Image Credit: Element Six
Diamond makes for an extraordinary engineering material due to its remarkable physical and chemical properties spanning extreme ranges of capability. It has the best thermal conductivity of any material (five times higher than copper), as well as high stiffness, considerable wear-resistance and extreme hardness. It is chemically inert, radiation hard and fosters superb electrochemical properties.
These attributes can be harnessed and controlled when the diamond is synthesized by chemical vapor deposition (CVD), and can be exploited in advanced engineering applications. Chemical vapor deposition of diamond is made possible by thermal disassociation of hydrogen and a gaseous source of carbon in plasma at temperatures above 2000 °C. After over 40 years of research, this technique has emerged as a preferred process because of the ability to control diamond purity and produce high-quality, free-standing polycrystalline and single crystal CVD diamond.
While natural diamonds often demonstrate the same extraordinary characteristics, their idiosyncratic make-up, as a consequence of Mother Nature’s growth process, means that no two are the same. Comparably, growing diamond in the laboratory allows the production of large plates, up to 100 mm in diameter and several millimeters thick, with consistent properties over and over. The synthesized diamond can be optimized for application-specific tasks, whether that be a radiation detector used in the search for the Higgs boson or a tweeter in a music hi-fi system.
The progression of a single crystal CVD diamond developed for mechanical applications has led the way in the production of many innovations, from the mirror finish of a smartphone to the manufacture of the copper wire used in airplanes. This has enabled solutions and approaches in high-power density optical applications that were previously deemed unattainable, as developments in single crystal CVD diamond mean it can now offer huge potential as an optical engineering material.
Image Credit: Element Six
Diamond has the broadest optical transparency of any material, ranging from ultraviolet (UV) to terahertz (THz) wavelengths, making it the perfect solution for transmissive optics. Diamond comes into its own in applications that leverage its other unparalleled properties, such as being a superb conductor of heat with excellent scratch resistance and great strength. Examples that exploit single crystal CVD diamond’s unique properties are diamond exit windows for high-power lasers and attenuated total reflectance (ATR) crystals for infrared (IR) spectroscopy.
Element Six developed a specific grade of single crystal CVD diamond for applications in the visible and near-IR range where low scatter is required, such as IR spectroscopy.
IR spectroscopy is a conventional technique used across an array of industries for identifying materials and substances. This includes performing soil analysis, testing water quality, developing pharmaceuticals, evaluating the composition of food products, and crime scene analysis, to name a few.
In ATR spectroscopy, the IR probe beam is internally reflected off the surface of the ATR crystal (in this case, the diamond), which is positioned directly in contact with the material under analysis. The interaction between the evanescent wave (the part of the IR beam which 'leaks' out of the crystal) and the sample can be measured, allowing for the generation of a spectral 'fingerprint' of the sample. One of the many benefits the ATR method holds over standard IR spectroscopy is its convenience – there is little to no sample preparation required, which allows for rapid analysis.
Single crystal CVD diamond ATR crystals are chemically inert and more scratch-resistant than other IR materials, which means that IR sampling of hard and abrasive samples and chemically hostile substances are possible without any deterioration of the ATR crystal.
Image Credit: Element Six
Optical single crystal CVD diamond is also being utilized in the development of cutting-edge laser technologies, opening up the potential for applications in many fields including astronomy, medicine (e.g. ophthalmic and skin therapies), laser radar, and the remote sensing of substances such as explosive materials.
Placing CVD diamond in intra-cavity (within the cavity of the laser resonator), puts more demands on the necessary quality of the diamond throughout these applications. Element Six has developed single crystal CVD diamond with low strain and low absorption rates that are needed to specifically support the latest laser technologies, optimizing beam quality and the efficiency of the laser.
Researchers at the Institute of Photonics, University of Strathclyde, exhibited a monolithic diamond Raman laser employing Element Six’s optical quality single crystal CVD diamond. They targeted wavelengths that are both difficult to attain and of commercial significance, by capitalizing on the high Raman gain coefficient of a diamond. The team at Strathclyde converted 532 nm light from a green pump laser to the yellow at 573 nm, with conversion efficiencies of up to 84%, a wavelength crucial for use in ophthalmic therapies.
Image showing a diamond Raman laser converting green to yellow light. Image Credit: The University of Strathclyde.
Furthermore, researchers at MQ Photonics Research Centre developed a diamond Raman laser that is 20 times more powerful than other diamond laser systems. Capable of delivering up to 380 Watts of output power, the equivalent of approximately 400,000 laser pointers, MQ Photonics Research Centre has demonstrated a laser that is powerful enough to cut through steel.
In 2016, using diamond as part of a new ultrafast high-power titanium sapphire pulse disk laser demonstrated significant progress. This compelling work was achieved via “TiSa TD” (Ultrafast High-Average Power Ti:Sapphire Thin-Disk Oscillators and Amplifiers), an EU-funded Seventh Framework project, combining the work and research of industry and academia across Europe.
Throughout this project the aim was to demonstrate how the targeted laser is expected to increase precision and productivity in micromachining and transparent materials such as glasses. The team presented the first lasing demonstration of a TiSa laser in a thin-disk geometry – with Element Six developing new methods to synthesize optical-quality 12 mm diameter single crystal diamond for the intra-cavity cooling components of the TiSa laser.
These are just some of the examples that notably illustrate the emergence and availability of single crystal CVD diamond as a consistent engineering material that enables the significant progress and development of new applications and technologies.
Element Six continually makes revisions to enhance the material design, as well as introducing grades that are specifically appropriate for various applications. Today, the company leads the way in research and development of this magnificent engineering material while demonstrating its position as a world-leader, having been granted more than 650 patents worldwide over approximately 70 patent families on its single crystal diamond technology alone.
This information has been sourced, reviewed and adapted from materials provided by Element Six.
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