GB2310077A

GB2310077A - Solid state laser apparatus

Info

Publication number: GB2310077A
Application number: GB9709648A
Authority: GB
Inventors: Kazuki Kuba; Masaki Seguchi; Akira Ishimori; Takashi Yamamoto
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1993-09-24
Filing date: 1994-01-18
Publication date: 1997-08-13
Anticipated expiration: 2014-01-18
Also published as: GB9710392D0; GB9709783D0; GB2310077B; GB2310532A; GB2310313A; GB9709648D0; GB2310313B; GB2310532B

Abstract

A slab-shaped laser medium 1, excited by a lamp 2 and cooled by a flow of water 5, is supported at side surfaces 12 by support members 5. Deviations 52 from a smooth plane surface are formed at an inner surface of the support members 5, facing the slab, or at a back surface. The deviations, in the form of grooves or concavities, can be used to control the temperature distribution of the laser medium. They may provide a coolant path, e.g. for a flow of water. The distribution of pitch, area and/or depth of the deviations can be varied in the longitudinal and/or transverse direction of the laser medium 1.

Description

SOLID STATE LASER APPARATUS The present invention relates to enhancement of beam quality, oscillation efficiency, and reliability of a slab solid state laser apparatus, and to enhancement of a performance of a laser machining apparatus by using the slab solid state laser apparatus.

Figs. 43 and +4 show a solid state laser apparatus including an exciting system and a cooling system for a conventional laser medium disclosed in, for example, Japanese Patent Application No. 64-84680 in addition to a conventional solid state laser apparatus disclosed in, for example, Japanese Patent Application Laid-Open No.

63-188980.

In Figs. 43 and 44, reference numeral 1 means a slab solid state laser medium (hereinafter referred to as slab) including a pair of opposing smooth surfaces 11, a pair of side surfaces 12, and a pair of end surfaces 13 serving as an entrance surface and an exit surface for a laser beam. The slab is made of, for example, Nd:YAG (Yttrium Aluminum Garnet) obtained by doping Nd.

Reference numeral 5 means a supporter disposed on the slab side surface 12, 2 means a lamp to perform light excitation of the slab 1, and 21 is the excitation light.

Reference numeral 7 means a frame integrally containing the slab 1 and the supporter 5, and an opening portion 711 is provided in tne frame 7 to extend over substantially an entire surface of the smooth surface 11 of the slab as shown in Fig. 45. Reference numeral 70 means a sealant to seal water 41 serving as a coolant for the slab, and the sealant 70 extends over an entirely peripheral length of a plane formed by the slab surface (the smooth surface) 11 and the supporters 5 disposed on the side surface as shown in Fig. 46. Reference numeral 3 means a condenser to condense the excitation light for irradiation of the slab 1, and 81 and 82 are housings containing the condensers 3. Reference numeral 40 means a partition plate to form a flow path 4 of the slab cooling water 41, and the partition plate 40 is transparent with respect to the excitation light.

A description will now be given of the operation.

The slab 1 absorbs the excitation light 21 emitted from the lamp 2 to form inverted population. Energy of the inverted. population is derived externally to the medium as a laser beam 100 which is propagated between the pair of opposing smooth surfaces 11 of the slab in a zigzag fashion while repeating internally total reflection. However, 50 % or more excitation light energy absorbed by the slab becomes thermal energy in the slab, and finally flows out of the slab into the coolant 41 which is filled to contact the opposing smooth surfaces 11 of the slab. At this time, as shown in Fig.

47, there are generated the square temperature distribution having a hot center portion, and the square refractive index distribution along with the square temperature distribution in a thickness direction of the slab. The laser beam 100 in the slab, however, follows a zigzag optical path so that an effect of the square refractive index distribution can be canceled, and no laser beam is distorted. The coolant 41 is sealed by the seal ants 70 on the opposing smooth surfaces 11 of the slab and the supporters 5 disposed on the side surfaces so as not to be externally leaked. The sealant 70 also serves as a supporter of the slab 1 to the frame 7.

In an ideal condition of slab laser, a laser medium can be uniformly excited in a width direction, and heat can also be uniformly generated in the width direction.

Further, the slab can uniformly be cooled from only the slab surfaces (the opposing smooth surfaces) 11, onedimensional square temperature distribution can be established in the thickness direction, and a uniform temperature distribution can be established in the width direction. For purpose of the ideal condition, the condenser 3 is employed such that the slab 1 can be irradiated with the most uniform and the most efficient excitation light 21 possible. For cooling, the coolant 41 uniformly flows on the slab surface 11, and the supporters 5 are adhered on the side surfaces 12 and are made of glass (having thermal conductivity K of 0.012 W/cm2deg), fluorocarbon resin (having thermal conductivity K of 0.0025 W/cm2deg), or siliconerubber (having thermal conductivity K of 0.0015 W/cm2deg) which has a higher heat insulation property than that of the laser medium (i.e., YAG having thermal conductivity K of 0.12 W/cm2deg).

