For the first time, lasing at NV− centers in an optically pumped diamond sample is achieved. A nanosecond train of 150-ps 532-nm laser pulses was used to pump the sample. The lasing pulses have central wavelength at 720 nm with a spectrum width of 20 nm, 1-ns duration and total energy around 10 nJ. In a pump-probe scheme, we investigate lasing conditions and gain saturation due to NV− ionization and NV0 concentration growth under high-power laser pulse pumping of diamond crystal.

Superluminescence of NV centres with a band peaking at λ = 718 nm in the phonon wing of the photoluminescence spectrum of a high-pressure high-temperature (HPHT) diamond sample under pulsed optical excitation at λ = 532 nm with an intensity of 2 – 46 MW cm-2 is demonstrated. Superluminescence is observed in the diamond crystal region containing 6 ppm NV centres and 150 ppm substituent nitrogen; it is absent in the crystal part with a lower nitrogen content. Superluminescence pulses are observed on the leading edge of the optical excitation pulse at λ = 532 nm and have an FWHM value of 4 ns. The enhancement of the photoluminescence of NV centres is suggested to be due to the total internal reflection in the diamond plate (waveguide effect).

No abstract

The results of experimental studies of the effect of polarity on the streamer velocity at various voltage amplitudes are presented. In the experiments, nanosecond voltage pulses were applied across an 8.5 mm point-to-plane gap filled with air at a pressure of 100 kPa. The formation of positive and negative streamers has been experimentally studied using a HSFC-PRO four-channel ICCD camera and a Hamamatsu C10910-05 streak camera. Waveforms of voltage and discharge current pulses were also recorded. The propagation velocity of streamers was estimated by streak images. It was found that a negative streamer crosses the gap faster than a positive one. This is most likely due to the presence of runaway electrons with the negative polarity of a pointed electrode. The experiment showed that runaway electrons are generated before the formation of a negative streamer. Runaway electrons can preionize the gas in the gap.