Bhar, G C

Ghosh, D K

IACS Institutional Repository

It\tlia" J. PhYB. MD, 88-04. (1080) Far infrared generation in chalcopyrite crystals D K GhoRh !IJld G C Bha.r Physic. D.partm.nt, Burdw&l1 Univers.ty, Burdw .. n 713 104 , Abstract. Ph .... ·m .. toh.d differ.noo·mixing of two oloe. f'"equency lasers In nonlinear crystals is considerod to gene .. a.te tuna.ble far infrared (Fm) radia-tion. The orystoJ anomaJQus dispersion i. utilis.d for ph ... e matohing and the ,,,, .. i1l1ble cryst, .. l birefringonoe fOl' tuning purpose. The ohllicopyrito .r)·stala .. ,'e oh'''IWtoriBed by high nonJinearity and many of them show wide ~'1R tran.· mlssion rBnge Whtl" their visible refractive index data. are 8vailftoblt,\, the corre.ponding FIR indioee aro ev .. lu .. ted from the refleotivity d .. ta. '\Analysis shows that while forward w .. ve mixing is permitted over .. wid. rangt\ for the studied soven H·IV·V. and seven J.Ill-VI. crystals, the backward\, mixing '. possible over a ,.ide tunmg r .. nge only £0.' ZnSiP •• CdBiP. and AgGaS •. 1. latroduetioa Chalcopyrit.e crystals ale iOlportanL for application in nonlinuar "pt,ieal (1e.viu~8 III the neal' a.nd m~dil\m infral'~d region. It IS mainly bccaUHe of theil' reason-ably high nonlinoarity effioiont tuna.ble laHors hllove boen mado with these within their transmil!siou range (Bhar 1974) and ~heir phase-matching properties (Bhar 1976) have lJeon eva.luated Boyd ct al (1972) first pointed out tho potentiality of the cha.lcopyrite. cry"tals for the generation of FIR l'o.diailon Unlike H-VI and rH-V crystals tllC chaloeopyritll Cl'ysia.la a.re birefringout, Many of them Hhow la.rge enough incromont in reflaotivo index while passing' through tl,o fundamental la.ttice vibration flOqU61\Py a.nd theroforo ca.n givo rise to pha.slI-mllotched nonlinear interaotiOns. Other established nonlinea.r ma.teria.ls a.re not stlitable becauso of their poor FIR tra.namillaion. In the following we oonsider the gellllra.tion of FIR radia.tioll by two forms of differeuoe-mixings : Forwl.wd-wave and ba.ckwlIord-wave. From tho melloBured infrared l'ell.eotivity dllota wo evaluate seven II-IV-V. and sovon I-III-Vr. cl)aleopyrite crystals for ph9.llo. ms;\;ched FIR generation. 2. Basic th~ory The Far Infra.red (FIR) generation of la.~er b6!1JllH by optical mixing has ~oo6ived lion increaaing a.ttention. It hllos the potential of providing a eoherent tUllable fa.r infra.red moleoula.r la.sor~ The !Uoat familia.r and {lsta.blished tllllhniquo ill tha.t of difference-frequency genera.tion by mixing two laser beams in a norl. contro·symmetric crysta.1. With the input pump I.Rers in the visible or infrared 88 Far infrared generation inoMloopyrite ory8l4ls 89 Ii froqu~ncies, this teohnique oa.n provide & f&r infrared sourQo discretely or oonti-nuously tuna.ble for 110 widfl rllollga of waveleugths in the FIR beyond