Coherent Superposition States of Atoms and Molecules in a Bose—Einstein Condensate with Exactly Bananced Photo—Associations and Photo—Dissociations

We show that there exist a series of coherent superposition states of atoms and molecules in a dilute Bose-Einstein condensate with exactly balanced photo-associations and photo-dissociations,and their analytical expressions are explicitly given.They also correspond to the coherent superposition states of two kinds of hpotons in optical second harmonic generation processes,which shows exactly balaced down-and up-conversions.     

A proposed method to characterize high harmonic microbunching in EEHG operation of SDUV-FEL

The echo-enabled harmonic generation （EEHG） scheme offers remarkable efficiency for generating high harmonic microbunching with a relatively small energy modulation. A proof of principle experiment of the EEHG scheme has been proposed at the Shanghai deep ultraviolet （SDUV） free electron laser （FEL） facility, where the 4th harmonic of the seed laser is amplified in the 9 m long radiator. To explore the advantages of the EEHG scheme, in this paper, a method of measuring the coherent high harmonic radiation of the radiator is proposed to investigate the electron beam microbunching corresponding to the 10th-20th harmonics of the seed laser. The principle of the proposed method, comparisons with existing methods and the simulation results are presented and discussed.     

High-Harmonic Generation by Initial Coherent States in a Short Laser Pulse

We study high-order harmonic generation (HHG) in an intense laser pulse when the initial state is prepared as a coherent superposition of the ground and first excited states. By examining the populations of these states for different laser intensity regions, the role of the excited state in the harmonic generation process can be identified. We also find that high conversion etticiency and high cutoff frequency of HHG can be achieved if the intensity of the laser pulse is high enough to cause considerable ionization of the first excited state but not sufficient to ionize the ground state.     

High—Order Harmonic Generation by Two Non—collinear Coherent Femtosecond

We have studied the high-order harmonic generated by two coherent pulses in argon gas produced by a gas jet. A loop in the relationship of the harmonic intensity versus the absolute values of relative phase difference was observed for non-collinear arrangement. Compared with the collinear arrangement, increase of 10 times of the conversion efficiency for 17th-order harmonic generation at an appropriate relative phase difference was obtained. The calulation of the intensity and phase for the laser field near the focus gives a simple reason for these phenomena.     

On Husimi Distribution for Systems with Continuous Spectrum

We propose a procedure to generalize the Husimi distribution to systems with continuous spectrum. We start examining a pioneering work, by Gazeau and Klauder, where the concept of coherent states for systems with discrete spectrum was extended to systems with continuous one. In the present article, we see the Husimi distribution as a representation of the density operator in terms of a basis of coherent states. There are other ways to obtain it, but we do not consider here. We specially discuss the problem of the continuous harmonic oscillator.     

Generation of NIulticomponent NIotional Coherent and Squeezed Coherent States of N Trapped Ions by a Dispersive Interaction

Following the recent proposal by Solano E et al. [Phys. Rev. Left. 87 (2001) 060402] a procedure is proposed to generate arbitrary discrete multicomponent motional coherent and squeezed coherent states of N trapped ions by additionally using a dispersive bichromatic interaction in a long-living and fast way. In this procedure, two lasers in the Raman configuration are tuned quasiresonant and resonant with N two-level ions under different conditions, respectively. Furthermore, we show how the idea can be used for the generation of two-mode SU(2) Schrdinger cat states for the vibrational motion of a single ion trapped in a two-dimensional harmonic potential.     

Experimental study of conversion from atomic high—order harmonics to x—ray emissions

There are two physical phenomena in a strong laser intensity. One is the high-order harmonic emission; the other is x-ray emission from optical-field ionized plasmas. The experiment of conversion from high-order harmonics to x-ray emissions was given with a 105fs Ti:sapphire laser by adjusting laser intensities. The ingredient in plasma was investigated by the numerical simulations.Our experimental results suggested that the free electrons have detrimental effects on harmonic generation but are favourable for x-ray emission from optical-field ionized plasmas. If we want to obtain more intense harmonic signals as a coherent light source in the soft x-ray region, we must avoid the production of free electrons in plasmas. At the same time, if we want to observe x-rays for the development of high-repetition-rate table-top soft x-ray lasers, we should strip all atoms in the plasmas to a necessary ionized stage by the optical-field-ionization in the field of a high-intensity laser pulse.     

High-order harmonics generation by few-cycle and multi-cycle femtosecond laser pulses

This paper investigates experimentally high-order harmonic generation(HHG) of neon gas with 5-fs and 25-fs driving laser pulses.It has been demonstrated that the cutoff energy of the harmonic extreme ultraviolet photons is extended to 131 eV and the HHG spectrum near the cutoff region becomes continuum as the driving laser pulse duration is 5 fs;whereas much lower cutoff photon energy and discrete harmonic spectrum near the cutoff region are presented as the laser pulse duration is 25 fs.The results can be explained by the fact that neutral atoms can be exposed to more intense laser field before they are depleted by ionization because of the extremely short rising time of the few-cycle pulse.The 5-fs driving laser pulse paves the way of generation of coherent x-ray in the water window and single attosecond pulse.     

Coupling Between the Group—Related Coherent States

When two representations of the Lie algebra are coupled,the coupling integral kernels are presented to relate the coupled to uncoupled group-related coherent states,These kernels have a connection with usual coupling coefficients.The explicit expressions of these kernels for SU(2),SO(4) and SUq(2) are given.When the direct product of three representations is formed in two ways,the recoupling integral kernels relating to the coupled group-related coherent states corresponding to two different schemes are introduced,and the relations between these kernels and the general recoupling coefficients are obtained.The properties of these kerels are discussed.