Developing, prototyping, and manufacturing a diffraction grating involves more than just solving the grating equation
mλ f = (n)2sinθ
Below are important parameters to take into consideration when designing a diffraction grating:
- Fundamental Grating Parameters
- Grating Geometry
- Diffraction Efficiency
- Stray Light
Fundamental Grating Parameters
For both transmission and reflection gratings, the wavelength range of use, configuration with respect to the incident beam(s), and grating pitch and profile, are the most fundamental design parameters. Other important parameters include diffracted wavefront, substrate size, shape, and material, incident beam polarization state, output orders of interest, stray light, and environmental requirements.
A complex grating geometry can greatly improve the performance while reducing the cost, complexity, & size of your optical system. This is achieved by adding higher-order terms to the grating design, in essence producing a flat grating with the optical performance of aspheric lenses or mirrors.
However, care must be taken because many grating designs that work on paper are impractical to manufacture. An experienced grating manufacturer is required to help guide you around the pitfalls of grating design.
Many optical systems demand high optical throughput. For e- beam written gratings, 1st order diffraction efficiencies of better than 95% are obtainable in either transmission or reflection. However, in order to achieve these high efficiencies in manufacturing, proper modeling tools as well as intuition and experience are required.
E-beam written gratings, that are blazed using Holographix’ proprietary ion beam milling process, offer lower stray light and structured noise than mechanically ruled gratings.
Choose diffraction gratings made of materials resistant to high temperatures and solvents. Replica gratings produced from thermal epoxies typically have low Tg (<80° C) and deform when exposed to harsh solvents. If durability is important, be sure to use cold formed gratings.
When coating a replicated diffraction grating with enhanced aluminum, gold, silver, or multilayer dielectrics, care must be taken to avoid crazing, defects, voids, and artifacts. Coating recipes that work on conventional lenses and mirrors often must be redesigned to work on diffraction gratings.
When quality is important, avoid committing to catalog stock gratings produced as 5th or 6th generation replicas.