the rost-Atra.hlan band, The basic requirements of & nonlinoar crystal, in a.d.dition tu that in normllJ Ilonlinellr lillVioes fot' the far infrllreCl. g,>nerlltion arc : I) Tho eryatal must have 110 good opticilol tranamission lit the operating input jllo\!er frequ~ncies as well &S lit the dosirod generllted FIR froquellOies, 2) The cryatal 8hould pOSSO~B sufficiont.ly large offective optic III birefringence to pel'mit phaso-JDlltched intol'lIctlOU Two typo~ of differenco fi'equoncy Iuixing lire utihsod for :FIR genor .. tioll. '.the ('Ollillnar f'orwu,rd WIIV" (FW) mixing tecl'.lliquo, when' the genarated wa-Va propa.gates in tl',l' ~amo (lil'l1(,tioll a.~ tho two driving wa.ves, requires Wp-Wj = W, Kp-Kj = K.o (1 a.) (lb) Thesll equatiol1~ !(lJjOW from tho moment.um a.nd enol'gy QO)lHon'atiou IIIWR wher" w, is tho output gOllol'atod difference frcqulilwy in tho FIR. Wt and w'" ar8 tho input pump la.sor ffl1qU0l1eil1~, u,nd l(,~ al'o tho corre~pol1dulg Wa.V(I veotcQrs which a.rn I'eiarod t.o tIll' fruquonl1Y w by Lho formula K = nw/c, n beiug thij rufl'aetive index cUl'l'espondll1g to tho fl'cqulmcy W a.nd 0 is the volocity of clootl'o-magnet.ic wav" Ths equa.tiulIR (la) u,ud (lb) call be written in the form ~ ~~ nj-np Wp '/4-71. Tho condition for phu,~e-ma-tchillg in t.his FW differellcll down conversion procoss in tcrmR of wavelength is thus (2) wherf) it's dellote tho corresponding wa.velellgth@. Tho bo,ckwo.rd wo.ve (BW~ difference flequonoy mixing ma-y also be lI~ed to geltero.te FIR ro,dia.tioll, wherij oue of tho wu"TeS sa.y, the FIR generated wa.Ve w" is baokwa.rd travelliug. The l'oquireIl1011t~ ill this oollinollr BW mixing tllChnique o,ro Wp-lIJj =w. Kp-K,= - K,. Thesl.l t~vo I.IqUa.tiOllij cl\n ~imila.rly b~ written in the form 12 (3110) (3b) 90 'D K Gh'08h, ~'G C Bhar The conditioll for phaso-matching fo~ this collinco.l' BW mixing. in rel~tion to tho wav610ngth ia thUR The phllollc-matching conditions_ IIquatiollri (2) a.nd (4-), ca.1l hi, Hati~ficd by proptll' choice of polariHa.tioll among the intoraatillg wu,vrH 111 aniHot,~opi() cry~tals. Til fa.et, t.he left. hand ,~1I1" of oach of tho oquations (2) ami (4) "an he groator than umty to aecommodato "-polarisatioll. 1'1\0 variation of the corro~ponding extraordinary refractivo inclnx togothcr with U~C fn'qllollcy of flUC of the input pump h~sCJ'a proyJ(lc~ tuning in th" gilllel'atod Hignal wavnlellgth it., ,,7hi1o tho condition (2) in tIlt, 1}J"o8ent fi1rm ii,r tunablo ]<'W gllllnraholl iH c,j"ior :t,o realist" a careful illsigl,t into the conultlOJl for B'V goul'l'atioll /'(\YOlll.