- Email: [email protected]
Growth of RbTiOPO4 single crystals from phosphate systems
Journal of Crystal Growth 125 (1992) 639—643 North-Holland
~
CRYSTAL GROWTH
Growth of RbTiOPO4 single crystals from phosphate systems Yuriy S. Oseledchik a Sergey P. Belokrys a Victor V. Osadchuk a, Andrey L. Prosvirnin Anatoly F. Selevich b Valery V. Starshenko a and Katrin V. Kuzemchenko a
a
Industrial Institute, 226 Lenin Avenue, 330006 Zaporozhye, Ukraine b Belarussian
State University, Minsk 220080, Belarus
Received 23 April 1992; manuscript received in final form 29 July 1992
The phase diagram of Rb20—P205—(Ti02)2 in the temperature range of 600—1100°Cis investigated. The existence of two isomorphic crystalline phases of RbTiOPO4 is revealed; one of them is similar to KTiOPO4 (rhombic system) and the other phase has cubic structure with space group Fd3m. The curves of the RTP solubility in the fluxes in the at temperatures in the range of 750—1050°Chave been determined. The nonlinear optical properties of RTP are briefly discussed.
1. Introduction Potassium titanyl phosphate KTiOPO4 (KTP) is known as an outstanding nonlinear optical material [1]. Numerous successful investigations of KTP properties and growth [2—111have provoked an interest in crystals which are isostructural to KTP [11—151.In particular rubidium titanyl phosphate RbTiOPO4 (RTP), first grown by the hydrothermal method [11, has demonstrated excellent nonlinear optical properties. RTP crystal growth by the flux method and the study of physical properties were reported in refs. [16,171. We have determined that the growth of RTP crystals from tungstate and molybdate solvents [111 leads to the inclusion of W and Mo in the crystal lattice, resulting in an enhancement of fragility, a reduction of the optical damage threshold, a decrease in the second harmonic generation efficiency and the appearance of colour centres. Phosphate systems are the more preferable for the growth of optically pure RbTiOPO 4 crystals and are investigated in this paper. The region of the Rb20—P2O5—(Ti02)2 phase diagram where RbTiOPO4 is the only solid phase in equilibrium with the melt under 800°C has been determined [21. In contrast to ref. [2], we have found the 0022-0248/92/$05.00 © 1992
—
region of RTP monophase crystallization to be narrower and a difference in the solubility curve at a temperature of 800°Cwas observed. A detailed study of the phase diagram enabled us to detect an RTP phase which is not isostructural to the earlier phase.
2. Investigation of phase diagrams The investigation of the M20—P205—(Ti02)2 (M = K, Rb, Cs) phase diagrams was performed in a resistive furnace with a platinum crucible. Reagents Ti02, M2C03 and MH2PO4 of analytical purity were used as starting materials to prepare compositions corresponding to different points on the ternary phase diagram (with the M20/P205 ratio being from 0.8 to 2.33). Then the3 compositions melted crucibles of 20 in volume, were exposed to aintemperature of cm 1100°C,cooled down to 600°Cat a rate of 10°C/h and washed with water. It was revealed by X-ray phase analysis that for RbTiOPO4, two nonisostructural phases exist. One of them being similar to the KTP structure (a-phase) belongs to the rhombic system with space group Pna21. The other phase belongs to the cubic system with space group Fd3m (a-phase). Thus, for KTP only
Elsevier Science Publishers B.V. All rights reserved
640
Yu.S. Oseledchik et a!.
/ Growth of RbTiOPO4 Table 1
i~o,
(fl02)~ R520 ~P10,:(T,0,)~ 30:50:20
from phosphate systems
X-ray diffraction hkl /3-RbTiOPO4 ~ dcaic data for f3-RbTiOPO4 “exp J3-CsTiOPO4 dexp anddcai. /3-CsTiOPO4 kxF, (A) (A) (%) (A) (A) (%)
Rb~0 Rb,0 ‘P,O, Ti0~ cm 50:0
220 311 111 222
3.53 3.02 5.74 2.88
3.54 3.02 5.77 2.89
25 100 6 30
3.58 3.05 5.78 2.91
3.57 3.04 5.83 2.91
49 100 5 11
400 331 422 333 511
2.49 2.29 2.04 2.928 1.928
2.50 2.29 2.04 1.925 1.925
49 266 26
2.52 2.32 2.06 1.939 1.939
2.52 2.31 2.06 1.942 1.942
158 13 19 19
20—P205—(Ti02)2 system: DEFG, investigated region; (———) solubility curves of a-RTP phase at 750°C(1), 800°C(2), 850°C(3), 900°C(4), 950°C(5), 1000°C(6) and 1050°C(7); BC, solubility curve at 800°C[2].
