Method for tailoring the dopant profile in a laser crystal using zone processing

Patent metadata

Field	Value
Publication number	US-9926644-B2
Application number	US-201414487295-A
Country	US
Kind code	B2
Filing date	Sep 16, 2014
Priority date	Aug 16, 2011
Publication date	Mar 27, 2018
Grant date	Mar 27, 2018

Abstract

A lasing medium having a tailored dopant concentration and a method of fabrication thereof is disclosed. The lasing medium has a single crystal having a continuous body having a selected length, wherein the crystal comprises dopant distributed along the length of the body to define a dopant concentration profile. In one embodiment, the dopant concentration profile results in a uniform heating profile. A method of fabricating a laser crystal having a tailored dopant concentration profile includes arranging a plurality of polycrystalline segments together to form an ingot, the polycrystalline segments each having dopant distributed, providing a crystal seed at a first end of the ingot, and moving a heating element along the ingot starting from the first end to a second end of the ingot, the moving heating element creating a moving molten region within the ingot while passing therealong.

First claim

What is claimed is:

1. A method comprising:
determining a target non-uniform dopant concentration profile of a laser crystal;
arranging multiple polycrystalline segments together in an order to form an ingot, each segment having dopant distributed substantially uniformly therein, each segment having a different dopant concentration than other segments, the order based on decreasing dopant concentration such that the segment at a first end of the ingot has a highest dopant concentration and the segment at a second end of the ingot has a lowest dopant concentration, each segment selected based on a predetermined specific gravity of the segment, the dopant selected based on a predetermined segregation coefficient of the dopant;
providing a seed crystal at a first end of the ingot; and
moving a heating element along the ingot from the first end to a second end of the ingot so as to create a single laser crystal having the target non-uniform dopant concentration profile, the target non-uniform dopant concentration profile changing smoothly and continuously from the first end of the ingot to the second end of the ingot, the moving heating element creating a moving molten region within the ingot while passing therealong, the heating element moved so as to create the moving molten region with a predetermined length,
wherein (i) the length of the moving molten region, (ii) the specific gravity of the polycrystalline segments, and (iii) the segregation coefficient of the dopant are predetermined to result in the target non-uniform dopant concentration profile.

2. The method of claim 1 , wherein the dopant comprises neodymium, ytterbium, erbium, holmium, or a combination thereof.

3. The method of claim 1 , wherein the heating element uses radio frequency (RF) induction.

4. The method of claim 1 , wherein each of the segments has a different length.

5. The method of claim 1 , wherein the seed crystal comprises a dopant concentration equal to a target concentration at the first end of the ingot.

6. The method of claim 1 , wherein the single laser crystal represents a continuous body with a selected length, the continuous body having a common crystal structure and a common lattice orientation as the seed crystal.

7. The method of claim 1 , wherein moving the heating element along the ingot comprises surrounding a portion of the ingot with the heating element.

8. The method of claim 1 , wherein interfaces between the moving molten region and the segments of the ingot are substantially normal to an axis of the ingot.

9. The method of claim 1 , wherein the laser crystal comprises Y 3 Al 5 O 12 , YLiF 4 , or Gd 3 Ga 5 O 12 .

10. A method comprising:
determining a target non-uniform dopant concentration profile of a laser crystal;
arranging multiple polycrystalline segments in an order to form an ingot, each segment having dopant distributed substantially uniformly therein, each segment having a different dopant concentration than other segments, the order based on decreasing dopant concentration such that the segment at a first end of the ingot has a highest dopant concentration and the segment at a second end of the ingot has a lowest dopant concentration, each segment selected based on a predetermined specific gravity of the segment, the dopant selected based on a predetermined segregation coefficient of the dopant;
providing a seed crystal at a first end of the ingot; and
moving a heating element along the ingot so as to create a single laser crystal having the target non-uniform dopant concentration profile, the target non-uniform dopant concentration profile changing smoothly and continuously from the first end of the ingot to the second end of the ingot, the moving heating element creating a moving molten region within the ingot while passing along the ingot, the heating element moved so as to create the moving molten region with a predetermined length,
wherein ((i) the length of the moving molten region, (ii) the specific gravity of the polycrystalline segments, and (iii) the segregation coefficient of the dopant are predetermined to result in the target non-uniform dopant concentration profile.

11. The method of claim 10 , wherein the dopant comprises neodymium, ytterbium, erbium, holmium, or a combination thereof.

12. The method of claim 10 , wherein the heating element uses radio frequency (RF) induction.

13. The method of claim 10 , wherein each of the segments has a different length.

14. The method of claim 10 , wherein the seed crystal comprises a dopant concentration equal to a target concentration at the first end of the ingot.

15. The method of claim 10 , wherein moving the heating element along the ingot comprises surrounding a portion of the ingot with the heating element.

16. The method of claim 10 , wherein interfaces between the moving molten region and the segments are substantially normal to an axis of the ingot.

17. The method of claim 10 , wherein the laser crystal comprises Y 3 Al 5 O 12 , YLiF 4 , or Gd 3 Ga 5 O 12 .

18. A method comprising:
determining a target non-uniform dopant concentration profile of a laser crystal;
obtaining an ingot comprising multiple polycrystalline segments arranged in an order, each segment having dopant distributed substantially uniformly therein, each segment having a different dopant concentration than other segments, the order based on decreasing dopant concentration such that the segment at a first end of the ingot has a highest dopant concentration and the segment at a second end of the ingot has a lowest dopant concentration, each segment selected based on a predetermined specific gravity of the segment, the dopant selected based on a predetermined segregation coefficient of the dopant;
providing a seed crystal at one end of the ingot; and
moving a heating element along the ingot so as to create a single laser crystal having the target non-uniform dopant concentration profile, the target non-uniform dopant concentration profile changing smoothly and continuously from the first end of the ingot to the second end of the ingot, the moving heating element creating a moving molten region within the ingot while passing along the ingot, the heating element moved in a manner such that a shape of the target non-uniform dopant concentration profile does not substantially change at points along a length of the ingot associated with interfaces between the segments, the heating element moved so as to create the moving molten region with a predetermined length,
wherein (i) the length of the moving molten region, (ii) the specific gravity of the polycrystalline segments, and (iii) the segregation coefficient of the dopant are predetermined to result in the target non-uniform dopant concentration profile.

19. The method of claim 10 , wherein the single laser crystal represents a continuous body with a selected length, the continuous body having a common crystal structure and a common lattice orientation as the seed crystal.

20. The method of claim 18 , wherein the single laser crystal represents a continuous body having a common crystal structure and a common lattice orientation as the seed crystal.

21. The method of claim 1 , wherein the dopant concentration at the second end of the ingot is at least double the dopant concentration at the first end of the ingot.

22. The method of claim 1 , wherein the target non-uniform dopant concentration profile is represented by the following equation:
C F ( x )= C I [1−(1− k )exp(− kx/L )],

Assignees

• Raytheon Co

Inventors

• Byren Robert W

Classifications

• H01S3/1643

  YAG · CPC title

• C30B13/20 Primary

  by induction, e.g. hot wire technique (C30B13/18 takes precedence) · CPC title

• H01S3/1611

  neodymium · CPC title

• C30B13/24 Primary

  using electromagnetic waves · CPC title

• C30B29/28

  with formula A3Me5O12 wherein A is a rare earth metal and Me is Fe, Ga, Sc, Cr, Co or Al, e.g. garnets · CPC title