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.
