Coherent light generators – Particular pumping means
Reexamination Certificate
2003-04-30
2004-05-18
Ip, Paul (Department: 2828)
Coherent light generators
Particular pumping means
C372S070000, C372S073000, C372S075000
Reexamination Certificate
active
06738407
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser light emitting apparatus for emitting laser light using a semiconductor laser, and a solid-state laser rod pumping module for optical pumping a solid-state laser rod using semiconductor laser light so as to generate desired laser light. More particularly, it relates to a semiconductor laser light emitting apparatus for generating semiconductor laser light of high-density power with a high degree of efficiency using an array-type semiconductor laser or stack-type semiconductor laser, and a solid-state laser rod pumping module for pumping a solid-state laser rod using semiconductor laser light of high power with a high degree of efficiency so as to generate laser light having a high beam quality.
2. Description of the Prior Art
Semiconductor laser light emitting apparatuses are intended to generate combined semiconductor laser light of high power density using one or more laser light beams, each of which will be referred to as semiconductor laser light in most cases, emitted out of one or more semiconductor lasers. In order to pump a solid-state laser rod with high power and with a high degree of efficiency and then generate laser light having a high beam quality using such a semiconductor laser light emitting apparatus, it is preferable to increase the efficiency of energy utilization of the semiconductor laser light generated by the semiconductor laser light emitting apparatus. The energy utilization efficiency is directly affected by how the semiconductor laser light is focused to pump the solid-state laser rod.
In a prior art solid-state laser rod pumping module of side-pumped type intended for high power using an array-type semiconductor laser that includes a plurality of laser-light-emitting end portions integrated and stacked in the direction of a slow axis thereof, and that is placed so that the slow axis of the semiconductor laser is parallel to the axis of the solid-state laser rod, the solid-state laser rod cannot be pumped with a high degree of efficiency because of a small cross-sectional area of the solid-state laser rod in the case that the semiconductor laser light emitted out of the semiconductor laser passes through the solid-state laser rod only once. In general, such a semiconductor laser emits laser light whose near-field pattern is an ellipse according to its characteristics, the laser light having different divergence angles with respect to two axes perpendicular to the optical axis thereof (i.e., in two perpendicular longitudinal sections). The laser light has a smaller divergence angle with respect to the direction of one of the two axes, which will be referred to as slow axis, and has a larger divergence angle with respect to the direction of the other one of the two axes, which will be referred to as fast axis. To solve the above problem, a method of pumping the solid-state laser rod with a high degree of efficiency has been proposed, the method comprising the steps of injecting the semiconductor laser light into a reflection tube surrounding the solid-state laser rod, and trapping the semiconductor laser light within the reflection tube so that it passes through the solid-state laser rod a number of times.
In the case that the efficiency of trapping the semiconductor laser light within the reflection tube is high, the prior art method offers the advantage of being able to increase the efficiency of the optical pumping of the solid-state laser rod. However, in order to increase the efficiency of trapping the semiconductor laser light within the reflection tube, it is necessary to decrease the amount of light that can escape from the interior of the reflection tube via an injection hole formed in the wall of the reflection tube, through which the semiconductor laser light has been injected into the reflection tube, that is, to minimize the size of the injection hole.
In general, in order to generate laser light of high power, a stack-type semiconductor laser is used as the semiconductor laser for optical pumping the solid-state laser rod. A stack-type semiconductor laser includes a plurality of bar-shaped (or rectangular) components (or arrays) that are stacked in the direction of the fast axis of the semiconductor laser, each of the plurality of bar-shaped arrays including a plurality of laser-light-emitting end portions that are aligned and integrated in the direction of the slow axis.
In order to generate laser light having a high-beam quality by optical pumping a solid-state laser rod, there is a need to reduce the wave aberration caused by the solid-state laser rod itself because of heat generated by the optical pumping of the solid-state laser rod. To that end, it is desirable that the solid-state laser rod be an ideal grated refractive index lens, by illuminating the solid-state laser rod with semiconductor laser light as uniformly as possible, making the distribution of the light intensity of the semiconductor laser light incident on the solid-state laser rod axisymmetric with respect to the axis of the solid-state laser rod and uniform, and making the radial distribution of temperature in the solid-state laser rod second-order axisymmetric with respect to the axis of the solid-state laser rod.
However, in such a prior art solid-state laser rod pumping module, the radial distribution of temperature caused by the optical pumping of the solid-state laser rod using semiconductor laser light cannot be a second-order axisymmetric one because the semiconductor laser light is injected into only a part of the solid-state laser rod when it enters the reflection tube first after it has passed through the injection hole, i.e. part of the solid-state laser rod that is opposite to (or facing) the injection hole, without its laser intensity being reduced. Therefore, although the prior art solid-state laser rod pumping module is capable of generating laser light having average laser power up to about 1 kW if the beam quality does not matter, it can only generate laser light having average laser power of the order, at most, of about 100 Watts in the case that a high beam quality is needed.
Referring now to
FIG. 19
, there is illustrated a cross-sectional view showing a prior art solid-state laser rod pumping module as shown in, for example, S. Fujikawa et al., “High-power high-efficient diode-side-pumped Nd: YAG laser”, technical digest of Advanced Solid-State Lasers '97, pp.296-299, 1997. In the figure, reference numeral
101
denotes a solid-state laser rod pumping module,
102
denotes a solid-state laser rod, and
103
denotes a cooling sleeve that is shaped like a tube and is transparent to semiconductor laser light. The cooling sleeve
103
is disposed on substantially the same axis as the solid-state laser rod
102
so that it surrounds the solid-state laser rod
102
. In the cooling sleeve
103
, a coolant for the solid-state laser rod
102
is circulated. In addition, reference numeral
104
denotes a diffusive reflection tube for diffusively reflecting semiconductor laser light incident thereon, which is disposed on substantially the same axis as the solid-state laser rod
102
so that it surrounds the solid-state laser rod
102
and the cooling sleeve
103
, the diffusive reflection tube
104
being able to trap the semiconductor laser light injected into the interior thereof,
105
denotes a semiconductor laser having a plurality of laser-light-emitting end portions that are aligned and integrated in a direction parallel to the axis of the solid-state laser rod
102
. In the example shown, the solid-state laser rod
102
is located so that its axis is parallel to the slow axis of the semiconductor laser
102
. The semiconductor laser light emitting apparatus included in the solid-state laser rod pumping module consists of the semiconductor laser
105
only. Furthermore, reference numeral
107
denotes a semiconductor laser light guiding component constructed of a sheet glass, which is inserted into the diffusive reflection tube
104
.
Hirano Yoshihito
Koyata Yasuharu
Pavel Nicolaie
Yamamoto Shuhei
Ip Paul
Jackson Cornelius H
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