an electrical discharge occurs between the anode and the cathode and the active gas such as co 2 between the two electrodes is excited to provide a laser beam . the laser beam thus provided is reflected repeatedly by a pair of reflection mirrors . the reflected laser beam is amplified while passing through the space where the discharge occurs , thus providing the function of a gas laser oscillator . although the amplification that occurs in the discharge zone between the electrodes , considerable laser beam absorption takes place in the space between the reflection mirrors and the electrodes . in this space , the amount of operating gas such as co 2 is reduced , or the space is evacuated . alternatively , the space is cooled by causing the gas therein to flow . a reduction in so - called laser beam absorption function is provided .