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Growth and characterization of high-quality Nd3+: YAP laser crystals
524
Journal of Crystal Growth 106 (~990)524—530 North-Holland
GROWTH AND CHARACTERIZATION OF HIGH-QUALITY Nd3 + : YAP LASER CRYSTALS LI Gansheng, SHI Zhenzhu, GUO Xibin, WU Jinhua, CHEN Ying and CHEN Jinfeng Fujian Institute of Research on the Structure of Matter, Academia Sinica, Fuzhou, Fujian, Peoples Rep. of China
Received 27 February 1990: manuscript received in final form U June 1990
During the growth of large Nd3~: YAP crystals by the Czochralski method, the temperature gradient requirenlents to eliminate cloudiness and twinning in the crystals are completely different. A larger gradient is required during growth, whereas a smaller gradient is needed after growth (during an annealing step done in the same chamber). By changing the atmosphere from N 2 during growth to a vacuum during annealing, a larger gradient could be created during the growth stage and a smaller gradient3’for the : YAP crystals annealing free process. from cloudiness With the above and twinning technique, wasthe obtained. annealing Rods period with was a diameter greatly of shortened 8 x 150 mm and could a hatch he of cuthigh-quality from the above Nd crystals and a maximum average power of up to 781 W laser output has been achieved by using only a unitary rod.
I. Introduction
increased considerably on the melt side of the solid—liquid interface, due to segregation effects.
Yttrium orthoaluminate (YA1O 3 or YAP) has a perovskite-like orthorhombic crystal structure with a space group of D~~Pnma. Neodymium doped 3~ YAP possesses several properties similar to Nd those of Nd3~: YAG (yttrium aluminium garnet) and in addition to that, it has some extra advantages: (1) the output radiation is polarized, (2) there are two laser wavelength emissions (1.064 and 1.079 ~.sm).depending on the orientation of crystal axis, and (3) the stimulated emission cross section (22 X 10—20 cm2) is 2.4 times greater than that of Nd3~: YAG at 1.34 j~m[11. Therefore it has opened up promising prospects for extensive applications, Owing to the large anisotropy of physical properties of the crystal and the intrinsic segregation behavior of Nd dopants, Nd~’: YAP crystals grown by Czochralski method usually tend to cxhihit cracking. twinning and cloudiness. Therefore, large-size high-quality Nd~: YAP single crystals are not easy to obtain [2—4]. Although the segregation coefficient of Nd ions in YAP is comparatively large (0.8). during crystal growth with a large pull rate (3.0 mm/h), low rotation rate (10--30rpm), and large crystal diameter 30 mm), the concentration of Nd ions is (—
0022.0248/90/803.50
1990
—
Once an external disturbance (such as a fluctuation in the heating power) occurs, it will easily result constitutional supercooling, thus leading to the information of defects such as cloudiness in the crystals. The usual solution to the above problem is to use a furnace geometry which increases the gas-liquid temperature difference and thereby acedcrates natural convection in the melt (enhance stirring) so as to decrease the Nd concentration at the solid--liquid interface. Thus, the cloudiness can be avoided in the crystals. On account of the large anisotropy of physical properties and the especially large difference of the coefficients of thermal expansion in Nd3~: YAP crystals (4.2, 11.7 and 5.1 x C for the a-, h- and c-axes, respectively), this difference can result in large thermal stresses in crystals grown at high temperature and then annealed in a large gas--liquid temperature difference, thereby causing (easily) the formation of twtnning on the (110) and (110) planes. Generally. a method is used to transfer at high temperature the large just-grown Nd3 : YAP single crystals into an afterheater and then reduce the temperature difference per unit length along °
Elsevier Science Publishers B.V. (North-Holland)
Li Gansheng et a!.
/
3+
Growth and characterization of high.qualits Nd
the crystals. Annealing in such a temperature field is certainly advantageous to decrease thermal stresses in the crystals. Thus, it is possible to avoid the formation of twinning in the crystals. In this case, of course, many difficulties will arise with a sealed induction heating chamber. In view of the above circumstances, a technique involving changing the ambient atmosphere from N-, to vacuum after growth and before annealing (the “vacuum natural cooling process”, VNCP) has been adopted to meet the two different temperature gradient requirements, i.e. a larger gradient during growth and a smaller gradient during annealing of the crystals in the same chamber. 3~: YAP single crystals with a diameter Large of 30 XNd 180 mm have been grown by the above technology. Twinning, cloudiness and laser properties have been examined and measured for all of the grown crystals. The results indicate that a great majority of the crystals have no cloudiness
.-
YAP laser crystals
525
and twinning and are suitable for high efficiency. high-power solid lasers at 1.079 or 1.34 ~sm.