A conventional laser oscillator is constructed as set forth above. There are problems in that heat insulating materials 5 on the slab side surfaces 12 and adhesives absorb the excitation light to generate heat, and generate a temperature distribution having hot side surfaces in a width direction and a concave lens-like optical distortion along with the hot temperature distribution on the side surface as shown in Fig. 48, resulting in degradation of beam quality and laser output. Further, there is another problem in that the beam quality varies according to an output level since the optical distortion depends upon excitation intensity.

In case reflectance of the supporter 5 with respect to the excitation light 21 is low, the excitation light 21 passes from the slab side surfaces 12 to the supporters 5 as shown in Fig. 49. Hence, there are other drawbacks in that a sufficient oscillation effect can not be provided, and uniform excitation can not be achieved due to degraded excitation intensity in the vicinity of the side surface.

When the slab 1 and the supporters 5 disposed on side surfaces thereof are contained in the frame 7, pressure caused by O-rings 70 in upper and lower surfaces apply force in a direction 510 to separate the slab 1 from the supporters 5 as shown in Figs. 50, 51 Consequently, the coolant 41 can not be sufficiently sealed due to reduced adhesive properties between the slab side surfaces 12 and the supporters 5 so that water leakage occurs on the slab end surface 13. Thus, there are serious problems in that a beam may be cut away, and contamination may occur on the beam entrance/exit end surface 13 which is optically polished.

Further, in case the slab is strongly excited, mechanical deformation is generated in the vicinity of the slab side surfaces and in the vicinity of the entrance/exit end as shown in Figs. 52, 53. As a result, there are problems in that the water leakage may occur due to reduced water-tightness between the slab side surfaces 12 and the supporters 5, the optical distortion may occur due to stress concentration 125 since the supporters 5 can contact the slab 1 with a pin point contact, and the slab 1 may be damaged if the worst happens.

Alternatively, substances having high reflectance may be employed as the supporter 5 in order to provide more enhanced oscillation efficiency. Most substances of this kind, however, have extremely poor adhesive properties, and it is typically difficult to provide compatibility of the heat insulating properties with the water-tightness for the slab side surface 12 even if the substances are used.

It would therefore be desirable to be able to provide a compact solid state laser apparatus at a lower cost, having higher efficiency, excellent beam quality and output stability, and higher reliability, and to provide a laser machining apparatus using the solid state laser apparatus.

SUMMARY OF THE INVENTION The present invention provides a solid state laser apparatus in which a so-called slab laser medium is employed, a pair of supporters are disposed on the right and left sides of the laser medium, and irregularity is provided in the supporter at an inner surface opposed to a side surface of the laser medium or at a back surface.

Thus an irregular construction is provided in the supporter at the surface opposed to the laser medium or at the back surface, and a concave portion may contain substances such as coolant (for example, water) having low absorbance, low heat generation and a sufficient cooling effect. It is thereby possible to optimize a thermal boundary condition of a slab side surface, and prevent temperature distributions from occurring in a slab width direction and in a longitudinal direction and optical distortion from occurring along with the temperature distribution.

A groove may be provided in an inner surface of the supporter to extend in a thickness direction of the laser medium so as to form the irregularity.

The groove may contain substances such as coolant (for example, water) having low absorbance, low heat generation, and a sufficient cooling effect. It is thereby possible to optimize a thermal boundary condition of a slab side surface, and prevent temperature distributions from occurring in a slab width direction and in a longitudinal direction and prevent optical distortion from occurring along with the temperature distribution.

Distributions in the slab thickness direction or the longitudinal direction may be provided for all or any one of the area, the pitch, and the depth of the irregularity of the supporter. Such distributions provide the optimal thermal boundary condition at any positions of a slab side surface in the thickness and the longitudinal directions. It is thereby possible to prevent temperature distributions from occurring in a slab width direction and in a longitudinal direction and prevent optical distortion from occurring along with the temperature distribution.

If the laser medium is cooled by coolant filled to contact each smooth surface, a pressure difference may be provided between the coolants on the upper and lower sides of the laser medium so as to generate a flow of the coolant in a concave portion in the inner surface of the supporter.

It is thereby possible to optimize a cooling condition on a contact interface between a slab side surface and the supporter, and prevent temperature distributions from occurring in a slab width direction and in a longitudinal direction and prevent optical distortion from occurring along with the temperature distribution.

An irregularity in the inner surface of the supporter may be formed by a groove extending diagonally with respect to a thickness direction of the laser medium. It is thereby possible to optimize a cooling condition on a contact interface between a slab side surface and the supporter, and prevent temperature distributions from occurring in a slab width direction and in a longitudinal direction and prevent optical distortion from occurring along with the temperature distribution.

Preferably, the supporter is made of the material having the high reflectance to the excitation light. It is thereby possible to perform highly efficient excitation, prevent reduction of excitation intensity in the vicinity of a slab side surface, and reduce generation of optical distortion.

The supporter may be contacted with a slab with pressure through an elastic body so that mechanical deformation of the slab and the supporter can be absorbed, and local stress concentration on a slab side surface can be relaxed so as to reduce stress deformation. In addition, it is possible to enhance adhesive properties between the slab side surface and the supporter so as to further improve water-tightness, and further stabilize a thermal boundary condition of the slab side surface so as to stabilize an optical characteristic of the slab medium.

