  Long-lived isotopes of plutonium were studied using two complementary
techniques, high-resolution resonance ionisation spectroscopy (HR-RIS) and
collinear laser spectroscopy (CLS). Isotope shifts have been measured on the
$5f^67s^2\ ^7F_0 \rightarrow 5f^56d^27s\ (J=1)$ and $5f^67s^2\ ^7F_1
\rightarrow 5f^67s7p\ (J=2)$ atomic transitions using the HR-RIS method and the
hyperfine factors have been extracted for the odd mass nuclei $^{239,241}$Pu.
Collinear laser spectroscopy was performed on the $5f^67s\ ^8F_{1/2}
\rightarrow J=1/2\; (27523.61\text{cm}^{-1})$ ionic transition with the
hyperfine $A$ factors measured for $^{239}$Pu. Changes in mean-squared charge
radii have been extracted and show a good agreement with previous non-optical
methods, with an uncertainty improvement by approximately one order of
magnitude. Plutonium represents the heaviest element studied to date using
collinear laser spectroscopy.
