WJEC Physics A-level: Lasers - Stimulated Emission

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the region where stimulated emission takes place in semiconductor lasers?

Pumping process

Two mirrors

Light beam

Atom medium (correct)

Why are two mirrors used in semiconductor lasers?

To emit light in multiple directions

To increase laser power

To reflect all light and transmit some light (correct)

To create multiple light beams

What makes semiconductor lasers suitable for domestic appliances like CD and DVD players?

Small size and lower cost (correct)

Complex operating mechanism

High voltage requirements

High power consumption

How do semiconductor lasers compare to other types of lasers in terms of power consumption?

They consume less power Signup and view all the answers

In addition to CD and DVD players, which other devices commonly use semiconductor lasers?

Barcode scanners and laser printers Signup and view all the answers

What is the main process by which lasers produce light?

Stimulated Emission Signup and view all the answers

Why is population inversion necessary for laser technology?

To have more electrons in the upper level than the lower level Signup and view all the answers

What is the key factor that differentiates the photons produced by stimulated emission from regular light?

Phase difference Signup and view all the answers

Why do two-state laser systems not usually exist?

The probability of absorption is higher than stimulated emission Signup and view all the answers

Which type of electron distribution in energy levels is required for successful laser operation?

More electrons in the upper level than the lower level Signup and view all the answers

What happens if a photon does not have enough energy to stimulate an electron to drop down to a lower level?

It will not trigger stimulated emission Signup and view all the answers

What is the main method to achieve a population inversion in a 3-level system?

Electrons are pumped to the third level and then decay rapidly to the second level. Signup and view all the answers

In a 4-level system, where do electrons accumulate to achieve a population inversion?

Third level Signup and view all the answers

What must happen in a 4-level system to form a population inversion?

A significant number of electrons must be on the third level compared to other levels. Signup and view all the answers

What is pumping in the context of achieving a population inversion?

The use of external energy to elevate ground state electrons to higher energy levels. Signup and view all the answers

Why do very few electrons sit on the fourth and second levels in a 4-level system?

Due to rapid decay from those levels without releasing radiation. Signup and view all the answers

What role does an amplifying medium play in a typical laser structure?

It stimulates emission of photons from excited electrons. Signup and view all the answers

Study Notes

Laser Basics

The pumping process involves atoms that are subject to stimulated emission, producing light in multiple directions.
Two mirrors, one reflective and one transmissive, are used to redirect the light into a single beam.

Semiconductor Lasers

They are smaller and cheaper to produce than other lasers.
They are often used in domestic appliances such as CD and DVD players, barcode scanners, and laser printers.
Semiconductor lasers use much less power and are more efficient than other lasers, allowing them to run on low voltage sources.

Stimulated Emission

It's the process by which lasers produce light, occurring when an electron is already in an excited state.
A photon with energy equal to the energy difference between the electron's excited level and the level below stimulates the electron to drop down, releasing a photon of equal energy.
The photons produced by stimulated emission have a constant phase difference and frequency, forming coherent light.

Population Inversion

It's a process required by laser technology, where there are more electrons in the upper level than the lower level.
A population inversion is necessary because otherwise, the process of absorption will have a higher chance of taking place than stimulated emission.
Two-state laser systems do not usually exist, and population inversion can be attained in 3 and 4-level systems.

Pumping and 3-Level Systems

Pumping is when external energy is used to cause ground state electrons to rise to the highest energy level.
In a 3-level system, electrons are pumped up to the third level, decay rapidly to the second level, and many electrons accumulate, attaining a population inversion.
At least half the electrons must be moved from the lowest level to the highest level, and the system must be 'very strongly pumped'.

4-Level Systems

It's like a three-level system except there is another level below.
Electrons are pumped up to the fourth level, decay rapidly to the third level, and some electrons fall down to the second level by spontaneous emission or stimulated emission.
Then, any on the second level rapidly decay to the first/ground level, forming a population inversion between the third and second levels.

Typical Laser Structure

A laser consists of an amplifying medium.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Learn about the physics topic of stimulated emission in lasers, where light is produced when an electron in an excited state is stimulated by a photon. This process is crucial for understanding the functioning of lasers.