2. Growth of Nd3~: YAP single crystals 2.1. A brief description of the growth process
In our Czochralski growth process, an Jr crucible was heated by a medium-frequency RF current under nitrogen atmosphere at a pressure of 1.6 X i0~Pa. A 1 kg charge of raw material with a purity of 99.999% was used with the composition Nd 0~1Y()99AlO3.The growth parameters included a pull rate of 3 mm/h, a rotation rate of 10—30 rpm and a crystal diameter of 30 mm. Although no twinning will occur in the large-size Nd3 ~ : YAP single crystals grown under a smaller gas—liquid temperature difference (<7°C) and annealed at a cooling rate of 100°C/h, cloudi-
Fig. 1. Light scattering by cloudiness in Nd35 YAP crystal. Viewed along the a-axis.
526
Li Gansheng eta!.
/ Growth and characterization .,.:~
3
of high-quality Nd
+
YAP laser crystals
-~
a axis
-~
~.
Fig. 2. Twinning pairs in Nd3 + YAP crystal on { 1 l0}.
ness will always appear. It is especially serious in the core region and results in a harmful light scattering, as shown in fig. 1. Even if the crystals are grown in a larger gas-liquid temperature difference (> 15°C) and annealed from high temperature to room temperature at a smaller cooling rate ( < 50°C/h). the twinning will still appear, as shown in fig. 2. However, when the crystals grown in the above large thermal gradient are then annealed by \TNCP annealing technique as described in section 2.2, a hatch of large-size Nd3~: YAP single crystals free from cloudiness and twinning has been grown.
ture gradient in the chamber, which will satisfy the requirement of the annealing temperature after growth of the crystals.
-
-
2.2. Fealures of the VNCP temperature field According to the heat transfer principles developed for the high-temperature growth chamber [5] shown in fig. 3, a higher pressure of nitrogen atmosphere will surely increase the convection in the gas. This will cause the quantity of heat to transfer easily from the inside to the outside of the chamber. This will be advantageous to the establishment of a large temperature gradient in the chamber and ensure the normal growth of the If th gas is pumped out and the growth chamher is changed into a vacuum state, then the transfer of heat by convection disappears and the temperature inside the chamber tends quickly to reach equilibrium, due to the thermal radiation of the internal wall of the chamber. This will be very favorable to the establishment of a small tempera-
5
,
:
.,.
C
.
I
C
.... .
~.
..
.
L -
... -
-.
-
..
..
2
. :•.
_____
~tIIII4IIIIII~IIIIEI~~ -
-
Fig. 3. Schematic diagram of growth chamber for large sii.e Nd35 YAP crystal (1) corundum plate; (2) corundum cylinder: (3) quartz cylinder; (4) Y 20 shield; (5) a-Al70 single crystal flake: (6) RF coil: (7) Ir crucible; (8) Zr02 powder.
3
Li Gansheng et a!. / Growth and characterization of high-quality Nd
+ .
YAP laser crystals
527
T(°C)
1500
1000
~
500
2
‘~
N.~
1
-~
0 0
50
100
150
200
t(min)
Fig. 4. The natural cooling rates in the chamber under vacuum and nitrogen atmoiphere. (•), (X) Temperatures at 150 mm above the crucible mouth for curves I and 2, respectively; (es), (0) temperatures at the crucible mouth for curves 1 and 2, respectively. (1) Nitrogen atmosphere at a pressuie of 1.6 x iO~Pa; (2) vacuum of 10 Pa.
The natural cooling rates of the chamber under a vacuum of 10 Pa and a nitrogen atmosphere of 1.6 x iO~ Pa, as well as the temperature dif-
ferences (AT) between the upper part (at 80 mm above the crucible mouth) and the lower part (at the crucible mouth) with the annealing tempera-
~T(°C) 800 700
100 0
___________________________
1700
130
1~00
900
700
~500
Tn(°C)
Fig. 5. The temperature differences between the upper and lower parts in the chamber during the natural cooling under two kinds of atmosphere. The upper part refers to 80 mm above the crucible mouth and the lower part to the crucible mouth. (I) Nitrogen atmosphere at a pressure of 1.6 X iO~Pa; (2) vacuum of 10 Pa.
