The Length Metrology Department carries out research for the maintenance and dissemination of the national length standard. The main research activities concern:
- realization and calibration of optical wavelength standards;
- realization of standards and measurement methods for dimensional metrology (gauge blocks, angles, diameters and roundness);
- nanometrology and co-ordinate measuring machines;
- dimensional metrology for space missions.
The activity of construction and maintenance of stabilised He-Ne lasers at different wavelengths for several research groups of the Institute has continued. The 532 nm wavelength standard has been improved.
Some components of the nanobalance facility (vacuum chamber, isolation system, electronics) have been revised in order to improve measurement performances. A contract with Alcatel Alenia Space Italia has been signed for transferring the facility to the Alcatel premises.
A detail of the nanobalance used to measure the force delivered by thrusters to be mounted on satellites.
Within the contract with Alenia-ESA "Laser Metrology and Optics Active Control", a Nd:YAG laser at 1064 nm has been frequency stabilized using as a reference a passive cavity, resulting in stability approaching 1·10-12. The laser has been used to measure length variations of a second cavity simulating one of the cavities to be mounted on the GAIA satellite.
Following an agreement with Alenia-ESA for the study of the mission "Satellite-satellite interferometer for the measurement of the Earth gravity field", an interferometer capable of measuring a distance of 10 km with a resolution of less than 1 nm has been designed. The mission will be sensitive to variations of the Earth's gravitational field caused by geoid deformations in the range of centimetres (glacier melting, continental plate motion, earthquakes).
Artist's view of the SSI mission: two satellites fly on the same orbit (350 km altitude) 10 km apart. The distance variations between two free falling masses are monitored by a heterodyne interferometer with a resolution of 1 nm on the frequency band (0.001- 0.1) Hz.
Within the "Euclid" project (Alenia-ASI collaboration), a heterodyne interferometer used for the stabilisation of a white light interferometer has been realised and tested showing a resolution of 1 nm on a band of 20 kHz.
A new XY-100 µm scanning device based on elastic hinges driven by bimorph piezoelectric plates has been developed for a sample-moving type Scanning Probe Microscope (SPM). The device has been designed to operate with samples to be imaged either in transmission or reflection mode by means of Near Field Optical Microscopy (SNOM) heads (co-operation with APE Research).
Optical-based methods have been investigated for critical dimension measurements on biomedical devices. A new approach based on the stitching of optical images taken at different orientations of the structure to be imaged has been experimented to overcome the limits of the optical methods with steep structures.
A drawing of the X-Y stage based on a parallelogram structure using elastic hinges.
The construction of a new measurement facility based on a mechanical comparator in an adiabatic chamber to be used for the study of phase correction in the absolute length measurements of gauge blocks has been completed.
With reference to the 1-D comparator (Moore M3) with interferometric measurement of displacements a new CMC for the calibration of precision linescales up to 300 mm has been submitted on the basis of the results of the NANO3 follow-up intercomparison.
A new metrological station, equipped with a novel autocollimator (angle amplifier) and a nano angle generator (NAG) capable of generating and measuring angles on a scale of 50 µrad with a resolution of less than 1 nrad, has been built.
Detail of the Nano Angle Generator (NAG): the moving arm made of Aluminium alloy, moved by a piezo-capacitive transducer, pivots around a steel elastic hinge.
The outcomes of the key comparison EUROMET.L-K2 on long gauge blocks have been disclosed, with very good results for the INRIM. This may be the basis for a reduction of the uncertainty in the relevant CMC.
After due preparation of the laboratory, a new top-class CMM (Co-ordinate Measuring Machine) has been bought and installed.
The new CMM has a working volume of (1200 X 1000 X 700) mm3. In the box, the probe touching a step-gauge.
It will be used for calibration of CMM specific artefacts (e.g. step gauges and ball plates), to provide INRIM internal traceability to different mechanical setups used in calibration and research, and to do CMM specific research.
The "ISO/TS 23165 GPS - Guide to the evaluation of CMM test uncertainty", whose project was led by IMGC, has been finalised. Based on this, a SIT guide on accreditation in the field of CMM performance verification has been developed and is close to finalisation; it includes first ever guidance for performing experimental auditing in this difficult field.
The Association "CMM Club Italia" -which operates under the aegis of the INRIM - has kept membership more than 70, issued its journal "Probing" and supplement "Probing Flash" regularly, and organised the two seminars InTeRSeC 10 (Milan, 2005-04-21) and InTeRSeC 11 (Modena, 2006-11-08).
A novel image spectrometer (or "hyperspectral" device) based on a modulated Fabry-Perot cavity has been built and the validity of the principle has been demonstrated. The instrument allows us to take a picture of an object where the spectrum of any pixel is recorded. Possible applications can be found in colorimetric, chemical, and thermal analysis, cultural heritages, fluorescence microscopy, life sciences.
The modulated Fabry-Perot cavity is the core of the image spectrometer. In the sketch below: the light (1) is collected by a lens (2) and focused on a CCD (4) passing through the modulated cavity (3). The recorded interferogram (6) is reconstructed (7) and transformed (FFT) to obtain the spectrum (8).
Within the CNR-SAV (Slovakia)collaboration to measure the Casimir force, an optical setup for the measurement of the vibration amplitude of a "tuning fork" sensor has been realized. The instrument allows us to measure displacements to the picometer level at the frequency of 32 kHz.
A device capable of measuring the power exchanged between two resistors not in thermal equilibrium has been built, opening up new possibilities in noise thermometry, and excess noise analysis.