阅读说明：本技术 一种生长梯度掺杂Yb: YAG单晶的方法 (Method for growing gradient Yb-YAG-doped monocrystal ) 是由 顾跃 丁雨憧 于 2021-07-09 设计创作，主要内容包括：本发明公开了一种生长梯度掺杂Yb:YAG单晶的方法,先配置不同掺杂浓度的Yb:YAG胚料,再将不同胚料按照浓度由高到低的顺序依次由前至后放置于舟型钼坩埚中,舟型钼坩埚头部放入籽晶,再将舟型钼坩埚放入晶体生长炉内的可移动分体式加热器中。加热器由多个独立加热单元组成,加热器中部加热功率最高,每个加热单元的位置和加热功率可分别控制。利用此加热器可以较精细调节胚料周围轴向温度梯度并形成可控的窄熔区,坩埚不动,移动加热器使窄熔区按需移动从而实现晶体生长。本发明实现了分凝系数接近于1的Yb:YAG梯度掺杂,材料内部微结构满足其功能要求,并且浓度梯度可控。(The invention discloses a method for growing gradient Yb/YAG-doped single crystals, which comprises the steps of firstly preparing Yb/YAG blanks with different doping concentrations, then sequentially placing the different blanks in a boat-shaped molybdenum crucible from front to back according to the sequence of the concentration from high to low, placing seed crystals at the head of the boat-shaped molybdenum crucible, and then placing the boat-shaped molybdenum crucible into a movable split-type heater in a crystal growth furnace. The heater consists of a plurality of independent heating units, the heating power of the middle part of the heater is the highest, and the position and the heating power of each heating unit can be respectively controlled. The heater can be used for finely adjusting the axial temperature gradient around the blank and forming a controllable narrow melting zone, the crucible is not moved, and the heater is moved to move the narrow melting zone as required so as to realize crystal growth. The invention realizes Yb: YAG gradient doping with segregation coefficient close to 1, the internal microstructure of the material meets the functional requirement, and the concentration gradient is controllable.)

1. A method for growing a gradient Yb/YAG-doped monocrystal is characterized by comprising the following steps: the method comprises the following steps of,

1) preparing raw materials: preparing Yb: YAG raw materials with different designed concentrations according to a stoichiometric ratio, respectively mixing and sintering the prepared raw materials with different concentrations into raw material blocks, and then placing the raw material blocks into a shoulder placing area and an equal-width growth area of a boat-shaped crucible from front to back according to the sequence of the concentrations from low to high; pure YAG seed crystals are placed in a seed crystal groove at the foremost end of the crucible;

2) charging: placing the crucible loaded with the raw material blocks into a pre-designed movable split heater in a single crystal furnace; the movable split heater is composed of a plurality of groups of independent heating units which are sequentially arranged along the length direction of the crucible, wherein the heating power of the heating unit positioned in the middle is the highest, and the heating power of the heating units on the two sides is sequentially reduced; placing the contact position of the raw material block and the seed crystal at the position corresponding to the heating unit with the highest heating power; packaging the furnace, and continuously extracting high vacuum; ensure the vacuum degree to be 10^-2Pa below;

3) and (3) heating: according to different set powers, different heating units in the movable split-type heater start to heat according to the preset power, and the heating time is 2-10 hours; the vacuum degree in the furnace is kept at 10 when the temperature is raised^-2Pa below;

4) manufacturing a narrow melting zone: after each heating unit reaches the set power, preserving the heat for 1-3 hours to enable the heating units to reach a stable state; observing a melting zone formed at the intersection interface of the raw material block and the seed crystal, and controlling the width of the melting zone to be 5-30mm to form a narrow melting zone;

5) seeding and shouldering: after the narrow melting zone is stable and does not change, all heating units in the movable split heater are enabled to move slowly towards the back of the crucible at the same speed in a collective mode, and the moving speed is 1-5 mm/h; in the moving process, the narrow melting zone moves along with the movement of the heating unit with the highest heating power and the width of the narrow melting zone is controlled to be 5-30mm all the time;

6) and (3) equal-width growth: after the narrow melting zone leaves the shouldering zone, keeping the power of each heating unit unchanged, and continuously moving the movable split-type heater backwards at the same speed as the shouldering stage until the movable split-type heater is integrally moved out of the crucible zone;

7) cooling and discharging: slowly cooling at the speed of 0.2-2kW/h, and waiting for 20-40 hours after cooling is finished, so that crystals can be taken out.

