ALPHAIODIC ACID: A SOLUTIONGROWN CRYSTAL FOR NONLINEAR OPTICALSTUDIES AND APPLICATIONSS. K. Kurtz, T. T. Perry, and J. G. Bergman Jr.

Citation: Applied Physics Letters 12, 186 (1968); doi: 10.1063/1.1651945 View online: http://dx.doi.org/10.1063/1.1651945 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/12/5?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Solutiongrown crystals of model ethylene copolymers J. Appl. Phys. 53, 6526 (1982); 10.1063/1.330079 Nonlinear polarizability of alphaiodic acid J. Chem. Phys. 62, 3571 (1975); 10.1063/1.430950 ALPHAIODIC ACID: A SOLUTIONGROWN CRYSTAL WITH A HIGH FIGURE OF MERIT FORACOUSTOOPTIC DEVICE APPLICATIONS Appl. Phys. Lett. 13, 156 (1968); 10.1063/1.1652551 Imperfections in SolutionGrown Silicon Carbide Crystals J. Appl. Phys. 39, 2324 (1968); 10.1063/1.1656553 Morphology of SolutionGrown Polypropylene Crystal Aggregates J. Appl. Phys. 36, 3017 (1965); 10.1063/1.1702920

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Volume 12, Number 5 APPLIED PHYSICS LETTERS 1 March 1968

olds than the one used in these experiments.

'C. L. Smith, E. Homentowski, and C. Stokes, Appl. Opt. 6, 1130 (1967).

2G. A. Askar'yan, E. Va. Gol'ts, and M. S. Rabinovich, Zhurnal

eksperemental'noi i teoreticheskoi jiziki, November, 1966.

3J. H. Goncz, and B. P. Newell,]. Opt. Soc. Am. 56, 87 (1966).

ALPHA-IODIC ACID: A SOLUTION-GROWN CRYSTAL FOR NONLINEAR OPTICAL STUDIES AND APPLICATIONS

S. K. Kurtz and T. T. Perry Bell T<;lephone Laboratories, Inc.

Murray Hill, New Jersey 07974

J. C. Bergman, Jr. Bell Telephone Laboratories, Inc.

Holmdel, New Jersey 07733 (Received 15 January 1968)

The linear and nonlinear optical properties of a-HI03 have been measured in the visible and near-infrared. Phase-matched second harmonic generation is shown to occur for both parallel and orthogonal input polariza­tions. The observed phase-matching surfaces are in agreement with theory. In addition, (a) large single crystals of high optical quality are easily grown from water solution; (b) the measured nonlinear coefficient d'4 is slightly larger than d3 , in LiNb03; and (c) no "optical damage" effects occur at high power densities. Preliminary results indicate that a substantial number of iodates exhibit similar nonlinear optical properties.

Since the initial discovery of phase-matched second harmonic generation (PMSHG) in KDP (KH2P04) by Giordmaine1 and Terhune and co­workers,2 there has been an intensive search for new phase-matchable materials having substantially larger nonlinear optical coefficients. This search has led to such diverse materials as lithium niobate (LiNb03),3 proustite (Ag3AsS3),4 and barium sodium niobate (Ba2NaNb5015).5 In this Letter we report on the nonlinear optical properties of a-iodic acid (HI03).6 The existence of strong PMSHG in this material was discovered using a recently developed powder survey technique.7

Large single crystals (several cm on a side and larger) of good optical quality a-HI03 have been grown from water solution by A. Holden.s The morphology of the crystals is identical to that re­ported by Groth.9 The crystalline solid is both hard and colorless, transmitting light without absorption over the range .4 IL to - 1.3 IL as shown in Fig. I.

The unit cell is orthorhombic with space group symmetry D24 - P2,P2,P2 , (refs. 10 and 11) and lattice constants ao = 5.5379 A, bo = 5.8878 A and Co =

7.7333 A. There are four molecules in a unit cell leading to a density of 4.63 g/cm3 . Perfect cleavage is obtained along {OIl} planes.

Values of the principal refractive indices were measured by the minimum deviation method on the apparatus of W. L. Bondl2 with the results

186

listed in Table I. From these values we see that the crystals are negative biaxial (nZ = nY > nX) with z = b, Y = -c, x = a. The acute bisectrix is the a axis (i.e., [100] direction) and the optic axial angle is 2V = 47°.

From the index values in Table I, the topology of the PM surfaces for SHG is readily determined from the recent work of Hobden on the PM prop­erties of biaxial crystalsP In this author's notation the indices satisfy the inequalities, ~z > n2Y > n{ > nlY > n{ > n{ and n{ < 1/2 (n{ + nlY ) where the subscripts I and 2 refer in the present work to the index evaluated at the fundamental light wave­length (1.065 IL) and the second harmonic wave­length (.5325 IL), respectively. A stereographic projection of the PM loci for a class-9 biaxial ma-

z o in CJ) 50 j CJ)

z ~ a: >-

WAVElENGTH (1')

Fig. 1. Optical transmission of a-H103 (I = 1.82 mm).

