Abstract:
A laser oscillator comprises a discharge tube for exciting laser medium, at least a pair of mirrors disposed along an optical axis of laser light emitted by the laser gas excited inside the discharge tube, a laser gas passage connected with the discharge tube, laser gas circulation means for circulating the laser gas inside the laser gas passage, and heat control means for controlling heat generated in at least one of the mirrors and the laser gas circulation means.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to a laser oscillator provided with temperature control means. In particular, the invention relates to the laser oscillator with capability of controlling temperature of a mirror and a laser gas circulating component.  
         BACKGROUND ART  
         [0002]    [0002]FIG. 7 to FIG. 10C illustrate gas laser oscillators of the prior art. First, FIG. 7 shows an example of general structure of an axial-flow type gas laser oscillator of the prior art. In FIG. 7, discharge tube  701  made of a dielectric material such as glass is provided with electrodes  702  and  703  on the perimetric sides thereof. Electrodes  702  and  703  are connected to power supply  704 . There is discharge space  705  formed inside discharge tube  701  between electrodes  702  and  703 . Final stage mirror  706  having a surface of generally all reflection and output mirror  707  having a surface of partial reflection are securely placed to both ends of discharge space  705 , and they constitute an optical resonator. Final stage mirror  706  and output mirror  707  are simply called mirrors. Arrow  709  represents a direction to which laser gas flows. The laser gas circulates inside the axial-flow type gas laser oscillator at a pressure of approximately 100 to 200 Torr. Heat exchangers  711  and  712  operate at all the time to lower temperature rise of the laser gas. Blower unit  713  circulates the laser gas to produce a flow of approximately 100 m/sec. in discharge space  705 . Laser gas passage  710  and discharge tube  701  are connected with laser gas ports  714 .  
           [0003]    The laser gas delivered by blower unit  713  passes through laser gas passage  710 , and it is introduced into discharge tube  701  from laser gas port  714 . Electrodes  702  and  703  generate electrical discharge inside discharge space  705  under the above condition. The laser gas receives energy of the electrical discharge, and it is excited in discharge space  705 . The excited laser gas turns into a resonant mode by the optical resonator composed of final stage mirror  706  and output mirror  707 , and laser beam  708  is output from output mirror  707 . This laser beam  708  is used for laser beam machining and the like.  
           [0004]    [0004]FIG. 8 shows a general structure of an optical bench portion of the axial-flow type laser oscillator of the prior art. Output mirror  807  is held in position by output side mirror retainer  815   a,  and final stage mirror  806  is held in position by final-stage side mirror retainer  815   b.  Mirror retainers  815   a  and  815   b  are provided with cooling plates  816   a  and  816   b  respectively, and coolant  817  keeps flowing through cooling plates  816   a  and  816   b  to remove heat at all the time. Temperature of coolant  817  is approximately 18° C., and it is introduced into the laser oscillator at a flow rate of approx. 100 l/min. from cooling system  818  provided outside of the laser oscillator.  
           [0005]    By the way, there are two states of operation of the laser oscillator when differentiated in a general sense. They are a state in which electrical discharge takes place inside discharge space  805  and another state in which no electrical discharge is produced. It is general practice to produce electrical discharge when laser beam needs to be generated, and the electrical discharge is ceased when the laser beam is not needed.  
           [0006]    The laser oscillator operates blower unit  813  to run continuously to keep circulation of the laser gas regardless of using or not using the laser beam, and it generates the electrical discharge each time when it produces the laser beam. It operates blower unit  813  to circulate the laser gas at all the time because it requires several tens of seconds to restart again once blower unit  813  is turned off. On the contrary, it requires only about several tens of milliseconds to stop and to restart the electrical discharge, which is an acceptable level for practical use without a problem.  
           [0007]    Although most of the laser beam is reflected by or penetrate through final stage mirror  806  and output mirror  807 , a small portion changes to heat due to absorption in them. Final stage mirror  806  and output mirror  807  generate heat when electrical discharge takes place, but they do not heat up when there is no electrical discharge because laser oscillation does not occur.  
           [0008]    When heat is generated, they need to be cooled with coolant  817 . In the actual practice, however, final stage mirror  806  and output mirror  807  are cooled at all the time while the laser oscillator is in operation regardless of generating or not generating the electrical discharge, since the cooling operation itself is not a problem even when there is no heat.  
