Two mechanisms for population inversion via two-colour coherent excitation in three-level systems

We analyse the physical origin of population inversion via continuous wave two-colour coherent excitation in three-level systems by dressing the inverted transition. Two different mechanisms are identified as being responsible for the population inversion. For V-configured systems and cascade (E) configured systems with inversion on the lower transition, the responsible mechanism is the selective trapping of dressed states, and the population inversion approaches the ideal value of 1. For Lambda-configured systems and Xi-configured systems with inversion on the upper transition, population inversion is based on the selective excitation of dressed states, with the population inversion tending towards 0.5. As the essential difference between these two mechanisms, the selective trapping of dressed states occurs in systems with strong decay into dressed states while the selective excitation appears in systems with strong decay out of dressed states.

Single sub-100 attosecond pulse generation in a two-colour time-gating laser field

We theoretically propose a method of generating a single sub-100 attosecond (as) pulse with a two-colour time-gating laser field. The field is synthesized by an 8 fs/800 nm (three optical cycles) pulse and a 24 fs/2400 nm (three optical cycles) pulse with an optimal time delay between them. In our simulation, we obtain a supercontinuum with an extremely broad spectrum of 150 eV and generate an isolated attosecond pulse with 96 as pulse duration without any dispersion compensation.

Two-colour laser-induced electron dynamics in two-level quantum system

To attempt to control the quantum state of a physical system with a femtosecond two-colour laser field, a model for the two-level system is analysed as a first step. We investigate the coherent control of the two-colour laser pulses propagating in a two-level medium. Based on calculating the influence of the laser field with various laser parameters on the electron dynamics, it is found the electronic state can be changed up and down by choosing the appropriate laser pulses and the coherent control of the two-colour laser pulses can substantially modify the behaviour of the electronic dynamics: a quicker change of two states can be produced even for small pulse duration. Moreover, the oscillatory structures around the resonant frequency and the propagation features of the laser pulses depend sensitively on the relative phase of the two-colour laser pulses. Finally, the influence of a finite lifetime of the upper level is discussed in brief.

Encircled energy measurement for focusing lens based on scanning Hartmann test

The encircled energy of a focusing lens is one of the parameters directly affecting the target efficiency in high-power laser facilities. The direct measurement method of the encircled energy for the focusing lens based on the scanning Hartmann test is proposed in this paper. With the scanning Hartmann test setup, the information in the whole aperture of the focusing lens can be achieved. The encircled energy can be obtained by analyzing the spot diagram on the focal plane of the focusing lens. In experiments, the encircled energy of an aspheric focusing lens is measured using this method. The measurement result is in good agreement with that derived from measurement data by an interferometer and the difference is 7.7%. (C) 2006 Elsevier GmbH. All rights reserved.

Aniracetam restores the effects of amyloid-beta protein or ageing on membrane fluidity and intracellular calcium concentration in mice synaptosomes

In the present study, we observed the in vitro effect of aniracetam on membrane fluidity and free calcium concentrations (Ca(2+)i) of frontal cortical (FC) and hippocampal (HP) synaptosomes of aged mice and young mice treated with amyloid-beta protein (A

Differential effects of ageing on the EEG during pentobarbital and ketamine anaesthesia

Background and objectives: Pentobarbital and ketamine are commonly used in animal experiments, including studies on the effects of ageing on the central nervous system. The electroencephalogram is a sensitive measure of brain activity. The present study i

The application of in vitro sperm competition test to evaluate the impact of ZP-derived peptides on fertilization capacity of cat sperm

The present study aimed to establish a sensitive in vitro assay to assess the binding capacity of cat spermatozoa. Cat oocytes and epididymal sperm cells were isolated from gonads and cultured for in vitro fertilization. Before fertilization, the sperm ce

Chronic effects of water-borne PFOS exposure on growth, survival and hepatotoxicity in zebrafish: A partial life-cycle test

Perfluorooctane sulfonate (PFOS) is widely distributed and persistent in the environment and wildlife. The main aim of this study was to investigate the impact of long-term exposure to low concentrations of PFOS in zebrafish. Zebrafish fry (F-0, 14d post-fertilization, dpf) were exposed via the water for 70d to 0 (control), 10, 50 and 250 mu g L-1 PFOS, followed by a further 30d to assess recovery in clean water. The effects on survival and growth parameters and liver histopathology were assessed. Although growth suppression (weight and length) was observed in fish treated with high concentrations PFOS during the exposure period, no mortality was observed throughout the 70d experiment. Embryos and larvae (F-1) derived from maternal exposure suffered malformation and mortality. Exposure to 50 and 250 mu g L-1 PFOS could inhibit the growth of the gonads (GSI) in the female zebrafish. Histopathological alterations, primary with lipid droplets accumulation, were most prominently seen in the liver of males and the changes were not reversible, even after the fish were allowed to recover for 30d in clean water. The triiodothyronine (T-3)) levels were not significantly changed in any of the exposure groups. Hepatic vitellogenin (VTG) gene expression was significantly up-regulated in both male and female zebrafish, but the sex ratio was not altered. The overall results suggested that lower concentrations of PFOS in maternal exposure could result in offspring deformation and mortality. (c) 2008 Elsevier Ltd. All rights reserved.