Can a Red Laser Create Beautiful Diffraction Patterns with Limited Materials?

[p.tryon]

Hi
I was wondering whether anyone could suggest ways of making nice diffraction patterns using a red laser. I work at a charitable school in Kazakhstan so am limited in terms of materials. Any suggestions would be appreciated. Thanks

 

[ks_physicist]

What kind of diffraction patterns do you want to look at?

Do you have an old CD or DVD laying around? Bouncing a laser off of that, it acts as a diffraction grating.

You can use two razor blades mounted to make a nice single slit. You can even put a thin wire between them on one end, and make the blade edges touch at the other, and have a continuous variable width single slit.

I've seen double slits made with two razor blades and a thin wire.

 

[thaddeus]

Turn the lights off in the lounge or kitchen etc .. and fire the laser beam at all sorts of stuff ..

Personally i like aiming at frosted or florescent light bulbs , but you will find all sorts of objects that work well in this regard (especially glancing angles where you aim at the edge of an object .

 

[ks_physicist]

Two more ideas. One that was done at my university and the photos featured in the Serway undergrad text...if you have a beam expander, make the beam larger than whatever small coin you have there. We generally use a penny or a dime, which are 9.25mm and 8mm in diameter, and are suspended by the thinnest thread we can find. When projected in a dark room, with a good expanded beam, you can see the shadow of the coin within the beam on a target some distance away. You will also see a bright spot in the CENTER of the target--a bright spot that can only be there because of diffraction. If it isn't clear, try moving the target closer or farther away--I don't recall the exact distance we used, but it was within an indoor laboratory.

Also, try stretching a hair straight and shining the laser on it. Try different hairs--see if the students can rank the hairs by thickness based on the diffraction pattern.

Use a piece of foil--even a candy wrapper--and make a tiny pinhole in it. I have made really small ones by placing the foil on a piece of glass, and tapping the pin on the surface of the foil. You'll see a circular aperture diffraction pattern--bright center spot, alternating dark/light rings.

 

[ks_physicist]

I found another I remembered--do you have a decent laser printer and transparency sheets that will work in it?

http://physics.bgsu.edu/~vanhook/gratings/

 

[p.tryon]

I love this site! Thank you so much for all these great ideas. I will try experimenting. The laser jet prints look amazing but I don't think we have the laser jet :-(

P.S. if we were investigating hair width based on the diffraction pattern is there an equation we would need?

Thanks again!

 

[thaddeus]

I would investigate first without an equation if i was you p.t .
Bring forth equation from observation is a encouraging cycle .

Another thing to mention is that by reflecting the coherent bean obliquely off an object you can achieve a primary dispersion pattern ..

The secondary linear filtering of this pattern through a window can reduce the Photon beam considerably .. which can be interesting .

Also using some small electric fans as oscillating gates the beam can be further reduced in volume ..

cheers

 

[ks_physicist]

You could "calibrate" the hair-measuring laser setup by using wire of known thickness...maybe magnet wire. Measure the characteristics of the diffraction pattern with the various thicknesses of wire, look for a mathematical relationship between the pattern and the wire thickness, then interpolate or extrapolate to the thickness of the hair.