Three - University of Arkansas Physics Department

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ELSEVIER PASICA @ Improvement of in-plane alignment of YBa2Cus0,-x films on polycrystallme alumina substrates using biaxially aligned CeOdYSZ buffer layers K. Y. Chen, S. Afonso, Q. Xiong, G. J. Salamo, and F. T. Chan Department of PhysicdHigh Density Electronics Center, University of Arkansas, Fayetteville, AR 72701, USA Biaxially ahgned superconducting YBazC~307.~ thin films have been fabricated on ceramic alumina substrates. Yttria-stabilized zirconia buffer layers were &st deposited on alumina using ion-beam assisted pulsed laser deposition. CeOz and YBCO films were subsequently deposited on the YSZ layer using pulsed laser deposition (PLD). All three layers were (001) oriented and biaxially textured. The YBCO films have Tc values of 89 K and Jc of 1x106 A/cm2 at 77 K. 1. INTRODUCTION The successful deposition of biaxially aligned YBazCus01.x WCO) films on polycrystalline metal alloy substrates 11-21 has prompted an interest in polycrystalline or amorphous dielectric substrates such as glass [3] and alumina. Polycrystalline ceramic alumina (AlzOs) has a dielectric constant and loss tangent lower than that of most single-crystal substrates suitable for YBCO film growth. This dielectric property is desirable for high frequency applications. The use of ceramic alumina also brings the advantages of isotropic dielectric properties, as well as lower cost. In this paper, we report the preparation of YBCO films on polycrystalhe alumina substrates with biaxially aligned CeOz/YSZ buffer layers. 2. EXPERIMENTS Biaxially aligned (001) YSZ fhs were first deposited on one side polished alumina substrates (Superstrate"996, Coors) using ion-beam assisted pulsed laser deposition. Deposition conditions have been given elsewhere [3]. In brief, about 5000-&thick YSZ films were deposited at room temperature in 3x10-4 Torr oxygen partial pressure. An argon ion beam bombarded the substrate at an incident angle of 55" from the 092 1 -45341971S 17.00 O Elsevier Science B.Y All rights reserved. PI1 SO92 14534(97)00435-8 substrate normal, while a 193 nm excimer laser ablated a YSZ target. It was observed that a thin CeOr layer (
CLE0'97. Conference on Lasers and Electro-Optics, v 11, p 216,1997 -- Requestors must comply with Copyright law (Title 17 U.S. Code) 216 / CLE0'97 / WEDNESDAY MORNING CWES 9:U am Self-trapplng of twedlmenslonal optloal beams and Ilght-Induced waveguldlng In photorefractlve InP at telecommunlcatlon wavelengths M. Chauver, S. A. Hawkins, G. J. Salamo, M. Segev,' D. F. Bliss,** G. Bryant," Depurtmenr of Physics, University ofArkan~s. Fayetteville. Arkansas 72701 Optical spatial soliton^^-'^ in photorefractive crystals offer potential applications in the field of all-optical switching and beam steering. A photorefractive solit011 is crcated when a photoinduced index change exactly compensates for thedifhction of the beam. In thissensethe beam is able to createits own waveguide. These effects have been extel~sively studied in Ferroelectric oxide and sillenite oxide crystals for visible wavelengths. For the near infrared wavelengths used in telecomm~mications. In- P:Fe crystals have already demonstrated intereslilig pliolorefractive proper tie^.".'^ Sdftrappin of a laser beam has been reported in 1nP:Fe.' In this paper we report the first observation of the use of a two-dimensional soliton formed at 1.3 pm in InP to produce a waveguide to guide a second lasu beam at 1.55 Pm. For the experiment, the beam from a Nd:Yas laser at 1.3 pm is collimated and focused with a 5-cn~ focal length lais on the entrance face of an 1nP:Fe crystal whose temperature is stabilized at 297 K. As shown in Fib 1, the electric tield, P., is applird along (I lo), the beam propagates along (I iO), and is polarized either horizontally or vertically at 45' From (110). The beam size at the entrance face of the crystal has a diameter of ahnut 55 pm and diverges to a 170 pm diameter a1 the exit face when no field is applied to the crystal. The 1nP:Fe crystal length is 1 cm in the direction of the propagation. Mien a 12 kV/cm field is applied to the crystal, the beam is trapped and the beam diameter at the exit face is reduced to about 55 ~m. Our experiments show that the beam is trapped to the same diameter for either a 1 cm or a 0.5 cm crystal length, supporting rhe condusion that the trapped diameter is the same throughout the crystal. To show that an efficient waveguide is formed in the crystal, we have also propagated a 1.55 pn (~0.1 ~~.Wlcm~) laser beam collinear to the 1.3 pm (I Wlcm2) trapped laser beam. To observe only the 1.55 pm beam, a color filter is placed after the crystal. When both beams are verti- CWE5 Fig. 1 ApyaraLus iud cryslal oricn~ation for observing two-dimensional waveguide formation by the 1.3 pm laser bcam and guiding of the 1.55 krn lascr bcam. CWE5 Fig. 2 Image of a 1.55 prn wavelength beam at