Sapphire optical viewport for high pressure and temperature applications

Abstract

We describe the design of a soldered sapphire optical viewport, useful for spectroscopic applications of samples at high temperatures and high pressures. The sapphire window is bonded via active soldering to a metal flange with a structure of two c-shaped rings made of different metallic materials in between, as to mitigate thermally induced stress. A spectroscopic cell equipped with two of the optical viewports has been successfully operated with alkali metals in a noble gas environment at temperatures in the range 20°C to 450°C at noble gas pressures from 10 −6 mbar to 330 bar. At the upper pressure range, we observe a leakage rate smaller than our readout accuracy of 30 mbar per day.

Spectroscopy of high pressure rubidium-noble gas mixtures

“…The experiments reported in this work have been carried out in a high pressure and high temperature resistant gas cell construction recently realised by our group, providing a very reliable spectroscopic environment at these conditions. The cell is made from high-temperature stainless steel (1.4841) whose openings are enclosed by flanges which house active-soldered sapphire-windows providing optical access [9]. For preparation, this cell is first baked out at around 720 K to remove contaminations.…”

“…In this paper we investigate absorption and emission spectra of rubidium-helium mixtures at a pressure of up to 188 bar and a temperature of 548 K in a table top laboratory experiment. The experiments benefit from using our proprietary high pressure cell equipped with soldered sapphire optical viewports, where the sapphire is bonded to a metal flange via active soldering making use of a compound intermediate structure allowing to mitigate thermally induced stress [9]. In the high density environment the frequent collisions lead to a thermalisation of the occupation distribution in the ground state and the excited state manifold.…”

Ammonothermal Crystal Growth of Functional Nitrides for Semiconductor Devices: Status and Potential

“…With sapphire as the optically transparent material being a usual choice for pressure vessel windows [339][340][341], video optical measurements were among the first imaging techniques investigated for application to ammonothermal processes. The construction of the first optical cell developed for ammonothermal conditions [298] can be seen in Figure 23.…”