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

Comparison Between Huygens and Ramsden Eyepieces

 

Postulates of Geometrical Optics

1. Light travels in straight lines in a homogeneous and isotropic medium.

2.When light reflects off a smooth surface, the angle of incidence is equal to the angle of reflection. The incident ray, reflected ray, and the normal to the surface at the point of incidence lie in the same plane.

3.When light passes from one medium to another, it bends according to Snell's Law:

where n₁ and n₂ are the refractive indices of the two media, and θ₁ and θ₂ are the angles of incidence and refraction, respectively.

4. The path of a light ray is reversible. If a ray of light follows a path from point A to point $B$, it will follow the same path in reverse when traveling from $B$to $A$.

5.Light rays do not interact with each other when they cross. The intensity at a point is the algebraic sum of the intensities of individual rays.

6.Light travels between two points along the path that requires the least time, which may be a straight or curved path depending on the medium.

Fermat's Principle of Least Time

Fermat's Principle of  Least Time : The path taken by light between two points is the path that requires the least time, compared to nearby paths.

Hero's Principle of Shortest Distance

Hero's Principle of  Shortest Distance : The path taken by light between two points is the path that requires the shortest distance, compared to nearby paths.

Consolidated Question Bank - Optics and Laser Physics - 23BPH4C1

UNIT - I
PART A - 2 MARK QUESTIONS

1.What is Fermat's Principle of Least Time?
2.State any two postulates of geometrical optics.
3.Define the focal length and power of a lens.

4.What are cardinal points of a lens system?
5.What is spherical aberration in a lens?

6.State Rayleigh's criterion for resolution.

7.List two merits of an eyepiece over a simple lens.

8.What is the resolving power of a telescope?
9.Define chromatic aberration in a lens.
10.What is the critical thickness of a thick lens?

11.What is the principle of a constant deviation spectroscope?

12.What are the main differences between Huygens' and Ramsden's eyepieces?

13.Write the formula for the resolving power of a diffraction grating.

14.Define resolving power.

15.What is the curvature of field in lens aberrations?

PART B - 5 MARK QUESTIONS

1.Explain Fermat's Principle of Least Time and its significance in geometrical optics.
2.Derive the lens maker’s formula for a thick lens and explain the significance of cardinal points.
3.Discuss the causes and corrections for chromatic aberration in lenses.

4.Explain the dispersion and deviation of light through a prism.

5.Compare Huygens' and Ramsden's eyepieces.

6.State and explain Rayleigh’s criterion for resolution. Derive the expression for the resolving power of a telescope.

7.Describe construction and working the constant deviation spectroscope.

8.What are spherical aberration, coma, and astigmatism in lenses?

9.Describe the chromatic aberration in lenses

10.Define resolving power. Derive an expression for the resolving power of a diffraction grating.

11.Explain the concept of narrow-angled prisms and derive the relation for minimum deviation.

PART C - 10 MARK QUESTIONS

1.Describe the concept of critical thickness and derive expressions for the focal length and power of a thick lens.

2.What is a constant deviation spectroscope? Explain its construction, working, and applications in detail.

3.Derive the lens maker’s formula for a thick lens. Discuss the significance of focal length, power, and cardinal points in optical systems.

4.Explain the working principles of Huygens' and Ramsden's eyepieces. Compare their construction, merits, and demerits, highlighting their applications.

5.Derive the expression for the resolving power of (i) a prism, (ii) a grating, and (iii) a telescope.

UNIT - II
PART A - 2 MARK QUESTIONS

1.What is interference of light?

2.Explain constructive ‘consecutive interference’ and

‘destructive interference’.

3.State the principle behind Fresnel’s biprism experiment.
4.Explain the formation of colors in thin films.
5.What is an air wedge?
6.Define Newton’s rings and mention one application.
7.What causes the bright and dark fringes in Newton’s rings

8.Write the uses of Michelson’s interferometer.

9.What is the difference between division of wavefront and division of amplitude in interference?

10.Why do Newton’s rings have a circular shape?

11.What are the conditions for constructive and destructive interference in thin films?

12.State two practical applications of interference in thin films.

PART B - 5 MARK QUESTIONS

1.Describe the working principle of Fresnel’s biprism. How are interference fringes formed?

2.Explain the formation of interference patterns in thin films due to reflected and transmitted light.

3.What are Newton’s rings? Derive an expression for the radius of the n^th ring in reflected light.

4.Explain the air wedge method and derive an expression for the thickness of a thin object placed between two glass plates.

