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Configuration Options

AABBBCCDD-420H Plane Holographic Diffraction Grating, 2400 g/mm, 270 nm, 200 nm - 800 nm

Grating Information

Diffraction Efficiency and Polarization Effects

Holographic diffraction gratings can have very high diffraction efficiency, even above that of flat aluminum reflectors, at the design wavelengths and orientation. Diffraction efficiency is highly dependent on the polarization state. Planar holographic gratings typically feature narrower spectral bandwidth, and have their peak efficiency at a shorter wavelength for P-polarization compared to S-polarization. For laser cavity applications this property may be used to feed light from a specifically chosen wavelength and polarization state back into the laser gain medium to control the output of the laser. Conversely, applications such as spectrometers designed to operate using unpolarized light may require the use of two gratings in conjunction with a polarizing beamsplitter to obtain optimum results.

Master 5498 (default) Maximum Ruled Area (mm): 102 x 128
Coating Aluminum
Spectral Order m = 1
Polarization(s) S, P & Average
Efficiency 420h_5498_m1_spa
Master 5499 Maximum Ruled Area (mm): 102 x 128
Coating Aluminum
Spectral Order m = 1
Polarization(s) S, P & Average
Efficiency 420h_5499_m1_spa
Master 6001 Maximum Ruled Area (mm): 102 x 102
Coating Aluminum
Spectral Order m = 1
Polarization(s) S, P & Average
Efficiency 420h_6001_m1_spa

Blazed Holographic Grating Construction

Holographic diffraction gratings typically have a sinusoidal surface profile generated optically by recording an interference pattern onto a photoresist-coated substrate. The photoresist is then coated with a vacuum deposited metal layer to produce a master grating, which may be used as a mold to produce replicated gratings. The final product typically consists of a substrate, a resin bonding layer, a patterned metal reflective layer, and a protective over coating. Holographic blazed gratings are generated by bombarding a holographically produced master with an angled beam of ions to etch the sinusoidal surface profile into a symmetric triangular profile. Holographic gratings are ideal for use in spectroscopy systems requiring very high resolution.

Ultrafast Pulse Amplification

Pairs of identical diffraction gratings that are tuned to the polarization and output wavelengths of a laser may be used to temporally compress ultrafast laser pulses, greatly increasing the peak power. When a spectrally broad laser pulse is incident on a diffraction grating, the various wavelength components will disperse, or diffract in different directions. If this pulse has its wavelength chirped (i.e. its frequency progressively increases during the length of the pulse) the first grating will diffract the leading portion of the pulse (consisting of longer wavelengths) at a greater angle compared to the trailing portion of the pulse (consisting of shorter wavelengths). When the light reaches the second grating with same periodicity the dispersion will be reversed from symmetry and the light will be collimated. Light from the leading edge of the pulse will travel a longer optical path through the pair of gratings, requiring more travel time. If the separation between the gratings is chosen so that the travel time difference matches the pulse duration, the laser power will be compressed into a nearly instantaneous pulse.

Dual Grating Compressor Setup Example

Two gratings and a mirror are used in the classic Mourou-Strickland setup, to fashion a basic ultrafast beam compressor. Gratings are typically chosen when a large amount of dispersion is required and can be used in higher energy applications because they are reflective. See the parts list of the shown setup example below.

Part No Description Quantity
Grating of Your Choice 2
DGA-25 Diffraction Grating Mount 2
481-A Rotation Stage 2
433 Linear Stage 1
20D20ER.2 2 in. Silver Mirror 1
M2 Mirror Mount 1
SP-2 Optical Post, 2 in. 1
SP-3 Optical Post, 3 in. 2
VPH-2 Post Holder, 2 in. 2
VPH-3 Post Holder, 3 in. 1

Optimum Grating Orientation

Like their ruled counterparts, holographic gratings are most efficient when used in the Littrow configuration, or aligned so that the diffraction angle of the dominant diffraction order is coincident with the input beam, effectively behaving as a retroreflector at a specific wavelength. This geometry is especially useful for applications using a diffraction grating inside a laser cavity to select a particular wavelength. Only the exact chosen wavelength will reflect into the laser cavity. Holographic gratings are particularly useful because they have peak efficiency only at a particular polarization, allowing them to be used as a substitute for a Brewster window to control the laser output polarization.

Handling Diffraction Gratings

Holographic gratings are patterned surface relief gratings, the surface cannot be touched with without damaging the fringe pattern and potentially seriously degrading the optical performance. Damage to the grating can take the form of contamination or distortion of the microscopic groove profile. Damage to this microscopic groove profile is, unfortunately, irreversible. The resin layer like modeling clay, will retain a permanent imprint. Contamination with finger oils, moisture, etc. is also often permanent. Because of the sensitive nature of the grating groove profile, it is imperative that the user take precautions in handling gratings. Do not touch the surface of the grating; handle the grating by the edges and always wear gloves or finger cots. Use a non-contact cleaning method such as dry, compressed air or a dust bulb to remove excess dust from a grating.

Float Glass Substrate

Float glass is made by floating molten glass over a bed of molten metal. While this is a low cost material that is used in commercial windows, the production method yields a very flat surface of uniform thickness making it a good choice for optics.

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.