           [0009]    However, a problem arises when the laser oscillator is used under such an environment as high temperature and high humidity that the components being cooled collect dew condensation. While a small amount of dew condensation does not pose a problem for the regular components, it gives a serious problem for final stage mirror  806  and output mirror  807 . No dew condensation occurs on final stage mirror  806  and output mirror  807  when they heat up in the presence of electrical discharge. However, they do collect dew condensation when there is no electrical discharge to produce heat in them. The dew condensation, if formed on any of final stage mirror  806  and output mirror  807 , increases absorption factor of the laser beam in the condensed area, which can result in damage to the mirror, and reduction in laser output.  
           [0010]    [0010]FIG. 9 shows a general structure of another example of the axial-flow type gas laser oscillator of the prior art. Discharge tubes  901  made of a dielectric material such as glass, electrodes  902  and  903  provided on the perimetric sides of discharge tubes  901 , power supplies  904  connected to electrodes  902  and  903 , discharge spaces  905  inside discharge tubes  901  provided between electrodes  902  and  903 , final stage mirror  906 , output mirror  907 , laser gas passage  910 , heat exchanger  911 , another heat exchanger  912  and blower units  913  correspond respectively to discharge tubes  801  made of a dielectric material such as glass, electrodes  802  and  803  provided on the perimetric sides of discharge tubes  801 , power supply  804  connected to electrodes  802  and  803 , discharge spaces  805  inside discharge tubes  801  provided between electrodes  802  and  803 , final stage mirror  806 , output mirror  807 , laser gas passage  810 , heat exchanger  811 , another heat exchanger  812  and blower units  813  shown in FIG. 8. In addition, a direction of laser beam  908  and flow direction  909  of laser gas also correspond to a direction of laser beam  708  and direction  709  of the laser gas in FIG. 7 respectively.  
           [0011]    Blower unit  913  produces a gas flow of approximately  100  m/sec in discharge spaces  905 . Inverter  913   a  controls a driving frequency for rotation of a propelling wheel of blower unit  913 .  
           [0012]    Laser gas deteriorates over time because it is dissociated by the electrical discharge. Therefore, gas discharge mechanism  915  discharges a certain amount of the laser gas at all times from laser gas passage  910 , and gas supply mechanism  916  continues to supply fresh laser gas from the outside to replace the amount of discharged gas. A gas pressure inside the laser gas supply passage is monitored at all the time with gas pressure sensor  917 . Gas pressure sensor  917 , gas discharge mechanism  915  and gas supply mechanism  916  are connected to gas pressure controller  918 . Gas pressure controller  918  maintains the gas pressure in the laser gas passage constant at all the time by controlling gas discharge mechanism  915  and gas supply mechanism  916 .  
           [0013]    However, conventional axial-flow type gas laser oscillator of the kind described above has problems, which will be discussed hereinafter.  
           [0014]    [0014]FIG. 10A through FIG. 10C show electric current characteristics of an ordinary type motor used in any of blower units  713 ,  813  and  913 .  
           [0015]    [0015]FIG. 10A shows a relation between temperature of gas suctioned into any of blower units  713 ,  813  and  913  and electric current to the motor. Abscissa  1001  represents temperature of the gas suctioned into blower units  713 ,  813  and  913 , and ordinate  1002  represents the electric current that flows to the motor. Line  1003  shows the relation between them.  
           [0016]    As is obvious from FIG. 10A, the lower the temperature of the gas suctioned into blower units  713 ,  813  and  913 , the larger the current drawn by the motor of blower units  713 ,  813  and  913 . This is because a mass per unit volume of the gas increases with decrease in temperature of the gas, which increases both the mass and flow rate of the gas delivered per each time period from blower units  713 ,  813  and  913 , which hence increases workload of the motor.  
           [0017]    [0017]FIG. 10B shows a relation between pressure of the gas suctioned in blower units  713 ,  813  and  913  and electric current to the motor. Abscissa  1011  represents pressure of the gas suctioned into blower units  713 ,  813  and  913 , ordinate  1012  represents the electric current that flows to the motor, and line  1013  represents the relation between them.  
           [0018]    As shown in FIG. 10B, the higher the gas pressure to blower units  713 ,  813  and  913 , the larger the electric current drawn by the motor. A reason of this is that a mass per unit volume of the gas increases with increase in gas pressure, which increases both the mass and flow rate of the gas delivered per each time period from blower units  713 ,  813  and  913 , and it hence increases workload of the motor.  
