Molecular laser stabilization at low frequencies for the LISA mission

Abstract

We have developed a 532 nm iodine stabilized laser system that may be suitable for the LISA mission (Laser Interferometer Space Antenna) or other future spaceborne missions. This system is based on an externally frequency-doubled Nd:YAG laser source and uses the molecular transfer spectroscopy technique for the frequency stabilization. This technique has been optimized for LISA: compactness (less than 1.1×1.1m2), vacuum compatibility, ease of use and initialization, minimization of the number of active components (acousto-optic modulators are both used for frequency shifting and phase modulating the pump beam). By locking on the a10 hyperfine component of the R(56)32-0 transition, we find an Allan standard deviation (σ) of 3×10-14 at 1 s and σ<2×10-14 for 20s≤τ≤103s. In terms of linear spectral density, this roughly corresponds to a stability better than 30Hz/Hz between 10-2 and 1 Hz with a stability decrease close to 1/f below 10 mHz

Iodine based optical frequency reference with 10^&#x2212;15 stability

“…Since their development in the 1990s [2], [3], numerous setups using modulation transfer spectroscopy (MTS) [4] have been realized in the last decades reaching frequency stability of 4 · 10 −15 at 200 s [5]. Compact and simplified versions have been investigated with respect to space missions as well [6]- [8].…”

A new RF frequency standard design based on a beat note between longitudinal modes of a frequency locked CW-laser

“…As the result the frequency-doubled radiation of the Nd:YAG stabilized by locking to the component a 10 of the transition 32-0, R(56) in molecular iodine was recommended by the International Committee of Weights and Measures for the practical realization of the meter and as a secondary frequency standard [Quinn]. Contemporary optical frequency standards demonstrate 15, 16 frequency stability of 10 -15 order at the integration time of 100 s and it was submitted on iodine-stabilized solid-state lasers for compact applications [16][17][18] which is evidence that iodine-stabilized lasers are still promising frequency standards for compact applications.…”

Saturation spectroscopy of iodine in hollow-core optical fiber

“…Iodine vapor has played a prominent role in the frequency stabilization of lasers over many years because it exhibits a large number of intrinsically narrow spectral lines across a large fraction of the visible and near-IR spectrum. Some of the best performing vapor-cell frequency standards have used iodine in large-diameter (∼ 10 cm) and long (∼ 1 metre) vapor cells [1][2][3][4][5][6]. The large diameter minimizes broadening associated with transit of the molecules through the probing laser beam, while the long length allows operation at low pressures, thereby avoiding collisional broadening, while still demonstrating strong absorption features.…”

“…This long spatial interaction allows for strong absorption, which delivers a high signal to noise ratio, while simultaneously minimising the density of the molecules, and thereby the pressure broadening. Furthermore, for both spectroscopy and frequency-standards work, it is a common desire to circumvent Doppler broadening [3] effects. In this regard, the fiber approach offers a great advantage over cell-based techniques because it automatically ensures that there is a stable and effective overlap between the counter-propagating pump and probe lasers beams required for saturated absorption techniques.…”