Thermal modeling and analysis of the volume absorber in the pulsed excimer laser calorimeters are very important. In this work, Gaussian distributions are used to model the temporal and spatial distributions of the laser beam and an exponential decay function is used to model the internal absorption of the laser power. A finite-element method is employed to simulate the space- and time-dependence of temperature in the volume absorber. A three-dimensional model and an axial-symmetric model are built and used to study the heating effects of single pulse and multiple pulses on the present design, respectively. Furthermore, a new design is proposed, in which the absorber is not optically thick. A one-dimensional model and an axial-symmetric model, in which the reflection at the interface and the absorption on the copper surface are considered, are used to study the heating effects of single pulse and multiple pulses on the new design. The comparison of the present design to the new design shows that the energy loss and nonequivalence in the new design are smaller than those in the present design. Hence, the new design can increase the accuracy and dynamic range of calorimeters.. This work will help the future design of optical calorimeters for measuring the pulse energy of excimer lasers in the deep ultraviolet.