Sapphire optical viewport for high pressure and temperature applications

TL;DR

This paper presents a novel sapphire optical viewport design for high-pressure and high-temperature spectroscopic applications, demonstrating its durability and low leakage in demanding environments.

Contribution

The paper introduces a soldered sapphire viewport with a stress-mitigating metal structure, enabling reliable high-pressure, high-temperature spectroscopic measurements.

Findings

Successfully operated with alkali metals at up to 450°C

Leakage rate below 30 mbar per day at high pressures

Demonstrated durability in high-pressure, high-temperature conditions

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 $20\,${\deg}C to $450\,${\deg}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.