Q-switched CO2 laser for material processing

Abstract

A simultaneously super pulsed Q-switched CO 2 laser system for material processing comprises sealed-off folded waveguides with folded mirrors that are thin film coated to select the output wavelength of the laser. The system also comprises a plurality of reflective devices defining a cavity; a gain medium positioned within the cavity for generating a laser beam; a cavity loss modulator for modulating the laser beam, generating thereby one or more laser pulses; a pulsed signal generation system connected to the cavity loss modulator for delivering pulsed signals to the cavity loss modulator thereby controlling the state of optical loss within the cavity; a control unit connected to the pulsed signal generation system for controlling the pulsed signal generation system; and a pulse clipping circuit receptive of a portion of the laser beam and connected to the pulsed signal generation system for truncating a part of the laser pulses.

1 . A super pulsed, Q-switched CO 2  laser system, comprising: 
 a plurality of mirrors defining an optical cavity;    a gaseous gain medium positioned within the optical cavity for generating laser light;    an RF source operable to energize the gaseous gain medium with a radio frequency pulse;    a Q-switch operative to switch the Q of the optical cavity; and    a system controller operable to control a relative timing of the RF source and the Q-switch in order to create at least one output pulse of laser light during an energized period of the gain medium.    
     
     
         2 . A laser system as recited in  claim 1 , wherein: 
 the system controller operates the Q-switch such that each successive output pulse of laser light during the energized period of the gain medium has increased energy relative to a previous output pulse.    
     
     
         3 . A laser system as recited in  claim 1 , wherein: 
 the RF source energizes the gaseous gain medium with a power that is greater than a maximum average radio frequency power corresponding to a stable continuous wave radio frequency power.    
     
     
         4 . A laser system as recited in  claim 3 , wherein 
 the system controller is operable to increase the power of the RF source relative to the maximum average radio frequency power by an amount that is inversely proportional to a change in the duty cycle.    
     
     
         5 . A laser system as recited in  claim 3 , wherein 
 the RF source energizes the gain medium with a radio frequency pulse having a power equal to twice the maximum average radio frequency power.    
     
     
         6 . A laser system as recited in  claim 3 , wherein 
 the RF source energizes the gain medium with a radio frequency pulse having a power equal to a integer multiple of the maximum average radio frequency power.    
     
     
         7 . A laser system as recited in  claim 1 , wherein: 
 the Q-switch is operable to switch the optical cavity between a high loss state and a low loss state, wherein during the high loss state a gain in the gain medium increases and thereafter when the Q-switch is changed to a low loss state the gain in the gain medium is depleted creating a high peak power pulse coupled out of the cavity as the pulse of laser light.    
     
     
         8 . A laser system as recited in  claim 1 , wherein: 
 the system controller includes a time delay circuit for detecting a portion of the laser pulse and providing a control signal for operating the Q-switch.    
     
     
         9 . A laser system as recited in  claim 1 , wherein: 
 the system controller triggers the Q-switch by applying a high voltage to an optical crystal of the Q-switch after a population build-up time, the population build-up time allowing a population inversion in the laser medium to rise to a predetermined level after application of the radio frequency pulse.    
     
     
         10 . A method of Q-switching a super pulsed CO 2  laser for material processing, the laser having a gaseous gain medium and a Q-switch, the method comprising the steps of: 
 energizing the gaseous gain medium with a radio frequency pulse; and    triggering the Q-switch to switch the Q of the optical cavity to create at least laser pulse during the radio frequency pulse.    
     
     
         11 . A method as recited in  claim 10 , wherein: 
 triggering the Q-switch includes operating the Q-switch to switch the optical cavity to a high loss state once the gain medium is energized in order to increase a gain in the gain medium, and switching the optical cavity to a lower loss state in order to deplete the gain in the gain medium and create a high peak power pulse that is coupled out of the cavity as the laser pulse.    
     
     
         12 . A method as recited in  claim 10 , wherein: 
 triggering the Q-switch includes applying a high voltage pulse to an optical crystal of the Q-switch.    
     
     
         13 . A method as recited in  claim 10 , wherein: 
 energizing the gaseous gain medium includes applying the radio frequency pulse with a power equal to an integer multiple of a maximum average radio frequency power.    
     
