The Effect of the Laser-Radiation Power on the Characteristics of the Raman Line for Diamond Single Crystals

The paper presents the results of the study of the effect exerted by exciting laser radiation on the Raman spectra of synthetic diamond single crystals plates (linear dimensions from 3 × 3 to 5 × 5 mm) having different impurity compositions. It has been found that an increase in laser radiation power from 70 to 480 mW (90–600 kW/cm2) leads to heating of the samples by a few tens of degrees, which results in shifting of the Raman line maxima by ~0.5 cm–1 and in increased Raman line half-width up to ~0.15 cm–1. As demonstrated by the spectral data, the heating temperature correlates with the optical density and geometry of the samples and also with the conditions of heat extraction from their surface. Based on the independent measurements of the crystal temperature at a certain distance from the excitation beam axis, it is shown that the variations of the characteristics of the principal Raman line are not determined by the local heating of the crystal studied under the effect of laser radiation. An analysis of the characteristics of the Stokes and anti-Stokes spectral components makes it possible to separate the temperature and impurity effects in the variations of the principal Raman line. Using diamond monocrystalline samples as an example, it has been revealed that the increased content of nitrogen as an impurity in the lattice from 3 up to 200 ppm leads to shifting of the Raman line maximum towards lower wave numbers by 0.08 cm–1 and to its broadening by 0.23 cm–1.