spektroskopy for fun and everyone!

[Krutz]

hi everybody!

just want to share what i have been up to last days..
you surely all know those "magic googles" (no, not those x-ray-googles!) you find in cereal boxes sometimes, those which make everything look colorful.
like here: http://astromedia.de/shop/images/MSF+Kerze1.jpg
they perhaps are the most common use of gratings. gratings are either reflective or transmissive. the transmissive is a foil or glassplate with many parallel lines on it. the reflective one is the same, with a mirror behind.
so everything i say about transmissive ones is valid for reflective ones too. here i will be talking about (my) transmissive grating. the distance between the lines is in the order of 1000 to 5000 nm, that is 500 to 1000 lines per millimeter! looking at one, it looks transparent, with a slight "oil-film" appearance.

the funny thing with those is:
-shine a (laser-) beam through it, it will go straight through
-a second (and third) dot will be visible next to the original dot

the distance between those two dots (the angle in fact) depends on the wavelength.
a blue dot will be nearer to the original dot than a red one.

so far for the theory.

some time ago, i bought some handheld-diy-cardboard spektroskopes here
http://astromedia.de/shop/csc_fullview.php?Artikelnummer=406.hsp (german)

with that, you can nicely analyse different lightsources, like actually seeing how a CRT monitor lights, the difference between candles, incan, leds, hid and fluorescent tubes. it is quite accurate, since you cant really screw up the sensitive distances in this build-up. 10$, one hour building.

i took the grating from a second (or was it third?) one, and built me a bigger spektroskope for analysing laserwavelengths. bigger to be able to measure on a bigger scale, and different setup, to not look directly into laserbeams!

first pic is the cardboard-model and some lasers.

 

[Krutz]

this here is the (almost) finished setup.
the skale is curved, so the distance between the lens/grating is the same. here it is 40cm, because of the 40cm focal length of said lens.

 

[Krutz]

here is the lens, all around painted in matte black against random reflections on the polished aluminum.

 

[Krutz]

you can see the grating glued here. it all isnt really fixed yet, but the distances and positions are about right.

 

[Krutz]

finally some coherent radiation:
blu-ray 405 nm diode, shining through the grating, the unchanged bright dot being at position 0 of the scale. you can see the dimmer second (and a third one) left of it.

 

[Krutz]

some more to the left than the second blue dot, the second dot from a green pointer...

 

[Krutz]

and dito for a red one.

 

[Krutz]

looks good, not? easy to read what wavelength you have!

now the smallprints:
as i found out, it isnt exactly trivial to print said scale. in theory, it should be easy: angle of 0° means 1nm, and 90° would be the distance between the lines of the gratings in nm, in my case 1111nm. sure, both a 1nm "light"source and an angle of 90° arent really possible in practise, but printing a scale with that data should be easy. unfortunaly that theory isnt true, although it sounds like that on what i read online. to make it short, the angle isnt totally linear in (my) practise. second problem: a scale up to 1111nm would be great, like being able to "see" (with my IR-webcam for example) 1064nm light from green pointers as well. unfortunately, that grating is transparent to 808nm light already. seems like it is a "printed" or photographically developed grating, with the dye being transparent to IR.
so for now, all i can do with it is what you saw on the pics. shine some lasers through it, see dots in different distance. no exact nm-reading, no IR.

 

[Krutz]

back to the original cardboard-model now.
here you see the outcome of a gas stove with salt in its flame, the distinct sodium line. because of the cam it isnt very bright, it looks even better in nature:

 

[Krutz]

and finally some lightsource. unfortunately i dont know what exactly it was.. either a short fluorescent tube or a hqi arc lamp. you see the three colors, either the stimulated three phosphors from the tube, or the three salts/gases inside the hqi bulb.

 

[Krutz]

thats it for now.
i hope you enjoyed it!
you can find much more about gratings, spektroskopy and the spektra of different lightsources online. too much to link here. start with "spectrum mercury" on google images for example.

comments welcome!
even more welcome: do experiments!

 

[chimo]

Great post(s)! Very interesting and well presented.

Paul

 

[Krutz]

thank you paul!

two things i forgot:
-my lens isnt a normal focussing lens, as i found out. it is the long "focussing" lens out of a ps3 assembly.
-you can use a cd or dvd as reflective grating. or a non-silver (but coated) cd/dvd from those big packs as transmissive grating. the dots wont be in a line, but somewhat curve, but its available, and (at least the "full" cd/dvd) works with IR too!

manuel

 

[Krutz]

okay, two links at least, both Sam's LaserFaq

http://repairfaq.ece.drexel.edu/sam/laserioi.htm#ioidpg1"
Using a Diffraction Grating to Check Laser Wavelength(s)

http://repairfaq.ece.drexel.edu/sam/laserioi.htm#ioidpg0
Diffraction Gratings
(and scroll down, next topic there is
Use of a CD, CDROM, CD-R, or DVD Disc as a Diffraction Grating

manuel

 

[SenKat]

Excellent ! That is very well done - I think perhaps I should mess around with one of those to properly classify each laser I have !

 

[disma]

wow, very nice!


Max