In quantum-optical studies, such as the analysis of luminescence centers in silicon, samples need to be optically accessed through windows. These samples are cooled down to mK temperatures with simultaneous control of a magnetic field vector.
In these kinds of experimental environments, Fourier transform infrared spectroscopy can be carried out in conjunction with optical Faraday Rotation to determine spin polarization and the corresponding processes.
System Design and Performance
A Triton 400 dilution refrigerator was combined with a split-pair 2/2/2 vector rotate magnet, which enabled optical access through horizontal windows. The integration of a bottom-loaded sample exchange mechanism allowed fast sample turnaround time (Figure 1).
Figure 1. Triton with optical ports and bottom loading mechanism
The vector magnet made it possible to rotate a 2 T modulus vector in random directions with a field uniformity better than 1 part in 1000 across a round sample volume of 10 mm diameter within the sample holder. Next, four perpendicular line-of-sight ports were integrated with fused polypropylene and quartz windows to prevent thermal radiation, and transmit wavelengths, spanning from visible to near infrared, towards the sample (Figure 2).
Figure 2. Sample holder with optical ports
With the help of the bottom-loaded sample holder, samples measuring up to 25 mm in diameter with 50 DC connections and 14 high-frequency (40 GHz) connections were cooled from room temperature to 10 mK within a period of 8 hours.
The patented clamping interface of the sample holder allowed excellent thermal contact with the refrigerator. Such contacts are required to obtain the lowest possible temperature when the sample is warmed by the heat load through the windows.
The sample holder cools down to less than 20 mK when all four windows were at room temperature, and all signal wires were joined to the sample. A Co60 nuclear orientation thermometer was used to confirm the temperature as it was the ideal instrument to perform such low temperature measurements.
This information has been sourced, reviewed and adapted from materials provided by Oxford Instruments Nanoscience.
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