Influence of femtosecond pulsed laser irradiation on bismuth germanium oxide single crystal properties

• Femtosecond pulsed laser improves optical properties of Bi12GeO20 crystals.
• Irradiation caused transmission increase and visible change of crystal color.
• Raman peaks are stronger, except E type peaks which disappear.
• XRD patterns confirmed structural changes induced by laser irradiation.

High quality bismuth germanium oxide single crystals were irradiated by a femtosecond pulsed laser beam of increasing power. Analyses performed on irradiated and unirradiated samples showed significant changes in transmittance, transmission spectra, sample color, Raman spectra, X-ray diffraction (XRD) pattern, Verdet constant, magneto-optical property, and absorption coefficient. After irradiation, the transmission spectra values increased whereas anisotropy detected in the transmission spectra of unirradiated samples disappeared. The change of color caused by irradiation was noticeable to the naked eye. The XRD measurements confirmed structural changes induced by laser irradiation, i.e., the laser-beam-incident side of the sample became almost amorphous, whereas the side opposite to the incident can be indexed to the Bi12GeO20 compound. Irradiation caused increase of Raman spectra peaks with the exception of crystal peaks of type E, which disappeared. The femtosecond pulsed laser irradiation can be used to improve bismuth germanium oxide single crystal optical properties.

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