C. Braxmaier

High-resolution Doppler-free molecular spectroscopy with a continuous-wave optical parametric oscillator.

We present a reliable, narrow-linewidth (100-kHz) continous-wave optical parametric oscillator (OPO) suitable for high-resolution spectroscopy applications. The singly resonant OPO with a resonated pump is based on periodically poled lithium niobate crystal and features a specially designed intracavity etalon, which permits precise tuning to any desired wavelength in a wide range. We demonstrate Doppler-free spectroscopy of a rovibrational transition of methane at 3.39 mum.

Picometer and nanoradian optical heterodyne interferometry for translation and tilt metrology of the LISA gravitational reference sensor

The Laser Interferometer Space Antenna (LISA) aims at detecting gravitational waves by referencing heterodyne interferometry to free-flying (inertial) proof masses, located at the corners of a triangle with 5 million kilometers arm length. The position of each proof mass with respect to the associated satellite must be measured with 1 pm Hz−1/2-sensitivity in translation measurement and below 10 nrad Hz−1/2-sensitivity in attitude. In this paper, we present a compact heterodyne interferometer utilizing polarizing optics combined with the method of differential wavefront sensing (DWS) serving as a demonstrator for a complete optical readout system of the proof mass translation and attitude aboard the LISA satellites. Our interferometer is based on a highly symmetric design, where reference and measurement beam have similar optical paths and equal polarization and frequency. Intensity stabilization of the laser radiation, phaselock of the laser frequencies at the fiber outputs and a digital phase measurement based on a field programmable gate array (FPGA) are implemented to achieve noise levels below 10 pm Hz−1/2 and 10 nrad Hz−1/2, respectively, for frequencies >10−2 Hz.

Ultrahigh long-term dimensional stability of a sapphire cryogenic optical resonator

We report on the ultrahigh long-term dimensional stability of a crystalline cryogenic optical resonator (CORE) cooled to liquid-helium temperature. The frequency of a Nd:YAG laser stabilized to a CORE was compared over long times with an independent laser system, a frequency-doubled Nd:YAG laser stabilized to a hyperfine line of molecular iodine at 532 nm. Over a 6-month period the drift was less than 3 kHz. The dimensional stability of the CORE is thus more than 2 orders of magnitude higher than that of the best ultralow-expansion glass ceramic cavities at room temperature.

Experimental limits for low-frequency space-time fluctuations from ultrastable optical resonators

It has been suggested that space-time might undergo fluctuations because of its intrinsic quantum nature. These fluctuations would pose a fundamental limit to the ability of measuring distances with arbitrary precision, beyond any limitations due to standard quantum mechanics. Laser interferometers have recently been proposed as being suited for a search for the existence of space-time fluctuations. Here we present results of a search for space-time fluctuations of very low fluctuation frequencies, in the range from 1 \ensuremath{\mu}Hz to 0.5 Hz. Rigid optical interferometers made out of sapphire and operated at cryogenic temperature were used. We find an upper limit of

High resolution Doppler-free spectroscopy of molecular iodine using a continuous wave optical parametric oscillator

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Picometer resolution interferometric characterization of the dimensional stability of zero CTE CFRP

for the normalized distance noise spectral density at 6 \ensuremath{\mu}Hz, and of

OPTICAL METROLOGY SUBSYSTEM OF THE LISA GRAVITATIONAL WAVE DETECTOR

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A high sensitivity heterodyne interferometer as a possible optical readout for the LISA gravitational reference sensor and its application to technology verification

above 5 mHz, and establish an experimental limit for the parameter of a recently proposed random-walk hypothesis.

A heterodyne interferometer for high resolution translation and tilt measurement as optical readout for the LISA inertial sensor

We report the application of an all solid-state optical parametric oscillator (OPO) system as a versatile light source for high resolution spectroscopy in the visible wavelength range. The new designed CW OPO showed a high frequency stability and a broad tuning range. We were able to perform Doppler-free saturation spectroscopy thereby resolving the hyperfine structure of molecular iodine at 580 nm. Possible applications and future improvements are discussed.

Optical fibers with interferometric path length stability by controlled heating for transmission of optical signals and as components in frequency standards

Highly stable but lightweight structural materials are essential for the realization of spaceborne optical instruments, for example telescopes. In terms of optical performance, usually tight tolerances on the absolute spacing between telescope mirrors have to be maintained from integration on ground to operation in final orbit. Furthermore, a certain stability of the telescope structure must typically be ensured in the measurement band. Particular challenging requirements have to be met for the LISA Mission (Laser Interferometer Space Antenna), where the spacing between primary and secondary mirror must be stable to a few picometers. Only few materials offer sufficient thermal stability to provide such performance. Candidates are for example Zerodur and Carbon-Fiber Reinforced Plastic (CFRP), where the latter is preferred in terms of mechanical stiffness and robustness. We are currently investigating the suitability of CFRP with respect to the LISA requirements by characterization of its dimensional stability with heterodyne laser interferometry. The special, highly symmetric interferometer setup offers a noise level of 2 pm/√Hz at 0.1Hz and above, and therefore represents a unique tool for this purpose. Various procedures for the determination of the coefficient of thermal expansion (CTE) have been investigated, both on a test sample with negative CTE, as well as on a CFRP tube specifically tuned to provide a theoretical zero expansion in the axial dimension.