Air Wedge: An air wedge is a thin film of air trapped between two glass plates or any two reflecting surfaces which are inclined at a very small angle. When monochromatic light is incident on an air wedge, interference patterns of dark and bright fringes are observed due to the difference in path length traveled by the light reflected from the two surfaces.
Different Types of LASER:
- Gas Lasers: Helium-Neon laser, CO2 laser
- Solid-State Lasers: Ruby laser, Nd:YAG laser
- Semiconductor Lasers: Diode lasers
- Liquid Dye Lasers: Tunable lasers using organic dyes in liquid solution
- Excimer Lasers: Use reactive gases like chlorine or fluorine mixed with inert gases like argon, krypton, or xenon
Valence Band and Conduction Band:
- Valence Band: The highest range of electron energies where electrons are normally present at absolute zero temperature.
- Conduction Band: The range of electron energies higher than those of the valence band where electrons are free to move and contribute to electrical conduction.
Formula for Dispersive Power of Prism:
Different Types of Pumping Methods:
- Optical Pumping: Using light (e.g., flash lamps, lasers)
- Electrical Discharge: Using an electric current (common in gas lasers)
- Chemical Reactions: Chemical energy to excite laser medium
- Direct Electron Excitation: Using electron beams
Insulator and Semiconductor:
- Insulator: Material with a large band gap (greater than 3 eV) where electrons are tightly bound and do not move freely (e.g., glass, rubber).
- Semiconductor: Material with a smaller band gap (about 1 eV) where electron movement can be easily controlled by adding impurities (doping) (e.g., silicon, germanium).
Define Interference: Interference is the phenomenon that occurs when two or more waves superimpose to form a resultant wave of greater, lower, or the same amplitude. It can be constructive (amplitudes add) or destructive (amplitudes subtract).
Discuss the Thermal Conductivity: Thermal conductivity is a measure of a material's ability to conduct heat. It is quantified by the amount of heat that passes in unit time through a unit area of a substance with a temperature gradient of one degree per unit distance. Materials with high thermal conductivity, like metals, are good conductors of heat, while materials with low thermal conductivity, like insulators, resist heat flow.
Different Types of Moduli:
- Young’s Modulus (E): Measures the stiffness of a material in tension/compression.
- Shear Modulus (G): Measures the stiffness of a material in shear.
- Bulk Modulus (K): Measures the stiffness of a material under uniform pressure.
Constructive and Destructive Interference:
- Constructive Interference: Occurs when the phase difference between the waves is a multiple of 2*pi (waves in phase), resulting in increased amplitude.
- Destructive Interference: Occurs when the phase difference is an odd multiple of pi (waves out of phase), resulting in decreased or zero amplitude.
Formula for Particle Size Determination Using Laser Light:
Young’s Modulus:
Pumping and Population Inversion:
- Pumping: The process of energizing the atoms or molecules in the lasing medium to achieve higher energy states.
- Population Inversion: A condition where the number of particles in an excited state exceeds those in lower energy states, essential for laser action.
Characteristics of Laser:
- High intensity
- Coherence
- Monochromaticity
- Directionality
Band Gap: The energy difference between the top of the valence band and the bottom of the conduction band in a semiconductor. It determines the electrical conductivity of the material.
Normalization Method in Spectrometer Grating: The normalization method in spectrometer grating involves adjusting the recorded intensities to account for variations in the light source and detector response. This typically means measuring the intensity of a reference wavelength and then dividing the measured intensity of each wavelength by this reference intensity. This process ensures that the spectrum is consistent and comparable by removing any artifacts caused by equipment variability.
Spontaneous and Stimulated Emission:
- Spontaneous Emission: An electron in an excited state falls to a lower energy level without external influence, emitting a photon randomly in any direction. This process results in incoherent light.
- Stimulated Emission: An electron in an excited state falls to a lower energy level when influenced by an incident photon with the same energy, resulting in the emission of a coherent photon in the same phase and direction as the incident photon. This is the principle behind laser operation.
Discuss the Angle of Minimum Deviation in Spectrometer Prism:
Optical Resonator: An optical resonator is a structure that confines and reflects light back and forth within a laser to amplify it. It typically consists of two mirrors placed at either end of the gain medium. The mirrors can be partially transparent to allow some of the amplified light to exit as the laser beam. Common types include Fabry-Pérot resonators and ring resonators.