Aruna-1 Spectrometer Design

The pictures below label the various components of the spectrometer. Using the handgrip, the user aims the entrance slit towards the light while looking through the diffraction grating. The spectrum of the light will be seen through the grating, off axis, at an angle on either left or right sides. The back of the mask plate and bottom of the top plate are flat black to provide a dark background against which to view the spectrum. An additional light shield (not shown in the pictures) prevents light, other than that passing through the entrance slit, from falling onto the grating.

Front view of the Aruna-1 with labelled components: mask plate, base plate (8"), slit plate, and hand grip. The light shield has been removed.

Back view of the Aruna-1 showing labelled components: top plate, diffraction grating, grating holder, base plate, mask plate, and slit plate. The light shield has been removed.

Major Components

The major components of the Aruna-1 spectrometer include the ones listed below. The components are held together using wood screws. A complete parts list, drawings of the components including dimensions and drill positions, and a drill table for hole sizes and depths are provided following the major components list.

Base Plate

The base plate is a rectangular plate to which the other major components are mounted, using screws. There are three different lengths for the baseplate, to accomodate the near-focus of the user: 6", 8", and 10".

Slit Plate

The slit plate is a rectangular metal plate on which the entrance slit is built. The entrance slit consists of two sharp knife blades placed close together to make a very narrow aperture to admit light from a source into the spectrometer. The slit plate mounts to the front of the base plate.

Grating Holder

The grating holder is a wooden holder, assembled from several smaller wooden pieces, and holds a diffraction grating, centered on the optical axis of the spectrometer. The grating holder is mounted towards the back of the base plate.

Mask/Viewing Plate

The mask or viewing plate is a rectangular wooden plate which has a rectangular cutout to admit light from a small region along the optical axis towards the grating, further restricting light from entering the grating except along the optical axis. The plate provides a dark background against which to view the spectrum formed by the grating and eye combination. The mask/viewing plate mounts to the base plate a few inches in front of the grating holder.

Top Plate

The top plate is a rectangular wooden plate, the same size as the mask/viewing plate, and also restricts off-axis light from entering the diffraction grating. The top plate shields the viewing area from external light, and mounts to the mask/viewing plate.

Light Shield

The light shield is a folded paper mask used to prevent additional stray light from reaching the diffraction grating, and producing unwanted spectra or brightness in the viewing area. Stiff paper such as material from a poster board is used to make the light shield, which encloses the region between the slit plate and the mask plate.

Hand Grip

The hand grip is a half-inch diameter wooden dowel, by which the user can hold and aim the spectrometer towards a light source. The hand grip mounts to the base plate.

Diffraction Grating

The diffraction grating is a low-cost holographic film grating card, 2" x 2", with 500 grooves/mm. This card will fit snugly in the grating holder, and the spectrum of the light source is viewed by looking into the grating at an angle.