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.

Search:

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

Showing 1 to 25 of 25 entries

Features

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 = sinβ_β / (n - cosβ_β)

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

λ_β (trans) / λ_β (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

λ_β (trans) / λ_β (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

λ_β = (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 BBB CC DD - EEE x

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.