Demonstration of Fiber Spectrometer

On Friday, the team got a fascinating demonstration by team member Chien-Wei Han (below) of a fiber spectrometer in the optics lab at Pima College. The device measures light intensity as a function of wavelength. One application is to analyze light reflected from a surface as a means of identifying the composition of the surface. The device is light enough to carry on a small air vehicle, and might be helpful in identifying closed vs. open portals at the IARC competition.

The device, manufactured by Ocean Optics, receives light through a fiber optic connection. The small size of the fiber optic input can be seen below-right. In the demonstration, helium and hydrogen are used as example light sources. The hydrogen source (below left, next to the spectrometer) emits light in several narrow spectral lines that are associated with atomic transitions.

Incoming light is dispersed with a diffraction grating and projected onto a linear CCD array with 2048 pixels. Since the angle of deviation is wavelength-dependent, the pixels can resolve intensity as a function of wavelength. The data is transmitted through a USB port to a PC, which displays the data graphically (below). Two hydrogen lines at wavelengths of 486 nm and 656 nm are clearly visible, and a third line at 434 nm is barely visible (click on picture for larger view).

Later on, a red HeNe laser (below) was used to demonstrate a sharp peak at a wavelength about 633 nm. We also looked at various other light sources, such as fluorescent lights, LEDs and camera flash units, each with their own characteristic spectra.