528
Li Gansheng eta!.
/ Growth and characterization
ture (Ta) in the chamber under two kinds of atmospheres, have been measured and compared. The results are shown in figs. 4 and 5, respectively, It can be seen from figs. 4 and 5 that: (1) The natural cooling rates in the chamber under vacuum of 10 Pa are much slower than those in the chamber under nitrogen atmosphere of 1.6 X i0~Pa. This indicates that the vacuum state is unfavorable to the transfer of heat from the inside to the outside of the chamber. The experimental facts are consistent with the above analyses.
3’
ofhigh-quality Nd
YAP laser cry.stal.s
(2) The temperature difference suffered by the two ends of the crystal during its natural cooling in vacuum (10 Pa) is only two-thirds to one-half of that in nitrogen atmosphere (1.6 x i05 Pa). This means that when the crystals grown in a nitrogen atmosphere of 1.6 X ~ Pa at high temperature are transferred and annealed in vacuum, it is possible to achieve the goal of the crystals grown in a large-gradient temperature field while annealed in a small-gradient temperature field.
Table I Examination of twinning and cloudiness in Nd’ : YAP crystals Crystal
Main growth parameters
No.
Growth rate (mm/h)
. Rotation rate (rpm)
. Crystal diameter (mm)
Heating power stability
S8601 S8602 S8603 S8604 S8605 S8606 S8607 S8608 S8609 S8610 S86l1 S8612 S8613 S8614 S8615 S8616 S8617
3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
20 20 20 20 20 20 20 20 29 10 10 10 10 10 10 10 20
30 30—40 28—31 30 26—29 26—29 27—29 27—28 25
27—31 26—30 24—28 25—30 25—28 26—28 25—28 25—28
Yes Yes (m), no Yes Yes Yes Yes Yes Yes Yes (m). no Yes Yes Yes Yes Yes Yes
S8618 S8619 S8620 S8621 S8622 S8623 S8624 S8625 S8626 S8627 S8628 S8629 S8630 S8631
3 3 3 3 3 3 3 3 3 3 3 3 3 3
10 20 10 10 10 10 10 10 10 10 10 10 10 10
26—30 28—30 25—30 24—28 23—28 25—29 25—27 25—27 25—30 25—29 26—30 25—28 26—28 26—30
Yes Yes (m), no (I). no Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes
Twinning
(‘loudiness
No No
No No
(m), 2 pairs No No No
No No No No
No NO No
No No No No
Remarks
-
No (iii).
2 pairs
Yes.
No
NO
NC)
No
NC)
NC)
NC)
No No
No (m). 1 pair No No (m). 2 pairs
(iii)
Yes, (h) (m), (I) NC) NC) NO
No
Yes, (I)
No
NO
No
No
No NO
No
No
No
No No
No No No No No
(h) in head part of crystal, (m) in middle part of crystal. (I) in lower part of crystal.
Raw material Contamination
No Loose seed No No Yes, in center Gas leak in chamber
Li Gansheng et a!.
/ Growth and characterization
3+
of high-quality Nd
.
529
YAP laser crystals
Table 2 Nd3 + : YAP laser performance Laser type
Diameter (mm)
Rod orientation
High average power laser
8
x150
a-axis
CW laser CW laser CW laser Pulse laser
6 X 110 5.83<111 6 3<100 7.2 x 150
a-axis a-axis a-axis a-axis
Long pulse laser Simultaneous, multiple wavelength laser
6 5
x 100
a-axis a-axis
~ Unit cell dimensions [61: a
=
5.33
A,
b
x104 7.375
A,
c = 5.180
0
Pump source
Laser mode
Laser wavelength (/zm)
Laser output power or energy
Kr lamp (7.5 ms. 15 pps) Kr lamp Kr lamp Kr lamp Kr lamp (7.5 ms) Xe lamp Kr lamp
Multi
1.079
781 W
Multi Multi TEMwt Multi
1.079 1.34 1.34 1.079
162 W 82 W 5.3 W 44 J
Multi Multi
1.34 1.079 1.34
2J 5.25 W 5.4W
A.
3. The characterization of Nd3.F : YAP crystals
high-power lasers, particularly at 1.34 ~im wavelength lasers.
3.]. The examination of twinning and cloudiness in. Nd3~ : YAP crystals 4.
