Laser oscillation apparatus

A laser oscillation apparatus includes: a laser cavity unit for generating laser light by being provided a voltage and optically amplifying the generated light by means of a pair of mirrors; and a DC power source for supplying the voltage required for generating the laser light to a pair of discharge electrodes of the cavity unit. Each of a cathode and an anode of the DC power source is grounded via a grounding resistor.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a laser oscillation apparatus for 
generating laser light by oscillation and optical amplification by means 
of a pair of optical amplification mirrors. In particular, the present 
invention relates to a laser oscillation apparatus improved with respect 
to at least one of a high voltage power source circuit for generating a 
discharge, resulting in an enhanced freedom in design, a control unit for 
a cooling mechanism which allows a stable laser output to be achieved in a 
short period of time after start-up in a cold atmosphere, and a laser 
light absorption unit for receiving and absorbing laser light and 
exchanging heat with a coolant. 
2. Description of the Related Art 
FIG. 14 is a diagram schematically illustrating a configuration around a 
laser cavity unit 1100 in a conventional laser oscillation apparatus. 
In the laser oscillation apparatus shown in FIG. 14, a laser cavity unit 
1100 includes a laser tube 106, a partially-transmissive reflection mirror 
104, and a total reflection mirror 105. A high voltage is applied from a 
DC high voltage power source 102 via discharge electrodes 103a and 103b to 
a gaseous laser medium 101 contained in the laser tube 106 so as to 
generate a glow discharge. A blower 107 ant a laser medium cooler 108 are 
serially connected to the laser tube 106 via laser medium conduits 109a 
and 109b. The laser medium 101 is forcibly circulated by the blower 107. 
Particularly, the gaseous laser medium 101, heated by the glow discharge, 
passes through the laser medium conduit 109b, is cooled by the laser 
medium cooler 108, passes through the blower 107 and the laser medium 
conduit 109a, and then is sent back to a glow discharge space in the laser 
tube 106. 
The total reflection mirror 105 is provided at one end of the laser tube 
106, and the partially-transmissive reflection mirror 104 is provided at 
the other end thereof. Laser light generated by a discharge passes through 
the partially-transmissive reflection mirror 104 and exits the laser tube 
106. 
In the laser oscillation apparatus shown in FIG. 14, the DC high voltage 
power source 102 is directly connected to the discharge electrodes 103a 
and 103b via feeder cables 111a and 111b. Furthermore, a cathode of the DC 
high voltage power source 102, which is connected to the discharge 
electrode 103b, is grounded by the grounding conductor 110. 
In the conventional laser oscillation apparatus having such a configuration 
as described above, during operation for producing laser light, a DC high 
voltage E (V), which corresponds to the supplied voltage level of the DC 
high voltage power source 102 (with the ground level being the reference 
level), appears at the discharge electrode 103a. (In this application, 
voltage that is expressed using the ground level as the reference level is 
deterred to as "voltage to ground".) In such a case, the feeder cable 111a 
must have a sufficient anti-breakdown property so that it can withstand 
the DC high voltage E (V). The need for a feeder cable with such a high 
anti-breakdown property disadvantageously increases cost for conventional 
laser oscillation apparatuses. 
Moreover, since the DC high voltage E; (V) appears at the discharges 
electrode 103a, it is necessary to provide components constituting the 
laser oscillation apparatus around the discharge electrode 103a (e.g., a 
casing body) so as to be disposed with a sufficient distance therebetween 
depending on the voltage level of E(V) in order to prevent a discharge 
from being generated between the discharge electrode 103a and the 
surrounding other components. As a result, design of a laser oscillation 
apparatus is limited, and further, miniaturization of a laser oscillation 
apparatus becomes difficult. 
Next, a cooling mechanism for optical components included in a conventional 
laser oscillation apparatus will be described with reference to FIGS. 15 
and 16. 
FIG. 15 is a diagram schematically illustrating an exemplary configuration 
of a cooling mechanism which can be used by being connected to the laser 
cavity unit 1100 of the laser oscillation apparatus described above. 
Elements in FIG. 15 which are also shown in FIG. 14 are denoted by the 
same reference numerals and will not be further described. 
In the configuration shown in FIG. 15, optical components such as the 
partially-transmissive reflection mirror 104 and the total reflection 
mirror 105 are held by a holder 207. During operation of the laser 
oscillation apparatus, some thermal energy from a discharge may be applied 
to the bolder 207, and thus, the holder 207 may be deformed by thermal 
expansion, resulting in deteriorated positional parallel relationship 
between the partially-transmissive reflection mirror 104 and the total 
reflection mirror 105. Similarly, when the temperature of the holder 207 
is considerably decreased, the partially-transmissive reflection mirror 
104 and the total reflection mirror 105 may be shifted with respect to 
each other from the predetermined positional parallel relationship due to 
contraction of the holder 207 induced by low temperature. This shift also 
leads to the deteriorated positional parallel relationship. If the 
partially-transmissive reflection mirror 104 and the total reflection 
mirror 105 are not disposed in parallel to each other, sufficient light 
amplification therebetween is not provided, in which case a stable laser 
light oscillation may not easily be achieved. 
In order to overcome such a problem, oil, for example, is circulated within 
the holder 207 by means of a pump 208 to cool the holder 207. In 
particular, such a cooling mechanism using oil includes a tank 211, the 
pump 208 for supplying the oil into the holder 207, a cooler 210 for 
cooling the oil, and a thermistor 209 for detecting the oil temperature. 
Moreover, a control unit 212 is provided for controlling the operation of 
the cooler 210 based on the oil temperature detected by the thermistor 
209. After the operation of the laser oscillation apparatus is initiated, 
the oil is cooled by controlling the operation of the cooler 210 according 
to a control loop as shown in a dashed line in FIG. 15. 
FIG. 16 shows diagrams provided for illustrating problems associated with 
such a cooling mechanism for optical components in the conventional laser 
oscillation apparatus. 
