---
title: "Getting synchrotron light onto a sample"
description: "Slits select directions, crystals select photon energies, and mirrors focus the accepted light. Follow what survives to the sample."
canonical_url: "https://sandboxphysics.com/stories/instruments/synchrotron-beamline/"
language: "en"
page_type: "story"
alternate_languages:
  zh-CN: "https://sandboxphysics.com/zh/stories/instruments/synchrotron-beamline/"
last_modified: "2026-11-12"
---

[How physics instruments measure](https://sandboxphysics.com/stories/instruments/)

# Getting synchrotron light onto a sample

A sample may be as small as a pinhead. An experiment needs X-rays to land on it, often with closely matched photon energies. The source supplies light; a beamline selects the part the experiment can use. Delivery depends on the whole route.

Sandbox Physics · 2026-11-12

## An electron takes many small turns

Fast electrons in a storage ring radiate as magnetic fields bend their motion. A row of alternating magnetic poles makes an electron wiggle gently along a straight section. This device is an undulator. Each oscillation contributes radiation.

At suitable photon energies and observation directions, the contributions reinforce one another. Peaks appear in the energy distribution, including higher harmonics. Changing the magnetic field moves the peaks and helps make useful X-ray energies available.

Sources: [1] [2]

## A slit selects directions and changes the spectrum

Close the gap between absorbing blades and some light strikes the material. Far from the source, a smaller opening accepts a narrower range of directions. Undulator energy and emission angle are related, so this also changes the transmitted energy distribution.

Flux counts photons per second through a stated window. Spectral brightness additionally describes how concentrated the light is in source area, direction and energy range. Coherence concerns relationships between light-field oscillations; it requires appropriate field or interference information.

Sources: [3]

## Two crystals select a narrow energy range

Atoms in a crystal form regularly spaced planes. X-rays scattered from successive planes travel slightly different distances. When those differences match the wavelength, reflection is enhanced: Bragg reflection. Rotating the crystal changes the selected wavelength and photon energy.

A double-crystal monochromator reflects the beam twice. The first crystal selects energy; the second turns the beam back toward its original direction. Maintaining a fixed exit height while changing energy also requires moving the second crystal. Tilting it alone can reduce throughput and steer the surviving light away from the sample.

$$
2d\sin\theta=n\lambda
$$

d is plane spacing, θ is the glancing angle, λ is wavelength and integer n is reflection order. Different orders can occur at the same angle, making an independent energy readout useful.

Sources: [4] [5]

## Mirrors bring the accepted light to a focus

Useful hard-X-ray reflection usually requires a shallow grazing angle along a surface. A curved mirror redirects the accepted light toward a focus. A Kirkpatrick–Baez, or KB, system uses two mirrors to focus in horizontal and vertical planes.

Near focus, light occupies a small region. Move the sample along the outgoing path and its spot can broaden. Finite mirrors intercept only part of the beam, and their coatings reflect only a fraction of what arrives. Spot size, energy range and delivered flux must be considered together.

Sources: [6] [7]

## Measure what the sample changes

A transmission measurement brackets the sample exposure with open-beam measurements. Agreement between the two open readings supports the comparison. Independent references must also calibrate detector efficiency, electronic response and exposure time.

A thicker sample generally leaves fewer photons in the original beam. For a known material and photon energy, that change can support a thickness estimate. Removal includes both absorption and scattering into other directions. Determining deposited heat requires further information.

Sources: [8]

## Each experiment needs a suitable beamline

Energy range, spot size and sample environment vary between experiments. At HEPS, the call issued on 12 October 2026 set a 30 November deadline and expected experiments from February 2027. These were the announced plans, checked on 12 November; individual beamline opening notes determine the conditions offered to users.

Sources: [9]

## [Follow photons down a beamline](https://sandboxphysics.com/labs/synchrotron-beamline/)

Turn the second crystal and compare delivered light, screen pixels and side counts.

A given electron source and finite optics teaching model; independent references support readouts, with model-accuracy limits retained separately.

