  Nearby Photo-Dissociation Regions (PDRs), where the gas and dust are heated
by the far UV-irradiation emitted from stars, are ideal templates to study the
main stellar feedback processes. With this study we aim to probe the detailed
structures at the interfaces between ionized, atomic, and molecular gas in the
Orion Bar. This nearby prototypical strongly irradiated PDR will be among the
first targets of the James Webb Space Telescope (JWST) within the framework of
the PDRs4All Early Release Science program. We employed the sub-arcsec
resolution accessible with Keck-II NIRC2 and its adaptive optics system to
obtain the most detailed and complete images, ever performed, of the
vibrationally excited line H$_2$ 1-0 S(1) at 2.12~$\mu$m, tracing the
dissociation front, and the [FeII] and Br$\gamma$ lines, at 1.64 and
2.16~$\mu$m respectively, tracing the ionization front. We obtained narrow-band
filter images in these key gas line diagnostic over $\sim 40''$ at spatial
scales of $\sim$0.1$''$ ($\sim$0.0002~pc or $\sim$40~AU at 414~pc). The
Keck/NIRC2 observations spatially resolve a plethora of irradiated
sub-structures such as ridges, filaments, globules and proplyds. A remarkable
spatial coincidence between the H$_2$ 1-0 S(1) vibrational and HCO$^+$ J=4-3
rotational emission previously obtained with ALMA is observed. This likely
indicates the intimate link between these two molecular species and highlights
that in high pressure PDR the H/H$_2$ and C$^+$/C/CO transitions zones come
closer as compared to a typical layered structure of a constant density PDR.
This is in agreement with several previous studies that claimed that the Orion
Bar edge is composed of very small, dense, highly irradiated PDRs at high
thermal pressure immersed in a more diffuse environment.
