Length and Dimensional


Length and Dimensional Metrology primarily covers the measurement of length, angle, and geometric relationships. It is important in supporting product quality control of the industry sectors, which will bring about higher productivity. The services by this lab extend from nano-, micro-, to macro-technology, which are aligned with internationally accepted quality system.

The SI of length is metre (m) and is realized at NMC using Iodine stabilised He-Ne laser and optical frequency comb with accuracy level up to 1x10-13Being an active member at APMP TCL and CIPM CCL, NMC stays updated in the development of the length community regionally and internationally.

Laser Frequency Standard - Optical Frequency Synthesiser

The standard is based on a femtosecond fibre laser frequency comb. The output of the laser is a sequence of pulses that are essentially copies of the same pulse separated by the round trip time. The spectrum of such a pulse train is a frequency comb separated by the repetition rate (the inverse of the round trip time) of the laser. The repetition rate and the carrier-envelope offset frequency of the frequency comb are locked to a 10 MHz reference signal from a Hydrogen Maser, the primary frequency standard.

NMC is able to calibrate absolute frequency of lasers with wavelength from 530 nm to 2100 nm. The best measurement uncertainty is in the order of a few hundred Hz.


Laser heads


Wavemeter


Optical frequency synthesiser

Nano-scale Standards

The Atomic Force Microscope (AFM) is one of the most powerful tools for measurement of surface texture of micro- and nano-structures at sub-nanometre resolution, with wide applications in nanotechnology. The metrological AFM provides direct traceability lacked by commercial AFMs through three laser interferometers installed in its metrological frame. The system is also featured with a very large scanning range and small uncertainty. An optical probe can replace the AFM head in the system for non-contact measurement.

The system developed at NMC is able to calibrate nano-scale artefacts with low measurement uncertainty of 5 nm or smaller.



Large range metrological AFM

Micro-CMM Standard for Complex Geometry

The micro coordinate measuring machine (CMM) is built on a highly accurate, air-bearing kinematics structure with linear drives and an active air damping base. The air bearings allow the platform sliding with almost no friction across the measuring table. Ultra-precise glass-ceramic scales are used as the length measuring systems for all three axes. The machine is equipped with both micro touch probes and an optical probe.

With the combination of both types of probes, NMC is able to provide accurate measurements of 2D and 3D features of tiny components with a volumetric measurement uncertainty of (0.25 + L/666) μm, where L is in mm.



Micro coordinate measuring machine


Fixtures and parts

2-D Vision Standard On Image Pattern

The standard is able to provide calibration on image pattern with sub micrometer uncertainty. It is built on an air-bearing kinematics structure with ball screw drives. Glass encoders with a thermal expansion coefficient of nearly zero are used as the length measuring systems for all three axes. The temperature inside the machine is well controlled with the prevention of heat generation from the motor and controlling the temperature of the compressed air. The traceability of this machine is built by verifying its performance against a laser interferometer.

This capability at NMC is able to provide:
- single axis measurement uncertainty at (0.25 + L/1000) μm, L in mm
- 2D measurement uncertainty: (0.5 + 2L/1000) μm, L in mm



2D vision measuring machine

Aspherical & Free Form Surface Standards

The standard is based on a precision stage, with position measured by He-Ne laser interferometers that provide direct traceability to the SI metre. The stylus moves in Z-axis and its contact with the part is controlled using a detection scheme similar to atomic force probe.

The main applications of the system developed at NMC is for the measurements of aspherical lens, fresnel optics and free form surfaces. The best measurement uncertainty is ~50 nm.



Aspherical & free form surface standard

Spherical Surface Standard

The standard is based on a laser Fizeau phase-shifting interferometer. The He-Ne laser beam is expanded to a collimated beam of 102mm diameter. Two reflection beams coming from a reference surface of transmission sphere/flat, and the part under test respectively recombine inside the interferometer and produce a fringe pattern. The form of the part under test is built on the image of the interference fringes that are captured by a CCD camera during the vertical PZT scanning process.

The system set up at NMC is for the calibration of lens, lens molds, hemispheres, precision spheres etc., with surface measurement uncertainty of λ/20 (~32 nm)



Spherical surface standard

Large Range Stylus Form Standard

The profilometer set up comprises an active anti-vibration mounts and an environmental enclosure to reduce the floor-borne or air-borne vibrations. The movement of the gauge is measured by a phase grating interferometer, through which, a high resolution measurement in a range of 25 mm can be achieved.

The development done at NMC is capable of high precision measurement of surface roughness, waviness, contour and form. The form measurement uncertainty is ~200 nm.



Large range stylus form standard


Surface roughness specimens

Roundness & Cylindricity Standards

The standard set up sits on an active anti-vibration isolation support frame to isolate against the floor borne vibration. Its rotary table is based on a diamond turned air-bearing spindle, which can achieve nanometric accuracy for both radial and axial performance.

The measurement uncertainty provided by NMC for roundness measurement is 10 nm + 0.3 nm/mm.



Roundness & cylindricity standard

Laser Confocal Microscope For Surface Standards

The system measuring objective is moved by a small vertical step, and the signal corresponding to the objective's position is measured by a displacement transducer.

The system developed at NMC is capable of carrying out surface profile measurement with sub-micrometre accuracy on both smooth and rough surfaces. The measurement uncertainty is ~0.2 µm.



Laser confocal microscope


Non-contact surface profile measurements