Consider the laser cavity below. Use d = 2.0 m and R2 = 1.0 m. Assume that M1 is a planar mirror. Figure 3: Schematic for Q3. (a) Show that the cavity is unstable. (b) Suppose that a ray starts out moving to the right at M1, at a height of 1 mm and parallel to the optical axis. Determine how many passes the ray will make through the cavity before it misses one of the mirrors.