Particularly, the portion (a) of FIG. 16 schematically illustrates the 
change in the temperature of the oil in the cooling mechanism from 
shutdown to some time after subsequent start-up. The temperature indicated 
therein can be considered as the temperature of the holder 207, which is 
cooled by the oil. Moreover, the portion (d) of FIG. 16 is a diagram 
schematically illustrating the change in the laser output of the laser 
oscillation apparatus after start-up, and the portions (b) and (c) of FIG. 
16 illustrate the operation timing of the pump 208 and the cooler 210, 
respectively, after start-up. 
When the conventional laser oscillation apparatus is standing in a cold 
atmosphere, for example, in winter, the temperature of the holder 207 
becomes considerably lower than the normal operating point temperature of 
the laser oscillation apparatus. Accordingly, the oil temperature becomes 
also low as shown in the portion (a) of FIG. 16. Due to such a 
considerably low temperature, a great amount of time may be required for 
warm up of the holder 207 to an operating temperature, which is shown as 
the oil temperature change in the portion (a) of FIG. 16, after the 
oscillation apparatus has started its operation at the time shown in the 
portion (d) of FIG. 16 and the pump 208 has accordingly started its 
operation at the time shown in the portion (b) of FIG. 16. Thus, the 
positional parallel relationship between the partially-transmissive 
reflection mirror 104 and the total reflection mirror 105 is shifted for a 
while after start-up, during which a stable light amplification (laser 
oscillation) can not be achieved, resulting in a lowered laser output. As 
a result, as shown in the portion (4) of FIG. 16, a great amount of time 
is required until the laser output becomes stable again at the normal 
operating level. 
Once the laser output becomes stable at the normal operating level, the 
control unit 212 acts to cause the cooler 210 to operate at an appropriate 
time as shown in the portion (c) of FIG. 16. This allows for a stable 
operation of the laser oscillation apparatus. 
Next, a laser light absorption unit included in the conventional laser 
oscillation apparatus will be described with reference to FIGS. 17 to 19. 
The laser light absorption unit is provided on the optical path of the 
generated laser light. Normally, the laser light absorption unit is 
located so as to block the optical path of the laser light, thereby 
preventing the laser light generated in the laser cavity unit from exiting 
the laser oscillation apparatus at any time other than a desired time, 
thus functioning as a safety apparatus. Then, once it is confirmed that 
the laser light may exit (e.g., in a manufacturing site, when it is 
confirmed that the laser light has been aimed to an object to be processed 
and that there is no obstruction in the intervening path), the laser light 
absorption unit is shifted aside the optical path of the laser light so 
that the laser light exits the laser oscillation apparatus. 
FIG. 17 is a cross-sectional view schematically illustrating a 
configuration of a conventional laser light absorption unit 1310. 
In the laser light absorption unit 1310, a conically-shaped inner cylinder 
301 is provided at an opening of an outer cylinder 304. The 
conically-shaped inner cylinder 301 includes a light-receiving surface 302 
and a heat-exchanging surface 303 respectively provided on the front 
surface and the rear surface of the inner cylinder 301. A space existing 
between the conically-shaped inner cylinder 301 and the outer cylinder 304 
provides a path 305 for a coolant 307. The conically-shaped inner cylinder 
301 is formed of a metallic material having a high thermal conductivity, 
e.g., copper or aluminum. 
The light-receiving surface 302 is formed in a conical shape with an angle 
of about 30.degree. or less with respect to the incident axis of the laser 
light 306 so that the incident laser light 306 is not directed externally 
after being reflected. Moreover, the light-receiving surface 302 is coated 
with a material having a high absorptivity for the wavelength of the laser 
light 306 to be oscillated. 
The laser light 306 incident upon the light-receiving surface 302 is 
quickly absorbed, and the heat produced by the Incident laser light 306 is 
transferred by conduction to the heat-exchanging surface 303. The coolant 
307 introduced into the path 305 through an inlet 308 exchanges heat at 
the heat-exchanging surface 303 and is drained through an outlet 309. 
FIGS. 18 and 19 are cross-sectional views schematically illustrating 
configurations of other conventional light absorption units 1320 and 1330, 
respectively. Elements in FIGS. 18 and 19 which are s also shown in FIG. 
17 are denoted by the same reference numerals and will not be further 
described. 
In the laser light absorption unit 1310 shown in FIG. 17, the 
light-receiving surface 302 is formed in a single conical shape. This 
necessarily causes the light-receiving surface 302 to be large with 
respect to the incident axis of the laser light 306. On the other hand, in 
each of the light absorption units 1320 and 1330 shown in FIGS. 18 and 19, 
respectively, the light-receiving surface 302 is shaped so as to form a 
plurality of conical shapes, thus reducing the overall size. Also in these 
cases, the light-receiving surface 302 forms an angle of about 30.degree. 
or less with respect to the incident axis of the laser light 306. 
Generally, laser light has the greatest energy concentration near the 
center thereof, while the energy concentration becomes smaller toward the 
peripheral portion of the laser light. Therefore, the light-receiving 
surface 302 in each of the laser light absorption units 1310 to 1330 must 
receive and absorb the greatest energy at the center thereof. The energy 
absorbed at the light-receiving surface 302 is transferred to the 
heat-exchanging surface 303 on the rear surface while substantially 
maintaining the temperature distribution thereof. Thus, the temperature on 
the heat-exchanging surface 303 also becomes highest at the center 
thereof, while the temperature becomes less toward the peripheral portion 
thereof. Accordingly, there are large differences in temperature along the 
radius direction on the light-receiving surface 302 and the 
heat-exchanging surface 303. 