~ t.hat t.hb quantil,y ill the left hand oide of equ .. t.ioll (4) viz, AA, ~ ll1tlti( 1'0 gl'U"Lef' tlltHl 2\", "" to p n \ Ratj~fytho phasc-mu.tching coudit,lOn (whcre B = ilj-np and 2.,,' = 1/.1+1!,.). Thi~ ma.y bo dJffictllt to !'ou.li~(l when all the int"l'a(lJ.illl,r WU.VOH II" in t,J',e nominal tra.nRmission lOLnge of the ,'rYRtai. Ho\\oY(ll', whm it. i~ tho l~JR l"(lgioll then: iH possibihty of achio\'llIg the conditlOll 'J'he alloma\()UH <lisp:,rsion jR t\'o,l'd'om ,'xpitJlt,pd for ]lhu.Hu-matllhillg !loud the a.vllilablc crYBial hil'Hfringe1\('c is utilisod for tUllmg pnrposl' All crystalR ~how a.largu illcroment in refraotive index while pas~il1g through tho fundamental lattice vibration froquenoy Tho l'nira"tiv" in!lirc'H haVe b,ion m"a~urcll by u. numbel' of inve_tigator's for ~uch nOIllineal' crYRtalH oVer a wid" range of wav,,-length from vissiblc ttl J R rogion. But the J!'lR roiracth'e index data. are nnt a.va.ila.blc for mo~t of thc o}>akop),nto crystalH We hONe used t,he lattice vibra-tional and reflectivity dat.a a.nrl "tlllll'utctl l'ctl'activc llldex valuc~ therofrom which is diacusHod in til" 110xt Heel.inn for the ()Yo.hlatinll "I' tl\(l matl'ria.1 in the FIR generation We undertook 110 tl'a.nsmissioll a.nu SUlJH()qtl~llt aualYHi~ to fiud out potential nonlinear ma.tcl'ialH lllC\tullllg' dimoud Jilw ul'Yllt,als (WhlCh f,\l'O crYHtu.ls of high nonlinoarity) for the gcnerf,\tioll of tllna.blc l~IR radia.tion, 'rhf;lHO "rysta.ls haN" a.Jrellody bec)) found to show good vissihle-noar illfra.red tl'Ilol1HmissitlJl As shown thcorcticaJJy hy Morns and Sheo (1977), tho IHR gCJlorat.JOll by differellce frequency mllting is strongly depelltlent on residual a.bsorption, This is the ma.lll rellson why tho FIR diffel'ellCO ti'cquellC,V genora.tion (DFG) in crystals in most cases has beeH rtl~t,rlCt,ed to t,ile range h(ltween 50 pm to I ongl1r wavclcngth~, Roughly spoa.king, with an absorption ~oAffieiellt. It, the cff{lctivtI length of thll crystal fOI' DFG cu,unot bo muoh more thu,n a fautor 2/",. An inCreu.be in a,bsolp-tion coeffioient ill~!'elLse~ tho pha.so-mismatch a.nd deorea~ea tho generated output power, The. arf(lct of a.bsorptioll Oil FIR output power is shown as per numericliol Far infrared generation in chalcopyrite orystals 91 (llWoulation ofM-orris a.nd ShQIl (1977). In Znq;,p" (Boyd et a11972) a.t a. f~!lquency of IV = 100 (m-I , the room temp~ra.tur(l ahsorption coefficient i~ Ol = 6 om-I. The IIobsorptioll oocffident of this magnitUlh, ill a ono centimeter oryataJ reduces the FIR output power hy 11 factor of '" 0·15 frolllltR cOI"l~sponding no-a.bsQrption-value for a focal I:\pot sizo of 25 pm of pump I",RefS. However, the roflidullol a.bsorptiQn due to latticll banll t:al1 be reducet' to a very low value by cooling tho nonlinear ~ry~tal t,o a very low tempel'ature: while that duo to froe callier to a lower minimum by (lompcns1Itioll amI coolmg th" Rampl". 