KR20010081666A - Solid state laser system - Google Patents

Abstract

PURPOSE: A solid laser system is provided to emit uniformly an excited beam on a surface of a solid crystal by using a compound parabolic concentrator. CONSTITUTION: A stacked diode array has a multitude of diode for emitting an excited laser beam. The diodes are arranged as a wide plane shape. A compound parabolic concentrator concentrates the excited laser beam emitted from the stacked diode array. A laser crystal bar generates the laser beam excited by the concentrated laser beam emitted from the compound parabolic concentrator. The laser crystal bar is located at a predetermined distance from the compound parabolic concentrator. A fused quartz tube for cooling is installed around the laser crystal bar.

Description

Solid state laser system

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid state laser system, and more particularly, to a solid state laser system that uses a reflective parabolic concentrator (CPC) to excite the excitation beam of a stacked diode array.

In general, in the development of solid state lasers that excite using diode array beams, it is very important to effectively couple the excitation beams of high power diode arrays to solid state laser crystals. At this time, the method of exciting the laser crystal is divided into two methods, a seed excitation and a side excitation, in order to develop a solid laser of a high average power, a lateral excitation method is used. The lateral excitation method includes a circularly symmetric close coupling method and a coupling method using an optical fiber or an imaging system.

On the other hand, when a high power solid state laser is developed in a close coupling method in which a diode array excitation source is coupled to a laser crystal, a large number of low power linear diode arrays are required, but a diameter of about 5 mm is required due to the volume of the linear diode array itself. There is a limit to the number of diode arrays that can be approached with the laser deciding rod.

In addition, the coupling method using the optical fiber has the advantage of increasing the excitation laser power per unit volume in the laser crystal. However, the optical system for coupling the diode array beam to the optical fiber is complicated and the price is high. The loss of the excitation beam has a big disadvantage.

In addition, the coupling method using the non-imaging optical system has been actively developed since a high power multilayer diode array can be used as the excitation source, and the optical system is simpler than the coupling method using the close coupling method and the optical fiber. It can be used in a gentle region beyond the peak of the laser crystal absorption spectrum, and a stable high power laser beam can be obtained. The cusp-type reflector and the basic reflection type CPC are used as the non-imaging optical system.However, in the case of the CUSP type reflector, the heterogeneous distribution in the laser crystal of the excitation laser beam is a problem. There is a problem that it is difficult to uniformly cool the laser crystal because it is in direct contact with.

The present invention has been made to solve the above problems of the prior art, the object of the invention is to use a reflective strain focusing device (CPC) having a gap between the excitation beam of a high-power stacked diode array of several hundred watts (W) class or more The present invention provides a solid-state laser system capable of uniformly injecting an excitation beam to the surface of a solid crystal by transversing a rod-shaped solid laser crystal.

In addition, another object of the present invention is to ensure that the focusing device (CPC) has a structure of combined parabolic surfaces without contacting the laser crystal to facilitate uniform cooling in each direction of the laser crystal, and at the same time the isotropy of the oscillated solid laser beam. To provide a solid state laser system that can improve the.

1 is a view showing the concept of a diode-excited solid-state laser device using a reflective strain focusing device (CPC).

2 is a view showing the body of the laser head according to the present invention;

3 is a view showing design parameters of a reflective strain focusing device (CPC) with a gap between the laser crystal and the focusing device (CPC) in the present invention

4 is a view showing a change according to the receiving angle and the size of the gap of the cross section of the focusing apparatus (CPC) in the present invention;

5a and 5b are views showing the distribution of the excitation beam absorbed in the laser crystal according to the change in the receiving angle of the focusing device (CPC) in the present invention

6a and 6b are views showing the distribution of the excitation beam absorbed in the laser crystal according to the change in the receiving angle of the focusing device (CPC) in the present invention

<Description of Symbols for Main Parts of Drawings>

1: stacked diode array 2: reflective strain focusing device (CPC)

3: laser crystal rod 4: molten quartz tube for cooling

5: incident surface of focusing device 6: diode emitting surface

According to a first aspect of the present invention for achieving the above object, a multi-layer diode array in which a plurality of laser diodes for emitting a laser excitation beam is arranged in a wide planar form, and a laser beam emitted from the stacked diode array In a solid-state laser system comprising a compound parabolic concentrator (CPC) and a laser deciding rod that is laterally excited by a laser beam collected by the reflective focusing apparatus to emit a laser beam,

The laser crystal rods are spaced apart from the reflective surface of the reflective focusing apparatus (CPC) by a predetermined interval, and the molten quartz tube for cooling is provided around the laser crystal rods.

