Ar-Kr resonance energy transfer in He/Ar/Kr optically pumped rare gas laser medium

Abstract

High metastable density is one of the research hotspots of optically pumped rare gas laser (OPRGL). Considering that the Ar metastable state energy level is only 20 cm<sup>–1</sup> different from the Kr excited state 5p[3/2]<sub>2</sub>, argon gas is added to the He/Kr discharge system. Owing to the long lifetime of the Ar metastable state atoms, through the collision resonance energy transfer process of Ar(4s[3/2]<sub>2</sub>)→Kr(5p[3/2]<sub>2</sub>), the purpose of supplementing and increasing the metastable density of Kr (Kr<sup>*</sup>) can be realized. In the case of obtaining the same metastable density, the pressure of the discharge power source is reduced, and a new idea is provided for further obtaining a high metastable density in a large discharge volume. In this work, the experimental analysis is carried out from the perspectives of spectral diagnosis and measurement of metastable density by laser absorption spectroscopy. The results show that the peak of radiative transition line of Kr high energy level atoms participating in the collision to the metastable state energy level is significantly enhanced after adding argon, and the tail signal of the transition line is extended within one discharge cycle. Under the gas conditions of 100 mbar, 1% Kr and 12.5% Ar, the peak value of the spectral line can be enhanced by about 10 times, and the tail signal of the transition line can be extended from 0.6 μs to 14.25 μs. At the same time, the density of Kr metastable energy level atoms is measured under different Ar content. Under the gas conditions of 100 mbar, 15% Ar and 1% Kr, the density of Kr<sup>*</sup> increases from 4.94×10<sup>11</sup> cm<sup>–3</sup> to 6.96×10<sup>12</sup> cm<sup>–3</sup>. At low pressure, the absorption linewidth of Kr metastable atoms narrows with the increase of Ar content. Under the gas condition of 600 mbar and 1% Kr, when the content of Ar is increased to 5%, the peak density of Kr<sup>*</sup> increases from 4.69×10<sup>13</sup> cm<sup>–3</sup> to 5.79×10<sup>13</sup> cm<sup>–3</sup>, i.e. the increment is 20%. Although the enhancement of metastable-atom-generation at high pressure is not so significant as those at low pressure, an increasing trend can still be observed. The results verify that the Kr metastable atoms generated in each discharge period can be supplemented by Ar-Kr resonance energy transfer.