Optical Materials and Their Preparation

Optical Materials and Their Preparation

A. Smakula, J. Kalnajs, and M. J. Redman

A variety of materials such as glasses, crystals, pressed materials, and thin films are available for opticalapplications. The influence of impurities on physical properties indicates that materials of higher purityare frequently required. Methods of impurity detection and purification are well developed but theiruse is quite complicated. Synthesis of purest materials is still in its infancy.

Introduction

The revival of interest in optics in recent years hasbeen stimulated by a strong demand for optical equip-ment in research and development projects, the use ofcomputers to facilitate the cumbersome computationof optical systems, and the discovery of optical masers.Development of new optical materials and improve-ments of old ones play an important role in the progressachieved.

Materials

Optical materials can be divided into four groups:glasses, crystals, pressed materials, and films.

Glasses are still the principal materials for optics.Old glasses have been improved by using Pt-shieldedcrucibles and purer starting materials.' New glasses(e.g., io 2 of highest purity 2 ) have been developed foruse in the vacuum ultraviolet spectral range with trans-mission down to 1600 A, and various nonsilica glasseswith transmission in the infrared above 5 .z A greatnumber of new glasses with expanded refraction anddispersion have also been produced. Special glasseswith densities up to 5.2 g/cm3 are now available forCerenkov counters,' and neodymium-doped glassentered the maser field.4

The chemistry of glasses is very complex becauseseveral compounds with different vapor pressures anddifferent reactivity with containers are involved si-multaneously. Bubbles, "Schlieren", coloration, andinhomogeneities have to be removed and thermalstresses eliminated by annealing. Despite these com-plexities optical glass blocks with variation in refrac-

The authors are with the Laboratory for Insulation Research,Massachusetts Institute of Technology, Cambridge, Massa-chusetts.

Received 17 October 1963.

tive index of less than 0.000005 or with diameters up to3.8 m are being made.'

Crystals, another group of optical materials,5' 6 supple-ment the glasses in chemical and thermal stability andin expanding the spectral range. They make it possibleto produce and study phenomena for which glass cannotbe used.

As prism materials in the 0. 16-u to 50-,u range, quartz,CaF2 , LiF, NaCl, KBr, CsBr, KRS-5, and CsI are con-tinuously used. Optical windows, a few millimetersthick, can be used between 0.11,4 and 60 A and reststrahlreflectors up to 300 . For achromatic lenses a com-bination of CaF2 , LiF, or MgO with quartz is used in theultraviolet, and of Si with Ge or As2S3 with LiF in theinfrared. A two-element germanium lens has goodoptical properties in a water-vapor window between 8 pand 14 g. For perfect polarizers between 0.25 and 2.5 ,u, quartz and particularly calcite are still thebest materials.

Doped crystals consisting of two or more componentsbecame very important for optical masers and forradiation detectors. A variety of doped crystals suchas ruby, CaF2 , CaWO4, and others serve as opticalmasers. 7-9 Their efficiency depends highly on theirintrinsic properties and their perfection and the uniformdistribution of the activator. Chromium or rare-earth ions in concentrations 0.01 mole-% to 5 mole-% aremostly used as dopants.

A number of inorganic and organic crystals serve asscintillation counters for high-energy quanta or par-ticles. 0 High efficiency and short decay time ofemission are among the most important properties ofscintillation counters. Some alkali halides, predomi-nantly NaI and CsI, doped with Tl and organic crystalsof anthracene are most useful, although their mechan-ical properties are very poor.

A variety of doped crystals are used as infrared de-

March 1964 / Vol. 3, No. 3 / APPLIED OPTICS 323

tectors,8 e.g., Ge doped with Au, Sb, Zn, Cu, Cd;Ge-Si alloys doped with Au, Zn, Sb; III-V compoundsof InSb, InAs, and Te. Single-crystal detectors aremore uniform, reproducible, and rigid than thin-filmdetectors, which consist mainly of PbS, PbSe, PbTe,and T12S.

