Build to Order Concave Holographic Diffraction Gratings



Concave holographic gratings function as both a dispersing and focusing element in monochromators and spectrographs. These gratings contain two focusing elements: the substrate, and the groove curvature. As a result, an instrument designer can replace a lens system by using concave gratings, leading to a reduction of optics in a system, and thus, cost. Another advantage of a system based on concave gratings is decreased optical aberrations such as coma and astigmatism. Concave holographic gratings make possible short radii gratings with low ƒ/# and flat-field imaging suitable for array spectrographs.

  • Works as both a dispersing and focusing element
  • Reduced astigmatism in flat-field spectrographs
  • High spectral imaging resolution in Rowland Circle spectrographs
  • Reduced astigmatism in constant-deviation monochromators


Figure_7-4_THUMB

Concave holographic gratings for are listed below in increasing groove frequency (grooves per mm) for several applications. Click on a Catalog Number to view grating efficiency curves. Request a quote by clicking the quote link. For the gratings listed in this table, the figure at left defines the following parameters:

ConcaveHoloReflect_Grating


  • α – incidence angle
  • r – distance from entrance slit to grating center
  • β – diffraction angle
  • r' – distance from grating center to image

The angles α and β are measured from the grating normal; their algebraic signs are opposite if they lie on opposite sides of the normal.

Master Grating Options for Flat-Field Spectrographs


By suitably curving the grooves on the grating, usually by holographic means, adequate spectral resolution can be achieved on a line instead of a circle. This lends itself naturally to use with linear or area detector arrays. While astigmatism is reduced, which increases throughput, the resolution of a flat-field spectrograph is never as great as for a Rowland Circle spectrograph. The advantage of flat-field spectrographs lies in achieving compact spectrometers with no moving parts.




Figure_7-7
Spectral resolution is optimized for a planar spectrum.
Catalog Number Grooves per mm Imaging Range 1, 2 (nm) Reciprocal Linear Dispersion (nm/mm) Entrance Slit r and α (mm, deg) λ1 focus r' and β (mm, deg) λ2 focus r' and β (mm, deg) Input f/no Ruled Area (mm) Substrate Size (mm) Request a Quote
52056BK-*-028C 200 290-1020 32.3 151, 5.0 153,2,-8.3 153,2,-17.0 3.5 Φ44 Φ50 Quote
52A16BK-*-307C 230 380-1080 31.2 137.4, -5.73 138.3,10.8 134.5,20.4 2.0 Φ68 Φ69.9 Quote
52066BK-*-018C 233.9 190-400 33 148, 3.0 116-5.6 113, -8.4 2.5 Φ60 Φ63.5 Quote
52A15BK-*-224C 278.3 350-1050 30 88.0, 6.37 118.14, -12.02 111.13, -23.77 2.5 Φ40 Φ45 Quote
52067BK-*-040C 282.7 190-545
545-900
14.5 235, -5.3
252, 0.4
219, 8.4 228, 14.3 3.9
4.2
Φ60 Φ63.5 Quote
52104BF-*-216C 310 470-680 33 100.9, -5.22 101, 13.7 101.7, 17.6 3.3 Φ32 Φ35 Quote
52146BK-*-332C 318 380-720 78.2 40.307, -2 41.86, 9.348 43.56, 15.737 1.5 Φ26 Φ28 Quote
52A14BK-*-221C 367.43 200-800 25.7 88.00, 7.03 104.91, -11.29 97.90, -24.60 2.5 Φ40 Φ45 Quote
52A14BK-*-234C 367.43 200-850 25.7 88.00, 7.03 104.91, -11.29 97.90, -24.60 2.5 Φ40 Φ45 Quote
52A25BK-*-255C 400 380-730 83 30, -5.66 31.96, 14.52 34.19, 23 1.2 Φ24 Φ26 Quote
52A16BK-*-324C 405 380-780 31.2 137.4, -5.73 137, 14.7 129.8, 24.6 2.0 Φ68 Φ69.9 Quote
52097BK-*-207C 430 250-800 24.9 86.4, 6.0 88.6, -12.24 85.4, -26.6 2.9 Φ35 Φ37 Quote
52097BK-*-208C 430 450-850 24.9 86.4, 6.0 85.4, 17.3 83.6, 28.0 2.9 Φ35 Φ37 Quote
52097BK-*-209C 430 300-850 24.9 86.4, 6.0 86.1, 13.5 83.6, 28.0 2.9 Φ35 Φ37 Quote
52112BK-*-261C 432 190-840 26.15 86.4, 6.0 89.4, -10.7 85.4, -26.7 3.6 Φ24 Φ25 Quote
52107BK-*-214C 435.9 190-680 19.5 111.48, 5.5 111.64, -11.82 108.25, -22.45 2.2 Φ51 Φ55 Quote
52057BK-*-014C 435.9 190-400 19.5 109, -6.1 114, 10.9 113, 16.3 2.3 Φ47 Φ50.8 Quote
52066BK-*-001C 454.27 285-720 17 130, 11.3 130, -3.8 128, 7.36 2.2 Φ58 Φ63.5 Quote
52101BF-*-212C 477 200-850 31 86.9, -6.7 60.9, 12.2 70.3, 30.8 3.5 Φ19 Φ20 Quote
52101BK-*-211C 477 200-850 31 86.9, -6.7 60.9, 12.2 70.3, 30.8 3.5 Φ19 Φ20 Quote
52114BK-*-323C 489.87 200-800 24 77.36, 6.65 66.98, -12.35 78.0, -30.52 2.4 28 x 28 30 x 30 Quote
52099BK-*-317CL 580 340-800 16 98.2, 0.00 100.5, 11.37 100.8, 29.54 3.5 37 x 27 40 x 30 Quote
52129BK-*-358C 586.23 340-800 19.8 90.8, -10.78 74.9, 22.7 74.0, 41.0 3.2 28 x 28 37 x 37 Quote
52105BF-*-198C 660 340-805 10.1 112.5, 4.9 122.3, -18.0 133.7, -38.0 3.0 Φ38 Φ40 Quote
52034BK-*-004C 664 340-700 18 80, -13.3 80, 0.2 84, -13.6 2.7 Φ29 Φ32 Quote
52001BK-*-021C 792.8 380-780 4.5 231, 3.0 223, 14.4 258, 34.5 2.4 Φ95 Φ100 Quote
52140BK-*-279C 800 325-800 10.7 86.3, 0 85, 18.2 104.5, 43.82 2.7 28 x 28 30 x 30 Quote
52066BK-*-002C 813.5 380-705 9.5 130, 22.3 128, -4.0 129, 11.2 2.2 Φ60 Φ63.5 Quote
52049BK-*-012C 1300 340-650 7.8 94, -31.1 99, 4.3 97, -19.1 2.9 Φ38 Φ42 Quote
52064BK-*-008C 1803.8 753-784 1.2 345, 67.5 387, -25.8 394, -29.4 6.3 50 x 50 Φ62.5 Quote
52071BK-*-007C 2197 277-313 1 575, 4.9 288, -43.9 296, -50.6 10.5 Φ55 Φ70 Quote
† This flat-field spectrograph grating is designed to produce two aberration-corrected spectra in the same place (using different entrance slit locations).

