Apl. Prof. Dr. Benno Willke
Group leader Laser Development & Advanced LIGO
Phone:+49 511 762-2360Fax:+49 511 762-2784

Benno Willke's homepage


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A highly stable 2 W Nd:YAG Laser as the "Work Horse" for Gravitational-wave Detection

Gravitational waves (GW) are ripples in space-time, predicted by Albert Einstein about 100 years ago. They are generated by the accelerated motion of astronomical masses. Their effect on Earth is extremely small, so that they have not been detected as of today. However, kilometer-scale interferometric gravitational-wave detectors (GWD) (GEO600, LIGO, Virgo) have reached a sensitivity at the verge of predicted signal strength, such that scientists expect the first detection of GW within this decade.

These GWDs need to measure a relative differential length change of perpendicular interferometer arms with a precision of ∆l/l≈10-22. This corresponds to measuring the distance between Earth and Sun to the diameter of a single atom. It is not surprising that an extremely stable laser source is required to illuminate these interferometers.

From gas lasers to solid-state NPROs

Commissioning work on the Advanced LIGO high-power laser. The Mephisto master laser can be seen in the lower left of the picture. Zoom Image
Commissioning work on the Advanced LIGO high-power laser. The Mephisto master laser can be seen in the lower left of the picture. [less]

Early GWD prototypes in the 1980s used argon-ion (Ar+) lasers as their light source. The invention of the non-planar ring-oscillator (NPRO) by Byer and Kane [1] in 1985 initiated a change from gas lasers to solid-state lasers as GWD light sources. NPROs offered much better wall-plug efficiency and a noise level several orders of magnitude lower than Ar+ lasers. For these reasons and as NPROs were commercially available from two companies (Lightwave USA, Innolight Germany), all proposed and later build kilometer-scale GWDs used Nd:YAG solid state lasers based on NPROs as their main light source.

Today NPROs are not only used as master/seed lasers in the high-power main light source of GWDs but as well to generate non-classical states of light (so-called squeezed states) to overcome the shot-noise limit in the GWD readout. They are also used as seed lasers for frequency-doubled laser systems for the arm-length stabilization of GWDs and in many other fields of high precision metrology and quantum communication.

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