The Experts below are selected from a list of 4965 Experts worldwide ranked by ideXlab platform
A J Kemp - One of the best experts on this subject based on the ideXlab platform.
-
laser spectroscopy of nv and nv0 colour centres in Synthetic Diamond
Optical Materials Express, 2017Co-Authors: E Fraczek, Mark E Newto, V G Savitski, Matthew Markham, Matthew W Dale, E Eeze, Phil Diggle, Andrew Enne, Harpreet Kau Dhillo, A J KempAbstract: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.
-
characterization of single crystal Synthetic Diamond for multi watt continuous wave raman lasers
IEEE Journal of Quantum Electronics, 2012Co-Authors: V G Savitski, M D Dawso, D. Urns, Ia Friel, Jennifer E. Hastie, A J KempAbstract:A continuous-wave Diamond Raman laser is demonstrated with an output power of 5.1 W at 1217 nm. This Raman laser is intracavity pumped by a side-pumped Nd:YLF rod laser: a 43-fold brightness enhancement between the Nd:YLF and Diamond Raman lasers is observed, with the M2 beam propagation factor of the Diamond Raman laser measured to be <; 1.2. Although higher output powers are demonstrated in a similar configuration using KGd(WO4)2 (KGW) as the Raman laser material (6.1 W), the brightness enhancement is much lower (2.5 fold) due to the poorer beam quality of the KGW Raman laser (M2 <; 6). The Raman gain coefficient of single-crystal Synthetic Diamond at a pump wavelength of 1064-nm is also measured: a maximum value of 21±2 cm/GW is returned compared to 5.7±0.5 cm/GW for KGW at the same wavelength.
-
1 6 w continuous wave raman laser using low loss Synthetic Diamond
Optics Express, 2011Co-Authors: Walte Lubeig, M D Dawso, D. Urns, V G Savitski, Gerald M Onne, Sarah Louise Geoghega, Ia Friel, Jennifer E. Hastie, A J KempAbstract:Low-birefringence (Δn<2x10−6), low-loss (absorption coefficient <0.006cm−1 at 1064nm), single-crystal, Synthetic Diamond has been exploited in a CW Raman laser. The Diamond Raman laser was intracavity pumped within a Nd:YVO4 laser. At the Raman laser wavelength of 1240nm, CW output powers of 1.6W and a slope efficiency with respect to the absorbed diode-laser pump power (at 808nm) of ~18% were measured. In quasi-CW operation, maximum on-time output powers of 2.8W (slope efficiency ~24%) were observed, resulting in an absorbed diode-laser pump power to the Raman laser output power conversion efficiency of 13%.
-
power scaling of nd yvo4 and nd gdvo4 disk lasers using Synthetic Diamond as a heat spreader
Optics Letters, 2009Co-Authors: Patricia Milla, A J Kemp, D. UrnsAbstract:A newly developed low-birefringence Synthetic Diamond is shown to be an effective intracavity heat spreader in Nd:YVO4 and Nd:GdVO4 disk lasers. A cw output power of 25.7 W from only one double pass of the pump is reported. The Diamond heat spreader is shown to increase the pump power density at which fracture occurs.
Hisao Kanda - One of the best experts on this subject based on the ideXlab platform.
-
spectroscopic study of cobalt related optical centers in Synthetic Diamond
Journal of Applied Physics, 1996Co-Authors: Simo C Lawso, Hisao Kanda, Kenji Watanabe, I Kiflawi, Yoichiro Sato, Ala T CollinsAbstract:This article presents evidence that cobalt forms a series of optically active defect centers in Diamond grown by high‐temperature, high‐pressure synthesis. Photoluminescence (PL) studies reveal that the newly observed vibronic systems with zero‐phonon energies at 1.989, 2.135, 2.207, 2.277, 2.367, and 2.590 eV appear only in samples grown using a cobalt‐containing solvent–catalyst. Results of an annealing study, carried out in the temperature range 1500 to 1800 °C, establish that many of the new bands appear during the temperature regime of nitrogen aggregation. It is therefore proposed that nitrogen forms complexes with cobalt to produce optically active centers, in a manner analogous to that of nickel point defects in Diamond. Detailed radiative decay time measurements and temperature dependence measurements show that all but one of the bands which are here associated with nitrogen–cobalt complexes have long radiative decay times (∼100 μs), and this again is a characteristic of the PL centers arising fr...
