Abstract:
There was the problem that the pressure of the laser medium rises from the target value by the heat when generating laser light. The laser oscillator includes a controller, laser medium flow path, resonator part, blower, pressure detecting part, laser medium supply-exhaust part, and temporary stop command part. The controller controls the resonator part to stop to generate laser light if a temporary stop is commanded, controls the blower 18 to slow the rotational speed of the blower from the first rotational speed to the second rotational speed, and controls the laser medium supply-exhaust part so that the pressure is the second target value lower than the pressure at the time when the rotational speed of the blower&#39;is the second rotational speed.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a laser oscillator which is provided with a blower. 
         [0003]    2. Description of the Related Art 
         [0004]    Known in the art is the art of controlling a pressure of a laser medium in a laser medium flow path of a laser oscillator when making operation of a laser oscillator temporarily stop (for example, Japanese Patent Publication No. 2011-228624A). 
         [0005]    In the above-mentioned such prior art, there was the problem that when ending the temporary stop of the laser oscillator to start the generation of laser light, the pressure of the laser medium ended up rising from the pressure target value when generating laser light due to the effects of heat etc. 
       SUMMARY OF THE INVENTION 
       [0006]    As an aspect of the invention, a laser oscillator comprises a controller, a laser medium flow path which forms a flow path of a laser medium, a resonator part which generate laser light by using the laser medium flowing through the laser medium flow path, and a blower which causes the laser medium to flow in the laser medium flow path. 
         [0007]    Further, the laser oscillator comprises a pressure detecting part which detects a pressure of the laser medium in the laser medium flow path, a laser medium supply-exhaust part which supplies the laser medium to the laser medium flow path and which exhausts the laser medium from the laser medium flow path, and a temporary stop command part which commands a temporary stop for generating laser light by the resonator part to the controller. 
         [0008]    Before the temporary stop command part commands the temporary stop, the controller controls the blower so as to rotate at a predetermined first rotational speed, and controls the laser medium supply-exhaust part so that the pressure is a first target value. 
         [0009]    When the temporary stop command part commands the temporary stop, the controller controls the resonator part so as to stop to generate laser light, and controls the blower so as to decrease the rotational speed of the blower to a second rotational speed lower than the first rotational speed. 
         [0010]    At this time, the controller also controls the laser medium supply-exhaust part so that the pressure is the second target value. The second target value is set to be lower than the pressure at the time when the rotational speed of the blower is the second rotational speed. 
         [0011]    The second target value P 2  may be obtained by formula P 2 =P n −P n ×ΔP a /P 1 . Here, P 1  is the first target value, P 2  is the second target value, P n  is the pressure at the time the rotational speed of the blower is the second rotational speed, and ΔP a  is the pressure increment generated when the controller restarts the operation of the stopped resonator part. The second rotational speed may be zero. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a view of a laser oscillator according to an embodiment of the invention. 
           [0013]      FIG. 2  is a block diagram of the laser oscillator shown in  FIG. 1 . 
           [0014]      FIG. 3  is a flow chart showing an example of an operation flow of the laser oscillator shown in  FIG. 1 . 
           [0015]      FIG. 4  is a graph showing the relationship between time “t” and rotational speed “R” of the blower. 
           [0016]      FIG. 5  is a graph showing the relationship between time “t” and pressure “P” of the laser medium when setting the second target value P 2  to the pressure P n  at the time when judging “YES” at step S 5  in  FIG. 3 . 
           [0017]      FIG. 6  is a graph showing the relationship between time “t” and pressure “P” of the laser medium when setting the second target value P 2  to be lower than the pressure P n  at the time when judging “YES” at step S 5  in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Below, embodiments of the invention will be explained in detail based on the drawings. First, referring to  FIG. 1  and  FIG. 2 , a laser oscillator  10  according to an embodiment of the invention will be explained. 
         [0019]    The laser oscillator  10  includes a controller  12 , a resonator part  14 , a laser medium flow path  16 , a blower  18 , a pressure detecting part  20 , a laser medium supply-exhaust part  22 , and a temporary stop command part  24 . The controller  12  directly or indirectly controls each element of the laser oscillator  10 . 
