Frequency doubling of femtosecond pulses in walk-off compensated npp

16 / QELS 2001 / MONDAY MORNING Ene gy (eV) 0.8 1.2 1.6 0.8 1.2 1.6 Re a dance A (A) QME3 Fig. 2. (a) THG in ensi y 13mm and (open and illed ci cles) as a unc ion o el- lip ici y o he inciden pho ons. F om his one ob ains (b) he phase di e ence and (c) he am- pli ude a io o he unde lying independen ele- men s o~x''). nonze o componen s a e x'2 = K= ei'oxx and x'& = 'cXY e'+q o he applicable 4/mmm sym- me y. As shown in Fig. 2a, we measu e he co e- sponding THG in ensi ies I2 and 1: as a unc- ion o ellip ici y o he inciden pulses ( e a dance A away om linea pola iza ion). F om his, one ob ains he phase di e ence 6 = 9, - 9, and ampli ude a io p = ".pa. These alues shown in Figs. 2(b,c) exhibi s ep-like changes concu en wi h he appea ance o he esonance (Fig. 1). The esonance hus a ec s di - e en ly he p oduc s o ma ix elemen s pa allel o he same axis, ~(2, and he mixed p oduc s, x(&,, implying a leas a signi ican con ibu ion o a pa i y o bidden ansi ion ac i e a 2w. Fu - he mo e, i can be shown ha lzXy = 0 occu s only o p = 3, a alue associa ed wi h an o e all sphe ical elec onic dis ibu ion. As shown in Fig. 2, while p = 3 a he esonance, he ansi ion h ough he esonance is associa ed wi h a change o symme y o he THG enso . Mo e de ailed calcula ions a e unde way o link hese no el e- sul s o he symme ies o he unde lying wa e- unc ions in he S ,CuO,CI, bands uc u e. Re e ences 1. 2. 3. M.Z. Hasan, e al. Science 288, 1811 (2000). Y.Y. Wang, e al. Phys. Re . Le . 77, 1809 (1996). H. Kishida, e al. Na u e 405,929 (2000). ~~~~~ Nonlocal e ec s in he nonlinea op lcal esponse o chi al molecules: Thi d-o de nonllnea ci cula dich oism H. Mesnil, M. C. Schanne-Klein and E Hache, Op ical Bioscience Labo a o y Ecole Poly echnique F-91128 Palaiseau-F ance; E nail: [email p o ec ed] Al hough i was p edic ed as soon as 1967,' hi d- o de nonlinea ci cula dich oism has ne e been expe imen ally obse ed. In his pape , we in es iga e his phenomenon in a liquid o chi al molecules. We i s pe o m a heo e ical calcula- ion including nonlocal e ec s in he nonlinea ligh -ma e in e ac ion ha allows o ge insigh in o he p ocess and o ob ain i s o de o magni- ude? We hen demons a e expe imen ally he exis ence o such a hi d-o de nonlinea ci cula dich oism wi h a Ru henium- is(bipy idy1) sal ha we ha e unde i s wo enan iome ic (A and A) o ms. Se e al expe imen s a e ca ied ou wi h a 1 kHz, 180 s lase sou ce: a one beam sa - u a ion expe imen whe e a sa u a ion o he ci - cula dich oism is clea ly obse ed3 and a pump- p obe expe imen . In he la e case, by modula ing he pola iza ion o he p obe o o he pump om a le o a igh ci cula one, we obse e an in ensi y-dependen ci cula dich o- ism ( ig. 1). All hese expe imen s a e shown o de i e om he same nonlinea mechanism, namely a chi al signa u e in he op ical Ke e - ec . We u he mo e show ha ou esul s a e in good ag eemen wi h ou heo e ical calcula ion.* Ex ension o his echnique o ime- esol ed ci - cula dich oism measu emen is discussed. 1. S.A. Akhmano andV.1. Zha iko , JETP Le . 6,137 (1967). 2. F. Hache, H. Mesnil and M.C. Schanne-Klein, Phys. Re . B 60,6405 (1999). 3. H. Mesnil and F. Hache, Phys. Re . Le . 