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Visible Transmission Gratings


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Visible Transmission Gratings

Grating Arrows
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Top Image: On one edge of the grating, an arrow parallel to the grating's surface indicates the blaze direction.
Bottom Image: On the opposite edge of the grating, an arrow perpendicular to the grating's surface indicates the transmission direction.
Common Specifications
Substrate MaterialSchott B270
Thickness3 mm Nominal
Dimensional Tolerance± 0.5 mm
Thickness Tolerance± 0.5 mm

Visible Grating Transmission Data
Click to Enlarge

Features

  • Optimum Performance in the Visible Spectrum
  • Ideal for Fixed Grating Applications such as Spectrographs
  • Schott B270 Substrate
  • Custom Sizes Available Upon Request

Thorlabs' Visible Transmission Gratings are ideal for fixed grating applications such as spectrographs. The incident light is dispersed on the opposite side of the grating at a fixed angle. Transmission gratings offer low alignment sensitivity, which helps minimize alignment errors. In most cases, the efficiency of these gratings is comparable to that of reflection gratings such as Ruled Gratings or Holographic Gratings when used in the same wavelength range.

Transmission gratings require relatively low groove densities to maintain high efficiency. As the diffraction angles increase with higher groove densities, the refractive properties of the substrate material limits the transmission at the higher wavelengths and performance drops off. The grating dispersion characteristics, however, lend themselves to compact systems utilizing small detector arrays. These gratings are also relatively polarization insensitive. Our visible transmission gratings are offered with four different groove densities in three different sizes. Please see the Selection Guide tab to choose the right grating type for your application.

Optical 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 us to learn more about our assembly capabilities.

Thorlabs offers 3 types of Reflection Gratings:

Ruled

Ruled Grating

Ruled gratings can achieve higher efficiencies than holographic gratings due to their blaze angles. They are ideal for applications centered at the blaze angle. Thorlabs offers replicated ruled diffraction gratings in a variety of sizes and blaze angles.

Holographic

Holographic Grating

Holographic gratings have a low occurance of periodic errors which results in limited ghosting, unlike ruled gratings. The low stray light of these gratings make them ideal for applications where the signal-to-noise ratio is critical, such as Raman Spectroscopy.

Echelle

Echelle Grating

Echelle gratings are low period gratings designed for use in the high orders. They are generally used with a second grating or prism to separate overlapping diffracted orders. The are ideal for applications such as high-resolution spectroscopy.

Thorlabs offers 3 types of Transmission Gratings:

UV Transmission

UV Transmission Grating

As with all of our transmission gratings, Thorlabs' UV transmission gratings disperse incident light on the opposite side of the grating at a fixed angle. They are ruled and blazed for optimum efficiency in the UV range, are relatively polarization insensitive, and have an efficiency comparable to that of a reflection grating optimized for the UV spectrum. They are ideal for applications that require fixed gratings such as spectrographs.

VIS Transmission

VIS Transmission Grating

As with all of our transmission gratings, Thorlabs' VIS transmission gratings disperse incident light on the opposite side of the grating at a fixed angle. They are ruled and blazed for optimum efficiency in the VIS range, are relatively polarization insensitive, and have an efficiency comparable to that of a reflection grating optimized for the VIS spectrum. They are ideal for applications that require fixed gratings such as spectrographs.

Near IR Transmission

NIR Transmission Grating

As with all of our transmission gratings, Thorlabs' NIR transmission gratings disperse incident light on the opposite side of the grating at a fixed angle. They are ruled and blazed for optimum efficiency in the NIR range, are relatively polarization insensitive, and have an efficiency comparable to that of a reflection grating optimized for the NIR spectrum. They are ideal for applications that require fixed gratings such as spectrographs.

Selecting a grating requires consideration of a number of factors, some of which are listed below:

Efficiency:
Ruled gratings generally have a higher efficiency than holographic gratings. However, holographic gratings tend to have less efficiency variation accross their surface due to how the grooves are made. The efficiency of ruled gratings may be desireable in applications such as fluorescence excitation and other radiation-induced reactions.