In this case, according to an additional feature of the present invention, the reflective focusing device (CPC) has an incidence surface thereof in contact with the emission surface of the stacked diode array, and a fast-axis divergence angle of the excitation beam of the stacked diode array is large. Direction is perpendicular to the longitudinal direction of the laser crystal rod, and the excitation beam of the multilayer diode array is configured to reflect the reflective surface of the reflective focusing apparatus (CPC) once and then enter the laser crystal rod.

In addition, in the molten quartz tube for cooling arranged around the laser crystal rod, a part of the cooling water flowing through the reflective focusing device (CPC) flows through the laser crystal rod to uniformly cool the laser crystal rod in each direction. For this purpose, it is preferable that a cooling water distributor having holes at uniform intervals in each direction is installed.

In addition, the reflective focusing apparatus (CPC) is preferably formed with a gold plating film or a gold plating and a coating film on the reflective surface in order to increase the reflectance.

In addition, the reflective focusing apparatus (CPC) has a cross section whose upper portion has a parabolic shape, and a lower portion having an involute shape on the surface of the laser crystal rod, and an arbitrarily given lower vertex is the laser. It is preferable to be spaced apart from the crystal rod by a predetermined interval.

In this case, the reflective focusing device (CPC) has a tangent on the surface of the laser crystal rod and the reflective focusing device (CPC) surface due to the boundary condition that the upper and lower portions must match at "θ = θ _i + π / 2". The distance ρ (θ) between the meetings is given by the following equation.

First, θ when,

,

On the other hand, θ when,

Where θ _i is The angle of incidence of the ambient light of the excitation beam, given by, is the linear distance between the surface of the laser crystal rod and the vertex C of the CPC.

In addition, the reflective focusing apparatus CPC may be designed by matching the reception angle θa with the incident angle of the ambient light of the excitation beam.

On the other hand, according to the second aspect of the present invention for achieving the above object, a multi-layer diode array in which a plurality of laser diodes for emitting a laser excitation beam is arranged in a wide planar shape, and the laser emitted from the stacked diode array A reflective parabolic concentrator (CPC) that collects the beams in one place, a laser deciding rod that is laterally excited by a laser beam collected by the reflective focusing apparatus, and emits a laser beam, and is provided around the laser deciding rod In the solid-state laser system comprising a cooling molten quartz tube for cooling the laser crystal rod,

The present invention provides a solid-state laser system including a lens disposed on an emission surface of the multilayer diode array and configured to be reflected by a reflective focusing apparatus after increasing the divergence angle of an excitation beam of a multilayer diode array having a small divergence angle.

The above objects and various advantages of the present invention will become more apparent from the preferred embodiments of the present invention described below with reference to the accompanying drawings by those skilled in the art.

Hereinafter, a preferred embodiment according to the present invention will be described in detail with reference to the accompanying drawings.

First, the present invention includes the design and fabrication technology of a reflective strain focusing device (CPC) and a solid state laser. The reflective strain focusing device (CPC) designed according to the present invention is large in terms of emitting a large planar diode array. A non-imaging optical excitation beam focusing device for transmitting isotropically radiated excitation light with a divergence angle to a solid laser crystal.

Unlike the conventional case, the reflective deformation focusing apparatus (CPC) has a parabolic structure in which the laser crystal and the focusing apparatus (CPC) are combined without contact.

In addition, in the present invention, the optimum shape of the reflective deformation focusing device (CPC) was designed and manufactured using a ray tracing code, and a solid state laser system using the reflective deformation focusing device (CPC) was proposed. By analyzing the excitation light absorption distribution of the proposed solid state laser system, the optimal design method of the solid state laser system was proposed.