5.Describe the construction and working of Michelson’s interferometer.

6.How can Michelson’s interferometer be used to determine the wavelength of a monochromatic light source? Explain in detail.

7.Describe how Michelson’s interferometer can be used to determine the difference in wavelengths of the D₁​ and D₂​ lines of sodium light.

PART C - 10 MARK QUESTIONS

1.Explain the principle, construction, and working of Fresnel’s biprism. Derive the expression for fringe width.

2.Derive the conditions for constructive and destructive interference in thin films. Explain the formation of colors in thin films with examples.

3.Discuss the air wedge method for determining the thickness of a thin wire. Derive the formula and explain the significance of the fringes observed.

4.Describe the Michelson interferometer in detail. Explain its construction, working, and applications for determining the wavelength of a monochromatic source and the thickness of a mica sheet.

UNIT - III
PART A - 2 MARK QUESTIONS

1.What are Fresnel’s assumptions?
2.What is a zone plate?
3.List two differences between a zone plate and a convex lens.
4.What is Fresnel diffraction?
5.What is Fraunhofer diffraction?

6.What is the width of the principal maxima in Fraunhofer diffraction at a single slit?
7.What is the difference between Fresnel and Fraunhofer diffraction?

8.Write the condition for the formation of principal maxima in a single slit Fraunhofer diffraction pattern.

9.Write the equation of positions of maxima in the diffraction pattern of a plane transmission grating in normal incidence.

PART B - 5 MARK QUESTIONS

1.State Fresnel’s assumptions and explain their significance in diffraction theory.

2.What is a zone plate? Describe its construction and principle of operation.

3.List the differences between a zone plate and a convex lens.

4.Describe the Fresnel diffraction at a straight edge.

5.Describe the diffraction pattern produced by a narrow slit under Fresnel diffraction

6.Derive an expression for the width of the principal maxima in Fraunhofer diffraction at a single slit.

8.Explain the working of a plane diffraction grating.

PART C - 10 MARK QUESTIONS

1.What is a zone plate? Derive an expression for its focal length and explain its action when a spherical wavefront is incident upon it. Compare its properties with those of a convex lens.

2.Discuss Fraunhofer diffraction at a single slit. Derive the expressions for the intensity distribution and the width of the principal maxima.

3.Describe Fresnel diffraction due to a narrow slit and derive the conditions for the formation of maxima and minima in the resulting diffraction pattern.

4.Explain the principle and working of a plane diffraction grating. Derive the condition for maxima and explain how it can be used to determine the wavelength of light.

UNIT - IV
PART A - 2 MARK QUESTIONS

1.What is optical activity?
2.What are optically active crystals? Give an example.
3.Define a polarizer and an analyzer.
4.What is double refraction?
5.What is the optic axis in a crystal?
6.What are polaroids? State one application.
7.What is a quarter wave plate?

8.What is a half wave plate?

9.What is circularly polarized light?

10.What is elliptically polarized light?

11.Define specific rotation / specific rotatory power.

PART B - 5 MARK QUESTIONS

1.Explain the concept of double refraction. Define optic axis and principal plane.

2.Give Huygens's explanation of Double refraction is

uniaxial crystals.

3. Explain the working of a quarter wave plate.

4.Explain the working of a half wave plate.

5.Give the mathematical treatment of Fresnel’s

theory of optical rotation.

6.What are polaroids? Explain their applications.

PART C - 10 MARK QUESTIONS

1.Discuss Fresnel’s explanation of circularly and elliptically polarized light. How can these types of light be detected experimentally?

2.Explain the construction, principle, and working of the Laurent half-shade polarimeter. Describe how it is used to determine the specific rotatory power of a substance.

UNIT - V
PART A - 2 MARK QUESTIONS

1.What are the general principles of lasers?
2.Define spontaneous emission.
3.What is stimulated emission?
4.Explain the concept of population inversion in lasers.
5.What is optical pumping ?
6.What is the principle of operation of a CO₂ laser?
7.Explain the working principle of a semiconductor laser.

8.List any two applications of lasers.

9.What is holography?

PART B - 5 MARK QUESTIONS

1.Explain the general principles of laser action.Discuss the processes of spontaneous and stimulated emission and their role in laser operation.

2.Describe the concept of population inversion in lasers. How is population inversion achieved using optical pumping?

3.Explain the working principle of a He-Ne laser.Discuss its construction and the process of laser action in detail.

4. What is the working principle of a CO₂ laser? Explain its applications in industry and medicine.

5.Describe the construction and working of a semiconductor laser. Discuss its advantages and applications.