Blaze Wavelength:
Ruled gratings have a sawtooth groove profile created by sequentially etching the surface of the grating substrate. As a result, they have a sharp peak around their blaze wavelength. Holographic gratings are harder to blaze, and tend to have a sinusoidal groove profile resulting in a less intense peak around the design wavelength. Applications centered around a narrow wavelength range could benefit from a ruled grating blazed at that wavelength.

Wavelength Range:
Groove spacing determines the optimum spectral range a grating covers and is the same for ruled and holographic gratings having the same grating constant. As a rule of thumb, the first order efficiency of a grating decreases by 50% at 0.66λB and 1.5λB, where λB is the blaze wavelength. Note: No grating can diffract a wavelength greater than 2 times the groove period.

Stray Light:
Due to a difference in how the grooves are made, holographic gratings have less stray light than ruled gratings. The grooves on a ruled grating are machined one at a time which results in a higher frequency of errors. Holographic grooves are made all at once which results in a grating that is virtually free of errors. Applications such as Raman spectroscopy, where signal-to-noise is critical, can benifit from the limited stray light of the holographic grating.

Resolving Power:
The resolving power of a grating is a measure of its ability to spatially separate two wavelengths. It is determined by applying the Rayleigh criteria to the diffraction maxima; two wavelengths are resolvable when the maxima of one wavelength coincides with the minima of the second wavelength. The chromatic resolving power (R) is defined by R = λ/Δλ = nN, where Δλ is the resolvable wavelength difference, n is the diffraction order, and N is the number of grooves illuminated.

For further information about gratings and selecting the grating right for your application, please visit our Grating Tutorial.

Caution:

The surface of a diffraction grating can be easily damaged by fingerprints, aerosols, moisture 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. Solvents will likely damage the grating's surface. No attempt should be made to clean a grating other than blowing off dust with clean, dry air or nitrogen. Scratches or other minor cosmetic imperfections on the surface of a grating do not usually affect performance and are not considered defects.

Diffraction Gratings Tutorial

Diffraction 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 experssion that can be applied to all diffractive gratings,

Grating Equation 1

(1)

Transmission Grating
Figure 1. Transmission Grating

known as the grating equation. The equation states that a grating with spacing a, of mth order, will diffract light at a wavelength of lambda at an angle of theta sub m. The diffracted angle, theta sub m, is the output angle as measured from the surface normal of the grating. It is easily observed from Eq. 1 that for a given order m, different wavelengths of light will exit the grating at different angles. For white light sources, this corresponds to a continuous, angle-dependent spectrum.

Transmission Grating

One popular style of grating is the transmission grating. This type of 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 grooves of narrow width and separation a. The incident light impinges on the grating at an angle theta sub i, as measured from the surface normal. The light of order m exiting the grating leaves at an angle of theta sub m, relative to the surface normal. Utilizing some geometric conversions and the general grating expression (Eq. 1) an expression for the transmissive diffraction grating can be found:

Grating Equation 2

(2)

Reflective Grating
Figure 2. Reflective Grating

Reflective Grating

Another very common diffractive optic is the reflective grating. A reflective grating is 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 general expression for the reflective grating is identical to the tranmission grating equation (see Eq. 2).

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, theta sub i = theta sub m, we find the only solution to be m=0, independent of wavelength or gratings spacing. At this condition, no wavelength-dependent information can be obtained, and all the light is lost to surface reflection or transmission.

This issue can be resolved by creating a repeating surface pattern, which produces a different surface reflection geometry. 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) Grating

Blazed Grating
Figure 4. Blazed Grating, 0th Order Reflection
Blazed Grating
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 a, the groove or facet spacing, and gamma, the blaze angle. The blaze angle gamma is the angle between the surface structure and the surface parallel. It is also the angle between the surface normal and the facet normal.