In addition, in the present invention, in order to determine the optimal shape of the reflective deformation focusing device (CPC), it was determined by varying the distance between the accommodating angle of the focusing device (CPC) and the vertex of the laser crystal and the focusing device (CPC) By analyzing the excitation light absorption distribution and the absorption power in the laser crystal of the focusing device (CPC), the optimal design method of the solid state laser system using the focusing device (CPC) according to the required laser beam characteristics is presented.

On the other hand, Figure 1 is a view showing the concept of a diode-excited solid-state laser device using a reflective strain focusing device (CPC), Figure 2 is a view showing the body of the laser head according to the present invention.

Referring to FIG. 1, the solid state laser system using the reflective strain focusing apparatus (CPC) according to the present invention includes a multilayer diode array 1, a reflective strain focusing apparatus (CPC) 2, a laser deciding rod 3, The molten quartz tube 4 for cooling etc. is comprised.

At this time, the incident surface 5 of the reflective deformation focusing apparatus (CPC) 2 is in contact with the emitting surface 6 of the laser diode, and the direction of the fast-axis of the divergent diode array beam has a large divergence angle. Set perpendicular to the longitudinal direction of the laser deciding rod 3 so that the beam of the stacked diode array 1 reflects once on the reflecting surface of the strain focusing device (CPC) 2 and then enters the laser deciding rod 3. It is. The laser crystal rod 3 is separated from the reflective surface of the reflective deformation focusing apparatus (CPC) 2, and a cooling molten quartz tube 4 is provided around the laser crystal rod 3.

The main components of the laser head, such as the multilayer diode array 1, the reflective strain focusing device (CPC) 2, the laser crystal rod 3, the cooling molten quartz tube 4, and the like, are provided in the head frame shown in FIG. Supported by. At this time, the excitation diode array is attached to the front surface (7) of the frame, the cooling water is supplied and drained from the rear surface (8) of the laser head, and branched through the cooling water branch system (9) installed on the left and right sides. A part of the branched cooling water flows through the molten quartz tube 4, and uniform cooling of each direction of the laser crystal rod 3 is possible. In addition, the remaining cooling water cools the focusing apparatus (CPC) 2 which is a reflector.

3 is a view showing a design variable of the reflective strain focusing device (CPC) with a gap between the laser crystal and the focusing device (CPC) in the present invention.

Referring to FIG. 3, the cross-section of the reflective strain focusing apparatus (CPC) for effectively exciting the laser deciding rod (3 in FIG. 1) consists of two parts, and the upper part 10 connecting the points A and B is a parabola. The lower part 11 connecting points B and C is an involute of the surface of the laser crystal which absorbs light, and the distance (g) between the vertex of the arbitrarily given focusing device (CPC) and the laser crystal is given. It is designed so that the upper part and the lower part coincide naturally.

The excitation light focused by the strain focusing device (CPC) designed as described above satisfies the principle of edge-rays. That is, the ambient light 12 generated in the diode array is reflected once on the surface of the focusing device CPC and then incident to the tangential direction of the laser crystal surface, and the remaining light rays pass through the laser crystal. In this case, the stacked diode array beam incident on the surface of the laser crystal is uniformly incident on the surface of the laser crystal rod, and the excitation beam absorbed by the laser crystal rod is absorbed by the laser crystal rod by injecting a large part of the rays in a direction tangential to the surface of the laser crystal rod. Has a distribution that is not focused at the center of the crystal and has a relatively uniform distribution, which is advantageous for high-power laser fabrication.

As shown in FIG. 3, the equation representing the shape of the focusing apparatus CPC may be described by a coordinate system having an origin at the center of the laser deciding rod, and the parabola and the new improved portion are “θ = θ _i + π / Given the boundary conditions that must coincide at 2 ", the distance ρ (θ) between the tangent of the laser crystal rod surface and the converging device (CPC) surface is given by

First, θ When given by

,

Θ also When you have a value of

Where θ _i is Is the angle of incidence of the ambient light of the excitation beam, where g is the linear distance between the surface of the laser crystal rod and the vertex C of the CPC.

The shape of the reflective deformation focusing apparatus CPC is designed by matching the reception angle θa of the CPC shown in FIG. 3 with the incident angle of the ambient light of the various types of excitation beams, or mismatching the reception angle with the incident angle of the ambient light. Can be designed.

