Active suppression of air refractive index fluctuation using a Fabry–Perot cavity and a piezoelectric volume actuator

Abstract

Air refractive index fluctuation (Δn(air)) is one of the largest uncertainty sources in precision interferometry systems that require a resolution of nanometer order or less. We introduce a method for the active suppression of Δn(air) inside a normal air-environment chamber using a Fabry-Perot cavity and a piezoelectric volume actuator. The temporal air refractive index (n(air)) at a local point is maintained constant with an expanded uncertainty of ~4.2 × 10(-9) (k = 2), a sufficiently low uncertainty for precise measurements unaffected by Δn(air) to be made inside a chamber.

Dimensional stability validation and sensor calibration with sub-nanometer accuracy

“…comb usage in [7,14]). Ambient climate conditions, such as humidity effects [15] or pressure fluctuations [16] limit the ultimately achievable measurement uncertainty. Recording and control of environmental parameters will be improved.…”

The Applications of the Heterodyne Interferoemetry

“…There are many methods can construct the optical frequency shift such as rotation or moving grating method [16,17], accousto-optical modulator (AOM) [18,19], electro-optical modulator (EOM) [20,21], and modulating two slightly different wavelengths of laser diodes [22]. Suzuki and Hioki [16] proposed the idea of moving grating method for constructing the heterodyne light source in 1967.…”

“…An acousto-optic modulator (AOM) uses the acousto-optic effect to diffract and shift the frequency of the light [18,19]. The piezoelectric transducer attaches to the quartz and the [17].…”

Refractive Index Compensation in Over-Determined Interferometric Systems

“…Other approaches represent completely different methods for determination of the refractive index of air, for example through the speed of sound in the ultrasonic frequency range [36]. Also, the control of the refractive index which is kept constant was suggested [37]. We proposed a concept with an over-determined counter-measuring interferometric displacement measuring setup [38–40] where the length in one axis was measured by two interferometers with their position fixed to a highly stable mechanical reference.…”