The blazed grating features the same geometries as the transmission and reflection gratings discussed thus far; the incident and exit angles are determined from the surface normal of the grating. However, the significant difference is the surface geometries are determined based on the blaze angle, gamma, and NOT the surface normal. This results in the ability to change the diffraction geometries by only changing the blaze angle of the grating.

The 0th order reflection from a blazed grating is shown in Figure 4. The incident light at angle theta sub i is reflected at theta sub m for m = 0. From Eq. 2, the only solution is theta sub i = theta sub m. This is analogous to specular reflection from a flat surface.

Blazed Grating
Figure 5. Blazed Grating, Specular Reflection

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, theta sub r, from a blazed grating occurs at the blaze angle geometry. Performing some simple geometric conversions, one finds that

                                          Grating Equation 3                                                      (3)

Utilizing Eqs. 2 and 3, we can find the grating equation for a blazed grating at twice the blaze angle:

                                          Grating Equation 4                                             (4)

Littrow Configuration
The Littrow configuration refers to a specific geometry for blazed gratings and plays an important role in monochromators and spectrometers. In this configuration, the angle of incidence of the incoming and diffracted light are the same, theta sub i = theta sub m, and m > 0 so

                                          Grating Equation 5                                            (5)

The Littrow configuration angle, Theta sub L, is dependent on the most intense order (m = 1), the design wavelength, lambda sub D, and the grating spacing a. It is easily shown that the Littrow configuration angle, Theta sub L, is equal to the blaze angle, gamma, at the design wavelength. The Littrow / Blaze angles for all Thorlabs' Blazed Gratings can be found in the grating specs tables.

It is easily observed that the wavelength dependent angular separation increases as the diffracted order increases for light of normal incidence (for theta sub i=0, theta sub m increases as m increases). There are two main drawbacks for using a higher order diffraction pattern over a low order one: (1) a decrease in efficiency at higher orders and (2) a decrease in the free spectral range, Free Spectral Range, defined as:

                                        Gratings - Free Spectral Range                                                     (6)

where lambda is the central wavelength, and m is the order.

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.

Holographic Gratings
Figure 6. Holographic Grating

Holographic Gratings

While 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 6.