     
         14 . A method as recited in  claim 13 , further comprising: 
 increasing the power of the radio frequency pulse by an amount that is inversely proportional to the duty cycle.    
     
     
         15 . A Q-switched CO 2  laser system, comprising: 
 a plurality of mirrors defining an optical cavity;    a gain medium positioned within the optical cavity for generating laser beam radiation;    a Q-switch within the optical cavity and including an optical crystal, the Q-switch being operative to create a high loss state in the cavity when zero voltage is applied to the crystal and a low loss state when a prescribed non-zero voltage is applied to the crystal, the gain medium being depleted when the Q-switch switches to a low loss state whereby a high peak power pulse is coupled out of the cavity as a laser pulse; and    a system controller for triggering the Q-switch.    
     
     
         16 . A system as recited in  claim 15 , wherein: 
 the system controller includes a time delay circuit for detecting a portion of the laser pulse and providing a control signal for triggering the Q-switch.    
     
     
         17 . A system as recited in  claim 15 , wherein: 
 the system controller includes a pulsed signal generation system configured to receive the control signal and connected to the Q-switch to apply a high voltage pulse to the Q-switch, thereby controlling the state of optical loss within the optical cavity.    
     
     
         18 . The laser system as set forth in  claim 15 , wherein the Q-switch includes: 
 an optical crystal having an entrance surface receptive of the laser beam and an opposing laser beam exit surface;    a first optical window having an optical entrance surface receptive of the laser beam and an opposing laser beam exit surface, the exit surface of the first optical window being in physical contact with the entrance surface of the optical crystal thereby defining a first optical interface; and    an optical reflector in physical contact with the laser beam exit surface of the optical crystal thereby defining a second optical interface, the optical reflector receptive of the laser beam from the optical crystal and operative to redirect the laser beam into the optical crystal.    
     
     
         19 . The laser system as set forth in  claim 15 , wherein: 
 the optical cavity includes a multiple pass optical assembly for directing the laser beam through the Q-switch multiple times.    
     
     
         20 . A method of operating a Q-switched laser system including an optical cavity, a gain medium located in the cavity, and a Q-switch located in the cavity operative to switch the cavity between a high loss state and a low loss state, the method comprising the steps of: 
 applying zero voltage to an optical crystal of the Q-switch to create a high loss state in the optical cavity;    applying a prescribed non-zero voltage to the optical crystal of the Q-switch to create a low loss state in the optical cavity, the gain medium being depleted when the Q-switch switches to a low loss state whereby a high peak power pulse is coupled out of the cavity as a laser pulse; and    detecting the laser pulse using a time delay circuit and providing a control signal for triggering the Q-switch; and    receiving the control signal to a pulsed signal generation system connected to the Q-switch for delivering one of the zero voltage and non-zero voltage to the Q-switch to control the state of optical loss in the optical cavity.    
     
     
         21 . A method as recited in  claim 20 , further comprising: 
 comparing a level of the output of the Q-switch pulse to a predetermined level and thereafter initiating a predetermined delay time between the detection of the portion of the laser pulse and the providing of the control signal.    
     
     
         22 . A super pulsed, Q-switched CO 2  laser system comprising: 
 a resonant cavity;    a gaseous gain medium located within the resonant cavity;    an RF power supply electrically coupled to the gain medium for exciting the gain medium;    a Q-switch located within the resonant cavity; and    a controller coupled to the RF power supply and the Q-switch, said controller for triggering the RF power supply to generate a sequence of pulses of RF energy, said controller further operating to trigger the Q-switch at least once during each pulse of RF energy, said Q-switch being triggered after the RF energy has built up gain in the gain medium, with the triggering of the Q-switch resulting in the generating of a high peak power output pulse.    
     
     
         23 . A laser system as recited in  claim 22 , wherein: 
 the controller functions to trigger the Q-switch at least two times during a selected pulse of RF energy to generate a sequence of output pulses.    
     
     
         24 . A laser system as recited in  claim 23 , wherein: 
 the controller operates the Q-switch so that the energy of each of the sequence of output pulses generated within one pulse of RF energy successively increases.