(SEM IV) THEORY EXAMINATION 2018-19 LASER SYSTEMS AND APPLICATIONS

LASER SYSTEMS AND APPLICATIONS – B.Tech (Semester IV), ROE-043

This is a 3-hour, 70-mark theory examination designed to test the student’s understanding of quantum physics, laser principles, laser types, coherence, holography, and laser applications.

The paper is divided into three sections, covering conceptual, mathematical, and application-based questions.
 

SECTION A — Short Answer Questions (2 × 7 = 14 Marks)

This section contains 7 brief questions that test fundamental concepts of quantum mechanics and laser physics.

Topics include:

Planck’s revolutionary idea (energy quantization)                       Quantum mechanical tunneling

Coherence length and coherence time from bandwidth             Population inversion & negative temperature concept

Metastable states and laser action                                               Role of He & N₂ in CO₂ laser

Difference between holography and photography

These questions ensure understanding of basic laser theory & quantum physics.
 

SECTION B — Descriptive Questions (7 × 3 = 21 Marks)

Attempt any 3 out of 5.
This section requires detailed derivations, diagrams, and explanations.

Topics include:

Schrödinger equation solution for 1D infinite potential well

Einstein A and B coefficients & derived relation

Q-switching concept and its methods

Neodymium Lasers (Nd:YAG): construction, energy-level diagram & applications

LIDAR vs RADAR, components & working principle

This section evaluates analytical thinking and deep theoretical knowledge.
 

SECTION C — Long Answer Questions (7 marks each)

Each question contains two alternative parts (a or b) requiring advanced understanding, calculations, and detailed diagrams.

Q3 – Atomic & Quantum Transitions

Spectral series of hydrogen atom + series limits

Quantum energy levels in a square well

Q4 – Coherence & Laser Temperature Relations

Temporal and spatial coherence, derivations of coherence lengths

Relative population using Boltzmann distribution for ruby laser

Q5 – Laser System Components & Threshold

Essential components of a laser system + pumping mechanisms

Loop gain expression, threshold condition for laser oscillation

Q6 – Laser Types: Excimer & Semiconductor

Excimer laser: why “self-illuminating”, excitation mechanism, energy diagrams

Semiconductor diode laser: excitation mechanism & LED vs LASER differences

Q7 – Holography & Laser Material Processing

Holography: principle, construction & reconstruction of holograms

Laser material processing applications & advantages

This section checks derivation-based, conceptual, and application-oriented mastery.
 

OVERALL PURPOSE OF THE EXAM

This paper evaluates a student’s ability to:

Understand quantum mechanical principles behind lasers

Explain laser operation: pumping, population inversion, metastable states

Solve quantum well problems

Understand coherence, holography & laser beam properties

Describe and compare different laser systems (Nd:YAG, CO₂, Excimer, Semiconductor)

Apply lasers in industry, medicine, communication & material processing

Interpret spectral series and calculate energy levels

Understand laser threshold, gain, and stability conditions

It tests both theoretical foundations and real-world applications of laser technology.