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I've run a lot of laser diffraction experiments with nothing more than a quality laser pen, some rasor blades, a human hair and a small hole in a Christmas card as demonstrations for laymen but I'm kind of bored with these now.

I'd really like to emulate X-ray crystallography diffraction, in a backyard lab setting but found it hard to get (Google) some information on that.

One possibility is to construct a macroscopic $\text{NaCl}$-style lattice from copper single filaments, with a $d$ of about $0.1\,\mathrm{mm}$. That would of course not be easy to pull off but not impossible either, IMO.

I do have another idea, which I want to keep 'under wraps' for now because I'll be test driving it shortly.

Searching P.SE for 'laser diffraction' I came across one intriguing comment claiming $\text{XRD}$-style laser diffraction may be possible with synthetic Opal. Googling then threw up large amounts of links to applications of laser diffraction in the field of particle characterisations (something I'm not interested in for now).

And then there's a paper titled Linear and Nonlinear Optics of Synthetic Opal by M. V. Vasnetsov, V. Yu. Bazhenov, V. V. Ponevchinsky, which throws a little light on the structure of (a) synthetic Opal: the structure of one synthetic Opal

But with a lattice $d \approx 100\,\mathrm{nm}$ it isn't clear how such a material could exhibit 'laser $\text{XRD}$'.

Commercial synthetic Opals are not expensive and readily available but the samples I've seen are all either non-transparent or transparent like glass, so it's hard to see how they could produce the effect I'm looking for.

A beautiful (commercial) sample of synthetic Opal (about $8\,\mathrm{g}$):

Opal

The fascinating coulours of Opals are attributed to diffraction.

Does anyone here have experience/information on laser $\text{XRD}$ with Opal or anyother substrates?

Gert
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    You should take a look at a book called "Atlas of Optical Transforms" by Harburn, Taylor and Welberry. – Xcheckr Nov 24 '21 at 16:39
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    Perhaps use a printer to print small black dots on a transparency and stack layers of small pieces of that to mimic a crystal structure, e.g., NaCl. Just a thought. – Ed V Nov 24 '21 at 16:57
  • @EdV Yup: like that idea! – Gert Nov 24 '21 at 17:22

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I cannot give you information about Opals but only last week I came across a rainbow coloured Happy Birthday banner as shown below.

enter image description here

I flattened one corner with a couple of microscope slides and a paper clamp.

enter image description here

Using a couple of holders (as I do not a third hand to take the photograph I was able to get a 2-D diffractions pattern from which I was able to evaluate the "crossed" grating line spacing.

enter image description here

Farcher
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  • Hey, that's wonderful! So you shone the laser (a pointer pen?) straight (perpendicularly) on the material? What gave you the idea? – Gert Nov 24 '21 at 17:25
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    I wondered about the colouration of the banner which was characteristic of a diffraction/interference pattern. Shifting colours as the banner or my eyes moved. – Farcher Nov 24 '21 at 18:26
  • Yes, of course. For that reason Opal should also be useable for 'laser $\text{XRF}$' because its fleeting colours are due also to diffraction. Time to buy! – Gert Nov 24 '21 at 18:56
  • I've also bought a similar Happy Birthday banner with those interesting 'ecanescent' colours, so time to experiment. – Gert Nov 24 '21 at 18:59
  • What laser did you use? With my $532,\mathrm{nm}$ green laser I'm getting very variable results but nothing as definite as your result. Interestingly my red $650,\mathrm{nm}$ laser shows $zero$ diffraction, indicating the "$d$" must be smaller than that value. – Gert Nov 26 '21 at 15:52
  • About seven years ago from Amazon (UK) Green/Red/Blue Beam Laser Pointer Combo 3 Laser Light Pens 1mw 532nm 650nm 405nm Triple Colors Astronomy Powerful. I would suggest it is the banner which might be at fault? I have just checked and the diffraction pattern can be formed from all parts of the banner although better when the light passes through the silver bit. – Farcher Nov 26 '21 at 17:05
  • Try making a double slit as I explained here, How can a double slit interference pattern be created without out going through a double slit to check the laser. PS I am just going to borrow my wife's opal! – Farcher Nov 26 '21 at 17:05
  • That's very interesting too. The banner show very vivid diffraction. The material is highly anisotropic though. I'll try that thing about the silver spots. The laser should be fine: I've run countless double slits before. Ta. – Gert Nov 26 '21 at 20:23
  • My result is great with a blue $432,\mathrm{nm}$ laser (unfortunately the photos are too heavy (>2 meg) to upload. It also seems my plastic generates much more scatter, at least with the green laser... – Gert Nov 29 '21 at 22:01
  • @Gert Were you able to get an estimate of the spacing? – Farcher Nov 29 '21 at 23:33
  • No, I need to look up how to do that again. Also, need to check for 2nd order. I would urge you to try with your $432,\mathrm{nm}$ laser. Also, it's clear your banner and mine aren't the same: with the green laser I get enormous amounts of scatter. – Gert Nov 30 '21 at 11:44