         [0020]    The resonator part  14  generates laser light in accordance with a command from the controller  12 . Specifically, the resonator part  14  includes an output mirror  26 , a rear mirror  27 , and a discharge tube  28 . The output mirror  26  and the rear mirror  27  are arranged to be opposite to each other. The discharge tube  28  is a hollow component arranged between the output mirror  26  and rear mirror  27 . 
         [0021]    The output mirror  26  is comprised of a partial reflecting mirror (i.e., a half mirror) having a 99% or more reflectance. On the other hand, the rear mirror  27  is comprised of a full reflecting mirror. The inside of the discharge tube  28  is in fluid communication with the laser medium flow path  16 . 
         [0022]    The discharge tube  28  includes discharge electrodes (not shown) arranged to be opposite to each other. These discharge electrodes are electrically connected to a laser power source  29 . The laser power source  29  applies voltage to the discharge electrodes in accordance with a command from the controller  12 . 
         [0023]    A laser medium such as carbon dioxide gas, nitrogen gas, or argon gas is supplied inside of the discharge tube  28 . If the voltage is applied to the discharge electrodes, the laser medium is excited due to the electric discharge generated between the discharge electrodes, whereby laser light is generated. The laser light generated inside the discharge tube  28  is amplified due to optical resonance generated between the output mirror  26  and the rear mirror  27 , and emitted outside via the output mirror  26  in the form of output laser light  30 . 
         [0024]    The laser medium flow path  16  is in fluid communication with the inside of the discharge tube  28 , and forms a flow path of the laser medium flowing through the inside of the discharge tube  28 . Specifically, the laser medium flow path  16  is comprised of a closed-loop flow path pipe which is connected to one end and the other end of the discharge tube  28 . The laser medium is enclosed in the laser medium flow path  16 . 
         [0025]    The blower  18  is provided at a predetermined position in the laser medium flow path  16 . Specifically, the blower  18  is comprised of e.g. a fan or blower, and includes a rotor having a plurality of vanes and a motor for rotating the rotor (both not shown). 
         [0026]    A blower inverter  32  is connected to the blower  18 . The blower inverter  32  supplies electric power to the blower  18  in accordance with a command from the controller  12 . The blower  18  rotates the rotor thereof with the electric power supplied from the blower inverter  32 . 
         [0027]    Due to this, the blower  18  causes pressure fluctuations in the laser medium in the laser medium flow path  16 , whereby causes the laser medium to flow in the direction indicated by the arrow  34  in  FIG. 1 . As a result, the laser medium is introduced into the discharge tube  28  through the laser medium flow path  16 , passes through the inside of the discharge tube  28 , and is exited from the discharge tube  28 . 
         [0028]    In order to prevent the blower  18  from being heated, a cooling device  36  is provided at the laser medium flow path  16 . The cooling device  36  includes a coolant circulating device  40  for circulating a coolant in a cooling passage  38 , and a coolant cooling device  42  for cooling the coolant. 
         [0029]    The blower  18  is cooled by the coolant flowing in the cooling passage  38 . For example, cooling water can be used as the coolant. The coolant circulating device  40  is comprised of e.g. a pump for pumping the coolant. On the other hand, the coolant cooling device  42  is comprised of e.g. a heat exchanger which exchanges heat with the air in order to cool the coolant. 
         [0030]    A first heat exchanger  44  and a second heat exchanger  46  are respectively arranged at the upstream side and downstream side of the blower  18  in the laser medium flow path. A coolant (e.g., cooling water) is supplied to each of the first heat exchanger  44  and second heat exchanger  46 . The laser medium is cooled by heat exchange with the coolant when passing through the first heat exchanger  44  and the second heat exchanger  46 , and maintained at a predetermined temperature. 
         [0031]    The pressure detecting part  20  is installed at a predetermined position in the laser medium flow path  16 . In this embodiment, the pressure detecting part  20  is installed at the upstream side of the blower  18  and the downstream side of the discharge tube  28 . 
         [0032]    The pressure detecting part  20  includes e.g. a pressure sensor capable of measuring a pressure of a fluid such as a gas. The pressure detecting part  20  measures the pressure of the laser medium in the laser medium flow path  16  in accordance with a command from the controller  12 , and sends data of the pressure to the controller  12 . 
