Optical quality diamond material

A CVD single crystal diamond material having a single substitutional nitrogen concentration of more than 3×1015 atoms/cm3 and less than 5×1017 atoms/cm3 as measured by electron paramagnetic resonance (EPR), which diamond material shows at least one of the following characteristics, when measured at room temperature (nominally 20°C.):

• i) a high optical homogeneity, with the transmitted wavefront differing from the expected geometrical wavefront during transmission through diamond of a specified thickness of at least 0.5 mm, processed to an appropriate flatness and measured over a specified area of at least 1.3 mm×1.3 mm, by less than 2 fringes, where 1 fringe corresponds to a difference in optical path length equal to ½ of the measurement wavelength of 633 nm;
• ii) a low optical birefringence, indicative of low strain, such that in a sample of a specified thickness of at least 0.5 mm and measured in a manner described herein over a specified area of at least 1.3 mm×1.3 mm, the modulus of the sine of the phase shift, |sin δ|, for at least 98% of the analysed area of the sample remains in first order (δ does not exceed π/2) and the |sin δ| does not exceed 0.9;
• iii) a low optical birefringence, indicative of low strain, such that in a sample of a specified thickness of at least 0.5 mm and measured in a manner described herein over a specified area of at least 1.3 mm×1.3 mm, for 100% of the area analysed, the sample remains in first order (δ does not exceed π/2), and the maximum value of Δn[average], the average value of the difference between the refractive index for light polarised parallel to the slow and fast axes averaged over the sample thickness, does not exceed 1.5×10−4;
• iv) an effective refractive index in a sample of a specified thickness of at least 0.5 mm, measured in a manner described herein over a specified area of at least 1.3 mm×1.3 mm, which has a value of 2.3964 to within an accuracy of +/−0.002;
• v) a combination of optical properties such that when the diamond material is prepared as a diamond plate in the form of an etalon of a specified thickness of at least 0.5 mm and measured using a laser beam with a wavelength near 1.55 μm and a nominal diameter of 1.2 mm over a specified area of at least 1.3 mm ×1.3 mm, it exhibits a free spectral range (FSR) which, when measured at different positions over the plate, varies by less than 5×10−3 cm−1;
• vi) a combination of optical properties such that when the diamond material is prepared as a diamond plate in the form of a Fabry-Perot solid etalon of a specified thickness of at least 0.5 mm, and measured using a laser beam with a wavelength near 1.55 μm and a nominal diameter of 1.2 mm over a specified area of at least 1.3 mm×1.3 mm, and which has no coatings applied to the optically prepared surfaces, it exhibits when measured at different positions over the plate a contrast ratio exceeding 1.5;
• vii) a combination of optical properties such that when the diamond material is prepared as a diamond plate in the form of an etalon of a specified thickness of at least 0.5 mm, and measured using a laser beam with a wavelength near 1.55 μm and a diameter of 1.2 mm over a specified area of at least 1.3 mm×1.3 mm, it exhibits an insertion loss not exceeding 3 dB;
• viii) a variation in refractive index over a volume of interest, said volume comprising a layer of a specified thickness of at least 0.5 mm, measured in a manner described herein over a specified area of at least 1.3 mm×1.3 mm, which is less than 0.002.