Ultra low-loss low-efficiency diffraction gratings.

The realization of ultra low-loss dielectric reflection gratings with diffraction efficiencies between 7% and 0.02% is presented. By placing the grating beneath the highly reflective layerstack scattering was significantly reduced. This concept allows the all-reflective coupling of high laser radiation to high finesse cavities, thereby circumventing thermal effects caused by absorption in the substrate.

MCC/IMS signals in human breath related to sarcoidosis-results of a feasibility study using an automated peak finding procedure.

A feasibility study using an ion mobility spectrometer coupled with a multi-capillary column (MCC) was started to identify characteristic peaks of volatile compounds in exhaled human breath samples of 10 ml volume. The breath of 20 patients with sarcoidosis and suspicion of sarcoidosis because of mediastinal lymph node enlargement was investigated. Using a set of procedures for data processing and scoring a sector of interest was determined within the IMS-chromatogram. It could be shown that a procedure related to a single peak in the IMS-chromatogram delivers differentiation into the two groups of patients with confirmed sarcoidosis and those suffering no sarcoidosis. The potential biomarker is characterized by the following parameters: inverse mobility (1/K(0)) 0.53 ± 0.01 V s cm(-2)-retention time 22 ± 5 s. These results are a first step in breath analysis by MCC/IMS in patients with sarcoidosis by an automated procedure applied to IMS-chromatograms directly.

Three-port beam splitters-combiners for interferometer applications.

We derive generic phase and amplitude coupling relations for beam splitters-combiners that couple a single port with three output ports or input ports, respectively. We apply the coupling relations to a reflection grating that serves as a coupler to a single-ended Fabry-Perot ring cavity. In the impedance-matched case such an interferometer can act as an all-reflective ring mode cleaner. It is further shown that in the highly undercoupled case almost complete separation of carrier power and phase signal from a cavity strain can be achieved.

Demonstration of three-port grating phase relations.

We experimentally demonstrate the phase relations of three-port gratings by investigating three-port coupled Fabry-Perot cavities. Two different gratings that have the same first-order diffraction efficiency but differ substantially in their second-order diffraction efficiency have been designed and manufactured. Using the gratings as couplers to Fabry-Perot cavities, we could validate the results of an earlier theoretical description of the phases at a three-port grating [Opt. Lett. 30, 1183 (2005)].

Optical characterization of ultrahigh diffraction efficiency gratings.

We report on the optical characterization of an ultrahigh diffraction efficiency grating in a first-order Littrow configuration. The apparatus used was an optical cavity built from the grating under investigation and an additional high-reflection mirror. The measurement of the cavity finesse provided precise information about the grating's diffraction efficiency and its optical loss. We measured a finesse of 1580 from which we deduced a diffraction efficiency of (99.635+/-0.016)% and an overall optical loss due to scattering and absorption of just 0.185%. Such high-quality gratings, including the tool used for their characterization, might apply for future gravitational wave detectors. For example, the demonstrated cavity itself presents an all-reflective, low-loss Fabry-Perot resonator that might replace conventional arm cavities in advanced high-power Michelson interferometers.

Input-output relations for a three-port grating coupled Fabry-Perot cavity.

We analyze an optical three-port reflection grating by means of a scattering matrix formalism. Amplitude and phase relations among the three ports, i.e., the three orders of diffraction, are derived. Such a grating can be used as an all-reflective, low-loss coupler to Fabry-Perot cavities. We derive the input-output relations of a three-port grating coupled cavity and find distinct properties that are not present in two-port coupled cavities. The cavity relations further reveal that the three-port coupler can be designed such that the additional cavity port interferes destructively. In this case the all-reflective, low-loss, single-end Fabry-Perot cavity becomes equivalent to a standard transmissive, two-port coupled cavity.

Limits on gravitational-wave emission from selected pulsars using LIGO data.

We place direct upper limits on the amplitude of gravitational waves from 28 isolated radio pulsars by a coherent multidetector analysis of the data collected during the second science run of the LIGO interferometric detectors. These are the first direct upper limits for 26 of the 28 pulsars. We use coordinated radio observations for the first time to build radio-guided phase templates for the expected gravitational-wave signals. The unprecedented sensitivity of the detectors allows us to set strain upper limits as low as a few times 10(-24). These strain limits translate into limits on the equatorial ellipticities of the pulsars, which are smaller than 10(-5) for the four closest pulsars.

Low-loss grating for coupling to a high-finesse cavity.

A concept for a low-loss all-reflective cavity coupler is experimentally demonstrated at a wavelength of 1064 nm. A 1450-nm period dielectric reflection grating with a diffraction efficiency of 0.58% in the - 1st order is used in the 2nd-order Littrow configuration as a coupler to form a cavity with a finesse of 400. The application of such reflective low-loss cavity couplers in future generations of gravitational-wave detectors and implementation issues are discussed.