Transportable clock laser system with an instability of 1.6 × 10⁻¹⁶

Abstract

We present a transportable ultra-stable clock laser system based on a Fabry–Perot cavity with crystalline Al0.92Ga0.08As/GaAs mirror coatings, fused silica (FS) mirror substrates, and a 20 cm-long ultra-low expansion (ULE) glass spacer with a predicted thermal noise floor of mod σy = 7 × 10−17 in modified Allan deviation at one second averaging time. The cavity has a cylindrical shape and is mounted at 10 points. Its measured sensitivity of the fractional frequency to acceleration for the three Cartesian directions are 2(1) × 10−12 /(ms−2), 3(3) × 10−12 /(ms−2), and 3(1) × 10−12 /(ms−2), which belong to the lowest acceleration sensitivities published for transportable systems. The laser system’s instability reaches down to mod σy = 1.6 × 10−16

Compact, Portable, Thermal-Noise-Limited Optical Cavity with Low Acceleration Sensitivity

“…Previous work on cavities ranging from 5 cm to 20 cm in length with cubic, spherical, and cylindrical geometries have demonstrated passive (without vibration feedforward correction) acceleration sensitivities in the 10 −11 𝑔 −1 to mid 10 −10 𝑔 −1 range [18,20,22,23,[44][45][46]. We simulated and measured the acceleration sensitivity of our FS-ULE cavity under a 2g static flip test [18,20,44].…”

“…The search for laser frequency reference cavities that are rigidly held, have reduced size and weight, and can operate in harsh and unpredictable environments has led to the development of both solid-state dielectric resonators [13][14][15][16][17], and compact vacuum-gap FPs [6,[18][19][20][21][22][23]. Solidstate dielectric resonators are impressively small, typically millimeter-scale, and, in some cases, can be manufactured at scale.…”

A high-power-handling deformable mirror system employing crystalline coatings

“…Extensive development efforts have led to the realization of large-area mirrors (now up to 100 mm in diameter) with a unique combination of part-permillion (ppm) levels of optical losses (including both optical scatter, S and absorption, A, with a current performance best of S+A < 2 ppm), intrinsically low stress, and a relatively high thermal conductivity (interface limited at 20-30 Wm -1 K -1 , with in-plane thermal conductivity up to 70 Wm -1 K -1 ), and low elastic losses yielding minimal Brownian noise for precision interferometry [8][9][10][11]. These coatings are now routinely employed in ultrastable optical reference cavities for optical atomic clocks [12] and are being actively investigated for future gravitational wave detectors [13].…”

Photo-birefringent effects of crystalline coatings in ultra-stable cavities

“…A demonstration has been reported on a transportable room-temperature cavity for strontium optical clocks. 12 Because the coating is only available in the infrared spectral region, this demonstration and other experiments indicate a convenient wavelength conversion method that uses frequency doubling to interrogate the transitions of strontium atoms. [12][13][14] In this work, we observe an unbalanced photo-birefringent effect in our 30-cm-long room-temperature ULE cavity, it introduced by the anisotropy of crystalline coatings, which is first reported on a room-temperature cavity to our knowledge.…”