           [0019]    [0019]FIG. 10C shows a relation between driving frequency and electric current to the motor of blower units  713 ,  813  and  913 . Abscissa  1021  represents the driving frequency of blower units  713 ,  813  and  913 , ordinate  1022  represents the electric current to the motor, and line  1023  represents the relation between them.  
           [0020]    As is apparent from FIG. 10C, the higher the driving frequency of blower units  713 ,  813  and  913 , the faster the rotating speed of a propelling wheel in blower units  713 ,  813  and  913 , and thereby the greater the workload to the motor, which also increases the current drawn by the motor.  
           [0021]    In general, increase in the motor current of blower units  713 ,  813  and  913  increases heat generated in the motor, which results in temperature rise of the motor. In light of the long-term reliability, it is desirable to use a blower unit with as low an amount of motor current as practically possible, since high temperature of the motor accelerates partial deterioration of a motor coil and the like if used continuously for a long period of time.  
           [0022]    Normally, the gas pressure inside laser gas passages  710 ,  810  and  910  is regulated to a predetermined pressure (e.g., approx. 20 kPa) within a range, which can provide an optimum mass and flow rate of the gas while restricting an increase in the amount of current that flows to the motor of blower units  713 ,  813  and  913 . In addition, temperature of the gas suctioned into blower units  713 ,  813  and  913  is controlled to be about 40 to 50° C. under the normal operating condition, in consideration of balancing between temperature of the laser gas heated during compression by blower units  713 ,  813  and  913  and heating by the electrical discharge, and cooling capacities of heat exchangers  711 ,  712 ,  811 ,  812 ,  911  and  912 .  
           [0023]    Problems are not anticipated so long as blower units  713 ,  813  and  913  are operated under the above condition at all the time, since the amount of current to the motor is restricted to a certain limit or below, approx. 36 amperes or less for instance. However, another problem comes up in a situation where temperature around the gas laser oscillator decreases in winter or for other reasons. In most cases, the gas laser oscillator is operated only in the daytime, while it is kept not operational during the night hours. The ambient temperature goes down to 5 to 10° C., for instance, when the laser oscillator is not operating during the nighttime in winter. Therefore, temperature of the laser gas inside the gas laser oscillator also goes down to as low a temperature as about 5 to 10° C. by the time the gas laser oscillator is started in the morning. When blower units  713 ,  813  and  913  are driven under this condition, an amount of current to the motor goes up temporarily to approx. 40 A as compared to the regular level of about 36 A, because temperature of the gas being suctioned in blower units  713 ,  813  and  913  is low.  
           [0024]    In reviewing further detail pertaining to temperature control of the gas suctioned in blower units  713 ,  813  and  913 , it is a general practice that the gas temperature is controlled for cooling only, simply with heat exchangers  711 ,  712 ,  811 ,  812 ,  911  and  912 . Any of heat exchangers  711 ,  712 ,  811 ,  812 ,  911  and  912  exchanges heat between the gas and cooling water brought in from the outside. Since temperature of the cooling water introduced from the outside is generally in the neighborhood of 15 to 20° C., it can cool the gas having temperature above 15 to 20° C. However, it cannot heat the gas if the temperature is about 5 to 10° C. In the normal operating condition, the gas temperature eventually settles to an expected level of approx. 40 to 50° C. within 10 to 20 minutes even if the gas laser oscillator is started in the low temperature condition with its gas temperature at around 5 to 10° C., because the gas is heated by the heat generated by electrical discharge and compression of the gas by blower units  713 ,  813  and  913 , and the temperature of the motor of blower units  713 ,  813  and  913  decreases into a normal state without problem. However, the blower unit is operated with the motor consuming a larger current than the anticipated level for a period of about 10 to 20 minutes immediately after the start-up. When the gas laser oscillator is operated everyday in this manner, partial deterioration of motor coils and the like advances in blower units  713 ,  813  and  913 , which consequently leads to a loss of reliability in the long-term use.  