A laser beam may be extracted by a stable resonator. The stable resonator can generate a laser beam having less distortion from a laser medium whose optical distortion is reduced.

A laser beam may be extracted from an anisotropic resonator serving as a stable resonator in a thickness direction of the laser medium and an unstable resonator in a width direction. The anisotropic resonator can generate a laser beam having less distortion, and excellent isotropy in a sectional form from the laser medium whose optical distortion is reduced.

A laser beam may be extracted by an anisotropic resonator serving as a stable resonator in a thickness direction of the laser medium and a single side negative branch unstable resonator in a width direction.

Laser beams emitted from different laser apparatus may be amplified by the laser apparatus according to the invention.

A laser beam is oscillated or amplified by an optical path folded in a width direction of the laser medium. Such an optical path can provide an equivalent medium section having less distortion and excellent isotropy in a sectional form from the laser medium whose optical distortion is reduced.

Laser machining may be performed by condensing a laser beam generated from the solid state laser apparatus by a condensing optical system As a result, the laser beam generated from the laser medium whose optical distortion is reduced has less distortion and excellent isotropy in a sectional form, and generates a small spot diameter and a deep depth of focus with excellent stability at a condensing position.

Laser machining may be performed by introducing the laser beam generated from the solid state laser apparatus through an optical fiber. Therefore, the laser beam generated from the laser medium whose optical distortion is reduced has less distortion and excellent isotropy in a sectional form, and generates a small spot diameter and a deep depth of focus with excellent stability in condensation to a fiber entrance end surface. As a result, it is possible to perform stable and highly efficient connection of the laser beam to the fiber and maintain high beam quality even after fiber transmission.

The invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawing. It is to be expressly understood, however, that the drawings are for purpose of illustration only and are not intended as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a front sectional view showing one embodiment of a laser apparatus according to the present invention; Fig. 2 is a side sectional view; Fig. 3 is a perspective view showing a configuration of a laser medium and supporters; Fig. 4 is an enlarged view showing the configuration of the supporter; Figs. 5A and B are diagrams showing an optical distortion distribution in a laser medium width direction; Figs. 6A and B are diagrams showing a configuration of a resonator used with the laser apparatus; Fig. 7 is a diagram showing an output characteristic of the laser apparatus; Fig. 8 is a perspective view showing another configuration of supporters; Fig. 9 is an enlarged section showing another configuration of a supporter; Fig. 10 is an enlarged perspective view showing another configuration of a supporter; Fig. 11 is an enlarged perspective view showing another configuration of a supporter; Fig. 12 is a front sectional view showing another embodiment of a laser apparatus according to the present invention; Fig. 13 is a sectional view illustrating a temperature distribution of the laser apparatus taken along the thickness and longitudinal directions of the laser medium; Fig. 14 is a perspective view illustrating a temperature distribution of the laser apparatus in a width direction of the laser medium; Fig. 15 is a top view showing a configuration of supporters of the laser apparatus; Fig. 16 is a top view showing another configuration of supporters; Fig. 17 is a top view showing another configuration of supporters; Figs. 1 8a to c are views taken along the thickness-width direction of the laser medium, illustrating temperature distributions of the laser apparatus; Fig. 19 is a front section view showing another configuration of a supporter; Fig. 20 is a front sectional view showing another configuration of a supporter; Fig. 21 is a perspective view showing another configuration of a supporter; Fig. 22 is a perspective view showing another configuration of a supporter; Fig. 23 is a perspective view showing another configuration of a supporter; Fig. 24 is a view showing a configuration of cooling means of the laser apparatus; Fig. 25 is a perspective view showing supporters and a laser medium in another embodiment of a laser apparatus according to the present invention; Fig. 26 is an enlarged perspective view showing the supporter; Figs. 27 to 29 are views showing an excitation distribution and a temperature distribution in a width direction of a laser medium of a laser apparatus; Fig. 30 is a top view of anotha embodiment of a laser apparatus according to the present invention; Fig. 31 is a sectional view on line A-A' in Fig. 30; Fig. 32 is a section view on line B-B' in Fig. 30 laser apparatus according to the eighteenth aspect of the present invention; Fig. 33 is a top view of another embodiment of a laser apparatus according to the present invention; Fig. 34 is a sectional view on line A-A' in Fig. 33; laser apparatus according to the fifteenth aspect of the present invention; Fig. 35 is a sectional view on line B-B' in Fig. 33; Fig. 36 shows a top view and a side view illustrating a resonator applied to a laser apparatus; Fig. 37 is a top view and a side view illustrating another resonator applied to a laser apparatus; Figs. 38A and B show a top view and a side view of a resonator and an amplifier applied to a laser apparatus; Figs. 39A and B show a top view and a side view of another resonator applied to a laser apparatus; Figs. 40A and B show a top view and a side view of another resonator and amplifier applied to a laser apparatus; Fig. 41 is a side view showing one embodiment of a laser machining apparatus; Fig. 42 is a side view showing another embodiment of a laser machining apparatus; Fig. 43 is a front sectional view showing a conventional laser apparatus; Fig. 44 is a side sectional view showing the conventional laser apparatus; Fig. 45 is a top view showing a laser medium, supporters, and a frame containing the laser medium and the supports of the conventional laser apparatus; Fig. 46 is a top view showing the laser medium and the supports of the conventional laser apparatus; Fig. 47 is a view showing a temperature distribution in a thickness direction of a laser medium, a zigzag optical path, and an equivalent optical path; Fig. 48 is a view a temperature distribution and a heat optical distortion in a width direction of the laser medium of the conventional laser apparatus; Fig. 49 is a view an excitation intensity distribution in a width direction of the laser medium of another conventional laser apparatus; Fig. 50 is a view showing force applied in a direction to separate the laser medium from the supporters of the conventional laser apparatus; Fig. 51 is a view showing water leakage on an end surface of the laser medium of the conventional laser apparatus; Fig. 52 is a view showing mechanical deformation at ends in a width direction of the laser medium of the conventional laser apparatus; and Fig. 53 is a view showing mechanical deformation at ends in a longitudinal direction of the laser medium of the conventional laser apparatus.

