  We present the development of an optically detected magnetic resonance (ODMR)
system, which enables us to perform the ODMR measurements of a single defect in
solids at high frequencies and high magnetic fields. Using the high-frequency
and high-field ODMR system, we demonstrate 115 GHz continuous-wave and pulsed
ODMR measurements of a single nitrogen-vacancy (NV) center in a diamond crystal
at the magnetic field of 4.2 Tesla as well as investigation of field dependence
($0-8$ Tesla) of the longitudinal relaxation time ($T_1$) of NV centers in
nanodiamonds.
