Distribution of optically-generated vortices in YBCO thin ®lm strips Takashi Fukui a , Akihiro Moto a , Hironaru Murakami a , Masayoshi Tonouchi a,b, * a Research Center for Superconductor Photonics, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan b PRESTO, Japan Science and Technology Corporation JST), 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan Received 16 October 2000; accepted 5 February 2001 Abstract An optical ¯ux generation in superconducting YBa 2 Cu 3 O 7Àd thin ®lm strips was demonstrated by exciting with femtosecondpulsedlaserFPL).Asaresult,thedistributionofthetrappedmagnetic¯uxwassuccessfullyobservedby terahertz radiation imaging system. The observed distribution of magnetic ¯ux density shows a good agreement with the optical beam pro®le of FPL. Ó 2001 Elsevier Science B.V. All rights reserved. PACS: 85.25.-j; 85.25.Am; 85.70.Sq Keywords: YBCO; Current modulation; Optical response; Optical magnetic ¯ux 1. Introduction High T c superconductors have a great potential to develop opto-electronic devices applicable for an ultrafast communication system in near future. Tonouchi et al. [1] demonstrated a magnetic ¯ux generation in a current biased superconductive loop by femtosecond pulsed laser FPL) irradia- tion, which is attributed to the ultrafast modu- lation of supercarriers within 300 fs. Based on this result, in the present study magnetic ¯ux generation was also tried in a biased current YBa 2 Cu 3 O 7Àd YBCO) strip line by FPL irradia- tion. 2. Experimental A 100-nm-thick YBCO thin ®lm was prepared on MgO100) substrate. The ®lm was patterned into a 120-lm-wide and 500-lm-long strip-line structure. Half of the strip area was patterned to havetheorderedarrayofholeswithadiameterof 1 lmatanintervalof4 lm see the left-hand side inthephotoimageofFig.1).Aftertheprocessing, resistive measurement showed the superconduct- ing transition temperature of 88 K and critical current of 450 mA. The sample was cooled down to17K,andappliedwiththebiasedcurrentof200 mA.Then,FPLbeamirradiation,atalaserpower of 30 mW was carried out in the order of circle Physica C 357±360 2001) 454±456 www.elsevier.com/locate/physc * Corresponding author. Address: Research Center for Su- perconductor Photonics, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan. Tel.: +81-68-79-7981; fax: +81- 68-79-7984. E-mail address: tonouchi@rcsuper.osaka-u.ac.jpM.Tonou- chi). 0921-4534/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0921-453401)00274-X