Improvement of magneto-optical quality of high purity Bi12GeO20 single crystal induced by femtosecond pulsed laser irradiation

Femtosecond pulsed laser irradiation can improve optical properties of Bi12GeO20 single crystals. We investigate if the effect occurs if the crystals are grown from high purity components. The samples are irradiated by a femtosecond pulsed laser beam of increasing power. The maximal transmittance of 44% occurs at the irradiating laser power of 451 mW. After irradiation, intensity of Raman spectra peaks increase, except for the peak at 203 cm–1, whose intensity decreases. The irradiation also changes the sample colour. Although the Verdet constant does not change, the absorption coefficient decreases significantly, which leads to magneto-optical quality improvement of approximately 70%.