Up-converted coherent light emission inside of polar nematic liquid crystalline media

Polar nematic liquid crystals (PNLCs) are kind of new types of fluid materials co-possessing fluidity and ferroelectricity. Since its discovery in 2017, it has attracted a lot of attention to the potential for novel applications such as flexible optical/optoelectrical devices. One of the most fascinating physical properties of PNLCs is efficient generation of optical second harmonics. Additionally, due to its fluidity, we can dope FNLCs with other functional molecules, enabling modification of their physical properties.

By taking such advantages of PNLCs, we herein demonstrate a flexible up-conversion system of coherent light emission. By doping fluorescent molecule into PNLCs and placing that into an optical cavity consisting of two dielectric mirrors, PNLCs layer can equip two functions for laser oscillation and second harmonic generation (SHG), simultaneously. Upon excitation of the doped fluorescent molecules by a pulsed laser light, clear and sharp emission peak with nonlinearity is confirmed beyond a certain excitation threshold. Under the lasing regime, additional emission peaks at the half wavelengths of lasing peaks are also detected, meaning intra-cavity wavelength conversion through the SHG process. The SHG efficiency of the intracavity conversion process is several hundred times higher than that of outside cavity without the laser oscillation process. Such a brand-new type of flexible up-conversion device must be promising for future optical/optoelectric devices.