However, in the conventional laser light absorption units 1310 to 1330, the 
coolant 307 flows irrespective of the temperature distribution in the 
heat-exchanging surface 303. Therefore, the amount of the coolant 307 to 
be supplied in the vicinity of the center of the heat-exchanging surface 
303, where the temperature is high, is not sufficient (i.e., the flow of 
the coolant 307 is insufficient). On the other hand, the amount of the 
coolant 307 to be supplied in the peripheral portion of the 
heat-exchanging surface 303, where the temperature is low, tends to be 
excessive. As a result, the heat exchange as a whole becomes non-uniform. 
Therefore, the temperature increases due to the insufficient cooling 
capacity near the center of the heat-exchanging surface 303, i.e., near 
the center of the light-receiving surface 302. This may result in 
considerable damage, and it would be difficult to maintain a sufficient 
quality of the laser light absorption units 1310 to 1330 over a long time. 
Furthermore, the temperature of the coolant 307 after the heat exchange 
near the central portion of the heat-exchanging surface 303 becomes 
extraordinarily high. In some cases, the coolant 307 boils, whereby some 
vibration is generated. Such vibration may cause some mechanical damage to 
the laser light absorption units 1310 to 1330 and may hinder the laser 
oscillation apparatus from operating stably. 
SUMMARY OF THE INVENTION 
A laser oscillation apparatus of the present invention includes: a laser 
cavity unit for generating laser light by application of a voltage and 
optical amplification of the generated light by means of a pair of 
mirrors; and a DC power source for supplying the voltage required for 
generating the laser light to a pair of discharge electrodes of the laser 
cavity unit. Each of a cathode and an anode of the DC power source is 
grounded via a grounding resistor. 
The voltages supplied to the pair of discharge electrodes can be 
substantially at a same level with each other. 
In one embodiment, the laser oscillation apparatus further includes: a 
holder: for holding at least the pair of mirrors; and a cooling mechanism 
for cooling the holder with a coolant. The cooling mechanism includes a 
pump for circulating the coolant, a detector for detecting a temperature 
of the coolant, a heater for heating the coolant, and a control unit, the 
control unit causing the pump and the heater to operate while the laser 
oscillation apparatus is standing so as to increase the temperature of the 
coolant. 
The cooling mechanism can further include a timer connected to the control 
unit. The control unit, for example, causes the pump and the heater to 
operate for a certain period of time prior to start-up of the apparatus in 
accordance with operation of the timer. 
In another embodiment, the laser oscillation apparatus further includes a 
laser light absorption unit which is provided so as to be movable between 
a first position where the laser light absorption unit blocks oscillated 
laser light to prevent the laser light from exiting the laser oscillation 
apparatus and a second position where the laser light absorption unit 
allows the laser light to exit the laser oscillation apparatus. The laser 
light absorption unit Includes an outer cylinder and an inner cylinder 
which is provided at an opening of the outer cylinder, the inner cylinder 
having at least one conical configuration in which a front surface thereof 
functions as a light-receiving surface for receiving laser light whereas a 
rear surface thereof functions as a heat-exchanging surface, with a space 
between the inner cylinder and the outer cylinder providing a path for a 
coolant. The laser light absorption unit further includes a flow path 
adjuster having a shape such that the coolant flows i.e. a concentrated 
manner in the vicinity of a central portion of the light-receiving 
surface. The flow path adjuster and the heat-exchanging surface are 
coupled together at an interface therebetween by using a coupling material 
having a thermal conductivity of about 10 W/m.cndot.K or greater. 
The flow path adjuster can be formed of at least one blade. 
In still another embodiment, the laser oscillation apparatus further 
includes: a holder for holding at least the pair of mirrors; a cooling 
mechanism for cooling the holder with a coolant; and a laser light 
absorption unit which is provided so as to be movable between a first 
position where the laser light absorption unit blocks oscillated laser 
light to prevent the laser light from exiting the laser oscillation 
apparatus and a second position where the laser light absorption unit 
allows the laser light to exit the laser oscillation apparatus. The 
cooling mechanism includes a pump for circulating the coolant, a detector 
for detecting a temperature of the coolant, a heater for heating the 
coolant, and a control unit, the control unit causing the pump and the 
heater to operate while the laser oscillation apparatus is standing so as 
to increase the temperature of the coolant. The laser light absorption 
unit includes an outer cylinder and an inner cylinder which is provided at 
an opening of the outer cylinder, the inner is cylinder having at least 
one conical configuration in which a front surface thereof functions as a 
light-receiving surface for receiving laser light whereas a rear surface 
thereof functions as a heat-exchanging surface, with a space between the 
inner cylinder and the outer cylinder providing a path for a coolant. The 
laser light absorption unit further includes a flow path adjuster having a 
shape such that the coolant flows in a concentrated manner in the vicinity 
of a central portion of the light-receiving surface. The flow path 
adjuster and the heat-exchanging surface are coupled together at an 
interface therebetween by using a coupling material having a thermal 
conductivity of about 10 W/m.cndot.K or greater. 
The cooling mechanism can further include a timer connected to the control 
unit. The control unit, for example, causes the pump and the heater to 
operate for a certain period of time prior to start-up of the apparatus in 
accordance with operation of the timer. Moreover, the flow path adjuster 
can be formed of at least one blade. 
According to another aspect of the present invention, a laser oscillation 
apparatus includes: a laser cavity unit for generating laser light with 
optical amplification by means of a pair of mirrors; a holder for holding 
at least the pair of mirrors; and a cooling mechanism for cooling the 
holder with a coolant. The cooling mechanism includes a pump for 
circulating the coolant, a detector for detecting a temperature of the 
coolant, a heater for heating the coolant, and a control unit, the control 
unit causing the pump and the heater to operate while the laser 
oscillation apparatus is standing so as to increase the temperature of the 
coolant. 
In one embodiment, the cooling mechanism further includes a timer connected 
to the control unit. The control unit, for example, causes the pump and 
the heater to operate for a certain period of time prior to start-up of 
the apparatus in accordance with operation of the timer. 
