Absorption measurements of periodically poled potassium titanyl phosphate (PPKTP) at 775 nm and 1550 nm.

Jessica Steinlechner, Stefan Ast, Christoph Kruger, Amrit Pal Singh, Tobias Eberle,¨Vitus Handchen and Roman Schnabel *¨Institut fu¨r Gravitationsphysik, Leibniz Universita¨t Hannover and Max-Planck-Institut fu¨rGravitationsphysik (Albert-Einstein-Institut), Callinstr. 38, 30167 Hannover, Germany* Author to whom correspondence should be addressed; E-Mail:roman.schnabel@aei.mpg.de;Tel.: +49-511-762-19169; Fax: +49-511-762-2784.Received: 1 November 2012; in revised form: 6 December 2012 / Accepted: 19 December 2012 /Published: 4 January 2013Abstract: The efficient generation of second-harmonic light and squeezed light requiresnon-linear crystals that have low absorption at the fundamental and harmonic wavelengths.In this work the photo-thermal self-phase modulation technique is exploited to measurethe absorption coefficient of periodically poled potassium titanyl phosphate (PPKTP) at1,550nm and 775nm. The measurementresultsare (84±40)ppm/cmand (127±24)ppm/cm,respectively. We conclude that the performance of state-of-the-art frequency doubling andsqueezed light generation in PPKTP is not limited by absorption.Keywords: PPKTP; absorption; photo-thermal1. IntroductionThere is a multitude of applications for squeezed light. Examples are fundamental research inquantum physics [1–3], the realization of quantum information protocols [4,5], and the sensitivityimprovement of gravitational wave detectors (GWDs) [6]. In 2010, a squeezed light laser operatingat a wavelength of 1,064nm was implemented in GEO 600 [7]. Design studies of future generations ofGWDs consider the application of strongly squeezed light at 1,064nm and 1,550nm [8]. State-of-the-artsetups for squeezed light generation require second-order nonlinear crystals that have low loss atthe fundamental (squeezed) wavelength as well as at the second-harmonic wavelength that pumps