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Volume 12, Number 5 APPLIED PHYSICS LETTERS I March 1968

Table I.

(ILm) nZ nY nX

.450 2.0560 2.0184 1.8798

.500 2.0192 1.9930 1.8621

.5325 2.0103 1.9829 1.8547

.550 2.0049 1.9787 1.8497

.600 1.9922 1.9665 1.8409

.650 1.9812 1.9571 1.8352

.700 1.9765 1.9505 1.8308

.800 1.9672 1.9407 1.8250

.850 1.9639 1.9378 1.8223

.900 1.9595 1.9347 1.8206 ,950 1.9564 1.9318 1.8180

1.000 1.9537 1.9292 1.8147 1.065 1.9508 1.9275 1.8123 1.100 1.9484 1.9260 1.8116 1.200 1.9436 1.9230 1.8086

terial (i.e., in Hobden's notation a material whose indices satisfy the inequalities given above: see Table I and Fig. 3, ref. 13) is shown in the upper right-hand corner of Fig. 2. Also shown in the same figure are the experimentally determined phase­matching surfaces, which are seen to be consistent with the topology predicted by Hobden.

The two sheets of the PM surface, designated I and II, correspond respectively to a process in­volving fundamental waves having parallel polari­zations and a process involving fundamental waves having orthogonal polarizations. In the negative uniaxial limit (e.g., nZ = nY = nO > nX = ne: 0 = ordi­nary, e = extraordinary) these two processes are the familiar e = 0 + 0 process and the e = 0 + e proc­ess.

The three nonzero components of the second­order polarizability tensor (drIC) for the rhombic disphenoidal point group 222 are JlI~ = 4~ = Jl2~ where use has been made of the Kleinman sym­metry conditions l4 and the customary contraction of indices. The expressions for the induced non­linear polarization components P~~y,Z<2w) for non­normal incidence on an arbitrarily oriented biaxial crystal are very complicated functions of the re­fractive indices and angle of incidence. For normal incidence and crystal orientation such that phase­matched propagation occurs in a principal optic plane (i.e., in the orthorhombic case a plane con­taining any two of the crystallographic axes) the expressions simplify greatly. For a Type-I PM process it can be shown that

Type!

PIJ:L(2w)=p~L(2w)=p~L(2w)= 0 (in all principal planes) (l )

Type II

PNL(2w) = cos f)'Pi'" + sin f)'Pi'" == dl4 E2 sin 2f)' (in the (001) plane) (2)

where f)' is angle between the [010] direction and phase-matching direction in the crystal.

The magnitude of the nonlinear coefficient dl4

has been estimated relative to dl1 for crystalline quartz and dal for LiNbOa by a comparison of har­monic intensities generated using the 1.065 IL fun­damental from a 400-Hz rotating mirror Q-switched YAG laser. 15 The experimental apparatus has been described elsewhere.7

drJOa = (1.5 ± .5) X d~INbOa

drlOa = (20 ± 5) X d~isi02 .

The Miller 8i~ calculated from these values is 8~~ = 3(±1) X 10-6 cm/statvolt which is consistent with the average valuel6 3(±2) X 10-6 cm/statvolts. An addi­tional criterion which must be met for high-power nonlinear optical applications is freedom from "optical damage" effects.17 Several crystals were subjected to high optical power densities at 4880 A from an argon laser. No trace of this deleterious effect was observed up to power densities of 2.5 X

105 W/cm2 over periods of time up to 10 min. By way of comparison LiNb03 damaged within a few seconds under identical conditions.

From Eqs. (I) and (2) it is evident that noncritical phase matchingl3 (i.e., PM along a, b, or c) is not possible in HI03 consistent with Hobden's results

-- CALCULATED .,--8 z(b) z(b) 00000 EXPERIMENTAL

y(-c)

Fig. 2. Phase-matching surfaces of a-HIOa for AI = 1.065 J.t.

