A crystal selects wavelength
Lattice-plane spacing d and glancing angle θ select constructive reflection at wavelength λ and order n. Independent angle and energy readouts together identify the order.
Synchrotron Beamline
Why can a bright source deliver very little light to a sample? A beamline selects the directions and energies that reach a sample. Slits and crystals remove part of the light; mirrors focus what survives. Independent counter calibration supports flux and transmission measurements.
Follow an undulator beam through a slit, two crystals and two focusing mirrors. Compare energy selection, focus and transmission using screen pixels and side-counter readouts.
What the instruments recorded
Screen widths and reference limits
These widths describe calibrated synthetic ray-model pixels, not precision predictions for a real beamline. A separate phase-preserving wave comparison found about 7.7% difference in vertical 80%-width for the 0.2 mm slit and about 0.8 pixel centroid displacement. Its own convergence remains unqualified. Readout uncertainties exclude these model differences; absolute subpixel alignment is withheld.
Independent energy, flux and clock references
Each cell receives its own counts. Held-out references do not set the response curve. Overrange readouts and insufficient reference information withhold the affected inference.
| Role | Known energy / eV | Known flux / photon s⁻¹ | Cell counts, min–max | Overrange |
|---|
Model prediction and photon ledger
Forward calculation, separate from measured inference. Missing reference data does not prevent raw-data reduction.
| Plane | Photons / s | Energy / W |
|---|
Keep or import the complete archive
Eight immutable records; 64 MiB decoded limit. JSON and CSV retain every raw observation and calibration. Import validates the whole archive before changing the session.
Open an empty session in another window · Use an empty session to reopen an entire exported archive without conflicting record identities.
Delivering light to a sample
BackgroundA slit, crystals and mirrors pass only the part of a source accepted by the beamline. The photon rate at the sample depends on every element along that path.
Why it mattersSelecting a narrower range or a smaller spot often costs photons. Following the path alongside the readouts reveals where delivery is lost.
- Focus question
- Why can a bright source leave the sample short of light?
- One-sentence intuition
- Slits select directions, crystals select energy, and mirrors set the focus. Independent response standards convert side counts into flux.
Core mathematical model
Bracket the sample with open measurements
The numerator is calibrated flux with the sample; the denominator comes from independent open exposures before and after it. An unstable bracket withholds transmission. Shared calibration errors retain their correlation.
Thickness for a given material
The total attenuation coefficient μ belongs to the given aluminium family. The central ray is normal to the sample; oblique rays use their actual path length. Total attenuation includes scattering out of the primary beam and is not a heat-deposition measurement.
Common difficulties
Side counts and flux
Typical misconceptionThe number counted each second equals the photons delivered to the sample.
Better mental modelA weak foil scatters a tiny fraction into a finite detector with its own response. Independent whole-path references support the conversion.
Brightness and coherence
Typical misconceptionMore photons in a smaller spot directly reveal coherence.
Better mental modelFlux describes the arrival rate. Coherence concerns stable relationships in the light field and needs suitable field or interference information.
Run the experiment
- 01
Follow the whole path
Open the crystal, mirror and sample views, then inspect the default screen and counter spectrum.
What to observe: Two crystal reflections return the beam to a direction parallel to its entrance. The two mirrors focus in different transverse planes. - 02
Narrow the doorway
Choose A narrower doorway and compare its saved measurement with the default.
What to observe: The slit removes some directions and changes delivered flux. A narrower profile does not directly identify coherence. - 03
Turn the second crystal
Choose The second crystal turns. Inspect endpoints, side counts and screen edges.
What to observe: The second reflection changes both acceptance and direction. Clipped pixels are retained while unsupported full-profile widths are withheld. - 04
Move beyond focus
Choose Beyond the focus and compare the separate screen exposures.
What to observe: Moving the sample plane broadens the spot. Independent camera references supply pixel scale and point-spread width. - 05
Thicken the sample
Choose Few photons get through and inspect individual cell counts and transmission uncertainty.
What to observe: Fewer counts increase statistical uncertainty. Insufficient references or signal withhold the affected thickness inference and retain the raw observations.
Related experiments and articles
You are hereSynchrotron Beamline
How physics instruments measure · Reading path
How physics instruments measure
Articles on this path that use this experiment, followed by the other experiments they suggest.