Generation Of Blue Light At 426 Nm By Frequency Doubling With A Monolithic Periodically Poled KTiOPO₄

Non-classical light at near-infrared wavelength is widely used in many fields, such as optical measurement, information storage and readout, nonlinear optics, quantum optics, quantum information and other fundamental researches in quantum physics. Specially, Non-classical light around the atom transition provides important quantum resources for the research of light-atom interaction, precision measurement and quantum storage. With the continuous development of quantum control, generation of various quantum resources has become an important issue. The optical parametric oscillator (OPO) is a common and important device for non-classical light generation, whose pump beam is usually from frequency doubling. Therefore, it’s necessary to develop research on frequency doubling process. Many groups have achieved high-power output of blue light via frequency doubling. Standing wave cavity and ring cavity with separated optical elements have been extensively studied. The advantage of such cavities is that they are flexible, easy to be aligned and the cavity length can be adjusted by electric piezo transducer. However, they also had the disadvantages with large internal losses and the cavity is usually not robust enough for long running due to the complex configuration and the fragile servos. The monolithic crystal cavity provides a new choice of cavity candidate with less intra-cavity losses and simple structure which is a prospective candidate for setting up a robust OPO. In this thesis, we will focus on the blue light generation by frequency doubling with a monolithic PPKTP cavity working at 852nm for the first time. The 15 mm-long monolithic PPKTP crystal acts as a standing-wave cavity, both ends of which are spherically polished (radius of curvature is 20 mm) and mirror-coated. A maximum power of 158 mW of blue light at 426 nm is obtained, with a measured conversion efficiency of 45%. Because of the short cavity length, the wide free spectral range (FSR) and bandwidth, it is easy to realize cavity resonance via temperature control.Another part of this thesis is the design of a OPO cavity for nonclassical beam generation around the transition of Cs atoms. OPO system is an important workhorse to generate quantum resources for precision measurement and light-atom interaction research. The bandwidth and squeezing degree are determined by proper selected parameters of the OPO cavity, such as cavity length, bandwidth, intra-cavity loss etc. On the other hand, the OPO cavity should satisfy stability condition. So it’s essential to design the OPO cavity configuration according to the conditions and requirements of our experiment. The ring cavity is flexible enough for beam alignment, while standing-wave cavity is more stable. We have discussed the design of both of these two cavity structures.