One method of gravitational wave detection uses the basic idea of a laser pointer interferometer. Assume that there are four test masses suspended from the ceiling. A monochromatic, frequency-stable laser is emitted from the laser. It is divided into two beams of equal intensity on the beam splitter, and one beam is reflected by the beam splitter into the Y arm of the interferometer. The other beam passes through the beam splitter and enters another X-arm perpendicular to it. Gravitational waves are not added for the first time. After the same time has passed, the two beams of light return and meet again on the beam splitter, causing interference.
By adjusting the length of the X and Y arms this time, the two beams are controlled to cancel each other. At this time, there is no light signal on the photodiode. After adding the gravitational wave in the second experiment, the gravitational wave enters from the direction perpendicular to the ceiling, which will lengthen one of the two arms and compress the other arm shortly, so the optical path difference between the two beams changes, which was originally coherent. The destructive conditions are destroyed, and a certain amount of light will enter the detector to obtain a gravitational wave signal.
The advantages of laser interferometers for resonant rods are obvious: first, the laser interferometer can detect gravitational wave signals of a certain range of frequencies, typically 20Hz-3000Hz; second, the arm length of the laser interferometer can be made very long, such as ground gravitational wave interference The arm length of the instrument is generally on the order of kilometers, far exceeding the length of the macrometer of the resonance rod, which will make the gravitational waves appear through the green laser pointer light detector.