In another embodiment, the laser oscillation apparatus further includes a 
laser light absorption unit which is provided so as to be movable between 
a first position where the laser light absorption unit blocks oscillated 
laser light to prevent the laser light from exiting the laser oscillation 
apparatus and a second position where the laser light absorption unit 
allows the laser light to exit the laser oscillation apparatus. The laser 
light absorption unit includes an outer cylinder and an inner cylinder 
which is provided at an opening of the outer cylinder, the inner cylinder 
having at least one conical configuration in which a front surface thereof 
functions as a light-receiving surface for receiving laser light whereas a 
rear surface thereof functions as a heat-exchanging surface, with a space 
between the inner cylinder and the outer cylinder providing a path for a 
coolant. The laser light absorption unit further includes a flow path 
adjuster having a shape such that the coolant flows in a concentrated 
manner in the vicinity of a central portion of the light-receiving 
surface. The flow path adjuster and the heat-exchanging surface are 
coupled together at an interface therebetween en by using a coupling 
material having a thermal conductivity of about 10 W/m.cndot.K or greater. 
The flow path adjuster can be formed of at least one blade. 
According to still another aspect of the present invention, a laser 
oscillation apparatus includes a laser light absorption unit which is 
provided so as to be movable between a first position where the laser 
light absorption unit blocks oscillated laser light to prevent the laser 
light from exiting the laser oscillation apparatus and a second position 
where the laser light absorption unit allows the laser light to exit the 
laser oscillation apparatus. The laser light absorption unit includes an 
outer cylinder and an inner cylinder which is provided at an opening of 
the outer cylinder, the inner cylinder having at least one conical 
configuration in which a front surface thereof functions as a 
light-receiving surface for receiving laser light whereas a rear surface 
thereof functions as a heat-exchanging surface, with a space between the 
inner cylinder and the outer cylinder providing a path for a coolant. The 
laser light absorption unit further includes a flow path adjuster having a 
shape such that the coolant flows in a concentrated manner in the vicinity 
of a central portion of the light-receiving surface. The flow path 
adjuster and the heat-exchanging surface are coupled together at an 
interface therebetween by using a coupling material having a thermal 
conductivity of about 10 W/m.cndot.K or greater. 
The flow path adjuster can be formed of at least one blade. 
Thus, the invention described herein makes possible the advantages of: (1) 
providing a laser oscillation apparatus in which a sufficient insulation 
distance can be easily provided between discharge electrodes and other 
components around the discharge electrodes, and in which freedom in design 
is improved in connection with, for example, the arrangement of the 
components around the discharge electrodes; (2) providing a laser 
oscillation apparatus which allows a stable laser output to be achieved In 
a short period of time in start-up; and (3) providing a laser oscillation 
apparatus including a laser light absorption unit which allows for a 
stable laser light absorption. 
These and other advantages of the present invention will become apparent to 
those skilled in the art upon reading and understanding the following 
detailed description with reference to the accompanying figures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Hereinafter, the present invention will be described by way of illustrative 
examples with reference to the accompanying figures. 
EXAMPLE 1 
FIG. 1 is a diagram schematically illustrating a configuration around a 
laser cavity unit 100 in a laser oscillation apparatus according to the 
present invention. 
In the laser oscillation apparatus shown in FIG. 1, a laser cavity unit 100 
includes a laser tube 6, a partially-transmissive reflection mirror 4, and 
a total reflection mirror 5. A high voltage is applied from a DC high 
voltage power source 2 via discharge electrodes 3a and 3b to a gaseous 
laser medium 1 contained in the laser tube 6 so as to generate a glow 
discharge. A blower 7 and a laser medium cooler 8 are serially connected 
to the laser tube 6 via a laser medium conduits 9a and 9b. The laser 
medium 1 is forcibly circulated by the blower 7. Particularly, the gaseous 
laser medium 1, heated by the glow discharge, passes through the laser 
medium conduit 9b, is cooled by the laser medium cooler 8, passes through 
the blower 7 and laser medium conduit 9a, and then is sent back to a glow 
discharge space in the laser tube 6. 
The total reflection mirror 5 is provided at one end of the laser tube 6, 
and the partially-transmissive reflection mirror 4 is provided at the 
other end thereof. Laser light generated by a discharge passes through the 
partially-transmissive reflection mirror 4 and exits the laser tube 6. 
Moreover, in the laser oscillation apparatus shown in FIG. 1, the DC high 
voltage power source 2 is directly connected to the discharge electrodes 
3a and 3b via feeder cables 11a and 11b. On the other hand, an anode and a 
cathode of the DC high voltage power source 2, which are respectively 
connected to the discharge electrodes 3a and 3b, are grounded via 
grounding resistors 12a and 12b. Since the grounding resistors 12a and 12b 
are connected to the anode and the cathode, respectively, of the DC high 
voltage power source 2, voltage to ground appearing at the discharge 
electrodes 3a and 3b are determined by the output voltage of the DC high 
voltage power source 2 and the ratio between the resistance values (i.e., 
the partial voltage ratio) of the grounding resistors 12a and 12b. As a 
result, even when the value of the output voltage of the DC high voltage 
power source 2 is the same as that of the conventional configuration, the 
voltage to ground of each of the discharge electrodes 3a and 3b can be 
made lower than that of the conventional configuration. 
According to the present invention, since the voltage to ground of each of 
the discharge electrodes 3a and 3b is thus reduced, the anti-breakdown 
level required for the feeder cables 11a and 11b, which connect the DC 
high voltage power source 2 to the discharge electrodes 3a and 3b, can be 
reduced as compared to the conventional configuration. Moreover, the 
insulation distance between the discharge electrodes 3a and 3b and other 
components disposed around the discharge electrodes 3a and 3b can also be 
reduced as compared to the conventional configuration. 