-
an annealing study of nickel point defects in high pressure Synthetic Diamond
Journal of Applied Physics, 1993Co-Authors: Simon C Lawson, Hisao KandaAbstract:Results of an annealing study, carried out in the temperature range 1500–1900 °C, of nickel‐related optical centers in high‐pressure Synthetic Diamond are presented. It is established that the well‐known 1.883 and 2.51 eV systems anneal out during the temperature regime of nitrogen aggregation and the concurrent growth of an array of structure, which extends throughout the visible region of the absorption spectrum, and gives the previously bright‐yellow‐colored Diamonds a rich golden‐yellow color, is observed. By carrying out the annealing sequence on Diamonds grown using various solvent catalysts a correlation is found between preanneal 1.883 eV absorption and maximized absorption of some of the annealed structure. From the results it is proposed that centers associated with nickel and nitrogen are produced and their possible natures are speculated on. It is found that the defect‐induced one‐phonon spectra of the Diamonds examined may be satisfactorily decomposed into three components. To account for cer...
-
an annealing study of nickel point defects in high pressure Synthetic Diamond
Journal of Applied Physics, 1993Co-Authors: Simon C Lawson, Hisao KandaAbstract:Results of an annealing study, carried out in the temperature range 1500–1900 °C, of nickel‐related optical centers in high‐pressure Synthetic Diamond are presented. It is established that the well‐known 1.883 and 2.51 eV systems anneal out during the temperature regime of nitrogen aggregation and the concurrent growth of an array of structure, which extends throughout the visible region of the absorption spectrum, and gives the previously bright‐yellow‐colored Diamonds a rich golden‐yellow color, is observed. By carrying out the annealing sequence on Diamonds grown using various solvent catalysts a correlation is found between preanneal 1.883 eV absorption and maximized absorption of some of the annealed structure. From the results it is proposed that centers associated with nickel and nitrogen are produced and their possible natures are speculated on. It is found that the defect‐induced one‐phonon spectra of the Diamonds examined may be satisfactorily decomposed into three components. To account for certain changes in the infrared spectra during the annealing sequences, and using previously reported results, it is proposed that one of these components may result from nitrogen in a positive charge state.
D J Twitche - One of the best experts on this subject based on the ideXlab platform.
-
magnetotransport study of valley polarized electrons in Synthetic Diamond
Physical Review B, 2016Co-Authors: Nattaka Suntornwipa, D J Twitche, Markus Gabrysch, Sama Majdi, Ja IsbergAbstract:We demonstrate that the highly stable valley-polarized electron states in ultrapure single-crystalline Diamond allow for investigation of charge transport, magnetoresistivity, and determination of ...
-
production of oriented nitrogen vacancy color centers in Synthetic Diamond
Physical Review B, 2012Co-Authors: A M Edmonds, Mark E Newto, D J Twitche, Ulrika F S Dhaenensjohansso, R J Cruddace, C Santori, Raymond G Eausoleil, Matthew MarkhamAbstract:The negatively charged nitrogen-vacancy (${\mathrm{NV}}^{\ensuremath{-}}$) center in Diamond is an attractive candidate for applications that range from magnetometry to quantum information processing. Here we show that only a fraction of the nitrogen (typically $l0.5$%) incorporated during homoepitaxial Diamond growth by chemical vapor deposition (CVD) is in the form of undecorated ${\mathrm{NV}}^{\ensuremath{-}}$ centers. Furthermore, studies on CVD Diamond grown on $(110)$-oriented substrates show a near 100% preferential orientation of NV centers along only the $[111]$ and $[\overline{1}\overline{1}1]$ directions, rather than the four possible orientations. The results indicate that NV centers grow in as units, as the Diamond is deposited, rather than by migration and association of their components. The NV unit of the ${\mathrm{NVH}}^{\ensuremath{-}}$ is similarly preferentially oriented, but it is not possible to determine whether this defect was formed by H capture at a preferentially aligned NV center or as a complete unit. Reducing the number of NV orientations from four orientations to two orientations should lead to increased optically detected magnetic resonance contrast and thus improved magnetic sensitivity in ensemble-based magnetometry.
