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

Yajun Wang,Wenhai Yang,Zhixiu Li,Yaohui Zheng

doi:10.1038/srep41405

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.

Highlights

Serious limitation for the quantum noise reduction because of the additional absorption loss and non-optimal mode-matching efficiency arising from the thermal effect[9,17]
A part of the 795 nm laser is injected into a four-mirror enhanced-external-cavity for continuous wave (CW) second harmonic generation (SHG), which is used as a laser source for the absorption measurement of 397.5 nm laser and the detailed SHG progress can be found in ref
PD2 detects the transmission power of 397.5 nm laser exporting from M2, and the circulating power in single resonant optical cavity (SROC) can be inferred from the dichroic mirror (DM) and M2 transmittance and the measured values of PD2

Summary

Introduction

Serious limitation for the quantum noise reduction because of the additional absorption loss and non-optimal mode-matching efficiency arising from the thermal effect[9,17]. With the same experimental condition and method above, a 397.5 nm and a 795 nm lasers are combined with a DM and collinearly propagate through the center of the crystal, which are focused to the waist radius of 38.9 μm and 27.6 μm with a telescope system, respectively, and the temperature of the cystal is adjusted to 70 °C to aviod the influence of nonlinear interaction process for absorption measurement.

Results

Conclusion