Spectral Analysis App
Purpose:
My classes are in need of a phone app that will analyze spectral images that are taken
with their phone cameras so that unknown gases can be identified.
Calibration:
The first step is to use a known spectrum and calibrate the imaging instrument. This is
an example of Hydrogen spectrum taken with my iphone. Notice that there are
emission lines on both sides of the gas tube (pink in the center). Only one side of is
needed for analysis. The wavelengths for hydrogen are in the following table:
Red
Blue
Violet 1
Violet 2
656.8 nm
486.1 nm
434.5 nm
410.7 nm
These wavelengths would then be used to scale the image in
nm/pix across a row of the image in a manner such that the origin
of the scale is the center of the emission tube.
Gaussian fitting using
is an ideal method of
determining the center of the observed emission line for accurate calculations. This is one possible
method that can determine if the outer-wings of emission lines are overlapping and appear blurred in
the image.
The relationship between the observed spectral lines and an intensity-vs-wavelength graph is
demonstrated below.
Spectral Analysis App
There is a continuous background and the emission lines are spikes above this continuum. Therefore,
background levels will need to be taken into account when determining the existence of an emission line
and the center of the line.
Experiment:
Using this calibrated scale, determine the wavelengths of the emission lines of unknown
gases. The examples below are Krypton and Mercury. Notice that due to the resolution
of the diffraction grating not all of the emission lines are observed by eye in this image.
However, large groupings of lines and relative brightness levels are significant and can
be used to identify the gases.
Krypton
Mercury
676.4 nm
568.2 nm
530.9 nm
520.8 mm
482.5 nm
476.3 nm
468.0 nm
415.4 nm
413.1 nm
406.4 nm
578 nm
546 nm
436 nm
405 nm
365 nm
334 nm
312-313 nm
297-302 nm
254 nm
Spectral Analysis App
Output:
The output of each image is an intensity-vs-wavelength plot with the emission lines
labeled, similar to the following graph.