3_ Results aDd disCDSSioD As is pointed out t no dcta.lln,l 1" [R tmmmiSKinn and l'cfrl~otive inrlex mea.snre-lUonts in ~hc ternary c-halcopyritc crYRtul~ are not yet available. FOI·tulll~tely, quite u numoor of literat,um OJ] tb, l'eftectivity !lonll Ia.tt,ice vibrational measure-munt ure ILn\ila.hll1 fur ~(;vllral (:ryrltal~ We explOIt 8uch mea~urementB fot, d.etcrmlUutioll ot F'IR t'I'lul~mIK"ion and l"fracHve indiceH. A eareful Rtlldy \'cWMIR t,h .. t unlil", Ow H-Vr and IIf-V hinary rrystal •. W.e tArnury chalcopYrIte I-III-Vr. auci JI-IV-V. group or cry~tuls Khow many rest,Htrahlen lmndR. Whilo tlle dominant, hand (Bh&l" 1978) determinos tho infrared t,ransmis.~ioll eut-off, nothing of thiM sort i~ fonnd for the FIR regiOlI Only a fow of the crystals havo 11 wldo traTL~miKSion mugc in t,l'c l~TR reglOn On iUvllRtigatioll, it Jla~ been obscrv~1l t·h!lot FIR trru1Km1881O)1 from __ 50 p.m t,n longoI" wavelongtha is ohto.in-uhlt· for (1uAlS. alld CuGaS. of [-Ill-VI. group uud, ZnSiP. and ZnSnP. belong-ing to IT-IV-V. group of cr.\'),Ito.l~ 'rho t,ranRmiR~lOn for c-polal'isation RtartR "t n. MlightIy ~horttH· wuydength tha.1I that foJ' o-polurisation dut: to pola.risation 8(msitivity of diffiw~n(, Ia,tticc vibra.tioll modCA. Such limit,; 3.fo shown in tablo 1 for phaso-matchell erYr:ltals, It i~ to 1m not.ed tha.t for cha.lcopyrito t:l'ystalR th~ b·u.nBlIll~Kion fnr r-polaristia.tioll iK Ilxtendcd Vt,ry nea\' t~) the rest-Rtrahlrn haml bncallR(' of IlltrrOWlleRH of the fundament",l 1a.tt.lC(1 absorptlOll hand of thut poiltT'iRUhou. We h!loVe utJliSt'c\ th,,, Ia.t.tletl l'ilJrntlOlIal a.nd refiectlvit,y data of thfl d·.aloo-pyrite crystal. t,o nl}vlna.tn tl\l\ "UIIl('K of "(,fr>Lctive inri.ex from tho rela.t;ioll 11= R being tho powor reflec.t.ioll «ocffiuient ut. t,he corrosponding wavelength. Wheraver pORsiblll, a. ~ca.ling has been ma.de of the FIR refract,iv", mdices with the mea.sured (Shay and Wfll"lllCk 1975) indices in t,ho vmsiblt: rogion. In the ma.jority of theM crysta.ls, the reftectiol1 coeffi(ji(\ll~ is more or lOllS COllsta.nt or variea slowly a.t tho invt,~tiga.tod FIR frequency rcgion. The ma.xim.um orror ill the meo.surement of reflection coefficiout by different inveat,iga.tor!l.ho.s been roport~d to be ±O'50/0, whioh l'l'sults in an t'lrror in the vruue of refra.ct.ive ind-ox 92. D K Gh081r. _ G a BM". to II. similar figure. Although BUch an errol,' in refraotive iudices oan alter phase-matching a.ngle in nonlinea.r intera.otionll; in the -pl'ell8nt. context, 80S wo 1101'0 interested only in finding suita.bility of the OTYAtlL1 for FIR generation, such an unoerta.inty ma.y at, moat Mift ~ho limiting wavl\length by few microns. ltis Table 1. FIR wBvelength tWling range Cryot.,,1 FIR t.8Dll- Input Pump Output FIR Reference. for mi •• ion .t •• - (1'lD) .ignal tum) relleotivity dat .. ting from in (JJD FW BW (0) 60 1.06 40 411 l.n!hP. (e) 30 2.36 100 G. D. Holah (~"7l!) 5.3 240 I' (0) 80 1.06 80 80 \. CdBiP. (p) Ino !.36 lIO M. Bettor., 0' al \ II.S 300 (1974) , (0) 200 .6943 50 100 ZnGeP. (0) 33 1.06 200 G. D. Holab (1974) 2_36 )00 3110 10.6 1000 (0) 1110 2.36 76 1116 CdGeAs. (e) on n.:) 300 A. (Miller (Pvt Comn) (0) 35 1.06 46 200 L. B. ZIBtkm eI al ZnBnP. (,,) 3/i 2.360 ~60 (197.) ZnBiA .. (0) 90 1.06 50 2110 W. H. Koachel et 0/ (e) 110 (ID74) OdGel'. (0) 100 1.06 JiO 2"0 G D. Rolah (1974) (e) 40 AgGaS. (0) 100 _6328 80 80 (e) 80 .8943 80 Van de. Ziel ~I tAl 1.08 100 (1974) 2.880 2&0 (0) 100 ... 