High Resolution Spectroscopy

This post isn't really about Astronomy but it's definitely related to the Rainbow Optics diffraction grating I bought last year.  Plus Atomic Spectra is just so cool that you can't not like it!

About six months ago a friend of mine gave me an article he wrote for the Journal of Chemical Education explaining how to build a high resolution spectroscope with materials you find around your house (with one exception). The construction process wasn't particularly difficult, but my meager woodworking skills meant it took a lot of time.  Eventually I asked one of my students to help me since he was in the middle of a woodshop course at school. 

The spectroscope itself is fairly simple.  Its a Littrow-type spectroscope that contains a single slit for light to pass through, a mirror, a lens, a high resolution diffraction grating and a focuser/lens.  After a few months I tweaked the focuser a bit so I could use a camera with it. 

The photo below is taken directly from the article (Vanderveen, Martin & Ooms, 2013) and shows all the pieces necessary to build the spectroscope.
The basic parts list as well as the approximate cost is below:

•  1/2" plane wood ($15)
• Screws, nuts, bolts of various sizes ($5)
• Knife or Razor blades ($5)
• Plane mirror ($5)
• Collimating lens ($15)
• Diffraction Grating ($130)
• Focuser ($20)
• Eyepiece ($15)

The spectroscope operation is fairly simple.  Light passes through a slit created by the two knife blades.  It is reflected 90 degrees by the plane mirror and travels through the Collimating Lens (I used an old photocopy lens).  It strikes the reflecting diffraction grating and is sent back through the lens and out to the eye piece where the spectrum can be seen or photographed. In actualilty putting everything together was a bit more challenging then it sounds; the biggest difficulty was getting the light rays to strike the mirror and diffracting grating at the right angle so it missed the edges of the lens and was sent back straight through the focuser.  All it took was a bit of tweaking but it ended up taking a lot of time.


Visually observing spectra was dead easy. However photographing it proved to be quite the challenge.  At first I was set on using my DSLR camera but that proved to be untenable.  The camera body was simply to large and in combination with the focuser I was using couldn't get the chip close enough to the lens inside the spectroscope to properly focus.  But once I switched to my Lumenera camera, which has a much smaller body, it was a breeze.  In addition to imaging the spectrum seen through the spectroscope I used the program RSPEC to further analyze it.  After some basic calibration it was clear that this spectroscope has a very high resolution.

 This is a calibration spectrum I took of a Compact Florescent light in my kitechen Despite other abient light from the windows and virtually no processing its very easy to identify several elements in the spectrum. 

Below my spectrum is a laboratory refrence of a CF bulb.  As you can see its very easy to identify the peaks!

Once the weather clears up I plan to take the entire set up outside and see if I can pull the Fraunhofer lines from the solar spectrum.  See! I told you there was an astronomy bent to this!