Thirty-one large-size Nd3 + : YAP boules have been grown by the above technique. Examination of twinning and cloudiness in each of the boules has been carried out. The twinning and cloudiness can be clearly observed by directing a strong white light along the (001) plane of the boules. The results and corresponding growth parameters are listed in table 1. It can be seen from table 1 that, except for the appearance of twinning and cloudiness in corresponding parts of boules subject to intense temperature (heating power) fluctuations, an air leak of the chamber or a loose seed, the great majority of boules grown even at rotation rates of 30 to 10 rpm have no twinning and cloudiness. 3.2. Measurements of laser properties
In order to determine the laser properties experimentally, different laser rods were cut out of the above boules. The measurement of laser performance was carried out in various active lasers. The main results are listed in table 2. It can be seen from table 2 that Nd3~: YAP single crystal is a very good laser material for
Conclusions
(1) By means of a vacuum annealing technique, the problem of growing large Nd3~: YAP single crystals without twins or scattering centers has been solved satisfactorily. It is therefore possible to provide large-size, high-quality laser rods for high power laser applications. (2) The VNCP technique can be expected to be applied to the growth of high-temperature anisotropic crystals similar to YAP crystals.
Acknowledgements The authors would like to thank Lu Jian and Yang Hua for their participation in the crystal growth, and Professor Shen Hongyuan for providing laser performance data. Thanks are also due to Professor Yixiong for his careful examination of thisFang manuscript. References [1] Hongyuan Shen, Tianquan Lian et al.. IEEE J. Quantum Electronics QE-25 (1989) 144.
530
Li Gansheng et al.
/ Growth and characterization
[2] AD. Morrison. R.R. Monchamp, M. Basset al., AD-743223 (1972) [3] R.F. Belt, R. Uhrin, R. Puttbach et al., in: Abstracts 3rd Am. Conf. on Crystal Growth, Am. Assoc. for Crystal Growth, Stanford, CA, 1975, p. 190.
3+
of high-quality Nd
.
YAP laser crystals
[4] iS. Abell and l.R. Harris, J. Mater. Sci. 7 (1972) 1088. [5] Li Gansheng. Shi Zhenzhu, Chen Ying et al., J. Synthetic Crystals 16 (1987) 33 (in Chinese) [61 R. Diehi. G. Brandi et al.. Mater. Res. Bull. 10 (1975) 85.
Journal of Crystal Growth 106 (~990)524—530 North-Holland
GROWTH AND CHARACTERIZATION OF HIGH-QUALITY Nd3 + : YAP LASER CRYSTALS LI Gansheng, SHI Zhenzhu, GUO Xibin, WU Jinhua, CHEN Ying and CHEN Jinfeng Fujian Institute of Research on the Structure of Matter, Academia Sinica, Fuzhou, Fujian, Peoples Rep. of China
Received 27 February 1990: manuscript received in final form U June 1990
During the growth of large Nd3~: YAP crystals by the Czochralski method, the temperature gradient requirenlents to eliminate cloudiness and twinning in the crystals are completely different. A larger gradient is required during growth, whereas a smaller gradient is needed after growth (during an annealing step done in the same chamber). By changing the atmosphere from N 2 during growth to a vacuum during annealing, a larger gradient could be created during the growth stage and a smaller gradient3’for the : YAP crystals annealing free process. from cloudiness With the above and twinning technique, wasthe obtained. annealing Rods period with was a diameter greatly of shortened 8 x 150 mm and could a hatch he of cuthigh-quality from the above Nd crystals and a maximum average power of up to 781 W laser output has been achieved by using only a unitary rod.
I. Introduction
increased considerably on the melt side of the solid—liquid interface, due to segregation effects.
