Fig. 2. Setup for vertical excitation. The entire setup is placed on a high-performance laminar-flow isolation table (1). The scanning laser Doppler vibrometer (SLDV) (2) is suspended and positioned in three dimensions by a telescopic lifting column (3) and a XY-translation stage (4). A solid extension arm (5), only used during vertical excitation, allowed positioning of the first-surface mirror (6), tilted at an angle of 45° in order to deflect the laser beam downwards by 90°. At the distal end of the extension arm, an accelerometer (7) monitored the motion of the arm during the experiment. The specimen was tightly mounted to a metal block (8), which was driven by the vibration exciter (9). In order to avoid transmission of vibrations to the SLDV via the supporting table, a rubber mat (10) on top of an open-cell foam mat (11) separated the table from the vibration exciter.