Paying attention to manufacturers’specifications can improve your lasers effectiveness and save you money.

SENSITIVE YET DURABLE is the laser machine tool dichotomy that mandates that gas delivery equipment is designed to meet specific purity, pressure, and flow requirements. A case in point is CO2 lasers used for semiconductor microprocessing. Purity plays a significant role, affecting resonator stability, beam mode quality,and performance.

System design and purity requirements vary from manufacturer to manufacturer. If the gas system does not encompass the right equipment, then both the laser and the manufacturer technician sit idle. Subsequently, if the resonator, beam-purge, or assist gas system is off specification, the laser will suffer from poor performance and excessive maintenance.
Following is a look into the symptoms a laser displays when the manufacturer’sguidelines are not followed.

Each laser manufacturer utilizes different combinations of helium, nitrogen, carbon monoxide, and carbon dioxide as the medium in the resonator lasing process. The lasing principles are very similar for all CO2 lasers, differing only by the method of exciting and cooling the gas mixture in the resonator cavity. Figure 1 illustrates the effect moisture has on the resonator gain or output measured in wattage. It is quite apparent that as the moisture level increases, the laser power output is adversely affected. As laser output is reduced, there is less energy available to melt the material, and the cut surface will develop coarse striations, or worse yet, incomplete penetration.

Herrit and Scatena [1] observed that excessive optic thermal absorption caused by deposited contaminates reduces power output and distorts beam quality. Albright and Khakhalev [2] identified hydrocarbon deposits from gas impurities as contaminate that cause optic absorption, which reduces power output.

As a short-term solution, the operator will either slow down the travel speed or increase the demand on the power supply. Choosing to neglect moisture and hydrocarbon contaminate problems will create more stress onthe internal optics and lead to costly repairs.

The solution is to maintain the purity level of the gas from the bottle to the laser. Most specialty gas regulators can offer a leak rate of 1x10-8He cc/sec and a stainless steel diaphragm, which prevents out-gassing of plasticizers into the gas stream. Plasticizers are produced from petroleum (i.e., hydrocarbons) and formulated into polymers such as neoprene diaphragms to maintain flexibility. However, a laser grade-regulator will have these features plus incorporate an integral purge and check-valve to prevent atmosphere from entering the gas stream during a cylinder exchange.