Differential optical shadow sensor for sub-nanometer displacement measurement and its application to drag-free satellites.

We present a method for 3D sub-nanometer displacement measurement using a set of differential optical shadow sensors. It is based on using pairs of collimated beams on opposite sides of an object that are partially blocked by it. Applied to a sphere, our 3-axis sensor module consists of 8 parallel beam-detector sets for redundancy. The sphere blocks half of each beam's power in the nominal centered position, and any displacement can be measured by the differential optical power changes amongst the pairs of detectors. We have experimentally demonstrated a displacement sensitivity of 0.87nm/Hz at 1 Hz and 0.39nm/Hz at 10 Hz. We describe the application of the module to the inertial sensor of a drag-free satellite, which can potentially be used for navigation, geodesy and fundamental science experiments as well as ground based applications.

Measuring finesse and gas absorption with Lorentzian recovery spectroscopy.

In this paper we present a method for obtaining accurate finesse by recovering the Lorentzian profile of cavity resonances with a laser continuously locked to the cavity and apply it to weak gas absorption measurements. The technique was implemented on our noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) experimental setup. The measurement is performed in the cavity-locked regime, leading to high repeatability and easy automation. The technique involves locking the carrier to a fundamental mode of the cavity and sweeping a second set of sidebands across adjacent cavity modes. The Lorentzian line shape can be reconstructed through a measurement of the transmitted optical power of the auxiliary sidebands. The cavity finesse and gas absorption can then be extracted from these power measurements. The accuracy of our measurements was verified by comparing our results to those obtained with the cavity ring down technique. We demonstrate the use of the technique in spectroscopy by measuring the absorption coefficient of the R(14) line of 12C16O that has been well characterized by others. The gas absorption results obtained were consistent with other experimental measurements and theoretical calculations.

Pico-Kelvin thermometry and temperature stabilization using a resonant optical cavity.

Ultra-high sensitivity temperature sensing and stable thermal control are crucial for many science experiments testing fundamental theories to high precision. Here we report the first pico-kevin scale thermometer operating at room temperature with an exceptionally low theoretical noise figure of ~70pK/Hz at 1 Hz and a high dynamic range of ~500 K. We have experimentally demonstrated a temperature sensitivity of <3.8nK/Hz at 1 Hz near room temperature, which is an order of magnitude improvement over the state of the art. We have also demonstrated an ultra-high stability thermal control system using this thermometer, achieving 3.7 nK stability at 1 s and ∼ 120 pK at 104 s, which is 10-100 times more stable than the state of the art. With some upgrades to this proof-of-principle device, we can expect it to be used for very high resolution tests of special relativity and in critical point phenomena.