(SEM III/IV) THEORY EXAMINATION 2017-18 LASER SYSTEMS AND APPLICATIONS

B.Tech III/IV Semester — Total Marks: 70 — Time: 3 Hours

This question paper evaluates a student’s knowledge of laser physics, quantum mechanics basics, laser device construction, optical cavities, laser applications, and numerical problem-solving.
It consists of three sections:
Short theory (A)
Medium explanatory questions (B)
Long derivation/numerical problems (C)

SECTION A — Short, 2-Mark Questions (2 × 7 = 14 Marks)

This section asks 7 brief conceptual questions testing the fundamentals of:

Quantum tunneling effect                                           Black-body radiation issue in classical mechanics

Role of reflectors in laser resonant cavity                           Characteristics of Copper Vapour lasers

Pulse power calculation using pulse duration & energy     Why dye lasers are tunable

Meaning of photocoagulation

These questions check basic understanding of quantum theory and laser fundamentals.
 

SECTION B — Medium, 7-Mark Questions (Attempt Any 3) (7 × 3 = 21 Marks)

These questions require descriptive explanations, diagrams, and derivations.

Topics include:

(a) Black body + Planck’s quantum theory + derivation of energy distribution

(b) Wave function + Schrödinger equations (time-dependent & time-independent)

(c) Optical cavity + types with diagrams

(d) Argon ion laser — construction, working & applications

(e) Dye laser — meaning, advantages, drawbacks, applications

This section tests theoretical understanding + laser device explanation skills.
 

SECTION C — Long, 7-Mark Analytical Questions (Attempt Any One from Each)

This section contains five descriptive/numerical problems, each with two choices.

Q3 – Quantum Tunneling / Probability Calculation

Tunnel effect + diagram + transmission coefficient
OR

Probability of particle in 1D infinite potential box

Q4 – Q-Switching / Population Inversion

Q-switching principle + various techniques
OR

Population inversion + numerical on population ratio using energy gap (1.62 eV)

Q5 – Lasers & Quantum Parameters

Alexandrite laser + tuning techniques
OR

Four-level vs three-level laser efficiency + Fermi temperature & velocity calculation (using Fermi energy 11.1 eV)

Q6 – Four-Level Laser / Semiconductor Laser

Four-level laser + diagram + rate equation
OR

Homojunction semiconductor laser — construction & working

Q7 – Optical Fibre Losses / Laser Material Processing

Types of losses in optical fibre
OR

Cutting & drilling using lasers — advantages & disadvantages

These questions test numerical skills, derivations, device physics, and engineering applications.
 

OVERALL PURPOSE OF THE EXAM

This exam evaluates whether the student can:

Understand basic quantum mechanics behind lasers

Explain black-body radiation & tunneling

Describe optical resonant cavities

Understand laser types (argon ion, dye, copper vapour, alexandrite, semiconductor)

Solve numerical problems (power, probability, population ratio, Fermi parameters)

Explain Q-switching & population inversion

Analyze optical fibre losses & laser machining processes

It checks both conceptual clarity and application of laser principles needed in physics, electronics, and photonics.