  Laser-produced plasmas (LPPs) engulf exotic and complex conditions ranging in
temperature, density, pressure, magnetic and electric fields, charge states,
charged particle kinetics, and gas-phase reactions, based on the irradiation
conditions, target geometries, and the background cover gas. The application
potential of the LPP is so diverse that it generates considerable interest for
both basic and applied research areas. Although most of the traditional
characterization techniques developed for other plasma sources can be used to
characterize the LPPs, care must be taken to interpret the results because of
their small size, transient nature, and inhomogeneities. The existence of the
large spatiotemporal density and temperature gradients often necessitates
non-uniform weighted averaging over distance and time. Among the various plasma
characterization tools, optical-based diagnostic tools play a key role in the
accurate measurements of LPP parameters. The optical toolbox contains optical
probing methods (Thomson scattering, shadowgraphy, Schlieren, interferometry,
velocimetry, and deflectometry), optical spectroscopy (emission, absorption,
and fluorescence), and passive and active imaging. Each technique is useful for
measuring a specific property, and its use is limited to a certain time span
during the LPP evolution because of the sensitivity issues related to the
selected measuring tool. Therefore, multiple diagnostic tools are essential for
a comprehensive insight into the entire plasma behavior. In recent times, the
improvements in performance in the lasers and detector systems expanded the
capability of the aforementioned passive and active diagnostics tools. This
review provides an overview of optical diagnostic tools frequently employed for
the characterization of the LPPs and emphasizes techniques, associated
assumptions, and challenges.
