Build to Order Transmission Diffraction Gratings

Transmission gratings have specialized uses in spectrometry. Any optical imaging system, such as a camera or telescope, can be converted into a spectrograph by placing a transmission grating in the system, typically in front of the objective lens. Transmission gratings also serve as convenient beamsplitters for monochromatic light sources such as lasers. The efficiency behavior of transmission gratings is simpler than that for reflection gratings, since no metals are present to introduce complicated electromagnetic effects and since the angles of diffraction are usually small. Thus, polarization effects are virtually absent.

  • Incident light is normal to the back surface
  • Low to medium blaze angles
  • Special-quality substrates with AR coating on back face


Master Grating Options

Plane transmission gratings are listed in order of groove frequency. Blaze wavelengths listed are for the first-order Littrow configuration. The maximum ruled area is groove length x ruled width. Click on a Master Grating Code (last 4 digits of a grating's part number) below to view master grating efficiency curves. Use the request a quote to get a quote based on your requirements. For additional diffraction grating options and custom capabilities, please see the Features section.

Master Grating Code Grooves per mm Nominal Blaze Wavelength Nominal Groove Angle Maximum Ruled Area (mm) Request a Quote
111R 720 550 nm 43.1° 156 x 206 Quote
132R 600 540 nm 34° 102 x 102 Quote
550R 600 460 nm 28.7° 154 x 206 Quote
560R 600 400 nm 22° 154 x 206 Quote
660R 600 540 nm 34° 154 x 206 Quote
231R 497 650 nm 34° 102 x 102 Quote
676R 420 620 nm 26.7° 52 x 52 Quote
650R 400 460 nm 18.7° 154 x 206 Quote
391R 360 500 nm 18.2° 64 x 64 Quote
775R 360 580 nm 21° 102 x 102 Quote
770R 300 580 nm 17.45° 154 x 206 Quote
806R 300 490 nm 14.6° 102 x 128 Quote
736R 300 725 nm 22° 102 x 102 Quote
801R 287.2 560 nm 16.2° 64 x 64 Quote
630R 200 505 nm 10° 102 x 102 Quote
633R 200 450 nm 8.95° 154 x 206 Quote
760R 150 580 nm 8.6° 154 x 206 Quote
810R 150 725 nm 10.8° 154 x 206 Quote
108R 100 465 nm 4.6° 156 x 206 Quote
755R 85 610 nm 5.1° 102 x 102 Quote
756R 75 490 nm 3.65° 102 x 102 Quote
750R 75 580 nm 4.3° 154 x 206 Quote
751R 75 730 nm 5.43° 154 x 206 Quote
131R 45 500 nm 2.22° 64 x 64 Quote
906R 35 640 nm 2.2° 65 x 76 Quote


Transmission Grating Geometry

Light incident on a transmission grating is often normal to the back surface of the grating (α = 0; see Fig. 1), in which case the familiar grating equation reduces to

mλ = d sinβ

Here m is the (integral) diffraction order (usually |m| = 2), λ is the wavelength, d the groove spacing and β the angle of diffraction (measured from the normal).

Transmission grating in use. The incident light is usually normal to the grating surface and strikes the back of the grating. Only three spectral orders are shown.

Blazed Transmission Gratings

The peak efficiency of a blazed (triangular-groove) transmission grating occurs when the refraction of the incident beam though the mini-prism that constitutes a groove lies in the same direction as the diffraction given by the grating equation. Unlike reflection gratings, the groove angle is much larger than the blaze angle for a transmission grating, since the phase retardation doubles upon reflection but is multiplied by n-1 for a transmission grating, where n is the refractive index of the grating medium.

Applying Snell's law to the interface between the groove facet and air,

n sinχ = sin(χ+β)

Combining this relation with the grating equation, yields the relationship between the blaze angle βB and the groove angle χ:

tanχ = sinββ / (n - cosββ)

For small groove angles and for λ << d, a useful approximation to Eq. (3) relates the blaze wavelength of a reflection grating to that of the corresponding transmission grating. For transmission gratings used in air or vacuum, the ratio of its blaze wavelength (for normal incidence) to that of the equivalent reflection grating (used in Littrow) is

λβ (trans) / λβ (ref) (n - 1) / 2

where is the blaze wavelength of the corresponding reflection grating. This approximate formula, rarely in error by more than ten percent, simplifies conversion of information in the Grating Catalog from reflection gratings to transmission gratings. Taking n ≈ 1.6, which is true for most transmission gratings, yields

λβ (trans) / λβ (ref) 0.3

A corollary to this approximation is that, for n ≈ 1.6, the grooves of a transmission grating are about 10/3 times as deep as those of the corresponding reflection grating. For small diffraction angles (i.e., diffraction near the normal), this ratio holds for the angle χ as well.

The choice of groove angle for transmission gratings is limited by total internal reflection effects:

χ ≤ arcsin (1/n)

For n ≈ 1.6, this yields about 40° as the upper limit on χ, though in many cases the effective limit is somewhat lower. This means that transmission gratings cannot be used for high-dispersion applications.

Transmission Grating Efficiency

The shape of an ideal efficiency curve for a blazed transmission grating is the same as for a reflection grating in the scalar region (χ < 8°). Peak efficiency occurs at

λβ = (n - 1) d sinχ

It can be shown that most of the incident light will be diffracted into either the zero order or positive first order if

(λ / (n - 1)) d sinχ > 0.85

very little light will go into the negative first order or higher orders.

Transmission Gratings as Beam Dividers

When the angle between two divided beams is small, transmission gratings serve as ideal beamsplitting elements. Most of the transmitted light will be in the zero and first diffracted order when the grating is used off-blaze, and the ratio of the zero order efficiency to the first order efficiency can be varied over a wide range. For three beams, a symmetrical groove profile is required.

Catalog Part Number System

All standard Richardson gratings have a part number according to the following format:


  • AA indicates the type of grating (e.g., diced, plano, grism).
  • BBB indicates the size of the grating substrate.
  • CC indicates the substrate material
  • DD indicates the type of coating
  • EEE indicates the master grating groove parameters
  • x indicates the master grating type (e.g., ruled, holographic, echelle)

Please see Diffraction Grating Part Number System for additional information.

Standard Substrate Sizes

Size Code BBB Substrate Dimensions (mm) Ruled Area (mm)
004 30 x 30 x 10 26 x 26
005 Ø50 x 10 30 x 32
006 58 x 58 x 10 52 x 52
008 Ø80 x 10 52 x 52
009 68.6 x 68.6 x 9.1 64 x 64
013 90 x 90 x 12 84 x 84
015 110 x 110 x 12 102 x 102

Transmission Grating Substrate Options

Substrate Material Code CC Substrate Material
BF Borosilicate float or equivalent
BK BK-7 glass or equivalent
FL Float glass
FS Fused silica or equivalent
LE Low-expansion glass
SP Special glass (unspecified)
TB BK-7, transmission grade
TF Fused silica, transmission grade
UL Corning ULE® glass
ZD Schott Zerodur®

Custom Diffraction Gratings

Newport is pleased to discuss special and unusual applications that are not addressed by our build to order catalog diffraction gratings. In some instances, none of the hundreds of master gratings we have in stock meet specifications, so a new master may be required. Please see Custom Diffraction Gratings for additional information on our capabilities.