Imaging sub-millimeter waves in planar cryoelectronic circuits by low temperature scanning laser
microscopy 

D. Abraimov and A. V. Ustinov, 
Physikalisches Institut III, Universität
Erlangen-Nürnberg, D-91058 Erlangen 

S. V. Shitov
Institute of Radio Engineering and Electronics,
Russian Academy of Science, Moscow, Russia 

Low temperature scanning laser microscopy (LTSLM) is shown to be capable of imaging the
sub-THz electromagnetic fields in cryoelectronic integrated structures. This method allows to
evaluate the spatial distribution of time-averaged field amplitudes with a resolution of about one
micrometer on samples with passive and active superconducting structures with characteristic
dimensions of the order of millimeters The principle of LTSLM is based on mapping the on-chip
detector voltage response as a function of the position of a focused laser beam on the sample
surface. The major effect is that a focused laser beam locally heats the sample and, therefore,
introduces an additional dissipation in the area of few micrometers in diameter. Such a dissipative
spot is scanned over the sample which electrical response (e.g., the detector current and voltage
variation) is recorded as a function of the beam coordinate. Laser scanning of passive
superconducting structures (striplines, slotlines, etc.) located on the chip contribute to the detector
response due to extra losses for sub-millimeter waves propagating there. Using LTSLM, we have
imaged complicated two-dimensional standing 500 GHz wave patterns in the integrated
superconducting receiver chip developed by SRON (Groningen) in collaboration with IREE (Moscow).