Coherent light generators – Particular pumping means – Pumping with optical or radiant energy
Reexamination Certificate
2001-12-18
2004-04-13
Ip, Paul (Department: 2828)
Coherent light generators
Particular pumping means
Pumping with optical or radiant energy
C372S070000, C372S107000
Reexamination Certificate
active
06721347
ABSTRACT:
TECHNICAL FIELD
This invention relates to a solid state laser apparatus, which is useful when applied, for example, as a semiconductor laser excited YAG laser apparatus for use in material processing, such as drilling, cutting or welding, and surface treatment, such as surface modification or marking.
BACKGROUND ART
Currently, a semiconductor laser (laser diode; may hereinbelow be referred to as LD) apparatus attracts attention as an exciting light source of a solid state laser apparatus such as a YAG laser apparatus. This LD apparatus generates semiconductor laser light from an LD device, and is excellent in oscillation efficiency and life as compared with a conventional pumping lamp.
FIG. 14
is a perspective view showing the configuration of a conventional LD-excited YAG laser apparatus. As shown in this drawing, a YAG laser apparatus
11
has a pair of LD apparatuses
2
as an exciting light source, and these LD apparatuses
2
are disposed so as to be opposed to both side surfaces
1
a
and
1
b
of a slab-shaped YAG crystal (hereinafter referred to simply as a crystal). An output mirror
3
and a total reflection mirror
4
are provided parallel on one side in the longitudinal direction (x-axis direction) of the crystal
1
, while a turnback total reflection mirror
5
and a turnback total reflection mirror
6
are provided parallel on the other side in the longitudinal direction of the crystal
1
. These mirrors
3
,
4
,
5
and
6
constitute a resonator. The illustrated example shows a YAG laser light path in the crystal as two axes, a YAG laser light path
10
a
and a YAG laser light path
10
b.
The LD apparatus
2
comprises many cooling blocks
8
stacked in the x-axis direction, each of the cooling blocks
8
having an LD device
7
fixed to the side surface thereof. The LD device
7
used here comprises several tens of active media arranged one-dimensionally (i.e., a one-dimensional LD array device), each of the active media having a cross sectional area of several micrometers×several hundred micrometers. The LD devices
7
are stacked, together with the cooling blocks
8
, to constitute a two-dimensional LD array device. By flowing a drive current in the stack direction of the cooling blocks
8
by a power source device (not shown), laser light
9
is emitted from the respective LD devices
7
, and this laser light
9
is directed, as exciting light, at the opposite side surfaces
1
a
and
1
b
of the crystal
1
. As a result, YAG laser light
10
is issued from the output mirror
3
of the resonator.
At this time, the YAG laser light paths
10
a
,
10
b
in the crystal are zigzag optical paths, in which laser light advances in the x-axis direction while being reflected by the opposite side surfaces
1
a
and
1
b
in the thickness direction (z-axis direction) of the crystal
1
, because the entrance and exit of the crystal
1
(the opposite end surfaces in the x-axis direction) have Brewster's angle. Thus, even if a temperature distribution occurs in the z-axis direction inside the crystal and a refractive index distribution according to this temperature distribution occurs, a thermal lens effect due to this phenomenon is compensated for.
For the refractive index distribution in the y-axis direction, on the other hand, the thermal lens effect is not compensated for. Thus, the refractive index distribution in the y-axis direction needs to be uniformized in the laser light path region. With the above-described conventional YAG laser apparatus
11
, however, a refractive index distribution occurs also in the y-axis direction within the crystal, because laser light
9
from the LD apparatus
2
is uniformly thrown at the entire side surface of the crystal
1
by adjusting the distance between the LD apparatus
2
and the crystal
1
.
That is, when laser light
9
is uniformly applied to the whole of the crystal side surfaces
1
a
and
1
b
, the applied light intensity distribution in the y-axis direction on these crystal side surfaces
1
a
and
1
b
is uniform all over the side surface as indicated by a solid line in FIG.
15
(
a
). The applied light intensity tends to be low at the upper and lower ends of the crystal side surfaces
1
a
and
1
b
. Thus, the temperature distribution in the y-axis direction within the crystal is a distribution having a maximum value at the crystal center portion as indicated by a solid line in FIG.
15
(
b
), because of heat conduction in the diametrical direction (y-axis direction) of a cross section of the laser light path. Hence, the refractive index distribution in the y-axis direction within the crystal is also a nonuniform distribution, as shown in FIG.
15
(
c
), in accordance with this temperature distribution.
Consequently, owing to the thermal lens effect, YAG laser light
10
is condensed or contorted in the YAG laser light paths
10
a
,
10
b
within the crystal, resulting in a deterioration of light quality. Condensation of the YAG laser light
10
within the crystal may make the diameter of the YAG laser light
10
smaller than a predetermined diameter. The decrease in the diameter of the YAG laser light
10
may lower the oscillation efficiency, or may further burn out the crystal
1
.
In the applied light intensity distribution shown in FIG.
15
(
a
), a portion contributing to optical excitation of the laser medium doped into the crystal
1
is only a region A of the two YAG laser light paths
10
a
and
10
b
, and the other portion is of no use. In other words, the applied light density in the laser light path region A is low. Thus, the utilization efficiency of the semiconductor laser light
9
is poor, and the semiconductor laser output is great relative to the necessary YAG laser output. The portion other than the laser light path region A in the crystal
1
is a portion necessary as a mechanism for cooling and maintaining the crystal
1
, and necessary for the optical axis adjustment of the YAG laser light
10
.
Thus, the present invention has been accomplished in light of the foregoing problems, and is aimed at providing a solid state laser apparatus having a high utilization efficiency of semiconductor laser light, and being capable of uniformizing the refractive index distribution in the width direction of side surfaces of a slab-shaped crystal in the laser light path region of the slab-shaped crystal.
DISCLOSURE OF THE INVENTION
The solid state laser apparatus of the present invention, which attains the above object, is characterized by the following features:
1) A solid state laser apparatus having an LD apparatus as an exciting light source, and adapted to direct laser light emitted from the LD apparatus, as exciting light, at the side surface of a slab-shaped crystal to emit solid state laser light, comprising:
light concentrating/applying means for concentrating and applying the laser light emitted from the LD apparatus onto a laser light path region of the slab-shaped crystal, or the laser light path region and the neighborhood thereof.
According to this invention, semiconductor laser light is concentrated and applied onto the laser light path region, or the laser light path region and its neighborhood. Thus, the utilization efficiency of the semiconductor laser light is increased, and when the same solid state laser output as before is to be obtained, the semiconductor laser output (input to the crystal) can be made smaller than before. In other words, when the same semiconductor laser output as before is given, a greater solid state laser output than before can be obtained.
2) In the solid state laser apparatus,
the light concentrating/applying means concentrates and applies the laser light such that a concentrated applied light intensity distribution in the side surface width direction of the slab-shaped crystal is a double-peak distribution.
According to this invention, compared with mere concentration and application of laser light, the temperature distribution in the side surface width direction within the crystal can be made uniform, and the refractive index distribution can als
Akaba Takashi
Kato Masahiro
Miki Susumu
Mizui Jyunichi
Al-Nazer Leith
Ip Paul
Mitsubishi Heavy Industries Ltd.
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