Pressed materials, consisting of randomly orientedmicrocrystals in close contact, are gaining importance inoptics. The pressed KBr pellets used in infrared spec-troscopy were the first such materials."1 In recent yearsthe following five materials have been developed byEastman Kodak:

Transmission >10% forName Composition 2-mm thickness ()

Irtran-1 Predominantly MgF2 0.45- 9.2Irtran-2 Zinc sulfide 0.57-14.7Irtran-3 Calcium fluoride 0.20-11.5Irtran-4 Zinc selenide 0.48-21.8Irtran-5 Magnesium oxide 0.39- 9.4

The main advantages of these materials are large size(diameter up to 17 cm and thickness up to 2.5 cm).They can withstand mechanical and thermal shockbetter than corresponding crystals and can be formedto any shape by pressing. Compared with single crys-tals, however, the pressed materials produce strong lightscattering at short wavelengths.

ThinfJilms,1 2- 8 generally polycrystalline, found broadapplication in optics, both in single or multiple layers.Metallic films are used mainly for broad wavelengthcoverage with high reflectivity. Dielectric films servein obtaining lowest or highest reflection or trans-mission interference filters in a restricted range and asprotective coatings.

For protective coatings the films must have high re-sistance to chemical and mechanical attack. A1203 ,SiO, Ta2O5, and TiO2 are commonly used for thispurpose. Films used for optical coating are charac-terized mainly by their refractive index. Table I liststhe materials most commonly used for optical coating.

Influence of Impurities

The influence of impurities on optical properties de-pends on the nature of the impurity and of the hostmaterial.s In glasses the transmission range can bemodified in either a desired or undesired manner. Forinstance, the ultraviolet absorption edge of fused silicamay be shifted toward longer wavelengths or infraredabsorption edge toward shorter wavelengths. Suchchanges are generally undesirable. In some cases ab-sorption bands appear, e.g., water absorption at 2.8 q.On the other hand, the addition of proper "impurities"can create a variety of optical filters. In crystals thesituation is somewhat more complicated. If the im-purity atoms have the same valence as the host atoms

Table I. Materials for Optical Coating

Chemical M.P. Refractive SpectralMaterial formula (0C) index range ()

Cryolite AIF3 3NaF 1000 1.35 <0.2 -10Magnesium

fluoride MgF 2 1395 1.38 0.12-5Thorium

fluoride ThF 4 1068 1.45 <0.2-10Cerium

fluoride CeF3 1324 1.62 0.3 ->5Silicon

monoxide SiO >1000 1.45-1.90 0.35-8Zirconium

dioxide ZrO2 2700 2.10 0.3 ->7Zinc sulfide ZnS >1900 2.30 0.4 -14Titanium

dioxide TiO2 1850 2.4-2.9 0.4 ->7Cerium

dioxide CeO2 1950 2.30 0.4 -5Silicon Si 1420 3.50 0.9 -8Germanium Ge 937 3.8-4.2 1.4 ->20Lead

telluride PbTe 917 5.10 3.9 ->20

and are similar in size and polarization, a solid solutionis formed. In that case the lattice structure remains,while the size of the unit cell is contracted or expanded.Actually, mixed crystals are always distorted because ofthe statistical distribution of impurities.20 The in-fluence on the transmission edge depends on the elec-tronic and vibrational excitation of the impurity. If, inthe ultraviolet, the electronic excitation of the impurityis lower than that of the host atoms, transmission isinfluenced.2 0 In the infrared, the opposite takes place:the higher atomic excitation of the impurity will in-fluence the absorption edge. An impurity will there-fore always show up either in the ultraviolet' or theinfrared because both excitations go parallel.

The presence of impurities strongly decreases thermalconductivity 2 l at low temperature, where the conduc-tivity increases exponentially. High thermal con-ductivity is very desirable to avoid the overheatingand to minimize local changes of refraction (e.g., inoptical masers) or thermal cracks.