On the other hand, Figure 4 is a view showing a change in accordance with the receiving angle and the size of the gap of the cross section of the focusing device (CPC) in the present invention.

Referring to Figure 4, (A) shows the shape of the modified CPC appearing when the acceptance angle of the CPC is different. In this case, when the modified CPC is used as the reflector, the optimal angle of the reflector decreases as the incident angle of the ambient light increases, thus enabling efficient coupling of the excitation beam into the laser crystal rod.

Meanwhile, in order to efficiently cool the laser crystal rod, the width of the incident surface of the CPC reflector can be fixed and the gap g can be increased, and the shape change of the CPC is as shown in FIG. 4B. At this time, the volume of the modified CPC decreases as the gap increases.

In the above, the light rays at the surface of the CPC should be reflected by the law of reflection, and the reflectance of the surface is an important factor in determining the beam transmission efficiency. The surface of the CPC used may be sufficient as gold plating after the surface processing of the optical level, but in order to increase the laser efficiency through the increase of the reflectance, it can be manufactured to have a reflectance of 93% or more at the excitation laser wavelength by secondary gold coating.

On the other hand, by analyzing the distribution of the excitation beam in the laser crystal rod using the ray tracing code for the reflective strain CPC shown in Figure 4, by varying the receiving angle and the gap (g) according to the output and beam characteristics of the desired solid laser Optimal design of the CPC is possible.

5A and 5B are diagrams illustrating a distribution of an excitation beam absorbed in a laser crystal according to a change in a receiving angle of a focusing device (CPC) in the present invention.

5A and 5B, in order to determine the change in absorption excitation output in the laser crystal according to the change in the receiving angle of the reflective strain CPC, the absorption distribution is calculated for the lattice points obtained by dividing the laser crystal using the polar coordinate system. Calculated. As shown by the solid line in FIG. 5A, the absorption distribution of the 25 ° CPC has a low distribution due to the large volume of the CPC and many rays passing through the laser crystal relatively, but the distribution of the center and the edge of the laser crystal is relatively low. Due to the low ratio, the effect of the heat-induced lens is small. In addition, the absorption distribution for a large acceptance angle of 55 ° is more concentrated in the center of the laser crystal rod as shown in (d) of FIG. 5b, which is advantageous for fabricating a laser having high laser excitation efficiency of low power.

6A and 6B are diagrams illustrating a distribution of an excitation beam absorbed in a laser crystal according to a change in a receiving angle of a focusing device (CPC) in the present invention.

6A and 6B, the change in absorption excitation output in the laser crystal according to the change in the gap g of the reflective strain CPC was calculated with respect to the fixed incident surface size. As shown in (a) of FIG. 6B, the absorption distribution has a more uniform distribution for a small gap. Therefore, it is necessary to minimize the gap when developing a high power laser. However, even if the gap is large to install a cooling molten quartz tube (4 in FIG. 1) around the laser crystal rod for effective cooling of the laser crystal, the loss due to the increase in the efficiency of the loss due to the volume of the CPC is reduced. Due to the increase, there is no significant loss in the absorbed excitation output as shown in FIG. 6A.

While the invention has been shown and described with respect to particular embodiments, it will be apparent to those skilled in the art that various modifications and changes can be made without departing from the spirit and scope of the invention as indicated by the appended claims. Anyone can grow up easily.

For example, the present invention has a form in which a rapid divergence direction of a stacked diode array having a large divergence angle is placed in the longitudinal axis direction of a laser crystal, and the output of the diode array is coupled to the laser crystal. When combining this small slow-axis in the longitudinal direction of the laser crystal, a lens is placed between the diode array and the entrance of the reflective focusing device (CPC) to increase the divergence angle of the diode excitation beam and then to the focusing device (CPC). ) May be used to bind to the laser crystals.

As described above, the solid-state laser system of the present invention has the advantage of uniformly inciting the excitation light of the diode array to the surface of the solid crystal, and because it is non-contact, it is possible to install a molten quartz tube for cooling around the solid laser crystal. Therefore, uniform cooling in each direction of the laser crystal is easy, and the cooling of the focusing device (CPC) and the laser crystal can be performed, thereby improving the isotropy of the oscillated solid laser beam.

