Stabilized lasers for advanced gravitational wave detectors

Second-generation interferometric gravitational wave detectors require high-power lasers with approximately 200 W of output power in a linear polarized, single-frequency, fundamental-mode laser beam. Furthermore very high temporal and spatial stability is required. This paper discusses the design of a 200 W pre-stabilized laser (PSL) system and the underlying concepts. The PSL requirements for advanced gravitational wave detectors as well as for the laser system are described. The laser stabilization scheme proposed for the Advanced LIGO gravitational wave detector and the so-called diagnostic breadboard will serve as examples to explain the general laser stabilization concepts and the achieved performance and its limitations

GEO600: status and plans

The GEO600 gravitational wave detector located near Hannover in Germany is one of the four detectors of the LIGO Scientific Collaboration (LSC). For almost the entire year of 2006, GEO600 participated in the S5 science run of the LSC. Overall an equivalent of about 270 days of science data with an average peak sensitivity of better than 3 × 10-22 Hz-1/2 have been acquired so far. In this paper, we describe the status of the GEO600 project during the period between January 2006 and February 2007. In addition, plans for the near-term and medium-term future are discussed

Laser power stabilization for second-generation gravitational wave detectors

We present results on the power stabilization of a Nd:YAG laser in the frequency band from 1 Hz to 100 kHz. High-power, low-noise photodetectors are used in a dc-coupled control loop to achieve relative power fluctuations down to 5×10−9 Hz−1/2 at 10 Hz and 3.5×10−9 Hz−1/2 up to several kHz, which is very close to the shot-noise limit for 80 mA of detected photocurrent on each detector. We investigated and eliminated several noise sources such as ground loops and beam pointing. The achieved stability level is close to the requirements for the Advanced LIGO gravitational wave detector

Automatic laser beam characterization of monolithicNd:YAG nonplanar ring lasers

A detailed beam characterization of continuous-wave single-frequency Nd:YAG solid-state ring lasers at a wavelength of 1064 nm is presented. The power noise, frequency noise, beam pointing fluctuations, spatial beam quality, and other properties of eight lasers of the same model were measured with a compact diagnostic instrument based on an optical ring resonator. One of the eight lasers was automatically characterized over a period of 3.5 months to investigate the long-term behavior. The results show that these lasers are highly stable laser sources, that the variations between different samples are rather small, and that these lasers are ideally suited for high precision optical experiments

Frequency stabilization of a monolithic Nd:YAG ring laser by controlling the power of the laser-diode pump source

The frequency of a 700mW monolithic non-planar Nd:YAG ring laser (NPRO) depends with a large coupling coefficient (some MHz/mW) on the power of its laser-diode pump source. Using this effect we demonstrate the frequency stabilization of an NPRO to a frequency reference by feeding back to the current of its pump diodes. We achieved an error point frequency noise smaller than 1mHz/sqrt(Hz), and simultaneously a reduction of the power noise of the NPRO by 10dB without an additional power stabilization feed-back system.Comment: accepted for publication by Optics Letter

Quantum correlation measurement of laser power noise below shot noise

In this Letter, the quantum correlation measurement technique as a method of power noise monitoring is investigated. Its principal idea of correlating two photodetector signals is introduced and contrasted to the conventional approach, which uses only a single photodetector. We discuss how this scheme can be used to obtain power noise information below the shot noise of the detected beam and also below the electronic dark noise of the individual photodetectors, both of which is not possible with the conventional approach. Furthermore, experimental results are presented, that demonstrate a detection of technical laser power noise one order of magnitude below the shot noise of the detected beam

Frequency domain interferometer simulation with higher-order spatial modes

FINESSE is a software simulation that allows to compute the optical properties of laser interferometers as they are used by the interferometric gravitational-wave detectors today. It provides a fast and versatile tool which has proven to be very useful during the design and the commissioning of gravitational-wave detectors. The basic algorithm of FINESSE numerically computes the light amplitudes inside an interferometer using Hermite-Gauss modes in the frequency domain. In addition, FINESSE provides a number of commands to easily generate and plot the most common signals like, for example, power enhancement, error or control signals, transfer functions and shot-noise-limited sensitivities. Among the various simulation tools available to the gravitational wave community today, FINESSE is the most advanced general optical simulation that uses the frequency domain. It has been designed to allow general analysis of user defined optical setups while being easy to install and easy to use.Comment: Added an example for the application of the simulation during the commisioning of the GEO 600 gravitational-wave detecto

Squeezed States of Light for Future Gravitational Wave Detectors at a Wavelength of 1550 nm

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