Tuesday / 68

11.45 CTuH3

Strong se l f -phase modula t ion i n per iodica l ly poled L i t h i u m N i o b a t e under subpicosecond pump pulses.

N.J. Traynor, L. Lefon, S. Alam, G. Biffi, A.B. Gmdmin, G W. Rois and D.C. Hanns Opiosiectranies Research Centre. Univemry of Southampton, Sourhampron SO17 181, UK

Tcl: +44 1703 592696 Fan: +44 1703 593142

Recenl progress m fabricauon of PPLK offers new effects, the observation of which is very difficult in tradilional nmtenals. So far the main aclir,ity has been focufsed on efficient second harmonic generation and paramrrnc oscillauon. Here w c present reults on strong nonlinear interactions in PPLN, which have io dale received little attention, but offer very interesting apphcationr requiring relatively low powcrr

Our experinicnlal setup IS 311 diode pumped and inwkcs amplific;ltm of sub picosecond pulses (YO0 fs) at 1543 om by a chuped pulse amplification (CPA) lechnique up to peak powen of - 40 k W with an avera!gr power oi - M)mW. l k s e pulses we then focussed to a spot SI= of 36x20 p dinmeler inside a 4 m m iong crystal of PPLN with a do-n reversal period of 18.3 pm held at the phase matching temperature of 150 C.

Figure I shows the internal efiiciency of second harmonic conyemion as a function af the peak parer of the input pulses. The maximum efficiency obtained was - 70% at a peak power of around 10 kW. Subsequently, the second harmonic poises ai 712 nm were launched into a second W L N crystal phave marched for doubling to 386 nrn through 3" order QPM. The internal afficleocy of this proceib

The unii~ual form of fig"= I can be expiaincd in terms of self-phase modulation of the fundamental pulrcs YIB cascading of second order nonlinearities [I]. This reeiu111 in back eonversion from second harmonic CO fundaments. as the pulse power i r increased, reducing the conversion efficiency. This SPM i s accompanied by avong spectral broadening at the f m d a m n t d wavelength as evidenced by figure 2. which s h o w the output fundamental spectrum and the emtra i t to the input spectrum (inset). The second harmonic spectrum shows a similar development at high powcis. From the splcrnim of figure 2 which indicates a nonlinear phase shift of more than n we are able 10 estimate ";"for PPLN and find B value of -1 10" cmzNv. This value i s obtained for a "near" phase matched iniemtion and IS in reusowble agreement with the results of reference [ll.

For the highest peak p u k powers (> 25 k W ) the conversion efficiency reaches a piateau at - SO S. I t can he speculated that this "'clamping" of the efficiency represents Some son of trapping effect between the fundamenmi and second harmonic wares [Z!.

I I O and coincided a,ith the peak efficiency of 712 nm generation.

i.BY,o..I ll".l 111,

Figure 1: Second harmonic converdoo eflidrncy as B function of peak pulse poxer.

[ I ] P. Vidakovic e! all Optics 11tleir 12. 227 (19971. 121 C.Y Chien el al. Opiicr Leirers 20,353 (19Y5)

&'iguro 2; Spectrum of trammilled fundanwntal wave at peak pulse power of 35 kU'nith the

inpvt sp~etmrn (inset).

12.00 CTuH4

Efficient, low t h r e s h o l d , collinear and n o n c o l l i n e a r BBO o p t i c a l p a r a m e t r i c oscillators

AnnMarie L Olen Coherent Technologies Inc. 3300 Mitchell Lane. Bouider. Colorado 80301, US,\

Phone I 303-449-8736 Fax i 303-449-8780

lain T hFKinnie, Piyush Jsin, Noah A Rurrrll and Donald M Warrington D s p m e n r o f Physics. Unirrrrify d o l a g o . Po Box 56, Duncdin. Ncw Zealand.

Phone6434797749 Fax643 4790964

Lnwrie A W GlosLer Dcpanmenl of Physics and AIYOnomy. Univeinty of Manchester. Manrhcrltr M 13 9PL. UK.

