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Research group | 3rd Generation Gravitational Wave Detector Laser Source

Working in the clean room on a high power amplifier system. Photo: Thomas Damm/QUEST

The interferometric detection of gravitational waves sets an exceptionally high requirements for the laser source used. Besides diffraction limited beam quality and the single-frequency emission, the extremely high output power needed for 3rd generation gravitational wave detectors is the major challenge. Depending on the mirror substrates used in the interferometers, either up to 1 kW of output power at a wavelength of 1064 nm or 100-200 W at a wavelength of 1.55 μm wavelength is needed. For the realization of such laser sources, different concepts are evaluated with respect to their suitability for low noise amplification of single-frequency radiation. 

In the 1.55 μm range, pure fiber based systems utilizing both Er-doped as well as Er/Yb-co-doped fibers are examined. At 1064 nm wavelength, hybrid fiber-solid state amplifiers using both Yb-doped fibers and Nd-doped laser crystals are realized. Due to the high intensity in the fiber core and the long interaction length, fiber based systems enable very high efficiency even in the low power range. However, the same properties can be limiting in the high power range as they favor non-linear scattering processes like the stimulated Brillouin scattering which increases the frequency and intensity noise. Thus, these amplifiers are complemented by solid-state amplifiers which need high input power for an efficient power extraction due to their large mode field areas.