## Sources and further reading

1. [ESRF · How does a synchrotron work?](https://www.esrf.fr/home/education/what-is-the-esrf/how-does-the-esrf-work.html)

   Read storage-ring, alternating-pole insertion-device and beamline descriptions; no brightness multiplier is adopted.

2. [Kwang-Je Kim · X-Ray Data Booklet, §2.1](https://xdb.lbl.gov/Section2/Sec_2-1.html)

   Read periodic magnetic structures, undulator harmonics and angular acceptance.

3. [Sanchez del Rio & Reyes-Herrera · Modelling undulators in ray tracing simulations (2025)](https://journals.iucr.org/s/issues/2025/02/00/yn5118/index.html)

   Read §§2.1–2.4 on angular–energy dependence, electron size and energy spread, field backpropagation and ray approximations.

4. [James H. Underwood · X-Ray Data Booklet, §4.1](https://xdb.lbl.gov/Section4/Sec_4-1.pdf)

   Read the crystal section and Bragg condition; no historical lattice value from its tables is adopted.

5. [ESRF BM05 · Two-crystals Monochromator](https://www.esrf.fr/home/UsersAndScience/Experiments/BM05/BeamlineGuide/OpticsHutch/TwoCrystalsMonochromator.html)

   Read fixed-exit geometry, particularly the second-crystal translation needed when the angle changes.

6. [Eric M. Gullikson · X-Ray Data Booklet, §4.2](https://xdb.lbl.gov/Section4/Sec_4-2.html)

   Read grazing-incidence reflectivity, complex refractive index and surface-roughness dependence.

7. [ESRF BM02 · KB Mirrors](https://www.esrf.fr/home/UsersAndScience/Experiments/CRG/BM02/equipment/kb-mirrors.html)

   Read the two-mirror horizontal and vertical focusing description; its performance is not transferred to the teaching model.

8. [NIST · X-Ray Mass Attenuation Coefficients, §2](https://physics.nist.gov/PhysRefData/XrayMassCoef/chap2.html)

   Read exponential attenuation, mass thickness and the absorption/scattering contributions to total attenuation.

9. [IHEP · HEPS second general-proposal call (12 October 2026)](https://english.ihep.cas.cn/heps/user/202610/t20261012_1202300.html)

   Checked 12 November 2026: proposal deadline and expected experiment schedule; planned dates remain conditional.

