Diffraction Efficiency

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.