         [0033]    The laser medium supply-exhaust part  22  supplies the laser medium to the laser medium flow path  16  and exhausts the laser medium from the laser medium flow path  16 , in accordance with a command from the controller  12 . Specifically, the laser medium supply-exhaust part  22  includes a supply flow path  48 , a supply device  50 , an exhaust flow path  52 , an exhaust valve  54 , and an exhaust device  56 . 
         [0034]    One end of the supply flow path  48  is connected to a tank (not shown) which stores the laser medium, while the other end of the supply flow path  48  is connected to the laser medium flow path  16  at the upstream side of the discharge tube  28 . The inner pressure of the tank is maintained to be higher than that of the laser medium flow path  16 . 
         [0035]    The supply device  50  is provided at the supply flow path  48 . The supply device  50  is comprised of a valve capable of opening and closing the supply flow path  48 , such as a variable valve which changes the opening area of the supply flow path  48 . The supply device  50  opens and closes the supply flow path  48  in accordance with a command from the controller  12 . If the supply device  50  opens the supply flow path  48 , the laser medium stored in the tank is supplied to the laser medium flow path  16  through the supply flow path  48 , as indicated by the arrow  58 . 
         [0036]    One end of the exhaust flow path  52  is arranged in e.g. an outside air, while the other end of the exhaust flow path  52  is connected to the laser medium flow path  16  at the upstream side of the discharge tube  28 . The exhaust valve  54  and exhaust device  56  are provided at the exhaust flow path  52 . 
         [0037]    The exhaust valve  54  is comprised of e.g. a valve capable of opening and closing the exhaust flow path  52 , such as a variable valve which changes the opening area of the exhaust flow path  52 . The exhaust device  56  is comprised of e.g. a fan which takes in the laser medium from the laser medium flow path  16 , and exhausts it from the laser medium flow path  16  through the exhaust flow path  52 , as indicated by the arrow  60 . 
         [0038]    The exhaust device  56  is electrically connected to the exhaust inverter  62 , and driven by electric power supplied through the exhaust inverter  62 . It is possible to exhaust the laser medium from the laser medium flow path  16  in response to the drive power (or rotational speed) of the exhaust device  56  and the degree of opening of the exhaust valve  54 . 
         [0039]    The temporary stop command part  24  receives from the user a command for temporarily stopping the generation of laser light in the resonator part  14 , and sends a temporary stop command to the controller  12 . As an example, the temporary stop command part  24  includes a pushbutton-type switch. In this case, the temporary stop command part  24  sends the temporary stop command to the controller  12  when the user pushes the switch. 
         [0040]    As another example, the temporary stop command part  24  may be built in an external device, such as a PC, which is connected to the controller  12 . In this case, the user operates the external device so as to input a temporary stop command. The temporary stop command part  24  sends the temporary stop command input by the user to the controller  12 . 
         [0041]    As still another example, the temporary stop command part  24  may be built in a host controller connected to the controller  12 . In this case, the temporary stop command part  24  receives a temporary stop command from the host controller, and sends it to the controller  12 . 
         [0042]    Next, referring to  FIG. 1  to  FIG. 3 , the operation of the laser oscillator  10  will be explained.  FIG. 3  is a flow chart which shows an example of the operation flow of the laser oscillator  10 . The flow shown in  FIG. 3  starts when the controller  12  receives an operating command for the laser oscillator  10  from the user or host controller and the laser oscillator  10  is transitioned to a normal operating mode. 
         [0043]    In this normal operating mode, the controller  12  controls the motor built in the blower  18  so that the rotor of the blower  18  rotates at a predetermined first rotational speed R 1 . In addition, the controller  12  controls the laser medium supply-exhaust part  22  so that the pressure P in the laser medium flow path  16  is a predetermined first target value P 1 . 
         [0044]    Specifically, the controller  12  controls the supply device  50 , exhaust valve  54 , and exhaust device  56  by a feedback control in response to the pressure value obtained from the pressure detecting part  20 , so as to control the pressure P in the laser medium flow path  16  to the first target value P 1 . 
         [0045]    Thus, in this embodiment, the pressure P at the position where the pressure detecting part  20  in the laser medium flow path  16  is installed (i.e., the position at upstream side of the blower  18 ) is controlled so as to be the first target value P 1 . 