         DISCLOSURE OF THE INVENTION  
         [0025]    A laser oscillator comprises a discharge tube for exciting laser medium, at least a pair of mirrors disposed along an optical axis of laser light emitted by the laser medium excited in the discharge tube, a laser gas passage connected with the discharge tube, laser gas circulation means for circulating the laser gas in the laser gas passage and heat control means for responsively controlling heat generated in at least one of the mirrors and the laser gas circulation means. 
       
    
    
     BRIEF DESCRIPTON OF THE DRAWINGS  
       [0026]    [0026]FIG. 1 is a structural diagram of a laser oscillator according to a first exemplary embodiment of the present invention.  
         [0027]    [0027]FIG. 2 is a structural diagram of a laser oscillator according to a second exemplary embodiment of the invention.  
         [0028]    [0028]FIG. 3 is a structural diagram of a laser oscillator according to a third exemplary embodiment of the invention.  
         [0029]    [0029]FIG. 4 is a structural diagram of a laser oscillator according to a fourth exemplary embodiment of the invention.  
         [0030]    [0030]FIG. 5 is a sequence chart for controlling a gas pressure according to temperature of gas being suctioned into a blower unit of the laser oscillator shown in FIG. 4.  
         [0031]    [0031]FIG. 6 is a sequence chart for responsively controlling a driving frequency of a blower unit according to temperature of gas being suctioned into the blower unit in a laser oscillator of a fifth exemplary embodiment of the invention.  
         [0032]    [0032]FIG. 7 is a general structural diagram of a gas laser oscillator of the prior art;  
         [0033]    [0033]FIG. 8 is a general structural diagram of an optical bench portion of the laser oscillator of the prior art.  
         [0034]    [0034]FIG. 9 is a general structural diagram of an axial-flow type gas laser oscillator of the prior art.  
         [0035]    [0035]FIG. 10A is a graphical chart showing an electric current characteristic of a motor in a commonly used blower unit.  
         [0036]    [0036]FIG. 10B is a graphical chart showing other electric current characteristic of the motor in the commonly used blower unit.  
         [0037]    [0037]FIG. 10C is a graphical chart showing still other electric current characteristic of the motor in the commonly used blower unit. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
     First Exemplary Embodiment  
       [0038]    [0038]FIG. 1 shows a structure of a laser oscillator according to the first exemplary embodiment of this invention.  
         [0039]    In FIG. 1, discharge tubes  101  made of dielectric material such as glass are provided with electrodes  102  and  103  on the perimetric sides thereof Electrodes  102  and  103  are connected to power supplies  104 . There are discharge spaces  105  formed inside discharge tubes  101  between electrodes  102  and  103 . Final stage mirror  106  having a surface of generally all reflection and output mirror  107  having a surface of partial reflection are securely placed to two ends of discharge spaces  705 , and they constitute an optical resonator. Laser beam  108  is output from output mirror  107 . Laser gas circulates inside the gas laser oscillator. Heat exchangers  111  and  112  responsively function to control temperature of the laser gas. Blower unit  113  circulates the laser gas. Laser gas passage  110  and discharge tubes  101  are connected with laser gas ports  114 .  
         [0040]    The laser gas delivered by blower unit  113  passes through laser gas passage  110 , and it is introduced into one of discharge tubes  101  from laser gas port  114 . Electrodes  102  and  103  generate electrical discharge in discharge spaces  105  under the above condition. The laser gas receives energy of the electrical discharge, and it is excited inside discharge space  705 . The excited laser gas turns into a resonant mode by the optical resonator composed of final stage mirror  106  and output mirror  107 , and laser beam  108  is output from output mirror  107 . This laser beam  108  is used for laser beam machining and the like.  
         [0041]    Output mirror  107  is held in position by output side mirror retainer  115   a,  and final stage mirror  106  is held in position by final stage side mirror retainer  115   b.  Output mirror  107  and final stage mirror  106  generate heat therein due to reflection and penetration of the laser beam. Output side mirror retainer  115   a  and final stage side mirror retainer  115   b  are provided with cooling plates  116   a  and  116   b,  and coolant  117  flows through cooling plates  116   a  and  116   b  to responsively remove the heat.  
         [0042]    Coolant  117  is introduced into the laser oscillator at a temperature of approx. 18° C. and a flow rate of approx. 100 l/min from cooling system  118  provided outside of the laser oscillator. Coolant  117  exchanges heat with a number of components in the laser oscillator, including cooling plates  116   a  and  116   b,  heat exchangers  111  and  112 , blower unit  113 , and so on, and it is returned again into cooling system  118  after the temperature goes up to approx. 20° C.  
