What Is Optical Metrology?

This blog explores what the meaning of optical metrology is and its applications. Further in the article, you’ll learn what are examples of optical metrology devices and their uses. 

What Are the Applications of Optics in Metrology?

To understand the answer to the question: “What is optical metrology,” we must first discuss optics. 

Optics is the study of the behaviors and properties of light. As the demand for high-precision tools increased, metrology manufacturers looked to various technologies to design high-accuracy measuring equipment. Optics was one of the areas they explored and found great success with. 

Today, optical sensors play a vital role in automated optical inspection (AOI) systems and image dimension measurement systems. Their addition to metrology devices enables specialists to measure more than mere dimensions and sizes. Excluding hardware defects, the only hindrance to optical measuring devices is quantum noise or laser noise, which can block a device from detecting light correctly. 

Given its incredible accuracy, optical metrology is prevalent in industries with strict compliance rules dictating tight tolerances (exceeding tolerances for parts used in manufacturing car engines, for example, can drastically lower product quality and compromise people’s safety):

  • Semiconductor and electronics manufacturing
  • Automobile manufacturing
  • Commercial goods manufacturing
  • Aerospace engineering
  • Defense
  • Telecommunications
  • Biomedical and life sciences

What Is the Meaning of Optical Metrology?

Bringing together the field of optics and metrology, we get optical metrology – a branch of metrology that uses light to collect data about an object’s physical properties. Optical metrology devices, therefore, use light to interact with an object and analyze those behaviors to measure physical properties like distances between two points, textures, dimensions, shapes, angles, etc. 

Optical metrology covers machines and techniques that leverage light properties like reflection, refraction, interference, diffraction, absorption, and transmission to determine high-precision measurements. Since these tools analyze how light behaves, they can measure a part’s properties without the components touching (non-contact measurement). This makes optical metrology ideal for measuring objects that are too big, heavy, or immovable in hard-to-reach places. 

What Are the Examples of Optical Metrology Equipment?

Now that you know the answer to “what is optical metrology,” let’s take a look at the most commonly used optical measuring devices:

  • Laser Measuring Devices: These are widely used in dimensional metrology because of their fast, precise measurements. These devices determine distances by measuring times-of-flight (the time elapsed between releasing a short laser pulse and the object reflecting the light), triangulation, phase shift methods, and interferometry. 
  • Optical Clocks: Optical clocks are known for their ultra-precise time measurements. They use optical frequencies, which are more stable and accurate than atomic clocks. The latter used to be the standard for time measurement, but today, optical clocks are being used to calibrate standard atomic clocks.  
  • Optical Profilometers: Metrology devices with optical profilometers are used for inspecting the surfaces of optical materials like glass, prisms, and mirrors. They are instrumental in semiconductor chip inspection and quality control. Optical profilometers are valuable when manufacturing parts whose specifications require a high-quality surface finish. Interferometers, interferometer microscopes, digital holographic microscopes, and triangulation sensors are examples of optical profilometers. If anyone wants to learn what the applications of optics in metrology are, these devices can demonstrate them. 
  • Optical Temperature Sensors: Metrology devices that use fiber optics can measure the temperatures of objects or the environment. What’s great about these sensors is they can also be used for disaster prevention. They are also insensitive to electromagnetic interference and can tolerate high and low temperatures.

Methods and Techniques

We briefly touched on how measuring devices use optics to determine accurate measurements when we discussed, “What is optical metrology?” This section takes a closer look at the techniques of optical metrology.

  1. Classical Interferometry: This technique creates light interference patterns using two or more light waves on an object. The device then analyzes the intensity and interference phases to measure dimensions, distances, surface irregularities, thickness, shape, refractive index, etc. Classical interferometry equipment can obtain microscopic and nanoscopic measurements.
  2. Confocal Microscopy: This is a type of image dimension measurement system because it creates high-resolution 3D images of the objects being measured. This technique focuses light beams on an object to get detailed images of the object’s surface. It can even capture subsurface features of opaque objects. 
  3. White Light Interferometry (WLI): This technique uses white light to create interference patterns and analyzes those patterns to measure surface distances. It also generates highly detailed 3D surface profiles with nanometer-level accuracy. 
  4. Moire Interferometry: This technique is a form of holographic interferometry wherein two transparent gratings are superimposed. Specialists then study the beat pattern formed and use the data to determine shape changes and deformations on an object. By analyzing interference patterns, moire interferometry devices can measure displacement, strain, shape, and material fault on an object.
  5. Optical Profilometry: Metrologists use one or more optical profilometers to measure surface topography by analyzing how light intensity varies as they change the illumination angle. This technique measures objects’ roughness, step heights, and other surface characteristics. 
  6. Digital Holographic Interferometry: This is one of the fastest, most accurate, and most universally applicable optical measuring techniques today. This technique employs a high-tech camera and digital holographic 3D measurement technology to capture height information from laser lights reflected or scattered by the object that is being measured. It uses multiple lasers with different wavelengths, which bring incredible detail to the holographic image of the object. This technique can be used to obtain measurements of large objects with submicron-level accuracy.

Achieve High-Speed, Non-Contact Measuring Capabilities with Optical Metrology Devices

Optical metrology can bring so much to an operation that relies heavily on metrology to maintain high production standards. It can speed up quality control and assurance processes, ensure compliance with regulatory requirements, and meet customers’ expectations. As a result, companies that utilize optical metrology to the fullest can enjoy long-term benefits that translate into orders, contracts, and sales. 

ATT Metrology Solutions, a Boeing and Airbus-certified metrology company, can help you acquire cost-effective optical metrology equipment to improve production processes and output. We offer consulting services, equipment rentals, top-tier engineering support, and a complete array of metrology services. 

Become the standard for precision and accuracy in your industry. Contact ATT Metrology Solutions to get started.