High resolution X-ray microcalorimeters

Recently we have produced X-ray microcalorimeters with resolving powers approaching 2000 at 5.9 keV using a spare XRS microcalorimeter array. In these experiments, we attached 400 μ m square, 8 μ m thick HgTe absorbers using a variety of attachment methods to an XRS array and tested the detector array at temperatures between 40 and 60 mK. The best results were for absorbers attached using the standard XRS absorber-pixel thermal isolation scheme utilizing SU-8 polymer tubes. In this scenario we achieved a resolution of 3.2 eV FWHM at 5.9 keV. Substituting a silicon spacer for the SU-8 tubes also yielded sub-5 eV results. In contrast, absorbers attached directly to the thermistor produced significant position dependence and thus degraded resolution. We discuss these new high resolution results, the various absorber attachment schemes, and planned future improvements.