-
charge transfer effects thermo and photochromism in single crystal cvd Synthetic Diamond
Journal of Physics: Condensed Matter, 2009Co-Authors: Rizwan Uddin Ahmad Kha, Philip Maurice Martineau, Mark E Newto, D J TwitcheAbstract:We report on the effects of thermal treatment and ultraviolet irradiation on the point defect concentrations and optical absorption profiles of single crystal CVD Synthetic Diamond. All thermal treatments were below 850 K, which is lower than the growth temperature and unlikely to result in any structural change. UV–visible absorption spectroscopy measurements showed that upon thermal treatment (823 K), various broad absorption features diminished: an absorption band at 270 nm (used to deduce neutral single substitutional nitrogen (NS0) concentrations) and also two broad features centred at approximately 360 and 520 nm. Point defect centre concentrations as a function of temperature were also deduced using electron paramagnetic resonance (EPR) spectroscopy. Above ~500 K, we observed a decrease in the concentration of NS0 centres and a concomitant increase in the negatively charged nitrogen–vacancy–hydrogen (NVH) complex (NVH−) concentration. Both transitions exhibited an activation energy between 0.6 and 1.2 eV, which is lower than that for the NS0 donor (~1.7 eV). Finally, it was found that illuminating samples with intense short-wave ultraviolet light recovered the NS0 concentration and also the 270, 360 and 520 nm absorption features. From these results, we postulate a valence band mediated charge transfer process between NVH and single nitrogen centres with an acceptor trap depth for NVH of 0.6–1.2 eV. Because the loss of NS0 concentration is greater than the increase in NVH− concentration we also suggest the presence of another unknown acceptor existing at a similar energy to NVH. The extent to which the colour in CVD Synthetic Diamond is dependent on prior history is discussed.
Amitava Ghosh - One of the best experts on this subject based on the ideXlab platform.
-
high vacuum brazing of Synthetic Diamond grits with steel using micro nano al2o3 reinforced ag cu ti alloy
Journal of Materials Processing Technology, 2019Co-Authors: Prithviraj Mukhopadhyay, Amitava GhoshAbstract:Abstract Ti activated 72Ag-28Cu filler alloy was reinforced with micro/nano-Al2O3 ceramic particles for active brazing of Synthetic Diamond grits with 1045 steel. Microstructural changes due to reinforcement and corresponding influence on abrasion resistance characteristics of the modified filler alloy were observed. Different weight percentages (wt%), each of micro and nano-Al2O3 reinforcements, were tried. Micro-Al2O3 ceramic reinforcements were found to be uniformly distributed in the microstructure of the modified filler material. Alumina particles reacted with titanium to form hard Cu3Ti3O and TiO reaction compounds. Nano-Al2O3 reinforcements showed a tendency to get clustered, impairing the improvement in abrasion resistance property of the primary filler alloy. 1 wt% micro-Al2O3 added filler alloy underwent 58% less volumetric wear than the primary Ag-Cu-Ti alloy during the pin-on-disc test. This micro- reinforced filler also could effectively braze Diamond grits with the steel without any significant deterioration in its wetting ability on Diamond surface and joint strength, compared to its counterpart having the primary formulation.