         [0043]    Coolant  117  is cooled down to about 18° C. in cooling system  118 , and introduced again into the laser oscillator. Coolant passage  119  leading to cooling plates  116   a  and  116   b  is provided with solenoid valve  120 , of which operation is controlled by controller  121 .  
         [0044]    The laser oscillator operates in a manner as described hereinafter. When the laser oscillator is activated, blower unit  113  starts operating, and the laser gas begins circulating. Electrical discharge can be initiated in this state to produce laser oscillation. While the coolant is introduced from cooling system  118  into circulation through the laser oscillator in this state, final stage mirror  106  and output mirror  107  are not cooled at this stage because solenoid valve  120  provided in coolant passage  119  to cooling plates  116   a  and  116   b  remains closed.  
         [0045]    Electrical discharge is now generated to produce a laser beam. Generation of the electrical discharge is controlled by controller  121 . Controller  121  opens solenoid valve  120  at the same time with generation of the electrical discharge, to let coolant  117  start flowing toward cooling plates  116   a  and  116   b.  When the electrical discharge is suspended, controller  121  closes solenoid valve  120  to stop the flow of coolant  117  to cooling plates  116   a  and  116   b.  However, coolant  17  continues flowing to the components other than cooling plates  116   a  and  116   b  regardless of generating or not generating the electrical discharge.  
         [0046]    With the structure as discussed above, final stage mirror  106  and output mirror  107  are cooled only when the electrical discharge takes place, or the laser is oscillating. They are thus cooled responsively and the temperature controlled responsively only when the cooling is needed. When the mirrors are cooled in an absence of electrical discharge under the environment of high temperature and high humidity, the mirrors produce dew condensation, which can be a cause of problems such as decrease in laser output due to damage to the mirrors. Such dew condensation does not occur in the structure of this exemplary embodiment.  
         [0047]    It may be considered to raise temperature of the coolant as an alternative measures to prevent dew condensation. As a conceivable example, the temperature of the coolant at the normal level of 18° C. may be raised to 25° C. However, the raise in temperature of the coolant results in a lowering of efficiency of heat exchangers  111  and  112 , and consequent increase in the laser gas temperature. On the principle of laser oscillation, increase in the laser gas temperature lowers efficiency of the laser oscillation and laser output. It is therefore not appropriate to raise the temperature of the coolant.  
         [0048]    There is another method, as has been tried in the past, in which a heater or the like is used to regulate temperature of only the coolant that flows to the mirrors in a manner to maintain it at a temperature above a dew point of the surrounding air. However, such a structure requires sensors for detecting the temperature and humidity as well as a temperature regulator, which increases a number of components and makes the structure complex, and it is therefore not considered practical. On the contrary, this exemplary embodiment can be considered superior both in cost and in reliability, since it is quite simple in its structure and operating principle without requiring such components as a sensor and new components.  
       Second Exemplary Embodiment  
       [0049]    [0049]FIG. 2 shows a structure of a laser oscillator according to the second exemplary embodiment of this invention.  
         [0050]    In FIG. 2, power supplies  204 , final stage mirror  206 , output mirror  207 , laser gas passage  210 , heat exchangers  211  and  212 , blower unit  213 , laser gas ports  214 , output side mirror retainer  215   a,  final stage side mirror retainer  215   b,  cooling plates  216   a  and  216   b,  coolant  217 , cooling system  218 , coolant passage  219 , solenoid valve  220  and controller  221  correspond analogously to power supplies  104 , final stage mirror  106 , output mirror  107 , laser gas passage  110 , heat exchangers  111  and  112 , blower unit  113 , laser gas ports  114 , output side mirror retainer  115   a,  final stage side mirror retainer  115   b,  cooling plates  116   a  and  116   b,  coolant  117 , cooling system  118 , coolant passage  119 , solenoid valve  120  and controller  121  shown in FIG. 1, respectively. Details of the individual components are therefore skipped.  
         [0051]    This second exemplary embodiment differs from the first exemplary embodiment in a respect that heat in the mirrors can be cooled sufficiently by natural heat dissipation to the surrounding air when the laser oscillator is used by generating electrical discharge with a reduced power, that is, an output power of the laser is reduced to a low level, since the heat generated in the mirrors is small. It is not even necessary in such a case to circulate the coolant for cooling down. It is more important to avoid the possibility of dew condensation without circulating the coolant.  
