The Infrared Optical Properties of CVD Diamond at Elevated Temperatures

Abstract

The combination of low absorption and extreme mechanical and thermal properties make diamond a compelling choice for some more extreme far infrared (8-14 mm) window applications. The optical properties of CVD diamond at elevated temperatures are critical to many of these extreme applications. The absorption coefficient of diamond has been assessed on polished diamond samples with a variety of optical characteristics by heating samples up to 550 C and measuring transmission in a grating IR spectrophotometer. High temperature transmission spectra in the range 5000-200 cm --1 (2-50 mm) for CVD diamond are presented. The transmittance at near IR wavelengths %4200 cm --1 (2.5 mm) appears to be only slightly affected by elevated temperatures and the three-and two-phonon regions exhibit the expected temperature dependence. In the far infrared, the transmission drops with a broad peak approximately centred at %1250 cm --1 (8 mm), a behaviour characteristic of all samples tested. The temperature dependency of the absorption coefficient has been deduced by assuming there are no additional scatter losses from the surface and calculating the refractive index at temperature, thus allowing the reflectance at that temperature to be estimated. Direct emissivity and photo-thermal deflection measurements are in agreement with these measurements. An empirical formula for predicting the variation of absorption coefficient at %1000 cm --1 (10 mm) with temperature, is presented.

High temperature thermal conductivity of free-standing diamond films prepared by DC arc plasma jet CVD

“…The introduction of Laser Flash technique has been depicted in details anywhere [10]. The pulse length of Xenon Flash lamp and Nd:YAG laser used in LFA447 and LFA457 was 0.06 ms and 0.33 ms respectively.…”

“…CVD diamond films exhibit some anisotropy in thermal conductivity due to their column growth [8], and in same cases they must be exposed to extreme operating temperatures when used in devices [6,9,10]. Various methods have been utilized to determine the temperature-dependent thermal properties of CVD diamond, such as laser flash technique [11], transient thermal grating technique [12], and steady-state heater bar method [13,14], et al, in which laser flash technique is a common and reliable method for through-thickness thermal conductivity diamond over a wide temperature range.…”

“…So the increasing demand is putting forward to heat dispersion of devices. High-quality CVD diamond films show highest thermal conductivity which is similar to natural IIa diamond[2], coupled with their low dielectic loss, broad optical transparency, making them as key materials for a host of applications, like high-power Nd:YVO 4 laser heat conductors [3], megawatt power gyrotrons [4,5], UV LEDs [6], Raman lasers [7], et alCVD diamond films exhibit some anisotropy in thermal conductivity due to their column growth [8], and in same cases they must be exposed to extreme operating temperatures when used in devices [6,9,10]. Various methods have been utilized to determine the temperature-dependent thermal properties of CVD diamond, such as laser flash technique [11], transient thermal grating technique [12], and steady-state heater bar method [13,14], et al, in which laser flash technique is a common and reliable method for through-thickness thermal conductivity diamond over a wide temperature range.…”

Infrared Reflectance and Emissivity Spectra of Nanodiamonds

“…Though literature on spectroscopic properties of diamond is immense, experimental data about its emissivity is scarce. Emission spectra of macroscopic diamonds in relatively narrow wavelength range relevant for diamond applications as optical windows for CO 2 lasers were reported by Mollart and Lewis (2001). It was shown that the emissivity (ε) spectra closely follow the expected behaviour 1-R, where R is the reflectivity.…”

Why Does Diamond Absorb Infra-Red Radiation?

“…They analysed their data using a model that has the inconsistency that the absorption derives from transitions associated with the creation of single phonons, which are forbidden in diamond [2][3][4][5]. Recently, Mollart and Lewis [6] published, without interpretation, experimental data of a careful study of the temperature dependence of the spectrum between 500 and 5000 cm À1 , and Meykens et al [7] have used a combination of laser calorimetry and photo-thermal deflection spectroscopy to measure the absorption of natural diamond at 10.6 mm for 300 K < T < 800 K. In this paper we present absorption data at the CO 2 laser wavelength of 10.6 mm for the temperature range of 300 to 650 K, taken on high-purity chemical vapor deposited (CVD) diamond. The absorption is shown to be caused by several processes, each of which may be calculated explicitly.…”