Development of high-purity optical grade single-crystal CVD diamond for intracavity cooling

Abstract

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.

Pure nanodiamonds for levitated optomechanics in vacuum

“…The upper-bound absorption coefficient at 1064 nm of the parent material used to make our nanodiamonds is 0.03 cm −1 [28]. This is slightly lower than the absorption coefficient of high purity silica (0.11 cm −1 ) [38], a material that has already been optically trapped in high vacuum in numerous studies [30][31][32][39][40][41].…”

“…We model the steady state temperatures as a function of pressure for 25 nm radius nanodiamonds (the average size of the nanodiamonds used in this study) using upper-bounds of the absorption coefficients measured in [28,29] by laser calorimetry. Assuming a linear relationship between defect concentration and absorption coefficient [47], we may also model diamonds for which the absorption coefficient is below the detection limit of laser calorimetry (0.001 cm −1 for a 1 mm thick sample [29]).…”

“…Standard grade (--) corresponds to the bulk diamond grade used to make the nanodiamonds used in this study, with an upper-bound absorption coefficient 0.03cm −1 . Low absorption grade (----) has 0.003cm −1 [28,29]. Electronic grade (LL) has a predicted absorption coefficient of 4.5×10 −5 cm −1 .…”

“…Our previous study had shown that commercial nanodiamonds (Adámas Nanotechnologies) milled from impure high-pressure high-temperature (HPHT) diamond can reach temperatures in excess of 800 K at 20 mbar, enough to burn or graphitize the nanodiamond [21]. In bulk diamond, the source of infrared absorption is known to be extrinsic [27][28][29]. It has been suggested that the source of heating was absorption of the trapping light by amorphous carbon on the surface of the nanodiamond and defects within the diamond [21].…”

Large single‐crystal diamond substrates for ionizing radiation detection

“…The enhanced sub‐bandgap responsivity of the “large” sample is mostly due to a better absorption of visible wavelengths, caused by the larger thickness. Absorption coefficient of “standard‐grade” samples ranges indeed from 0.6 down to 0.1 cm −1 in the range 300–600 nm , thus an increase of thickness from 0.5 to 1.2 mm can make the difference in light absorption. However, the larger thickness cannot be the only responsible for the enhanced sub‐bandgap responsivity of the “large” sample.…”