The advanced LIGO gravitational wave detectors need high power laser sources with excellent beam quality and low-noise behavior. We present a pre-stabilized laser system with 70 W of output power ...that was used in the third observing run of the advanced LIGO detectors. Furthermore, the prototype of a 140 W pre-stabilized laser system for future use in the LIGO observatories is described and characterized.
Advanced gravitational wave detectors require highly stable, single mode, single frequency and linear polarized laser systems. They have to deliver an output power of ∼200 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:YVO 4 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.
Design studies for the next generation of interferometric gravitational wave detectors propose the use of low-noise single-frequency high power laser sources at 1064 nm. Fiber amplifiers are a ...promising design option because of their high output power and excellent optical beam properties. We performed filled-aperture coherent beam combining with independently amplified beams from two low-noise high-power single-frequency fiber amplifiers to further scale the available optical power. An optical power of approximately 400 W with a combining efficiency of more than 93% was achieved. The combined beam contained 370 W of linearly polarized TEM
-mode and was characterized with respect to the application requirements of low relative power noise, relative beam pointing noise, and frequency noise. The noise performance of the combined beam is comparable to the single amplifier noise. This represents, to our knowledge, the highest measured power in the TEM
-mode of single frequency signals that fulfills the low noise requirements of gravitational wave detectors.
Interferometric displacement measurements, especially in space interferometry applications, face challenges from thermal expansion. Bonded assemblies of ultra-low thermal expansion glass-ceramics ...offer a solution; however, transitioning from light transport in fibers to free beam propagation presents a notable challenge. These experiments often need an interface to convert between laser beams propagating through fiber optics into a well-defined free beam and vice versa. These interfaces must also be made of rigid glass pieces that can be bonded to a glass base plate. Current designs for these fiber collimators, often called fiber injector optical sub-assemblies, require multiple glass parts fabricated to very tight tolerances and assembled with special alignment tools. We present a simplified quasi-monolithic fiber collimator that can generate a well-collimated laser beam. The complexity and tolerances of bonding are reduced by combining the alignment of the fiber mode to the imaging lens in one step with active mode control: the welding of the fiber to the glass body. We produce several of these designs and test that the desired light field is achieved, its profile is described as a Gaussian beam, and the beam-pointing stability is acceptable for such a piece. In each case, they perform at least as well as a standard commercial fiber collimator. These Quasi Monolithic Fiber Collimators offer a promising and easy-to-implement solution to convert between free beam and fiber-coupled lasers in experiments sensitive to long term thermal drifts.
Thermal noise of the dielectric mirror coatings can limit laser-optical
high-precision measurements. Coatings made of amorphous silicon and silicon
nitride could provide a remedy for both ...gravitational-wave detectors and
optical clocks. However, the absorption spectra of these materials require
laser wavelengths around 2 $\mu$m. For GW detectors, ultra-stable laser light
of tens or hundreds of watts is needed. Here, we report the production of
nearly 30 W of ultra-stable laser light at 2128 nm by frequency conversion of
1064 nm light from a master oscillator power amplifier system. We achieve an
external conversion efficiency of (67.5 $\pm$ 0.5) % via optical parametric
oscillation and a relative power noise in the range of
$10^{-6}$/$\sqrt{\text{Hz}}$ at 100 Hz, which is almost as low as that of the
input light and underlines the potential of our approach.
Precision measurements of space and time, like those made by the detectors of the Laser Interferometer Gravitational-wave Observatory (LIGO), are often confronted with fundamental limitations imposed ...by quantum mechanics. The Heisenberg uncertainty principle dictates that the position and momentum of an object cannot both be precisely measured, giving rise to an apparent limitation called the Standard Quantum Limit (SQL). Reducing quantum noise below the SQL in gravitational-wave detectors, where photons are used to continuously measure the positions of freely falling mirrors, has been an active area of research for decades. Here we show how the LIGO A+ upgrade reduced the detectors' quantum noise below the SQL by up to 3 dB while achieving a broadband sensitivity improvement, more than two decades after this possibility was first presented.
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