Yttrium orthoaluminate (YA1O 3 or YAP) has a perovskite-like orthorhombic crystal structure with a space group of D~~Pnma. Neodymium doped 3~ YAP possesses several properties similar to Nd those of Nd3~: YAG (yttrium aluminium garnet) and in addition to that, it has some extra advantages: (1) the output radiation is polarized, (2) there are two laser wavelength emissions (1.064 and 1.079 ~.sm).depending on the orientation of crystal axis, and (3) the stimulated emission cross section (22 X 10—20 cm2) is 2.4 times greater than that of Nd3~: YAG at 1.34 j~m[11. Therefore it has opened up promising prospects for extensive applications, Owing to the large anisotropy of physical properties of the crystal and the intrinsic segregation behavior of Nd dopants, Nd~’: YAP crystals grown by Czochralski method usually tend to cxhihit cracking. twinning and cloudiness. Therefore, large-size high-quality Nd~: YAP single crystals are not easy to obtain [2—4]. Although the segregation coefficient of Nd ions in YAP is comparatively large (0.8). during crystal growth with a large pull rate (3.0 mm/h), low rotation rate (10--30rpm), and large crystal diameter 30 mm), the concentration of Nd ions is (—
0022.0248/90/803.50
1990
—
Once an external disturbance (such as a fluctuation in the heating power) occurs, it will easily result constitutional supercooling, thus leading to the information of defects such as cloudiness in the crystals. The usual solution to the above problem is to use a furnace geometry which increases the gas-liquid temperature difference and thereby acedcrates natural convection in the melt (enhance stirring) so as to decrease the Nd concentration at the solid--liquid interface. Thus, the cloudiness can be avoided in the crystals. On account of the large anisotropy of physical properties and the especially large difference of the coefficients of thermal expansion in Nd3~: YAP crystals (4.2, 11.7 and 5.1 x C for the a-, h- and c-axes, respectively), this difference can result in large thermal stresses in crystals grown at high temperature and then annealed in a large gas--liquid temperature difference, thereby causing (easily) the formation of twtnning on the (110) and (110) planes. Generally. a method is used to transfer at high temperature the large just-grown Nd3 : YAP single crystals into an afterheater and then reduce the temperature difference per unit length along °
Elsevier Science Publishers B.V. (North-Holland)
Li Gansheng et a!.
/
3+
Growth and characterization of high.qualits Nd
the crystals. Annealing in such a temperature field is certainly advantageous to decrease thermal stresses in the crystals. Thus, it is possible to avoid the formation of twinning in the crystals. In this case, of course, many difficulties will arise with a sealed induction heating chamber. In view of the above circumstances, a technique involving changing the ambient atmosphere from N-, to vacuum after growth and before annealing (the “vacuum natural cooling process”, VNCP) has been adopted to meet the two different temperature gradient requirements, i.e. a larger gradient during growth and a smaller gradient during annealing of the crystals in the same chamber. 3~: YAP single crystals with a diameter Large of 30 XNd 180 mm have been grown by the above technology. Twinning, cloudiness and laser properties have been examined and measured for all of the grown crystals. The results indicate that a great majority of the crystals have no cloudiness
.-
YAP laser crystals
525
and twinning and are suitable for high efficiency. high-power solid lasers at 1.079 or 1.34 ~sm.
2. Growth of Nd3~: YAP single crystals 2.1. A brief description of the growth process
In our Czochralski growth process, an Jr crucible was heated by a medium-frequency RF current under nitrogen atmosphere at a pressure of 1.6 X i0~Pa. A 1 kg charge of raw material with a purity of 99.999% was used with the composition Nd 0~1Y()99AlO3.The growth parameters included a pull rate of 3 mm/h, a rotation rate of 10—30 rpm and a crystal diameter of 30 mm. Although no twinning will occur in the large-size Nd3 ~ : YAP single crystals grown under a smaller gas—liquid temperature difference (<7°C) and annealed at a cooling rate of 100°C/h, cloudi-
Fig. 1. Light scattering by cloudiness in Nd35 YAP crystal. Viewed along the a-axis.
526
Li Gansheng eta!.
/ Growth and characterization .,.:~
3
of high-quality Nd
+
YAP laser crystals
-~
a axis
-~
~.
Fig. 2. Twinning pairs in Nd3 + YAP crystal on { 1 l0}.
ness will always appear. It is especially serious in the core region and results in a harmful light scattering, as shown in fig. 1. Even if the crystals are grown in a larger gas-liquid temperature difference (> 15°C) and annealed from high temperature to room temperature at a smaller cooling rate ( < 50°C/h). the twinning will still appear, as shown in fig. 2. However, when the crystals grown in the above large thermal gradient are then annealed by \TNCP annealing technique as described in section 2.2, a hatch of large-size Nd3~: YAP single crystals free from cloudiness and twinning has been grown.
ture gradient in the chamber, which will satisfy the requirement of the annealing temperature after growth of the crystals.
