Abstract —The pulsed ruby laser (347 nm) flash photolysis technique has been used to measure the triplet-triplet absorption spectra and triplet lifetimes of trans -retinal, N-frans -retinylidene- n -butylamine (NRBA), and protonated NRBA (NRBAH+) at room temperature. In methylcyclohexane solution, the triplet lifetimes are in the range 10–20 μs and decrease in the order NRBAH+ > NRBA > trans -retinal. Intersy stem-crossing efficiencies (φISC) were determined by a comparison technique using anthracene and 1,2-benzanthracene as reference compounds. For trans -retinal, φISC is 0–50 pM 0–05 in methylcyclohexane and 0–08 in methanol, which confirms that earlier values of 0–11 and 0–017 in these solvents are in error. For NRBA and NRBAH+ in methylcyclohexane, ΦISC values are 0008 and < 0–001, respectively. Evidence is presented for a significant solvent effect in the isomerization of retinal via the triplet state, and that cis φ trans isomerization occurs from the triplet state of NRBAH+. The relation between the intersystem-crossing properties of model compounds and the photochemistry of rhodopsin is discussed. 相似文献
A novel signal encoding and decoding method for laser ranging is proposed and experimentally demonstrated. The coherent-burst method uses a quasi-continuous interrupted burst of modulated laser radiation to achieve high-precision ranging at all distances. Both time of flight and phase shift are determined based on an amplitude-modulation pattern that has electronic coherence with a master oscillator. High-frequency modulation provides high absolute precision, while measured temporal delay from transmission to reception eliminates potential uncertainty from aliasing. The method is demonstrated with low-power diode lasers that can be modulated at frequencies in excess of 250 MHz. 相似文献
A ponderomotive-optical trap for energetic free electrons has been generated with a single, high-peak-power laser beam. The focal region consists of an intensity minimum at the center of the focus, with increasing intensities in all directions. The focus can be generated with a two-zone binary phase plate, or with a novel, coaxially segmented wave plate. This scheme can also be used to trap neutral atoms. 相似文献
Free-energy functionals suitable for describing realistic, nonuniform systems near criticality are discussed with emphasis on the advantages of a local formalism. It is proposed to investigatemicro canonical functionals in which both the usual order-parameter (or magnetization) density m(r)and the local energy density (r), which has independent critical fluctuations, are employed. This approach is tested by an exact calculation of the microcanonical functional [{m}, {}] in the continuum limit for a one-dimensional Ising model. Remarkably, the microcanonical functional is found to be local irrespective of the proximity to the critical point (located at zero temperature and zero field). Furthermore, its form relates closely to the scaling postulate advanced earlier by de Gennes and Fisher and displays features of conformal covariance. 相似文献