Diffraction

What is diffraction? Diffraction is the spreading of waves in the presence of obstacles. It occurs with sound and electromagnetic radiation, such as light, X-rays, and gamma rays. Light diffraction is when light bends around corners, causing it to roll out and brighten places where a shadow is expected. The silver line seen in the sky is due to light diffraction.

The wave bends when the light goes around an edge or through a slit. This bend is diffraction. Diffraction may be demonstrated using a candle or a tiny bright flashlight bulb and a slit formed with two pencils. The diffraction pattern, formed when light bends around an edge or edges, demonstrates that light has wavelike qualities.  Read along to know all about the phenomenon known as diffraction.

Diffraction Phenomenon

To know what diffraction is, it is important to go into its details. The diffraction phenomenon is the spreading out of waves as they pass through an aperture (an opening or hole) or around objects. It occurs when the dimension of the aperture or obstacle is of the same order of magnitude as the wavelength of the incident wave. The vast majority of the wave is blocked in the diffraction phenomenon for tiny aperture sizes. The wave passes by or through the obstacle without significant diffraction for large apertures. In an aperture with a width smaller than the wavelength, the wave transmitted through the aperture spreads around and behaves like a point source of waves. 

Single-slit Diffraction Experiment

In the single-slit diffraction experiment, light from a coherent source interferes with itself. It resulted in a distinct pattern on the screen called the diffraction pattern. Diffraction is observable when the sources are tiny enough compared to the wavelength of light.

Light is diffracted into a succession of circular waves by a long slit of microscopic width, irradiated by light. The wavefront that emerges through the slit is a cylindrical wave with a constant intensity.

Interference effects are produced by the region downstream of a slit, wider than a wavelength. The slit acts as though it contains several point sources uniformly dispersed over its width.

The light incident at a certain area downstream of the slit comprises contributions from multiple point sources. Minima and maxima in diffracted light are seen if the relative phases of these contributions differ by 2π  or more. Phase variations are caused by differences in the journey lengths required by contributing rays to reach the point from the slit.

The above logic computes the angle at which a first minimum is obtained in diffracted light. When the path difference between the two sources is equal to λ/2, the light from the top edge of the slit interacts destructively with light from the centre of the slit.

Similarly, the source just below the slit’s top will interfere destructively with the source just below the slit’s centre at the same angle. To summarise, the requirement for destructive interference over the full slit is the same as the condition for destructive interference between two narrow slits separated by half the slit width.

Application of Diffraction

Some diffraction examples are:

• Holography

An example of diffraction is holography. An interference pattern of alternating dark and light lines occurs when two laser beams collide at an angle on the surface of a photographic plate or another recording medium. This procedure creates high-quality holographic diffraction gratings because the lines are precisely parallel, uniformly spaced, and equally wide. Any hologram (holos—whole; gram—message) may be a complex diffraction grating. A hologram is created by combining a laser beam and an object’s unfocused diffraction pattern. An illuminating beam is diffracted by planar surfaces inside the hologram, using Bragg’s Law to rebuild a picture of the item (holography is also known as wavefront reconstruction). It allows an observer to view it with all the 3D details.

• X-ray diffraction

Another example of diffraction is X-ray diffraction. X-rays are light waves with extremely short wavelengths. The atoms in a solid crystal substance refract the light when irradiated. As crystals are made up of equally spaced atoms, the diffraction patterns produced are used to compute atom locations and distances. The current x-ray diffraction research uses a diffractometer to detect the structure of new materials. It is used to create diffraction patterns compared to those of known crystals.

• Spectrometer

The spectrometer is another well-known example of diffraction. All waves propagate and have a spectrum. The same is true for light waves, and as the name implies, a spectrometer is a piece of equipment used in spectroscopy. A spectrometer aids in the examination of light waves of a particular spectrum. We can thoroughly examine the material with this research and observation. Therefore, it is also used to identify distinct materials.

Spectroscopy is used in astronomy to determine the elements that make up a star.

Diffraction of light aids in determining the precise wavelength of light in spectroscopy. Astronomers may evaluate the components of a star by measuring the wavelength of light from stars using a diffraction grating.

Conclusion 

The article helps us understand what diffraction is and how the diffraction phenomenon unfolds. Diffraction is the spreading of waves in the presence of obstacles. It is explained in detail through the single-slit experiment. The phenomenon of diffraction is an important topic from the point of view of several competitive exams.