         [0052]    In the structure of FIG. 2, therefore, temperature detection means  222  such as a thermistor disposed to output side mirror retainer  215   a  monitors a temperature, and flow control means lets coolant  217  flow only when the temperature reaches a predetermined value, to control cooling and hence temperature of output side mirror retainer  215   a  and final stage side mirror retainer  215   b  responsively. Although the second exemplary embodiment shown in FIG. 2 requires the temperature detection means as compared to the first exemplary embodiment, it is still superior in both cost and reliability, since it does not require a temperature regulator of the type discussed in the example of the prior art.  
       Third Exemplary Embodiment  
       [0053]    [0053]FIG. 3 shows a structure of a laser oscillator according to the third exemplary embodiment of this invention.  
         [0054]    In FIG. 3, power supplies  304 , final stage mirror  306 , output mirror  307 , laser gas passage  310 , heat exchangers  311  and  312 , blower unit  313 , laser gas ports  314 , output side mirror retainer  315   a,  final stage side mirror retainer  315   b,  cooling plates  316   a  and  316   b,  coolant  317 , cooling system  318 , coolant passage  319 , solenoid valve  320  and controller  321  correspond analogously to power supplies  104 , final stage mirror  106 , output mirror  107 , laser gas passage  110 , heat exchangers  111  and  112 , blower unit  113 , laser gas ports  114 , output side mirror retainer  115   a,  final stage side mirror retainer  115   b,  cooling plates  116   a  and  116   b,  coolant  117 , cooling system  118 , coolant passage  119 , solenoid valve  120  and controller  121  shown in FIG. 1, respectively. Details of the individual components are therefore skipped.  
         [0055]    This third exemplary embodiment differs from the first and the second exemplary embodiments in a respect that humidity detection means  323  are used to monitor dew points of the air around output side mirror retainer  315   a  and final stage side mirror retainer  315   b,  and temperature control is performed in a responsive manner by reducing a flow rate of coolant  317  and the like if there is a risk of dew condensation. In the structure of FIG. 3, although humidity detection means  323  such as a humidity sensor is needed, it is still superior in both cost and reliability, since it does not require a temperature regulator of the type discussed in the example of the prior art.  
         [0056]    Any of the first through the third exemplary embodiments discussed above provides the laser oscillator which is superior in respects of the cost and reliability, capable of preventing dew condensation on the mirrors with their simple structures, and produces steady laser output at all the time.  
       Fourth Exemplary Embodiment  
       [0057]    [0057]FIG. 4 is a structural diagram of a laser oscillator according to the fourth exemplary embodiment of this invention.  
         [0058]    In FIG. 4, discharge tubes  401 , electrodes  402  and  403 , power supplies  404 , discharge spaces  405 , final stage mirror  406 , output mirror  407 , laser beam  408 , laser gas passage  410 , heat exchangers  411  and  412 , blower unit  413  and laser gas ports  414  are analogous to discharge tubes  101 , electrodes  102  and  103 , power supplies  104 , discharge spaces  105 , final stage mirror  106 , output mirror  107 , laser beam  108 , laser gas passage  110 , heat exchangers  111  and  112 , blower unit  113  and laser gas ports  114  shown in FIG. 1 respectively. Details of the individual components are therefore skipped.  
         [0059]    Inverter  413   a  controls a driving frequency for rotation of a propelling wheel of blower unit  413 . Arrow  409  represents a direction of the laser gas delivered by blower unit  413 .  
         [0060]    Laser gas deteriorates over time because it is dissociated by electrical discharge. Therefore, gas discharge mechanism  415  adaptively discharges a certain amount of the laser gas from laser gas passage  410 , and gas supply mechanism  416  adaptively supplies fresh laser gas from the outside to replace the amount of discharged gas. A gas pressure inside the laser gas supply passage is monitored at all the time with gas pressure sensor  417 . Gas pressure sensor  417 , gas discharge mechanism  415  and gas supply mechanism  416  are connected to gas pressure controller  418 . Gas pressure controller  418  maintains the gas pressure in the laser gas passage  410  constant at all the time by controlling gas discharge mechanism  415  and gas supply mechanism  416  in a responsive manner.  