FIG. 2 illustrates the relationship between the ratio of resistance values 
of the grounding resistors 12a and 12b (i.e., the partial voltage ratio) 
and the respective absolute values of voltages to ground at the anode and 
the cathode of the DC high voltage power source 2. 
In FIG. 2, E represents the output voltage value of the DC high voltage 
power source 2. The anode and the cathode of the DC high voltage power 
source 2 are respectively connected to the discharge electrodes 3a and 3b 
via the feeder cables 11a and 11b. A voltage drop across the feeder cable 
11a or 11b is negligible, and therefore, the vertical axis in FIG. 2 can 
be considered to represent the voltages to ground of the discharge 
electrodes 3a and 3b. 
When the resistance values of the two grounding resistors 12a and 12b shown 
in FIG. 1 are equal to each other, i.e., when the partial voltage ratio of 
the grounding resistors 12a and 12b is 1, the absolute values of the 
voltages to ground of the anode and cathode of the DC high voltage power 
source 2 are equal to each other to be E/2, as shown in FIG. 2. In such a 
case, the voltages to ground of the anode and cathode of the DC high 
voltage power source 2, as well as the voltages to ground of the discharge 
electrodes 3a and 3b, becomes minimal. 
On the other hand, when the partial voltage ratio of the two grounding 
resistors 12a and 12b is not 1, either the anode or the cathode of the DC 
high voltage power source 2 has a voltage to ground which is greater than 
the above voltage level of E/2, as shown in FIG. 2. As a result, the 
anti-breakdown level required for the feeder cable 11a or 11b connected to 
the anode or the cathode becomes greater than that in the case where the 
partial voltage ratio of the grounding resistors 12a and 12b is 1. 
However, unless the partial voltage ratio is far removed from 1, the 
voltages to ground of the anode and the cathode of the DC high voltage 
power source 2 (the voltages to ground of the discharge electrodes 3a and 
3b) are still lower than the maximum level thereof (i.e., the output 
voltage level E of the DC high voltage power source 2), which can appear 
at the discharge electrode in the conventional configuration without the 
grounding resistors. Thus, the above-described effects can be realized, 
such as the reduction in the anti-breakdown level required for the feeder 
cable 11a or 11b, and the improvement of the freedom in design around the 
discharge electrodes 3a and 3b. 
The output voltage E(V) of the DC high voltage power source 2 is typically 
about 40 to 50 kV, and the partial voltage ratio of the grounding 
resistors 12a and 12b can be set in such a manner that, for example, (a 
resistance value of the grounding resistor 12a):(a resistance value of the 
grounding resistor 12b)=3:1. In such a case, the resistance value of the 
grounding resistor 12b can typically be set to several hundred M. By 
intentionally setting the partial voltage ratio of the grounding resistors 
12a and 12b to any value other than 1, the voltages to ground appearing at 
the discharge electrodes 3a and 3b can respectively be set to desired 
values. Thus, in the case where a sufficient insulation distance cannot be 
provided around one of the discharge electrodes 3a and 3b, it is possible 
to allow voltages to ground of a desired level to appear at the discharge 
electrodes 3a and 3b according to the respective insulation distances 
which can be provided around the discharge electrodes 3a and 3b without 
changing the value of the output voltage of the DC high voltage power 
source 2. 
As described above, the laser oscillation apparatus according to the 
present example includes the laser cavity unit 100 for generating laser 
light by discharge-induced excitation of the gaseous laser medium 1 in the 
laser tube 6 and optical amplification of the generated light by means of 
a pair of the optical amplification mirrors 4 and 5, and the DC high 
voltage power source 2 for activating a discharge. Particularly, the 
grounding resistors 12a and 12b are respectively connected to the anode 
and the cathode of the DC high voltage power source 2. This enables the 
voltages to ground of the discharge electrodes 3a and 3b which are 
respectively connected to the anode and the cathode of the DC high voltage 
power source 2 to be lowered. This, in turn, allows for use of a feeder 
cable whose anti-breakdown level is low, and also reduces the insulation 
distance around the discharge electrodes 3a and 3b so as to increase the 
freedom in design of the entire oscillation apparatus, thereby 
facilitating the designing of the apparatus. 
EXAMPLE 2 
Next, a cooling mechanism for optical components included in a laser 
oscillation apparatus according to the present invention will be described 
with reference to FIGS. 3 to 6. 
FIG. 3 is a diagram schematically illustrating an exemplary configuration 
of a cooling mechanism which can be used along with the laser cavity unit 
100 of the laser oscillation apparatus. Elements in FIG. 3 which are also 
shown in FIG. 1 are denoted by the same reference numerals and will not be 
further described. 
In the configuration shown in FIG. 3, optical components such as the 
partially-transmissive reflection mirror 4 and the total reflection mirror 
5 are held by so the holder 207. A coolant, for example, oil is circulated 
within the holder 207 by means of the pump 208 to cool the holder 207. In 
particular, such a cooling mechanism using the coolant, e.g., oil, 
includes the tank 211, the pump 208 for supplying the oil into the holder 
207, the cooler 210 for cooling the oil, and the thermistor 209 for 
detecting the oil temperature. Moreover, a heater 13 for heating the oil 
is provided between the thermistor 209 and the tank 211. Furthermore, a 
control unit 14 controls the operation of the cooler 210 and the heater 13 
based on the oil temperature detected by the thermistor 209. 
As described above in connection with the conventional laser oscillation 
apparatus, there is a problem associated with the temperature change of 
the holder 207 when the laser oscillation apparatus is standing in a cold 
atmosphere. According to the present example, in order to overcome this 
problem, the heater 13 is provided in the coolant conduit, and the control 
unit 14 is used to appropriately control the operation of the heater 13 so 
as to control the oil temperature by heating the oil in a laser 
oscillation start-up. Thus, it is possible to keep the temperature of the 
holder 207 at a predetermined temperature (e.g., the operating point 
temperature) while standing in a cold atmosphere, so that the positional 
parallel relationship between the partially-transmissive reflection mirror 
4 and the total reflection mirror 5 can be maintained. As a result, even 
in a laser oscillation start-up after standing in a cold atmosphere, a 
stable laser output can be achieved in a short period of time. 