Master Grating Options for Rowland Circle Spectrographs


A "classical" concave grating (one whose grooves are straight, parallel and equally spaced) can be generated on a ruling engine or by recording a laser interference pattern in photoresist (to form a holographic grating). If the object (e.g., entrance slit or fiber) is placed on the Rowland circle (whose diameter equals the radius of curvature of the grating blank), high spectral imaging resolution is obtained.

The detectors or output fibers must be located on the Rowland circle, since that is where the slit images are focused. While the images are narrow in the spectral direction, they suffer from a large amount of astigmatism inherent in this type of grating system.




Figure_7-5
The entrance slit and diffracted spectrum lie on the Rowland Circle, which also passes through the center of the grating surface.

Catalog Number Grooves per mm Concave Radius (mm) Recommended Spectral Region Ruled Area (mm) Substrate Size (mm) Request a Quote
52102BF-*-315C 390 350 300 nm-1 μm Φ48 Φ50.8 Quote
52102BF-*-316C 390 350 300 nm-1 μm Φ48 Φ50.8 Quote
52088BK-*-257C 678 83.7 200 nm-800 nm Φ32 Φ38 Quote
52A02BF-*-356C 900 750 120 nm-500 nm Φ75 Φ80 Quote
52011BK-*-003C 1200 498.1 300 nm-900 nm Φ60 Φ63.5 Quote
52A02BF-*-556C 1500 750 120 nm-500 nm Φ75 Φ80 Quote
52071BK-*-025C 1760 352 200 nm-1.1 μm Φ65 Φ70 Quote
52017BK-*-009C 1800 750 250 nm-900 nm Φ59 Φ63.5 Quote
52021BK-*-032C 2160 998.8 210 nm-350 nm Φ59 Φ63.5 Quote
52017BK-*-247C 2400 750 200 nm-700 nm Φ59 Φ63.5 Quote
52017BK-*-434C 2400 750 200 nm-700 nm Φ60 Φ63.5 Quote
52017BK-*-482C 2400 750 150 nm-800 nm Φ60 Φ63.5 Quote
52017BK-*-484C 2400 750 150 nm-800 nm Φ60 Φ63.5 Quote
52A23BK-*-375C 2400 398.8 200 nm-700 nm Φ33 Φ35 Quote
52017BK-*-520C 3600 750 150 nm-500 nm Φ60 Φ63.5 Quote
52011BK-*-521C 3600 498.1 150 nm-500 nm Φ60 Φ63.5 Quote
52011BK-*-530C 3600 498.1 180 nm-500 nm Φ60 Φ63.5 Quote

Master Grating Options for Constant-Deviation Monochromators




Curving the grating grooves can also reduce aberrations in monochromators, in which only a small part of the spectrum is viewed at a time; wavelengths are scanned by rotating the grating. Again, astigmatism is usually reduced (though for part of the spectrum only) to increase throughput, but the resolution is less than for a Rowland Circle spectrograph.