In semiconductors impurities create bound or freecharge carriers (electrons and holes) which cause eitherbroad bands or continuous infrared absorption. 2 2 Foroptical elements (lenses, windows) the materials musttherefore be free of impurities.

The presence of impurities in crystals frequentlycauses inhomogeneities2 3 because of the differences ofimpurity concentrations in the solid, liquid, or solutionstate. In most cases the concentration of impurities incrystals increases in the direction of growth. Thisalso happens in doped crystals, except when the dis-tribution coefficient is unity (e.g., some rare earths inCaF2). Homogeneous mixed crystals can be grownonly if they have a minimum or maximum melting

324 APPLIED OPTICS / Vol. 3, No. 3 / March 1964

Table II. Impurity Concentration of the Purest Commer-cially Available Salts, in ppm

NaCl KCl KBr KI

Al 10Ba 15 20 20 20

Ca 20 20 50 50Fe 3 5 3K 50Li 10Mg 50 50 50Na 200 200Pb 5 5 5

Sr 10Br 100 100 100

Cl 400 100I 20NO3 30P04 20 10

S0 4 30 5 50

point to which their composition corresponds exactly.Some solid solutions are stable at high temperature butdecompose at room temperature (e.g., NaCl-KCl).24

Impurities of a valence differing from that of thehost atoms (e.g., Ca in KC126 or Na in CaF2

26 ) causeinterstitials or vacancies, which bring about a greatenhancement of diffusion, ionic conductivity,2 7 andcoloration by high-energy radiation. 28

The preparation of crystals is frequently seriouslyaffected by impurities,2 9 which can either promote orpoison homogeneous nucleation or else cause spuriousnucleation. Constitutional supercooling caused by im-purities may give rise to mosaic structure of crystal.Segregated impurities may cause microscopic stress,and insoluble impurities dislocations and light scatter-ing.30 The presence of gaseous impurities may causeformation of bubbles.

Purity of Materials

The quality of optical materials depends on the purityof starting materials and the technique of preparation.Since impurities can cause a variety of macroscopic orstructural defects, commercial materials of highestpurity must be used. The purity is frequently given inpercentage of the main component, up to 99.9999(= 6N), the rest being unknown impurities. The numberof six nines, although very impressive, indicates thatsuch ultrapure materials still contain a very great num-ber, about 1016, of impurity atoms per cubic centimeter.Some of these impurities might be noncritical butothers are supercritical. It is therefore necessaryto know the kind and concentration of all impurities.

The purity of ultra- or superpure elements, as givenby suppliers, can be subdivided into three groups:

1. impurity concentration 0.1 to 10 ppm,2. impurity concentration 10 to 100 ppm,3. impurity concentration 100 to 1000 ppm.

To the first group belong such elements as: Ag, Al, Be,Bi, B, Cd, Cr, Co, Cu, Ge, Pb, Tl, Zn. To the secondbelong the alkali and alkaline earth metals; and to thethird the rare-earth elements. In no case are all im-purities known; particularly nonmetallic impurities areoften not given. In some cases (e.g., Si, Ge) some im-purities may be lower by several orders of magnitudewhile some others are higher by like amounts. Asexamples, Table II lists impurities of four purest salts,as supplied by the manufacturers. The concentrationof impurities varies from a few to several hundred partsper million. In most other materials the situation ispresumably similar or even worse.

Trace Analysis

A variety of methods exist for the detection anddetermination of impurity concentration."' 32 Themost important are x-ray (absorption, emission, fluores-cence), optical (absorption, emission), mass spectro-scopy, and neutron activation. Their absolute sensi-tivity ranges from 10-7 to 10-'3 g in the order the meth-ods are listed. The sensitivity of one element can varyby several orders of magnitude for the various methods.The sensitivity within one method can also differ fromone element to another. A comparison of variousmethods for all elements is given by Meinke.3 ' It istherefore practically impossible to determine the vari-ous impurities in any one sample with the same ac-curacy, even when using several methods.

