A comparative study of ablation plasma plumes originated from single crystal graphite (SCG) and amorphous carbon (a-C) targets during the preparation of diamond-like carbon (DLC) films by KrF excimer pulsed laser deposition (PLD) has been carried out by means of a monochromator equipped with an intensified optical multichannel analyzer. In high vacuum, the emission lines of carbon neutral C and ions of C+, C2+, and C3+ can be observed from both the SCG and a-C plasma plumes. The emission intensity from C atoms increases with laser energy density (EL) increase for both cases. The C2 emission intensity from the SCG plasma plume changes drastically with EL, while that from the a-C plasma plume is almost constant. The C2/C emission intensity ratio for the a-C case decreases with EL increase. As for the SCG case, the C2/C ratio decreases with EL increase up to 3.0 J/cm2, and increases slightly with further EL increase. Nanohardness of the deposited films decreases with the increase of the C2/C emission intensity ratio. It is suggested that for both the SCG and a-C target cases, the C2 molecule in the ablated plasma plume may not pl- ay an important role in producing high quality DLC films. It is further proposed that the threshold of laser fluence for the formation of diamond-like character film using KrF excimer PLD is 2.1 J/cm2(0.84×108 W/cm2) for the a-C target and 3.0 J/cm2(1.2×108 W/cm2) for the SCG target. The C2 vibrational temperature of the SCG and the a-C plasma plumes show different features on both the laser energy density and nitrogen pressure dependencies. Through optical emission spectroscopy and Langmuir probe measurements in vacuum and nitrogen background, it is concluded that there are many particles with higher mass in the SCG plasma plume, especially at relatively lower laser energy density below 3.0 J/cm2. © 2000 American Institute of Physics.