2.8 lasers Flashcards
(22 cards)
What is stimulated emission?
The process by which lasers produce light when an electron in an excited state drops to a lower energy level releasing a photon of equal energy to the incoming photon.
What type of light do photons produced by stimulated emission form?
Coherent light as they have a constant phase difference and frequency.
What is population inversion in laser technology?
A condition where there are more electrons in the upper energy level than in the lower energy level necessary for stimulated emission to dominate over absorption.
Why do two-state laser systems usually not exist?
Because the probability of an incoming photon causing an electron to be excited is equal to the probability of it causing the electron to fall back down preventing a population inversion.
How is a population inversion achieved in a three-level laser system?
Electrons are pumped to the third level then decay rapidly to the second level
What is the requirement for achieving population inversion in a three-level system?
At least half of the electrons must be moved from the lowest level to the highest level requiring very strong pumping.
Describe the process in a four-level laser system.
Electrons are pumped to the fourth level decay to the third level
What is pumping in the context of lasers?
The process of using external energy to raise ground state electrons to a higher energy level.
What is the role of the amplifying medium in a laser?
It is composed of atoms that undergo the pumping process and where stimulated emission occurs.
How do mirrors function in a laser system?
One mirror reflects all light while the other transmits some light redirecting the light into a single beam.
What are semiconductor lasers known for?
They are smaller cheaper to produce
Where are semiconductor lasers commonly used?
In domestic appliances such as CD and DVD players barcode scanners
What advantage do semiconductor lasers have over other lasers?
They use much less power and can operate on low voltage sources.
What happens to electrons in a three-level laser system after being pumped?
They decay rapidly to the second level without releasing radiation transferring energy to heat.
In a four-level laser system what happens to electrons on the second level?
They rapidly decay to the first/ground level without releasing radiation.
What is the significance of having fewer electrons on the fourth and second levels in a four-level system?
It allows most electrons to accumulate on the third level facilitating population inversion.
What is the energy requirement for a photon to stimulate emission?
The photon must have energy equal to the energy difference between the excited level and the level below.
What is the outcome of stimulated emission?
The release of a photon of equal energy to the incoming photon contributing to coherent light.
What is a key characteristic of the light produced by lasers?
The light is coherent meaning it has a constant phase difference and frequency.
Why is strong pumping necessary in laser systems?
To ensure that more electrons are in the upper energy level than in the lower energy level allowing stimulated emission to dominate.
What is the difference between a three-level and a four-level laser system?
A three-level system has one upper and one lower level while a four-level system includes an additional lower level
What type of energy sources can power semiconductor lasers?
Low voltage sources making them suitable for domestic appliances.