-
on bond wear grit alloy interfacial chemistry and joint strength of Synthetic Diamond brazed with ni cr b si fe and ti activated ag cu filler alloys
International Journal of Refractory Metals & Hard Materials, 2018Co-Authors: Prithviraj Mukhopadhyay, Amitava GhoshAbstract:Abstract A multi-point brazed Diamond tool requires high wear resistance of bonding alloy and strength of the brazed joint. In this work, two active brazing alloys, i.e., Ni-Cr-B-Si-Fe and Ag-Cu-Ti were used for brazing Synthetic Diamond grits on a medium carbon steel substrate under a high vacuum environment. The performance of the brazed joints was subsequently investigated and compared. The microstructure of the filler alloys was found to play a key role in influencing the bond wear characteristics, grit-alloy interfacial chemistry and strength of the brazed joint. Formation of Cu4Ti compounds in Ag-Cu-Ti alloy and boride and silicide compounds in case of Ni-Cr alloy contributed to the enhancement of hardness of the alloys. The bond wear characteristics of Ni-Cr alloy were substantially superior to that of Ag-Cu-Ti alloy. A single grit test of the brazed samples was carried out to investigate the failure pattern of the brazed joints. Ni-Cr brazed joints predominantly failed at the bond level. The residual stress and microstructural flaws in the form of microcracks at alloy-grit interface of the as-brazed test samples led to such a failure. In contrast, no such crack was detected in the case of Ag-Cu-Ti alloy and the joints failed by ductile fracture of alloy near to the interface, leading to Diamond pull out. The present study elucidates the differences in wear, strength of bond and failure pattern of the brazed joints in the light of alloy and interfacial microstructure.
-
challenges in brazing large Synthetic Diamond grit by ni based filler alloy
Journal of Materials Processing Technology, 2017Co-Authors: Prithviraj Mukhopadhyay, Raghava D Simhan, Amitava GhoshAbstract:Abstract Large size D711 Synthetic single crystal Diamonds are vacuum brazed with medium carbon steel using a Ni-Cr-Fe-B-Si alloy and inherent difficulties are critically investigated. Although, the alloy shows appreciable wetting on Diamond at the brazing temperature of 1050 °C, micro-cracks develops and pronounces at the bond level in all as-brazed samples. The crack is not arrested even by using cooling rate, as slow as 5 °C/min. The large difference in Young’s modulus and thermal expansion coefficient of the substrate, alloy and grit results in unfavorable tensile residual strain on Diamond at bond level, causing detrimental stress. Formation of a partially coherent chromium iron carbide phase is identified which seems to facilitate the micro-crack formation under residual stress. The residual stress distribution at the interface region is mapped through finite element analyses. No noticeable difference in the strength of joint is recorded on reducing the cooling rate, up to 5 °C/min. Failure pattern of grits suggests a predominant bond-level breakage of Diamond grits, indicating prevalence of residual stresses at bond level. The (110) crystallographic plane of Diamond suffers significant graphitization at higher temperatures, even under a very high vacuum environment.
Philip Maurice Martineau - One of the best experts on this subject based on the ideXlab platform.
