Ring Spectrometers

US Patent US20110273707 A1, David Labrecque, UMaine Chemistry Dept.,
davidlab@maine.edu, 581-1195, PhysicsGuy.Org

The University of Maine has received a full patent on a new type of optical component invented by David Labrecque called a ring diffraction grating. A ring grating is a bowl-shaped diffraction grating that diffracts and concentrates light into spectral rings for analysis. Ring spectrometers typically utilize a large ring grating, an array sensor, a fiber optic and processing software to generate emission, absorption and fluorescence graphs.  Scientists use graphs like these to identify chemicals on surfaces, in test tubes, in stars, and even on planets using Mars Rover-type robots.

The ring grating has some advantages over traditional gratings: The ring grating is circular and works well with low-cost circular lenses and mirrors. Circular gratings can be made to capture and concentrate more light than traditional gratings. There is less need for additional optics and more expensive detectors and light sources.  Separate arc segments of the ring spectra can be filtered and/or processed differently, enabling robust ring spectrometers without moving parts to be designed to do multidimensional experiments like three dimensional (emission, excitation, intensity) fluorescence scans.

A wide range of scientific instruments can utilize this new type of optical component. The range goes from low-cost instruments to be used in astrophysics, chemistry and physics labs in high schools and colleges, to high performance atomic absorption, fluorescence and Raman instruments to be utilized in research labs and industry.


DIY Ring Spectrometer











Standard off-the-shelf optical design software does not include ring gratings as a building block, so interactive software was developed to design ring spectrometers. This software shows how and where the rings are formed for a point light source. The software also reveals that a flat ring grating (with an infinite radius of curvature) creates virtual spectral ring images that can be photographed by a camera. The interactive software allows the designer to move the ring grating and other optical elements around with a mouse and instantly observe the light-rays and ring patterns. It can be used to design ring spectrometers for a wide range of applications.

For example, the software was used to design $50 UV-Vis Ring Spectrometers. A 50 cent DVD is used as a large ring grating along with a fiber optic and a modified webcam as the array sensor. It has a wavelength range of 350 nm to 900 nm with a resolution of 2 nm. The one on the left shown below has an internal light source and cuvette holder. The right one has an external cuvette holder and a mercury-argon light source. This spectrometer was used to generate the emission ring image shown here for mercury and argon.

Ring Spectrometer Prototypes















This low-cost powerful tool allows students to interactively investigate the world around them. By pointing the detection end of the fiber optic in various directions, they can study mercury lines in compact fluorescent lamps, how low-E window glass blocks near infrared and how gases and liquids absorb light. Many labs written for more expensive spectrometers are already available. Imagine how much interactive learning could take place if every student in a chemistry, physics or astrophysics lab had their own personal spectrometer.