Preferred embodiments of laser apparatus will now be described in detail referring to the accompanying drawings.

Embodiment 1 Referring now to Figs. 1 to 7, a description will be given of one embodiment of a solid state laser apparatus according to the present invention. Fig. 1 is a front sectional view showing the embodiment, Fig. 2 is a side sectional view thereof, Fig. 3 is a perspective view of a laser medium and supporters, and Fig. 4 is a partially enlarged view of Fig. 3.

In Figs. 1 and 2, reference numeral 1 denotes a solid state laser medium (hereinafter referred to as slab) including a pair of upper and lower smooth surfaces 11 extending parallel to each other, a pair of side surfaces 12 extending vertically on the right and left sides, and a pair of end surfaces 13 serving as an entrance/exit surface for a laser beam.

Reference numeral 5 means a supporter disposed along the side surface 12 of the slab 1. Reference numeral 7 means a frame integrally containing the slab 1 and the supporters 5, and 70 is a sealant to seal water 41 serving as a coolant for the slab. The sealant 70 extends over an entirely peripheral portion of the slab 1 and the respective supporters 5 along a plane perpendicular to a longitudinal direction (i.e., back and forth directions) of the slab 1. Reference numeral 2 means a lamp for light excitation of the slab 1, and 21 is the excitation light. Reference numeral 3 means a condenser to condense the excitation light 21 for irradiation of the slab 1, and 8 is a housing to contain the condensers 3. Reference numeral 40 means a partition plate to form a flow path 4 of the slab cooling water 41, and the partition plate 40 is transparent with respect to the excitation light 21.

In the embodiment, a plurality of vertical grooves 52 are provided in the supporters 5 at inner surfaces 51 opposed to the side surfaces 12 of the slab 1 to extend in a thickness direction (a vertical direction) of the slab at predetermined pitches as shown in Figs. 3 and 4.

Thereby, the inner surface 51 has an irregular construction.

A description will now be given of the operation. A basic operation is identical with the operation of a conventional apparatus, and descriptions thereof are omitted. Thus, a description will now be given of the operation and a detailed embodiment of the supporters 5 having the vertical grooves 52 disposed on the slab side surfaces 12.

Problems in the conventional solid state laser apparatus are an increased temperature due to absorption of the excitation light 21 or heat generation in the supporter 5, and the side surfaces of the slab 1 having a hot temperature distribution in a width direction (i.e., in a lateral direction) along with the increased temperature. In the embodiment, the vertical cooling grooves 52 are provided in the slab facing/contacting surfaces 51 of the supporters 5 in order to overcome the problems. The water 41 serving the coolant for the slab 1 infiltrates into the vertical grooves 52 so that the interfaces 51 of the supporters can be cooled. It is thereby possible to reduce optical distortion by optimizing the temperature distribution in the width direction of the slab 1. In this case, since a substance infiltrating the grooves 52 is water, there is little absorption or heat generation of the excitation light 21, and a cooling effect more increases as a groove width 522 is more extended.

In actuality, for YAG slab having a thickness of 6 mm, a width of 25 mm, and an excitation length of 150 mm, RTM TeflonXresin (Spectralon) was employed as the supporter 5 to measure optical distortion (heat lens) in the slab width direction. As a result, in case electrical input for the excitation lamp was 30 kW with no groove, an intensive concave lens distribution was exhibited at side ends as shown by the curve c in Fig. 5. Further, in case the groove width 522 was set at 0.5 mm, and the pitch 521 was set at 1 mm, and a groove depth 523 was set at 0.2 mm, an intensive convex lens distribution was exhibited at side ends as shown by the curve a in Fig. 5.

Subsequently, the groove width 521 was varied while the pitch 521 and the depth 523 were left as they were.

Consequently, for the groove width of 0.1 mm and the pitch of 1 mm, it was possible to provide a condition having substantially no heat lens as shown by the curve b in Fig. 5.