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Posted Comments:
Poster: besembeson
Posted Date: 2014-06-12 08:43:04.0
Response from Bweh at Thorlabs Newton-USA: Thanks for contacting Thorlabs. We do offer customized solutions for these gratings. I will follow up with you by email to get your complete specifications for a quotation.
Poster: roman.wieser
Posted Date: 2014-06-06 11:03:30.203
Dear Ladies and Gentlemen, we are looking for diffraction gradings or transmission gradings. We need other dimensions then written on your web pages. Dimensions are 5mm x 160 / 320mm. You are able to deliver such sizes and if yes with how much grooves it will be possible. And logically how expensive it will be. kind regards Roman Wieser
Poster: besembeson
Posted Date: 2014-02-12 04:15:03.0
Response from Bweh E at Thorlabs: Thanks for the suggestions. We will be looking into such mounts. We may be able to offer a special circular grating to you. I will follow-up with you by email to discuss your requirements for such circular gratins.
Poster: dsablowski
Posted Date: 2014-02-10 18:19:46.167
Hey, it would be very useful to have round sized gratings, which fit to your tube system! Or rectangular mounts which fit to the tube system. Additionally some more angled optics mounts which fit to the center wavelength of each grating. This would help to implement gratings to optical set-ups.
Poster: jeffreyb
Posted Date: 2013-09-24 13:46:32.203
Hi, I have been using these gratings to make direct view, low-dispersion spectrographs. I couple the grating to the hypotenuse of 30 60 90 prism made from SF2 (ZF1 in china) The blaze angle of this grating nearly matches the 30 deg apex angle of a Littrow prism. You do not offer a SF2 prism (you used to have it in your catalog as a "Littrow dispersing prism") so, I had them made in China for ~$100 each. The hypotenuse face is 50mm x 50mm and un-coated (this face matches the grating size). The entrance face is anti reflection coated. I use an index matching grease to couple the grating to the prism (optical epoxy would be better). I would think that you could market such a grism assembly for ~$600-$900 maybe more......given that the component parts would cost ~$300 or so. Just having a high dispersion material (ZF1 or SF2) 30 60 90 prism would be very useful for those who would want to make the grism. A short tutorial could be made to demonstrate the principle of the grism...
Poster: cdaly
Posted Date: 2013-10-10 16:08:00.0
Response from Chris at Thorlabs: Thank you for your feedback. We greatly appreciate you suggestion, which I will share with our optical engineers. I will contact you directly to discuss this further.
Poster: tcohen
Posted Date: 2012-11-13 17:47:00.0
Response from Tim at Thorlabs: Gratings are very easily damaged on contact. They should be handled only on the sides and stored in the supplied case when not in use which suspends the grating. Cleaning should only be attempted by lightly blowing off dust with clean, dry air or nitrogen.
Poster: mathieu.perrin
Posted Date: 2012-11-13 07:54:29.123
Hello, I own the 830 mm-1 transmission grating. Can it be cleaned and how?
Poster: tcohen
Posted Date: 2012-06-15 11:20:00.0
Response from Tim at Thorlabs: Thank you for your feedback! We are adding a photo to the overview tab explaining what the arrows are and we are revising our diagrams in our grating tutorial. We will also link the tutorial to this page and I have contacted you with this information on using your grating.
Poster: jcanseco
Posted Date: 2012-06-11 01:07:45.0
On the side surface of the grating, there is a long arrow. I assume this indicates the direction of the grating blaze. Do I have align the input beam in the same direction as arrow, or opposite to the arrow? In other words, should the propagation direction of the input beam follow the direction that the arrow is pointing at or go against it? Thank you.
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300 Grooves/mm Visible Transmission Gratings
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GT13-03 Support Documentation
GT13-03 Vis Trans Grating, 300 Grooves/mm, 17.5° Blaze Angle, 12.7 mm x 12.7 mm
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GT25-03 Support Documentation
GT25-03 Vis Trans Grating, 300 Grooves/mm, 17.5° Blaze Angle, 25 mm x 25 mm
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GT50-03 Vis Trans Grating, 300 Grooves/mm, 17.5° Blaze Angle, 50 mm x 50 mm
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600 Grooves/mm Visible Transmission Gratings
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GT13-06V Support Documentation
GT13-06V Vis Trans Grating, 600 Grooves/mm, 28.7° Blaze Angle, 12.7 mm x 12.7 mm
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GT25-06V Support Documentation
GT25-06V Vis Trans Grating, 600 Grooves/mm, 28.7° Blaze Angle, 25 mm x 25 mm
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GT50-06V Support Documentation
GT50-06V Vis Trans Grating, 600 Grooves/mm, 28.7° Blaze Angle, 50 mm x 50 mm
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830 Grooves/mm Visible Transmission Gratings
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GT13-08 Support Documentation
GT13-08 Vis Trans Grating, 830 Grooves/mm, 29.87° Blaze Angle, 12.7 mm x 12.7 mm
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GT25-08 Support Documentation
GT25-08 Vis Trans Grating, 830 Grooves/mm, 29.87° Blaze Angle, 25 mm x 25 mm
$104.90
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GT50-08 Support Documentation
GT50-08 Vis Trans Grating, 830 Grooves/mm, 29.87° Blaze Angle, 50 mm x 50 mm
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1200 Grooves/mm Visible Transmission Gratings
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GT13-12 Support Documentation
GT13-12 Vis Trans Grating, 1200 Grooves/mm, 36.9° Blaze Angle, 12.7 mm x 12.7 mm
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GT25-12 Support Documentation
GT25-12 Vis Trans Grating, 1200 Grooves/mm, 36.9° Blaze Angle, 25 mm x 25 mm
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GT50-12 Support Documentation
GT50-12 Vis Trans Grating, 1200 Grooves/mm, 36.9° Blaze Angle, 50 mm x 50 mm
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