[How a vernier reads between millimetres](https://sandboxphysics.com/stories/instruments/length-metrology/) [Air helps hold up the object on a balance](https://sandboxphysics.com/stories/instruments/precision-balance/) [How Cavendish Measured the Attraction Between Spheres](https://sandboxphysics.com/stories/instruments/cavendish-balance/) [Which pressure does a liquid column measure?](https://sandboxphysics.com/stories/instruments/manometer/) [The cup absorbs heat too](https://sandboxphysics.com/stories/instruments/calorimeter/) [Rotational rheometers need both torque and speed](https://sandboxphysics.com/stories/instruments/rotational-rheometer/) [Why the air beyond a pipe changes its resonance](https://sandboxphysics.com/stories/instruments/resonance-tube/) [How a seismometer reads the ground through motion inside its case](https://sandboxphysics.com/stories/instruments/seismometer/) [Why does a meter change the circuit?](https://sandboxphysics.com/stories/instruments/electrical-meters/) [How a null detector reveals a resistance](https://sandboxphysics.com/stories/instruments/resistance-bridges/) [Why a capacitor can behave like an inductor](https://sandboxphysics.com/stories/instruments/lcr-impedance/) [Where does the slow wave on an oscilloscope come from?](https://sandboxphysics.com/stories/instruments/digital-oscilloscope/) [How a lock-in amplifier finds a signal buried in noise](https://sandboxphysics.com/stories/instruments/lock-in-amplifier/) [Where a small peak in a spectrum can come from](https://sandboxphysics.com/stories/instruments/spectrum-analyzer/) [How a network analyzer separates the cable from the device](https://sandboxphysics.com/stories/instruments/vector-network-analyzer/) [When a slower quartz crystal can measure added mass](https://sandboxphysics.com/stories/instruments/quartz-microbalance/) [How an echelle spectrograph gives overlapping colors a second direction](https://sandboxphysics.com/stories/instruments/echelle-spectrograph/) [How total brightness reveals many infrared colors](https://sandboxphysics.com/stories/instruments/ftir-spectrometer/) [Measuring a Solution’s Concentration with Light](https://sandboxphysics.com/stories/instruments/uv-vis-spectrophotometer/) [How an ellipsometer reads thin-film thickness from reflected light](https://sandboxphysics.com/stories/instruments/spectroscopic-ellipsometer/) [How a polarimeter reveals mixed polarization](https://sandboxphysics.com/stories/instruments/mueller-polarimeter/) [How individual photons reveal a fluorescence lifetime](https://sandboxphysics.com/stories/instruments/tcspc-fluorescence-lifetime/) [Brillouin Microscopy Listens to Sound with Light](https://sandboxphysics.com/stories/instruments/brillouin-microscope/) [How a white sphere compares a lamp’s total output](https://sandboxphysics.com/stories/instruments/integrating-sphere-radiometer/) [How powder rings reveal atomic spacing](https://sandboxphysics.com/stories/instruments/powder-xray-diffractometer/) [How Small-Angle X-ray Scattering Reads a Particle Halo](https://sandboxphysics.com/stories/instruments/small-angle-xray-scattering/) [Why X-ray fluorescence depends on sample thickness](https://sandboxphysics.com/stories/instruments/xray-fluorescence-spectrometer/) [Why an AFM makes a bump look wider](https://sandboxphysics.com/stories/instruments/atomic-force-microscope/) [How a small indentation separates hardness from elasticity](https://sandboxphysics.com/stories/instruments/nanoindenter/) [How Differential Scanning Calorimetry Reads a Melting Peak](https://sandboxphysics.com/stories/instruments/differential-scanning-calorimeter/) [How thermogravimetry separates mass loss from the gas around it](https://sandboxphysics.com/stories/instruments/thermogravimetric-analyzer/) [How a diamond anvil cell reads pressure in ruby light](https://sandboxphysics.com/stories/instruments/diamond-anvil-cell/) [How diamond fluorescence reveals a magnetic-field direction](https://sandboxphysics.com/stories/instruments/nv-center-magnetometer/) [Reading a magnetic field in the rhythm of atoms](https://sandboxphysics.com/stories/instruments/optically-pumped-magnetometer/) [Keeping a laser in time with atoms](https://sandboxphysics.com/stories/instruments/optical-lattice-clock/) [Why a Kibble balance needs two experiments](https://sandboxphysics.com/stories/instruments/kibble-balance/) [How a dilution refrigerator keeps carrying heat away](https://sandboxphysics.com/stories/instruments/dilution-refrigerator/) [Why a bigger vacuum pump may barely help the sample](https://sandboxphysics.com/stories/instruments/ultra-high-vacuum-system/) [How microwaves read a superconducting qubit](https://sandboxphysics.com/stories/instruments/superconducting-qubit-readout/) [How current leaves a voltage across a thin sheet](https://sandboxphysics.com/stories/instruments/four-probe-hall/) [How an ion flight becomes a mass spectrum](https://sandboxphysics.com/stories/instruments/time-of-flight-mass-spectrometer/) [How four straight rods select ion mass](https://sandboxphysics.com/stories/instruments/quadrupole-mass-filter/) [How a rapidly reversing field can hold ions](https://sandboxphysics.com/stories/instruments/paul-ion-trap-mass-spectrometer/) [How a cyclotron keeps a proton on the accelerating beat](https://sandboxphysics.com/stories/instruments/cyclotron-synchrocyclotron/) [Why the drift tubes in an RF linac get longer](https://sandboxphysics.com/stories/instruments/radio-frequency-linac/) [The directions hidden inside a small beam spot](https://sandboxphysics.com/stories/instruments/beam-diagnostics/) [How defocusing magnets help a beam stay in a ring](https://sandboxphysics.com/stories/instruments/synchrotron-storage-ring/) [Why a collider cannot keep every collision](https://sandboxphysics.com/stories/instruments/collider-trigger-daq/) [How a free-electron laser gathers electrons into a brighter beam](https://sandboxphysics.com/stories/instruments/xray-free-electron-laser/) [Following energy exchange with neutron flight times](https://sandboxphysics.com/stories/instruments/pulsed-neutron-time-of-flight/)

