MVLscope LESSON 10 / About 32 min
Read the signal by following its origin
Interactions with Matter
Track light, fluorescence, electrons and probe forces from the specimen interaction to the detector. Learn what a signal can — and cannot — establish.
Before you begin
Illumination · Contrast · Noise
Try a setting, save an observation, then change one thing. The explanation checks are optional.
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MAKE SENSE OF WHAT YOU SEE
A QUESTION TO THINK ABOUT
See the assembly in 3D Optional · all controls also work above
Optional 3D view. The calculated diagram above is the measurement reference.
YOUR EVIDENCE
Keep the comparison.
Saved images and readouts stay as they were when you captured them. Save a second setting to compare side by side.
Your notebook is empty. Use “Save this observation” beside an experiment.
Lesson outline
Where did the light go?
A dark image can have several causes. A photon can keep travelling in the original direction, be absorbed, or be redirected by scattering. The detector only counts the part of the outgoing light that reaches it.
Darkness alone does not identify an interaction. State what the detector collected before interpreting brightness.
Follow a fluorescence photon budget
Fluorescence converts absorbed excitation into a new optical signal. The fluorophore, its environment and the collection path determine how much of that signal becomes data.
Absorption, emission and detection are separate efficiencies. Report excitation and emission conditions as well as image brightness.
One electron beam, several information depths
An SEM probe can be much narrower than the region in which electrons scatter. Secondary electrons, backscattered electrons and X-rays carry different information from that region.
Choose the signal before interpreting the image. Probe size and sampled volume answer different questions.
Thin enough for the question
TEM uses electrons that pass through a specimen. The transmitted beam contains electrons with different scattering histories, and the optics decide which contribute to the image.
Specify specimen thickness, scattering regime and detector acceptance; a TEM image is not an untouched shadow of the object.
A probe changes what it touches
An AFM senses a force between a tip and a surface. A soft cantilever bends, and a soft specimen can deform too. The measured displacement has more than one contribution.
The signal is an interaction with the specimen. Test whether changing the measurement force changes the apparent structure.
Model, limits & sources
All figures are explanatory models, not experimental images or predictions for a particular instrument.
Light fractions describe first events; multiply scattered paths and interfaces are excluded. Fluorescence pairs are illustrative, with no real dye spectra.
Electron range is an empirical bulk estimate. Coloured SEM volumes are not Monte Carlo simulations or calibrated information depths.
TEM uses independent-event probabilities, not electron-wave propagation. AFM uses two linear springs, not a material-specific contact model.
Read further
- IUPAC Gold Book — Beer–Lambert law and its conditions ↗
- IUPAC Gold Book — Stokes shift ↗
- Nikon MicroscopyU — Introduction to fluorescence microscopy ↗
- NIST — SEM dimensional metrology and the Kanaya–Okayama range ↗
- JEOL — Secondary electrons and their signal origins ↗
- JEOL — Scanning Electron Microscope A to Z ↗
- TU Delft — Biological electron microscopy: sample preparation ↗
- Bruker — Atomic force microscopy for life sciences ↗
PUT THE IDEA TO WORK
Use signal origin, specimen state and the research question to build a defensible measurement plan.