85, 4257 (2000). QME5 1115 am F equencydoubllng o em osecond pulses in walk-o compensa ed N-( 4ni ophenyl)-L-p olinol Juan P. To es, Sil ia Ca asco and Lluis To ne , Lab. o Pho onics, Poly echnic Uni . o ca alonia, UPC 03, Ba celona 08034, Spain E ic W. VanS yland, CREOL, Uni e si y o Cen al Flo ida, O lando, Flo ida 32826, USA N-(4-ni ophenyl)-L-p olinol (NPP) is an o - ganic molecula c ys al de elopped by molecula I .8 . I .6 1 .4 I .I I .o 0.8 0.6 0.4 0.2 0 .O .0.2 -0.4 -0.6 .0.8 .I .o -1.2 Ill, QME4 1100 am -0.8 0.0 0.2 0.4 0.6 0.8 1.0 111, QME4 Fig. 1. Pump induced ci cula dich o- ism o a pola iza ion-modula ed pump (a) o p obe (b) s pump in ensi y. Squa es and do s: A and A enan iome s, iangles: acemic mix u e. enginee ing,' ha exhibi s one o he highes phase-ma chable second-o de suscep ibili ies epo ed so a in he nea -in a ed spec al ange (deE = 56 pm/V). Howe e , he la ge spa ial and empo al walk-o exis ing in NPP can limi se- e ely he use ulness o he ma e ial away om he nonc i ical phase-ma ching (ncpm) wa e- leng h and o sho e pulses.2 He e we show ha subpicosecond pulses can be e icien ly equency-doubled and mixed in NPP wi h mode a e pump in ensi ies, by employ- ing il ed pulse echniques.' which makes use o he la ge Poyn ing ec o walk-o exhibi ed by NPP c ys als ou side he ncpm. Such echniques a e based on he di ac ion o he inpu pump wa e by a g a ing so ha each spec al compo- nen is dispe sed in a di e en di ec ion, hus he esul ing signal is a il ed pulse. When he beam wid h o he inciden signal on he g a ing is la ge (i.e., a ew mm), he e ec o di ac ion can be accoun ed o by conside ing empo al e olu ion only bu wi h new e ec i e in e se g oup eloci- ies u = k', + an(y ) an(p )/c and g oup- eloc- i y dispe sions g, = V'" - ( an(V)/c)'/k,,. He e, is he il angle, c is he eloci y o ligh in acuum, k, a e he linea wa enumbe s, k', a e he in e se g oup eloci ies, IC', a e he g oup eloci y dispe - sion (GVD) and p a e he Poyn ing- ec o wak- o angles. We p oceed as ollows. Fi s , we calcula e he phase-ma ching angle €Ip n a he pump wa e- leng h using he app op ia e Sellmeie equa ions. Second, we ind he alue o he il y ,, equi ed o g oup eloci y misma ch (GVM) cancela ion (U' = u2). All his hen gi es he e ec i e GVDs, g,,. Figu e 1 shows ha a il -accep ance o se e al deg ees is ob ained wi h walk-o leng hs in ex- cess o 5 mm. Simila ly, o a ixed il a wa e- -1 I E 6- 4 II II SH I . -,- - - - 10 20 30 40 Til (deg ees) 0 ----- ~ 1.5 1.55 1.6 1.65 1.7 Wa eleng h@ n) QME5 Fig. 1. In (a): E ec i e dispe sion leng hs, L,, a he undamen al (FF) and second- ha monic (SH) equencies (solid lines), and empo al walk-o leng h, L,, (dashed lines), as a unc ion o he il angle o a ixed pump wa e- leng h h = 1.6 pm. In (b): Dispe sion and walk- o leng hs as a unc ion o pump wa eleng h o a ixed il angle y o = 24.9'. In bo h cases: €I = €Ipm, T = 100 s ( ull wid h hal maximum a in ensi y). MONDAY MORNING / QELS2001 / 17 P. A echnique o de e mining o a ional in a i- an s o p by means o Kleinman disallowed hype -Rayleigh sca e ing was designed and e- po ed e~en ly.~ A quan um mechanical sum- o e -s a es heo y o he molecula hype pola iz- abili y indica ed ha low-lying s a es wi h ansi ion dipole momen s pe pendicula o he molecule axis (i.e. B-s a es) a e esponsible o nonze o Kleinman-disallowed (including he second- ank) pa o p. Molecules o C,, o simi- la symme y a e common in o ganic nonlinea op ics as hey do no ha e he in e sion cen e (a majo equi emen o NLO ma e ials), and hey also o en ha e a la ge pe manen dipole momen ha made hem sui able o elec ic ield poled ma e ials. On he o he hand, his symme y al- lows he exis ence o elec onic s a es ha a e odd wi h espec o wo- old o a ion (co esponding o B- ep esen a ions), which, in u n, esul s in a second- ank enso con ibu ion o p. Ea ly s ud- ies showed ha A-shaped ch omopho es, i.e. hose ha ing an elec on accep o (dono ) con- nec ed o wo dono (accep o ) g oups wi h n- conjuga ed b idges o o m a A shape, may be o in e es as hey may ha e a la ge second- ank componen o p ha can be employed in align- men schemes as men ioned abo e. He e we p es- en sys ema ic measu emen s o he o a ional in- a ian igu es o me i o se e al A-shaped ch omopho es (Figu e 1). Table 1 summa izes he da a o he s udied ma e ials. One can no ice ha he