440 620 533 622
1.771 1.586 1.528 1.511
1.768 1.581 1.525 1.508
23 10 9 6
1.783 1.596 1.541 1.524
1.784 1.595 1.539 1.521
20 9 7 2
the a-phase is known, while RTP forms both a-phase and /3-phase. Similar investigations detected, for CsTiOPO4 (CTP), the /3-phase only. The part of the Rb20—P205—(Ti02)2 ternary phase diagram where the region of a-RTP monophase crystallization borders upon the regions of /3-RTP, RbTi2(P04)3 and Ti02 crystallization is shown in fig. 1. Solid lines mark the boundaries of regions, determined by X-ray phase analysis. It is evident that the region of a-RTP crystallization is somewhat narrower as compared to the corresponding ABC region represented in ref. [21. The temperatures of incongruent melting of a-RTP phase and j3-RTP phase are defined to be
1.5, 1.74 and 2.0 to define the borders of the monophase crystallization region for different temperatures of the noncentrosymmetrical aRTP phase on the Rb20—P205—(Ti02)2 phase diagram. The crucible was mounted into the furnace at a point with cooler melt surface. The temperature of solution saturation was determined by dissolution of a trial seed. Solubility curves (fig. 2) have been used to calculate isothenns, which are the temperature borders of the a-RTP phase crystallization region. The
RbT2(P0,
TO~)~ ~2Q312:30:40 P2°5:( Ti02)~ Rh20 (r.~oIZ) Fig. 1. Ternary phase diagram of Rb
of
Rb207030:0 P20, (
equals 1140°C. X-ray diffraction investigations were carried 1150onand melting point out an 1160°C,respectively. X-ray diffractometerThe HZG-4/A (Carl Zeiss, Jena) with Cu K radiation. X-ray diffrac-
20
4.5
CTP
tion data for /3-RTP and f3-CTP are represented in table 1; for a-RTP our data coincide with ref. [171. The /3-phase of RTP and CTP belongs to the cubic systems, space group Fd3m, with lattice parameters a 10.00(3) A for f3-RbTiOPO4 and a 10.09(3) A for /3-CsTiOPO4. Concentration curves were obtained from RTP-solvent lines with ratio Rb20/P205 1.3, =
=
=
C
1,
/
I~r2
>
..-~Io. a
05
0
j~j~
4100
~r~
Fig. 2. Solubility curves of RbTiOPO4 in the polyphosphate solvent. Rb20/P205 = 1.3 (1), 1.5 (2), 1.74 (3) and 2.0 (4).
Yu.S. Oseledchik et a!.
/
Growth of RbTiOPO
isotherms are shown in fig. 1. The discrepancy between curve 2 of RTP solubility for 800°cand the corresponding curve BC from ref. [2] may be explained by the error of indirect definition of solubility and position of curve BC. Gravimetric measurements have proved the volatility of composition to enhance with decrease of Rb20/P205 ratio. The shift of the point on the ternary phase diagram to compositions with greater Rb20/P205 ratio, and therefore to greater relative RTP concentration in solution, is a result of evaporation. The specific volatility for compositions with Rb2O/P205 = 1.5 is found to be 10—s cm —2 h~ (1000°C).
4 from phosphate systems
641
201
Ott
1(0 -
X
204
9
O1~
Fig. 4. Morphology of flux grown RTP crystal.
