stray light etc. Raytheon's use of a Faraday element to split internal frequencies introduces however optical 1/f noise and renders the device non-optimal as a gyro. 2. If the fourth mirror is suspended such that it can rotate around a horizontal axis, the appearance of is extremely sensitive to the mirror's rotation. In a reasonable arrangement, an angular sensitivity of ±3 picoradian or 0.6 microarcsecond is estimated. With a mass suspended on the rotatable mirror, a simple gravitational wave detector can be constructed. Lock-in and pulling These are new phenomena in rings. The lock-in frequency fL, is the frequency at which the difference between the beam frequencies becomes so small that it collapses, synchronizing the two counterrotating beams. Generally, if the theoretical frequency difference is ft, the actual signal frequency f is . This equation says that even slightly above lock-in, there is already a reduction in frequency (i.e. pulling) relative to the theoretical frequency. In the presence of several satellites, only the major signal is pulled. The other satellites have their proper, non-pulled, frequency separation from the major signal. This opens the way to classic precision side-band spectroscopy as is known in microwaves, except that the ring laser has side bands down to nHz. When the dependence on perimeter L is taken into account for large rings, the relative difference between theoretical output frequency ft and actual output frequency f is inversely proportional to the fourth power of L: . This is a huge advantage of large rings over small ones. As an example, small navigational gyros have lock-in frequencies on the order of 1 kHz. The first large ring had a lock-in frequency of about 2 kHz, and the first ring that could measure the Earth's rotation rate had a lock-in frequency of about 20 Hz. The cavity The quality factor Q of the cavity, as well as the time duration of the measurement, determines the achievable frequency resolution of a ring to a large extent. The quality factor depends largely on the reflection properties of the mirrors. For high quality rings, reflectivities larger than 99.999% (R = 1-10 ppm) are indispensable. At this time, the main limitation of mirrors is the extinction coefficient of the evaporated high-index material TiO2. The size and shape of the cavity as well as the presence of interfaces also influence the quality factor. Quality factor Q It is quite important for large