光磁共振实验中壁弛豫过程与外磁场的关系

利用改进后的DH807型光磁共振实验装置,在静态磁场下精确测量了抽运信号的弛豫饱和值与外磁场的关系,从而得到壁弛豫速率与外磁场的关系,并建立模型对其原理进行了探讨.     

A novel demonstration of photoacoustic Raman spectroscopy with combined stimulated Raman pumping in H2 molecule

We present the experimental demonstration of a novel, efficient, and vibrational selective technique to prepare population in vibrational level v″ = 1 using the stimulated Raman pumping. Photoacoustic Raman signal has been studied in non-radiative transitions in the molecule H₂ (v″ = 0) and (v″ = 1). The population fraction in the v″ = 1 level can be estimated by using combined photoacoustic Raman spectroscopy with stimulated Raman pumping for the first time.     

Parametric amplification at low-frequency pumping and generation of four-mode entangled states

We show that parametric amplification at low-frequency pumping can be implemented in aperiodic nonlinear photonic crystals. In this process, the intensities of the waves with frequencies higher than the pumping frequency increase with increase in the interaction length as in the case of the standard process of parametric amplification at high-frequency pumping. The process under consideration includes a nondegenerate parametric down-conversion followed by two parametric up-conversions in the same pumping wave. As a result, generation at four new frequencies arises. Quantum analysis of the process demonstrates the presence of entanglement in the states of four modes. Talk presented at the oral issue of J. Russ. Laser Res. dedicated to the memory of Professor Vladimir A. Isakov, Professor Alexander S. Shumovsky, and Professor Andrei V. Vinogradov held in Moscow February 21–22, 2008.     

Pressure dependence of the spectral lines of a high power, high pressure atomic fluorine laser pumped by a charge transfer from He2

Various transitions of a pressure tunable atomic fluorine laser have been observed over a rather wide spectral range, 634.8–755.2 nm, by exciting the atmospheric pressure of helium containing 0.2% F₂ in a preionized Blumlein discharge device with a charging voltage of 10–15 kV. The intensity of two quartet transitions, 739.9 and 755.2 nm, increases with pressure, whereas that of the other quartet and doublet lines, 634.8, 641.4, 712.8 and 731.1 nm, decreases with increasing atmospheric fill-pressure. The pumping mechanisms at high pressures appear to be different from those at relatively low pressures.     

Performance of a small air-lift pump

Pumping of liquids using two-phase flow has been examined experimentally in small air-lift pumps with 12—19 mm bore plexiglass tubes. An air injection system was devised to create and maintain ‘perfect’ slug flow in the vertical riser tube. An equation has been derived, based on momentum conservation considerations, which correlates well with the measurements obtained. Slip variation, or liuid holdup, between the two phases and the formation of the ‘entrance’ section part of the pump (suction pipe) were taken into consideration. Unlike its predecessors, this equation predicts the reversal in the pump performance curve observed experimentally.     

Experimental determination of spin-rotation and spin-spin magnetic interactions in by nuclear spin conversion

When a gas sample of ¹³CH₃F is prepared with a population of isomers (ortho and para forms) far from the equilibrium given by nuclear spin statistics, it relaxes towards this equilibrium with an exponential decay rate. This phenomenon called nuclear spin conversion is mainly governed by intramolecular spin-spin and spin-rotation interactions. In the quantum relaxation model [P.L. Chapovsky, Phys. Rev. A 43, 3624 (1991)], two pairs of ortho-para levels (J = 9, K = 3; J' = 11, K' = 1) and (J = 20, K = 3; J' = 21, K' = 1) are principally responsible for the conversion. The levels of the second pair are coupled by both spin-spin and spin-rotation interactions. The application of an electric field (up to 10 kV/cm) induces a crossing of the Stark components of this pair, which is observed for the first time. A specific experimental set-up based on an electric field of alternating triangular shape is used, which allows the determination of the strength of both interactions via the measurement of the spin conversion decay rates. This work yields the first experimental value for the electronic contribution to the spin-rotation interaction in ¹³CH₃F. Received 23 May 2002 / Received in final form 18 September 2002 Published online 21 January 2003 RID="a" ID="a"e-mail: Patrice.Cacciani@univ-lille1.fr     

Efficient population transfer by delayed pulses despite coupling ambiguity

In traditional schemes of multilevel multilaser excitation, each laser pulse interacts with only one pair of states, and the rotating wave approximation (RWA) is applicable. Here we study the population transfer process in a three-state system when each of the two lasers interacts with each of the pair of states and when the Rabi frequencies characterizing the interaction strengths of the system are comparable to or larger than the difference of the transition frequencies. We show that complete and robust population transfer is possible under conditions more general than those hitherto considered necessary for stimulated Raman adiabatic passage (STIRAP) or for successive π pulses. Using adiabatic Floquet theory we show that successful population transfer can be interpreted as adiabatic passage by means of a transfer state which connects the initial and final states. The Floquet picture offers a convenient interpretation of the population transfer as accompanied by multiple absorption of photons from or emission into the laser fields.     

890 mW Diode Pumped Nd:YVO4 Intracavity-doubled Red Light Laser

A diode-pumped Nd3+:YVO4 emitting at 1342 nm and 671 nm was developed. Low concentration neodymium doped Nd:YVO4 shows excellent stability at 1342 nm. With a type-Ⅱ noncritical phase-matched LBO crystal as the intracavity frequency doubler, 890 mW of 671 nm light was obtained at 11.2 W incident pumping power, the optical-optical conversion efficiency is 7.9%.     

内壳层跃迁--实现超短波长激光的途径

内壳层跃迁机制是实现超短波长激光的一种很有潜力的方案，随着近年来超短超强激光技术和X射线激光实验方法的进展，实现内壳层跃迁机制的超短波长硬X射线激光不再是遥不可及的梦想，文章详细介绍了内壳层跃迁机制X射线激光的原理，并讨论了开展内壳层跃迁机制X射线激光实验的一些实际相关问题。     

Comparison of characteristics of an x-ray preionized XeCl laser, pumped by water transmission line and low inductance capacitor bank

With a high uniformity of x-ray preionization, a long pulse duration and a high specific energy (9 J l^-1), an XeCl excimer laser output has been obtained by using a compact low inductance capacitor bank as the laser excitation circuit. The superior features of the low inductance capacitor bank (LICB) compared to the water transmission line (WTL) are attractive for repetitively pulsed XeCl excimer lasers.