2. YAG single crystal growing gradient doped Yb, according to claim 1, characterized in that: each heating unit comprises an upper heating tungsten rod and a lower heating tungsten rod which are opposite, the heating tungsten rods are transversely arranged relative to the crucible, the crucible is positioned between the upper heating tungsten rod and the lower heating tungsten rod, and two ends of each heating rod extend out of two sides of the crucible and are bent towards the middle.

3. YAG single crystal growing gradient doped Yb, according to claim 1, characterized in that: the number of the heating units forming the movable split heater is 5-15 and is odd; the heating power of the heating unit at the middle is the highest; the other heating units are symmetrically arranged at two sides of the heating unit at the middle, and the heating power of any two-side heating unit symmetrically arranged relative to the heating unit at the middle is the same; the position and power of each heating unit can be adjusted individually.

4. YAG single crystal growing gradient doped Yb, according to claim 1, characterized in that: and 3) in the temperature rising process, if the vacuum is reduced, the temperature rising is suspended until the vacuum is stable, and then the temperature rising is continued.

5. YAG single crystal growing gradient doped Yb, according to claim 1, characterized in that: in the step 4), if the narrow melting zone is found to exceed the set width or be lower than the set width, the power and the relative position of each heating unit are adjusted to ensure that the width of the narrow melting zone meets the requirement.

6. YAG single crystal growing gradient doped Yb, according to claim 1, characterized in that: and 5) in the shouldering moving process, correspondingly increasing the power of each heating unit according to the characteristic that the length of the melting zone is longer and the quality is gradually increased, and ensuring that the narrow melting zone always exists and the width meets the requirement.

Technical Field

The invention relates to a crystal growth technology, in particular to a method for growing a Yb-YAG (Yb-doped yttrium aluminum garnet) single crystal, belonging to the technical field of crystal materials.

Background

In recent years, Yb: YAG has been widely used as a laser crystal material having the simplest energy level structure. Yb of³⁺The ions have the advantages of low quantum defect (8.6%), long fluorescence life, wide absorption spectrum line, no excited state absorption, energy up-conversion and the like, and the YAG matrix provides excellent optical and thermal properties, so that the Yb: YAG crystal becomes one of ideal gain media of a high-power compact solid laser. The average output power of the diode pumping laser adopting Yb: YAG reaches kilowatt level at present, meanwhile, besides the traditional rod-shaped crystal, researchers design various structures based on the Yb: YAG crystals of lath shape, disc shape and the like, and the diode pumping laser is applied to the research of ultrashort, ultrafast and heavy frequency lasers.

The gradient doped Yb-YAG crystal has excellent thermal management performance when working in a laser while maintaining the advantages of common Yb-YAG, can be used as a laser weapon-grade high-power LD pumped solid laser, and solves the pain of uneven heating and high local heating of the current Yb-YAG. However, because of Yb³⁺The segregation coefficient of ions in a YAG matrix is close to 1, and the commonly used pulling method at present is to melt all raw materials and then grow the raw materials, so that the grown Yb: YAG crystals are close to homogeneous doping, and the gradient doped Yb: YAG crystals cannot be produced. Aiming at the current horizontal directional crystallization method, the heaters are integrally connected in series and have consistent power, the seeding positions are positioned at the edges of the heaters, the whole heater area is provided with a melt, the melting area is larger, and Yb is caused³⁺The ion concentration tends to be uniform, and a gradient doped Yb: YAG crystal cannot be grown. While movement of the crucible can affect crystal quality. Therefore, the search for a method suitable for growing gradient doped Yb: YAG crystals is of great significance for the development of compact high-power lasers.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a method for growing a Yb/YAG gradient doped single crystal, the method realizes Yb/YAG gradient doping with the segregation coefficient close to 1, and the internal microstructure of the material meets the functional requirements. And the concentration gradient is controllable.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a method for growing a Yb/YAG gradient doped monocrystal comprises the following steps,