3. Crystal growth A one-zone vertically oriented furnace system for crystal growth was equipped with a temperature controller of RIF-lOl type and a Pt/Pt—Rh thermocouple as the temperature pickup. A schematic sketch of the crystal growth setup is given in fig. 3. A dehydrated furnace charge (RbH2PO4, RbCO3, TiO2, H3P04 of a grade not lower than analytically pure) was loaded in3.aThe platinum vessel experimenwith a volume of 200—300 cm tally selected crucible position in the furnace was determined by a necessary temperature profile in ~ -______
—
—
______
2
I L
3 ______ ____
~
:--=~.~
5 6 ~—
7
Fig. 3. Scheme of crystal growth setup: (1) reverse rotation and crystal lifting mechanism; (2) alumina seed shaft; (3) heater; (4) platinum seed shaft; (5) thermocouple; (6) seed; (7) platinum crucible; (8) ceramic tube,
the melt and above it. Furnace changes were exposed to a temperature exceeding the calculated crystallization temperature by 50—100°Cfor 20—30 h (to homogenize the melt). Etching of the trial seed indicated the temperature of melt saturation. To refine the seed surface, the trial crystal was submerged into the melt at 5—10°Cabove the solution saturation temperature for a certain time. Then the melt cooled to saturation temperature. During thewas growth runs, cooling rates ranged from 0.05 to 0.35°C/h. Growth experiments routinely lasted 2—3 weeks. The crystal was withdrawn from the melt and cooled to room temperature (quick cooling leads to cracking of the crystal along the XZ plane). Crystal growth in both X and Z axis direction showed the best results. The relative growth rate ratios in X, Y and Z directions were estimated to be 1: 1.35: 1.64. Typical RTP crystal morphology is represented in fig. 4. The largest dimension of the RTP crystal mounted to 30 X 40 x 60 mm3. The trapped and included melt, being the principal type of the RTP crystal impurities, is caused by unstable temperature control, high cooling rates, unsatisfactory temperature profile and unsatisfactory dynamics of the melt flowing around the crystal. Selection of growth parameters, reverse crystal rotation and forced melt stirring aid in crystal growth without optically observed microscopic inclusions. .
642
Yu.S. Oseledchik et a!.
/ Growth
ofRbTiOPO
4 from phosphate systems
4. Nonlinear optical properties
5. Conclusion
The optical properties of the RTP crystals obtained are similar to those of KTP crystals [18—20]. For both RTP and KTP, the transparency region is 350—4500 nm. The angles between optical axes are 42.5° in RTP and 43.19°in KTP at A = 532.5 nm. Study with crossed polaroids revealed the sectonal structure of the crystal. Converters of laser radiation were fabricated from core-free crystal regions. The nonlinear optical properties of RTP were investigated by (Nd means of laser) radiation with wavelength 1064 nm : YAG and 1079 nm (Nd : YAP laser). Experimentally determined phase-matching angles for RTP and KTP crystals are represented in table 2. The uniformity of crystal structure can be testified by the uniformity of radiation conversion into the second harmonic in a wide beam all over the crystal field. The efficiency of SHG for pulsed laser radiation with wavelengths of 1079 and 1064 nm attains 60—70% with high crystal uniformity. The highest efficiency achieved in KTP was 80% [21]. The surface optical damage threshold was 900 MW/cm2 for RTP crystals [18] as against 400 MW/cm2 for KTP. An angle phase-matching bandwidth for the RTP crystal as large as 5.0 X 6.0 x 3.6 mm3 was defined to be 2.3° at the half-level of intensity. The temperature matching bandwidth for RTP equalled 50°C/cm,while for KTP it was 25°C/cm.
The ternary phase diagram of Rb20—P2O5— (Ti02)2 was studied in detail. The existence of two crystalline phases of rubidium titanyl phosphate was revealed, only one of them being described earlier. The region of a-RTP monophase crystallization in a temperature range of 600— 1100°C was determined. The curves of a-RTP solubility in phosphate solvents with ratios Rb20/P205 = 1.3, 1.5, 1.74 and 2.0 were obtamed. Optically3, pure RTP as large as suitable forcrystals fabrication of laser 30 x 40 x 60frequency mm radiation converters, were grown. Comparison of RTP and KTP nonlinear optical characteristics has shown RTP crystal to possess a somewhat higher optical damage threshold and a twice as large temperature phase-matching bandwidth. These properties made it possible to use RTP crystals in a quasi-continuous regime under high average radiation power.
