Characteristics of laser light include monochromaticity, coherence, directionality,
and high intensity.
The important components of a laser include an active medium (such as a crystal or
gas), an energy source (such as a flash lamp or electrical discharge), and an
optical resonator (such as mirrors).
A two-level system cannot be used to produce laser because it does not have the
necessary population inversion.
The principles of laser action include population inversion, stimulated emission,
and optical feedback.
The conditions needed for laser action include population inversion, optical
feedback, and a gain medium.
Numerical aperture of an optical fiber can be calculated using the formula NA =
√(n1^2 - n2^2), where n1 is the refractive index of the core and n2 is the
refractive index of the cladding.
Numerical aperture can be calculated using the formula NA = √(n1^2 - n2^2), where
n1 is the refractive index of the core and n2 is the refractive index of the
cladding.
The conditions to be satisfied for total internal reflection include light
traveling from a denser medium to a less dense medium at an angle greater than the
critical angle.
Attenuation refers to the loss of signal strength as light travels through an
optical fiber.
Critical angle is defined as the angle of incidence at which light is refracted at
90 degrees.
Mean free path is defined as the average distance traveled by a particle between
collisions while collision time is defined as the average time between collisions.
Drift velocity of electrons is defined as the average velocity at which electrons
move in response to an electric field.
Relaxation time is defined as the average time it takes for an electron to lose its
energy through collisions with other particles.
Mobility can be calculated using the formula μ = vd/E, where vd is drift velocity,
E is electric field strength, and μ is mobility.
Electrical conductivity can be calculated using the formula σ = neμ, where n is
electron density and μ is mobility.
Fermi energy of a metal refers to the energy level at which all available states
below that level are filled with electrons while all states above that level are
empty.
Merits of classical free electron theory include its ability to explain many
properties of metals such as electrical conductivity and thermal conductivity.
Advantages of classical free electron theory include its simplicity and ability to
explain many properties of metals such as electrical conductivity and thermal
conductivity.
Density of energy states refers to the number of available energy states per unit
volume in a material.
Drawbacks of classical free electron theory include its inability to explain
certain properties such as specific heat capacity and magnetic susceptibility.
Properties of semiconductors include their ability to conduct electricity under
certain conditions and their sensitivity to impurities or doping agents.
A semiconductor is a material that has electrical conductivity between that of a
conductor and an insulator. Examples include silicon, germanium, and gallium
arsenide.
Silicon is preferred for transistors because it has good thermal stability and can
be easily doped while GaAs is preferred for laser diodes because it has a direct
bandgap which allows for efficient light emission.
Doping refers to intentionally adding impurities to a semiconductor in order to
alter its electrical properties.
Law of mass action in semiconductors states that at thermal equilibrium, the
product of electron density and hole density in a semiconductor equals a constant
value known as intrinsic carrier concentration squared divided by temperature
squared.
When temperature increases in semiconductors, their conductivity increases while in
conductors their resistance increases due to increased scattering of electrons by
lattice vibrations.
Intrinsic semiconductors are pure semiconductors while extrinsic semiconductors
have impurities added intentionally in order to alter their electrical properties.
N-type semiconductors have excess electrons while p-type semiconductors have excess
holes or positive charge carriers.
Hole current refers to current flow due to movement of holes or positive charge
carriers in a semiconductor material.
30.Band gap refers to the difference in energy between valence band and conduction
band while nano materials have unique properties due to their small size such as
high surface area-to-volume ratio and quantum confinement effects.
