Improving the performance of THz delivery from a quantum cascade laser within a dry 3He dilution refrigerator

We demonstrate a substantial enhancement to the integration of a quantum cascade laser into a dilution refrigerator via waveguides by the inclusion of a multi-mesh 6THz low-pass filter to block IR radiation, and a Winston cone to focus light output from the waveguide. These alterations allow us to lower the base temperatures to $\sim 114$ mK, and the sample temperature to $\sim 160$ mK while detecting a cyclotron resonance (CR) response in a 2DEG illuminated within the refrigerator. For comparison, before these changes we achieve a base temperature of 206mK and an effective sample temperature of 430mK while detecting CR [1].