In addition, oscillation experiments were performed under the respective conditions by using a stable resonator as shown in Fig. 6. Fig. 7 shows output characteristics for the respective conditions. While a laser output substantially proportionally increased to the electrical input of 30 kW under the optimized condition b, large output saturation was observed at the electrical input of 20 kW or later under conditions a and c having the optical distortion.

The embodiment is characterized by thermal boundary conditions of the slab side surface 12 which are optimized by only variation in the width 522 of the groove 52 provided in the supporter 5, an extremely simple construction, and the optimal condition which can invariably be found. Heat lens refracting power under the optimized condition is equal to 0.1 M or less for the electrical input of 30 kW and the laser output of 1 kW or more. Absolute value of the heat lens refracting power is smaller than heat lens refracting power of 2 m~l in a rod YAG, and has smaller electrical input dependency than that of the rod YAG.

The embodiment as shown in Figs. 1 and 2 has been discussed with reference to a case where, as the coolant infiltrating groove 52, the groove extends parallel to the slab thickness direction. However, the same effect can be provided by grooves extending parallel to the longitudinal direction of the slab as shown in Figs. 8 and 9, or by finely irregular constructions as shown in Figs. 10 and 11.

Embodiment 2 Referring now to Figs. 12 to 15, a description will be given of one embodiment according to the present invention.

In a slab laser, a rod-like lamp 2 and a rod-like condenser 3 are employed so as to provide the most uniform excitation/heat generation possible in a longitudinal direction as well as a width direction. In actuality, excitation intensity, however, is more reduced at ends of an excitation length than would be in the vicinity of a longitudinal intermediate portion, resulting in a temperature distribution as shown in Fig.

13. The heat generation on slab facing surfaces 51 of supporters 5 is more reduced toward the ends.

Accordingly, the ends are too cooled under the same cooling condition as that at the intermediate portion so that the optical distortion in the width direction exhibits a concave lens distribution at the longitudinal ends as shown in Fig. 14. Hence, in the embodiment, groove widths 522 have more thin forms in a direction closer to the longitudinal ends of the slab as shown in Fig. 15 so as to reduce a cooling effect, and minimize the optical distortion even in the vicinity of the ends.

As set forth above, according to the embodiment, it is possible to provide the optimal thermal boundary condition at any desired position in the longitudinal direction the slab side surfaces 12 as well as in the lateral direction of the slab 1 so as to provide more uniform and higher quality laser beam.

In the embodiment, the cooling condition is varied by reducing only the width 522 while keeping the groove depth 523 and the pitch 521 constant. However, it is also possible to vary the cooling condition by varying the pitch and the groove depth as shown in Figs. 16 and 17.

Further, the embodiment has been described with reference to a case where there is the intensive excitation intensity at the longitudinally intermediate portion. However, it must be noted that the optical distortion may be minimized by adjusting the pitch, the width, and the depth of the groove at the respective longitudinal positions even if, for example, the intensive excitation intensity is generated at the longitudinal ends.

Embodiment 3 Referring now to Figs. 18 to 20, a description will be given of another embodiment according to the present invention.

The embodiments 1 and 2 have been described with reference to a constant thermal boundary condition (a cooling condition) of slab side surfaces 12 in a thickness direction. In the embodiment, a distribution is generated in the thermal boundary condition in the thickness direction. A slab 1 is cooled through both ends (smooth surfaces) 11 thereof so that the slab 1 exhibits the square temperature distribution whose center portion in the thickness direction is hot. In case the slab side surfaces 12 are completely insulated to cause no heat generation, the temperature distribution should become uniform in a width direction as shown in Fig.

18(a) (at an upper stage). In actuality, however, temperature distributions as shown in Figs. 18(b) (at a middle stage) and 18(c) (at a lower stage) are generated due to thermal conduction and heat generation of a supporter.

Hence, in the embodiment, a distribution is provided for a groove configuration in the thickness direction as shown in Figs. 19 and 20 such that a slab facing surface 51 of the supporter 5 can have the same square temperature distribution in the thickness direction as that under an ideal condition for the slab. It is thereby possible, even in material having the heat generation and the thermal conduction to some extent, to provide the same temperature distribution as that of a completely insulated medium generating no heat. Further, it is possible to enhance quality of a laser beam by optimizing the thermal boundary condition in the slab thickness direction.

Embodiment 4 Referring now to Figs. 21 and 22, a description will be given of another embodiment according to the present invention.

In the embodiment, in order to provide the optimal thermal boundary condition at any desired positions in longitudinal and thickness directions of a slab side surface 12, grooves 52 are provided in a supporter 5 in both the longitudinal and thickness directions as shown in Fi

Embodiment 5 Referring now to Figs. 23 and 24, a description will be given of one embodiment according to the present invention.

In the embodiment 1, water 41 serving as coolant simply infiltrates into vertical grooves 52 in a supporter 5, and a cooling effect can mainly be provided by only thermal conduction inherent in the water. In contrast with this, in this embodiment a slight difference AP - iP1 - P21 is given to water pressure in a cooling water path 4 in both slab surfaces as shown in Fig. 23. This pressure difference generates a flow 452 of the cooling water 41 in the vertical grooves 52 of the supporter so as to enhance a cooling effect of an interface between the supporter 5 and a slab side surface 12.