the exit face of the crystal without (left) and with (right) the 1.3 pm trapped bean1 prewr. Top: both beams vertically polarized; bottom: 1.3 pm beam horizontally polarized and 1.55 pm beam vertically polorizcd. % = 12 kVlcm. cally polarized, the 1.55 p.m beam is observed to be guided along the same direction as the 1.3 pm beam (Fig. 2a). However, when the pokrization of the 1.3 pm beam is horizontal and the 1.55 pm beamverlid, the 1.55 pm beam is guided on the tide of the 1.3 pn trapped beam (Fig. 2b). While in both cases the 1.55 pm beam is effectively guided, we can see that when the 1.3 p.m beam is horizontally polar- bed, tlie 1.55 w~i bed111 is efficier~tly guided and has a near circular profile. To measure the index change responsible for the formation of the waveguide we added an interferometer to the apparatus. This measurement gives an increase of the refranive index in the center of the horizontally polarized 1.3 p11ibeamandaslrongdarm (lo-') of the index on one side of beam. 'lhis amazinglystrongdecrcaseof the indeximplies that a large photorefractive space charge field is present. We calculate this space chqe field to be about 50 KV/cm when the applied external field across the crystal is only 5 KVIcm. When the polarization ofthe 1.55 w beam is made vertical the large index change on the side of the focused 1.3 lr~n beam is seen as an increase in index and the 1.55 pm beam is guided. Despite the small value of the electro-optic codficient it is clearly possible to induce large index changes. Physically, the large index change is due to the large space charge field that call be created as a result of the intensity temperature resonance and the low value of the dielectric constant associated with InP. *Depamnent of Electrical Engineering and Advnnccd Crntrrfir Photmics and Optoelectronic Mnrerials, Princeton University, Princeton, New Jersey 08544 **U.S. Air Force, Rome Laboratory. Hanscom Air Force Bare, Marsachusetts 01731 1. M. Segev, B. Crosignani, A. Yariv, D. Fischer. Phys. Rev. Lett. 68.923 (1992). 2. G. Duree, 1. L. Shulk, G. Salamo, M. Segev, A, Yariv, B. Croaignani, P. DiPorto, E. Sharp, R2 Neurgaodar, ~hys. RW. Lctt. 71,533 (19.93). 3. G. C. Valley, M. Segev, B. Crosignanj, A. Yariv, M. M. Fejcr, M. Bashaw, Phys. Rev. A 50, Rapid Comm., R4457 (1994). 4. M. Taya, M. Bashaw, M. M. Fejer, M. Segev,G. C. Valley, Phys. Rev. A 52,3095 (1995). 5. M. Segev, G. C. Valley, R. Crosignani, P. DiPorto, A. Yoriv, Phys. Rev. Lett. 73, 3211 (1994). 6. D. N. Christodoulides, M. I. Carvalho, I. Opt. Soc. Am. B 12, 1628, (1995). 7. M. Segev, M. Shih, G. C. Valley, J. Opt. Soc. Am B 13,706 (1996). 8. Study-stale self-focusing effects in a biased photorefractive crystal were first observed by M D. Iturbe-Castillo, P. A. Marqua-Aguh, 1. J. Sanchez-Mondragon, S. Stepanov, V. Vysloukh. Appl. Phys. Lett. 64,408 (1994). 9. M. Shih, M. Segev, G. C, Valley, G. Salamo, B. Crosignani, P. DiPurto, Electron. Lett. 31, 826 (1995); M. Shih, P. Leach, M. Segev, M. Garrett. G. Salamo, G. C. Valley, Opt. Lett. 21,324 (1996). 10. Mitchell, 2. Chen, M. Shih, M. Segev, Phys. Rev. Lett. 77,490 (1996). 11. V. Vieux,P. Gravey,N. Wolfer, G. Picoli, Appl.Phys. Lett. 58,2880 (1991). 12. ti. Picoli, P. Gravey, C. Ozkul, V. Vieux, J.Appl. Phys. 66,3798 (1989). 13. M. Chauvet, S. A. Hawkins, G. I. Salamo, M. Segn: D. F. Bliss, G. Blyant, Opt. Lett. 21, 1333 (1996). Gagphase reducedbackIpound abeorptlon spectroscopy John N. Sweetser, Rick'l'rebino, Combustion Research Fuciliry. MS9057, Sandin National Laboratories, Livermore, California 94551 - 0969; E-mail. jnsweet@sandia.gov An important ~oal in optical diagnostics for trace species detection in combustion is to be able to perform sensitive absorption spectroscopy. Current methods that achieve this goal, such as frequency-modulation, Fourier-transform, cavity-ring-down, multi-photon, and photoacoustic spectroscopies all require scanning in frequency or time, which is slow compared with the relevant time scale for variation in tl~e medium under study. A sensitive singleshot (i.e., rapid) method is therefore highly desirable. It is straightfonvard to obtain a single-shnt absorption spectrum simply by sendinga burst of broadband light or an ultlashort laser pulse through the absorbing medium and then Leasuring the spectrum of the transmitted pulse with a spectrometer. Unfortunately, such a simple method has severely limited sensitivity. Small changes in the light spectrum resulting from ahsorption are dwarfed by the spectnmm of the input light and pixel-to-pixel variation ir~ resyonsivily of the dctectur. If one could reduce this background, without significantly reduangthe absorption dips, then the goal of a sensitive single-shot absorption-spectroscopy method would be achievcd. Techniquesthat attempt to accomplish this eoal with use of interferometers fail because interferometers are too sensitive to alignment,
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