstable once again.     

双色高频激光作用下原子低阶次谐波的理论研究

通过数值求解含时薛定谔方程,研究了高频双色激光脉冲与原子相互作用产生的光辐射.研究表明,光辐射谱中既有基频光的谐波,又可观测到谐波能量附近的多个频率的光辐射产生,且辐射的峰值强度随着入射激光强度的提高呈指数增强,相邻辐射频率差值为入射的两束激光脉冲频率差.     

Demonstration of the interaction between two stopped light pulses

This study reports the first experimental demonstration that two light pulses were made motionless and interacted with each other through a medium. The scheme with motionless light pulses maximizes the interaction time and can achieve a considerable efficiency even below single-photon level. To demonstrate the enhancement of optical nonlinear efficiency, the experiment in this study used the process of one optical pulse switched by another based on the effect of electromagnetically induced transparency. Moving light pulses activate switching at an energy per area of 2 photons per atomic absorption cross section as discussed in [Phys. Rev. Lett. 82, 4611 (1999)]. This study demonstrates that motionless light pulses can activate switching at 0.56 photons per atomic absorption cross section, and that the light level can be further reduced by increasing the optical density of the medium. The result of this work enters a new regime of low-light physics.     

Optical properties and chemical structures of Kapton-H film after proton irradiation by immersion in a hydrogen plasma

Proton irradiation of Kapton-H films was physically simulated in plasma immersion configuration with hydrogen plasmas. Hydrogen ion was implanted into the samples biased to a negative pulse of 20 kV. Optical transmittance of the sample in the wavelength region of 200-2500 nm was determined by a UV-vis-NIR scanning spectrophotometer, and the functional group evolution was examined by X-ray photoelectron spectroscopy (XPS). Atomic force microscopy (AFM) was utilized to determine the roughness and morphology of the samples, and the bulk modification was analyzed by FTIR. The experimental results showed the optical transmittance of the treated sample in the wavelength of 500-2000 nm weakened after proton irradiation, and decreased with the increase of irradiation time. Finger-like bulges emerged on the surface of the sample irradiated by ion irradiation for 30 min, and became bigger and denser with the increase of the irradiation time. The content of C element of the sample increased after proton irradiation, while that of N and O elements decreased because of the bonds breakage of CO, COC and CN during irradiation process.     

Maximum in vibrational frequency shift of a hydrogen molecule in solid hydrogen under pressure

Raman measurements on solid hydrogen show a maximum in the vibrational frequency of a H₂ molecule as a function of pressure, around 350 Kbar. We give an interpretation of this experimental data by considering a model in which a single H₂ molecule is immersed in a dielectric medium, and enclosed in a spheroidal box to simulate the effect of pressure. The maximum results from a balance between a decreasing equilibrium bond length of H₂ with pressure at low pressures and a term which reflects the pressure dependence of the dielectric constant. Our results are consistent with available calculations which give a much lower vibrational frequency at a much higher pressure, for a H₂ molecule embedded in a metallic medium.     

On the role of pressure pulses in clusterization processes under irradiation

Expressions are obtained for dynamic stresses appearing when high-energy particles pass through a crystal. The nonuniform distribution of stresses over the crystal can lead to the rearrangement of atoms knocked out by a particle, as well as to the formation of clusters.     

Probing of ultrasonic pulses by multidirectional light

An acousto-optical reconstruction method for acoustic signals using multidirectional light diffraction by finite amplitude ultrasonic pulses is presented. When crossing the ultrasonic field, the far field diffracted laser light intensity of an incident convergent lightbeam becomes modulated in time. It is found that for special conditions, concerning direction of observation, ultrasonic frequency, power level and interaction length, the modulated light intensity is almost an exact copy of the diffracting acoustic pulse. Reconstruction can be completed by applying a fast Fourier transform (FFT) routine. Examples are provided and applications of this optical probing technique are suggested.     

Behavior of hydrogen in stainless steel under irradiation

A nondestructive method of the simultaneous analysis of hydrogen and helium in combination with the technique of studying hydrogen migration provides fundamentally new information about the hydrogen behavior in metal-hydrogen systems: about hydrogen migration in metals directly under irradiation and about the mutual effect of implanted hydrogen and helium in constructional materials of nuclear and thermonuclear reactors. The irradiation of metals and alloys with ionizing radiation (ion beams, electrons, and x-ray quanta) causes intense hydrogen migration due to the excitation of electron states from metal-hydrogen bonds whose lifetime is sufficient for hydrogen to leave its regular positions and for nonequilibrium migration. Hydrogen migration over and escape from metals and alloys under the action of electrons and x-ray quanta with an energy below the threshold of defect formation are accompanied by the rearrangement of the defect structure of the material: the annealing of defects of the hydrogen origin due to the annihilation of defects (interstitial atoms and hydrogen-free vacancies). Hydrogen dissolved in metals and alloys reduces the trapping coefficient of the implanted helium, which is due to the formation of fine complexes HV and HV₂ and, as a result, to a decrease in the probability of formation of large vacancy complexes which are effective traps for helium.     

Numerical simulation and experimental investigation of parametric generation of light pulses in a KTP crystal

Numerical simulation and experimental investigation of the process of parametric generation of light inside a KTP crystal excited by laser pulses have been performed. The calculation method includes the solution of a system of coupled truncated equations, which describe the three-wave interaction in a laser resonator partially filled with a KTP crystal, with the use of reflection boundary conditions for amplitudes together with initial conditions corresponding to the level of noises. The time profile of the intensities of the interacting pulses and their energies were calculated. The results obtained make it possible to determine the optimal values of optical parameters of the resonator that ensure the maximum efficiency of conversion. The calculated values of the conversion efficiency are in good agreement with experimental data. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 56–60, January–February, 2000.     

Multiple synchronous interaction of a train of ultrashort light pulses with the first stokes component in compressed hydrogen

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 49, No. 5, pp. 761–766, November, 1988.     

Modification of polyethylene terephthalate by proton irradiation

Polyethylene terephthalate (PET) films were irradiated with 3 MeV proton beams at different fluences. The microhardness, electrical, thermal and structural studies were carried out using microhardness tester, LCR meter, thermogravimetric analysis (TGA) and FTIR spectroscopy. Vickers' hardness has been observed to increase with the fluence. The true bulk hardness of the film was obtained at loads greater than 400 mN. The AC electrical conductivity is practically unaffected by irradiation up to a frequency of 10 kHz, but it is found to increase exponentially at a frequency of 300 kHz. The loss factor and dielectric constant are observed to change appreciably with the fluence. It is observed that there is no significant change in the stability of the polymer up to the fluence of 10¹⁴ ions cm^?2 as revealed by TGA and FTIR spectroscopy.