-
charge transfer effects thermo and photochromism in single crystal cvd Synthetic Diamond
Journal of Physics: Condensed Matter, 2009Co-Authors: Rizwan Uddin Ahmad Kha, Philip Maurice Martineau, Mark E Newto, D J TwitcheAbstract:We report on the effects of thermal treatment and ultraviolet irradiation on the point defect concentrations and optical absorption profiles of single crystal CVD Synthetic Diamond. All thermal treatments were below 850 K, which is lower than the growth temperature and unlikely to result in any structural change. UV–visible absorption spectroscopy measurements showed that upon thermal treatment (823 K), various broad absorption features diminished: an absorption band at 270 nm (used to deduce neutral single substitutional nitrogen (NS0) concentrations) and also two broad features centred at approximately 360 and 520 nm. Point defect centre concentrations as a function of temperature were also deduced using electron paramagnetic resonance (EPR) spectroscopy. Above ~500 K, we observed a decrease in the concentration of NS0 centres and a concomitant increase in the negatively charged nitrogen–vacancy–hydrogen (NVH) complex (NVH−) concentration. Both transitions exhibited an activation energy between 0.6 and 1.2 eV, which is lower than that for the NS0 donor (~1.7 eV). Finally, it was found that illuminating samples with intense short-wave ultraviolet light recovered the NS0 concentration and also the 270, 360 and 520 nm absorption features. From these results, we postulate a valence band mediated charge transfer process between NVH and single nitrogen centres with an acceptor trap depth for NVH of 0.6–1.2 eV. Because the loss of NS0 concentration is greater than the increase in NVH− concentration we also suggest the presence of another unknown acceptor existing at a similar energy to NVH. The extent to which the colour in CVD Synthetic Diamond is dependent on prior history is discussed.
-
x ray topography studies of dislocations in single crystal cvd Diamond
Diamond and Related Materials, 2008Co-Authors: M P Gaukroger, Philip Maurice Martineau, Ian Friel, M J Crowder, S D Williams, Daniel James TwitchenAbstract:X-ray topography has been used to study single crystal Diamond samples homoepitaxially grown by microwave plasma-assisted chemical vapour deposition (CVD) on high pressure high temperature (HPHT) and CVD Synthetic Diamond substrates. Clusters of dislocations in the CVD Diamond layers emanated from points at or near the interface with the substrate. The Burgers vectors of observed dislocations have been determined from sets of {111} projection topographs. Dislocations have line directions close to the [001] growth direction and are either edge or 45° mixed dislocations. Where groups of dislocations originated at isolated points they tended to be of the edge variety. Where the substrate surface was deliberately damaged before growth, two sets of dislocations were observed to have propagated from each line of damage and there was a tendency for dislocations to be of the 45° mixed variety with a component of their Burgers vector parallel to the polishing direction. It is demonstrated that X-ray topography can be used to deduce the growth history of CVD Synthetic Diamond samples produced in multiple growth stages.
-
Identification of Synthetic Diamond Grown Using Chemical Vapor Deposition (CVD)
Gems & Gemology, 2004Co-Authors: Philip Maurice Martineau, Simon Craig Lawson, Andy J. Taylor, Samantha J. Quinn, David J. Evans, Michael J. CrowderAbstract:encountered by the gem trade, but until recently attention has focused almost exclusively on the kind produced by exposing carbon-containing solids to high pressures and temperatures (HPHTgrown Synthetic Diamond; see, e.g., Shigley et al., 1986, 1987). For many years, however, scientists have known that it is also possible to synthesize Diamond at low pressures from carbon-containing gases, using chemical vapor deposition (CVD) techniques. Although the gem trade has been relatively unaware of CVD, over the last two decades this method of Diamond synthesis has been the subject of intense worldwide research because of the many potential technological applications of CVD Synthetic Diamond material. Apollo Diamond Inc. of Boston, Massachusetts, has spent many years developing CVD Synthetic Diamond material for use in technological applications and jewelry. In August 2003, this company announced plans to begin selling limited quantities of faceted material starting in the fourth quarter of 2003 (Pridy, 2003). Butler et al. (2002) presented analytical results for one faceted sample of single-crystal CVD Synthetic Diamond produced by Apollo Diamond. Preliminary notes on examination of several Apollo samples appeared in the Gem News International section of the Fall 2003 issue of this journal. Then, in the Winter 2003 issue, Wang et al. gave a thorough description of the results of their study of 13 samples provided by Apollo Diamond, offering useful indicators to aid identification of CVD Synthetic Diamond of the kind proposed for commercial jewelry production. Since the late-1980s, the Diamond Trading Company, a De Beers Group company, has carried out proactive research to investigate the implications