-
-
2.2. Fealures of the VNCP temperature field According to the heat transfer principles developed for the high-temperature growth chamber [5] shown in fig. 3, a higher pressure of nitrogen atmosphere will surely increase the convection in the gas. This will cause the quantity of heat to transfer easily from the inside to the outside of the chamber. This will be advantageous to the establishment of a large temperature gradient in the chamber and ensure the normal growth of the If th gas is pumped out and the growth chamher is changed into a vacuum state, then the transfer of heat by convection disappears and the temperature inside the chamber tends quickly to reach equilibrium, due to the thermal radiation of the internal wall of the chamber. This will be very favorable to the establishment of a small tempera-
5
,
:
.,.
C
.
I
C
.... .
~.
..
.
L -
... -
-.
-
..
..
2
. :•.
_____
~tIIII4IIIIII~IIIIEI~~ -
-
Fig. 3. Schematic diagram of growth chamber for large sii.e Nd35 YAP crystal (1) corundum plate; (2) corundum cylinder: (3) quartz cylinder; (4) Y 20 shield; (5) a-Al70 single crystal flake: (6) RF coil: (7) Ir crucible; (8) Zr02 powder.
3
Li Gansheng et a!. / Growth and characterization of high-quality Nd
+ .
YAP laser crystals
527
T(°C)
1500
1000
~
500
2
‘~
N.~
1
-~
0 0
50
100
150
200
t(min)
Fig. 4. The natural cooling rates in the chamber under vacuum and nitrogen atmoiphere. (•), (X) Temperatures at 150 mm above the crucible mouth for curves I and 2, respectively; (es), (0) temperatures at the crucible mouth for curves 1 and 2, respectively. (1) Nitrogen atmosphere at a pressuie of 1.6 x iO~Pa; (2) vacuum of 10 Pa.
The natural cooling rates of the chamber under a vacuum of 10 Pa and a nitrogen atmosphere of 1.6 x iO~ Pa, as well as the temperature dif-
ferences (AT) between the upper part (at 80 mm above the crucible mouth) and the lower part (at the crucible mouth) with the annealing tempera-
~T(°C) 800 700
100 0
___________________________
1700
130
1~00
900
700
~500
Tn(°C)
Fig. 5. The temperature differences between the upper and lower parts in the chamber during the natural cooling under two kinds of atmosphere. The upper part refers to 80 mm above the crucible mouth and the lower part to the crucible mouth. (I) Nitrogen atmosphere at a pressure of 1.6 X iO~Pa; (2) vacuum of 10 Pa.
528
Li Gansheng eta!.
/ Growth and characterization
ture (Ta) in the chamber under two kinds of atmospheres, have been measured and compared. The results are shown in figs. 4 and 5, respectively, It can be seen from figs. 4 and 5 that: (1) The natural cooling rates in the chamber under vacuum of 10 Pa are much slower than those in the chamber under nitrogen atmosphere of 1.6 X i0~Pa. This indicates that the vacuum state is unfavorable to the transfer of heat from the inside to the outside of the chamber. The experimental facts are consistent with the above analyses.
3’
ofhigh-quality Nd
YAP laser cry.stal.s
(2) The temperature difference suffered by the two ends of the crystal during its natural cooling in vacuum (10 Pa) is only two-thirds to one-half of that in nitrogen atmosphere (1.6 x i05 Pa). This means that when the crystals grown in a nitrogen atmosphere of 1.6 X ~ Pa at high temperature are transferred and annealed in vacuum, it is possible to achieve the goal of the crystals grown in a large-gradient temperature field while annealed in a small-gradient temperature field.
Table I Examination of twinning and cloudiness in Nd’ : YAP crystals Crystal
Main growth parameters
No.
Growth rate (mm/h)
. Rotation rate (rpm)
. Crystal diameter (mm)
Heating power stability
S8601 S8602 S8603 S8604 S8605 S8606 S8607 S8608 S8609 S8610 S86l1 S8612 S8613 S8614 S8615 S8616 S8617
3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
20 20 20 20 20 20 20 20 29 10 10 10 10 10 10 10 20
30 30—40 28—31 30 26—29 26—29 27—29 27—28 25
27—31 26—30 24—28 25—30 25—28 26—28 25—28 25—28
Yes Yes (m), no Yes Yes Yes Yes Yes Yes Yes (m). no Yes Yes Yes Yes Yes Yes
S8618 S8619 S8620 S8621 S8622 S8623 S8624 S8625 S8626 S8627 S8628 S8629 S8630 S8631
3 3 3 3 3 3 3 3 3 3 3 3 3 3
10 20 10 10 10 10 10 10 10 10 10 10 10 10
26—30 28—30 25—30 24—28 23—28 25—29 25—27 25—27 25—30 25—29 26—30 25—28 26—28 26—30
Yes Yes (m), no (I). no Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes
Twinning
(‘loudiness
No No
No No
(m), 2 pairs No No No
No No No No
No NO No
No No No No
Remarks
-
No (iii).