Particularly, in the configuration shown in FIG. 3, the oil temperature is 
detected by the thermistor 209 while the laser oscillation apparatus is 
standing. When a decrease in the temperature beyond a predetermined range 
is detected, the control unit 14 activates the pump 208 and the heater 13. 
Thus, the holder 207 is heated by circulating heated oil therein so that 
the temperature of the holder 207 is raised to an appropriate value even 
while standing. After start-up, the oil is cooled by controlling the 
operation of the cooler 210 based on the oil temperature detected by the 
thermistor 209, thereby maintaining the temperature of the holder 207 at 
an appropriate value. 
Due to such a configuration, the positional parallel relationship between 
the partially-transmissive reflection mirror 4 and the total reflection 
mirror 5 can be always maintained even when the laser oscillation 
apparatus is placed in a cold atmosphere. 
FIG. 4 shows diagrams provided for illustrating the operation of the 
cooling mechanism for optical components in the laser oscillation 
apparatus shown in FIG. 3. 
Particularly, the portion (a) of FIG. 4 schematically illustrates the 
change in the temperature of the oil in the cooling mechanism from 
shutdown to some time after subsequent start-up. The temperature indicated 
therein can be considered as the temperature of the holder 207, which is 
cooled by the oil. Moreover, the portion (e) of FIG. 4 is a diagram 
schematically illustrating the change in the laser output of the laser 
oscillation apparatus after start-up, and the portions (b), (c) and (d) of 
FIG. 4 illustrate the operation timing of the pump 208, the heater 13 and 
the cooler 210, respectively. 
In accordance with the present invention, while standing in a cold 
atmosphere, the pump 208 and the heater 13 are intermittently operated at 
appropriate times as shown in the portions (b) and (c) of FIG. 4. Thus, as 
shown in the portion (a) of FIG. 4, the oil temperature is maintained at 
around a predetermined operating point temperature while standing in a 
cold atmosphere. Thus, a stable laser oscillation can be achieved in a 
short period of time after start-up as shown in the portion (e) of FIG. 4. 
Once the laser output becomes stable at the normal operating level, the 
control unit 14 acts to cause the cooler 210 to operate at an appropriate 
time as shown in the portion (d) of FIG. 4. This allows for a stable 
operation of the laser oscillation apparatus. The oil temperature is 
typically maintained at around 28.degree. C. 
In the conventional configuration described with reference to FIGS. 15 and 
16, it typically takes about 30 minutes to achieve a stable laser output 
in the laser oscillation start-up after standing in a cold atmosphere. On 
the contrary, in the configuration of the present example having the 
above-described function, a stable laser output is typically achieved in 
only about 5 minutes. 
FIG. 5 is a diagram schematically illustrating an exemplary configuration 
of another cooling mechanism which can be used along with the laser cavity 
unit of the laser oscillation apparatus. Elements in FIG. 5 which are also 
shown in FIG. 3 are denoted by the same reference numerals and will not be 
further described. 
Moreover, FIG. 6 shows diagrams provided for illustrating the operation of 
the cooling mechanism for optical components in the laser oscillation 
apparatus shown in FIG. 5. Particularly, the portion (a) of FIG. 6 
schematically illustrates the change in the temperature of the oil in the 
cooling mechanism from shutdown to some time after subsequent start-up. 
The temperature indicated therein can be considered as the temperature of 
the holder 207, which is cooled by the oil. Moreover, the portions (e) of 
FIG. 6 is a diagram schematically illustrating the change in the laser 
output of the laser oscillation apparatus after start-up, and the portions 
(b), Cc) and (d) of FIG. 6 illustrate the operation timing of the pump 
208, the heater 13 and the cooler 210, respectively. 
In the configuration shown in FIG. 5, a timer 15 is further added to the 
control unit 14 in the configuration previously described with reference 
to FIG. 3. As shown in FIG. 6, when the oil temperature is decreased to a 
certain level, the timer 15 acts to cause the heater 13 and the pump 208 
to operate for a certain period of time for heating the oil so that the 
oil temperature recovers to around the predetermined operating point 
temperature. 
Alternatively, in the case where, for example, the laser oscillation 
apparatus is installed in a manufacturing apparatus in a plant and is 
scheduled such that the operation starts at a certain time (e.g., at 8:00 
a.m. every morning), the timer 15 can act to cause the heater 13 and the 
pump 208 to operate for a certain period of time from a predetermined time 
prior to the scheduled start-up time for heating the oil. This allows the 
oil temperature to recover to around the predetermined operating point 
temperature by the scheduled time for starting up the laser oscillation 
apparatus. Such a configuration also allows a stable laser oscillation to 
be achieved in a short period of time after the start-up as shown in the 
portion (e) of FIG. 6. 
Once the laser output becomes stable at the normal operating level, the 
control unit 14 acts to cause the cooler 210 to operate at an appropriate 
time as shown in the portion (d) of FIG. 6. This allows for a stable 
operation of the laser oscillation apparatus. 
As described above, according to the present example, the heater 13 in 
addition to the pump 208, thermistor 209 and the cooler 210 is provided in 
the coolant conduit to the holder 207 which holds optical components such 
as the partially-transmissive reflection mirror 4 and the total reflection 
mirror 5. The control unit 14 is provided to appropriately control the 
operation of the pump 208, the heater 13 and the cooler 210. Thus, even 
during start-up after standing in a cold atmosphere, a stable laser output 
can be achieved in a short period of time. 