References [1] F.C. Zumsteig, J.D. Bierlein and T.E. Gier, J. AppI. Phys 47 (1976) 4980. [2] T.E. Gier, US Patent, 4,231,838 (November, 1980). [31J.C. Jacco, G.M. Loiacono, M. Jaso, G. Mizell and B. Greenberg, J. Crystal Growth 70 (1984) 484. [4] R.A. Laudise, RJ. Cava and A.J. Caporaso, J. Crystal Growth 74 (1986) 275. [5] P.F. Bordui, J.C. Jacco, G.M. Loiacono, R.A. Stolzenand J.J. Zola, Crystal Growth Izv. 84 (1987) [6] berger V.!. Voronkova and J.V.K. Yanovsky, Akad.403. Nauk SSSR, Neorgan. Mater. 24 (1988) 273. [7] J.D. Bierlein and H. Vanherzeele, J. Opt. Soc. Am. B 6 (1989) 622. 18] G.M. Loiacono, T.F. McGee and G. Kostecky, J. Crystal Growth 104 (1990) 389. [9] A.A. Ballman, H. Brown, D.H. Olson and C.E. Rice, J.
Table 2 Phase-matching angles for RTP and KTP ____________________________________________________ Wavelength Plane Angle (deg) (nm) RTP KTP __________________________________________________ 1064 XY 58.0 24.0 YZ 76.0 69.2
Crystal Growth 75 (1986) 390. [101 K. Iliev, P. Peshev, V. Nikolov and I. Koseva, J. Crystal Growth 100 (1980) 219,225. [11] L.K. Cheng, J.D. Bierlein and A.A. Ballman, J. Crystal Growth 110 (1991) 697. [12] N.S. Slobodyanik, P.G. Nagorny, V.V. Skopenko and E.S. Lugovskaya, J. Inorg. Chem. (USSR) 32 (1987) 1023. [13] L.K. Cheng, J.D. Bierlein, C.M. Fans and A.A. Ballman,
1079 XY 48.5 4.1 YZ 73.5 67.3 ________________________________________________________
J. Crystal Growth 112 (1991) 309. [14] (1990) P.A. Thomas. and B.E. Watts, Solid State Commun. 73 97.
Vu. S. Oseledchik et aL
/
Growth of R6TiOPO
[15] J.D. Bierlein, H. Vanherzeele and A.A. Ballman, AppI. Phys. Letters 54 (1989) 783. [16] J.Y. Wang, Y.G. Liu, J.Q. Wei, L.P. Shi and M. Wang, Z. Krist. 191 (1990) 231. [17] J.Y. Wang, Y.G. Liu, L.P. Shi, M. Wang and JO. Wei, J. Chinese Ceram. Soc. 18 (1990) 165 (in Chinese). [18] Yu.S. Oseledchik, Al. Pisarevsky, A.L. Prosvirnin, V.N. Lopatko, L.E. Holodenkov, E.F. Titkov, A.A. Demiovich and A.P. Shkaparevich, in: Proc. 6th All-Union Conf. on Laser Optics, Leningrad, March 1990, p. 440. [19] V.A. Matusevich, V.A. Maslov, Yu.S. Oseledchik, A.L.
4 from phosphate systems
643
Prosvirnin, Al. Pisarevsky, V.V. Starshenko and O.P. Shaunin, presented at 10th Intern. Vavilov Conf. on Nonlinear Optics, Novosibirsk, June 1990, unpublished. [20] A.!. Pisarevsky, A.L. Prosvirnin, Yu.S. Oseledchik, V.V. Osadchuk, S.P. Belokrys, V.V. Starshenko and MM. Kasyan, in: Proc. 14th Intern. Conf. on Coherent and Nonlinear Optics (ICONO ‘91), Leningrad, September 1991, Vol. 3, p. 166. [21] G.I. Dyakonov, V.A. Maslov, V.A. Mihaylov, S.K. Pak, V.N. Semenenko and IA. Shcherbakov, Kvantov. Elektron. 16 (1989) 1601.
