Optimization of laser parameters for polarizing protons in naphthalene crystals

Protons in a crystal of naphthalene doped with pentacene have been polarized to 37% in a magnetic field of 0.3 T and at a temperature of 100 K. In order to improve the proton polarization further, a study to find an optimal condition for polarizing protons has been carried out by using a proton polarizing system with a cylindrical microwave cavity. As a part of the study, the dependencies of the polarization rate at an early stage of the build-up and of the relaxation rate during laser irradiation on the operation current of the laser have been measured.