igu e o me i o he second- ank com- ponen o all ma e ials eaches, and in some E- =*' *- = m QME5 Fig. 2. De ailed e olu ion o he SH pulse. (a): Wi h GVM compensa ion; (b): wi h- ou GVM compensa ion. Condi ions: h = 1.6 pm, 8 = epm, 7 = 100 s, I,, = 10 MW/cmZ (peak in en- si y) and a,, = 3 mm (beam wais ). No SH pulse a he impu . leng h bandwid h o se e al ens o nanome e s is ob ained. Figu e 2 shows he de ailed SH pulse e olu ion whe he he e is walk-o compensa- ion o no , by sol ing nume ically he e olu ion equa ions. The di e ence is clea ly isible: while wi hou walk-o compensa ion no use ul sec- ond-ha monic (SH) is gene a ed, a clean, na ow high in ensi y SH pulse is ob ained wi h he il ed pulse. Losses would educe he e iciency o e- quency doubling in hick c ys als, bu a high quali y ou pu second ha monic pulse is always ob ained. In conclusion, we p edic ha highly e icien equency doubling o subpicosecond pulses can be accomplished in walk-o compensa ed NPP wi h peak pump in ensi ies in he MW/cm2 ange, in a wide wa eleng h band cen e ed a ound he hi d elecommunica ion window. Resul s a e belie ed o g ea ly expand he po en- ial applica ions o NPP o he implemen a ion o pa ame ic de ices and cascading phenomena in gene al. Re e ences 1. 2. 7. Zyss, J.F. Nicoud, and M. Coquillay, J. Chem. Phys. 81,4160 (1984). 2. Wang e al., J. Op . Soc. Am. B 14, 76 (1997); G.P. Ban i a al., Op . Le . 23, 439 (1998). V.D.Voloso e al., So . J. Quan um Elec on. 4, 1090 (1975); G. Szabo and 2s. Bo , Appl. Phys. 58,237 (1994).; R. Danielius e al., Op . Le . 21,973 (1996). 3. QME6 W30 am Op imiza ion o A-shaped molecules o second ha monic gene a ion in media wi h nonpola alignmen V. Os o e kho , R. G. Pe schek, K. D. Singe , Depa men o Physics, Case Wes e n Rese e Uni e si y, Cle eland, Ohio, USA; Email: [email p o ec ed] M. He and R. I, Twieg, Depa men o Chemis y, Ken S a e Uni e si y, Ken , Ohio, USA Conside able e o has been di ec ed owa ds c ea ing o ganic nonlinea ma e ials o second ha monic gene a ion elec o-op ic con ol ha would implemen he non- ec o i educible componen s o he i s hype pola izabili y en- so .',' In pa icula , he second- ank enso com- ponen can gi e ise o mac oscopic nonlinea i y x(') in sys ems ha ing chi al nonpola symme y o he bulk, such as 0, o D2. These ypes o alignmen can be achie ed in uniaxially o biaxi- ally s e ched chi al polyme s, o in a ious uni- axial (N, SmA) and biaxial (SmC) liquid c ys al phases. To make an e icien equency con e - sion ma e ial, one has o op imize bo h he mo- lecula esponse o he ac i e ch omopho e and he mac oscopic alignmen scheme. The mic oscopic aspec o he p oblem is ad- d essed by he quan um mechanical heo y o he i s hype pola izabili y combined wi h measu e- men s o he o a ionally in a ian igu es o me i o he ele an i educible componen s o RT9090 (480nm) c : (588Nn) MG: (615nm) BG: (625~11) 1955-49 (498nm) QME6 Fig. 1. Molecula s uc u es and maximum abso p ion wa eleng hs o s udies ma e ials. QME6 Table 1. Ro a ional in a ian o measu ed A-shaped ch omopho es Ma e ial (h, nm) I I PISS I I I I PImm I I I I Pzmm I I I I P ss I I (esu X~O-~~) pNA ( e e ence) c MG BG pNA ( e e ence) RT9090 1955-49 pNA ( e e ence) c pNA ( e e ence) c MG BG RT9090 1955-49 1560 nm 7.12 2 0.16 83.5 2.1 69.8 1.8 92.7 2.1 1340 8.09 2 0.09 266.8 2 5.5 316.0 2 9.4 1064 11.2 1.6 305 I 58 780 nm 56.4 I 5.9 552 42 122 10 1422 11 278 2 21 289 22 0.0 2.1 72.2 2 2.1 14 30 24 24 3.0 I 2.6 84.1 6.5 38.6 9.5 57.6 I 6.1 0.0 2.4 3.6 2 1.1 15 I41 128.8 4.9 0 98 4.6 1.2 341 72 2 I 18 162 I 18 186 16 112 27 119 25 180 35 2.1 2.6 276 52 23.4 I 3.8 353 34 309 36 120 I 13 136 2 12 135 I 19 167 16 ~~ 4.95 0.23 76.0 4.2 54.0 5.0 68.0 3.2 5.40 2 0.19 201.4 4.6 215 2 11 8.2 1.2 398 81 38.3 - 4.1 287 31 131 2 14 153 13 198 16 200 16