Photorefractive-resistant Hafnium-doped Lithium Niobate Crystals at very low Dopant Concentration

To investigate the effective threshold in hafnium-doped lithium niobate crystals, two different parameters are measured. The photorefractive effect as a function of the intensity I of the illuminating beam, and the phase-matching (PM) temperature for second harmonic generation (SHG) at fixed pump wavelength for different Hf concentration.