Compact laser oscillator

Details Compact laser oscillator Compact laser oscillator

1996-01-22

2001-07-31

Arroyo, Teresa M. (Department: 2881)

Coherent light generators

Particular resonant cavity

C372S099000, C372S108000

Reexamination Certificate

active

06269111

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a laser oscillator, and more particularly, to a laser oscillator used in a laser processing apparatus.
BACKGROUND ART
A laser processing apparatus has been widely used as one of machine tools for thermal treatment of metals and nonmetals, such as laser cutting, laser welding, etc.
FIG. 1
shows an outline of a conventional laser processing apparatus. The laser processing apparatus
1
comprises a laser oscillator
90
, a laser beam machine
3
, and a numerical control device
4
. A laser beam emitted from the laser oscillator
90
passes through a shading duct
5
, and reaches a processing head
6
of the laser beam machine
3
. The vertical position of the processing head
6
, which has a condenser lens, is adjusted by means of a Z-axis movement mechanism (not shown) in response to a command from the numerical control device
4
. The condenser lens of the processing head
6
converges the laser beam on a processing point of a workpiece
7
, which is placed on an X-Y table of the laser beam machine
3
, where the workpiece
7
is processed.
FIGS. 2
a
,
2
b
and
2
c
show an arrangement of a conventional laser resonator
80
which is provided in the laser oscillator
90
. The laser resonator
80
is provided with a frame
9
, a gas exciting device
10
, and a gas cooling device
11
. The frame
9
, comprising front and rear aluminum plates
12
and
13
and four rods
14
which connect the front and rear plates
12
and
13
, is constructed firmly lest it be easily deformable by external force. Each rod
14
is in the form of a tube made of a material such as invar in order to minimize a heat-induced dimensional change of the frame
9
. While the laser resonator
80
is operating, cooling water is circulated in the rods
14
. Thus, the frame
9
is designed so that its thermal deformation is extremely small.
The gas exciting device
10
comprises discharge tubes
15
a
and
15
b
arranged parallel to each other, electrodes
16
a
and
16
b
arranged on the respective peripheral walls of the discharge tubes
15
a
and
15
b
facing each other, and a high-frequency power source
16
connected to the electrodes
16
a
and
16
b
. The opposite ends of each of the two discharge tubes
15
a
and
15
b
are fixed to the front and rear plates
12
and
13
by means of discharge tube holders
20
, respectively. The rear plate
13
is fitted with a turn-back block
21
having two reflectors
18
which are arranged at right angles to each other, whereby the discharge tubes
15
a
and
15
b
are connected to each other. The respective inside spaces of the discharge tubes
15
a
and
15
b
are coupled to each other by means of the block
21
, thus forming one resonant space. An output mirror
17
is attached to one end of the discharge tube
15
a
which is situated near the front plate
12
, and a rear mirror
19
is attached to one end of the discharge tube
15
b
which is situated near the front plate
12
.
Electric power from the high-frequency power source
16
is applied to cause electric discharge between the electrodes
16
a
and
16
b
, whereby CO
2
gas in each of the discharge tubes
15
a
and
15
b
is excited. Laser emitted from the excited gas is amplified as it repeatedly reciprocates in the discharge tubes between the output mirror
17
and the rear mirror
19
. Part of the laser constitutes a laser beam
22
, which is emitted forward (to the left of
FIG. 2
) from the output mirror
17
.
The gas cooling device
11
is composed of a Roots blower
23
, heat exchangers
24
and
25
arranged on the intake and discharge sides of the Roots blower
23
respectively, and a pipe
26
. When the Roots blower
23
is activated, the gas, adjusted in temperature by means of the heat exchangers
24
and
25
, circulates in the pipe
26
, whereby the gas in the discharge tubes
15
a
and
15
b
is cooled.
A shutter mirror
27
is used in suspending laser processing. When the shutter mirror
27
is in the optical path, as indicated by dotted line, the laser beam
22
is caused to deviate from the main optical path for processing, and is absorbed by a beam absorber
28
. A beam phase adjusting unit
29
has a phase lag reflector
30
and a zero-shift reflector
31
therein. The beam phase adjusting unit
29
serves to convert a linear polarized laser beam into a circular polarized laser beam.
In general, the laser processing is effected by converging the laser beam outputted from the laser oscillator
80
. In such a case, the distance between a laser beam outlet of the laser oscillator
80
and the processing point greatly influences the laser processing performance.
FIG. 5
schematically shows the discharge tubes
15
of the laser resonator and the laser beam
22
. The laser beam
22
, repeatedly reflected and amplified in a section A between the rear mirror
19
and the output mirror
17
on the discharge tubes
15
and emitted through the output mirror
17
, has the property of spreading as the optical path length increases. The laser processing performance, which changes depending on various factors, is largely influenced by the diameter of the laser beam
22
at the position of the condenser lens, spread angle, and intensity distribution (transverse mode), in particular. Thus, the distance (optical path length) between the output mirror
17
of the laser resonator and the processing point of the laser beam machine
3
is an important factor as it restricts the laser processing performance.
For example, in the case of laser cutting, the spread angle of the laser beam
22
is narrow in a zone B; the transverse mode is a low-order multi-mode or ring mode, as indicated by (I) or (II); and satisfactory cutting cannot be achieved due to the influence of diffraction of light emitted from the edge portion of the output mirror
17
. In a zone D, the diameter of the laser beam
22
is too large. In a zone C, on the other hand, the transverse mode resembles a single mode, as indicated by (III), and the spread of the laser beam
22
is appropriate and best suited for the laser cutting. According to the result of a cutting test using a CO
2
gas laser beam, the aforesaid zone C is situated within the range of 3 m to 6 m from the output mirror
17
, and the distance between the output mirror
17
and the processing point obtained when the condenser lens is located within this range is an optimum optical path length.
Conventionally, in order to obtain the aforesaid optimum optical path length, a relatively long light guide distance L
1
is secured between the laser oscillator
20
and the laser beam machine
3
, as shown in
FIGS. 1 and 3
. Such a long light guide distance L
1
, however, places a limitation not only on the compactness of the arrangement of the laser processing apparatus
1
as the whole but also on the degree of freedom of design. Moreover, in a conventional arrangement, the beam phase adjusting unit
29
is externally attached in the manner as is shown in
FIG. 3
where a circular polarized laser beam is needed at the processing point. In this arrangement, however, dust is liable to adhere to the reflectors in the unit, thereby lowering the laser processing performance.
DISCLOSURE OF THE INVENTION
The present invention provides a laser oscillator which allows the distance between a laser beam machine and the laser oscillator to be reduced.
A laser oscillator according to the present invention comprises a laser resonator for emitting a laser beam and turn-back means for reflecting and turning back the laser beam emitted from the laser resonator, the laser beam emitted from the laser resonator being outputted from the laser oscillator after being turned back by the turn-back means and traveling for a predetermined optical path length.
According to an aspect of the present invention, the turn-back means reverses the direction of the laser beam emitted from the laser resonator, and the laser beam emitted from the laser resonator is outputted from the laser resonator after traveling at least through an optical path of a length equivalen

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