Direct Multiphoton Femtosecond Infrared Laser Excitation of a Diamond Lattice in the Two-Phonon Region and Modification of Color Centers

The nonlinear absorption of ultrashort laser pulses with intensities of 0.17–1.7 TW/cm 2 at an intrinsic two-photon absorption wavelength of 4673 nm in type IIb diamond has been studied experimentally. It has been shown that the main absorption mechanism in the studied sample is two-photon absorption with a coefficient of β 2 = (72 ± 7) cm/TW. Transmission microspectroscopy, visible photoluminescence, and infrared Fourier-transform microspectroscopy have demonstrated the possibility of laser-induced transformation of nitrogen impurity centers in synthetic type Ib diamond at higher radiation intensities.