# Laboratory of Length Measurement Standards and Metrological Lasers

**Laboratory of Length Measurement Standards and Metrological Lasers**

The D.I.Mendeleyev Institute for Metrology (VNIIM) since 1950ies has been working on development of interferometers to reproduce and transfer the unit of length through wavelengths of standard radiation sources.

M.F.Romanova, A.I.Kartashev and others made a remarkable contribution to this activity. In 1954 Dr. Brzhezinsky developed a universal interference comparator to measure line scales. These works made the basis for the realization of the new definition of the metre through the krypton radiation wavelength, which was approved in 1960.

With the advent of stabilized lasers VNIIM launched the work on development of a He-Ne/I_{2} laser stabilized by the saturated absorption in I-127. Since 1983 it has been included into the State primary standard (SPS) of length.

The present definition of meter approved in 1983 combined the unit of length with that of time and frequency through one of fundamental constants - velocity of light, the value of which is accepted by international agreement. With the introduction of this definition an opportunity of realization of a single standard time, frequency and length appeared. With this purpose, VNIIM developed a standard setup on the basis of a Fabry-Perot interferometer to measure wavelength (frequency) ratios of He-Ne/CH_{4} laser ( *λ*=3.39 nm) included into the State Primary Measurement Standard (SPMS) of time and frequency (VNIIFTRI, Moscow) and He-Ne/I_{2} laser ( *λ*=0.63 nm) included into the SPMS of length.

In 1980 the State primary standard of plane angle was established, which was based on a laser-interference tester ensuring the realization and transfer of the unit of angle to standard autocollimators of goniometer system.

In 2000, a Nanometrology Centre was set up in the Laboratory to deal with measuring standards of small length intended for transferring the unit of length below 1 µm.

**Main Activities of the Laboratory:**

- Maintenance of the State Primary Measurement Standard (SPMS) of length of Russia intended for realization the length unit and its transfer to secondary measurement standards, reference measurement standards and to standard radiation sources.

This SPMS includes:- a source of standard radiation - a He-Ne/I
_{2}laser stabilized by saturated absorption in molecular I-127 - a setup to measure the wavelength ratio of radiation sources
- an interference comparator with a laser interference refractometer

- The length measurement range is 5-1.0 m
- The wavelength of the standard radiation source is 0.63299139822 µm, the standard deviation is 2 , the non-excluded systematic error is 1.5 . The unit of length is transferred from the SPS to material measures of length, linear displacement meters, and linear displacement transducers using the interference method with the total error (0,015 + 0,01
*L*) µm, where*L*is the length in meters.

- a source of standard radiation - a He-Ne/I
- Maintenance of the State Primary Measurement Standard of the plane angle.

The standard includes:- laser interference tester
- goniometer system
- dodecahedron quartz prism

^{o}, the standard deviation is 0.01’’, and the non-excluded systematic error is 0.02’’.

The primary standard is used for metrological investigations of secondary and working standards: autocollimators, polyhedral prisms and goniometric systems in accordance with GOST 8.016-81. - Development and manufacturing of new standard radiation sources:
- He-Ne/I
_{2}stabilized laser with a iodine cell, the wavelength 633 nm and stability 2^{.}10^{-11} - He-Ne/I
_{2}stabilized laser with a iodine cell, the wavelength 612 nm and stability 2^{.}10^{-11} - Nd:YAG/I
_{2}stabilized laser with a iodine cell, the wavelength 512 nm and stability 1^{.}10^{-11} - visible semiconductor lasers stabilized by an external standard, the stability 10
^{-7}

- He-Ne/I
- Development of means and methods for measurement assurance of length measuring instruments in submicron and nanometric ranges: optical, electronic, tunneling and atomic-force microscopes, profilometers, thickness gauges and surface roughness gauges. The Laboratory applies a laser interference diffractometer to standardize periodic gauges (diffraction gratings), a laser heterodyne interferometer to standardize step height standards, a high-resolution optical microscope to standardize line width standards, an atomic-force microscope.
- Performance of State testing of any length measures.

**International cooperation:**

Nine items have been published in the BIPM database of the CMC’s claimed by the Laboratory:

- Laser radiation: stabilized laser, absolute frequency, wavelength 633 nm
- End standards: gauge block, 1-100 mm
- End standards: length bar, long gauge block, 200-1000 mm
- Line standards: line scale, 0.01-1000 mm
- 1-D gratings: pitch L, 270-1000 nm
- Angle by circle dividers, optical polygon: face angle, 0-360
^{o} - Angle by circle dividers, rotary table, 0-360
^{o} - Angle instruments: autocollimator, 600''
- Surface texture, step height: laser heterodyne interferometer, micro-interferometer

The equivalence of our measuring standards to the international ones was approved by the international comparisons:

- lasers: CCL-K10, CCL-K11
- end gauges: CCL-K2, long gauge blocks by interferometry, 1999-2001
- angle: CCL-K3, angle standards, 2000-2002
- nanometrology:

CCL-S1, one-dimensional gratings, 1999-2000

CCL-S2, step height standards, 2000-2002

The Laboratory executes international contracts for manufacturing standard setups, stabilized lasers and interferometers developed at VNIIM. Stabilized He-Ne/J_{2}, Nd:YAG/J_{2} lasers have been manufactured recently for Bulgaria, South Korea, Belarus, Kazakhstan, as well as standard setups to standardize line scale and end gauges for Bulgaria, Kazakhstan and Uzbekistan. The research officers of the Laboratory can perform the orders for development and manufacturing of new length standards: measurement of different gauges and samples, displacements, wavelengths, etc. on the basis of various modifications of stabilized lasers and laser interferometers.

In 2000 the research officers of the Laboratory organized and held the international seminar “Modern methods and means for reproduction and transfer of the units of length and plane angle”. The metrologists from Russia, Ukraine and Estonia took part in it. Eight reports were presented by researchers from VNIIM.

**Contact:**

**Dr. Konstantin V. Chekirda** (Laboratory Head)