In some cases a knowledge of the total impurity con-centration is insufficient; even its microscopic distribu-tion can be very important. In these cases x-rayemission from a very small area (1 g2 ) bombarded withfine electron beam must be used.33

Purification

Knowing the impurities present, it is essential to findout which ones do actually influence the respectiveproperties. Mainly those impurities have to be re-moved or at least reduced. One can either purify thestarting material, provided it is possible to avoid subse-quent contamination, or subject the final material topurification. Both methods are used.

Drying is very essential if hydrolysis can take place,as is the case in most alkali halides. As a result ofhydrolysis the materials are contaminated by oxygenand/or hydroxyl. Adsorbed or trapped water can beeliminated by drying under vacuum and slowly increas-ing temperature, and eventually sweeping inter-mittently with inert gas, for about a day. Chloridescan also be purified by treatment with gaseous Cl2 orHCl,3 4 -36 and HBr can be similarly used for bromides.

Heavy metals as organic complexes have been re-moved from alkali chlorides and carbonates by solventextraction. 7 Purification of alkali halides from other


alkali ions can be achieved by preparation of alums,since their solubility varies.3 8

Slow precipitation allows the formation of more nearlyperfect crystallites which generally contain fewer im-purities than do aggregates of very small particles ob-tained by fast precipitation. Since nucleation in super-saturated solutions starts at impurities, the solution ispurified by filtering out the first visible particles. Sub-sequent recrystallization may lead to pure material.

Ion exchange is based on the diffusion process and ex-change between the ions in solution and those present ina porous frame (resin)." An application of this methodto KCl proved its usefulness.4 0 Our investigation ofNaCl and KCl showed the reduction of the following im-purities: Li, Ba, Sr, Ca, Al, Fe, Si, Br, and K in NaCl,and Na in KCl.4' One disadvantage of this method is,however, contamination by resins which must be re-moved before the material can be used for crystalgrowth.

Distillation in vacuum can be used if the vaporpressure of the impurities differs sufficiently from that ofthe main material and if no chemical decompositiontakes place. This method has been used in the purifica-tion of IKCl.42

143 AgCl prepared from recrystallized

AgNO3 and fractionally distilled HCl showed a reduc-tion of the Fe, Ca, Mg, and Na impurities.4 4

The scavenger method is very useful for the eliminationof oxides and hydroxides from earth alkaline fluorides.45

Here chemical reaction between PbF2 and the impuritiestakes place, forming PbO which evaporates.

Electrolysis can be used for purification if the mobilityof the impurity ions is larger than that of the mainmaterial. This method has been used for the purifica-tion of KCl and NaCl. 46

,47

Zone refining48 proved to be extremely successful inthe purification of semiconducting materials. Theefficiency of purification depends on the value of thedistribution coefficient. The smaller the distributioncoefficient, the more effective the purification; thelarger the radius of impurity atoms, the smaller thedistribution coefficient.4 9 So far this method has beenapplied to only a few optical materials, and the limit ofpurification has been reached in no case. Of the alkalihalides, mostly KCl has been studied.35

,50- 52 After

fifty to seventy zone passes with a rate 0.6 to 10 cm/hthe Ca contamination is reduced by a factor of 10 to10g. Since the distribution coefficient of Ca in KC is0.4 and that of Na 0.1,5' the removal of Na is fasterthan that of Ca.

KBr,3 5 KI,53 and CsI5 4 have been also zone-refined.Surprisingly, Ca could not be removed from NaCl evenafter sixty zone passes.55 Of the other halides only Ag-Cl56 and AgBr57 have been purified by zone refining up tonow.

Zone freezing has been used for the removal ofdeliberately added radioactive 22Na and 90Sr from

KCl.58 Na has been reduced twenty-eight times afterten passes and Sr sixty-five times after twenty passes.

