Laser pulse transmission and damage threshold of silica fibers with.pdf

Laser pulse transmission and damage threshold of silica fibers with antireflective coatings St. Meister, A. Wosniok, Th. Riesbeck, Ch. Scharfenorth, and H. J. Eichler TU Berlin, Optisches Institut, P 1 -1 , Str. des 1 7. Juni 1 35, 10623 Berlin, Germany Phone: +49/30/3 1426227, Fax: +49/30/3 1426888, email: smeister@physik.tu-berlin.de ABSTRACT Standard 200 jtm multimode fibers with Ta205 I Si02 antireflective coatings reach a transmission of more than 99.5% below the threshold of stimulated Brillouin scattering. The laser-induced damage threshold measured at 1064 nm and 24 ns pulse duration was about halfthan the LIDT ofuncoated fibers. Keywords: fiber optics, antireflective coating, laser damage, pulse transmission, stimulated Brilloum scattering 1. INTRODUCTION In optical fibers, the maximum transmission is limited by the losses due to Fresnel-reflection at the fiber end-faces. To minimize these losses, we developed antireflective coatings on the fiber faces. These antireflective coatings should meet high requirements so that the coated fibers can be used as phase conjugate mirrors in master oscillator power amplifier systems [1]. Furthermore, a high laser-induced damage threshold is demanded for high power laser beam transmission and realization of fiber lasers. Silica fibers with a core diameter of 200 im were coated with a Ta205 I Si02 antireflective coating. Laser pulse transmission at 1064 nm was measured depending on the beam coupling optics. The laser-induced damage threshold (LIDT) ofthe fibers with antireflective coating was determined and compared with the LIDT ofuncoated fibers. 2. EXPERIMENTAL SETUP We used a Q-switched Nd:YAG laser as the source to produce 24 ns pulses at 1064 nm. The laser provides a maximum pulse energy of 10 mJ. The laser could be operated with a repetition rate of 200 Hz or with single shot. The near TEM?o beam quality was better then M2 = 1.2. Telescope Photodiode i : , , . Joulemeter Farady isolator Lens Fibermount Jouleter - p