In the double-slit experiment with single particles or photons, ensuring that only one particle or photon is fired at a time is crucial to observe the interference pattern characteristic of wave-like behavior. Several techniques can be employed to achieve this:
Source Control: The source of particles or photons is typically designed in such a way that it emits them one at a time. For example, a source of single photons can be created using techniques like spontaneous parametric down-conversion, where a photon source generates pairs of entangled photons, and one of the entangled photons is selected and used as a single-photon source.
Low Intensity: Another approach is to reduce the intensity of the particle or photon source to a level where the probability of more than one particle being present in the experimental apparatus at the same time is extremely low. By ensuring a low particle flux, the likelihood of multiple particles simultaneously passing through the slits is minimized.
Time Gating: In some experiments, the particles or photons are detected one at a time using detectors that have a very short temporal response. By using detectors with fast response times, it is possible to gate the detection window and ensure that only one particle is present in the apparatus at a time.
Regarding the material used for the walls of the slits, it depends on the nature of the particles or photons being used. For experiments with particles such as electrons, protons, or neutrons, the slits are typically made of a material that can act as a barrier to the particles, such as a thin metal foil or a semiconductor. The choice of material is made based on its properties, such as its ability to block or scatter the particles.
For experiments involving photons, the slits can be made using materials that are transparent to the specific wavelength or range of wavelengths being used. In optical double-slit experiments, materials like thin films or glass plates with narrow slits etched or fabricated onto them are commonly employed.
It is important to note that the choice of material and the design of the experiment depend on the specific requirements of the experiment and the nature of the particles or photons being used. Various factors, including the wavelength, energy, and behavior of the particles, are considered when designing the experimental setup.