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Volume 12, Number 5 APPLIED PHYSICS LETTERS 1 March 1968

for the point group 222. For the Type-II PM proc­ess near the b axis, coherence lengths of several cm are possible if the beam divergence is ~ 10-3 rad. The "walk-off" angle for normal incidence is around 3° giving a maximum path length to beam width ratio of -1 :20. Increases in the interaction length could also be obtained using the beam cross­ing scheme of Ashkin et al. 18 The "walk-off" angle can also be reduced to around 1 ° by using plates cut for nonnormal incidence such that the ray vectors of the two fundamentals are parallel. Another point which should be emphasized is that for PM in a principal plane the PM is only critical (i.e., lakl = Ik2 - k\ - k"ll ex: 8 rather than 82

, where 8 is the angu­lar deviation from PM) for rotation about an axis normal to the principal plane. It is noncritical (i.e., lakl ex: 82) for rotations about directions lying in the principal plane. For example, in the case of Type-II phase matching close to the b axis (in the a-b plane) angular rotations of as much as ±25° about the a

axis have been observed to produce less than a 20% change in the harmonic intensity.

a-Iodic acid is optically active exhibiting a rota­tionl9 of 58.7°/mm at 5461 A and 74S/mm at 4360 A. For propagation directions well away from the optic axis (tens of degrees) these rotations are greatly reduced and were found experimentally to have no effect on the PM properties for the Type-II process. An optically flat «t wave) polish was ob­tained by lapping on tin with H yperez diamond paste. It was found that the surface finish deterio­rates very slowly with time. After several weeks in contact with air an irregular patchiness developed which is believed to be formation of 120 5 through loss of H20 in the reaction20

2 HI03 ~ 120 5 + H20.

Techniques for eliminating this effect such as sur­face coatings or equilibrating with an HI03 powder in an enclosure are being investigated.

Powder measurements7 on a number of iodates such as KI03 , Li103 , TlI03 and Rbl03 have shown that these materials also have large nonlinear co­efficients and are phase matchable. While the difficulties in growing these materials are substan­tially greater, their symmetry (e.g., Lil03 point group 6, KI03 and TlI03 probably point group 3m)

does allow noncritical phase matching. In summary, a-HI03 shows considerable promise

188

for nonlinear device applications since in addition to being phase matchable, (1) it is readily grown from water solution in high optical quality single crystals of large size, (2) the nonlinear coefficient dl4 is about 1.5 times larger than LiNb03 , and (3) it does not exhibit optical damage effects even at very high optical power densities.

The authors are indebted to J. A. Giordmaine and R. A. Laudise for their advice and encourage­ment in this study. Valuable conversations with L. B. Kreuzer are gratefully acknowledged. Special thanks are extended to J. P. Remeika for supplying us with crystals, W. L. Bond for making available unpublished data as well as advice on the refractive index measurements, Miss D. M. Dodd for making the optical and infrared transmission measure­ments, and S. Bortas for his excellent technical assistance.

1 J. A. Giordmaine, Phys. Rev. Letters 8, 19 (1962). 2P. D. Maker, R. W. Terhune, M. Nisenoff, and C. M. Savage,

Phys. Rev. Letters 8,21 (1962). 3G. D. Boyd, R. C. Miller, K. Nassau, W. L. Bond, and A. Sav­

age, Appl. Phys. Letters 5, 234 (1964). 4 K. F. Hulme, O. Jones, P. H. Davies, and M. B. Hobden,

Appl. Phys. Letters 10, 133 (1967). 5 J. E. Geusic, H. ]. Levinstein, J. J. Rubin, S. Singh, and L. G.

Van Uitert, Appl. Phys. Letters 11, 269 (1967). 6M. T. Rogers and L. Helmholz,]. Am. Chem. Soc. 63, 278

(1941); J. J. Gilman, The Art and Science of Growing Crystals, Chap. II (john Wiley and Sons, New York, 1963), p. 194.

7S. K. Kurtz and T. T. Perry, unpublished. 8 A. Holden, private communication. 9P. Groth, Chemische Krystallographia, Vol. I (Leipzig, 1906),

p. 125. lOR. W. G. Wyckoff, Crystal Structures, Vol. II, 2nd Ed. (Inter­

science Publishers, New York, 1964), p. 387. 11 G. S. Garrett, U.S. Atomic Energy Comm. Report ORNL-1745,

p.97. 12W. L. Bond,]. Appl. Phys. 36, 1674 (1965). 13M. V. Hobden,J. Appl. Phys. 38, 4365 (1967). 14 D. A. Kleinman, Phys. Rev. 126, 1977 (1962). 15]. E. Geusic, M. L. Hensel, and R. G. Smith, Appl. Phys. Letters

6, 175 (1965). 16F. N. H. Robinson, Bell System Tech.]. 46, 913 (1967). 17 A. Ashkin, G. D. Boyd,]. M. Dziedzic, R. G. Smith, A. A. Ball­

man, H. ]. Levinstein, and K. Nassau, Appl. Phys. Letters 9, 72 (1966).

18 A. Ashkin, G. D. Boyd, and D. A. Kleinman, Appl. Phys. Let­ters 6,179 (1965).

19 International Critical Tables, Vol. III, National Research Council, (McGraw Hill, 1929), p. 353.

20]. W. Mellor, Compo Treatise on Inorganic and Theoretical Chem­istry, Vol. II (Longmans, Green and Co., London, 1927), p. 305.

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