Harpreet Kaur Dhillon

Effect of off-axis growth on dislocations in CVD diamond grown on {001} substrates

Single crystal CVD synthetic diamond samples grown on substrates close to (001) have been studied using X-ray topography, photoluminescence imaging and Nomarski microscopy. The substrates used for this study were polished up to 15 degrees from (001). Nomarski images of the final growth surface have been compared with X-ray section topographs and photoluminescence images, both sampling a plane close to the surface of a (010) cross-sectional slice. The photoluminescence images provide evidence of the direction of step flow growth which was compared with the surface morphology. Samples grown on substrates polished off-(001) about [010] by greater than 10 degrees exhibit regions possessing both [001] and [101] dislocations as a result of on-axis and off-axis step flow growth respectively. Our previously published model suggests relatively low angle surface inclinations arising from risers are needed to switch dislocation direction from [001] to [101] line direction, and core energies per unit length suggest a minimum riser angle of 10 degrees is required. Samples grown on substrates polished greater than 10 degrees from (001) exhibit dislocations with a [101] line direction consistent with the model. Below this angle the dislocations do not switch line direction. Possible mechanisms influencing dislocation line direction via off-axis growth are discussed.

Color alterations in CVD synthetic diamond with heat and UV exposure: implications for color grading and identification

In response to heat and UV exposure, some synthetic diamond gemstones grown by chemical vapor deposition exhibit large, reversible changes in color. A significant reduction in color was achieved by heating several CVD synthetic gemstones to >450 degrees C. Conversely, a darker color was observed in samples following exposure to UV radiation (such as that used in gem testing). Both the heated and UV-exposed samples returned to their initial (stable) color when they were illuminated for >30 minutes with a standard daylight-equivalent lamp used for grading. However, these color states did not change with time when the samples were kept in the dark. Heating and UV exposure also influenced the strengths of various IR absorption features that might be used to identify such a sample as a CVD synthetic. These nonpermanent changes might affect the apparent color grade of a CVD synthetic diamond, and care must be employed in the interpretation of spectroscopic features used to determine a stones natural or synthetic origin.

Development of High-Purity Optical Grade Single-Crystal CVD Diamond for Intracavity Cooling

Microwave assisted chemical vapour deposited bulk diamond products have been used in a range of high power laser systems, due to low absorption across a range of wavelengths and exceptional thermal properties. However the application of polycrystalline products has frequently been limited to applications at longer wavelengths or thermal uses outside of the optical path due to the birefringence and scatter that are intrinsic properties of the polycrystalline materials. However, there are some solid state structures, including thin disc gain modules and amplifiers, that will gain significantly in terms of potential output powers if diamond could be used as a heat spreader in the optical path as well as a heat spreader on the rear surface of the disk. Therefore single crystal grades of diamond have been developed that overcome the limitations of the polycrystalline material, with low absorption, low scatter and low birefringence grades for demanding optical applications. We will present new data, characterising the performance of these materials across infra-red and visible wavelengths with absorption coefficient measured by laser calorimetry at a range of wavelengths from 1064 nm to 452 nm.

Laser spectroscopy of NV- and NV0 colour centres in synthetic diamond

In this paper, we analyse the prospects for using nitrogen-vacancy centre (NV) containing diamond as a laser gain material by measuring its key laser related parameters. Synthetic chemical vapour deposition grown diamond samples with an NV concentration of ~1 ppm have been selected because of their relatively high NV concentration and low background absorption in comparison to other samples available to us. For the samples measured, the luminescence lifetimes of the NV- and NV0 centres were measured to be 8 ± 1 ns and 20 ± 1 ns, respectively. The respective peak stimulated emission cross-sections were (3.6 ± 0.1) × 10−17 cm2 and (1.7 ± 0.1) × 10−17 cm2. These measurements were combined with absorption measurements to calculate the gain spectra for NV- and NV0 for differing inversion levels. Such calculations indicate that gains approaching those required for laser operation may be possible with one of the samples tested and for the NV- centre.

Laser-related spectroscopic parameters of NV colour centres in diamond

One of the most common impurities in synthetic diamond is single substitutional nitrogen, which is incorporated in the diamond lattice substituting a carbon atom [1]. If the nitrogen is adjacent to a vacancy in the diamond lattice, it forms the nitrogen-vacancy (NV) colour centre (CC) [1]. The negatively charged state of this CC, NV-, is particularly well studied since its quantum properties are suitable for applications such as quantum information processing, single-photon sources and optical magnetometry [2]. NV CCs in the neutral state (NV0) are less widely studied. This CC exhibits broadband luminescence at slightly shorter wavelengths than NV-, and hence is also potentially of interest for tuneable and ultrafast visible laser applications. In this report, we present a detailed study of the laser-related spectroscopic properties of a diamond containing NV0 and NV-CCs.

Optical detection of magnetic resonance in nitrogen vacancy centre ensembles in bulk diamond using an off-resonant probe laser beam

Nitrogen vacancy (NV) centres are a type of defect in diamond that exhibit a number of interesting properties. NV centres can be optically excited around 450–650 nm and emit fluorescence at around 550–800 nm [1]. The optical excitation also spin polarises the negatively charged NV centres, permitting optical detection of magnetic resonance [2]. This allows nanotesla scale sensitive magnetometry to be performed with nanometre scale spatial resolution [3].

A review of state of the art CVD diamond: Synthesis, processing, and scalability (Conference Presentation)

Microwave plasma chemical vapour deposition (CVD) of diamond has enabled a multitude of optical applications due to its range of extreme properties. Transparency from the ultra-violet to the infra-red is complemented by the highest thermal conductivity of any bulk material, high laser damage threshold, low thermal expansion and chemical inertness. Element Six will review and summarize key progress made in state of the art diamond for a number of case studies, including high power laser optics, cooling in high power disk lasers, diamond Raman lasers and photonics applications.