The invention may include the following method for giving the pressure difference to the cooling water 41 on the slab surface. As shown in Fig. 24, flow controlling valves 401, 402, 403, and 404 are provided at an inlet and an outlet for the water in the respective slab cooling water paths, and these valves are adjusted to give the difference AP - IP1 - P2 to the water pressure P1 and P2 on the slab surface. At this time, the adjustment may be made so as to provide the same pressure differences AP1 and AP2 at the inlet and the outlet of the respective water paths, and generate no difference in a flow rate of the cooling water on both the surfaces of the slab. As a result, both the surface of the slab can have the same cooling ability to cause no problem.

Further, the valves 401, 402, 403, and 404 may be adjusted to vary the water pressure difference JP1 - P2 between the slab cooling water paths, and control the flow rate of the cooling water flowing in the vertical grooves 52 in the supporter so as to vary a cooling condition on the slab side surface. As a result, it is possible to control a temperature distribution in a slab width direction, and optical distortion generated along with the temperature distribution.

Embodiment 6 Referring now to Figs. 25 and 26, a description will be given of one embodiment according to the present invention.

In th;s embodiment external valves adjust pressure in cooling water paths in a slab surface in order to cause a flow 452 of coolant in vertical grooves 52 of supporters. However, as shown in Figs. 25 and 26, the cooling grooves 52 may be provided in the supporters 5 to extend diagonally to a slab thickness direction, and cooling water 41 may flow on the slab surface in a slab longitudinal direction. Consequently, there is generated a pressure difference between both ends 520 of the cooling groove so that the flow 452 of the coolant can be caused without pressure difference between the cooling water paths of the slab surface. As an oblique angle between the cooling groove 52 and the slab thickness direction becomes larger, the pressure difference between both the ends of the cooling groove becomes larger.

Embodiment 7 Referring now to Figs. 27-29 a description will be given of one embodiment according to the present invention.

Light 211 is emitted to slab facing surfaces 51 of supporters 5, and once passes through a laser medium 1 serving as an absorber. The light 211 contains a considerable spectral component which is effective in excitation. Therefore, if the excitation light 211 emitted to the supporter 5 is returned into the slab medium 1 again by providing the supporter surfaces 51 having high reflectance as shown in Fig. 27, it is possible to provide higher efficient excitation.

Specially, in case there are provided a proximately coupling condenser 3, and diffuse reflectance type of supporters made of, for example, Spectralon or macerite to have high reflectance, light intensity in the condenser is enhanced, and slight reflection loss on the supporter side surface 51 has a significant effect on excitation efficiency. Further, low reflectance of the supporter surface 51 reduces the excitation efficiency, and reduces excitation intensity in the vicinity of slab side surfaces, resulting in generation of an excitation distribution as shown by the broken line in Fig. 28.

Concurrently, there are generated a temperature distribution and optical distortion in a width direction as shown by the broken line in Fig. 29.

It is thereforenecessary to reduce the generation of the optical distortion-by providing the highest reflectance of the supporter surface 51 possible, and the most uniform excitation distribution possible even at width directional ends as shown by the solid line in Fig. 25.

Alternatively, in case the reflectance of the supporter 5 decreases due to absorbance of light rather than transmission of the light, there are problems in that an increase in excitation input increases heat generation of the supporter itself, and the optical distortion becomes worse as the supporter becomes more hot. Thus, the supporter 5 requires optical characteristics of less absorption of the excitation light 21 (having a wavelength in the range of 200 to 1000 nm), and higher reflectance. Suitable materials for the supporter 5 may include Spectralon, macerite, gilt plate glass or the like.

Embodiment 8 Referring now to Figs. 30 to 32, a description will be given of one embodiment according to the present invention.

In a conventional solid state laser apparatus, a supporter 5 is adhered to a slab side surface 12 by silicon rubber adhesives, adhesive tapes or the like.

When a slab 1 and the supporters 5 disposed on side surfaces thereof are integrally contained in the frame 7, pressure caused by an O-ring 70 serving as sealant for coolant apply force 510 in a direction to separate the slab 1 from the supporters (insulator) 5.

Consequently, a coolant 41 can not be sufficiently sealed due to reduced adhesive properties between the slab side surfaces 12 and the supporters 5 so that water leakage occurs on a slab end surface 13.

Thus, there are serious problems in that a beam may be cut away, and contamination may occur on the entrance/exit end surface 13 for the beam which is optically polished.

Hence, in this embodiment of the invention, screw holes are provided in a slab containing frame 7 at a position 710 opposed to the supporter to extend substantially perpendicular to a supporter back surface 53 as shown in Figs. 30 and 32. Further, a distal end of a screw (a screw member) 715 fitted into the screw hole pushes the back surface 53 of the supporter 5 to contact the supporter 5 with the slab side surface 12 with pressure.

In this construction, it is possible to adjust contact pressure by externally rotating the screw 715 even after the frame 7 contains the slab 1 and is attached to a condenser and a lamp housing 8. It is also possible to adjust the contact pressure so as to minimize mechanical stress and optical distortion, and prevent water leakage from a joint between the supporter 5 and the slab side surface 12.

grooves52 (an irregular construction) described in, for example, the embodiment 1 are provided in an inner surface of the supporter 5.