Crystals grown from purified materials generally con-tain known impurities of the order of a few ppm.59

The concentration of unknown impurities can runseveral orders of magnitude higher. Only in somespecial cases are some of the impurities lower.

Material Synthesis

Starting materials of desired purity are only avail-able when a material has attained broad application.In most cases it has to be purified; this is quite an in-volved problem. Sometimes elements or compounds ofhigh purity from which the desired material can bemade are available.

Only half of the twenty alkali halides gained impor-tance in optical applications. Their purity is betterthan that of other materials but not good enough.Table II shows that the principal impurities in alkalihalides are other alkali halides and alkaline earthhalides. The best materials are obtained by chemicalreaction between carbonates or nitrates and the corre-sponding acids. Rubidium and cesium salts are lesspure than other halides by 102 or 103. Here the mainimpurities are other alkali halides.

Fluorides require special attention. They are pre-pared from carbonates or hydroxides by reaction withhydrofluoric acid.6 0 The main problem here is con-tamination by oxygen that can produce oxides orhydroxides. To avoid hydrolysis, drying has to be doneunder vacuum at low temperature or else in HF atmo-sphere. Exposing to higher temperatures or meltinghas to be done in an inert atmosphere or in vacuumunder complete exclusion of water vapor and oxygen.Hydroxide can be eliminated by vacuum fusion.6

Carefully selected natural fluorite is still the mostuseful material for the growth of CaF2 crystals.6 2

Synthetic CaF2 , SrF2 , and BaF2 of good quality can beobtained by precipitation from high-temperaturemelts,6 3 e.g., CaC 2 + 2NaF-CaF 2 + 2NaCl or by HFtreatment at high temperatures.6 4 MgF2 of high purityhas been prepared by evaporating molten dried materialfrom graphite crucible in vacuum.6 5

PbF2 and CdF2 can be synthetized from semi-conductor-grade Pb and Cd by being converted firstinto nitrates and then into fluorides.66

A1203 of high purity is made by thermal decompositionof recrystallized alum.67 A reduction of impurities inrefractory oxides can be achieved by evaporation in asolar furnace.f8

TiO2 is prepared either by the direct conversionof TiCl4 or from the thermal decomposition of a doubletitanyl sulfate or oxalate.6 9

SrTiO3 is prepared similarly by the thermal decom-position of strontium titanyl oxalate.7 0


CaWO4 and SrMoO4 are formed by melting togetherof the corresponding oxides, carbonates, or nitrates. 7

Conclusion

A variety of elements and compounds are now used foroptical materials, although their purity is not sufficient.Methods of impurity detection are well developed andfar ahead of those of purification. A systematic studyof the preparation of highest purity materials practicallydoes not exist. There are laboratories for the prepara-tion and investigation of such materials, but unfor-tunately not in the U.S.A.

References

1. See, e.g., J. G. Baker, Appl. Opt. 2, 111 (1963).2. R. Bauple, A. Gilleo, J. Romand, and B. Vodar, J. Opt.

Soc. Am. 40, 788 (1950).3. See, e.g., P. W. Kruse, L. D. McGlauchlin, and R. B.

McQuistan, Elements of Infrared Technology (Wiley, NewYork, 1962).

4. E. Snitzer, Phys. Rev. Letters 7, 444 (1961).5. See, e.g., A. Smakula, Einkristalle (Springer, Berlin, 1962).6. A. Smakula, Opt. Acta 9, 205 (1962).7. 0. S. Heavens, Appl. Opt. Suppl. 1, 1 (1962).8. E. V. Ashburn, J. Opt. Soc. Am. 53, 647 (1963).9. A. Yariv and J. P. Gordon, Proc. IEEE 51, 3 (1963).

10. See, e.g., G. T. Reynolds, in Methods of Experimental Phys-ics, L. Marton, ed. (Academic, New York, 1961), Vol. 5,Pt. A, p. 120.

