title: Inside a spectrometer subtitle: diff types, how to build one, use cases + more
date: 07/22
intro
used to measure the composition (chemical) of a particle
we are splitting electromagnetic radiation into its individual wavelengths
background
an electromagnetic spectrum is made up of electromagnetic radiation, with varying frequency. each frequency has an associate wavelength, which has its own photon energy.
which section of a electromagnetic spectrum does spectroscopy work on?
the electromagnetic spectrum can be organized by defining specific frequency
ranges as bands that correlate to how those waves are produced, interact with
matter, and are formed. this is what we see as radio waves, microwaves,
infrared,
visible light,
ultraviolet,
X-rays, and
gamma rays 
energy - photons used for work ? wavelength is actually based on frequency.
what has energy here? what is electromagnetic radiation?
the electromagnetic FIELD (not spectrum anymore) is made up of waves with specific characteristics, like being able to propogate freely in space without needing added input (also why its called the far field, it can move a great distance away from the source that produced it). they carry momentum and electromagnetic radiant energy.
light is both a particle and a wave
types
- mass spec - takes a gas and is able to measure the spectrum of masses of all
the gases/particles
- tells you the mass to charge ratio of ions which allows you to know exactly what the chemical composition is of what you are looking at
- optical spectrometer - is able to separate the unique wavelengths that make
up visible light
- can only work on specific sections of the electromagnetic spectrum (probably the part to the right and left of the visible spectrum)
- different wavelengths of light are separated by refraction in a prism) or by diffraction by a diffraction grating
- apparently what you are actually measuring is the irradiance (intensity) or polarization state
- includes infrared
- nmr
- raman spectroscopy and infrared spectroscopy are often used in conjunction
- uses a beam of light (like a laser) to excite a bunch of photons and create raman scattering
- how much the resulting photons shift up or down decides what the chemical bonds in the sample are
Collecting evidence
https://hubblesite.org/contents/articles/spectroscopy-reading-the-rainbow fun article from hubble space
https://www.instructables.com/DIY-Low-Cost-Spectrometer/
- doable
- visible light spectrum
how this worked:
make a completely black box (to absorb any light not coming from the light source)
make a box with a tiny slit in the front for which light can enter from
put a webcam in the box and connect it to a camera, place a diffraction grating on it (like a cd) which takes light and diffracts it based on the wavelength
shine light into the box, it will hit the diffraction grating and scatter into individual wavelengths of EMR which will show up in the image the webcam produces.
you convert the image into wavelengths using opencv + a simple script (attached)
to look at the wavelengths/compositions of certain media, can pass it through a clear box of that liquid
http://engineering.nyu.edu/gk12/amps-cbri/pdf/visible_light_spectrophotometer.pdf
- spectrophotometer from NYU
near-IR spectrometer
https://caoyuan.scripts.mit.edu/ir_spec.html goated af
https://physicscourses.colorado.edu/phys4430/phys4430_fa18/Labs/Build a spectrometer v2.pdf requires materials that i dont have but great intro to diffraction grating
measure chemical composition of air
when you are trying to measure things you cant see on the visible eye, you have to use something longer or shorter to fix the wavelength.
a visible light beam (like a laser) will still interact with the particles, but only ones within a specific frequency range. ER source and particle you are looking for must be in the same frequency range?
do diffraction graters differ depending on the light source and sample?
GREENHOUSE GASES (characteristically) ABSORB INFRARED. they trap heat energy that would otherwise leave as infrared light.
greenhouse gases take infrared light emitted as a result of chemical reactions and absorb it, keeping heat in the atmosphere that otherwise would have left.
infrared working group at NCAR: https://www2.acom.ucar.edu/irwg
network for the detection of atmospheric composition change:
Lidar, which stands for Light Detection and Ranging, is a remote sensing method that uses light in the form of a pulsed laser to measure ranges (variable distances) to the Earth.
used to tell distance from source
FTIR spectroscopy is very optimal method of analyzing IR light
cool guy at nasa, official https://ndacc.larc.nasa.gov/instruments/ftir-spectrometer
https://airbornescience.nasa.gov/person/Gao_Chen
how ftir operates/Spectroscopy/Vibrational_Spectroscopy/Infrared_Spectroscopy/How_an_FTIR_Spectrometer_Operates)
Jesse Kroll - atmospheric composition at mit
https://climate.mit.edu/users/mit-department-earth-atmospheric-and-planetary-sciences
https://climate.mit.edu/users/mit-joint-program-science-and-policy-global-change
agriculture, climate
how much carbon is ur farm sequestering? low quality because we dont know what form/how long. we only know flux.
better way to measure is by sampling for carbon in the soil - through fractionation, we can tell what forms/pools its in, but fractionation assays are so EXPENSIVE
small experiment could be measuring carbon flux through a medium
then measuring it through soil
then being able to quantify net in and net out
aka making a Gas Analyzer Spectrometer or any infrared analyzer
ai, quantum computing for climate analysis, gas analysis, gas flux, spectroscopy, precision agriculture, etc.
satellite things
https://www.ycombinator.com/companies/wyvern
call for projects in electro-geo chemistry http://carbon.ycombinator.com/electro-geo-chemistry/
autochambers for greenhouse gas analysis → useful but why is this company so poor?
https://agri-epicentre.com/solutions/soil-crop-technology/soil-flux-360/
papers on ghg and gas flux
https://www.frontiersin.org/articles/10.3389/fclim.2021.742320/full
https://www.nature.com/articles/s41477-021-01042-5
diy raman spectroscope: https://pubs.acs.org/doi/10.1021/acs.jchemed.1c00584#
different production systems, their practices and their reasons for emitting what they do?
https://www.usda.gov/sites/default/files/documents/USDATB1939_07072014.pdf
estimating carbon flux with quantum computing:
Professor Milton Halem at University of Maryland Baltimore County