HIGH PEAK POWER AND HIGH-REPETITION-RATE CHARACTERISTICS IN A CURRENT-PULSED Q-SWITCHED CO2-LASER WITH A MECHANICAL SHUTTER

An electro-mechanical Q-switched (EMQ) CO2 laser is Q-switched by a me chanical beam chopper in combination with a pulsed discharge current. Such a system can produce pulses with high peak powers (> 10 kW) and h igh repetition rates (> 1 kpps). In order to analyze the output charac teristics, the peak power and the duration of the output pulses have b een measured experimentally in detail over a wide range of Q-switching times up to 250 ns. For a low-pressure (< 4 kPa) CO2 gas system, the standard rate equations adequately explain the experimental results by introducing a new switching function for the form of the cavity loss for the mechanical chopper. In an EMQ-laser with a high initial invers ion density (4.5.10(15)/cm3 at 150 mA peak current), multiple peak pul ses or pulse distortion have been observed. This is due to the plasma screening effect induced by the burning of the metal shutter blades pl aced inside the cavity. It is found that tungsten metal shutter blades can be used up to a power density of 259 MW/cm2 for a focused beam wi thout this effect occurring. The solutions of the rate equations show that optimum coupling can prevent the plasma screening effect even for a Q-switching time longer than the pulse buildup time. The EMQ-laser configured for optimum coupling has produced a peak output power of 30 kW for the 9P20 transition branch in the CO2 spectrum without any pul se distortion. This value has been obtained even though the discharge length was only 1.3 meters.