The Study On He-Ar Radio-frequency Capacitive Discharge At Atmospheric Pressure

In recent years,optically pumped metastable argon lasers have attracted much attention due to the stable chemical properties,the emission of near infrared lasers,high beam quality,high quantum efficiency and the possibility of extending to high power lasers.The particle density of the lower pump level of the laser Ar 1s₅?3s²3p⁵4s ³P₂?is the key to the laser,but the position of its energy level is considerably high?11.548 eV?,which is difficult to obtain large occupation.Therefore,how to produce enough Ar 1s₅ particle density is an important issue in the study of such lasers.The common way to generate excited gas is gas discharge.In this paper,radio frequency?RF?discharge with RF frequency of 13.56 MHz and discharge gas of He-Ar mixture is adapted.In order to judge the discharge state,the discharge voltage is measured by a high pressure probe,and several important parameters of the plasma,such as rotational temperature,electronic temperature,electron density and Ar 1s₅ particle density,are measured by optical emission spectroscopy,in which the gas rotational temperature is obtained by fitting the N₂ second positive band spectrum?C ³?47?_u?B³?47?_g?,the electronic temperature by the two lines method and the Boltzmann's plot method,the electron density by Stark broadening at 696.54 nm of argon atom spectrum,the Ar 1s₅ particle density by line ratio of 419.83 nm and 420.07 nm.By these methods,the effects of gas ratio,pressure,flow rate and discharge power on the state of static or flow discharge with bare metallic electrodes or dielectric barrier discharge?DBD?were studied experimentally.In the scheme of static discharge with bare metallic electrodes,it is found that the Ar 1s₅ particle density increased with the increase of discharge power at 100 kPa.The Ar 1s₅ particle density get its peak at 4%among the volume content of argon between 2%and 5%,which is 1.5×10⁹ cm^-3 at 70 W of discharge power.In the scheme of static DBD with argon content of 3%,the Ar 1s₅ particle density decreases with the increase of pressure,and the electric parameters are slightly higher than those of bare metallic electrode under the same conditions.When the discharge gas is in flowing state,the variation of each parameter is similar to that in the scheme of static DBD.The difference is that the Ar 1s₅ particle density is higher than that of static discharge.In the scheme of flow DBD,the Ar 1s₅ particle density get its highest value when the argon content is 4.2%and the flow rate is 2.0 L/min.The discharge spectra show that in the scheme of static discharge,the intensity of H₂O rotational line in the range of 400⁶00 nm increases continuously with the increase of the discharge time,and the spectral intensity of the argon atom decreases.The spectral intensities of argon atoms and oxygen atoms in the range of 752⁸07 nm decrease to different degrees,in which the decrease of the intensities of the lines of argon atoms is larger.During gas flowing discharge,the spectral intensities are increased and rotational lines of H₂O are invisible,indicating that the impurity gas in the discharge region decreases and the energetic particles increase.The spectral intensities of argon atoms and oxygen atoms in the range of 752⁸07 nm is slightly increased,and the intensity of oxygen atoms is strong,which indicates that the content of oxygen atoms in the discharge chamber is stable and can not be eliminated by flow.