Optical metrology

Optical metrology is the science and technology of measurement with light. It involves the use of optical instruments to enable an uncountable number of applications. 

It is possible to accurately measure dimensions, shapes, roughness or refractive indices, among many others. Manufacturing, quality control or scientific research, are fields that make an intensive use of optical metrology solutions.

There are several optical metrology techniques with different characteristics in terms of field-of-view, vertical and spatial resolution, range of measurement or speed. For example, interferometry is a technique that uses the interference of light waves to measure distances and dimensions. It usually provides a high vertical and spatial resolution but within a narrow field of view. Instead, LIDAR provides lower vertical and spatial resolution but offers a wide field of view and short computing times.

Optical metrology is becoming increasingly important in a wide variety of industries, including manufacturing, aerospace, and medical diagnostics.

Here are some techniques used in optical metrology:

• Interferometry: Interferometers use the interference patterns of light waves to measure distances, surface profiles, and optical components' quality. There are several types of interferometric setups that are best suited to different applications (White Light Interferometry, Moiré Interferometry, Shearography, etc.)
• Optical Coherence Tomography (OCT): OCT is a non-invasive imaging technique used in medical and industrial applications to obtain cross-sectional images of tissues, structures, and surfaces.
• Confocal profilometry: Confocal technology is able to measure the surface height converting conventional images into optical sections where the signal is preserved for those areas within the depth of focus of the objective, improving the image contrast and the lateral resolution and system noise.
• LIDAR: Light Detection and Ranging (LIDAR) is a remote sensing technology that uses laser pulses to measure distances to objects, generating precise three-dimensional maps or models of landscapes, terrains, or objects.
• Structured light patterns: A light pattern carefully arranged in light and dark areas is used in 3D scanning and computer vision to capture surface information and create depth maps of objects or scenes.
• Phase-Shifting Interferometry: This technique measures phase differences in interferometric patterns, which are used for surface profiling, wavefront analysis, and displacement measurements. 
• Photogrammetry: Photogrammetry is a technique for obtaining precise measurements and three-dimensional data of objects or environments by analyzing photographs or digital images taken from multiple angles.
• Holography: Holography creates 3D images called holograms, which are used in art, security, and scientific applications for recording and visualizing objects or scenes.
• Ellipsometry: Ellipsometers measure the change in polarization of light after interaction with a sample to determine properties like thickness, refractive index, and film quality.
• Speckle metrology: Speckle metrology is an optical non-contact whole field technique that provides the means to measure; deformation and displacement, object shape, surface roughness, vibration, and dynamic events, on rough surfaces and with a sensitivity of the order of a light wavelength.

Photonics is a powerful tool for optical metrology, and it is continuing to play an increasingly important role in this field.