1) preparing raw materials: preparing Yb: YAG raw materials with different designed concentrations according to a stoichiometric ratio, respectively mixing and sintering the prepared raw materials with different concentrations into raw material blocks, and then placing the raw material blocks into a shoulder placing area and an equal-width growth area of a boat-shaped crucible from front to back according to the sequence of the concentrations from low to high; pure YAG seed crystals are placed in a seed crystal groove at the foremost end of the crucible;

2) charging: placing the crucible loaded with the raw material blocks into a pre-designed movable split heater in a single crystal furnace; the movable split heater is composed of a plurality of groups of independent heating units which are sequentially arranged along the length direction of the crucible, wherein the heating power of the heating unit positioned in the middle is the highest, and the heating power of the heating units on the two sides is sequentially reduced; placing the contact position of the raw material block and the seed crystal at the position corresponding to the heating unit with the highest heating power; packaging the furnace, and continuously extracting high vacuum; ensure the vacuum degree to be 10^-2Pa below;

3) and (3) heating: according to different set powers, different heating units in the movable split-type heater start to heat according to the preset power, and the heating time is 2-10 hours; the vacuum degree in the furnace is kept below 10-2Pa when the temperature is raised;

4) manufacturing a narrow melting zone: after each heating unit reaches the set power, preserving the heat for 1-3 hours to enable the heating units to reach a stable state; observing a melting zone formed at the intersection interface of the raw material block and the seed crystal, and controlling the width of the melting zone to be 5-30mm to form a narrow melting zone;

5) seeding and shouldering: after the narrow melting zone is stable and does not change, all heating units in the movable split heater are enabled to move slowly towards the back of the crucible at the same speed in a collective mode, and the moving speed is 1-5 mm/h; in the moving process, the narrow melting zone moves along with the movement of the heating unit with the highest heating power and the width of the narrow melting zone is controlled to be 5-30mm all the time;

6) and (3) equal-width growth: after the narrow melting zone leaves the shouldering zone, keeping the power of each heating unit unchanged, and continuously moving the movable split-type heater backwards at the same speed as the shouldering stage until the movable split-type heater is integrally moved out of the crucible zone;

7) cooling and discharging: slowly cooling at the speed of 0.2-2kW/h, and keeping for 20-40 hours after cooling is finished, thus obtaining the crystal.

Furthermore, each heating unit comprises an upper heating tungsten rod and a lower heating tungsten rod which are opposite, the heating tungsten rods are transversely arranged relative to the crucible, and the crucible is positioned between the upper heating tungsten rod and the lower heating tungsten rod; in order to heat both sides of the raw material, both ends of the heating rod are extended out of both sides of the crucible and bent toward the middle.

Preferably, the number of the heating units constituting the movable split heater is 5-15 and is odd; the heating power of the heating unit at the middle is the highest; the other heating units are symmetrically arranged at two sides of the heating unit at the middle, and the heating power of any two-side heating unit symmetrically arranged relative to the heating unit at the middle is the same; the position and power of each heating unit can be adjusted individually.

And 3) in the temperature rising process, if the vacuum is reduced, the temperature rising is suspended until the vacuum is stable, and then the temperature rising is continued.

In the step 4), if the narrow melting zone is found to exceed the set width or be lower than the set width, the power and the relative position of each heating unit are adjusted to ensure that the width of the narrow melting zone meets the requirement.

And 5) in the shouldering moving process, correspondingly increasing the power of each heating unit according to the characteristic that the length of the melting zone is longer and the quality is gradually increased, and ensuring that the narrow melting zone always exists and the width meets the requirement.