         [0046]    Then, the controller  12  sends a command to the laser power source  29  so as to apply voltage to the discharge electrodes provided at the discharge tube  28 . Due to this, the resonator part  14  generates laser light and emits the output laser light  30  from the output mirror  26 . In this way, the laser oscillator  10  is transitioned to the normal operating mode. 
         [0047]    After starting the flow shown in FIG:  3 , at step S 1 , the controller  12  determines whether the temporary stop command from the temporary stop command part  24  has been received. When it is determined that the controller  12  has received the temporary stop command (i.e., determined “YES”), the controller  12  proceeds to step S 2 . On the other hand, when it is determined that the controller  12  has not received the temporary stop command (i.e., determined “NO”), the controller  12  proceeds to step S 14 . 
         [0048]    At step S 2 , the controller  12  controls the resonator part  14  so as to stop the operation of generating laser light. Specifically, the controller  12  controls the laser power source  29  so as to stop to apply voltage to the discharge electrodes provided at the discharge tube  28 . As a result, the operation of generating laser light in the resonator part  14  is stopped. 
         [0049]    At step S 3 , the controller  12  controls the blower  18  so as to decrease the rotational speed R of the blower  18  to a second rotational speed R 2  smaller than the first rotational speed R 1 . As an example, the second rotational speed R 2  is set to zero (i.e., R 2 =0). 
         [0050]    In this case, the controller  12  sends a command to the blower inverter  32  so as to stop the electric power to be supplied to the motor of the blower  18  from the blower inverter  32 . As a result, the rotational speed of the blower  18  gradually decreases until reaching zero. 
         [0051]    At step S 4 , the controller  12  stops the operation of supplying-exhausting the laser medium by the laser medium supply-exhaust part  22 . Specifically, the controller  12  sends commands to the supply device  50  and exhaust valve  54  so as to close the valve of the supply device  50  and exhaust valve  54 . Thus, the supply flow path  48  and exhaust flow path  52  are closed. In addition, the controller  12  sends a command to the exhaust inverter  62  so as to stop the operation of the exhaust device  56 . 
         [0052]    This step S 4  is executed in view of the following matter. Specifically, the blower  18  does not immediately decelerate to the second rotational speed R 2  after starting step S 3 . In contrast, as explained above, the blower  18  gradually decelerates over a certain period of time until becoming the second rotational speed R 2  (e.g., until the stop of rotation). 
         [0053]    During the rotational speed R of the blower  18  decreases in this way, the pressure P in the laser medium flow path  16  does not stabilize. In view of this, at this step S 4 , the controller  12  stops the operation of supplying-exhausting the laser medium until the rotational speed R of the blower  18  is stable. 
         [0054]    At step S 5 , the controller  12  determines whether the rotational speed R of the blower  18  is the second rotational speed R 2 . As an example, the controller  12  monitors the feedback value (e.g., feedback current, or load torque) from the blower inverter  32 . When the feedback value is within a range between predetermined threshold values, the controller  12  determines that the rotational speed R of the blower  18  is the second rotational speed R 2 . 
         [0055]    In this case, a correlation between the rotational speed R of the blower  18  and the feedback value from the blower inverter  32  is recorded in advance. The controller  12  compares the feedback value from the blower inverter  32  with the pre-recorded correlation, and determines whether the rotational speed R of the blower  18  is the second rotational speed R 2 . 
         [0056]    As another example, the controller  12  may determine whether a predetermined time τ 1  has elapsed after carrying out step S 3 , thereby determine whether the rotational speed R of the blower  18  is the second rotational speed R 2 . 
         [0057]    In this case, a correlation between the rotational speed R of the blower  18  and the elapsed time τ 1  is recorded in advance. The controller  12  compares the elapsed time τ 2  with the correlation, and determines whether the rotational speed R of the blower  18  is the second rotational speed R 2 . 
         [0058]    The blower inverter  32  may operate in accordance with a predetermined operating program. In this case, it is possible to obtain the correlation between the rotational speed R of the blower  18  and the elapsed time τ from the operating program. 
         [0059]    When it is determined that the rotational speed R of the blower  18  is the second rotational speed R 2  (i.e., determined “YES”), the controller  12  proceeds to step S 6 . On the other hand, when it is determined that the rotational speed R is not the second rotational speed R 2  (i.e., determined “NO”), the controller  12  returns to step S 3 . 
