Speaker
Description
We have developed a versatile cryogenic platform for research in optics. The optical cryostat offers an experimental volume of 100 x 100 x 100 mm with up to five 2-inches optical accesses. The cold plate is cooled to a temperature below 2K with 50 mW power available. The cryogenic system is based on a two-stages 4 Kelvin Pulse Tube and a 2 K helium Joule-Thomson cooler. The Pulse-Tube cold head is separated in a ‘coldbox’ in order to minimize the occupation on the optical table. The thermal coupling is realized by an active pressurized helium circulation loop between the Pulse-Tube first stage and the optical experiment cold chamber. The circulating helium line additionally reduces the vibrations induced by the cryoocoler in the experimental chamber, which are generally very detrimental in optics.
We describe the design and the performances of the system in operation. The integration of the Joule-Thomson cooler minimizes the cooldown time of the optical cold chamber with the addition of a pre-cooling circulation loop.
To vary the temperature according to the user's needs, we control a flow restriction that changes the evaporator pressure and, in turn, the temperature of the cold plate between 2 - 4 K. To achieve higher temperatures (4 K – 300 K), we propose to control the flow in the pre-cooling loop.
We evaluate the vibrations transmitted to the optical chamber by using a laser velocimeter with a sensitivity of 20 nm/s/Hz ½ in the frequency range 0.5 Hz – 22 kHz. In terms of displacements, this method is able to measure a few nm at 1 Hz. Because the mechanical links between the cryocooler and the optical platform is made by a fluid circulation, the vibration transmission is expected to be reduced. We describe the method used to minimize that transmission by a very soft suspension of the cold box. The results are discussed and the compatibility with Raman measurements at temperatures below 2 K discussed.
As a first application, we study the thermal coupling of an Erbium-doped crystal by optical spectroscopy. To do so, we have developed an original method for in-situ optical sensing of the sample temperature, based on the particular electronic structure of erbium under magnetic field.
Acknowledgments
This work has been financed by Absolut System, CNRS-G2ELAB-Absolut System (research con-tract#116420) and the ANRT/CIFRE grant contract N°2021/0803 to support Marek Zeman’s PhD the-sis
| Submitters Country | France |
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