What is diffraction efficiency?
Diffraction efficiency (DE) is the percentage of light sent into a particular diffraction order. Diffraction efficiency depends on a variety of factors:
- Amplitude or phase CGH
- Duty cycle
- (Phase CGH only): Depth of structures, material refractive index, and test wavelength
What are the diffraction efficiency equations?
What diffraction efficiency do CGHs from AOM typically have?
- Typical diffraction efficiency in the 1st diffraction order for an amplitude CGH with 50% duty cycle is ~10%.
- Typical diffraction efficiency in the 1st diffraction order for a phase CGH with 50% duty cycle and structure depth of λ/2(n-1) is ~40%*. (λ=test wavelength, n=refractive index of structure).
*Note: AOM requires a nonzero percentage of diffraction efficiency in the 0 order to measure a Transmitted Wavefront Error map of the substrate. To do this, etch depth is modified to reduce DE in the 1st (design) order and add diffraction efficiency to the 0 order.