About this previous year paper
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.