Unit V : Laser 2 Marks

 1. What is stimulated emission?

When an excited electron in an atom or molecule returns to a lower energy level due to interaction with an incoming photon, it emits a second photon with the same energy, phase, direction, and polarization. This is called stimulated emission. 

2. What is population inversion?

Population inversion is a condition where more atoms or molecules are in an excited state than in the ground state. This is usually achieved using external energy (optical pumping).

3. Define optical pumping.

The process of supplying energy to the laser medium (using light, electrical discharge, or chemical reaction) to excite electrons to higher energy levels in order to achieve population inversion is called optical pumping.

4. What are metastable states?

Metastable states are energy levels where excited electrons stay longer than usual. The longer lifetime allows more atoms to accumulate in this state, aiding in achieving population inversion.

5. Write note amplification of light in laser.

As light photons travel through the medium, they stimulate more emissions, resulting in amplification of light. The chain reaction of stimulated emission increases the intensity of light.

6. What is coherence of light?

Light is said to be coherent, when the photons are having constant phase difference in time and space. 

7. What is an optical resonator?

A pair of mirrors placed at both ends of the laser medium forms an optical resonator. One mirror is fully reflective and the other is partially reflective, allowing some light to escape as a laser beam. The resonator helps amplify the light and ensure that only certain directions and wavelengths are sustained.

Fresnel Assumptions

1. The entire wavefront can be divided into a large number of elements or zones of small area such that each of these elements acts as a source of secondary waves emitting waves in all directions.
2. The effect at any point “O” will be the resultant of the secondary wavelets reaching “O” from various elements of the wavefront.
3. The effect at any point due to a particular zone depends on (a). the distance of point from the zone. (b). the inclination of the point with reference to zone under consideration.(c). area of the zone.

What to Study With Priority In Optics and Laser Physics?

 Unit I : Lens and Prisms: 
2 Marks :

1. State Fermat's Principle of Least Time
2. Write any two postulates of geometrical optics
3. Define Focal Length and Power of a lens.
4. What is a narrow angled prism?
5. What is spherical aberration?
6. Define coma.
7. State any two advantages of an eyepiece over a simple lens
8. Define resolving power.
9. What is Rayleigh criterion for resolution?

5 Marks: 

1. List the postulates of geometrical optics.

2. Differentiate between thin an thick lenses

3. Discuss how chromatic aberration is eliminated using an achromatic doublet.

4. Explain how deviation without dispersion can be achieved using a combination of prisms.

5.  Explain how dispersion without deviation can be achieved using a combination of prisms.
6. Explain the working of Huygens Eyepiece.

7. Explain the working of Ramsden Eyepiece.

8. Explain the construction and working of constant deviation spectroscope.

10 Marks:

The above 5 mark questions can also be asked as 10 mark questions. Depends on your luck!

Unit II : Interference: 

2 Marks :

1. What is division of wavefront?

2. What is division of amplitude?

3. What is an air wedge?

4. State the applications of Michelson interferometer.

5. Define interference. 

5 & 10 Marks :

1. Explain how colors appear in thin films reflecting white light.

2. Derive an expression for the fringe width of fringed obtained in air wedge.

3. Provide the theory of Newton's rings.

4. Explain how the wavelength of light emitted from monochromatic light source can be determined using Michelson interferometer.

5. Describe the determination of thickness of a thin mica sheet using Michelson interferometer.

6. Describe how the Michelson interferometer is used to determine the wavelength separation of Sodium D lines.

Unit III : Diffraction: 

2 Marks:

1. What is Fresnel zone plate?

2. State Fresnel assumptions.

5 Marks:

1. List the differences between Zone plate and convex lens.

2. Distinguish between Fresnel and Fraunhofer diffraction.

3. Explain Fresnel diffraction at a single slit.

10 Marks:

1. Discuss the Fraunhofer diffraction of light through a single slit.

2.Give the theory of plane transmission grating. Describe an experiment to determine the wavelength of sodium light.

Unit IV : Polarization: 

2 Marks:

1. What is a polarizer?

2. State any two applications of polaroid.

3. Define specific rotatory power/specific rotation.

4. What is double refraction?

5 Marks:

1. Give the Huygens theory of double refraction in a uniaxial crystal.

2. Give the theory of quarter wave plate.

3. Give the theory of half wave plate.

10 Marks:

1. Explain Fresnel theory of optical rotation.

2. Explain the production and detection of plane, circularly and elliptically polarized light.

3. Describe Laurent’s half shade polarimeter and explain how specific rotary power is determined.

Unit V : Lasers:

2 Marks:

1. Define spontaneous emission.

2. What is stimulated emission?

3. What is optical pumping?

4. List any two applications of Lasers. 

5. Write note on holography.

5 Marks:

1. Write short note population inversion.

2. Describe the construction and working of a semiconductor laser.

3. Write note on holography.

10 Marks:

1. Describe the construction and working of He-Ne laser.

2. Explain how CO₂ laser works with suitable diagrams.

Fresnel Zone Plate - Lecture Notes