Compared with the prior art, the invention has the following beneficial effects:

1. the Yb-YAG gradient doping with segregation coefficient close to 1 is realized by the sectional raw material configuration and the narrow melting zone growth means. The internal microstructure of the material meets the functional requirements. In addition, parameters such as concentration gradient, maximum concentration, minimum concentration and the like can be regulated and controlled.

2. The heating unit is made of a tungsten rod and is high-temperature resistant. Each heating rod can independently control the power and the position, and the axial temperature field environment of crystal growth can be finely adjusted. The narrow melting zone and the proper temperature gradient can be obtained by regulating and controlling the axial temperature field, the defects of cracking (too large temperature gradient), cloud layer (too small temperature gradient) and the like in the crystal are reduced, and the high-quality crystal is easy to grow.

3. The invention has the advantages that the positions of the crucible and the raw materials are unchanged in the stages of seeding, shouldering and equal-width growth, and the heater moves backwards, so that the defects of fluid vibration and crystals generated by the movement of the crucible and the raw materials are avoided.

4. The heating unit with the highest heating power is mainly used for manufacturing a narrow melting zone, and the heating units on two sides are used for sequentially preheating the unmelted raw material blocks on one side and sequentially preserving the heat of the grown crystals on the other side so as to keep the crystals at a reasonable temperature gradient and ensure the high quality of the crystals.

The doping gradient is closer to linear distribution when the number of the raw material blocks is larger; the greater the number of heating units, the more easily the temperature gradient can be controlled, which can be determined by a combination of product use requirements and manufacturing costs.

Drawings

FIG. 1-schematic view of the crucible charging and heating of the present invention.

FIG. 2 is a graph showing the change of doping concentration at different sites of a Yb: YAG single crystal produced in example 1 of the present invention.

FIG. 3 is a graph showing the change of doping concentration at different sites of a Yb: YAG single crystal produced in example 2 of the present invention.

FIG. 4 is a graph showing the variation of doping concentration at different sites of a Yb: YAG single crystal produced in example 3 of the present invention.

Detailed Description

The invention relates to a general idea for growing a Yb-doped YAG (Yb-doped yttrium aluminum garnet) single crystal in a gradient way: YAG crystals with different concentrations are prepared and sintered, and are sequentially placed in a boat-shaped crucible from a head in the sequence of concentration from low to high, and pure YAG seed crystals are placed in the head of the crucible. The boat-shaped crucible is placed in a split heater in a heating furnace, the split heater is heated after being vacuumized, the power and the position of each heating unit of the split heater are adjusted, the initial narrow melting zone is manufactured at the contact position of raw material seed crystals, other zones are not melted except the narrow melting zone, then the heater is slowly moved backwards, the narrow melting zone is moved along with the narrow melting zone, and therefore seeding, shouldering and equal-width growth processes are completed, and finally the crystal is cooled and taken out.

The specific steps of the present invention are carried out as follows,

1) preparing raw materials: preparing Yb: YAG raw materials (Yb-doped yttrium aluminum garnet mixture materials) with different designed concentrations according to a stoichiometric ratio, respectively mixing and sintering the prepared raw materials with different concentrations into raw material blocks, and then placing the raw material blocks into a shoulder-placing area and an equal-width growth area of a boat-shaped crucible from front to back according to the sequence of the concentrations from low to high; pure YAG seed crystals are placed in a seed crystal groove at the foremost end of the crucible;

the crucible is composed of three sections, the crucible is respectively provided with a seed crystal groove, a shoulder placing area and an equal-width growth area from front to back, two ends of the shoulder placing area are connected with the seed crystal groove and the equal-width growth area, the seed crystal groove is a long and narrow equal-width area, the side surface of the seed crystal groove is a right-angled triangle, the thickness of the seed crystal groove is gradually increased from the tip to the back, the top of the seed crystal groove is kept horizontal and is as high as the top of the shoulder placing area and the equal-width growth area, and the bottom of the seed crystal groove is increased from the tip to the back; the shoulder-placing area is in a triangular shape; the equal-width growth area is rectangular and the width of the equal-width growth area is consistent with that of the tail end of the shoulder-laying area; the equal-width growth area and the shoulder-laying area are equal in height.

