In this paper, dynamic response of 1-inch hard disk drive (HDD) head arm assembly (HAA) against an impact load is obtained by means of a 3D non-linear finite element model in ANSYS/LS-DYNA and experiments using Optical method. A mass is modeled as a rigid body and is made to collide with the arm. The velocity, displacement, acceleration and the inertial force of the mass are obtained from the time- history of finite element analysis (FEA). In the experiment, a mass that is levitated with an aerostatic linear bearing, and hence encounters negligible friction, is made to collide with the HAA and the dynamic bending test for the arm is realized. During the collision the Doppler frequency shift of the laser beam reflecting from the mass is accurately measured using an optical interferometer. The velocity, the position, the acceleration and the inertial force of the mass are calculated from the measured time-varying Doppler frequency shift. A good correlation between the experimental data and FEA results is observed.