  Superconducting excitations --Bogoliubov quasiparticles -- are the quantum
mechanical mixture of negatively charged electron (-e) and positively charged
hole (+e). Depending on the applied voltage bias in STM one can sample the
particle and hole content of such a superconducting excitation. Recent Scanning
Tunneling Microscope (STM) experiments offer a unique insight into the inner
workings of the superconducting state of superconductors. We propose a new
observable quantity for STM studies that is the manifestation of the
particle-hole dualism of the quasiparticles. We call it a {\em Bogoliubov
angle}. This angle measures the relative weight of particle and hole amplitude
in the superconducting (Bogoliubov) quasiparticle. We argue that this quantity
can be measured locally by comparing the ratio of tunneling currents at
positive and negative biases. This Bogoliubov angle allows one to measure
directly the energy and position dependent particle-hole admixture and
therefore visualize robustness of superconducting state locally. It may also
allow one to measure the particle-hole admixture of excitations in normal state
above critical temperature and thus may be used to measure superconducting
correlations in pseudogap state.
