Gas laser oscillator

Details Gas laser oscillator Gas laser oscillator

1998-07-28

2002-01-08

Davie, James W. (Department: 2881)

Coherent light generators

Particular beam control device

Optical output stabilization

C372S033000, C372S055000

Reexamination Certificate

active

06337869

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a gas laser oscillator low in fluctuation rate of a laser beam, capable of producing a laser beam stably, and free from malfunction.
First, a conventional gas laser oscillator is described by referring to FIG.
11
. In
FIG. 11
, reference numeral
1
is a discharge tube for forming a discharge space
5
inside, and the inside of the discharge tube
1
is filled with laser gas, or laser gas is circulating by a circulating device not shown in the drawing. Reference numeral
2
is an electrode provided at one end of the discharge tube
1
,
3
is an electrode provided at the other end of the discharge tube
1
,
4
is a direct-current high voltage power source for applying a voltage for discharging between the electrodes
2
and
3
, and
6
is a fully reflective mirror, which is combined with a partially reflective mirror
7
to compose an optical resonator for amplifying the laser light. Reference numeral
9
is an output control device for controlling the direct-current high voltage power source
4
.
This is the basic constitution of the gas laser oscillator. In this constituted gas laser oscillator, the operation of its basic portion is described below. First, according to the command from the output control device
9
, a direct-current high voltage in pulse form is applied between the electrodes
2
and
3
from the direct-current high voltage power source
4
for discharging between the electrodes
2
and
3
. By this discharge energy, the laser gas in the discharge space
5
is excited. The excited laser gas is set in resonant state by the optical resonator composed of the fully reflective mirror
6
and partially reflective mirror
7
, and the light is amplified, and a laser beam
8
is issued from the partially reflective mirror
7
. The produced laser beam
8
is used in laser processing such as cutting and piercing.
In such a gas laser oscillator, also on standby while not processing, discharge occurs in the discharge tube
1
, and the laser beam
8
is issued from the partially reflective mirror
7
at a preset output level. However, since an absorber
10
is disposed ahead of the partially reflective mirror
7
, the produced laser beam
8
is intercepted by the absorber
10
and does not leak outside.
When processing by the laser beam
8
, by the command from an absorber control device
12
, an absorber drive device
11
operates the absorber
10
, and the passage of laser beam
8
is opened, and the laser beam
8
is emitted outside to process the workpiece
15
.
On the other hand, at the side closer to the workpiece
15
from the absorber
10
on the optical axis of the laser beam
8
, a beam splitter
14
is disposed. The laser beam
8
is separated by this beam splitter
14
, and the straightforward portion
8
a
reaches the workpiece
15
, and processes by cutting or piercing. The portion
8
b
reflected and separated by the beam splitter
14
is focused by a focusing lens
16
, and is irradiated onto a detector
17
. The detector
17
irradiated by the separated portion
8
b
detects that the laser beam
8
is being emitted. This detection signal is amplified by an amplifier
18
, and is issued from a terminal
19
.
However, the conventional gas laser oscillator as explained above had several problems.
First was a problem of fluctuation of laser beam output in a transient state from standby by cutting off the laser beam
8
by the absorber
10
to processing by passing the laser beam
8
by setting aside the absorber
10
. That is, in the standby state (A) as shown in
FIG. 7
, a signal for obtaining an output of low level necessary for maintaining discharge is issued from the output control device
9
, and a direct-current high voltage corresponding to the signal level is applied between the electrodes
2
and
3
to maintain discharge. Once a processing start signal is entered and the absorber
10
is opened to be in state (B), the processing start signal
13
is sent from the absorber control device
12
into the output control device
9
. Receiving this signal
13
, the output control device sends out a signal having a level and waveform necessary for obtaining the output of pulse laser beam
8
suited to the purpose of processing. In the conventional control, however, since the discharge state in the discharge space
5
on standby is different from the discharge state in the discharge space
5
during processing, the dissociation state of laser gas is different between processing and standby. As a result it takes time until the dissociation state of laser gas is stabilized from start of processing and fluctuations of laser output in the initial period of processing are large so that stable processing is disabled. Upon start of processing, further, it takes time to stabilize owing to the presence of an unstable period due to heat effects of the fully reflective mirror
6
and partially reflective mirror
7
for composing the optical resonator and unstable period of surface state of the electrode
2
and electrode
3
, which is also a cause of an unstable output of the laser beam
8
in the initial period of processing. This unstable output of the laser beam
8
in the initial period of processing was a serious problem in processing for a short time, in particular.
Another problem is related to the laser beam detecting device that is indispensable for accurate control of the gas laser oscillator. In the conventional constitution shown in
FIG. 11
, after dismounting the beam splitter
14
for the purpose of an adjustment of the gas laser oscillator or the like, if laser processing is done without reassembling the beam splitter
14
, the laser beam
8
not attenuated by the beam splitter
14
directly irradiates to the workpiece
15
. As a result, the workpiece is irradiated with an excessive laser beam
8
, and a processing failure may occur.
Also, there is a possibility that when adjusting the gas laser oscillator, if a laser beam
8
over the allowable capacity of the detector
17
is irradiated by mistake, the detector
17
may be broken.
Further, the detector
17
may fluctuate in the detecting sensitivity due to fluctuations of temperature depending on heat generation by incident of laser beam
8
b
or ambient temperature. A fluctuation of detecting sensitivity of the detector
17
may cause output of wrong information. For example, if the detecting sensitivity is raised, although the laser beam
8
is not emitted, it may be falsely recognized that the laser beam
8
is emitted, or if the detecting sensitivity is lowered, although the laser beam
8
is emitted, it may be falsely recognized that the laser beam
8
is not emitted. Hence, accurate control of the gas laser oscillator may be disabled.
Moreover, if used for a long period, dust may deposit on the beam splitter
14
, focusing lens
16
, or detecting surface of the detector
17
, and the detecting sensitivity may be lowered.
SUMMARY OF THE INVENTION
The invention is hence devised to solve the above plural problems, and it is a first object thereof to transfer promptly to a state of stable and favorable laser processing by eliminating the unstable period of laser beam output in the transient state of changing from standby to processing.
It is a second object to solve the problems relating to the laser beam detector, including prevention of processing failure by irradiation of laser beam of excessive energy to the workpiece if forgetting to mount the beam splitter, prevention of damage of the detector due to excessive input to the detector by wrong adjustment, and prevention of wrong control of gas laser oscillator due to malfunction of detector caused by fluctuations of detector temperature or deposit of dust.
To achieve the objects, the gas laser oscillator of embodiment 1 of the invention comprises:
a discharge tube for forming a discharge space inside,
a fully reflective mirror disposed toward the opening at one end of the discharge space for composing an end mirror,
a partially reflective mirror disposed toward the opening at the

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