Figure_7-9
The angle between the slits remains constant as the grating is rotated to scan wavelengths.
Catalog Number Grooves per mm Nominal Blaze Wavelength (1st Order Littrow) Imaging Range 1, 2 (nm) Reciprocal Linear Dispersion (nm/mm) Entrance Slit r (mm) Exit Slit r' (mm) Deviation Angle 2K (deg) Input f/no Ruled Area (mm) Substrate Size (mm) Request a Quote
52073BK-*-037C 570 2 μm 1100-2500 10 203.9 184.1 38 2.4 Φ84 Φ90 Quote
52073BK-*-278C 1140 1 μm 550-1200 3 201 182.7 38 2.3 Φ84 Φ90 Quote
52094BK-*-096C 1198 300 nm 200-1000 7 105 100 34.7 2.5 38 x 38 42.4 x 42.4 Quote
52094BK-*-097C 1198 450 nm 350-1590 7 105 100 34.7 2.5 38 x 38 42.4 x 42.4 Quote
52094BK-*-098C 1198 375 nm 200-900 7 105 100 34.7 2.5 38 x 38 42.4 x 42.4 Quote
52105BK-*-226C 1200 250 nm 200-800 8.5 100 94 61.6 3.6 Φ36 Φ40 Quote
52111BK-*-228C 1200 350 nm 200-800 8.5 100 94 61.6 3.1 28 x 28 32 x 32 Quote
52085BF-*-246C 1200 250 nm 200-600 7 99.3 103.5 28 3.5 29 x 29 33 x 33 Quote
52085BF-*-251C 1200 250 nm 200-600 7 99.3 103.5 28 3.5 29 x 29 33 x 33 Quote
52085BF-*-364C 1200 225 nm 200-600 7 99.3 103.5 28 3.5 29 x 29 33 x 33 Quote
52085BF-*-433C 1200 225 nm 200-600 7 99.3 103.5 28 3.5 29 x 29 33 x 33 Quote
52027BK-*-006C 1200 200 nm 200-800 8.5 100 94 61.6 3.6 30 x 30 32 x 32 Quote
52057BK-*-020C 1200 450 nm 325-950 7 91.1 117.7 51.2 2.5 Φ47 Φ50.8 Quote
52057BK-*-022C 1200 350 nm 325-950 7 91.1 117.7 51.2 2.5 Φ47 Φ50.8 Quote
52057BK-*-238C 1200 275 nm 200-800 8.5 100 94 61.6 2.5 Φ45 Φ50.8 Quote
52052BF-*-023C 1350 250 nm 190-700 8 91.3 91.3 45 2.3 Φ40 Φ45 Quote
52093BK-*-095C 1500 250 nm 200-800 8 74.73 80 47.1 3.7 24 x 24 28 x 28 Quote

Features

Typical Spectral Images with Concave Holographic Gratings

Concave gratings have an advantage over conventional plane grating systems in that concave gratings perform both imaging as well as dispersion (wavelength separation). This reduces the cost of the optical components in the instrument, reduces alignment time, and perhaps minimizes reflective and refractive energy losses as well. Typical spectral images are shown at three wavelengths from (a) a Rowland Circle spectrograph, (b) a flat-field spectrograph, and (c) a constant-deviation monochromator. Note that resolution (image width) degrades as astigmatism (image height) is reduced.

NO-image

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.

Grating Substrate Material Options

The standard substrate material for small and medium-sized gratings is specially annealed borosilicate crown glass. Low expansion material can be supplied on request. Float glass may be used for small, diced gratings. In addition, replicas may be furnished on metal substrates, such as copper or aluminum, for applications with extreme thermal conditions. The substrate material codes CC are given below:

Substrate Material Code CC Substrate Material
AL Aluminum
BF Borosilicate float or equivalent
BK BK-7 glass or equivalent
CU Copper
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®

Diffraction Grating Coating Options

All reflection gratings include a standard aluminum (Al) reflectance coating (Coating Code "01"). Gratings can also be replicated in gold (Au), or overcoated with magnesium fluoride (MgF2) or silver (Ag), to enhance reflectivity in certain spectral regions. The coating material codes DD are shown below:

Coating Code DD Coating Material Application
01 Aluminum (Al) General purpose applications.
02 Gold (Au) Offers higher reflectivity in the infrared.
03 Magnesium Fluoride (MgF2) Used to prevent oxidation of aluminum (Al) coatings, which helps maintain high reflectivity in the ultraviolet over time.
06 Protected Silver (Ag) Offers higher reflectivity in the visible and near infrared. Silver is protected from tarnishing by a dielectric coating, which helps maintain reflection over time.

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.

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