Fourier Spectroscopy with the Michelson Interferometer

Results and Discussion

HeNe Laser

The HeNe Laser was used in this experiment because of its known wavelength. Using the Fourier transform for this light source, I was able to calibrate the other graphs accordingly. It was also hoped that the HeNe laser would provide for a very narrow peak showing its monochromatic nature. The following graphs show the results of the HeNe laser transform.

Interferogram- HeNe laser
Spectrum- HeNe laser spectrum showing monochromatic laser light.

While these graphs do show a single frequency existent in the laser light, the width of the spectrum is greater than had been hoped for. This is most likely due to the small amount of time (180 seconds) during which data was taken. More data would most likely narrow this peak around 632.8 nm.

Sodium Lamp

The sodium lamp emits light in the visible spectrum mostly in the yellow region. The sodium spectrum shows many lines in this range. Also note the waving of the sodium inteferogram. The sodium lamp emitted a very inconsistent intensity of light.
Interferogram- Sodium lamp shows wandering intensities
Spectrum- Sodium lamp spectrum; accepted wavelengths shown in blue.

The sodium spectrum does show a strong wavelength presence near 585 nm.

Cadmium Lamp

The cadmium lamp emits visible light in the green-blue range. It also has a strong presence of in the ultraviolet range which the data was able to pick out.
Interferogram- Cadmium lamp shows well the beat pattern associated with multiple wavelengths.
Spectrum- Cadmium lamp spectrum; accepted wavelengths shown in blue.

Filtered White Light

The white light filter used passes a band of wavelengths centered around 632.8 nm with a FWHM of 10 nm. The interferogram shows that the interference pattern exists only in one small range of path-length differences.
Interferogram- Filtered white light shows a narrow band of interference patterns.
Spectrum- Spectrum shows a band of wavelengths centered at 632.8 nm

White Light

Similar to the filtered white light, the white light inteferogram shows an even narrower interference pattern.
Interferogram- White light shows narrowest band of interference
Spectrum- White light consists of a large band of wavelengths across the spectrum

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