K. Mossavi

The GEO 600 gravitational wave detector

The GEO 600 laser interferometer with 600 m armlength is part of a worldwide network of gravitational wave detectors. Due to the use of advanced technologies like multiple pendulum suspensions with a monolithic last stage and signal recycling, the anticipated sensitivity of GEO 600 is close to the initial sensitivity of detectors with several kilometres armlength. This paper describes the subsystems of GEO 600, the status of the detector by September 2001 and the plans towards the first science run.

Status of the GEO600 detector

Of all the large interferometric gravitational-wave detectors, the German/British project GEO600 is the only one which uses dual recycling. During the four weeks of the international S4 data-taking run it reached an instrumental duty cycle of 97% with a peak sensitivity of 7 × 10−22 Hz−1/2 at 1 kHz. This paper describes the status during S4 and improvements thereafter.

The status of GEO 600

The GEO 600 laser interferometer with 600m armlength is part of a worldwide network of gravitational wave detectors. GEO 600 is unique in having advanced multiple pendulum suspensions with a monolithic last stage and in employing a signal recycled optical design. This paper describes the recent commissioning of the interferometer and its operation in signal recycled mode.

Single-shot autocorrelator for KrF subpicosecond pulses based on two-photon fluorescence of cadmium vapor at λ = 508 nm

By excitation of cadmium vapor with a high-peak-power KrF excimer laser pulse, fluorescence of an atomic transition at lambda = 508 nm is induced by a two-photon ionization process followed by fast recombination. The nonlinear response of the medium is used to develop a simple single-shot autocorrelator for subpicosecond KrF excimer laser pulses operating down to intensities of less than 10(9)W/cm.(2) We have measured 360-fs (FWHM) pulses at lambda = 248 nm with a time resolution of 15 fs.

Spectrally compensated sum-frequency mixing scheme for generation of broadband radiation at 193 nm

A dispersively compensated scheme for sum-frequency mixing of broadband ultrashort laser pulses is reported. An increase of the bandwidth of the sum-frequency mixing process by 12 times compared with the noncompensated bandwidth of the given crystal has been demonstrated. Mixing radiation at 266 and 707 nm in a 1-mm-thick beta-barium metaborate crystal by using the compensated scheme results in an output bandwidth of 0.6 nm at 193 nm, which corresponds to a minimum output pulse duration of 90 fs.

Ultrahigh‐brightness, femtosecond ArF excimer laser system

An ultrahigh‐brightness ArF excimer laser system is described that is capable of generating pulse energies of 60 mJ with a pulse duration of ∼700 fs. The system utilizes a newly developed seed pulse generation scheme based on spectrally compensated sum‐frequency mixing in beta‐barium metaborate (BBO), and a double‐pass discharge pumped ArF excimer preamplifier followed by an electron beam pumped power amplifier.

Mode-cleaning and injection optics of the gravitational-wave detector GEO600

The British–German interferometric gravitational-wave detector GEO600 uses two high-finesse triangular ring cavities of 8 m optical pathlength each, as an optical mode-cleaning system. The modecleaner system is housed in an ultrahigh-vacuum environment to avoid contamination of the optics and to minimize both the influence of refractive index variations of the air and acoustic coupling to the optics. To isolate the cavities from seismic noise, all optical components are suspended as double pendulums. These pendulums are damped at their resonance frequencies at the upper pendulum stage with magnet-coil actuators. A suspended reaction mass supports three coils matching magnets bonded onto the surface of one mirror of each cavity, allowing length control of the modecleaner cavities to maintain resonance with the laser light. A fully automated control system stabilizes the frequency of the slave laser to that of the master laser, the frequency of the master laser to the length of the first modecleaner and the length of the first to the length of the second modecleaner. The control system uses the Pound–Drever–Hall sideband technique and operates autonomously over long time periods with only infrequent human interaction. The duty cycle of the system was measured to be 99.7% during an 18 day period. The throughput of the whole modecleaner system is about 50%. In this article, we give an overview of the mechanical and optical setup and the achieved performance of the double modecleaner system.

The AEI 10 m prototype interferometer

A 10 m prototype interferometer facility is currently being set up at the AEI in Hannover, Germany. The prototype interferometer will be housed inside a 100 m 3 ultra-high vacuum envelope. Seismically isolated optical tables inside the vacuum system will be interferometrically interconnected via a suspension platform interferometer. Advanced isolation techniques will be used, such as inverted pendulums and geometrical anti-spring filters in combination with multiple-cascaded pendulum suspensions, containing an all-silica monolithic last stage. The light source is a 35 W Nd:YAG laser, geometrically filtered by passing it through a photonic crystal fibre and a rigid pre-modecleaner cavity. Laser frequency stabilisation will be achieved with the aid of a high finesse suspended reference cavity in conjunction with a molecular iodine reference. Coating thermal noise will be reduced by the use of Khalili cavities as compound end mirrors. Data acquisition and control of the experiments is based on the AdvLIGO digital control and data system. The aim of the project is to test advanced techniques for GEO 600 as well as to conduct experiments in macroscopic quantum mechanics. Reaching standard quantum-limit sensitivity for an interferometer with 100 g mirrors and subsequently breaching this limit, features most prominently among these experiments. In this paper we present the layout and current status of the AEI 10 m Prototype Interferometer project.

Commissioning, characterization and operation of the dual-recycled GEO 600

The German-British laser-interferometric gravitational-wave detector GEO 600 is currently being commissioned as part of a worldwide network of gravitational-wave detectors. GEO 600 recently became the first kilometre-scale interferometer to employ dual recycling-an optical configuration that combines power recycling and signal recycling. We present a brief overview of the commissioning of this dual-recycled interferometer, the performance results achieved during a subsequent extended data-taking period, and the plans intended to bring GEO 600 to its final configuration.

Generation of short-pulse VUV and XUV radiation

Starting from intense short-pulse KrF (248 nm, 25 mJ, 400 fs), ArF (193 nm, 10 mJ, ∼1 ps), and Ti:sapphire (810 nm, 100 mJ, 150 fs) laser systems, schemes for the generation of fixed-frequency and tunable VUV and XUV radiation by nonlinear optical techniques are investigated. With the KrF system, a four-wave mixing process in xenon yields tunable radiation in the range of 130–200 nm with output energies of, so far, 100 μJ in less than 1 ps. For the XUV spectral range below 100 nm, nonperturbative high-order harmonic generation and frequency mixing processes in noble gas jets are considered. To achieve tunability, the intense fixed-frequency pump laser radiation is mixed with less intense but broadly tunable radiation from short-pulse dye lasers or optical parametric generator-amplifier systems. In this way, tunability down to wavelengths of less than 40 nm has been demonstrated.