  Dynamics of the electron-nuclear and heteronuclear polarization-transfer
processes in the optically oriented semi-insulating iron-doped indium phosphide
were investigated through the characteristic time scales of the processes. (1)
We find in the optical nuclear orientation process that the buildup times for
31P and 115In nuclear polarizations are of the same order. From the analysis of
the cross-relaxation process between photo-excited electrons and nuclei, it is
concluded that electron-nuclear dipolar-couplings are responsible for the
polarization transfer in this case. This example shows that the nuclear-site
dependence of the buildup time can be utilized to identify hyperfine couplings
responsible for the process. (2) We find in the heteronuclear polarization
transfer (cross polarization) process between optically oriented 31P and 115In
that the cross-relaxation time is rather short; it is an order of magnitude
shorter than that expected for nuclear dipolar couplings when a magnetic field
is applied parallel to the crystalline [100] axis. From the cross polarization
spectral density analysis, it is concluded that a large J-coupling of the order
of 2 kHz exists between these nuclei and that its angular dependence is not of
a simple pseudo-dipolar type.
