ABSTRACT:The multiphoton association reaction He þ H þ ! HeH þ in the electronic ground state is investigated using the time-dependent quantum wave packet method. It is shown that the collision pairs He þ H þ in continuum state transfer into m ¼ 0 state and then produce stable molecules HeH þ through emission of two or three photons. The multiphoton transition takes place via intermediate states, and the transfer probability is determined by the collision energy and the intermediate states. The populations of the intermediate states and m ¼ 0 state can be controlled by the laser duration. The three-photon transition is more efficient than the two-photon transition for producing the molecule HeH þ in m ¼ 0 state.

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The ladder transitions controlled by two harmonic pulses are investigated theoretically using a time-dependent quantum wave packet method for the ground electronic state of HF molecule. By choosing [Formula: see text], [Formula: see text] and [Formula: see text] schemes, the population can be transferred to target states [Formula: see text]. The population distribution can be controlled by the average amplitude of total electric field which depends on the relative phase of two pulses. With the variation of the relative phase between [Formula: see text] and [Formula: see text] pulses, the variation of population has a period of [Formula: see text]. For [Formula: see text] and [Formula: see text] schemes, the population distributions show oscillation behavior with a period of [Formula: see text] by varying the relative phase. The two harmonic pulses can realize a nearly complete population transfer to the target state.

The population transfer controlled by fundamental, 2nd-harmonic and 3rd-harmonic pulses is investigated by using the time-dependent quantum wave packet method. By varying the phase of the fundamental pulse, it can be coherent with the 2nd-harmonic and 3rd-harmonic pulses. Compared with two harmonic pulses, the phase in three harmonic pulses is more efficient in controlling population transfer. Molecular orientation can be controlled by the phases of the three pulses. The value of molecular orientation mainly depends on the phase coherence between the fundamental and 2nd-harmonic pulses.

The optical absorption and emission intensity of luminescent and birefringent crystal ErBa3B9O18were examined from optical absorption data based on Judd-Ofelt theory. The three intensity parametersΩt(t=2,4,6) are 3.10 × 10−20, 0.87 × 10−20, and 1.80 × 10−20 cm2, respectively. From the obtained intensity parameters, the radiative probabilitiesAr, radiative lifetimeτf, fluorescence branching ratiosβc, and integrated emission cross sections∑have been calculated. In comparison with other Er-doped luminescent crystals, ErBa3B9O18may find application in thin disk laser.