Near-infrared refractive index of synthetic single crystal and polycrystalline diamonds at high temperatures

Abstract

We measured the refractive index n(T) and thermo-optical coefficient β(T) = (1/n)(dn/dT) of high quality synthetic diamonds from room temperature to high temperatures, up to 1520 K, in near-infrared spectral range at wavelength 1.56 μm, using a low-coherence interferometry. A type IIa single crystal diamond produced by high pressure–high temperature technique and a transparent polycrystalline diamond grown by chemical vapor deposition were tested and revealed a very close n(T) behavior, with n = 2.384 ± 0.001 at T = 300 K, monotonically increasing to 2.428 at 1520 K. The n(T) data corrected to thermal expansion of diamond are well fitted with 3rd order polynomials, and alternatively, with the Bose-Einstein model with an effective oscillator frequency of 970 cm−1. Almost linear n(T) dependence is observed above 800 K. The thermo-optical coefficient is found to increase monotonically from (0.6 ± 0.1) × 10−5 K−1 (300 K) to (2.0 ± 0.1) × 10−5 K−1 (1300 K) with a tendency to saturation at >1200 K. These β(T) values are an order of magnitude lower than those known for Si, GaAs, and InP. The obtained results significantly extend the temperature range, where the refractive index of diamond was previously measured.

In situ doping of epitaxial diamond with germanium by microwave plasma CVD in GeH4–CH4–H2 mixtures with optical emission spectroscopy monitoring

“…Alternatively, the substrate temperature was measured with a low-coherence optical interferometer (LCI), as described elsewhere. 25,26 The LCI continuously measures the optical thickness nd of the transparent sample at a wavelength of 1.55 μm, where n and d are the refraction coefficient and the thickness, respectively. As the product n ( T ) d ( T ) is temperature dependent (increases with T ) through the thermooptical coefficient and thermal expansion coefficient, the measurement of n ( T ) d ( T ) allows the determination of the temperature using a calibration for n ( T ) d ( T )/ nd (25 °C), as reported in.…”

“…As the product n ( T ) d ( T ) is temperature dependent (increases with T ) through the thermooptical coefficient and thermal expansion coefficient, the measurement of n ( T ) d ( T ) allows the determination of the temperature using a calibration for n ( T ) d ( T )/ nd (25 °C), as reported in. 25 After the plasma ignition in pure H 2 , the targeted substrate temperature was established according to LCI readings by tuning pressure and microwave power, while further temperature monitoring was performed with the pyrometer. After adding CH 4 and GeH 4 , the growth rate and film thickness were measured in situ with LCI, as described in, 27 to achieve a finite film thickness of about 5 μm.…”

The scaling potential of beam-splitter-based coherent beam combination

“…For synthetic diamond, the critical absorbed power is about three orders of magnitude larger than in fused silica due to its enormous thermal conductivity [32] while the remaining thermomechanical and thermo-optical properties are comparable [33]. However, the bulk absorption is also three orders of magnitude larger compared to fused silica [34], again resulting in no significant benefit for either type of combining architecture.…”

Nanostructured diamond for biomedical applications

“…The exceptional hardness, wear resistance, and corrosion resistance of nanostructured diamond coatings can provide a hermetic seal around a medical device that prevents degradation [42][43][44][45][46][47][48][49][50]. The high refractive index [51,52] of diamond can potentially allow more compact lenses to be used for ophthalmic devices and other types of medical devices. Diamond nanoparticles are being considered for use in medical imaging, drug delivery, gene delivery, and tissue engineering applications; for example, the delivery of drugs for the treatment of osteoporosis and cancer using diamond nanoparticles has been demonstrated [53][54][55][56][57][58][59][60][61][62][63].…”