ABSTRACT
The generation of strongly squeezed vacuum states of light is a key technology for future ground-based gravitational wave detectors (GWDs) to reach sensitivities beyond their quantum noise limit. For some proposed observatory designs, an operating laser wavelength of 1550 nm or around 2 µm is required to enable the use of cryogenically cooled silicon test masses for thermal noise reduction. Here, we present for the first time the direct measurement of up to 11.5 dB squeezing at 1550 nm over the complete detection bandwidth of future ground-based GWDs ranging from 10 kHz down to below 1 Hz. Furthermore, we directly observe a quantum shot-noise reduction of up to (13.5±0.1) dB at megahertz frequencies. This allows us to derive a precise constraint on the absolute quantum efficiency of the photodiode used for balanced homodyne detection. These results hold important insight regarding the quantum noise reduction efficiency in future GWDs, as well as for quantum information and cryptography, where low decoherence of nonclassical states of light is also of high relevance.
ABSTRACT
Advanced gravitational wave detectors require highly stable, single mode, single frequency and linear polarized laser systems. They have to deliver an output power of â¼200 W and need to provide suitable actuators for further stabilization via fast, low noise feedback control systems. We present such a laser system based on sequential Nd:YVO4 amplifiers and its integration into a typical laser stabilization environment. We demonstrate robust low noise operation of the stabilized amplifier system at 195 W, which makes it a viable candidate for use in gravitational wave detectors.
ABSTRACT
The next generation of interferometric gravitational wave detectors will use low-noise single-frequency laser sources at 1064 nm. Fiber amplifiers are a promising design option because of high efficiency, compact design, and superior optical beam properties compared to the current generation of laser sources for gravitational wave detectors. We developed a reliable 200 W single-frequency fiber amplifier architecture to meet the application requirements regarding relative power noise, relative pointing noise, frequency noise, linear polarization, and beam quality. We characterized several of these amplifiers and discuss performance variations resulting from manufacturing tolerances and variations in amplifier architecture. This study serves as a baseline for further power scaling via e.g., coherent beam combining experiments.
ABSTRACT
Low noise, high power single-frequency lasers and amplifiers are key components of interferometric gravitational wave detectors. One way to increase the detector sensitivity is to increase the power injected into the interferometers. We developed a fiber amplifier engineering prototype with a pump power limited output power of 200 W at 1064 nm. No signs of stimulated Brillouin scattering are observed at 200 W. At the maximum output power the polarization extinction ratio is above 19 dB and the fractional power in the fundamental transverse mode (TEM 00) was measured to be 94.8 %. In addition, measurements of the frequency noise, relative power noise, and relative pointing noise were performed and demonstrate excellent low noise properties over the entire output power slope. In the context of single-frequency fiber amplifiers, the measured relative pointing noise below 100 Hz and the higher order mode content is, to the best of our knowledge, at 200 W the lowest ever measured. A long-term test of more than 695 h demonstrated stable operation without beam quality degradation. It is also the longest single-frequency fiber amplifier operation at 200 W ever reported.