11. M. M. Stimson, Anal. Chem. 23, 1050 (1951).12. H. Mayer, Physik dnner Schichten (Wissenschaftliche

Verlagsgesellschaft, Stuttgart, 1950 and 1955), Vols. 1 and2.

13. A. Vasicek, Optics of Thin Films (North-Holland, Amster-dam, 1960).

14. W. Welford, Vacuum 4, 1 (1954).15. 0. S. Heavens, Optical Properties of Thin Solid Films (But-

terworths, London, 1955); Rept. Progr. Phys. 23, 1 (1960).16. L. Holland, Vacuum Deposition of Thin Films (Chapman

and Hall, London, 1956).17. M. Auwirter, Ergebnisse der Hochvakuumtechnik und der

Physik dnner Schichten (Wissenschaftliche Verlagsgesell-schaft, Stuttgart, 1957).

18. G. Hass, ed., Physics of Thin Films (Academic, New York,1963), Vol. 1.

19. See, e.g., H. G. van Bueren, Imperfections in Crystals (Inter-science, New York, 1960).

20. A. Smakula, N. C. Maynard, and A. Repucci, J. Appl.Phys. Suppl. 33, 453 (1962).

21. A. Eucken and G. Kuhn, Z. physik. Chem. 134, 193 (1928).22. See, e.g., T. S. Moss, Optical Properties of Semiconductors

(Academic, New York, 1959).23. A. Smakula, in Molecular Science and Molecular Engineering,

A. von Hippel, ed. (The Technology Press of MIT andWiley, New York, 1959), p. 182.

24. W. G. Burgers and G. W. Tichelaar, Proc. Koninkl. Ned.Akad. Wetenschap. B57, 73 (1954).

25. H. Pick and H. Weber, Z. Physik 128, 409 (1950).26. W. J. Scouler and A. Smakula, Phys. Rev. 120,1154 (1960).27. See, e.g., A. B. Lidiard, Encyclopedia of Physics (Springer,

Berlin, 1957), Vol. 20.28. J. H. Schulman, J. Phys. Chem. 57, 749 (1953).

29. See, e.g., W. A. Tiller, in Crystal Growth in ThermoelectricityR. K. Heikes and R. W. Ure, Jr., eds. (Interscience, NewYork, 1961), p. 181.

30. K. G. Bangisir and E. E. Schneider, J. Appl. Phys. Suppl.33,383 (1962).

31. W. W. Meinke, in Trace Analysis, J. H. Yoe and H. G.Koch, eds. (Wiley, New York, 1957).

32. M. G. Ingram, in Methods of Experimental Physics, L.Marton, ed. (Academic, New York, 1959), Vol. 6, Pt. A,p.29.

33. R. Castaing and A. Guinier, Anal. Chem. 25, 724 (1953).34. H. von Wartenberg, Z. Angew. Chem. 69, 258 (1957).35. H. Gruendig, Z. Physik 128, 577 (1960).36. D. A. Otterson, J. Chem. Phys. 34, 1849 (1961).37. J. J. Angelov, M. M. Shvartz, E. U. Buris, and S. I. Khain-

son, Tr. Vses. Nauch. Issled. Inst. Khim. Reaktivov 22,159 (1958).

38. Reference 37, p. 40.39. See, e.g., F. Helferich, Ion Exchange (McGraw-Hill, New

York, 1962).40. W. J. Fredericks and J. L. Hatchett, International Sym-

posium on Color Centers, Stuttgart, Germany (21-24 August1962).

