摘要： The creation of well-thermalized, hot and dense plasmas is attractive for warm dense matter studies. We investigate collisionally induced energy absorption of an ultraintense and ultrashort laser pulse in a solid copper target using particle-in-cell simulations. We ?nd that, upon irradiation by a 2 × 1020 W cm?2 intensity, 60 fs duration, circularly polarized laser pulse, the electrons in the collisional simulation rapidly reach a well-thermalized distribution with ～3.5 keV temperature, while in the collisionless simulation the absorption is several orders of magnitude weaker. Circular polarization inhibits the generation of suprathermal electrons, while ensuring ef?cient bulk heating through inverse bremsstrahlung, a mechanism usually overlooked at taking account of both collisional and ?eld ionization, yields similar results: the bulk electrons are heated to ～2.5 keV, but with a somewhat lower degree of thermalization than in the pre-set, ?xed-ionization case. The collisional absorption mechanism is found to be robust against variations in the laser parameters. At ?xed laser pulse energy, increasing the pulse duration rather than the intensity leads to a higher electron temperature.