  This work reports on the application of a novel electric field-ionization
setup for high-resolution laser spectroscopy measurements on bunched fast
atomic beams in a collinear geometry. In combination with multi-step resonant
excitation to Rydberg states using pulsed lasers, the field ionization
technique demonstrates increased sensitivity for isotope separation and
measurement of atomic parameters over non-resonant laser ionization methods.
The setup was tested at the Collinear Resonance Ionization Spectroscopy
experiment at ISOLDE-CERN to perform high-resolution measurements of
transitions in the indium atom from the 5s$^2$5d~$^2$D$_{5/2}$ and
5s$^2$5d~$^2$D$_{3/2}$ states to 5s$^2$($n$)p~$^2$P and 5s$^2$($n$)f~$^2$F
Rydberg states, up to a principal quantum number of $n$ = 72. The extracted
Rydberg level energies were used to re-evaluate the ionization potential of the
indium atom to be 46670.1055(21) cm$^{-1}$. The nuclear magnetic dipole and
nuclear electric quadrupole hyperfine structure constants and level isotope
shifts of the 5s$^2$5d~$^2$D$_{5/2}$ and 5s$^2$5d~$^2$D$_{3/2}$ states were
determined for $^{113,115}$In. The results are compared to calculations using
relativistic coupled-cluster theory. A good agreement is found with the
ionization potential and isotope shifts, while disagreement of hyperfine
structure constants indicates an increased importance of electron correlations
in these excited atomic states. With the aim of further increasing the
detection sensitivity for measurements on exotic isotopes, a systematic study
of the field-ionization arrangement implemented in the work was performed and
an improved design was simulated and is presented. The improved design offers
increased background suppression independent of the distance from field
ionization to ion detection.
