Young’s two-slit experiment

Fraunhofer was also the inventor of diffraction grating, a series of parallel wires separated by variable distances as small as 0.005 cm, which acted like an enhanced version of Young s two-slit experiment and could also be used as a replacement for the prism. Passing light through the spaces between the wires forms an interference pattern beyond the grating, and the direction of constructive interference is different for each wavelength. 

When using an interferometer one is measuring coherence functions (Haniff 2007). In this section the focus is on the spatial coherence function, which is the case associated with measuring the electric field from a source at two locations but at the same time. This is equivalent to the Young s two slit experiment. 

Stellar Interferometry is based on the Young s two slit experiment, where incoming light from a source falls on two apertures (or telescopes) which then are made to interfere onto a screen. The measured quantity is the complex visibility V( , v). By selecting the position of the telescopes the Mv-map is sampled. The brightness distribution on the plane of the source is recovered by Fourier transforming the complex visibility. The aperture separation, or baseline, defines the angular resolution of the interferometer. 

Figure 7.1 Experiments using scattering methods rely on interference between wave-like radiation, here illustrated schematically in Young s two-slit experiment.

Young s double-slit experiment and the Stem-Gerlaeh experiment, as described in the two previous sections, lead to a physical interpretation of the wave function associated with the motion of a particle. Basic to the concept of the wave function is the postulate that the wave function contains all the... 

There is a direct analogy with the fringe pattern that is seen in a Young s double slit experiment, in which the diffraction pattern from two slits produces periodic fringes whose spacing varies inversely with the separation of the slits. The oscillations can also be interpreted in terms of the distortions of the reflected wavefronts in Fig. 7.2 at the Rayleigh angle (Atalar 1979). 

Sofar the imaging results of Fig. 3.1 were discussed in very classical terms, using the notion of a set of trajectories that take the electron from the atom to the detector. However, this description does not do justice to the fact that atomic photoionization is a quantum mechanical proces. Similar to the interference between light beams that is observed in Young s double slit experiment, we may expect to see the effects of interference if many different quantum paths exist that connect the atom to a particular point on the detector. Indeed this interference was previously observed in photodetachment experiments by Blondel and co-workers, which revealed the interference between two trajectories by means of which a photo-detached electron can be transported between the atom and the detector [33]. The current case of atomic photoionization is more complicated, since classical theory predicts that there are an infinite number of trajectories along which the electron can move from the atom to a particular point on the detector [32,34], Nevertheless, as Fig. 3.2 shows, the interference between trajectories is observable [35] when the resolution of the experiment is improved [36], The number of interference fringes smoothly increases with the photoelectron energy. 

Figure 1.7 In Young s double slit experiment, light passes through one slit and then into two slits. The patterns produced by the light proved that light travels as waves rather than particles.

The uncertainty principle can also be demonstrated using a modern-day version of Young s double-slit experiment. Consider that a beam of electrons is fired at a screen having two narrow slits. A suitable detector is placed some distance behind the screen in order to monitor the positions of the electrons. When one of the slits is closed, the electrons striking the detector form a Gaussian distribution exactly opposite the open slit, as might be expected. If this slit is then closed and the other one opened, a second Gaussian distribution appears at the detector opposite the... 

The radiation from an extended source LS of size b illuminates two slits Si and S2 in the plane A at a distance d apart (Young s double-slit interference experiment, Fig. 2.24a). The total amplitude and phase at each of the two slits are obtained by superposition of all partial waves emitted from the different surface elements d/ of the source, taking into account the different paths d/-Si and d/-S2. 

If, instead of one hole in the plate P, there are two narrow slits close together, we have a Young s interference experiment, and the intensity of the waves will not be uniform on the plates, but will be distributed in narrow bands as we have seen. In this case the particle will be certain to fall in one of the bands, and not in between two bands. 

---