National Astronomical Observatory of Japan



Large-scale Cryogenic Gravitational Wave Telescope


What is the Large-scale Cryogenic Gravitational Wave Telescope KAGRA?

The Large-scale Cryogenic Gravitational Wave Telescope KAGRA is a gravitational wave detector under construction underground in the Kamioka mine in Kamioka, Hida, Gifu Prefecture, Japan. KAGRA is a laser interferometer with a baseline length of 3 kilometers. When completed, it will be one of the most precise gravitational wave detectors in the world. We aim to build a worldwide gravitational wave detector network together with LIGO in the USA and Virgo in Europe. The construction of KAGRA is carried out by an international collaboration of many research institutes including The Institute for Cosmic Ray Research, University of Tokyo as the main host, and NAOJ and the High Energy Accelerator Research Organization as co-hosts.

Large-scale Cryogenic Gravitational Wave Telescope KAGRA


Gravitational waves are like ripples traveling in space-time. An optical-infrared telescope like the Subaru Telescope and a radio telescope like ALMA are instruments that capture electromagnetic waves, which are oscillations in the electromagnetic field. On the other hand, KAGRA captures gravitational waves, deformations in space-time that are transmitted as waves. Therefore, its detection principle differs fundamentally from telescopes that capture electromagnetic waves. KAGRA uses a technique called laser interferometry. It detects how space expands and contracts with the gravitational wave by looking at the interference fringes between laser beams propagated along orthogonal paths. In order to improve the precision of this interferometer, not only a long baseline length but also a high-power laser source, large aperture/ultralow loss mirrors, and ultrahigh-vacuum equipment are necessary. We develop and adopt various leading technologies in KAGRA. We are preparing so that we can lead the coming era of gravitational wave astronomy.

The coalescence of binary neutron star is one of the sources of gravitational waves. This astrophysical phenomenon can also be observed through electromagnetic waves such as gamma rays, optical, infrared and radio waves. We are seeking collaborations with observation instruments other than gravitational wave telescopes, such as the Subaru Telescope.


LocationKamioka, Hida, Gifu, Japan
DetectorLaser interferometer (Michelson interferometer)
Baseline length3 kilometers
CharacteristicsThere are four main characteristics of KAGRA:
- The size of the detector is 3 kilometers.
- It is located in a stable underground site that is favorable for detecting gravitational waves.
- The temperature of the mirrors is cooled down to -250 degrees Celsius to reduce the thermal noise that shakes the mirrors.
- The use of sapphire, which exhibits excellent properties at low-temperatures, as the material of the mirrors.


January 20, 2012Groundbreaking ceremony.
May 2012Tunnel excavation started.
March 31, 2014Tunnel excavation finished.
March 25, 2016Test operation started.