# What are diffraction orders in nano-structures?

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1. Oct 20, 2014

Can someone please describe the diffraction orders on a nano-grating?

I am reading articles about imaging devices, and I cannot understand the diffraction orders

For example, incident wave can be mapped into a propagating wave through the -1, 0, and+1 diffraction orders.

Is any of these orders preferred over others? What is their difference?

2. Oct 20, 2014

### Hyo X

Zero order is the wave passing through without interference. The -1 and 1 are the interference peaks on either side at one wavelength away. Assuming a linear grating

3. Oct 20, 2014

I know the theory, also the equation for k'= k+ n 2 pi/period, n being the diffraction order. I want a more physical interpretation. How is it possible that the wavelength is changed when you say at one wavelength away?

4. Oct 20, 2014

### Hyo X

verbatim http://en.wikipedia.org/wiki/Diffraction_grating

"Since the path length varies, generally, so will the phases of the waves at that point from each of the slits, and thus will add or subtract from one another to create peaks and valleys, through the phenomenon of additive and destructive interference. When the path difference between the light from adjacent slits is equal to half the wavelength, λ/2, the waves will all be out of phase, and thus will cancel each other to create points of minimum intensity. Similarly, when the path difference is λ, the phases will add together and maxima will occur. "

if this is problematic you can revisit constructive or destructive interference, or the wave-particle duality and the double-slit experiment.

5. Oct 22, 2014

I have another question now, is every diffraction order a portion of the initial incident light being propagated within the medium to produce other diffraction orders or different pulses produce different diffraction orders?

6. Oct 22, 2014

### Hyo X

Do you have a reference to the paper you are reading or the source you're trying to understand?

By pulses, I assume you mean the light source is not continuous: it is an on/off/on/off/on/off blinking light source, like a laser with a chopper in front of it. Each pulse is identical and indistinguishable from each other pulse. In a standard diffraction grating, each pulse will produce all of the diffraction peaks. -n, ... -1, 0, 1, ... n.
Physically, How many peaks are observed (the number n) is determined by the quality/uniformity of the grating, the intensity and collimated -ness of the light source, and the sensitivity of the detector.

7. Oct 23, 2014