Unit 2.8)lasers

Question 1

What is stimulated emission?

Answer 1

This is the process by which lasers produced light. It occurs when an electron is already in an excited state. If a photon has an energy equal to the energy difference between the electron’s excited level and the level below, it can stimulate the electron to drop down to that lower level, releasing a photon of equal energy to the incoming photon.
The photons produced by stimulated emission have a constant phase difference and frequency (because they are of the same energy) and therefore form coherent light.

Question 2

What is population inversion?

Answer 2

Population inversion is a process required by laser technology, when there are more electrons in the upper level than the lower level. More electrons need to be in the upper level compared to the lower level because otherwise, the process of absorption will have a higher chance of taking place as apposed to stimulated emission.
(necessary for a laser to operate)
It is not (usually) possible with a 2-level energy system.

Question 3

What are semiconductor lasers?

Answer 3

In comparison with other lasers(see above), semiconductor lasers are smaller and cheaper to produce. Therefore they are often used in domestic appliances such as CD and DVD players. Barcode scanners and lasers printers will also use semiconductor lasers. In addition to this, semiconductor lasers use much less power (and are more efficient) than other lasers allowing them to be run on low voltage sources suitable for domestic appliances.

Question 4

What is the amplifying medium?

Answer 4

A laser consists of an amplifying medium. This is a medium composed of atoms which are subject to the pumping process. This is the region where stimulated emission takes place.

Question 5

State 4 safety precautions that must be followed when using a laser?

Answer 5

1. Wear safety goggles.
2. Don’t shine the laser at reflective surfaces.
3. Display a warning sign.
4. Never shine the laser at a person.

Question 6

How is population inversion attained in 3 and 4 level energy systems?

Answer 6

Population inversion is a crucial condition for laser operation. Let’s explore how it is achieved in 3-level and 4-level energy systems:

1. 3-Level Energy System:
   
   • In a 3-level laser, we have three energy levels: E1 (ground state), E2 (metastable state), and E3 (pump state).
   • The process:
     
     • Electrons are pumped from E1 to E3 (higher energy state) using an external energy source.
     • These electrons then fall back to E2 (metastable state) with a longer lifetime.
     • When electrons transition from E2 to E1, they emit photons (spontaneous emission).
     • Achieving more electrons in E2 than in E1 results in population inversion.
     • This inversion allows stimulated emission, leading to laser amplification.
2. 4-Level Energy System:
   
   • In a 4-level laser, we add an additional energy level (E4) above E3.
   • The process:
     
     • Electrons are pumped to E4 (higher energy state) from E1.
     • From E4, they quickly transition to E3.
     • E3 is the metastable state with a longer lifetime.
     • Electrons in E3 then transition to E2, emitting photons.
     • Population inversion occurs between E2 and E1, enabling laser action.

Remember, achieving population inversion is essential for efficient laser operation

Question 7

What is the process of pumping and its purpose?

Answer 7

Laser pumping refers to introducing energy into a laser system to produce a population inversion, where there are more atoms or molecules in an excited state than in the ground state. This increases the probability of stimulated emission of light and enables lasing to occur. In simpler terms, laser pumping is like ‘fueling’ the laser with energy to make it work.
The purpose of laser pumping is to energize the laser medium (such as a solid, liquid, or gas) so that it achieves population inversion.

Question 8

The structure of a typical laser?

Answer 8

an
amplifying medium between two mirrors, one
of which partially transmits light.