         [0061]    Blower unit  413  is provided with temperature sensor  419  at a suction side thereof to measure a temperature of the gas to be suctioned, and this temperature sensor  419  is connected to gas pressure controller  418 .  
         [0062]    Since a pressure and temperature of the laser gas are maintained in this manner, heat generated during operation of the blower unit for delivery of the laser gas is controlled responsively, to achieve responsive temperature control.  
         [0063]    [0063]FIG. 5 is a flowchart showing an operation sequence of the structure shown in FIG. 4.  
         [0064]    First, a temperature of the gas suctioned into blower unit  413  is measured in the step  501 , and the measured temperature is judged in the step  502  as to whether it is above or below a predetermined temperature (e.g., 40° C.). Temperature sensor  419  keeps monitoring the temperature of the gas suctioned in blower unit  413  at all the time from the start-up of the laser oscillator. Assume that the gas laser oscillator is started in a winter morning, for example. Temperature of the laser gas inside the gas laser oscillator may be as low as about 5 to 10° C. when the gas laser oscillator is started, and temperature sensor  419  detects this temperature.  
         [0065]    When the temperature of the gas suctioned into blower unit  413  is judged to be equal to or above the predetermined temperature (e.g., 40° C.) in the step  502 , the process goes on to the step  503 . In the step  503 , the gas laser oscillator is operated with a pressure of the gas suctioned into blower unit  413  at the regular value (e.g., 20 kPa).  
         [0066]    If the temperature of the gas suctioned into blower unit  413  is judged below the predetermined temperature (e.g., 40° C.) in the step  502 , the process goes on to the step  504 . In the step  504 , the pressure of the gas suctioned into blower unit  413  is regulated to a low level (e.g., 18.7 kPa). Gas pressure controller  418  receives temperature information from temperature sensor  419 , and lowers the regulating value of the gas pressure automatically by approx. 1.3 kPa. In other words, the pressure of the gas suctioned into blower unit  413  is normally in the neighborhood of 20 kPa, and this value is lowered to about 18.7 kPa. Temperature of the suctioned gas has fallen to 5 to 10° C. here, although it normally is 40 to 50° C. If blower unit  413  is driven under this condition, the current drawn by the motor increases undoubtedly, because the gas temperature is so low. For instance, although the normal electric current is about 36 A, it increases to approx. 40 A due to the low temperature of the suctioned gas. Since the pressure of the suctioned gas is lowered to 18.7 kPa from the normal value of 20 kPa, in the embodied structure of FIG. 4, the load of the motor is balanced, and the motor current is maintained consequently to the normal value of approx. 36 A.  
         [0067]    The process is then goes back again to the step  501  from the step  503  or the step  504 , and temperature of the gas suctioned into blower unit  413  is measured again. Operation of the gas laser oscillator is continued even when the process goes on through the step  504 , and the process eventually advances to the step  503  when the temperature of the gas suctioned into blower unit  413  rises gradually and exceeds the predetermined value (e.g., 40° C.). The gas pressure inside laser gas passage  410  is then brought back to the normal value (e.g., 20 kPa) in the step  503 .  
         [0068]    The laser gas oscillator operated in this manner can maintain the electric current to the motor below a certain value at all the time even under such a condition as an early start-up in the morning of winter day which is likely to increase the current to the motor of blower unit  413 . The load of the motor is regulated in this manner to responsively control the temperature affected by heat generated therein. As a result, this invention reduces deterioration of the motor components attributable to temperature rise of the motor, thereby providing the laser gas oscillator with high reliability for a prolonged time.  
         [0069]    A matter of concern here is that a laser output decreases when gas pressure in laser gas passage  410  is reduced. A reduction in gas pressure inside of laser gas passage  410  means reduction in gas pressure in discharge space  405 , which leads to decrease in both mass and flow rate of the laser gas that circulates through discharge space  405 . Since an output of laser beam  408  produced by the laser oscillator changes in proportion to the mass and flow rate of the laser gas flowing through discharge space  405 , the laser output decreases as the gas pressure decrease. However, the laser oscillator has such a characteristic that an efficiency of laser oscillation increases, and hence the laser output increases, when temperature of the laser gas decreases, according to the principle of laser oscillation. That is, the laser output has a tendency of decreasing if the gas pressure is lowered. On the other hand, since the laser oscillation efficiency increases due to decrease in temperature of the laser gas, they consequently cancel with each other, to provide a characteristic of the laser output that hardly varies in power from that of the normal condition.  