~
CRYSTAL GROWTH
Growth of RbTiOPO4 single crystals from phosphate systems Yuriy S. Oseledchik a Sergey P. Belokrys a Victor V. Osadchuk a, Andrey L. Prosvirnin Anatoly F. Selevich b Valery V. Starshenko a and Katrin V. Kuzemchenko a
a
Industrial Institute, 226 Lenin Avenue, 330006 Zaporozhye, Ukraine b Belarussian
State University, Minsk 220080, Belarus
Received 23 April 1992; manuscript received in final form 29 July 1992
The phase diagram of Rb20—P205—(Ti02)2 in the temperature range of 600—1100°Cis investigated. The existence of two isomorphic crystalline phases of RbTiOPO4 is revealed; one of them is similar to KTiOPO4 (rhombic system) and the other phase has cubic structure with space group Fd3m. The curves of the RTP solubility in the fluxes in the at temperatures in the range of 750—1050°Chave been determined. The nonlinear optical properties of RTP are briefly discussed.
1. Introduction Potassium titanyl phosphate KTiOPO4 (KTP) is known as an outstanding nonlinear optical material [1]. Numerous successful investigations of KTP properties and growth [2—111have provoked an interest in crystals which are isostructural to KTP [11—151.In particular rubidium titanyl phosphate RbTiOPO4 (RTP), first grown by the hydrothermal method [11, has demonstrated excellent nonlinear optical properties. RTP crystal growth by the flux method and the study of physical properties were reported in refs. [16,171. We have determined that the growth of RTP crystals from tungstate and molybdate solvents [111 leads to the inclusion of W and Mo in the crystal lattice, resulting in an enhancement of fragility, a reduction of the optical damage threshold, a decrease in the second harmonic generation efficiency and the appearance of colour centres. Phosphate systems are the more preferable for the growth of optically pure RbTiOPO 4 crystals and are investigated in this paper. The region of the Rb20—P2O5—(Ti02)2 phase diagram where RbTiOPO4 is the only solid phase in equilibrium with the melt under 800°C has been determined [21. In contrast to ref. [2], we have found the 0022-0248/92/$05.00 © 1992
—
region of RTP monophase crystallization to be narrower and a difference in the solubility curve at a temperature of 800°Cwas observed. A detailed study of the phase diagram enabled us to detect an RTP phase which is not isostructural to the earlier phase.
2. Investigation of phase diagrams The investigation of the M20—P205—(Ti02)2 (M = K, Rb, Cs) phase diagrams was performed in a resistive furnace with a platinum crucible. Reagents Ti02, M2C03 and MH2PO4 of analytical purity were used as starting materials to prepare compositions corresponding to different points on the ternary phase diagram (with the M20/P205 ratio being from 0.8 to 2.33). Then the3 compositions melted crucibles of 20 in volume, were exposed to aintemperature of cm 1100°C,cooled down to 600°Cat a rate of 10°C/h and washed with water. It was revealed by X-ray phase analysis that for RbTiOPO4, two nonisostructural phases exist. One of them being similar to the KTP structure (a-phase) belongs to the rhombic system with space group Pna21. The other phase belongs to the cubic system with space group Fd3m (a-phase). Thus, for KTP only
Elsevier Science Publishers B.V. All rights reserved
640
Yu.S. Oseledchik et a!.
/ Growth of RbTiOPO4 Table 1
i~o,
(fl02)~ R520 ~P10,:(T,0,)~ 30:50:20
from phosphate systems
X-ray diffraction hkl /3-RbTiOPO4 ~ dcaic data for f3-RbTiOPO4 “exp J3-CsTiOPO4 dexp anddcai. /3-CsTiOPO4 kxF, (A) (A) (%) (A) (A) (%)
Rb~0 Rb,0 ‘P,O, Ti0~ cm 50:0
220 311 111 222
3.53 3.02 5.74 2.88
3.54 3.02 5.77 2.89
25 100 6 30
3.58 3.05 5.78 2.91
3.57 3.04 5.83 2.91
49 100 5 11
400 331 422 333 511
2.49 2.29 2.04 2.928 1.928
2.50 2.29 2.04 1.925 1.925
49 266 26
2.52 2.32 2.06 1.939 1.939
2.52 2.31 2.06 1.942 1.942
158 13 19 19
20—P205—(Ti02)2 system: DEFG, investigated region; (———) solubility curves of a-RTP phase at 750°C(1), 800°C(2), 850°C(3), 900°C(4), 950°C(5), 1000°C(6) and 1050°C(7); BC, solubility curve at 800°C[2].
