Gravitational waves:
Gravitational waves, also known as gravity waves, are ripples in the fabric of space-time that travel at the speed of light, as predicted by Einstein’s general theory of relativity. These waves represent a disturbance in the curvature of space-time, similar to how electromagnetic waves are produced when charged particles accelerate. In the case of gravitational waves, it is the mass of an object that causes such radiation when accelerated.
These waves share some similarities with gravity waves found in fluid mechanics. For instance, when a liquid surface or internal mass moves due to density differences, the combined forces of gravity and buoyancy cause it to oscillate, resulting in fluctuations. However, gravitational waves in physics are fundamentally different from these fluid-based phenomena, as they are related to the structure of space-time itself.
Gravitational waves originate from changes in the distribution and motion of mass across space. Their detection has opened a new window into understanding the universe, allowing scientists to observe cosmic events that were previously invisible to traditional telescopes.
The discovery of gravitational waves:
In September 2015, American scientists using the Laser Interferometer Gravitational-Wave Observatory (LIGO) made the first direct detection of gravitational waves. On February 11, 2016, LIGO announced the detection of a gravitational wave signal caused by the collision of two black holes approximately 1.3 billion years ago. The signal was detected on September 14, 2015, and confirmed the final missing piece of Einstein's general theory of relativity, which had been theorized over a century earlier.
Gravitational wave detection:
Gravitational waves are transverse waves that propagate through space-time. They have two independent polarization states and carry energy. However, their intensity is extremely weak, and materials absorb them very inefficiently, making direct detection extremely challenging. The strongest gravitational waves observed on Earth come from violent cosmic events, such as collisions between neutron stars or black holes. These events can cause tiny distortions in space-time, altering the distance between objects on Earth by less than a fraction of a proton’s diameter—on the order of 10-19 meters.
Since 1991, the Massachusetts Institute of Technology and the California Institute of Technology, under the National Science Foundation (NSF), have been building the LIGO facility. The main part of the observatory consists of two perpendicular arms, each 4 kilometers long. A laser beam is split and sent down both arms, reflected back, and recombined to create interference patterns. When a gravitational wave passes, it slightly stretches one arm while compressing the other, causing a detectable shift in the interference pattern.
LIGO’s detection system is based on the Michelson interferometer. To detect such small disturbances, longer arms are better. The 4 km arms were extended using Fabry-Perot cavities, effectively increasing the optical path to 1,120 km.
To achieve this, LIGO uses a "power recycling mirror" to reduce the required laser power from 750 kW to just 200 W. Additionally, LIGO employs a dual damping system: an active isolation system (ISI) and a passive isolation system (quad). These systems protect against external vibrations that could overwhelm the gravitational wave signal.
The passive system uses a four-stage pendulum mechanism called a "quad" to isolate the optics from ground vibrations. This ensures only gravitational waves remain in the signal.
LIGO also features an ultra-high vacuum system inside its cavity, with pressure levels one trillionth of atmospheric pressure. This prevents air molecule heat transfer and airflow, which could distort the laser beam, and eliminates dust that might cause stray light.
Significance:
The discovery of gravitational waves marks a major milestone in science. From a theoretical perspective, gravitational waves offer a direct link to the Big Bang. Since general relativity predicts that gravitational waves were generated during the early universe, detecting them today could reveal secrets about the origin and evolution of the cosmos.
The discovery of gravitational waves is a result of advanced optomechanical technology:
The Laser Interferometer Gravitational-Wave Observatory (LIGO) relies heavily on optical components and precision engineering. Key technologies include vibration isolation, which is essential for maintaining the accuracy of high-precision instruments like those used in gravitational wave detection. Vibration isolation performance directly affects the reliability of experimental results in fields such as aerospace, precision manufacturing, and scientific research.
Zhuoli Hanguang has focused on improving the dynamic properties of optical platforms and developing advanced vibration isolation systems. Their optical platforms are widely used in research institutions and universities, offering reliable solutions for precision experiments.
Since 2015, Zhuoli Hanguang has integrated welding brackets into its optical platforms, enhancing structural stability and vibration isolation performance.
2. Michelson interferometer experimental device:
The optical principle of LIGO is based on the Michelson interferometer. Zhuoli Hanguang provides a complete kit for Michelson interferometer experiments, including the following components:
Schematic:
Kit photo:
Experimental device composition:
Zhuoli Hanguang also offers a wide range of precision displacement products, optical mounts, and optical components, supporting the development of various optical systems and experiments.
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