In this case, the supporter 5 contacting the side surface 12 of the slab 1 with pressure can further stabilize an effect obtained by providing the supporter inner surface with an irregular construction, i.e. an effect to optimize a thermal boundary condition between laser medium side surfaces and the supporter.

Further, this contact with pressure can enhance watertightness. As a result, it is possible to improve reliability, and realize a laser operation having more excellent stability in beam quality.

on the mod;f;ed embodiment shown in Figs. 33 to 35, adhesive properties are specially important in vicinities 511 of contact positions with an O-ring 70 land transparent silicone rubbers 54 are disposed only in the vicinities 511 of the contact positions; no transparent silicone rubber is disposed on excitation area corresponding portions 512. Though water-tightness at seal positions of the O-ring 70 is very important in view of prevention of water leakage, there may be provided the adhesive properties to stabilize a thermal boundary condition at portions rather than the seal positions. Thus, no problem occurs even if water 41 serving as coolant infiltrates into an interface between the supporter 5 and the slab side surface 12.

In Fig 36 a hybrid resonator serving as a symmetrically positive branch unstable resonator in a width direction and as a stable resonator in a thickness direction is applied to a slab laser medium 1 having little optical distortion described in the embodiments 1 to 8. The resonator includes a cylindrical concave surface mirror 61 having curvature only in a slab width direction, a cylindrical convex surface mirror 62, and a convex lens 63 having refracting power only in the slab thickness direction. Reflection reducing coating is applied to both ends 622 of the cylindrical convex mirror 62, and a laser beam 100 is outputted from both the ends 622.

Since the slab laser medium 1 is provided with a rectangular section having a high aspect ratio, laser oscillation by using a typical stable resonator causes a higher-order transverse mode in the range of tens order to hundreds order in a width direction to provide a larger opening, and causes a divergent angle of tens millimeters rad. It is thereby impossible to provide a high focusing performance. On the other hand, the laser oscillation causes a transverse mode of about tenth order in a thickness direction to provide a smaller opening, and causes a divergent angle of several millimeters rad, resulting in another problem of anisotropy in the focusing performance.

Hence, in the embodiment, there is formed a onedimensional symmetrically positive branch unstable resonator in the width direction to provide the larger opening so as to provide a beam having a higher focusing performance which is several times diffraction limit.

Further, there is formed a lower-order stable resonator in the thickness direction so as to reduce the anisotropy in the focusing performance of the beam. It is generally possible to provide a beam having an excellent focusing performance even in the larger opening by using the unstable resonator. However, the unstable resonator can provide lower tolerance for optical distortion in the resonator such as heat lens than that of the higher-order stable resonator. In the embodiment, constructions as described in the embodiments 1 to 8 are employed to reduce the optical distortion in a slab width direction in case the unstable resonator is employed. It is thereby possible to realize unstable type oscillation which becomes stable even in a high output area, and provide a beam having a higher focusing performance and excellent isotropy.

In Fig.37 cylindrical concave surface mirrors 61 and 61 having curvature in a slab width direction are provided to form a single side negative branch unstable resonator. In a one-dimensional symmetrically unstable resonator described in the embodiment 24, beams are separately outputted from both ends in a slab width direction. On the other hand, in the single side negative branch unstable resonator, a solid type beam 100 is outputted from a mirror cut-out portion 622 on the single side in the slab width direction, resulting in a more improved focusing performance. Further, the negative branch unstable resonator can provide higher tolerance for optical distortion than that of the positive unstable resonator described above, thereby realizing a more stable operation.

In Figs38 Aand B , a slab laser medium 1 is employed as an amplifier of a laser beam. In the slab laser medium 1, optical distortion is reduced by constructions described in the embodiments 1 to 8. A laser apparatus serving as an oscillator shown on the left side in Fig is an oscillator including a stable resonator shown in Fig. 6. Another laser apparatus serving as the amplifier shown on the right side is combined with no resonator. The laser apparatus on the right side amplifies a beam 100 outputted from the oscillator on the left side as an input beam so as to generate a high power output beam 1000.

In the laser beam amplifying operation, in case the amplifier has optical distortion with an aberration component while the input beam 100 has a high focusing performance, the resultant output beam is affected by the optical distortion so that the focusing performance is degraded. In the embodiment, the optical distortion of the slab medium serving as the amplifying medium is reduced by methods discussed in the above embodiments.

It is thereby possible to amplify the input beam without degradation of the focusing performance of the input beam, and provide the high power output beam.

In Figs.39A -d b , optical distortion of a slab laser medium 1 is reduced by constructions discussed in the above embodiments 1 to 8, and a rectangular prism 69 is used together with the slab laser medium 1 to form a stable resonator having an optical path which is folded by the rectangular prism 69 in a width direction. By folding the optical path, it is possible to compress an equivalent section in the width direction of the medium 1, and provide a laser beam which is excellent in a focusing performance and isotropy even in a typical stable oscillator which is rotationally symmetric with respect to the optical path formed by a spherical total reflection mirror 61 and a spherical partial reflection mirror 62. In this case, in the folded optical path, an effect due to the optical distortion is superimposed proportional to the number of folding. Accordingly, in order to realize a stable laser operation, there is no other choice to considerably reduce the optical distortion of the laser medium 1 as described in the embodiment.