2 pairs
Yes.
No
NO
NC)
No
NC)
NC)
NC)
No No
No (m). 1 pair No No (m). 2 pairs
(iii)
Yes, (h) (m), (I) NC) NC) NO
No
Yes, (I)
No
NO
No
No
No NO
No
No
No
No No
No No No No No
(h) in head part of crystal, (m) in middle part of crystal. (I) in lower part of crystal.
Raw material Contamination
No Loose seed No No Yes, in center Gas leak in chamber
Li Gansheng et a!.
/ Growth and characterization
3+
of high-quality Nd
.
529
YAP laser crystals
Table 2 Nd3 + : YAP laser performance Laser type
Diameter (mm)
Rod orientation
High average power laser
8
x150
a-axis
CW laser CW laser CW laser Pulse laser
6 X 110 5.83<111 6 3<100 7.2 x 150
a-axis a-axis a-axis a-axis
Long pulse laser Simultaneous, multiple wavelength laser
6 5
x 100
a-axis a-axis
~ Unit cell dimensions [61: a
=
5.33
A,
b
x104 7.375
A,
c = 5.180
0
Pump source
Laser mode
Laser wavelength (/zm)
Laser output power or energy
Kr lamp (7.5 ms. 15 pps) Kr lamp Kr lamp Kr lamp Kr lamp (7.5 ms) Xe lamp Kr lamp
Multi
1.079
781 W
Multi Multi TEMwt Multi
1.079 1.34 1.34 1.079
162 W 82 W 5.3 W 44 J
Multi Multi
1.34 1.079 1.34
2J 5.25 W 5.4W
A.
3. The characterization of Nd3.F : YAP crystals
high-power lasers, particularly at 1.34 ~im wavelength lasers.
3.]. The examination of twinning and cloudiness in. Nd3~ : YAP crystals 4.
Thirty-one large-size Nd3 + : YAP boules have been grown by the above technique. Examination of twinning and cloudiness in each of the boules has been carried out. The twinning and cloudiness can be clearly observed by directing a strong white light along the (001) plane of the boules. The results and corresponding growth parameters are listed in table 1. It can be seen from table 1 that, except for the appearance of twinning and cloudiness in corresponding parts of boules subject to intense temperature (heating power) fluctuations, an air leak of the chamber or a loose seed, the great majority of boules grown even at rotation rates of 30 to 10 rpm have no twinning and cloudiness. 3.2. Measurements of laser properties
In order to determine the laser properties experimentally, different laser rods were cut out of the above boules. The measurement of laser performance was carried out in various active lasers. The main results are listed in table 2. It can be seen from table 2 that Nd3~: YAP single crystal is a very good laser material for
Conclusions
(1) By means of a vacuum annealing technique, the problem of growing large Nd3~: YAP single crystals without twins or scattering centers has been solved satisfactorily. It is therefore possible to provide large-size, high-quality laser rods for high power laser applications. (2) The VNCP technique can be expected to be applied to the growth of high-temperature anisotropic crystals similar to YAP crystals.
Acknowledgements The authors would like to thank Lu Jian and Yang Hua for their participation in the crystal growth, and Professor Shen Hongyuan for providing laser performance data. Thanks are also due to Professor Yixiong for his careful examination of thisFang manuscript. References [1] Hongyuan Shen, Tianquan Lian et al.. IEEE J. Quantum Electronics QE-25 (1989) 144.
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[2] AD. Morrison. R.R. Monchamp, M. Basset al., AD-743223 (1972) [3] R.F. Belt, R. Uhrin, R. Puttbach et al., in: Abstracts 3rd Am. Conf. on Crystal Growth, Am. Assoc. for Crystal Growth, Stanford, CA, 1975, p. 190.
3+
of high-quality Nd
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YAP laser crystals
[4] iS. Abell and l.R. Harris, J. Mater. Sci. 7 (1972) 1088. [5] Li Gansheng. Shi Zhenzhu, Chen Ying et al., J. Synthetic Crystals 16 (1987) 33 (in Chinese) [61 R. Diehi. G. Brandi et al.. Mater. Res. Bull. 10 (1975) 85.