2) Charging: placing the crucible loaded with the raw material blocks into a pre-designed movable split heater in a single crystal furnace; the movable split heater is composed of a plurality of groups of independent heating units which are sequentially arranged along the length direction of the crucible, wherein the heating power of the heating unit positioned in the middle is the highest, and the heating power of the heating units on the two sides is sequentially reduced; placing the contact position of the raw material block and the seed crystal at the position corresponding to the heating unit with the highest heating power; packaging the furnace, and continuously extracting high vacuum; ensuring the vacuum degree below 10-2 Pa;

3) and (3) heating: according to different set powers, different heating units in the movable split-type heater start to heat according to the preset power, and the heating time is 2-10 hours; the vacuum degree in the furnace is kept below 10-2Pa when the temperature is raised; if the vacuum drops, the temperature rise is suspended until the vacuum is stabilized, and then the temperature rise is continued.

4) Manufacturing a narrow melting zone: after each heating unit reaches the set power, preserving the heat for 1-3 hours to enable the heating units to reach a stable state; observing a melting zone formed at the intersection interface of the raw material block and the seed crystal, and controlling the width of the melting zone to be 5-30mm to form a narrow melting zone; and if the narrow melting zone is found to exceed the set width or be lower than the set width, adjusting the power and the relative position of each heating unit to ensure that the width of the narrow melting zone meets the requirement. The length of the melting zone corresponds to the width of the crucible; the width of the molten zone is along the length of the crucible.

5) Seeding and shouldering: after the narrow melting zone is stable and does not change, all heating units in the movable split heater are enabled to move slowly towards the back of the crucible at the same speed in a collective mode, and the moving speed is 1-5 mm/h; in the moving process, the narrow melting zone moves along with the movement of the heating unit with the highest heating power and the width of the narrow melting zone is controlled to be 5-30mm all the time; step 5) in the shouldering moving process, correspondingly increasing the power of each heating unit according to the characteristic that the length of the melting zone is longer and the mass is gradually increased (under the same width), so as to ensure that the narrow melting zone always exists and the width meets the requirement, otherwise, the melting zone is narrowed to a certain extent so as to have the risk of disappearance;

6) and (3) equal-width growth: after the narrow melting zone leaves the shouldering zone, keeping the power of each heating unit unchanged, and continuously moving the movable split-type heater backwards at the same speed as the shouldering stage until the movable split-type heater is integrally moved out of the crucible zone;

7) cooling and discharging: slowly cooling at the speed of 0.2-2kW/h, and keeping for 20-40 hours after cooling is finished, thus obtaining the crystal.

In specific implementation, each heating unit comprises an upper heating tungsten rod and a lower heating tungsten rod which are opposite, the heating tungsten rods are transversely arranged relative to the crucible, and the crucible is positioned between the upper heating tungsten rod and the lower heating tungsten rod. In order to heat both sides of the raw material, both ends of the heating rod are extended out of both sides of the crucible and bent toward the middle.

The number of the heating units forming the movable split heater is 5-15 and is odd; the heating power of the heating unit at the middle is the highest; the other heating units are symmetrically arranged at two sides of the heating unit at the middle, and the heating power of any two-side heating unit symmetrically arranged relative to the heating unit at the middle is the same; the position and power of each heating unit can be adjusted individually.

FIG. 1 is a schematic view of the crucible charging and heating of the present invention. Wherein reference numeral 1 is a crucible; reference numeral 2 is a YAG seed crystal; the reference numeral 3 is a raw material block obtained by mixing and sintering Yb and YAG; reference numeral 4 is a tungsten rod; reference numeral 5 is a narrow melting zone. Normally, the narrow melting zone should be located at a position corresponding to the heating unit at the middle, and the position is shielded in the state shown in the figure; to facilitate the display of the general shape of the narrow melt zone, the narrow melt zone is intentionally shifted to the left in the figure. In the figure, 7 heating units are arranged, and the heating power of the heating unit positioned at the middle is the highest. A total of 12 feedstock blocks; wherein, the triangular shouldering area is provided with 4 raw material blocks, and the equal-width area is provided with 8 raw material blocks; the doping concentration of the raw material blocks is gradually increased from right to left, and the junction of the YAG seed crystal and the adjacent raw material blocks is shielded by the heating unit at the middle.

