"; _cf_contextpath=""; _cf_ajaxscriptsrc="/cfthorscripts/ajax"; _cf_jsonprefix='//'; _cf_websocket_port=8578; _cf_flash_policy_port=1244; _cf_clientid='F875EF383AC29BEDD18172A0C0720835';/* ]]> */
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Visible Ruled Reflective Diffraction Gratings![]()
GR50-0605 50 mm x 50 mm GR25-1204 25 mm x 25 mm GR13-1205 12.7 mm x 12.7 mm See the Gratings Tutorial Tab Below for Definitions and Equations ![]() Please Wait
![]() Click to Enlarge Diffraction Grating Mounted in Polaris Mirror Mount Using Diffraction Grating Adapter Features
Thorlabs offers ruled diffraction gratings for use in the visible region. These gratings will have a relatively sharp efficiency peak about their blaze wavelength and are produced from ruled originals. They are offered with different blaze angles to suit a variety of applications in spectroscopy and analysis where high efficiency is of primary concern. For more information, please click on the Gratings Tutorial tab above. We also offer holographic gratings, which do not produce ghosting effects at the expense of efficiency. For information regarding the differences between grating types, please click on the Gratings Guide tab above. ![]() Click to Enlarge Ruled Diffraction Grating Used in Littrow Configuration (θi=γ) (Note: 1st Order Beam is Collinear and Antiparallel to Incident Beam) Please note that these gratings are bare aluminum and do not contain an overcoat. However, custom MgF2 or gold coatings are available to protect the aluminum surface of the gratings. The gold coating offers high performance in the IR, while the MgF2 coating offers the best protection; contact Tech Support for further details. Mounts and AdaptersThorlabs offers a variety of mounts and adapters for precise and stable mounting and aligning square optics. All of Thorlabs' gratings can be mounted directly into the KM100C Right-Handed or KM100CL Left-Handed Kinematic Rectangular Optic Mount. Gratings can also be mounted in one of three Kinematic Grating Mount Adapters which can be used with any of Thorlabs' Ø1" Mirror Mounts, including the POLARIS-K1 Ultra-Stable Kinematic Mirror Mount. WarningOptical gratings can be easily damaged by moisture, fingerprints, aerosols, or the slightest contact with any abrasive material. Gratings should only be handled when necessary and always held by the sides. Latex gloves or a similar protective covering should be worn to prevent oil from fingers from reaching the grating surface. No attempt should be made to clean a grating other than blowing off dust with clean, dry air or nitrogen. Solvents will likely damage the grating's surface. Thorlabs uses a clean room facility for assembly of gratings into mechanical setups. If your application requires integrating the grating into a sub-assembly or a setup please contact Tech Support to learn more about our assembly capabilities. Diffraction Gratings TutorialDiffraction gratings, either transmissive or reflective, can separate different wavelengths of light using a repetitive structure embedded within the grating. The structure affects the amplitude and/or phase of the incident wave, causing interference in the output wave. In the transmissive case, the repetitive structure can be thought of as many tightly spaced, thin slits. Solving for the irradiance as a function wavelength and position of this multi-slit situation, we get a general expression that can be applied to all diffractive gratings when ![]() (1) known as the grating equation. The equation states that a diffraction grating with spacing
Figure 1. Transmission Grating Transmission GratingsOne popular style of grating is the transmission grating. This type of diffraction grating is created by scratching or etching a transparent substrate with a repetitive, parallel structure. This structure creates areas where light can scatter. A sample transmission grating is shown in Figure 1. The transmission grating, shown in Figure 1, is comprised of a repetitive series of narrow-width grooves separated by distance ![]() (2) where both
Figure 2. Reflective Grating Reflective GratingsAnother very common diffractive optic is the reflective grating. A reflective grating is traditionally made by depositing a metallic coating on an optic and ruling parallel grooves in the surface. Reflective gratings can also be made of epoxy and/or plastic imprints from a master copy. In all cases, light is reflected off of the ruled surface at different angles corresponding to different orders and wavelengths. An example of a reflective grating is shown in Figure 2. Using a similar geometric setup as above, the grating equation for reflective gratings can be found: ![]() (3) where Both the reflective and transmission gratings suffer from the fact that the zeroth order mode contains no diffraction pattern and appears as a surface reflection or transmission, respectively. Solving Eq. 2 for this condition, This issue can be resolved by creating a repeating surface pattern, which produces a different surface reflection geometry. Diffraction gratings of this type are commonly referred to as blazed (or ruled) gratings. An example of this repeating surface structure is shown in Figure 3.
