  Effects of radio-frequency power and driven frequency on the two-dimensional
(axial and radial) distributions of electron density and temperature were
experimentally investigated in low pressure capacitively coupled argon plasmas.
The intensity profiles of 696.5 nm and 750.4 nm emission lines were detected by
employing a spatially resolved diagnostic system, which consists of a charge
coupled device (CCD) and bandpass interference filters. The two-dimensional
distributions of electron density and electron temperature were calculated from
the spatial distributions of emission intensities via a collisional radiative
model (CRM). It is found that the axial and radial distributions of electron
density are more uniform at a lower RF power. The axial uniformity of electron
density is better at a lower driven frequency, while the radial profiles of
electron temperature is flatter at a higher excitation frequency. In all the
cases, the electron temperature is extremely uniform in the bulk plasma.
Moreover, a mode transition from the {\alpha} to the {\gamma} mode is observed
with the increase of input RF power at 13.56 MHz, which causes a significant
increase of electron density and an abrupt decrease of electron temperature.
