Laser energy absorption is being studied by measuring reflected laser beam in Brookhaven National Laboratory. To provide highly charged heavy ion beams using laser ion source (LIS), efficient laser energy absorption to the plasma is important. In the plasma heating stage, laser beam penetrates outer layer of induced plasma. When the laser beam reaches a cutoff electron density of the plasma, the beam is reflected. If the absorption layer of the plasma plume is not thick enough, a considerable fraction of the laser energy is just bounced back and heating efficiency is low. In the plasma heating process, not like other ion sources, magnetic field confinement is not used and the induced plasma keeps expanding. Therefore, the plasma expansion velocity influences the laser energy absorption process. By changing the laser irradiation properties, efficient laser energy absorption condition is explored. In the conference, the measured latest results will be discussed.