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Application of Structured light projection

Structured light projection (SLP) is a non-contact optical metrology method which can measure to the micron scale. The technique involves projecting a known light irradiance pattern onto the surface under test, which then scatters the light creating a 3D image on the surface. The scattered light is recorded by one or more cameras and the scattered pattern is compared to the modeled projected pattern to determine the surface profile.  For a test surface to be measurable with the SLP technique, it must be a scattering surface over the spectrum of light that is projected on to it. Typically, visible light is used for a SLP device, as the light sources and projection mechanisms are more straightforward to achieve, although another wavelength can be used when necessary. Figure below demonstrates a projected fringe pattern that was captured by a camera, and the corresponding surface that was calculated. Surface height accuracy The surface height features that are measurable by the SLP techni
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Applications of Machine vision

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Machine vision is a very wide area, encompassing practically any system that uses a camera and processing unit to perform an inspection or measurement task. The hardware is typically off-the-shelf components (e.g., telecentric camera) with potentially custom software written to control the devices. The systems help automate processes, speed up manufacturing, and increase yield by replacing a task done by a human that can fatigue and make mistakes. Surface defect inspection Machine vision systems have become widely used in production environments for their automation of an operator’s manual inspection process. Such systems can be used to quantify the geometric dimensions of mechanical features [12]. More recently, machine vision has been applied to the assessment of optical surface quality (scratch dig), typically a task performed by an expert operator. The automation of surface quality inspection affords a repeatable and standardized assessment at the cost of single-purpose systems tha
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What is Reflective Coatings?

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A very important coating is a reflective version that produces mirrors, coated on the front or back transparent optical material or on the front surface of metallic substrates. This kind of coating reflects a high amount of energy (light in the visible range), which is important for its intended use. As the AR coatings, reflective coatings are also designed for different regions of the spectrum. Aluminum is the most common metallic coating material. Table below shows different kinds of coating materials and the percentage of reflection in different wavelengths. The other type of optical coating used for reflection purposes is the dielectric coating, which uses thin layers of transparent dielectric materials with different refractive indices (e.g., magnesium fluoride or calcium fluoride) and various metal oxides that are deposited onto the optical substrate.
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What is AR Coating?

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The principle of reducing reflection and increasing transmission of light works due to the "interference" phenomenon. In the visible spectrum range, each surface of an optical glass element reflects about 4% energy; thus, if 100% energy enters the first surface, about 92% comes out of the second surface. This is bad for optics. Table below shows two examples of what happens if more elements (and more surfaces) are in the optical assembly. The reflection of light from one surface is given by where N0 is the refractive index of the first medium, and N is the refractive index of the second medium. When the first medium is air (N0 = 1), the reflection from the uncoated surface can be expressed by For normal incidence light (perpendicular to the surface), the reflection can be calculated by where m0 is the number of surfaces, and n is the refractive index of the medium (material). But how do the interference phenomena work? The addition of a layer with a thickness one-quarter of t
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Classification of Optical Coating

Optical-element surface coatings have an important task in the functionality of optical elements and optical assemblies. In most cases they enable the elements or assemblies to perform according to systems requirements. Coating requirements, specifying mostly optical and durability properties, are defined in the drawing of the element to be coated and in a special coating specification. Optical coatings can be classified as follows: According to its function Reflective coatings (metallic and dielectric), Antireflective (AR) coatings (single- or multi-layer, narrow- or broadband), Transparent conductive coatings, Beamsplitters, Filters (high-, low-, and band-pass), High-efficiency (HE) coatings, High durability (HD) coatings, and Diamond-like carbon (DLC) coatings; According to the spectral wavelength range Ultraviolet: ~0.2–0.4 mm, Visible: ~0.40–0.75 mm, Near infrared (NIR): ~0.75–3.00 mm, Mid infrared: ~3–5 mm, and Far infrared: ~5–20 mm. Reflective coatings can be classified in the
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What is Resolving power (or resolution)?

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The resolving power (or resolution) is the ability of an optical system to separate two closely spaced point sources, i.e., resolve detail in an object being imaged at the nominal distance. A resolution test is a visual test of the resolution limit (resolving power) of an imaging optical system. The test is conducted by viewing an illuminated-resolution test pattern comprising groups of black and white bars with 100% contrast. Each group represents a different spatial frequency in cycles per millimeter (cy/mm). The largest frequency that cannot be resolved defines the resolution limit of the tested system.
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What is Minimum resolvable contrast?

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The MRC function is the visible (VIS) imaging system equivalent to MRTD for infrared (IR) imaging systems. It describes the sensitivity of an optical system in the presence of noise—a difference in contrast between a target bar and a background. The measurement is made by observing the minimum required contrast for each special frequency. The USAF 1951 target bar, which conforms to the MIL-STD-150A standard (see Fig below), is used as a standard target for MRC measurements. The resolution bars are arranged in groups and elements (horizontal and vertical directions) of different sizes for different frequencies. The variation of contrast is achieved by illuminating the background from the front, the smallest resolvable group can be selected by a trained observer, and a chart of contrast levels against the spatial frequency at a given illumination level will be provided. Different kind of targets may be used according to the optical system’s needs.
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