In the above description, the present invention is described by way of an 
example where oil is used as the coolant for adjusting the temperature of 
the holder 207. However, the coolant to be used for this purpose is not 
limited to oil, but water, solution containing ethylene glycol, solution 
containing polyhydric alcohol, or the like can also be used. 
Moreover, the thermistor 209 is used for the purpose of detecting the 
temperature of the coolant such as oil in the above description. However, 
any temperature sensors other than a thermistor, such as platinum-type 
temperature detector, thermo couple, or the like, can also be used for 
this purpose. 
EXAMPLE 3 
Next, a laser light absorption unit included in the laser oscillation 
apparatus of the present invention will be described with reference to 
FIGS. 7 to 13. 
FIG. 13 is a diagram schematically illustrating positional relationship of 
a laser light absorption unit 300 with respect to an optical path of a 
laser light 306 emitted from the laser cavity unit 100. 
Particularly, the laser light absorption unit 300 is provided on the 
optical path of the laser light 306 irradiated from the laser cavity unit 
100 in the laser oscillation apparatus. Normally, the laser light 
absorption unit 300 is located so as to block the optical path of the 
laser light 306, thereby preventing the laser light 306 generated in the 
laser cavity unit 100 from exiting the laser oscillation apparatus, and 
thus functioning as a safety apparatus. Then, once it is confirmed that 
the laser light 306 may exit (e.g., in a manufacturing site, when it is 
confirmed that the laser light 306 has been aimed to an object to be 
processed and that there is no obstruction in the intervening path), the 
laser light absorption unit 300 is shifted aside from the optical path of 
the laser light 306, e.g., as shown by an arrow in FIG. 13, so that the 
laser light 306 exits the laser oscillation apparatus. 
As described previously, the conventional laser light absorption unit has 
non-uniform heat exchange due to the non-uniformity of the temperature 
distribution at the heat-exchanging surface, the imbalance of the coolant 
supply, or the like. In order to overcome such a problem, the laser light 
absorption unit of the present invention is formed by coupling an inner 
cylinder having a conical configuration in which the light-receiving 
surface for receiving laser light and the heat-exchanging surface are 
provided on the respective front and rear surfaces of the configuration 
and an outer cylinder forming a path for a coolant between the outer 
cylinder and the heat-exchanging surface of the inner cylinder, and 
moreover, a flow path adjuster is provided in the path for the coolant. 
The flow path adjuster causes the coolant to flow in a concentrated manner 
in the vicinity of the central portion of the heat-exchanging surface of 
the inner cylinder. Furthermore, the flow path adjuster and the 
heat-exchanging surface are coupled together at the interface therebetween 
by using a coupling material having a thermal conductivity of about 10 
W/m.cndot.K or greater. 
With the laser light absorption unit of the present invention having such a 
structure, sufficient heat exchange is provided in the central portion of 
the heat-exchanging surface, where the temperature becomes highest due to 
the laser light absorption. 
Moreover, the flow path adjuster is coupled to the heat-exchanging surface 
by using a coupling material having a thermal conductivity of about 10 
W/m.cndot.K or greater. Thus, the heat given to the central portion of the 
heat-exchanging surface in a concentrated manner is efficiently 
transferred to the flow path adjuster and is further dissipated to the 
ambient space through the outer cylinder. As a result, the temperature 
increase in the central portion of the heat-exchanging surface is 
considerably reduced. Furthermore, since the flow path adjuster itself 
functions as an extension of the heat-exchanging surface, the heat 
exchange area in the entire apparatus is effectively increased, thereby 
improving the heat exchange performance. 
The above functions are sufficiently realized if the flow path adjuster is 
formed of at least one or more flat fixed blades. Thus, the flow path 
adjuster of the present invention can be realized with a simple structure, 
and provides cost advantage. 
FIG. 7 is a cross-sectional view schematically illustrating a configuration 
of a laser light absorption unit 350 of the present invention. Moreover, 
FIG. 8 is a cross-sectional view taken along the line 8--8 in FIG. 7. 
In the laser light absorption unit 350, the inner cylinder 301 is provided 
at an opening of the outer cylinder 304. The inner cylinder 301 includes 
the light-receiving surface 302 and the heat-exchanging surface 303 
respectively on the front surface and the rear surface of the inner 
cylinder 301. A space existing between the inner cylinder 301 and the 
outer cylinder 304 provides the path 305 for the coolant 307. The inner 
cylinder 301 is formed of a metallic material having a high thermal 
conductivity, e.g., copper, aluminum, brass, stainless steel, or the like. 
Water can be used as the coolant 307, for example. Alternatively, oil, 
solution containing ethylene glycol, solution containing polyhydric 
alcohol, or the like can be used as the coolant 307. 
The light-receiving surface 302 is formed by combining a plurality of 
conical configurations. Each of the conical surfaces of the conical 
configurations forms an angle of about 30.degree. or less with respect to 
the incident axis of the laser light 306 so that the incident laser light 
306 is not directed externally after being reflected. Moreover, the 
light-receiving surface 302 is coated with a material having a high 
absorptivity for the wavelength of the laser light 306 to be oscillated. 
The laser light 306 incident upon toe light-receiving surface 302 is 
quickly absorbed, and the heat thereof is transferred by conduction to the 
heat-exchanging surface 303. 
A flow path adjuster 310 formed of the fixed flat blade is provided within 
the path 305 for the coolant 307. The flow path adjuster 310 is formed of, 
for example, a metallic material having a high thermal conductivity such 
as copper, aluminum, brass, stainless steel, or the like. The coolant 307 
introduced into the path 305 through an inlet 308 exchanges heat at the 
heat-exchanging surface 303, and is drained through an outlet 309. During 
such a flow, the coolant 307 is blocked by the flow path adjuster 310 so 
that the coolant 307 passes in a concentrated manner through an opening 
311 formed in the vicinity of the central portion of the heat-exchanging 
surface 303. 