The following examples are presented to aid in a better understanding of the present teachings.

Example 1:

respectively preparing Yb and YAG raw materials of 1%, 2%, 3%, 4%, 5%, 6%, 7% and 8%, respectively mixing uniformly, sintering at 1500 ℃ for 1 hour, putting the sintered raw materials with different concentrations into a boat-shaped molybdenum crucible (160 x 100 x 40mm) from front to back according to the gradually increased concentration, and putting pure YAG seed crystals into the head of the crucible. The crucible and the raw materials are put into a split type movable heater in the single crystal furnace. The connection position of the seed crystal and the raw material is positioned in the middle of the heater. The heater was sealed and high vacuum was started.

When the vacuum degree reaches 2 x 10^-3And when Pa, turning on a heating power supply, and starting heating the heater. The heater comprises five groups of heating units, wherein the temperature of the middle group of heating units is raised to 24kW, the temperature of the adjacent two groups of heating units is raised to 22kW, and the temperature of the outermost two groups of heating units is raised to 21 kW. After the temperature rise is finished for 3 hours, the temperature is kept for 1 hour, the raw material and the seed crystal positioned in the middle of the heater are observed through the observation hole, the contact part of the raw material and the seed crystal is molten, and the width of the molten zone is about 20 mm. And starting a program of automatically moving the heater backwards at the moving speed of 3mm/h for 70 hours, wherein each heating unit is heated at the speed of 0.05kW/h in the first 14 hours in the moving process, and the power is kept unchanged in the last 56 hours.

And (4) cooling after 70 hours, reducing the power of the heater to 0kW after 40 hours, closing the vacuum equipment after 20 hours, opening the single crystal furnace, and taking out the crystal.

Example 2:

preparing 200g of Yb and YAG raw materials of 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% and 5%, respectively mixing uniformly, sintering at 1500 ℃ for 1 hour, putting the sintered raw materials with different concentrations into a boat-shaped molybdenum crucible (160 x 100 x 40mm) from front to back according to the gradually increasing concentration, and putting pure YAG seed crystals into the head of the crucible. The crucible and the raw materials are put into a split type movable heater in the single crystal furnace. The connection position of the seed crystal and the raw material is positioned in the middle of the heater. The heater was sealed and high vacuum was started.

When the vacuum degree reaches 5 x 10^-3And when Pa, turning on a heating power supply, and starting heating the heater. The heater comprises five groups of heating units, wherein the temperature of the middle group of heating units is raised to 23.9kW, the temperature of the adjacent two groups of heating units is raised to 21.8kW, and the temperature of the outermost two groups of heating units is raised to 20.8 kW. After the temperature rise is finished for 3 hours, the temperature is kept for 1 hour, the raw material and the seed crystal positioned in the middle of the heater are observed through the observation hole, the contact part of the raw material and the seed crystal is molten, and the width of the molten zone is about 5 mm. And starting a program of automatically moving the heater backwards at the moving speed of 3mm/h for 70 hours, wherein each heating unit is heated at the speed of 0.05kW/h in the first 14 hours in the moving process, and the power is kept unchanged in the last 56 hours.

And (4) cooling after 70 hours, reducing the power of the heater to 0kW after 40 hours, closing the vacuum equipment after 20 hours, opening the single crystal furnace, and taking out the crystal.

Example 3:

respectively preparing 150g of Yb and YAG raw materials of 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18% and 20%, respectively uniformly mixing, sintering at 1500 ℃ for 1 hour, putting the sintered raw materials with different concentrations into a boat-shaped molybdenum crucible (180 x 90 x 35mm) from front to back according to the gradually increasing concentration, and putting pure YAG seed crystals into the head of the crucible. The crucible and the raw materials are put into a split type movable heater in the single crystal furnace. The connection position of the seed crystal and the raw material is positioned in the middle of the heater. The heater was sealed and high vacuum was started.

