High-precision thermal expansion measurements using small Fabry-Perot etalons

Abstract

Coefficient of thermal expansion (CTE) measurements using small Fabry-Perot etalons were conducted on high and low thermal expansion materials differing in CTE by a factor of nearly 400. The smallest detectable change in length was ~10 -12 m. The sample consisted of a mm-sized Fabry-Perot etalon equipped with spherical mirrors; the material-undertest served as the 2.5 mm-thick spacer between the mirrors. A heterodyne optical setup was used with one laser locked to an ~780 nm hyperfine line of Rb gas and the other locked to a resonance of the sample etalon; changes in the beat frequency between the two lasers as a function of temperature directly provided a CTE value. The measurement system was tested using the high-CTE SCHOTT optical glass N-KF9 (CTE = 9.5 ppm/K at 23 o C). Measurements conducted under reproducibility conditions using five identically-prepared N-KF9 etalons demonstrate a precision of 0.1 ppm/K; absolute values (accuracy) are within 2-sigma errors with those made using mechanical dilatometers with 100-mm long sample rods. Etalon-based CTE measurements were also made on a high-CTE (~10.5 ppm/K), proprietary glass-ceramic used for high peak-pressure electrical feedthroughs and revealed statistically significant differences among parts made under what were assumed to be identical conditions. Finally, CTE measurements were made on etalons constructed from SCHOTT's ultra-low CTE Zerodur ® glass-ceramic (CTE about -20 ppb/K at 50 o C for the material tested herein).

Numerical 2D And 3D Simulations of a Spherical Fabry–Pérot Resonator for Application as a Reference Cavity for Laser Frequency Stabilisation

“…These constants can vary across a wide range depending on the chosen supplier and material. Currently, the materials that could be used for laser frequency stabilisation application are the Corning ULE glass [14], Schott Zerodur glass [23], silica glass [24] and monocrystalline silicon [25], [26]. The basic mechanical parameters and zero expansion temperature, if inherit, are displayed in Table 2 As a reference and calculation starting point, we used the Corning ULE glass FP cavity with E=67.6 GPa, Poisson ratio p=0.17 and density ρ=2210 kg/m 3 .…”

A Dual Cavity Fabry–Perot Device for High Precision Doppler Measurements in Astronomy

“…Alternatively, optical-beat measurement with two lasers yields much better sensitivity when the cavity is used in reflection mode, i.e. PDH locking (Reiners et al, 2014;Davis et al, 2007). For example, a fractional change 10 −10 of the cavity length would induce a readily measurable frequency excursion of ∼ 40 kHz in the optical-beat signal obtained with PDH setup using 780 nm laser.…”