Humidity coefficient correction in the calculation equations of air refractive index by He–Ne laser based on phase step interferometry

A review of state-of-the-art 1D length scale calibration instruments

“…Bönsch and Potulski further refined the modified Edlén equation, specifically the humidity term, based on refractometer measurements reporting standard uncertainties of 1 × 10 −9 and a total uncertainty for refractive index including sensor uncertainties of 1 × 10 −8 for measurement in humid air (the uncertainty in dry air is less) [54]. This work was continued by Chen et al [55] who further improved the humidity term by making measurements with three stabilised lasers in a phase step interferometer. This last work reports the highest accuracy of any of the empirical equations, stating that it is superior to that reported by Bönsch and Potulski without giving a numerical value, though as yet no instrument has been reported as utilising it.…”

Diffractive Sensor Elements for Registration of Long-Term Instability at Writing of Computer-Generated Holograms

“…Long duration of large CGH writing is inherent to all the mentioned types of SLLSs. Following sources of instability can have a significant impact on the long writing process: Drift of various mechanical units of the system (change of air bearings gaps, thermal expansion) due to changes in their temperatures [ 15 ]; Focused laser beam drift (due to instability of beam pointing diagram and optical axis of focusing lens moved by the electrodynamic or piezoelectric actuator of the autofocus system); A change in the wavelength of a laser interferometer that controls linear displacements, which can be not fully compensated when using the formula for dependence of refractive index on the temperature, pressure and humidity of the ambient air [ 16 ]; Displacement of the hologram substrate on the spindle faceplate or linear displacement table due to sharp acceleration or vibration at insufficient mechanical fixation. …”

“…A change in the wavelength of a laser interferometer that controls linear displacements, which can be not fully compensated when using the formula for dependence of refractive index on the temperature, pressure and humidity of the ambient air [ 16 ];…”