PART C - 10 MARK QUESTIONS

1.Describe the principle, construction, and working of a He-Ne laser. Discuss the role of population inversion and optical pumping in achieving laser action in a He-Ne laser.

2.Explain the working principle of a CO₂  laser. Describe its construction and applications in industry, medicine, and communication systems.

Syllabus : OPTICS AND LASER PHYSICS - IV SEMESTER - COURSE CODE : 23BPH4C1

UNIT - I LENS AND PRISMS

Fermat's Principle of Least Time - Postulates of Geometrical Optics - Thick and Thin Lenses - Focal Length, Critical Thickness, Power and Cardinal Points of a Thick Lens - Narrow Angled Prism. Lens - Aberrations - Spherical Aberration, Coma and Astigmatism - Curvature of Field - Distortion - Chromatic Aberration Methods. Prism - Dispersion, Deviation, Aberrations - Applications: Rainbows and Halos - Constant Deviation Spectroscope Eyepieces - Advantage of an Eyepiece Over a Simple Lens - Huygens' and Ramsden's Eyepieces, Construction and Working - Merits and Demerits of the Eyepiece Resolving Power - Rayleigh's Criterion for Resolution - Limit of Resolution for the Eye - Resolving Power of (I) Prism (II) Grating and (III) Telescope

UNIT - II INTERFERENCE

Division of Wave Front - Fresnel's Bibrism - Fringes with White Light - Division of Amplitude : Interference in Thin Films Due to (I) Reflected Light (II) Transmitted Light - Colors of Thin Films Applications - Air Wedge - Newton's Rings Interferometers - Michelson's Interferometer - Applications, (I) Determination of the Wavelength of a Monochromatic Source of Light  (II) Determination of the Wavelengths and Separation of D₁ and D₂ Lines of Sodium Light, (III) Determination of Thickness of a Mica Sheet.

UNIT - III DIFFRACTION

Fresnel's Assumptions - Zone Plate - Action of Zone Plate for an Incident Spherical Wave Front -Differences Between a Zone Plate and a Convex Lens Fresnel Type of Diffraction - Diffraction Pattern Due to A Straight Edge - Positions of Maximum and Minimum Intensities - Diffraction Due to a Narrow Slit Fraunhofer Type of Diffraction - Fraunhofer Diffraction at a Single Slit - Plane Diffraction Grating - Experiment to Determine Wavelengths - Width of Principal Maxima

UNIT - IV POLARIZATION

Optical Activity - Optically Active Crystals - Polarizer and Analyzer - Double Refraction - Optic Axis, Principal Plane - Huygens' Explanation of Double Refraction in Uniaxial Crystals - Polaroids and Applications Circularly and Elliptically Polarized Light - Quarter Wave Plate - Half Wave Plate - Production and Detection of Circularly and Elliptically Polarized Light - Fresnel's Explanation - Specific Rotation - Laurent Half Shade Polarimeter - Experiment to Determine Specific Rotatory Power

UNIT - V LASERS

General Principles of Lasers - Properties of Lasers Action - Spontaneous and Stimulated Emission - Population Inversion - Optical Pumping - He-Ne Laser [Principle and Working] - CO₂ Laser [Principle and Working] - Semiconductor Laser - Laser Applications - Holography

UNIT - VI PROFESSIONAL COMPONENTS

Expert Lectures - Seminars - Webinars - Industry Inputs - Social Accountability - Patriotism

TEXT AND REFERENCE BOOKS

Text Books
1. Subramaniyan N and Brijlal, 2014, Optics, 25^th Edition, S.Chand and Co.
2. P.R.Sasikumar, 2012, Photonics, PHI Pvt Ltd, New Delhi.
3. V.Rajendran, 2012, Engineering Physics, Tata McGraw Hill.
Reference Books
1. Sathyaprakash, 1990,Optics,VII edition, Ratan Prakashan Mandhir, New Delhi.
2. Ajoy Ghatak, 2009,Optics, 4^th edition, PHI Pvt Ltd, New Delhi.
3. D.Halliday,R.Resnick and J. Walker, 2001, Fundamentals of Physics, 6^th edition, Willey, New York.
4. F. Jenkins, A.Francis and White, 2011, Fundamentals of Optics, 4^th edition, McGraw Hill Inc., New Delhi.

WEB RESOURCES

1. The Electromagnetic Spectrum - NASA
2. Imagine the Universe! - NASA
3. Why The Sky is Blue: Lord Rayleigh, Sir Raman, and Scattering