Hrgii power. broadly lunablc visiblc and infrared sourccs bascd on optical paramcrnc osc~11moo !OPOrI and diffcience frequency peration (UFO) are k ing dcveloped for applications m a r e a such h remole sensing. lidar and spectroscopy In may cmis there LOYTCCI are bued on inl iedly phue.marched (CPM) pmceirei ~n highly hirrfnngcnt matrnals such as P-bmum boiare IBBO) O W operating effmonsm. paniculariy !n the high powei iegime, are limited by crystal asccpr;m:e anpies snd Poynling vwmr walkoff of e-polmlied bcumi Recent iesul~s~.? indicate that improved opcmcing efficiencies c m be achicrcd usmg noncollinear CPM ~onfiguraiioor Poynfine vector walkoff ~ o m ~ ~ s l l m n ! P W C and inneaicd pump cryrral auxplance angle PI the mEei 01 ian8s"tial-ph~e-marh,"g (TPM) have k e n propied si poriibla mechanisms for m e enhancad opeiauon.

Here %e deremmc. far the fin, lime CO s u r knowlcdgc, ihc ~ e l ~ l i v e imponsncs of PVWC and TPM ~n a 355 nm pumped BBO OPO under a m p c olpumpinp conditions. Modelling of the type I mrractron ~n BBO indicrtcr that the conditions for PVWC and TF'M mqulrc opporlie diremonl o f noncalhneanl) and cannoi be simullaneaurly rariified or even appranchcd In all c m s inveinpared here the OPO UBI rinpiy reionmi for the lower wwelcngth signal emssan. and meuured output energies conenpond 10 h e combined lrignairidlrrl enngy The noncoltin~ar mple IS defined Bs r k angle berween iignai and pump w a v e ~ ~ i l o n ouaide Ihr BBG

For B 10% divergencs pump I ~ s m !c 300 micromdianr,, we 6nd that collinear opc~atton 15 uptmrl and thrr. far (he noncoliinear case. walkoff compenralion is more iawurable than Incrrued crystal acceptancc angllc. Figure I s h o w rewits for a pump divergence of 100 p a d and pump ~pol i i ie i of la) 2 mm and ihl 5mm. GPO ikrhold energy m r e ~ s ~ s with mcmasing noncollinearity in both dsccuanr. bus lower ihxrholdr are obtained lor lnepauve) ioiaiioni towwds P W C W h e n rhe pump b c m divergeore cxeeedr the 210 prad collinear cr)sal acceptance angle. our ICIUIE indicalc that increased riysal = L C C P ~ ~ " C I anpie LS more mponant ?ban u,ulloff compcnsaimn With B pump direqcnce of 1.2 mad ffigurc 2aI. coliinc&r opcrzllion is s l i l l the most efficient In this c u e (poslri~e) mMion cowards TPM becomes more larowable than negative mtation. mddlcaung that the jnmaied crys18I acceplancc angle t i now more iigndcani than PVWC. Howrver. ai a higher p m p dircrgcnce of 4 mrad (figure 2b). noncollinear operalion becomer opilmd for the Girt time In fact for L noncdlintdr angle of 183 mdliradianr ,he dopp efficiency 0137% exceeds the ben collinear perEormance i i3s1 we ohraired for a iow divergence pwnp. indicating that the full range of pump waveve~ior diremom i i being cflecrivel? coupled ~n the Ihice-wave ~mcraction A higher noncollinear am& of +IW mad iclose 10 (hi TPM condiuonl pave even higher reion8ni signal output. bui in this cue the idlrr beam was clippcd by the limilcd c ' y i t r l rpcrlurc.

A theoretical analysis of TPM and PVWC has also been carried OYI far other DFG and OPO 3y3tcmr Good agreement h u k e n obmned withrepaned cxpcnmcnral mCubYrEmenti of n ~ n ~ o l l m ~ ~ r phose-masbng m woe I1 KTP. cype I lilhium niobare. type II KTA and type I POM.

C I p t a l .

References I . 5

L A.W. Glorter. I.T. McKinnie and T.A. King. Opt. Commun. 112. 328 (1994). R. Unchel. U Bider, A. Borrur&y and R. Wallenrein. OSA TOPS 10. Adranced Solid State Lsreri. CR Poilock and WR Bosenberg ads. !OSAI. ppY4-96.