In 2005-2006 I decided I wanted to build
another spectrograph for science fair (and life in general). The main reason I
wanted a new spectrograph was because I wanted higher-resolution than my classical spectrograph;
also, I was building another instrument anyway, a Raman system.
Because I wanted to be able to attach the
spectrograph to my telescope and use it in physical chemistry—a spectrograph
is a spectrograph, no matter what field you use it in—I encountered some design
constraints. If I had wanted to use the new spectrograph only for astronomy, I
could have given it a focal ratio of 10 (the same as my Meade SCT); but the
Raman head that I’d already began to build had a much shorter light cone (about
f/4), and, since Raman is such a sensitive process, I wanted as much light as I
could get. The other issue was how small / compact to make the spectrograph;
with Raman it didn’t matter so much—it wasn’t as though the Raman system would
be very mobile—but that was very important for astronomy, because if my
spectrograph was too long or heavy it would cause problems on my telescope,
jarring it out of alignment, getting stuck, and so forth.
In the end I ended up building a
spectrograph with a focal ratio of about 4.8, which was—for its resolution,
about 8000—very small and compact. I had been interested in building a
spectrograph called a Littrow spectrograph for a long time, and it seemed to
offer the solution to my problem of wannting a small, fast spectrograph. I also
chose to use the Littrow design because it was cheaper, needing only one lens
(or, so I thought; in the end it probably costed just as much as a classical
spectrograph because of the extra diagonal mirror and other appendages).
It was much harder to build and align (for
me) then the classical spectrograph. In a Littrow spectrograph basically light
passes through the collimation lens one time, on its way to the grating,
reflected from a diagonal and the slit; then the diffracted spectrum passes
through the collimation lens again and hits the camera chip. The grating acts
as a mirror in one direction and disperses the spectrum in another.
Here I have uploaded an original copy of
our research paper, as well as drawings, photos, etc. for anyone interested in
building an amateur astronomical spectrograph of their own.
·
Research paper –
Construction and Operation of a Littrow Spectrograph
·
Photos / drawings of
spectrograph
·
Powerpoint
Presentation of Project
·
American
Astronomical Society abstract for presentation at 2006 meetingican Astronomical Society
abstract
Please send questions or
comments to marymast@gmail.com
last updated June 15, 2006