       Fifth Exemplary Embodiment  
       [0070]    [0070]FIG. 6 is a sequence chart representing the fifth exemplary embodiment of this invention, wherein a laser oscillator responsively controls a driving frequency of blower unit  413  according to temperature of gas suctioned into blower unit  413 .  
         [0071]    Because the step  601  and step  602  are analogous to the corresponding steps  501  and  502  of FIG. 5 respectively, individual explanation is not repeated here in detail.  
         [0072]    When temperature of the gas suctioned into blower unit  413  is judged equal to or above a predetermined temperature (e.g., 40° C.) in the step  602 , the process goes on to the step  603 . In the step  603 , blower unit  413  is operated with a normal driving frequency (e.g., 700 Hz).  
         [0073]    If the temperature of the gas suctioned into blower unit  413  is judged below the predetermined temperature (e.g., 40° C.) in the step  602 , the process goes on to the step  604 . In the step  604 , the driving frequency of blower unit  413  is lowered, and operated with a frequency of 650 Hz, for instance. Gas pressure controller  418  receives temperature information from temperature sensor  419 , and lowers the driving frequency of blower unit  413  automatically by about 50 Hz. In other words, the driving frequency of blower unit  413  is normally 700 Hz, but this figure is lowered to approx. 650 Hz. Assuming that the laser oscillator is started early in the morning of a winter day, temperature of the suctioned gas has fallen to 5 to 10° C., although it should be normally 40 to 50° C. If blower unit  413  is driven under this condition, the current consumed by the motor increases because the gas temperature is so low. For instance, although the normal electric current is about 36 A, it increases to approx. 40 A because of the low temperature of the suctioned gas. Since the driving frequency of blower unit  413  is lowered to 650 Hz from the normal frequency of 700 Hz, in the structure of FIG. 4, the load of the motor is balanced, and the motor current is maintained consequently to the normal value of approx. 36 A.  
         [0074]    The process is then goes back again to the step  601  from the step  603  or the step  604 , and temperature of the gas suctioned into blower unit  413  is measured. Operation of the gas laser oscillator is continued even when the process goes on through the step  604 , and the process eventually advances to the step  603  when the temperature of the gas suctioned into blower unit  413  rises gradually and exceeds the predetermined value (e.g., 40° C.). The driving frequency of blower unit  413  is then brought back to the normal frequency (e.g., 700 Hz).  
         [0075]    The operation shown in FIG. 6 can thus maintain electric current to the motor below a certain value at all the time even under such a condition as an early start-up in the morning of winter day that is likely to increase the current to the motor of blower unit. The load of the motor is regulated in this manner to responsively control the temperature affected by heat generated therein. As a result, this invention reduces deterioration of the motor components attributable to temperature rise of the motor, thereby providing the laser gas oscillator with high reliability for a long period of time.  
         [0076]    A matter of concern here is that a laser output decreases when the driving frequency of blower unit  413  is lowered. A low driving frequency of blower unit  413  means decrease in gas volume delivered by blower unit  413 , which leads to decrease in both mass and flow rate of the laser gas that flows through discharge space  405 . Since an output of laser beam  408  produced by the laser oscillator varies in proportion to the mass and flow rate of the laser gas flowing through discharge space  405 , the laser output decreases as the driving frequency of blower unit  413  is lowered. However, the laser oscillator has such a characteristic that an efficiency of laser oscillation increases, and hence the laser output increases, when temperature of the laser gas decreases, according to the principle of laser oscillation. That is, the laser output has a tendency of decreasing if the driving frequency of blower unit  413  is lowered. On the other hand, the laser oscillation efficiency increases due to decrease in temperature of the laser gas. In consequence, they cancel with each other, so as to provide a characteristic of the laser output that hardly varies in power from that of the normal condition.  
         [0077]    As described explicitly, this fifth exemplary embodiment can provide the gas laser oscillator with high reliability, which can be used steadily for a long period of time.  
       Industrial Applicability  
       [0078]    A gas laser oscillator of this invention has capability of controlling heat and temperature responsively by overcoming a variety of troubles attributable to temperature changes, and providing high reliability for long term of steady operation.