Day 1: Spectroscopy session

Communities Great Lakes GOSH
1

Attendees

Peter @mkdryden @AlexSk @dbldutch @asmithw @gbathree @ryanfobel

Summary

  • Discussed attendees’ projects and associated problems
  • Use of coherent light from the sun and how to standardize it
  • Ideas for building different types of spectrometers
  • Ideas for performing hyperspectral imaging

Notes

Context:

  • Coherent light is useful, but lasers are expensive

    • Getting coherent light from LEDs/the Sun
    • Can do interesting spectroscopy using new methodologies

  • Standards

    • Sharing data with others
    • Calibration/ wavelength standards

  • Accessibility issues

    • Expensive laser vs. laser pointer
    • Micro-LEDs and the Sun

Discussion:

  • The sun as a source
    • Big advantage of using Sun as source: The sun can be used as a standard.
      • Almost any camera/sensor can be calibrated by measuring solar light
      • Makes spectroscopy hackable
      • Can we make it consistent?
    • Coherence
      • Some amount of solar photons are coherent
        • Not as efficient, but can do some of the things we can do with lasers
      • Standardization:
        • Coherence length
        • Wavelength
        • Atmospheric effects?
  • Greg’s spectrometer
    • Uses absorbance
      • Internally referenced
      • More noise
      • Limitations in samples
      • Sensitivity
      • Standardization for absorbance:
        • Standardized filters
        • Some common methods exist
        • Intensity needs to remain constant
          • Pulse LEDs instead of constant current to hold temperature constant
      • Problems with LEDs shifting with temperature
        • Needs a lot of light for improved sensitivity
        • Currently putting devices in the oven to generate temperature calibration curves
        • Drift check routine
        • Currently getting ~10% variance
        • Use LED voltage to measure LED temperature
        • One possible solution: heat LEDs to constant temperature
    • Adam showed off dual beam phone-based spectrophotometer
      • Light source passes through both sample and reference and diffraction image of both sample and reference taken together
    • Big problem with cuvettes/mechanical differences inducing error with diffuse reflectance
    • Example applications:
      • Chlorophyll in leaves
      • Soil
      • Few things in cuvettes
  • Spectrometers:
    • Hamamatsu MEMS
    • TI Nano-spec
      • Digital micromirror device spatial light modulator
    • Neospectra
    • Cell phones
      • a lot of variability
      • Need a lot of calibration
    • DSLRs
      • more consistent
  • Fibre optics for spectroscopy
    • Coupling losses
    • Availability for citizen scientists is difficult
    • Acrylic light guides
      • UV-transmissive acrylic available now
      • Hamamatsu MEMS spectrometer
    • Coherent light sheets
      • Different layers of different colours
      • Use linear detector
  • Air quality measurements
    • Public use commonly available sensors
      • Low quality, but can help identify areas where we can come in with more sophisticated systems
      • Need a lot of data
  • Image-type data
    • A lot of research/tools available in image processing
    • Hadamard-type imaging for hyperspectral imaging
    • Vibrating fibre to image in particular pattern
  • Raman spectroscopy
    • Shifted technique
      • 6 bands of light on RGB sensor
        • Linear gradient filter
        • multiband dichroic

Action Items:

  • Application areas for spectrometers
    • air, water, food
    • VOCs in air with raman
  • Image-based sensors may be better to engage public as visual data is more interesting
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Here is a link to one example of the non-raster scanning method mediated by an oscilating (in a lissajous pattern) fiber tipped with a grin lens (https://www.nature.com/articles/s41598-019-38762-w). There are various ways of building such scanning fibers (http://dx.doi.org: 10.1364/OL.39.006675; 10.1364/OE.26.005576; 10.1364/OL.44.002232. This is something that the right engineer could comment upon. There are various ways of coating and modifying grin lens to make them achromatic (10.1364/OPTICA.5.000099). These are not your run of the mill DIY compoments. But they can be mass produced and intgrated into a trully open science harware device for the right project. Alternatively, they can be integrated into a crafted limited run device used to inspire functionally equivalent alternative designs. Sience does not answer questions, it poses them in ways that suggest plausible answers that can be interpreted provisionally and pramatically always recognizing that what we think is going on may be wrong

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