In addition, the excitation incident on the laser crystal is compared to the design method in which the focusing device (CPC) is designed assuming a large diameter of the laser crystal, and then a space is separated between the focusing device (CPC) and the laser crystal using a small diameter laser crystal. The beam loss can be reduced, and the uniformity of the excitation beam distributed in the laser crystal can be improved compared to the cusp-shaped focusing body.

In addition, the optical mechanical design of the laser system is facilitated by changing the shape of the focusing device (CPC) for the emission surface and divergence angle of the excitation beam of a given diode array by varying the receiving angle and clearance of the modified reflective focusing device (CPC). It is possible to design and manufacture a solid laser system having a simple structure.

In addition, the stacked diode array having a 20W class diode array laminated and then linearly coupled again can be effectively coupled to the laser crystal, thereby increasing the output of the solid state laser.

Claims (9)

A multilayer diode array in which a plurality of laser diodes emitting laser excitation beams are arranged in a wide planar shape, a reflective parabolic concentrator (CPC) for collecting the laser beams emitted from the multilayer diode array into one place; In the solid-state laser system comprising a laser deciding rod which is transversely excited by the laser beam collected by the reflective focusing device to emit a laser beam, The laser crystal rod is a solid laser system, characterized in that spaced apart from the reflective surface of the reflective focusing device (CPC), a cooling molten quartz tube is installed around the laser crystal rod. The method of claim 1, The reflective deformable focusing apparatus (CPC) has an incident surface in contact with the emission surface of the multilayer diode array, and a fast-axis direction with a large divergence angle of the excitation beam of the multilayer diode array is perpendicular to the longitudinal axis direction of the laser crystal rod. In other words, the solid-state laser system of claim 1, wherein the excitation beam of the multilayer diode array is configured to reflect a reflection surface of the reflective focusing apparatus (CPC) once and then enter the laser crystal rod. The method of claim 1, In the cooling molten quartz tube arranged around the laser crystal rod, a part of the cooling water flowing through the reflective deformation focusing apparatus (CPC) flows through the laser crystal rod to uniformly cool the laser crystal rod in each direction. And a coolant distributor having holes spaced evenly in each direction. The method of claim 1, The reflective deformation focusing apparatus (CPC) is a solid-state laser system, characterized in that the gold plating film or gold plating and coating film formed on the reflective surface to increase the reflectance. The method of claim 1, The reflective deformation focusing apparatus (CPC) has a cross section whose upper portion has a parabolic shape, and a lower portion having an involute shape on the surface of the laser crystal rod. Solid-state laser system, characterized in that spaced apart from the rod by a predetermined interval. The method of claim 5, The reflective deformable focusing device (CPC) is formed between the tangent of the surface of the laser crystal rod and the surface of the reflective focusing device (CPC) by the boundary condition that the upper part and the lower part must coincide at θ = θ _i + π / 2. The distance ρ (θ) is given by the following equation. θ is when, , θ is when, Where θ _i is The angle of incidence of the ambient light of the excitation beam, given by, is the linear distance between the surface of the laser crystal rod and the vertex C of the CPC. The method of claim 5, The reflection type deformable focusing apparatus (CPC) has an optimal absorption design in the laser crystal by matching or increasing or decreasing its reception angle θa with the incident angle of the ambient light of the excitation beam. The method of claim 5, The reflective deformation focusing apparatus (CPC) is a solid-state laser system characterized in that the excitation beam absorption distribution in the laser crystal is optimally designed by increasing or decreasing the distance g between the lower vertex and the laser crystal rod. A multilayer diode array in which a plurality of laser diodes emitting laser excitation beams are arranged in a wide planar shape, a reflective parabolic concentrator (CPC) for collecting the laser beams emitted from the multilayer diode array into one place; And a laser crystal rod that is horizontally excited by a laser beam collected by the reflective focusing device to emit a laser beam, and a molten quartz tube for cooling that is installed around the laser crystal rod to cool the laser crystal rod. In And a lens disposed on an emission surface of the stacked diode array, the lens configured to be reflected by the reflective focusing apparatus after increasing the divergence angle of the excitation beam of the stacked diode array having a small divergence angle.