Sealed Off Operation of a High Repetition Rate TEA CO2 Laser
Abstract: Design and construction of a high repetition rate miniature TEA CO2 laser using low purity industrial gases is reported. An abnormal drop in laser power around input pulse energy of Ein=150-200 mj was observed. In spite of gas velocity importance in attaining uniform plasma under high voltage discharge pulse at high frequency operation it has no influence on this anomalous treatment. Degradation of gas molecules in plasma region at present of arc free glow discharge was considered. After 3×10Exp5 shots laser output power is decreased around 10% while working in closed-cycle laser gas mixture.
There are many scientific and technical applications for small compact transverse, electric, atmospheric (TEA) CO2 lasers[1], such as laser radar[2], multi-photon induced chemistry including a heavy molecular Excitation [3], and laser material processing[1] . In    contrast   to continuous wave CO2 lasers which play indispensable roles in present industry ,high repetition rate TEA CO2 lasers are far from being accomplished ,in spite of enormous efforts since 1960s.Until now ,two major factors limiting the operational life are the short lifetime of a discharge switch and degradation of the laser gas. Several experimental and theoretical efforts have been reported on using solid-state switches instead of expensive gas switches [4,5] and closed-cycle laser gas mixture [5].There have been few reports for the high Pulse Repetition Frequency closed-cycle TEA CO2 laser . In this article we have reported a high PRF closed-cycle TEA CO2 laser .We have used industrial N2 and CO2  gases,  which is contaminated by the various impurities. Around 10% decreasing of laser power after 3*10exp5 shots among operation in closed-cycle gas mixture is recorded.                                                   
Experimental Setup:
A metallic cylindrical chamber capable of holding vacuum acts as a gas vessel is consisted of laser head fans and cooling radiators as shown in figure 1.The discharge volume is 23 cm long, 5mm (width) ×5mm (height). The UV pre-ionization is provided by 24 steel pin spark arrays located along both sides of brass electrodes. Because the UV pre-ionization used for getting a homogeneous and stable excitation discharge are more compact and more technically reliable for the high repetitive operation than other pre-ionizations, they have been widely applied to the TEA CO2 lasers, including our laser device .The metallic chamber volume is around 10000 times discharge region volume so before doing  any experiment this chamber is evacuated down to -500 torr and after that the main laser gas CO2/N2/He=20/20/60 fills the chamber up to atmosphere pressure .This process allows  to economize  laser gas mixture and working in closed-cycle mode for more than  3.5×10Exp5 shots.