         [0060]    At step S 6 , the controller  12  controls the pressure P in the laser medium flow path  16  to the second target value P 2 . Specifically, the controller  12  controls the supply device  50 , exhaust valve  54 , and exhaust device  56  by a feedback control in response to the pressure value obtained from the pressure detecting part  20 , so as to control the pressure P in the laser medium flow path  16  to the second target value P 2 . 
         [0061]    In this embodiment, the second target value P 2  is set to be lower than the pressure P n  of the laser medium at the time when the rotational speed R of the blower  18  is the second rotational speed R 2  (i.e., when determined “YES” at step S 5 ). As an example, the second target value P 2  is defined as shown in the following formula 1: 
         [0000]        P   2   =P   n   −P   n   ×ΔP   a   /P   1    (formula 1)
 
         [0062]    Here, P 1  is the first target value, P n  is the pressure of the laser medium when determined “YES” at step S 5 , and ΔP a  is a pressure increment. Note that, the pressure increment ΔP a  will be explained later. 
         [0063]    At step S 7 , the controller  12  determines whether it has received a command for lifting the temporary stop command which has been received from the temporary stop command part  24  at step S 1 . For example, when the temporary stop command part  24  includes the pushbutton-type switch, the user operates the switch to release it from being pushed in. 
         [0064]    If the temporary stop command part  24  detects that the switch is released from being pushed-in, the temporary stop command part  24  sends a push-in release signal to the controller  12 . When having received the push-in release signal, the controller  12  determines that it has received a command for lifting the temporary stop command from the user (i.e., determines “YES”). 
         [0065]    When it is determined that the controller  12  has received the command for lifting the temporary stop command, the controller  12  proceeds to step S 8 . On the other hand, when it is determined that the controller  12  has not received the command for lifting the temporary stop command (i.e., determined “NO”), the controller  12  returns to step S 6 . 
         [0066]    At step S 8 , the controller  12  controls the blower  18  so as to increase the rotational speed R of the blower  18  from the second rotational speed R 2  to the first rotational speed R 1 . For example, when the rotational speed R 2  is set to zero (i.e., R 2 =0), the controller  12  sends a command to the blower inverter  32  so as to restart the supply of electric power from the blower inverter  32  to the blower  18 . As a result, the rotational speed R of the blower  18  is gradually increased until reaching the first rotational speed R 1 . 
         [0067]    At step S 9 , the controller  12  stops the supply-exhaust operation of the laser medium by the laser medium supply-exhaust part  22 , in the same way as the above-mentioned step S 4 . Specifically, the controller  12  controls the supply device  50 , exhaust valve  54 , and exhaust inverter  62  so as to stop the supply-exhaust operation of the laser medium. 
         [0068]    At step S 10 , the controller  12  determines whether the rotational speed R of the blower  18  is the first rotational speed R 1 . As an example, the controller  12  monitors the feedback value (e.g., feedback current and load torque) from the blower inverter  32 . When the feedback is within a range between predetermined threshold values, the controller  12  determines that the rotational speed R of the blower  18  is the first rotational speed R 1 . 
         [0069]    As another example, the controller  12  determines whether or not a predetermined time τ 2  has elapsed after carrying out step S 8 , thereby determines whether or not the rotational speed R of the blower  18  is the first rotational speed R 1 . 
         [0070]    In this case, a correlation between the rotational speed R of the blower  18  and the elapsed time τ 2  is recorded in advance. The controller  12  may compare the elapsed time τ 2  with the correlation, and determine whether or not the rotational speed R of the blower  18  is the first rotational speed R 1 . 
         [0071]    When it is determined that the rotational speed R of the blower  18  is the first rotational speed R 1  (i.e., determined “YES”), the controller  12  proceeds to step S 11 . On the other hand, when it is determined that the rotational speed R is not the first rotational speed R 1  (i.e., determined “NO”), the controller  12  returns to step S 8 . 
         [0072]    At step S 11 , the controller  12  controls the pressure P in the laser medium flow path  16  to the first target value P 1 . Specifically, the controller  12  controls the supply device  50 , exhaust valve  54 , and exhaust device  56  by a feedback control in response to the pressure value obtained from the pressure detecting part  20 , so as to control the pressure P in the laser medium flow path  16  to the first target value P 1 . 