843 HIO 125 AgGaSe. (e) 80 1.08 300 M,ll •• 6t al (1976) 2.380 400 CoAlS. (0) 50 1.06 110 160 Heneymau (19881 (e) 40 II.S60 100 -300 Koochel eI al (1873) to be Ilot~d that in ZnGePz for which both FIR retleotivity and lLooura1;o refrau-tive indox data IUD available our method of evruuation of refraotive indices predicts- .. pha.ae·ma.tohing limit which agroo@ fa.irly well with that found by the meuured l't!f'ra.otive index da.t,a. Far infrared generation in chalcopyrite crY8talB 93 " FW 'interaction: ;Fo/' t.ho forward WaVl' rliffr,ronco-froqnollcy mixing tho two oln~o frequency pump J~ger~ lie within tl1.(\ tra.nsmission range of the cryst.a.l, while the generated diffarcn(lo fr.~qurmcy in tho FIR, The moat, oonyontient pumpR may ho two dyu lasel'a, t.wo CO2 lal!ers 1)1' a ruby a.nd a. ruby pumped dye la.st:l'. Rowover other solid state lasorR may also he used, Using t,hi~ tochnique, IJ'IR generation haH hrmn ma.de in GaAR hy Aggarwal et al (1973) and also in ZnGeP2 by Boyd et al (1972), Wo have examinod tho bmary cry~t.aIH and found t.hat, FrR gf,noration abOVe - 200 p.m can bo ma.do ill a number of (lryst.a.IA of If-IV such a.H, ZnS, ZnSc, ZnTc, CdS, CdTo and ZnO to ~ome extent. No mat,nl'ial athol' than GaAs ill group III-V has henn found snitable for thi~ type of pha.so-llla.tohod int~raetinn so far For ch~I(',(lpYl'ito el'y~tal~ (I-nI-VI., II-IV-Vs) having u. lugh nonliuoa.r flguro of fll(lrit" \\"0 h"vo tJ,nalYMd to find tha.t tl,c FW interaotion is permittod fOl' FIR rllodlaiion from .... 50 p.m to IOllgcr wavolcngt,h Jor somo Il.ml from .... lOll 11m to [ongm' wavol(mgth for other., The rO~lIltR !Un ~hown in ta.hlo I Tuning cnll partly hu l'cu.liH<lfl llY altcring crystal bil'cfringonc(l ~nd hy J1onCIll\incar pha90mat"l\ing (Aggal\val r<t aT 1973), BW inlemclioll ' Next w" ,>xploT() tl\ll Itll1.8ibilit.y of lJlJ,okward wayo diffm'(,nco frequoncy mixing fo1' the gtlnCl'a.t.illll of FIR rarlla.tlOll, whermn on" of j,11(, mtercaet,ing WIJ.'r0H IS haJkward travelling Tho Jlhase-matchod BW iuteru.ct,ion, howevl'l', m!luil'oK ,1, I~rg" effoetivIl hil'"fringenco. and hoellousc of thill ~tringent (louditirJ)l, thill pror'PKR haH RO far heen of I imitod usc. By oxploiting alloDlalouR diaper"ion pha~(l DlIttLhiug a.nd largo iuc')'(lment in I'tlfractive imlox Lfl[,W(lt>1I vi.ibIc-n{'ltr IUfl'amd 11nd :I<'IR l'!1giOll we lutVo ealeu/a.tod to find ou~ t,hat cryst.oJR Kuit.able j,,1' tllis pnTl)ORe are Oil Iy ZnHe and CdS which HhoWK II. goneration from ...... 