CENTRAL UNIVERSITY OF
JHARKHAND
Topic: Fraunhofer diffraction- diffraction by a single slit
Submitted to: Submitted by:
Dr. Dharmendra Singh Suraj kumar
23160503021
Department of Physics 4th Semester
Contents
1. Introduction
2. Fraunhofer diffraction
3. Fraunhofer’s diffraction at a single slit
4. Position of maxima and minima
5. Applications
6. Conclusion
1. Introduction
The spreading of out a wave when it passes through a narrow opening is usually
referred to as diffraction, and the intensity distribution on the screen is known as the
diffraction pattern.
2. Fraunhofer Diffraction
In Fraunhofer diffraction, the source and the screen are effectively placed
at infinity using two convex lenses. The first lens positioned at the
source’s focal plane, converts divergent light into a parallel beam. The
second lens placed before the screen, refocuses this parallel beam onto the
screen.
This setup ensures that diffraction pattern is observed under ideal
Fraunhofer condition.
3. Fraunhofer Diffraction at a single slit
Let a parallel beam of monochromatic light of wavelength (λ) be incident
normally upon a narrow slit of width (AB), placed perpendicular to the
plane of paper. The diffraction light be focused by a convex lens on the
screen (XY), placed in the focal plane of the lens.
The diffraction pattern obtained on the screen consists of a central bright
and having alternative dark and weak bright of decreasing intensity on the
both sides.
4. Position of maxima and minima
At point O , on screen we get maximum intensity and
therefore point O is known as “central maxima”.
Condition for dark fringes
A dark fringes occurs when destructive interference happens.
bsinθ= nλ ; n =1,2,3... ; b = slit width
Condition for bright fringes
A bright fringe (other than the central maximum) occurs
when the intensity is not completely zero, but these are
much less bright than the central maximum.
bsinθ= (n+1)λ/2 ; n=1,2,3... ; b = slit width
• Central maximum is the brightest and occurs at θ = 0, with
no path difference.
5. Applications
1. Optical Instrumentation – Used in designing optical devices like microscopes, telescopes,
and spectrometers to analyze light patterns and improve resolution.
2. Spectroscopy – Helps in studying the wavelength composition of light by analyzing
diffraction patterns, essential in identifying elements in stars and materials.
3. Resolving Power of Optical Systems – Determines the ability of lenses and apertures to
distinguish between closely spaced objects, crucial in astronomy and microscopy.
4. Laser Beam Profiling – Used to analyze the intensity distribution of laser beams in optics
and engineering applications.
6. Conclusion
• Fraunhofer diffraction through a single slit demonstrates the wave
nature of light.
• As seen in the formation of alternating bright and dark fringes. The
central maximum is the brightest.
• With subsequent maxima of decreasing intensity on either side.
• Wave optics and has applications in spectroscopy, optical
instruments, and resolving power analysis of optical systems.
