Femtosecond laser irradiation-induced phase transformation on titanium dioxide crystal surface

Titanium dioxide (TiO2) rutile single crystal was irradiated by infrared femtosecond (fs) laser pulses with repetition rate of 250 kHz and phase transformation of rutile TiO2 was observed. Micro-Raman spectra show that the intensity of Eg Raman vibrating mode of rutile phase increases and that of A1g Raman vibrating mode decreases apparently within the ablation crater after fs laser irradiation. With increasing of irradiation time at laser average power of 300 mW, the Raman vibrating modes of anatase phase emerged. Rutile phase of TiO2 single crystal is partly transformed into anatase phase. The anatase phase content transformed from rutile phase increased to a maximum and then decreased with increasing of fs pulse laser irradiation time. The line mapping of micro-Raman spectrum at the crater, irradiated by fs pulse laser for 100 s at average power of 300 mW, indicates more rutile phase are transformed into anatase phase at the center