Determination of blue-light-induced infrared absorption based on mode-matching efficiency in an optical parametric oscillator

Abstract

Non-classical squeezed states of light at a compatible atomic wavelength have a potential application in quantum information protocols for quantum states delaying or storaging. An optical parametric oscillator (OPO) with periodically poled potassium titanyl phosphate (PPKTP) is the most effective method for generating this squeezed state. However, it is a challege for the nonlinear interaction in PPKTP crystal at the D1 line of rubidium atomic, due to a strong blue-light-induced infrared absorption (BLIIRA). In this paper, we report an indirect measurement method for the BLIIRA through measuring the mode-matching efficiency in an optical parametric oscillator. In contrast to previous works, our method is not limited by the absolute power variation induced from the change of frequency conversion loss and the impedance matching originated from the change of absorption loss. Therefore, the measurement process is performed at the phase-matching condition. The measured results show that BLIIRA coefficient is quadratic dependence of blue light intensity below 1 kW per square centimeter in our PPKTP device, which will provide important basis for optimizing squeezed state generation at 795 nm.

Detection and perfect fitting of 132 dB squeezed vacuum states by considering green-light-induced infrared absorption

“…GLIIRA loss is measured by comparing mode-matching efficiency of an optical cavity with and without 532 nm laser illuminating, which has a measurement sensitivity better than 10 −5 ∕cm [38,39]. We perform the measurement of GLIIRA at the pump power from 50 mW to 230 mW with a step of 15 mW, corresponding to the power density from 2.9 kW∕cm 2 to 13.34 kW∕cm 2 in PPKTP, and the GLIIRA absorption coefficient from 1.21 × 10 −4 ∕cm to 1.12 × 10 −3 ∕cm.…”