When the vacuum degree reaches 1 x 10^-3And when Pa, turning on a heating power supply, and starting heating the heater. The heater consists of 9 groups of heating units, and the target power of the heating units from the middle to the two sides is 23.6kW, 23.2kW, 23.1kW, 23kW and 23kW in sequence. The vacuum was found to rise to 2 x 10 at 0.6 hour of temperature rise^-2And Pa, stopping heating, continuously pumping vacuum, and continuing heating after the vacuum is reduced to 4 x 10-3 Pa. After the temperature rise is finished for 3 hours, the temperature is kept for 2 hours, the raw material and the seed crystal positioned in the middle of the heater are observed through the observation hole, the contact part of the raw material and the seed crystal is molten, and the width of the molten zone is about 10 mm. And starting a program of automatically moving the heater backwards at the moving speed of 2mm/h for 100 hours, wherein each heating unit is heated at the speed of 0.01kW/h in the first 20 hours in the moving process, and the power after heating is kept unchanged in the last 80 hours. When the furnace is moved for 3 hours, the width of the melting zone is found to be reduced to 3mm, the risk that the melting zone disappears exists, the heater is stopped moving at the moment, the power of the intermediate heating unit is increased by 0.1kW, the width of the melting zone is observed to be recovered to about 8mm, the heater is continuously moved at the moment, and the original power increasing program is maintained.

And (3) cooling after the movement is finished, reducing the power of the heater to 0kW after 50 hours, closing the vacuum equipment after 30 hours, opening the single crystal furnace, and taking out the crystal.

YAG crystal of different parts of Yb doping obtained from three examples is ground into powder by taking a small amount, and the Yb ion concentration of different positions of the grown crystal is tested by ICP (inductively coupled plasma), and the results are as follows:

example 1

Sample numbering	Sample distance from rear end of seed crystal (mm)	Yb ion concentration at%
			1	10	0.98
2	30	1.87
			3	50	2.89
4	70	4.03
			5	90	4.96
6	110	6.13
			7	130	6.89
8	150	7.91

Example 2:

sample numbering	Sample distance from rear end of seed crystal (mm)	Yb ion concentration at%
			1	10	1.43
2	30	2.01
			3	50	2.58
4	70	2.90
			5	90	3.41
6	110	3.99
			7	130	4.52
8	150	4.98

Example 3:

sample numbering	Sample distance from rear end of seed crystal (mm)	Yb ion concentration at%
			1	10	2.11
2	30	3.92
			3	50	5.94
4	70	8.01
			5	90	10.11
6	110	12.07
			7	130	14.18
8	150	15.94
			9	170	18.16
10	190	19.85

It can be seen that the test result is basically consistent with the prediction, the Yb ion doping concentration in the crystal shows a trend of changing from low to high, the linearity is good, and the concentration change is well controlled, so that the method can prepare the gradient doped crystal which is in line with the expectation, and the gradient doping is feasible.

The method comprises the steps of firstly preparing Yb: YAG blanks with different doping concentrations, then sequentially placing the different blanks in a boat-shaped molybdenum crucible from front to back according to the sequence of the concentration from low to high, and placing triangular seed crystals at the head of the boat-shaped molybdenum crucible. The boat-shaped molybdenum crucible is placed into a split type movable heater in a crystal growth furnace. The split type movable heater can be used for finely adjusting the axial temperature gradient around the blank, thereby realizing the purpose of growing high-quality gradient Yb/YAG doped crystals in a narrow melting zone.

The above examples of the present invention are merely illustrative of the present invention and are not intended to limit the embodiments of the present invention. Variations and modifications in other variations will occur to those skilled in the art upon reading the foregoing description. Not all embodiments are exhaustive. All obvious changes and modifications of the present invention are within the scope of the present invention.