41. M. J. Redman and J. Hwang, Progress Rept. No. XXXII,Lab. Ins. Res., M.I.T. (January 1963), p. 34.

42. K. Kobayashi and T. Tomiki, J. Phys. Soc. Japan 15,1982 (1960).

43. H. Kanzaki and K. Kido, J. Phys. Soc. Japan 15, 529(1960).

44. N. R. Nail, F. Moser, P. E. Goddard, and J. Urbach, Rev.Sci. Instr. 28,275 (1957).

45. D. C. Stockbarger, J. Opt. Soc. Am. 39, 731 (1949).46. F. Kerkhoff, Z. Physik 130, 449 (1951).47. M. Chemla, Ann. Phys. 1, 959 (1956).48. W. G. Pfann, Zone Melting (Wiley, New York, 1958).49. J. A. Burton, E. D. Kolb, W. P. Slichter, and J. D. Struth-

ers, J. Chem. Phys. 21, 1991 (1953).50. S. Anderson, J. S. Wiley, and J. Hendricks, J. Chem. Phys.

32,949(1960).51. M. Inone and H. Mizuno, J. Phys. Soc. Japan 16, 128

(1961).52. H. Kanzaki, K. Kido, and T. Ninomiya, J. Appl. Phys.

Suppl. 33, 482 (1962).53. U. Haupt, Z. Physik 157, 232 (1960).54. H. Besson, D. Chauvy, and J. Rossel, Helv. Phys. Acta

35,211 (1962).55. R. W. Dreyfus, in Alkali Halides in the Art and Science of

Growing Crystals, J. J. Gilman, ed. (Wiley, New York,1963).

56. F. Moser, D. C. Burnham, and R. H. Tippins, J. Appl.Phys. 32,48 (1961).

57. P. SUptitz, Ann. Phys. 9, 133 (1962).58. F. Pauly and P. Sue, Compt. Rend. 266, 2722 (1957).59. C. T. Butler, W. A. Sibley, and E. Sonder, Res. Mat.

Information Center, Oak Ridge Natl. Lab., Oak Ridge,Tenn. (June 1963), p. 11.

60. D. C. Stockbarger, Discussions Faraday Soc. 5, 299 (1949).61. M. A. Vasilyeva, in Growth of Crystals, A. V. Shubnikov

and N. N. Sheftal, eds., translation from Russian (Con-sultants Bureau, New York, 1959), Vol. 1, p. 191.

62. D. C. Stockbarger, Discussions Faraday Soc. 5, 294 (1949).63. A. Sinyukova and I. V. Stepanov, in Growth of Crystals,

A. V. Shubnikov and N. N. Sheftal, eds., translation fromRussian (Consultants Bureau, New York, 1959), Vol. 2, p.86.

64. H. J. Guggenheim, J. Appl. Phys. 32, 1337 (1961).


65. W. D. Scott, J. Am. Ceram. Soc. 45, 586 (1962).66. J. S. Preuer and J. D. Kingsley, J. Chem. Phys. 35, 2256

(1961).67. I. G. Farben, FIAT, Final Report No. 655 (1945).68. J. Trombe and M. Foex, Compt. Rend. 238, 1419 (1954).

69. L. Merker and H. Espenschied, U.S. Pat. 2,521,392 (5September 1950).

70. L. Merker, AIME Trans. 202, 645 (1955).71. L. G. van Uitert and R. R. Soden, J. Appl. Phys. 31, 328

(1960).

Meeting Reports continued from page S22

to be produced commercially in Australia, incorporating replicasof gratings ruled on the C.S.I.R.O. engine in Melbourne; andJ. Ramsey C.S.I.O., Sydney, described elegant methods he haddevised for automatically controlling the separation of the platesin a Fabry-Perot interferometer. This instrument is expectedto be produced commercially in Australia.

An important part of the conference was an exhibition by fifteenfirms of commercial spectroscopic equipment. Of particularinterest was the exhibition of Australian-made equipment in-cluding an atomic absorption spectrophotometer, atomic spectrallamps, the C.S.I.R.O. monochromator, and microwave-poweredRaman lamps.