440 620 533 622
1.771 1.586 1.528 1.511
1.768 1.581 1.525 1.508
23 10 9 6
1.783 1.596 1.541 1.524
1.784 1.595 1.539 1.521
20 9 7 2
the a-phase is known, while RTP forms both a-phase and /3-phase. Similar investigations detected, for CsTiOPO4 (CTP), the /3-phase only. The part of the Rb20—P205—(Ti02)2 ternary phase diagram where the region of a-RTP monophase crystallization borders upon the regions of /3-RTP, RbTi2(P04)3 and Ti02 crystallization is shown in fig. 1. Solid lines mark the boundaries of regions, determined by X-ray phase analysis. It is evident that the region of a-RTP crystallization is somewhat narrower as compared to the corresponding ABC region represented in ref. [21. The temperatures of incongruent melting of a-RTP phase and j3-RTP phase are defined to be
1.5, 1.74 and 2.0 to define the borders of the monophase crystallization region for different temperatures of the noncentrosymmetrical aRTP phase on the Rb20—P205—(Ti02)2 phase diagram. The crucible was mounted into the furnace at a point with cooler melt surface. The temperature of solution saturation was determined by dissolution of a trial seed. Solubility curves (fig. 2) have been used to calculate isothenns, which are the temperature borders of the a-RTP phase crystallization region. The
RbT2(P0,
TO~)~ ~2Q312:30:40 P2°5:( Ti02)~ Rh20 (r.~oIZ) Fig. 1. Ternary phase diagram of Rb
of
Rb207030:0 P20, (
equals 1140°C. X-ray diffraction investigations were carried 1150onand melting point out an 1160°C,respectively. X-ray diffractometerThe HZG-4/A (Carl Zeiss, Jena) with Cu K radiation. X-ray diffrac-
20
4.5
CTP
tion data for /3-RTP and f3-CTP are represented in table 1; for a-RTP our data coincide with ref. [171. The /3-phase of RTP and CTP belongs to the cubic systems, space group Fd3m, with lattice parameters a 10.00(3) A for f3-RbTiOPO4 and a 10.09(3) A for /3-CsTiOPO4. Concentration curves were obtained from RTP-solvent lines with ratio Rb20/P205 1.3, =
=
=
C
1,
/
I~r2
>
..-~Io. a
05
0
j~j~
4100
~r~
Fig. 2. Solubility curves of RbTiOPO4 in the polyphosphate solvent. Rb20/P205 = 1.3 (1), 1.5 (2), 1.74 (3) and 2.0 (4).
Yu.S. Oseledchik et a!.
/
Growth of RbTiOPO
isotherms are shown in fig. 1. The discrepancy between curve 2 of RTP solubility for 800°cand the corresponding curve BC from ref. [2] may be explained by the error of indirect definition of solubility and position of curve BC. Gravimetric measurements have proved the volatility of composition to enhance with decrease of Rb20/P205 ratio. The shift of the point on the ternary phase diagram to compositions with greater Rb20/P205 ratio, and therefore to greater relative RTP concentration in solution, is a result of evaporation. The specific volatility for compositions with Rb2O/P205 = 1.5 is found to be 10—s cm —2 h~ (1000°C).
4 from phosphate systems
641
201
Ott
1(0 -
X
204
9
O1~
Fig. 4. Morphology of flux grown RTP crystal.
