Optical Setup for a Piston-Cylinder Pressure Cell: A Two-Volume Approach

Measurement of the absolute value of the applied pressure in high-pressure muon and neutron experiments is a complicated task. It often requires the presence of a calibration material inside the sample volume, and could also cause additional time to obtain the response of the calibrant. Here we describe the use of optical calibrants for precise determination of the pressure value inside the pistoncylinder clamp cells. Utilizing the concept of separate volumes for the sample and the optical media, a setup for conducting in situ pressure measurements is successfully tested. Pressures in both the "sample" and the "optical" volumes are proved to be the same within experimental accuracy. The use of SrB4O7 : (0.01 Sm2+, 0.03 Eu2+) as a pressure calibrant allows for a high accuracy of pressure determination by considering up to eight fluorescence lines.