Pulsed UV-laser-induced chemistry of perfluoropolyether lubricant film

We investigate the molecular structure change of laser-irradiated perfluoropolyether lubricant on disk media by using mass spectroscopy. A KrF excimer laser with a wavelength of 248 nm was used to irradiate the lubricant film (2 nm) on a carbon overcoat surface. We found that two unique mass peaks emerged from the laser-irradiated lubricant mass spectra, which are attributed to OH-CHF-O(:H⁺)-CHF-OH and F-COO-CF₂-CF₂-CF₂-CF₂ ⁺ respectively. When thelaser fluence increases to 100 mJ/cm², these two unique mass peaks start to be enhanced drastically while the abundance of the end group of the lubricant, CF₂CH₂OH, remains almost constant, indicating that the two unique species are generated from the scission and re-arrangement of the backbone ether chains. With a laser fluence beyond 140 mJ/cm², the disk media surface damage is observable and lubricant evaporation is the main pathway. Received: 24 October 2001 / Accepted: 3 December 2001 / Published online: 3 May 2002     

Phase-matched electrooptic modulator at 84 GHz for blue light: Theory,experimental test and applications

We describe the theory and experimental realization of an ultrafast phase-matched electrooptic modulator, working with 486 nm light and a modulation frequency of 84 GHz. To achieve phase matching for arbitrarily high modulation frequencies the laser beam is guided with several internal total reflections along a zig-zag path through a LiTaO₃ crystal. The method was studied experimentally with a 84 GHz modulator and a highly stable 486 nm dye laser. The maximum modulation index of this setup was about 5.0%. Beat signals between either the first- or the second-order sidebands and another laser were observed. This modulator was used to directly measure the 671 GHz 1S–2S isotope shift of hydrogen and deuterium with radio-frequency accuracy.     

Light-driven molecular switches and motors

Technology is omnipresent in our modern-day society and it is hard to imagine a world without machines, computers or robots. One of the main current scientific challenges is the bottom-up construction of systems that represent nanosize analogues of switches, devices and motors. Our efforts in this area have focussed on the construction of devices based on sterically overcrowded alkenes. In this paper, we present our ongoing research on the construction of binary molecular switches, which has recently led to genuine molecular motors. The control of chirality in a molecular switching system allows interconversion between molecules of opposite helicity using different wavelengths of light. Such bistable chiral switches are of potential use in optical data storage and processing at the molecular level. The control of molecular chirality is even more subtle in the case of molecular motor systems. The exquisite control of chirality using light as an energy source has resulted in a controlled, repetitive 360° unidirectional rotation in two generations of molecular motor systems. Received: 21 January 2002 / Accepted: 11 February 2002 / Published online: 22 April 2002     

Quantum ergodicity and energy flow in molecules

We review a theory for coupled many-nonlinear oscillator systems that describes quantum ergodicity and energy flow in molecules. The theory exploits the isomorphism between quantum energy flow in Fock space, that is, vibrational state space, and single-particle quantum transport in disordered solid-state systems. The quantum ergodicity transition in molecules is thereby analogous to the Anderson transition in disordered solids. The theory reviewed here, local random matrix theory (LRMT), describes the nature of the quantum ergodicity transition, statistical properties of vibrational eigenstates, and quantum energy flow through the vibrational states of molecules. Predictions of LRMT have been observed in computational studies of coupled nonlinear oscillator systems, which are summarized here. We also review applications of LRMT to molecular spectroscopy and chemical reaction rate theory, including adoption of LRMT in theories that predict rates of conformational change of molecules taking place at energies corresponding to those below and above the quantum ergodicity transition. A number of specific examples are reviewed, including the application of LRMT to predict (1) dilution factors of IR spectra of organic molecules, (2) rates of conformational change in chemical and photochemical reactions, (3) conformational dynamics of biological molecules in molecular beams, (4) rates of hydrogen bond breaking and rearrangement in clusters of biological molecules and water, and (5) excited state proton transfer reactions in proteins.     

Rn+1上广义Carlesori测度与Hp函数的导数

在单位回盘上广义Carleson只解决了2镇p相似文献   

Derivative estimates of averaging opera tors and extension

We study the derivative operator of the generalized spherical mean S^γt. By considering a more general multiplier m^Ωγ,b=Vn-2/2+γ(|ξ|)|ξ|^bΩ(ξ') and finding the smallest γ such that m^Ωγ,b is an Hp multiplier, we obtain the optimal range of exponents (γ,β,p)to ensure the H^p(R^n) boundedness of a^βS^γ1f(x). As an application, we obtain the derivative estimates for the solution for the Cauchy problem of the wave equation on H^p(R^n) spaces.     

Nanosecond and femtosecond UV laser ablation of polymers: Influence of molecular weight

We examine the nanosecond and femtosecond UV laser ablation of poly(methyl methacrylate) (PMMA) as a function of molecular weight (M_w). For laser ablation with nanosecond laser pulses, at the excimer wavelengths 248 nm and 193 nm, we show that high temperatures develop; yet the dynamics of material ejection differs depending on polymer M_w. The results on the nanosecond ablation of polymers are accounted within the framework of bulk photothermal model and the results of molecular dynamics simulations. Turning next to the 248 nm ablation with 500 fs laser pulses, the ablation threshold and etching rates are also found to be dependent on polymer M_w. In addition, ablation results in morphological changes of the remaining substrate. Plausible mechanisms are advanced.     

All-Optical Modulation with a Surface Plasmon Mach-Zehnder Interferometer

We use two parallel nano-slits in a silver film to form a surface plasmon Mach Zehnder interferometer （MZI）, based on the interference of two surface plasmon waves propagating along the two surfaces of the silver film. Coating the silver film with a photoinduced birefringence polymer film, we achieve optical modulation of the MZI output by changing the refractive index of the polymer film with a pump beam. An on/off ratio 0f 2. 7 is obtained for a probe wavelength of 865 nm.     

Generation of Optical Vortex Using a Spiral Phase Plate Fabricated in Quartz by Direct Laser Writing and Inductively Coupled Plasma Etching

A simple, economical and reliable technique is proposed for fabricating a spiral phase plate （SPP） in a quartz substrate to generate optical vortex with a unit topological charge at the wavelengths of 632.8nm. The spiral phase plate is first formed in the photoresist by direct laser writing lithography and then transferred into the quartz substrate by inductively coupled plasma etching. The performance of the fabricated SPP is verified by using beam intensity distribution, which is in agreement with the theoretical calculation result. The interference measurement suggests that we have succeeded to generate optical vortex with a unit topological charge with the fabricated SPP.     

Measurement of small chirp-parameter for Mach-Zehnder-type optical modulator

A new measurement method of chirp-parameters is proposed for electro-optic (EO) intensity modulators with the Mach-Zehnder (MZ) waveguide interferometer. This method is suitably applied for the measurement of the small chirp with operation at a specific RF-frequency. To determine the chirp-parameter, optical spectrum components of the modulated light are observed with varying the relative optical phase difference between the two arms of the MZ waveguide interferometer. The chirp-parameter of 0.17, which is a value small enough for EO intensity modulation, was successfully measured by the experiment.