3. Crystal growth A one-zone vertically oriented furnace system for crystal growth was equipped with a temperature controller of RIF-lOl type and a Pt/Pt—Rh thermocouple as the temperature pickup. A schematic sketch of the crystal growth setup is given in fig. 3. A dehydrated furnace charge (RbH2PO4, RbCO3, TiO2, H3P04 of a grade not lower than analytically pure) was loaded in3.aThe platinum vessel experimenwith a volume of 200—300 cm tally selected crucible position in the furnace was determined by a necessary temperature profile in ~ -______
—
—
______
2
I L
3 ______ ____
~
:--=~.~
5 6 ~—
7
Fig. 3. Scheme of crystal growth setup: (1) reverse rotation and crystal lifting mechanism; (2) alumina seed shaft; (3) heater; (4) platinum seed shaft; (5) thermocouple; (6) seed; (7) platinum crucible; (8) ceramic tube,
the melt and above it. Furnace changes were exposed to a temperature exceeding the calculated crystallization temperature by 50—100°Cfor 20—30 h (to homogenize the melt). Etching of the trial seed indicated the temperature of melt saturation. To refine the seed surface, the trial crystal was submerged into the melt at 5—10°Cabove the solution saturation temperature for a certain time. Then the melt cooled to saturation temperature. During thewas growth runs, cooling rates ranged from 0.05 to 0.35°C/h. Growth experiments routinely lasted 2—3 weeks. The crystal was withdrawn from the melt and cooled to room temperature (quick cooling leads to cracking of the crystal along the XZ plane). Crystal growth in both X and Z axis direction showed the best results. The relative growth rate ratios in X, Y and Z directions were estimated to be 1: 1.35: 1.64. Typical RTP crystal morphology is represented in fig. 4. The largest dimension of the RTP crystal mounted to 30 X 40 x 60 mm3. The trapped and included melt, being the principal type of the RTP crystal impurities, is caused by unstable temperature control, high cooling rates, unsatisfactory temperature profile and unsatisfactory dynamics of the melt flowing around the crystal. Selection of growth parameters, reverse crystal rotation and forced melt stirring aid in crystal growth without optically observed microscopic inclusions. .
642
Yu.S. Oseledchik et a!.
/ Growth
ofRbTiOPO
4 from phosphate systems
4. Nonlinear optical properties
5. Conclusion
The optical properties of the RTP crystals obtained are similar to those of KTP crystals [18—20]. For both RTP and KTP, the transparency region is 350—4500 nm. The angles between optical axes are 42.5° in RTP and 43.19°in KTP at A = 532.5 nm. Study with crossed polaroids revealed the sectonal structure of the crystal. Converters of laser radiation were fabricated from core-free crystal regions. The nonlinear optical properties of RTP were investigated by (Nd means of laser) radiation with wavelength 1064 nm : YAG and 1079 nm (Nd : YAP laser). Experimentally determined phase-matching angles for RTP and KTP crystals are represented in table 2. The uniformity of crystal structure can be testified by the uniformity of radiation conversion into the second harmonic in a wide beam all over the crystal field. The efficiency of SHG for pulsed laser radiation with wavelengths of 1079 and 1064 nm attains 60—70% with high crystal uniformity. The highest efficiency achieved in KTP was 80% [21]. The surface optical damage threshold was 900 MW/cm2 for RTP crystals [18] as against 400 MW/cm2 for KTP. An angle phase-matching bandwidth for the RTP crystal as large as 5.0 X 6.0 x 3.6 mm3 was defined to be 2.3° at the half-level of intensity. The temperature matching bandwidth for RTP equalled 50°C/cm,while for KTP it was 25°C/cm.
The ternary phase diagram of Rb20—P2O5— (Ti02)2 was studied in detail. The existence of two crystalline phases of rubidium titanyl phosphate was revealed, only one of them being described earlier. The region of a-RTP monophase crystallization in a temperature range of 600— 1100°C was determined. The curves of a-RTP solubility in phosphate solvents with ratios Rb20/P205 = 1.3, 1.5, 1.74 and 2.0 were obtamed. Optically3, pure RTP as large as suitable forcrystals fabrication of laser 30 x 40 x 60frequency mm radiation converters, were grown. Comparison of RTP and KTP nonlinear optical characteristics has shown RTP crystal to possess a somewhat higher optical damage threshold and a twice as large temperature phase-matching bandwidth. These properties made it possible to use RTP crystals in a quasi-continuous regime under high average radiation power.
