  A high-resolution background-oriented schlieren (BOS) technique, which
utilizes a high-resolution camera and a microdot background pattern, is
proposed and used to measure the pressure field of an underwater shock wave in
a microtube. The propagation of the shock wave subsequently reaches a concave
water-air interface set in the microtube resulting in the ejection of a focused
microjet. This high spatial-resolution BOS technique can measure the pressure
field of a shock front with a width as narrow as the order of only 101 {\mu}m
with a peak pressure as large as almost 3 MPa, which is significantly narrower
and larger, respectively, than a previous study [1]. This significant
breakthrough has enabled the simultaneous measurement of the pressure impulse
of the shock front and the velocity of the microjet tip. As a result, we have
experimentally observed the linear relation between the velocity of the
microjet tip and the pressure impulse of the shock front for the cases without
secondary cavitation in the liquid bulk. Such relation was
theorectically/numerically predicted by Peters [2]. This study demonstrated the
capability of the proposed high-resolution BOS technique as a microscale
contactless pressure measurement tool for underwater shock waves and
potentially other micro- and nano-fluids.
