Plane gravitational waves

The first known solution was that of Schwarzschild that provides the origin of the notion of a black hole. Let us also mention the Kerr solution, plane gravitational waves, the general first order solution, the successive approximations of the two black hole problem hundreds of rigourous solutions are known today. 

A third classical solution of the Grossmann equation is the plane gravitational wave , with u = ct - x ... 

The second solution is the use of Fabry-Perot cavities, where the laser spots from aU reflections coincide. A Fabry-Perot cavity consists of two plane mirrors at distance L. The power transmitted by the cavity is maximum at the resonance, when kL = nit, where is the wave vector. In this case, the power trapping in the cavity replaces the many round-trips of the laser beam. The phase of the light leaving from the cavity depends on the cavity length. If the cavity is working at resonance, the passage of a gravitational wave produces a phase shift near the resonance. The resonance characteristics of the Fabry-Perot cavity are described by the finesse F, which is related to the reflectivities ri, ri of the mirrors ... 

---