Superconducting excitations--Bogoliubov quasiparticles--are the
quantum-mechanical mixture of negatively charged electron -e and
positively charged hole +e. Recent ARPES and STM experiments offer
unique insight into the inner workings of the superconducting state of
cuprates. We propose an observable quantity for ARPES and STM studies
that is a manifestation of the particle-hole dualism of the
quasiparticles. We call it a Bogoliubov angle. This angle measures the
relative weight of particle and hole amplitudes in the superconducting
Bogoliubov quasiparticle. We argue that this quantity can be
measured locally by comparing the ratios of tunneling currents at
positive and negative biases. This Bogoliubov angle allows one to
measure directly the energy and position dependent particle-hole
admixtures 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.