Custom Gratings, Graticules & Resolution Charts
Knight Optical can provide custom gratings, graticules and resolution charts which are manufactured to our customers requirements. Whether is it an alternative substrate, dimensions or a fully custom pattern to be etched or deposited on to a substrate, Knight Optical will work with you to provide an optical component tailored to your application.
- Bar charts usually consist of a chromium pattern of equally spaced lines and spaces deposited on to a glass substrate. Bar gratings can be used for optical testing methods such as Ronchi mirror testing and creating a Moiré pattern. The line spacing is given as line pair per millimetre (lp/mm).
- Diffraction gratings are designed to separate light into different wavelengths or orders. Knight Optical can provide ruled, holographic and blazed diffraction gratings to suit your application. Diffraction gratings can work via transmission or reflection, dependent on their design purpose.
- Graticules, also known as reticules, are optical components with a customised pattern, commonly scales or crosshairs, deposited on to the substrate via photolithography.
- Resolution charts: Knight Optical stocks USAF 1951 0-7, NBS 1963A and Cobb (BS1613) charts for resolution testing which can be found here. Custom patterns can also be applied with spatial frequencies that are dependent on the specification and application.
Patterns can be deposited on optics such as windows, filters and prisms, and the glass substrate used is dependent on the application, for example, calcium fluoride (CaF2) can be used for applications ranging from UV to IR. Knight Optical can also apply antireflective coatings to enhance the performance at specific wavelengths.
Our typical manufacturing capabilities vary for each component type but specific capability sheets can be found below. If you have a custom design, please contact our technical sales team with your requirements.
- Diffraction gratings can be split into two types:
- Ruled: grooves are etched into the coating on the substrate. These offer a high level of efficiency but can cause stray light which can be problematic in applications such as spectroscopy.
- Holographic: Rather than etched grooves, an optical pattern is deposited via techniques such as photolithography which allows for a finer grating pattern. This can reduce the amount of stray light, but the efficiency is also decreased.
- Blazed (or echelette) gratings are designed to have maximum efficiency at a certain wavelength, the blaze wavelength. To achieve this maximum efficiency for a specific wavelength the grooves have to be cut at a certain angle (known as the blaze angle) with a certain spacing between them.
Knight Optical can also apply a wide range of coatings to your optical component to enhance their transmission or increase their durability:
- Antireflective (AR) coatings, including broadband coatings, to optimise the transmission at certain wavelengths or across a range.
- Hydrophobic coating to repel water from a surface.
- More specialist coatings such as anti-fog and oleophobic.
- Using our Starrett AV300 Knight Optical can ensure the etched or deposited patterns are to the desired specification, including positioning on the substrate.
- Any flatness and irregularity requirements are tested on our Zygo Verifire XPZ interferometer, where we can also test the transmitted wavefront error.
- Transmission, reflection and optical density measurements are conducted on our Agilent Cary 7000 Spectrophotomer which can perform spectral scans at multiple angles of incidence and different polarisations.
- We can also test infrared optical components on our Agilent Cary 660 FTIR spectrometer.
- All optics are 100% visually inspected before packaging, our staff are trained to ISO 10110 and MIL-0-13830A, and can check down to 10/5 scratch/dig which is especially critical in laser applications.
- Graticules are used in a variety of applications including microscopy and in telescopes. The pattern etched on them is dependent on their use. For example, in microscopes the eyepiece graticule may have a linear scale.
- Diffraction gratings are often used in monochromators and spectrometers to split the incident light into its component wavelengths before they are reflected off a focussing mirror (a concave mirror or parabolic mirror) and the selected wavelength exits through to the detector via a slit to block any unwanted wavelengths. The diffraction grating is a dispersive element, and can be rotated to change the wavelength that exits the system.
- Diffraction gratings are often used as an end mirror in external-cavity diode lasers which are in the Littrow configuration, by rotating the grating the wavelength can be tuned, however this can also change the direction of the output beam which is can be a disadvantage in some applications.