In Figs. A and B a laser beam 100 having an excellent focusing performance and excellent isotropy is outputted from a slab laser oscillator including a hybrid resonator disclosed in Figs.39A and B. B-BThen, the laser beam 100 is amplified by a slab laser apparatus having the same folded optical path as that described in the embodiment 27 so as to provide a high power beam 1000 which is excellent in the focusing performance and isotropy. The embodiment is characterized in that the input beam 100 and an amplifying medium have equivalent sections which are matched in a width direction as well as in a slab thickness direction, and highly efficient amplification can be made.

In Flg. 41 a laser beam 100 is generated from a solid state laser apparatus whose optical distortion is reduced by constructions described in the above embodiments 1 to 8. The laser beam 100 is transferred in the atmosphere, and is condensed by a condensing lens 801 after a direction of the laser beam 100 is changed by a reflection mirror 601. The condensed laser beam is used for machining a work piece 800.

In the embodiment, the laser beam to be condensed is generated from the slab laser medium 1 whose optical distortion is reduced, and the laser beam is excellent in stability and has a high focusing performance.

Therefore, the beam at a condensing position can have an extremely small spot diameter and a deep depth of focus so as to realize high quality laser machining for the work piece in high efficiency. In particular, the focusing performance of the laser beam in the embodiment is constant irrespective of output. This eliminates the need for adjustment of a condensing lens position for each output level which is conventionally required, and considerably reduces a time required for maintenance.

The embodiment has been described with reference to the solid state laser apparatus employing the laser oscillator including a stable resonator described in the embodiment 1. However, it is possible to provide higher performance machining by using a solid state laser apparatus described in another embodiment which is more excellent in a beam focusing performance.

In Fig. 42 a laser beam 100 is generated from a solid state laser apparatus whose optical distortion is reduced by constructions described in the above embodiments 1 to 23. The laser beam 100 enters an end 6021 of an optical fiber 602 through a condensing lens 603, and is transferred through the fiber.

Thereafter, the beam exits an exit end 6022, and is condensed by condensing lens 604 and 801. The condensed laser beam is used for machining a work piece 800.

In the embodiment, the laser beam to be condensed is generated from the slab laser medium 1 whose optical distortion is reduced, and is excellent in stability and has a high focusing performance, and the laser beam enters the fiber end surface. Therefore, the beam at a condensing position of the fiber entrance end surface can have an extremely small spot diameter and a deep depth of focus so as to stably and efficiently perform connection of the beam to the fiber and maintain high beam quality even after fiber transmission. As set forth above, the laser beam even after being emitted from the fiber has the high focusing performance, the beam at the condensing position for laser machining has the extremely small spot diameter and the deep depth of focus, and high quality laser machining for the work piece can be realized in high efficiency. In particular, the focusing performance of the laser beam in the embodiment is constant irrespective of output. This eliminates the need for adjustment of a machining lens position for each output level which is conventionally required, and considerably reduces a time required for maintenance.

The embodiment has been described with reference to the solid state laser apparatus employing a laser oscillator including a stable resonator described in the embodiment 1. However, it is possible to provide higher performance machining by using a solid state laser apparatus described in another embodiment which is more excellent in a beam focusing performance.

Claims

Claims:

1. A solid state laser apparatus comprising: a laser medium having a rectangular plate form including upper and lower smooth surfaces extending substantially parallel to each other, opposed side surfaces extending substantially perpendicular to said smooth surfaces, and end surfaces for entrance/exit of a laser beam; a pair of supporters disposed on the opposed sides of said laser medium; a frame containing said supporters; a light source for exciting said laser medium; a condenser to condense excitation light from said light source for irradiation of said laser medium; and cooling means for cooling said laser medium via at least one of said smooth surfaces thereof; wherein irregularity, in the form of deviations from a smooth plane surface, is formed in a said supporter at an inner surface facing said laser medium or at a back surface.

2. A solid state laser apparatus according to claim 1, wherein a groove extending in a thickness direction of said laser medium is provided in said inner surface of said supporter to form said irregularity.

3. A solid state laser apparatus according to claim 1 or 2, having a given distribution of pitch, area, or depth of said irregularity in a longitudinal or transverse direction.

4. A solid state laser apparatus according to any preceding claim, wherein cooling of said laser medium is performed by coolant filled to contact its upper and lower surfaces, and a pressure difference is provided between said upper and lower surfaces of said laser medium so as to generate a flow of said coolant in a concave portion in an inner surface of said supporter.

5. A solid state laser apparatus according to any preceding claim, wherein irregularity in said inner surface of said supporter is formed by a groove extending obliquely to the thickness direction of said laser medium.

6. A solid state laser apparatus according to any preceding claim, wherein said supporter has high reflectance to excitation light.

7. A solid state laser apparatus substantially as described with reference to any of embodiments 1 to 8 herein.