Traditionally the extreme hardness of diamond materials has made the machining of diamond optical components exceptionally difficult and limited applications to mostly flat components. Recent advances in diamond processing technology have made it possible to fabricate curved optical components or lenses in single crystal and polycrystalline diamond. This paper analyses a multi-spectral infrared imaging system incorporating a diamond lens and compares performance to equivalent systems that use other common infrared optical materials. Due to the broad transmission spectrum of diamond, which ranges all the way from the UV to microwave, these curved optics could find use in many different imaging applications throughout the electro-magnetic spectrum. Consideration is given to other advantages that diamond brings to the multi-spectral imaging application including small variations in refractive index as a function of both wavelength and temperature, a large Abbe number and material resilience under harsh conditions. As the development of large-area single crystal (SC) chemical vapour deposition (CVD) diamond advances, SC diamond lenses for multispectral imaging become a real possibility, with a number of advantages that we present in this paper.
Synthetic CVD diamond has exceptional properties, including broad spectral transmission, physical and chemical robustness, and the highest thermal conductivity of any known material, making diamond an attractive material for medium to high power optical and laser applications, minimizing the detrimental effects of thermal lensing and radiation damage. Example applications include ATR prisms, Raman laser crystals, extra- and intra-cavity laser cooling. In each case the demands on the fundamental material properties and fabrication routes are slightly different. In recent years, there has been good progress in the development of low-loss, single crystal diamond, suitable for higher power densities, higher pulse rates and more demanding intra- and extra-cavity thermal management. The adoption of single crystal diamond in this area has however, been hindered by the availability of large area, low birefringence plates.
To address this, we report a combination of CVD growth and processing methods that have enabled the manufacture of large, low defect substrates. A final homoepitaxial, low absorption synthesis stage has produced plates with large area (up to 16 mm edge length), low absorption (α<0.005 cm-1 at 1064 nm), and low birefringence (∆n <10-5), suitable for double-sided intra-cavity cooling. We demonstrate the practical advances in synthesis, including increasing the size while reducing in-use losses compared to previous generations of single crystal material, and practical developments in processing and implementation of the single crystal diamond parts, optimizing them for use in a state-of-the-art femto-second pulsed Ti:Sa thin disk gain module, all made in collaboration with the wider European FP7 funded Ti:Sa TD consortium.
High-power and high-energy laser systems have firmly established their industrial presence with applications that span materials processing; high – precision and high – throughput manufacturing; semiconductors, and defense. Along with high average power CO2 lasers operating at wavelengths of ~ 10 microns, solid state lasers and fiber lasers operating at ~ 1 micron wavelength are now increasingly being used, both in the high average power and high energy pulse regimes.
In recent years, polycrystalline diamond has become the material of choice when it comes to making optical components for multi-kilowatt CO2 lasers at 10 micron, outperforming ZnSe due to its superior thermo-mechanical characteristics. For 1 micron laser systems, fused silica has to date been the most popular optical material owing to its outstanding optical properties. This paper characterizes high - power / high - energy performance of anti-reflection coated optical windows made of different grades of diamond (single crystal, polycrystalline) and of fused silica. Thermo-optical modeling results are also presented for water cooled mounted optical windows. Laser – induced damage threshold tests are performed and analyzed. It is concluded that diamond is a superior optical material for working with extremely high-power and high-energy laser beams at 1 micron wavelength.
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.
Chemical vapour deposited bulk diamond products have already found significant applications in high power laser systems including heatspreaders, output couplers and active components such as raman shifting or beam combining crystals. However, as new applications require ever increasing power densities the synthesis, processing and integration of diamond parts to fully utilise its exceptional properties becomes more challenging. We report on innovation in synthesis and processing of diamond that enables its properties to be fully exploited. Diamond parts with larger dimensions than previously achieved at extremely low defect density have been synthesised, and processed to flatness and roughness significantly beyond those previously reported. The achievements reported have allowed a number of exciting new developments in the use of diamond in high power laser systems.