## Keep reading

How physics instruments measure · Reading path

### How physics instruments measure

1. [Article **How a vernier reads between millimetres**](https://sandboxphysics.com/stories/instruments/length-metrology/)
2. [Article **Air helps hold up the object on a balance**](https://sandboxphysics.com/stories/instruments/precision-balance/)
3. [Article **How Cavendish Measured the Attraction Between Spheres**](https://sandboxphysics.com/stories/instruments/cavendish-balance/)
4. [Article **Which pressure does a liquid column measure?**](https://sandboxphysics.com/stories/instruments/manometer/)
5. [Article **The cup absorbs heat too**](https://sandboxphysics.com/stories/instruments/calorimeter/)
6. [Article **Rotational rheometers need both torque and speed**](https://sandboxphysics.com/stories/instruments/rotational-rheometer/)
7. [Article **Why the air beyond a pipe changes its resonance**](https://sandboxphysics.com/stories/instruments/resonance-tube/)
8. [Article **How a seismometer reads the ground through motion inside its case**](https://sandboxphysics.com/stories/instruments/seismometer/)
9. [Article **Why does a meter change the circuit?**](https://sandboxphysics.com/stories/instruments/electrical-meters/)
10. [Article **How a null detector reveals a resistance**](https://sandboxphysics.com/stories/instruments/resistance-bridges/)
11. [Article **Why a capacitor can behave like an inductor**](https://sandboxphysics.com/stories/instruments/lcr-impedance/)
12. [Article **Where does the slow wave on an oscilloscope come from?**](https://sandboxphysics.com/stories/instruments/digital-oscilloscope/)
13. [Article **How a lock-in amplifier finds a signal buried in noise**](https://sandboxphysics.com/stories/instruments/lock-in-amplifier/)
14. [Article **Where a small peak in a spectrum can come from**](https://sandboxphysics.com/stories/instruments/spectrum-analyzer/)
15. [Article **How a network analyzer separates the cable from the device**](https://sandboxphysics.com/stories/instruments/vector-network-analyzer/)
16. [Article **When a slower quartz crystal can measure added mass**](https://sandboxphysics.com/stories/instruments/quartz-microbalance/)
17. [Article **How an echelle spectrograph gives overlapping colors a second direction**](https://sandboxphysics.com/stories/instruments/echelle-spectrograph/)
18. [Article **How total brightness reveals many infrared colors**](https://sandboxphysics.com/stories/instruments/ftir-spectrometer/)
19. [Article **Measuring a Solution’s Concentration with Light**](https://sandboxphysics.com/stories/instruments/uv-vis-spectrophotometer/)
20. [Article **How an ellipsometer reads thin-film thickness from reflected light**](https://sandboxphysics.com/stories/instruments/spectroscopic-ellipsometer/)
21. [Article **How a polarimeter reveals mixed polarization**](https://sandboxphysics.com/stories/instruments/mueller-polarimeter/)
22. [Article **How individual photons reveal a fluorescence lifetime**](https://sandboxphysics.com/stories/instruments/tcspc-fluorescence-lifetime/)
23. [Article **Brillouin Microscopy Listens to Sound with Light**](https://sandboxphysics.com/stories/instruments/brillouin-microscope/)
24. [Article **How a white sphere compares a lamp’s total output**](https://sandboxphysics.com/stories/instruments/integrating-sphere-radiometer/)
25. [Article **How powder rings reveal atomic spacing**](https://sandboxphysics.com/stories/instruments/powder-xray-diffractometer/)
26. [Article **How Small-Angle X-ray Scattering Reads a Particle Halo**](https://sandboxphysics.com/stories/instruments/small-angle-xray-scattering/)