The heat-exchanging surface 303 and the flow path adjuster 310 are coupled 
together at an interface 312 therebetween (see FIG. 8) by using an 
appropriate coupling material. The coupling material is a material having 
a thermal conductivity of about 10 W/m.cndot.K or greater. Particularly, a 
brazing filler metal can be used, for example. Alternatively, materials 
such as a metallic material (e.g., copper, aluminum, brass, stainless 
steel, or the like) can be used as the coupling material. 
As shown in FIG. 9, when the thermal conductivity of the coupling material 
is about 10 W/m.cndot.K or greater, the temperature of the light-receiving 
surface 302 around the center thereof stands at about 400K. On the other 
hand, when the thermal conductivity of the coupling material is less than 
about 10 W/m.cndot.K, the temperature of the light-receiving surface 302 
around the center thereof rapidly increases. Therefore, in order for the 
coupling material to serve as a thermal conductor, the thermal 
conductivity thereof must be about 10 W/m.cndot.K or greater. 
The laser light 306 incident upon the light-receiving surface 302 is 
absorbed by the light-receiving surface 302, and the heat thereof is 
transferred by conduction to the heat-exchanging surface 303 through the 
so inner cylinder 301. A portion of heat transferred to the 
heat-exchanging surface 303, especially at a central portion where the 
temperature is high, is further transferred to the flow path adjuster 310 
through the interface 312. Thus, the flow path adjuster 310 itself 
functions as the heat-exchanging surface, so that the temperature increase 
at the center of the heat-exchanging surface 303 is reduced. 
FIG. 10 illustrates an exemplary thermographic measurement of the 
temperature distribution in the heat-exchanging surface 303 of the inner 
cylinder 301. The horizontal axis represents the location on the 
heat-exchanging surface 303, whereas the vertical axis represents the 
measured temperature (K) at each position. The measured data for the 
present invention (represented by 7; the dashed line) shows that, as 
compared to the measured data for the conventional configuration 
(represented by the solid line), the temperature In the central portion is 
reduced while the temperature in the peripheral portion is increased. 
Thus, in accordance with the present invention, the temperature on the 
whole heat-exchanging surface 303 is more balanced. 
In the conventional technique, the dissipation of heat has been achieved 
only on the heat-exchanging surface 303. According to the present 
invention, heat in the central portion of the heat-exchanging surface 303 
is transferred to the flow path adjuster 310 through thermal conduction as 
described above, so that the dissipation of the absorbed heat is also 
provided on the surface of the flow path adjuster 310. Moreover, since the 
coolant 307 passes in a concentrated manner through the opening 311 formed 
in the vicinity of the central portion of the heat-exchanging surface 303, 
as shown in FIGS. 7 and 8, the heat exchange performance at the central 
portion of the heat-exchanging surface 303 is improved. Due to such a dual 
effect, the laser light absorption unit 350 of the present invention 
allows for a stable heat exchange as a whole. 
In the laser light absorption unit 350 of the present invention, since the 
light-receiving surface 302 is always exposed to the irradiation of the 
laser light 306, damage thereto is inevitable. However, by making the 
temperature of the heat-exchanging surface 303 uniform as described above, 
the temperature of the light-receiving surface 302 also becomes uniform, 
and in particular, the temperature increase in the central portion is 
reduced. Therefore, the damage to the light-receiving surface 302 can be 
minimized, thereby allowing for a long-term stable use of the apparatus. 
FIG. 11 is a cross-sectional view schematically illustrating a 
configuration of another laser light absorption unit 360 according to the 
present invention. Moreover, FIG. 12 is a cross-sectional view taken along 
the line 12--12 in FIG. 11. Elements in FIGS. 11 and 12 which are also 
shown in FIGS. 7 and 8 are denoted by the same reference numerals and will 
not be further described. 
In the laser light absorption unit 360, the flow path adjuster 310 is 
formed of two fixed flat blades orthogonally crossing each other. Due to 
such a configuration, as compared to the above-described laser light 
absorption unit 350, the contact area at the interface 312 between the 
heat-exchanging surface 303 and the flow path adjuster 310 is increased, 
so that a further improved heat conduction effect can be realized. 
Moreover, since the surface area of the flow path adjuster 310 is 
increased, the heat exchange area in the entire apparatus is increased, 
thereby also improving the diffusion effect for the absorbed heat. 
As described above, in the laser light absorption unit of the present 
invention, the flow path adjuster is provided in the coolant path so that 
the coolant flows in a concentrated manner in the vicinity of the central 
portion of the heat-exchanging surface of the conically-shaped inner 
cylinder. Moreover, at the interface between the flow path adjuster and 
the heat-exchanging is surface, a coupling material having a thermal 
conductivity of about 10 W/m.cndot.K or greater is provided. Thus, the 
temperature distribution on the light-receiving surface is made uniform, 
thus allowing for a long-term stable laser light absorption. 
In the above, some embodiments of the present invention have been 
individually described in connection with the connection circuit for the 
laser cavity unit (the discharge electrodes) of the DC high voltage power 
source for the laser oscillation apparatus, the cooling mechanism for the 
holder of the optical components, and the laser light absorption unit, 
respectively. However, the contents of the respective examples area not 
only applicable individually, but also applicable in combination. 
Moreover, the various examples of the present invention have been described 
above in connection with a gas laser (e.g., a CO.sub.2 laser) in which the 
gaseous laser medium in the laser cavity unit is excited through discharge 
which is generated upon application of voltage. However, application of 
the contents of the present invention is not limited to such a gas laser. 
In fact, similar effects can be realized when applied to a laser 
oscillation apparatus including a laser cavity unit of other types, e.g., 
a YAG laser or the like. 
Various other modifications will be apparent to and can be readily made by 
those skilled in the art without departing from the scope and spirit of 
this Invention. Accordingly, it is not intended that the scope of the 
claims appended hereto be limited to the description as set forth herein, 
but rather that the claims be broadly construed.