Pre-ionization method for co2 gas-discharge laser

In an RF powered gas-discharge laser, including discharge electrodes and a lasing gas mixture between the electrodes, the lasing gas mixture being ionized when the RF power is applied to the electrodes and laser action being initiated when the RF power has been applied for a duration sufficient to ignite a discharge, a method of pre-ionizing the lasing gas mixture, comprising the steps of:

• (a) determining a maximum time period during which the RF power can be applied to the electrodes without expecting laser action to occur;
• (b) initiating application of RF power to the electrodes;
• (c) monitoring RF power reflected back from the electrodes;
• (d) if before RF power has been applied to the electrodes for the estimated maximum time period the monitored reflected RF power falls below a predetermined level indicative of the imminent onset of laser action, terminating the application of the RF power to the electrodes before the estimated time has elapsed to prevent the laser action from occurring, else terminating the application of the RF power to the electrodes when the estimated maximum time has elapsed;
• (e) repeating steps (b), (c), and (d) a predetermined number of times with a predetermined time between repetitions;
• and
• (f) if the monitored reflected power does not fall below the predetermined level indicative of the imminent onset of laser action during any of the repetitions of steps (b), (c) and (d), providing a fault-signal indicating that this is the case.

In an RF powered gas-discharge laser, including discharge electrodes and a lasing gas mixture between the electrodes, the lasing gas mixture being ionized when the RF power is applied to the electrodes and laser action being initiated when the RF power has been applied for a duration sufficient to ignite a discharge, a method of pre-ionizing the lasing gas mixture, comprising the steps of:

• (a) determining a first maximum time period during which the RF power can be applied to the electrodes without expecting laser action to occur;
• (b) estimating a second maximum time period during which the RF power can be applied to the electrodes without initiating laser action, the second maximum time being significantly less than the first maximum time period;
• (c) initiating application of RF power to the electrodes;
• (d) monitoring RF power reflected back from the electrodes;
• (e) if no RF power is monitored during step (d), terminating the application of the RF power to the electrodes when the second estimated maximum time has elapsed, repeating steps (c), (d), and (e), with a first predetermined interval between repetitions, and providing a first fault signal indicating that no reflected RF power has been monitored;
• else
• (f) if before RF power has been applied to the electrodes for the estimated maximum time the monitored reflected RF power falls below a predetermined level indicative of the imminent onset of laser action, terminating the application of the RF power to the electrodes before the estimated first time has elapsed to prevent the laser action from occurring, else terminating the application of the RF power to the electrodes when the first estimated maximum time has elapsed.

Gas discharge laser apparatus, comprising:

• a laser head including discharge electrodes and a lasing gas mixture between the electrodes;
• an RF power supply for supplying RF power to the electrodes for exciting the lasing gas mixture therebetween;
• a sensor for monitoring RF power reflected back from the electrodes as a result of an impedance mismatch between the RF power supply and the electrodes;
• and
• control circuitry cooperative with the reflected RF power monitor and arranged to repeatedly initiate and terminate RF power delivery to the electrodes by the RFPS for providing simmer-pulses for pre-ionizing the lasing gas mixture, said control circuitry being arranged to terminate a simmer pulse when the reflected RF power monitor detects a fall in the reflected RF power below a predetermined level indicative of the onset of laser action in the laser head.