         [0073]    At step S 12 , the controller  12  determines whether or not the pressure P in the laser medium flow path  16  is the first target value P 1 . Specifically, the controller  12  determines whether or not the pressure value obtained from the pressure detecting part  20  is the first target value P 1 . 
         [0074]    When it is determined that the pressure P in the laser medium flow path  16  is the first target value P 1  (i.e., determined “YES”), the controller  12  proceeds to step S 13 . On the other hand, when it is determined that the pressure P in the laser medium flow path  16  does not become the first target value P 1  (i.e., determined “NO”), the controller  12  returns to step S 11 . 
         [0075]    At step S 13 , the controller  12  operates the resonator part  14  so as to start an electric discharge therein. Specifically, the controller  12  sends a command to the laser power source  29  so as to apply voltage to the discharge electrodes provided at the discharge tube  28 . Due to this, an electric discharge occurs in the discharge tube  28 , thereby laser light is generated. 
         [0076]    At step S 14 , the controller  12  determines whether or not a command for ending the operation of the laser oscillator  10  has been received. As an example, the controller  12  determines that it has received a command for ending the operation of the laser oscillator  10  (i.e., determines “YES”), when having received from the user or a host controller an instruction indicating that all of the processes (e.g., laser processing on the workpiece) to be executed by the laser oscillator  10  have been completed. 
         [0077]    When the controller  12  determines that it has received the command for ending the operation of the laser oscillator  10 , the controller  12  ends the flow shown in  FIG. 3 . On the other hand, when the controller  12  determines that it has not received the command for ending the operation of the laser oscillator  10  (i.e., determines “NO”), it returns to step S 1 . 
         [0078]    As explained above, in this embodiment, the second target value P 2  is set to be lower than the pressure P n  of the laser medium at the time when determined “YES” at step S 5 . The technical significance of this feature will be explained with reference to  FIG. 4  to  FIG. 6 . 
         [0079]      FIG. 4  is a graph showing the relationship between the time “t” and the rotational speed R of the blower  18  during carrying out the above-mentioned steps S 1  to S 13 . Note that,  FIG. 4  shows a case where the rotational speed R 2  is set to zero. 
         [0080]      FIG. 5  is a graph showing the relationship between the time “t” and the pressure P of the laser medium while carrying out steps S 1  to S 13 , when the second target value P 2  is set to the pressure P n  at the time when determined “YES” at step S 5 . 
         [0081]      FIG. 6  is a graph showing the relationship between the time “t” and the pressure P of the laser medium while carrying out steps S 1  to S 13 , when the second target value P 2  is set to be lower than the pressure P n  at the time when determined “YES” at step S 5 . 
         [0082]    The times t 1 , t 2 , t 3 , and t 4  in  FIG. 4  to  FIG. 6  respectively correspond to the point of time when the above-mentioned step S 3  is started, the point of time when it is determined “YES” at step S 5 , the point of time when step S 8  is started, and the point of time when step S 13  is started. As shown in  FIG. 4 , after the start of step S 3 , the rotational speed R of the blower  18  gradually decreases from the time t 1 , and reaches the second rotational speed R 2 (=0) at the time t 2 . 
         [0083]    As the rotational speed R of the blower  18  decreases in this way, the pressure P at the position of the upstream side of the blower  18  in the laser medium flow path  16  gradually increases from the pressure P 1 , as shown in  FIG. 5  and  FIG. 6 . Then, the pressure P reaches the pressure P n (&gt;P 1 ) at the time t 2 . 
         [0084]    Firstly, considering a case where the pressure P is controlled to the pressure P n  during the time period from the time t 2  to the time t 3  (i.e., the time period of temporary stop) as shown in  FIG. 5 . In this case, when step S 8  is started at the time t 3  and the rotational speed R of the blower  18  is accelerated from the second rotational speed R 2 (=0), the pressure P decreases inversely proportional to the rotational speed R. 
         [0085]    Then, when step S 13  is started at the time t 4  and the discharge in the resonator part  14  is carried out, the temperature of the laser medium increases due to the discharge, as a result of which the pressure P of the laser medium increases as indicated by ΔP b  in  FIG. 5 . 
