Coherent light generators – Particular temperature control – Liquid coolant
Reexamination Certificate
1998-10-29
2001-07-24
Arroyo, Teresa M. (Department: 2881)
Coherent light generators
Particular temperature control
Liquid coolant
C372S109000
Reexamination Certificate
active
06266352
ABSTRACT:
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
The entire disclosure of U.S. patent application Ser. No. 08/885,101 filed Jun. 30, 1997 is expressly incorporated by reference herein.
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
103
a
and
103
b
to a gaseous laser medium
101
contained in the laser tube
106
so as to generate a glow discharge. A blower
107
and a laser medium cooler
108
are serially connected to the laser tube
106
via laser medium conduits
109
a
and
109
b
. 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
109
b
, is cooled by the laser medium cooler
108
, passes through the blower
107
and the laser medium conduit
109
a
, 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
103
a
and
103
b
via feeder cables
111
a
and
111
b
. Furthermore, a cathode of the DC high voltage power source
102
, which is connected to the discharge electrode
103
b
, 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
103
a
. (In this application, voltage that is expressed using the ground level as the reference level is referred to as “voltage to ground”.) In such a case, the feeder cable
111
a
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 discharge electrode
103
a
, it is necessary to provide components constituting the laser oscillation apparatus around the discharge electrode
103
a
(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
103
a
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 holder
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-tra
Eguchi Satoshi
Hayashikawa Hiroyuki
Yamashita Takayuki
Arroyo Teresa M.
Inzirillo Gioacchino
Matsushita Electric - Industrial Co., Ltd.
Ratner & Prestia
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