Long gauge blocks

A interferometer combining white light and laser light is a great tool for interferometric calibration of long gauge blocks. The VTT MIKES device uses white light interference together with laser light interference to determine the initial length of the gauge. As a result, calibration does not require prior information on the length of the gauge block, as with most other long gauge block interferometers. The exact mean length and surface flatness are obtained with nine-point phase stepping. The temperature of the gauge block is measured with four Pt100 sensors and the thermal expansion is compensated for. Air temperature, pressure and humidity are measured and the length is calculated from the refractive index obtained from the environmental sensors. The operating principle of the device is described in [1], after which the device has been updated to use nine-point phase stepping to measure the mean length and the variation of the length. The interferometer can also be used for measurements in the so-called double-ended configuration [2].

Measurement uncertainty ​in long gauge block calibrations.

Measuring rangeExpanded 
uncertainty (k=2)
​100...1000 mmU = Q[30; 0.11L] nm L in millimetres,  Q[x; y]=√(x2+y2)
IMG_8401_uusi kuva pitkiin mittapaloihin.jpg  

Interferometer for measurement of long gauge blocks at VTT MIKES.

The performance of the VTT MIKES interferometer is tested by regular participation in international comparisons organized by EURAMET and CCL. The latest comparison is EURAMET.L–K1.2011 [3]. The results of the comparison supported the reported measurement uncertainty of VTT MIKES long gauge block interferometer. 

 [1]  E. Ikonen and K. Riski, Gauge-block Interferometer based on one stabilized laser and a white-light source, 
30, 95–104 (1993). https://doi.org/10.1088/0026-1394/30/2/006.

 [2]  A. Lassila and V. Byman, Wave front and phase correction for double-ended gauge block interferometry,   
       Metrologia 52, 708–716 (2015). https://doi.org/10.1088/0026-1394/52/5/708.

 [3]  M. Matus et. al, Measurement of gauge blocks by interferometry, Metrologia 53, 04003 (2016).


  • Antti Lassila, Team leader, tel. +358 40 767 8584, email antti.lassila(at)vtt.fi

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