         [0086]    If the pressure increment ΔP b  occurs in this way, it is necessary to additionally control the pressure P to the first target value P 1 , thereby a time period T 1  should be taken until the pressure P is stabilized at the first target value P 1 . Further, in order to cancel the pressure increment ΔP b , it is necessary to exhaust the laser medium from the laser medium flow path  16  so as to lower the pressure P, so the laser medium should be wasted. 
         [0087]    In order to overcome the defects derived from the pressure increment ΔP b , in this embodiment, the pressure P in the laser medium flow path  16  is controlled to the second target value P 2  lower than the pressure P n , during the time period of temporary stop from the time t 2  to the time t 3 . 
         [0088]    Below, referring to  FIG. 6 , the change in the pressure P in this embodiment will be explained. Note that, in  FIG. 6 , for comparison, the graph of the pressure P according to this embodiment is indicated by the solid line  70 , while the graph shown in  FIG. 5  is indicated by the one-dot chain line  72 . 
         [0089]    During the time period of temporary stop from the time t 2  to the time t 3 , at step S 6 , the controller  12  controls the laser medium supply-exhaust part  22  so as to reduce the pressure P to the second target value P 2  from the pressure P n . 
         [0090]    Then, step S 8  is started at the time t 3 . As the rotational speed R of the blower  18  increases from the time t 3 , the pressure P decreases inversely proportionally to the rotational speed R, and reaches a pressure P 3 , which is lower than the first target value P 1  by a value ΔP a , at the time t 4 . 
         [0091]    The value ΔP a  corresponds to a pressure increment due to an increase in temperature of the laser medium derived from the electric discharge when starting step S 13  at the time t 4 . This pressure increment ΔP a  can be estimated by an experimental method, theory, or simulation, etc. Further, the second target value P 2  is defined by the pressure P n , first target value P 1 , and pressure increment ΔP a , as shown in the above-mentioned formula 1. 
         [0092]    In this embodiment, by controlling the pressure P to the second target value P 2  during the time period of temporary stop, even if the pressure P increases by the pressure increment ΔP a  after the start of electric discharge, the increased pressure P can be made to be closer to the first target value P 1 . Accordingly, it is possible to quickly control the pressure P to the second target value P 2 . 
         [0093]    Further, according to this embodiment, by making the pressure P after the start of electric discharge closer to the second target value P 2 , it is possible to make the laser power and beam mode of the laser light more accurate and stable with little change along with time. 
         [0094]    Further, according to this embodiment, the operation of the resonator part  14  is temporarily stopped so as to stop the generation of laser light, while the rotation of the blower  18  is stopped. Therefore, it is possible to reduce the power consumption in the laser oscillator  10 . 
         [0095]    Note that, in the above embodiment, the second target value P 2  is defined in accordance with formula 1, and is set to be larger than the first target value P 1 . However, the second target value P 2  may be at least a value lower than the pressure P n , and may be set to a value substantially the same as the first target value P 1 . 
         [0096]    Further, in the above embodiment, the controller  12  determines the rotational speed R of the blower  18  based on the feedback value from the blower inverter  32  or elapsed time τ at step S 5  and S 10 . 
         [0097]    However, a rotation detector capable of measuring the rotational speed of the blower  18 , such as an encoder, may be provided at the blower  18 . In this case, the controller  12  may determine the rotational speed of the blower  18  based on an output signal from the rotation detector. 
         [0098]    Above, embodiments of the invention were used to explain the invention, but the above embodiments do not limit the inventions according to the claims. Further, combinations of the features which are explained in the embodiments of the invention may also be included in the technical scope of the invention. However, not all of the combinations of these features are necessarily essential for the solution of the invention. Further, the fact that the above embodiments can be changed or improved in various ways would be clear to a person skilled in the art. 
         [0099]    Further, it should be noted that the operations, routines, steps, stages, and other processing in the device, system, program, and method in the claims, specification, and drawings, unless particularly clearly indicated by “before”, “in advance of”, etc. or the output of prior processing being used for later processing, can be realized in any order. In the flow of operations in the claims, specification, and drawings, even if explained using “first”, “next”, “then”, etc. for convenience, this does not mean the execution in this order is essential.