  The contemporary superconductive electronics is widely using planar circuits
with micrometer-scale elements for a variety of applications. With the rise of
complexity of a circuit and increased number of its components, a simple
impedance measurement are often not efficient for diagnostics of problems, nor
for clarifying the physics underlying the circuit response. The established
Scanning Laser Microscope (LSM) technique generates the micrometer-scale images
of the amplitude of the microwave currents in a planar superconductive circuit,
but not the phase of the oscillating currents. Here we present a novel, more
powerful type of LSM imaging containing the signal phase information. We employ
a fast optical modulator in order to synchronize the phase of the laser
intensity oscillation with the phase of the probing microwave signal. The loss
induced in laser illuminated area strongly depends on the phase difference
between the RF probing signal and the laser beam modulation. We explain the
detection principle of the phase sensitive LSM and experimentally demonstrate
the capability of this method using superconductive microwave resonators. The
described technique facilitates understanding of complex RF current
distributions in superconductive circuits.
