Ring lasers are not the only devices that allow rotation sensing with high resolution. This chapter looks at alternative rotation sensing concepts and their physical realization, to put the achievements reported in Chapters 3 and 4 into perspective. We briefly introduce passive Sagnac interferometers, small and large fiber optic gyros, helium SQUID gyros, atom interferometry and Coriolis force-exploiting sensors. It turns out that every application has a different set of requirements, and some types of sensors are better suited for the respective purposes than others. Here we illustrate how the purpose ultimately defines the best technical solution. A book like this would not be complete without looking at solid state ring lasers. However, we also show that in terms of sensitivity and stability, the large ring laser gyroscope takes a prominent role in inertial rotation sensing.

We learn about unbound states and find that the energies are no longer quantized. We learn about momentum eigenstates and superposing momentum eigenstates in a wave packet. We apply unbound states to the problem of scattering from potential wells and barriers in one dimension.