In order
to realize laser-plasma particle accelerators, we are performing experiments
on the monoenergetic electron acceleration by raising the laser power
from 2 TW to 2.6 TW. The optimal electron density for monoenergetic
acceleration shifted from (1-1.5)x10^20 cm^-3 to around 4x10^19 cm^-3.
Energy gain was increased from 7-15 MeV to 25 MeV. This and previous
results enable us to make the empirical scaling law of the monoenergetic
acceleration, i.e. the energy gain vs. electron density and laser power,
charge vs. laser power, etc.