27. [Article **Why X-ray fluorescence depends on sample thickness**](https://sandboxphysics.com/stories/instruments/xray-fluorescence-spectrometer/)
28. [Article **Why an AFM makes a bump look wider**](https://sandboxphysics.com/stories/instruments/atomic-force-microscope/)
29. [Article **How a small indentation separates hardness from elasticity**](https://sandboxphysics.com/stories/instruments/nanoindenter/)
30. [Article **How Differential Scanning Calorimetry Reads a Melting Peak**](https://sandboxphysics.com/stories/instruments/differential-scanning-calorimeter/)
31. [Article **How thermogravimetry separates mass loss from the gas around it**](https://sandboxphysics.com/stories/instruments/thermogravimetric-analyzer/)
32. [Article **How a diamond anvil cell reads pressure in ruby light**](https://sandboxphysics.com/stories/instruments/diamond-anvil-cell/)
33. [Article **How diamond fluorescence reveals a magnetic-field direction**](https://sandboxphysics.com/stories/instruments/nv-center-magnetometer/)
34. [Article **Reading a magnetic field in the rhythm of atoms**](https://sandboxphysics.com/stories/instruments/optically-pumped-magnetometer/)
35. [Article **Keeping a laser in time with atoms**](https://sandboxphysics.com/stories/instruments/optical-lattice-clock/)
36. [Article **Why a Kibble balance needs two experiments**](https://sandboxphysics.com/stories/instruments/kibble-balance/)
37. [Article **How a dilution refrigerator keeps carrying heat away**](https://sandboxphysics.com/stories/instruments/dilution-refrigerator/)
38. [Article **Why a bigger vacuum pump may barely help the sample**](https://sandboxphysics.com/stories/instruments/ultra-high-vacuum-system/)
39. [Article **How microwaves read a superconducting qubit**](https://sandboxphysics.com/stories/instruments/superconducting-qubit-readout/)
40. [Article **How current leaves a voltage across a thin sheet**](https://sandboxphysics.com/stories/instruments/four-probe-hall/)
41. [Article **How an ion flight becomes a mass spectrum**](https://sandboxphysics.com/stories/instruments/time-of-flight-mass-spectrometer/)
42. [Article **How four straight rods select ion mass**](https://sandboxphysics.com/stories/instruments/quadrupole-mass-filter/)
43. [Article **How a rapidly reversing field can hold ions**](https://sandboxphysics.com/stories/instruments/paul-ion-trap-mass-spectrometer/)
44. [Article **How a cyclotron keeps a proton on the accelerating beat**](https://sandboxphysics.com/stories/instruments/cyclotron-synchrocyclotron/)
45. [Article **Why the drift tubes in an RF linac get longer**](https://sandboxphysics.com/stories/instruments/radio-frequency-linac/)
46. [Article **The directions hidden inside a small beam spot**](https://sandboxphysics.com/stories/instruments/beam-diagnostics/)
47. [Article **How defocusing magnets help a beam stay in a ring**](https://sandboxphysics.com/stories/instruments/synchrotron-storage-ring/)
48. [Article **Why a collider cannot keep every collision**](https://sandboxphysics.com/stories/instruments/collider-trigger-daq/)
49. [You are here **Getting synchrotron light onto a sample**](https://sandboxphysics.com/stories/instruments/synchrotron-beamline/)
50. [Article **How a free-electron laser gathers electrons into a brighter beam**](https://sandboxphysics.com/stories/instruments/xray-free-electron-laser/)
51. [Article **Following energy exchange with neutron flight times**](https://sandboxphysics.com/stories/instruments/pulsed-neutron-time-of-flight/)