Blazed (Ruled) GratingsFigure 4. Blazed Grating, 0th Order Reflection Figure 3. Blazed Grating Geometry The blazed grating, also known as the echelette grating, is a specific form of reflective or transmission diffraction grating designed to produce the maximum grating efficiency in a specific diffraction order. This means that the majority of the optical power will be in the designed diffraction order while minimizing power lost to other orders (particularly the zeroth). Due to this design, a blazed grating operates at a specific wavelength, known as the blaze wavelength. The blaze wavelength is one of the three main characteristics of the blazed grating. The other two, shown in Figure 3, are The blazed grating features geometries similar to the transmission and reflection gratings discussed thus far; the incident angle ( The 0th order reflection from a blazed grating is shown in Figure 4. The incident light at angle ![]() Figure 6. Blazed Grating, Incident Light Normal to Grating Surface Figure 5. Blazed Grating, Specular Reflection from Facet The specular reflection from the blazed grating is different from the flat surface due to the surface structure, as shown in Figure 5. The specular reflection, ![]() (4) Figure 6 illustrates the specific case where ![]() (5) Littrow ConfigurationThe Littrow configuration refers to a specific geometry for blazed gratings and plays an important role in monochromators and spectrometers. It is the angle ![]() (6) ![]() Figure 7. Littrow Configuration The Littrow configuration angle, ![]() (7) It is easily observed that the wavelength dependent angular separation increases as the diffracted order increases for light of normal incidence (for ![]() (8)
where The first issue with using higher order diffraction patterns is solved by using an Echelle grating, which is a special type of ruled diffraction grating with an extremely high blaze angle and relatively low groove density. The high blaze angle is well suited for concentrating the energy in the higher order diffraction modes. The second issue is solved by using another optical element: grating, dispersive prism, or other dispersive optic, to sort the wavelengths/orders after the Echelle grating.
Figure 8. Holographic Grating Holographic Surface GratingsWhile blazed gratings offer extremely high efficiencies at the design wavelength, they suffer from periodic errors, such as ghosting, and relatively high amounts of scattered light, which could negatively affect sensitive measurements. Holographic gratings are designed specially to reduce or eliminate these errors. The drawback of holographic gratings compared to blazed gratings is reduced efficiency. Holographic gratings are made from master gratings by similar processes to the ruled grating. The master holographic gratings are typically made by exposing photosensitive material to two interfering laser beams. The interference pattern is exposed in a periodic pattern on the surface, which can then be physically or chemically treated to expose a sinusoidal surface pattern. An example of a holographic grating is shown in Figure 8. Please note that dispersion is based solely on the number of grooves per mm and not the shape of the grooves. Hence, the same grating equation can be used to calculate angles for holographic as well as ruled blazed gratings. Reflective GratingsReflective grating master copies are made by depositing a metallic coating on an optic and ruling parallel grooves in the surface. Thorlabs' reflective gratings are made of epoxy and/or plastic imprints from a master copy, in a process call replication. In all cases, light is reflected off of the ruled surface at different angles corresponding to different orders and wavelengths. All of Thorlabs' ruled reflective diffraction gratings exhibit a sawtooth profile, also known as blazed, while our reflective holographic diffraction gratings exhibit a sinusoidal profile. For more information, please refer to the Gratings Tutorial tab.
Transmission GratingsTransmission gratings are created by scratching or etching a transparent substrate with a repetitive, parallel structure. This structure creates areas where light can scatter. Thorlabs' transmission gratings are manufactured using the ruled method, which creates a sawtooth diffraction profile. Transmission gratings can also be made of epoxy and/or plastic imprints from a master copy, in a process call replication. For more information, please refer to the Gratings Tutorial tab.
Selecting a grating requires consideration of a number of factors, some of which are listed below:Efficiency: Blaze Wavelength: Stray Light: Resolving Power: For further information about gratings and selecting the grating right for your application, please visit our Gratings Tutorial. Caution:
![]() | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|