It was announced that the Fifth Australian Spectroscopy Con-ference will be held in Perth during 165 but no date has yet beenfixed. The organizers of that conference will have reason to beproud if they can match the smooth organization and stimulatingprogram of this highly successful Fourth Conference in Canberra.

pnoto Australian Iews and njornmatton BureauThe Australian Academy of Science, Canberra, A.C.T. by night.

Sixth Annual Rocky Mountain SpectroscopyConference, Denver, Colorado, 12-13 August 1963Reported by Wilbur Kaye, Beckman Instruments

One hundred nine registrants participated in the Sixth AnnualRocky Mountain Spectroscopy Conference and as usual, thisregional meeting of the Rocky Mountain section of the Society forApplied Spectroscopy emphasized the analytical aspects of thespectroscopy of minerals. Panel discussions on techniques ofx-ray fluorescence, gas chromatography, and optical spectroscopywere held, with the emphasis of interest mainly on sample prepara-tion and particle size in x-ray fluorescence analysis. The gaschromatography panel was primarily concerned with columnpreparation.

Several papers discussed the use of infrared data in organicand mineralogical analysis: the use of ion exchange resins forthe concentration of SO4, NO3, MoO3, and U308 anions prior toinfrared identification was reported by D. M. Hansen UnionCarbide; L. D. Fredrickson Spectron Laboratories presented aninteresting paper on the use of hydrazine for the preparation ofthe azines of aldehydes and ketones (the exact value of the C=N

infrared group frequencies proved characteristic); A. J. P.Lyon Stanford Research Institute discussed the use of infraredemission spectra for the analysis of terrestrial and lunar rocks;H. H. Adler Atomic Energy Commission delivered a report on theuse of infrared spectra for determination of the internal environ-ment of groups such as carbonates and sulfates in minerals. Thesplitting of bands may yield unique information about the sym-metry of molecular forces acting on the vibrating dipole.

A. Volborth University of Nevada reported unusually goodreproducibilities (0.05%) in the analysis of rocks by x-ray fluores-cence techniques. He emphasized the importance of grindingtechniques in samples containing biotite which pulverizes withpronounced cleavage planes. W. G. Schrenk Kansas StateUniversity discussed the effect of electron density in flames onthe intensity of emission lines from ions in the flame.

The papers presented and the main topics of discussions on thepanels contributed to making this annual conference most in-teresting. Both the contributed papers and the panel discussionswere in the tradition set by the previous conferences.

SPSE Symposium on Color Photographic Systems,Washington, D. C., 17-19 October 1963

Reported by Jack E. Pinney, Eastman Kodak

The SPSE Color Symposium drew about 320 participants fromindustry, government, education, and the armed forces. At theopening session, the general chairman, Howard Colton, East-man Kodak, announced that the purpose of a symposiumwas to discuss a particular subject. He urged that, in ad-dition to discussion of the formal presentations, the participantstake other opportunities to meet and talk with one another.There proved to be ample opportunities for talking, and theparticipants took full advantage of them. Adequate time wasmade available for discussion of individual papers, and schedulingran so well that there were a number of "discussion breaks" inwhich everyone stood up and talked with his neighbors for a fewminutes! I

Four of the sessions commenced with a Visual Encyclopediapresentation, a project of the Rochester Chapter of SPSE. TheVisual Encyclopedia consists of brief, well-illustrated talks whichcover fundamental areas of photographic science and engineering.The need for such information arises from the fact that photo-graphic scientists and engineers are seldom formally trained inphotography. The Rochester Chapter starts its meeting withthese talks and then makes them available to other chapters andgroups. At this symposium, all o the Visual Encyclopedia talkswere concerned with color and color photography.

Considering that a Color Symposium has not been held by theSPSE for several years, there was little totally new informationpresented. Contributed papers were heavily dominated by thephotographic industry, reflecting the fact that the bulk of photo-graphic research and development work is supported by in-dustry rather than by educational institutions or government.A few comments concerning papers of particular interest to thewriter follow:

continued on page 339


Documents

Optical Materials and Their Preparation