3.2.2. Mechanics

Mechanics is divided into three parts. The first is an aluminum breadboard that hosts the electronics, the laser and the reference optics (Figure 4 Left). The breadboard is framed into a structure that fits a plastic suitcase for easy transportation. The other two parts of the mechanics are mounted onto the stack. The launching/receiving optics can be seen in Figure 4 Center. The laser beam is shot across the stack, onto a mirror (Figure 4 Right), which directly reflects the beam onto the detector, for a total of two passes inside the stack. The mechanical stability of the system relies on the flanges protruding out the stack. All the optical ports are sealed by 1" anti-reflection coated BK7 windows (Thorlabs WG11050-C).

**Figure 4.** (**left**): main plate of the mechanics, together with the waveform generator and the laptop; (**center**): launching optics, driven by the yellow optic fiber, and detector; (**right**): steering mirror, which reflects the laser beam onto the detector.