400 pm to longer wavnlellgth, The other Jilemhors of bina,ry crysta.ls are not, Buita"lu for illsnffiClont. effoctivo hil'oti-ingenco, Then collleR chalcopyl'ite erysta.l fa.lllily (I-III-VI •. II-IV-V.), '1'ho refrae-tiv(I index data £01' many ohalcopyrite crystals in t,ho Yissihle a.nd infrarod region are ILvlLila.hlll whiiOl for FIR rango. wo ovaluat.e them fmm the oorrl)sponding reftoctivity data, WI' ha.ve eairmiat,ed tho possihility of thiN pha!!()-ma.tchod interaction for ReVoll rT-I\'-V. a.ud another Bovon I·III·VI. d\a.lcopyrito cl'ysta.ls for generation of tUllable FIR ra.diation. Thtl rosults fOl' m()~t favoura,ble caRes arc shown in tabl~ L Tn a.ll tilOS(l J!'W and BW cij,lculation~ we havo indica,t,ed in the ta,blo only t.he hlgh fl'OqUllllCY limit for <'"eh cryst,a,l and th .. tuning is permittod from there t.owa.rds the longer wa,veleugth side. 94 D K GhoBh and G a Bha,r 4. Condll.ion Reven I-JIJ-V[2 and Boven TI-JV-V~ ch~lcopyrit(\ crYstals ha.ve bOim a.na.lYijed for t.llna.hle 'FIR gen('rA.t.ion hy nonlinear difference mixing. Their transmission ranges have heen chu.r'LotOI'IRed. It ha.s b(lCIl found ~hat FW intoraotion is possible in nil theRe ery~t!Lls whil~ BW mixing iR pcrmittod in ZnRiP2' CdSiP2 IIond AgGaS2 ovor an "'ppmciahle tuning range Aclmowledgment The at,thul" Me gl'l1tuful t.o tho DopaJ'tm!lllt. of Atomio 'Enm'gy, Govt;rmnent of' India, for fill!lncia.l ~llpport. References Aggarwal R L and Lax BI973 Appl. Phy •. Lett. III 329 \ Bettini M. BBuhofer W, Cardona M and Nitsche R 1974 Ph.ll Sr. •. l. Soli,h(b) 63 641 \' Bhar G V 1974 J. 01'18. 3 72 I. Dhar G. C. 1976 Appl. Opllcs 15 30:; Dhar a C 1978 Phy. Rev. B181790 Boyd G D. Dridge. T J. Buehler E ami P .. M C K N 1972 Appl. Phil" L.II. 21, 5Ii:l Rolah G D 1972 J. Phy" C5 1893 Rolah G D. M,llel' A Bn!1 Clerk W C 1974 ,J. Phya. OI .. m. Solitls 11I6RIi Honeyman W N 1969 J. PIIIIJH. Ohorn. SaUd. 301935 Koschc! W H. ~1ohler V, Rauher A and Baar •• J 1973 Sol.tl State, 01)71 .... 18, lOll Koschel W H. Sorgel' F alld BaRrs .T 1974 Solid Stat. O.,.,.n. 1& 719 Miller A, Ralah G D, Dunnett W J) and lsoklr G W (P"ivaw COIIIIll.) Miller A, Halah a D. Dunnett W D and I •• ler G W 1976 P/'1I8. Stat Solwi(b) Morri. ,1 R Btld Shen Y R 1977 Ph" •. Rot •. A 15 114:1 RhBY J J, .. nd Wernir.k .T R 197(, Tel'nar.y chnlrlJrll"i/e l'I'y,t"l. : a,o"oth Eledr(}'/lir p,'op.,t .... GIld Applicatio"", Porgamon, Kew York Van .[er Ziel J p, Melxnel' A E, Ka.spe.' Ii 111 !t11(1 Dit,,"nb.r~ol ,1 A JiIH PIIY' Rev. BII 4286 ZIatkin L B 01 a! 1069 P"U. Stal, i'Jolidi 38 47:1 Zlatkm L B, Markov ,J F, Htekhanov A J and Ahc'll 1\1 H 1060 Phy. Stul, Solidi I .. ) 82 473 

Far Infrared Generation in Chalcopyrite Crystals

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Far Infrared Generation in Chalcopyrite Crystals

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