References [1] F.C. Zumsteig, J.D. Bierlein and T.E. Gier, J. AppI. Phys 47 (1976) 4980. [2] T.E. Gier, US Patent, 4,231,838 (November, 1980). [31J.C. Jacco, G.M. Loiacono, M. Jaso, G. Mizell and B. Greenberg, J. Crystal Growth 70 (1984) 484. [4] R.A. Laudise, RJ. Cava and A.J. Caporaso, J. Crystal Growth 74 (1986) 275. [5] P.F. Bordui, J.C. Jacco, G.M. Loiacono, R.A. Stolzenand J.J. Zola, Crystal Growth Izv. 84 (1987) [6] berger V.!. Voronkova and J.V.K. Yanovsky, Akad.403. Nauk SSSR, Neorgan. Mater. 24 (1988) 273. [7] J.D. Bierlein and H. Vanherzeele, J. Opt. Soc. Am. B 6 (1989) 622. 18] G.M. Loiacono, T.F. McGee and G. Kostecky, J. Crystal Growth 104 (1990) 389. [9] A.A. Ballman, H. Brown, D.H. Olson and C.E. Rice, J.
Table 2 Phase-matching angles for RTP and KTP ____________________________________________________ Wavelength Plane Angle (deg) (nm) RTP KTP __________________________________________________ 1064 XY 58.0 24.0 YZ 76.0 69.2
Crystal Growth 75 (1986) 390. [101 K. Iliev, P. Peshev, V. Nikolov and I. Koseva, J. Crystal Growth 100 (1980) 219,225. [11] L.K. Cheng, J.D. Bierlein and A.A. Ballman, J. Crystal Growth 110 (1991) 697. [12] N.S. Slobodyanik, P.G. Nagorny, V.V. Skopenko and E.S. Lugovskaya, J. Inorg. Chem. (USSR) 32 (1987) 1023. [13] L.K. Cheng, J.D. Bierlein, C.M. Fans and A.A. Ballman,
1079 XY 48.5 4.1 YZ 73.5 67.3 ________________________________________________________
J. Crystal Growth 112 (1991) 309. [14] (1990) P.A. Thomas. and B.E. Watts, Solid State Commun. 73 97.
Vu. S. Oseledchik et aL
/
Growth of R6TiOPO
[15] J.D. Bierlein, H. Vanherzeele and A.A. Ballman, AppI. Phys. Letters 54 (1989) 783. [16] J.Y. Wang, Y.G. Liu, J.Q. Wei, L.P. Shi and M. Wang, Z. Krist. 191 (1990) 231. [17] J.Y. Wang, Y.G. Liu, L.P. Shi, M. Wang and JO. Wei, J. Chinese Ceram. Soc. 18 (1990) 165 (in Chinese). [18] Yu.S. Oseledchik, Al. Pisarevsky, A.L. Prosvirnin, V.N. Lopatko, L.E. Holodenkov, E.F. Titkov, A.A. Demiovich and A.P. Shkaparevich, in: Proc. 6th All-Union Conf. on Laser Optics, Leningrad, March 1990, p. 440. [19] V.A. Matusevich, V.A. Maslov, Yu.S. Oseledchik, A.L.
4 from phosphate systems
643
Prosvirnin, Al. Pisarevsky, V.V. Starshenko and O.P. Shaunin, presented at 10th Intern. Vavilov Conf. on Nonlinear Optics, Novosibirsk, June 1990, unpublished. [20] A.!. Pisarevsky, A.L. Prosvirnin, Yu.S. Oseledchik, V.V. Osadchuk, S.P. Belokrys, V.V. Starshenko and MM. Kasyan, in: Proc. 14th Intern. Conf. on Coherent and Nonlinear Optics (ICONO ‘91), Leningrad, September 1991, Vol. 3, p. 166. [21] G.I. Dyakonov, V.A. Maslov, V.A. Mihaylov, S.K. Pak, V.N. Semenenko and IA. Shcherbakov, Kvantov. Elektron. 16 (1989) 1601.