Dynamic and Spectral Features of Superluminescence under Optical Pumping at λ = 532 nm in Synthetic HPHT Diamond with NV¯ Centers

A comparative analysis has been made of the superluminescence spectra of two HPHT diamond samples with NV¯-centers with the concentration in the growth sectors {111} of NV¯-centers ≈10 ppm and of C-centers ≈ 45 ppm. A broad structureless superluminescence band with a maximum about 706 nm and a narrow band in the region of 705 to 720 nm were identified in the spectral range of 650–750 nm when excited by pulsed laser radiation at λ = 532 nm. It was found that the narrow-band superluminescence was not excited by pumping with continuous radiation at λ = 532 nm and the intensities of both types of superluminescence were summated under simultaneous pumping by continuous and pulsed radiation at λ = 532 nm. These data indicate either the different nature of the two types of superluminescence or that they belonged to NV¯ centers but with different excitation mechanisms. The existence of connection between the shape of the spectra of narrow-band superluminescence and of radiation pulses has been demonstrated. The observed features of narrow-band superluminescence are explained for the first time by the occurrence of mode-locking laser generation. The mode-locking laser generation without the use of reflective coatings on the sample or an external resonator on other laser materials has not been observed before.