  Archival Hubble Space Telescope WFPC2 images were used to search for optical
emission associated with the radio jets of a number of luminous quasars. From
this search, we report new optical hotspot detections in the well-known blazar
3C~454.3 and the lobe-dominated quasars 3C~275.1 and 3C~336. We also find
optical emission in the vicinity of the hotspot in 3C~208, but believe this is
a chance alignment. Optical emission from the arcsecond-scale jet in 3C~454.3
is also detected. Multi-frequency archival radio data from the VLA and MERLIN
are analyzed, and the synchrotron spectra of these high-power hotspots are
presented. We estimate that their break frequencies are in the range of
$10^{10}-10^{11}$ Hz, with large uncertainties due to the wide gap in frequency
coverage between the radio and optical bands. We also calculate their
equipartition magnetic fields, and find that the anti-correlation between break
frequency and magnetic field found by Brunetti et al. for lower power hotspots
extends to these high power hotspots. This supports their model of hot-spots
based on shock acceleration and synchrotron losses.
