Differential Plane Mirror Interferometer Research Articles

Traceable analysis of the performance of an ultra-fine positioning stage using a differential plane mirror interferometer

Traceable analysis of the performance of an ultra-fine positioning stage using a differential plane mirror interferometer

Roll angle measurement system based on differential plane mirror interferometer.

A precision roll angle measurement system based on differential plane mirror interferometer (DPMI) is proposed and the measurement principle has been analyzed theoretically in detail. This system uses DPMI with wedgy angle prism and wedgy angle reflector to produce diagonal symmetry of the two frequency beams. The residual of nanopositioning stage and roll angle system is less than 1 μrad, which has verified the correctness of the measuring principle. As result, the stability of the roll angle measurement system is satisfactory, and the average deviation of measurement experiments is less than 5 μrad.

High resolution and stability roll angle measurement method for precision linear displacement stages.

A method for high resolution roll angle measurement of linear displacement stages is developed theoretically and tested experimentally. The new optical configuration is based on a special differential plane mirror interferometer, a wedge prism assembly, and a wedge mirror assembly. The wedge prisms assembly is used as a roll angle sensor, which converts roll angle to the changes of optical path. The special interferometer, composed a polarization splitter plane, a half wave plate, a beam splitter, a retro-reflector and a quarter wave plate, is designed for high resolution measurement of the changes of the optical path. The interferometric beams are a completely common path for the adoption of the centrosymmetrical measurement structure, and the cross talk of the straightness, yaw, and pitch errors is avoided. The angle measurement resolution of the proposed method is 3.5 μrad in theoretical with a phase meter which has a resolution of 2π/512. The experimental result also shows the great stability and accuracy of the present roll angle measurement system.

Measurement of straightness without Abbe error using an enhanced differential plane mirror interferometer.

This paper presents an enhanced differential plane mirror interferometer with high resolution for measuring straightness. Two sets of space symmetrical beams are used to travel through the measurement and reference arms of the straightness interferometer, which contains three specific optical devices: a Koster prism, a wedge prism assembly, and a wedge mirror assembly. Changes in the optical path in the interferometer arms caused by straightness are differential and converted into phase shift through a particular interferometer system. The interferometric beams have a completely common path and space symmetrical measurement structure. The crosstalk of the Abbe error caused by pitch, yaw, and roll angle is avoided. The dead path error is minimized, which greatly enhances the stability and accuracy of the measurement. A measurement resolution of 17.5 nm is achieved. The experimental results fit well with the theoretical analysis.

High resolution heterodyne interferometer without detectable periodic nonlinearity

A high resolution heterodyne laser interferometer without periodic nonlinearity for linear displacement measurements is described. It uses two spatially separated beams with an offset frequency and an interferometer configuration which has no mixed states to prevent polarization mixing. In this research, a simple interferometer configuration for both retroreflector and plane mirror targets which are both applicable to industrial applications was developed. Experimental results show there is no detectable periodic nonlinearity for both of the retro-reflector interferometer and plane mirror interferometer to the noise level of 20 pm. Additionally, the optical configuration has the benefit of doubling the measurement resolution when compared to its respective traditional counterparts. Because of non-symmetry in the plane mirror interferometer, a differential plane mirror interferometer to reduce the thermal error is also discussed.

Development and characterization of a new instrument for the traceable measurement of areal surface texture

Modern manufacturing industry is beginning to benefit greatly from the ability to control the three-dimensional, or areal, structure of a surface. To underpin areal surface manufacturing, a traceable measurement infrastructure is required. In this paper, the development of a new traceable instrument for the measurement of areal surface texture is presented. The instrument uses a two-axis coplanar air-bearing slideway to move the measured surface beneath a stylus probe. The motion of the slideway is measured using linear and angular interferometers. The key to the new instrument is a novel probing system incorporating a cylindrical air-bearing guideway and an electromagnetic system to maintain a constant stylus force on the surface. The deflection of the stylus is measured using a differential plane mirror interferometer thereby minimizing the effect of any error motion in the metrology frame. The uncertainties of the instrument are calculated using a Monte Carlo approach and are evaluated to be 5 nm in the z axis and 16 nm in the x and y axes (all at k = 2). The results are given for the instrument and are compared to results from a traceable profile measuring instrument and a coherence scanning interferometer.

A neural network approach to correcting nonlinearity in optical interferometers

Real interferometers with phase quadrature detecting subsystems usuallydemonstrate nonlinearity with length measurements. Conventional nonlinearitycorrection techniques based on elliptical fittings are reviewed and their limitationis investigated using computer simulations. A new approach based on neuralnetworks (NNs) for correcting nonlinearity in optical interferometers for lengthand displacement measurements is introduced, the principle of which is given(including the architecture of the NN) and its training method. An experimentalsetup was developed based on a differential plane-mirror interferometer fortesting the proposed method. The experimental results show that this newapproach is successfully applicable to real, noisy interferometer signals.

The METAS 1 kg vacuum mass comparator - adsorption layer measurements on gold-coated copper buoyancy artefacts

A new 1 kg mass comparator has been designed at the METAS to be used for research activities in comparing 1 kg mass and buoyancy artefacts between air and vacuum environments. The instrument is a single-pan mass comparator using electromagnetic force compensation. A novel feature is a wire suspension system for the balance beam. This suspension, together with the differential plane mirror interferometer used for the alignment, provides a very high resolution of 50 ng. The reproducibility of the comparator in vacuum is 0.8 µg. The vacuum mass comparator was first characterized and then used for the determination of the adsorption layers on special 1 kg gold-coated copper buoyancy artefacts with large variations in surface area. The adsorption layer information is used to correct the mass value (determined in air) for a watt balance experiment in which measurements on a gold test mass are performed under vacuum.

The use of x-ray interferometry to investigate the linearity of the NPLDifferential Plane Mirror Optical Interferometer

The x-ray interferometer from the combined optical and x-rayinterferometer (COXI) facility at NPL has been used to investigate theperformance of the NPL Jamin Differential Plane Mirror Interferometer whenit is fitted with stabilized and unstabilized lasers. This Jamin interferometeremploys a common path design using a double pass configuration and one fringeis realized by a displacement of 158 nm between its two plane mirrorretroreflectors. Displacements over ranges of several optical fringes weremeasured simultaneously using the COXI x-ray interferometer and the Jamininterferometer and the results were compared. In order to realize the highestmeasurement accuracy from the Jamin interferometer, the air paths wereshielded to prevent effects from air turbulence and electrical signalsgenerated by the photodetectors were analysed and corrected using anoptimizing routine in order to subdivide the optical fringes accurately. Whenan unstabilized laser was used the maximum peak-to-peak difference betweenthe two interferometers was 80 pm, compared with 20 pm when the stabilizedlaser was used.

Verification of the sub-nanometric capability of an NPL differential plane mirror interferometer with a capacitance probe

A differential plane mirror interferometer developed at the NPL has been built into a system designed to calibrate and certify displacement transducers. Two electrical signals generated from the optical outputs of the interferometer and a voltage output of the transducer to be calibrated are read by a computer and mathematically analysed in order to calculate the proportionality and linearity of the displacement transducer. In order to realize the highest measurement accuracy from the interferometer the interferogram signals are analysed and corrected by an optimizing routine in order to interpolate the fractioning of the optical fringes accurately. Without computer optimization of the signals a standard deviation of measurement of a few nanometres is typical, whereas after optimization this is reduced to a fraction of a nanometre. The interferometer has been used to calibrate a high-precision capacitance probe and the results of these measurements are shown and discussed.