Gravitational waves:
Gravitational waves are also called gravity waves. Gravitational waves are a kind of space-time fluctuations propagating at the speed of light predicted by Einstein's general theory of relativity. They are a way of perturbation of space-time curvature in the form of traveling waves. Electromagnetic radiation is emitted when the charge is accelerated, and gravitational radiation is emitted when the same mass of the object is accelerated. This is an important prediction of general relativity.
Gravitational waves are similar to gravity waves in fluid mechanics. When the liquid surface or internal liquid mass leaves the original position due to the difference in density, under the combined action of gravity and buoyancy, the liquid mass will vibrate up and down to reach equilibrium, that is, the fluctuation occurs. .
Gravitational waves are caused by fluctuations in space due to changes in space quality and speed.
The discovery of gravitational waves:
American scientists used the Laser Interference Gravitational Wave Observatory (LIGO) to detect gravitational waves for the first time in September last year. On February 11, 2016, LIGO announced the “detection of the existence of gravitational wavesâ€, a gravitational wave that was transmitted by two black holes colliding and combining about 1.3 billion years ago. It arrived on Earth on September 14, 2015. , detected by LIGO's precision instruments. The existence of gravitational waves confirms the predictions that Einstein made 100 years ago, and the last piece of missing "puzzles" in Einstein's general theory of relativity experimentation was filled.
Gravitational wave detection:
The gravitational wave is a transverse wave, which is a plane wave at a distant source; it has two independent polarization states; it carries energy. Gravitational waves carry energy, which should be detected, but the intensity of gravitational waves is very weak. Moreover, the absorption efficiency of gravitational waves by materials is extremely low, and it is extremely difficult to directly detect gravitational waves. The strongest gravitational waves we observe on Earth come from far-reaching and ancient events in which a large amount of energy moves violently (examples include collisions between two neutron stars or two very heavy black holes) . Such fluctuations can cause changes in the relative distances of the Earth, but the magnitude of these changes should be very small. In the arms of the LIGO gravitational wave detector, this change is less than one thousandth of the diameter of a proton. That is 10
-19Around the meter.
In 1991, the Massachusetts Institute of Technology and the California Institute of Technology, under the auspices of the National Science Foundation (NSF), began to jointly build the Laser Interference Gravitational Wave Observatory (LIGO).
The main part of LIGO is two mutually perpendicular interference arms with an arm length of 4,000 meters. At the intersection of the two arms, the light beam emitted from the laser source is split into two, respectively, into two hollow cylinders that are perpendicular to each other and maintained in an ultra-vacuum state, and then reflected by the specular surface of the terminal back to the original starting point, where interference occurs. If a gravitational wave passes, it will cause deformation in time and space. The length of one arm will be slightly longer and the length of the other arm will be slightly shortened. This will cause the optical path difference to change, so the laser interference fringe will change accordingly. . The schematic is as follows:
In fact, LIGO's gravitational wave detection device is made using the principle of a Michelson interferometer.
In order to detect super slight disturbances, the longer the arms of the Michelson interferometer, the better. LIGO's arms were eventually designed to be 4 kilometers long. In fact, the 4 km long optical path is not enough, so LIGO added a Fabry-Perot interference cavity to the arms, and obtained an optical path equivalent to 1,120 km long.
In addition, there is a problem. Although the equivalent optical path reaches 1120 km, if the gravitational wave is directly detected, the power of the laser theoretically needs to reach 750,000 watts (750 kW). In order to solve this problem, LIGO is in the laser and A "power recycling mirror" has been added between the beamers to successfully reduce the laser power by 3,750 times, so in fact, LIGO's laser output power is only 200W.
In addition, LIGO requires extreme sensitivity to disturbances, so that any slightly larger vibration within a few thousand miles may overwhelm the gravitational wave signal. So LIGO uses a dual damping system: an "active" damping system and a "passive" damping system.
The “active†damping system consists of the Internal Seismic Isolation (ISI) system. The principle is to detect the vibration of all frequencies on the surrounding ground, and then actively generate a reverse vibration to cancel it and retain the gravitational wave. Vibration.
The “passive†isolation system consists of a complex system that suspends the lens through a 4-stage pendulum mechanism (LIGO calls it “quadâ€).
The entire quad mechanism is on both sides, the "main chain" side (the "Main Chain" side) faces the laser beam, and the "Reaction Chain" side ("Reaction Chain" side) is used to further eliminate external disturbances, ensuring that only gravitational waves are left. Vibration.
In addition, LIGO also has a very powerful vacuum system, the vacuum inside the cavity is one trillionth of the sea level pressure. There are two main reasons for this high vacuum:
1. Eliminate air molecule heat transfer and flow: the lens may be deformed by heat transfer. In addition, if there are too many air molecules in the cavity, airflow may occur. When the light passes through the airflow, it will refract, causing the light to deviate from the straight line, just like the heat wave formed on the road.
2. Eliminate any dust entering the laser cavity, causing the possibility of stray light.
significance:
The discovery of gravitational waves is of great significance. From a scientific point of view, gravitational waves can be directly connected to the Big Bang. The gravitational waves predicted in general relativity can also be generated in the Big Bang, which means that the gravitational waves at the beginning of the big bang can still be detected today after 13.7 billion years. Once you discover the gravitational waves of the Big Bang, you can uncover the mysteries of the universe and even understand the beginnings and operating mechanisms of the universe.
The discovery of gravitational waves is the result of the full application of optomechanical products:
The Laser Interference Gravitational Wave Observatory (LIGO) uses a large number of optical products and its design principles in devices that detect and detect gravitational waves, such as:
1. Vibration isolation technology:
Because the external micro-vibration directly affects the measurement accuracy of precision instrumentation equipment (such as gravitational wave detection equipment). Therefore, in the optical, electronic, precision machinery manufacturing, metallurgy, aerospace, aviation, navigation, precision chemical and non-destructive testing and other mechanical industries, the key equipment of the vibration isolation of precision test instruments and equipment, the vibration isolation performance is good or bad. Directly affect the accuracy and reliability of the test results.
In recent years, Zhuoli Hanguang has also been paying attention to and improving the dynamic mechanical properties of optical platforms, and is committed to the study of vibration isolation performance of optical platforms. The optical platform produced and sold by Zhuoli Hanguang is a high-tech product developed through the continuous improvement of vibration isolation technology and through experiments, demonstrations and innovations including research institutes and universities.
Since 2015, Zhuo Li Hanguang's optical platform has adopted an integrated welding bracket, which has a more stable structure and better vibration isolation effect.
2. Michelson interferometer experimental device
The description of the LIGO detection gravitational wave device has been mentioned. The optical principle of the device is based on the Michelson interferometer. Zhuo Li Hanguang can provide the Michelson interferometer experimental device kit. The related products are as follows:
Schematic:
Kit photo:
Experimental device composition:
In addition, Zhuoli Hanguang also offers a variety of precision displacement products, optical mounts, optical components and other products, providing you with a wide range of options for expanding similar optical systems or building various optical experiments.
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