Lasers and Optics

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is a characteristic of the output of gas lasers?

High monochromaticity and high stability of frequency (correct)

High output power

Pulsed duration of microseconds

Full-spectrum white light

What is the pumping method used in He-Ne lasers?

Chemical pumping

Electrical pumping (correct)

Mechanical pumping

Optical pumping

What is a common application of lasers?

Medical imaging

Water purification

Generating electricity

Welding and cutting of materials (correct)

What is a type of laser that uses a solid-state gain medium?

Ruby laser Signup and view all the answers

What is a characteristic of flashtubes?

Producing extremely intense, incoherent, full-spectrum white light Signup and view all the answers

What is an advantage of He-Ne lasers over ruby lasers?

Longer operation duration Signup and view all the answers

What is a unique feature of laser beams?

High intensity Signup and view all the answers

What is another application of lasers besides welding and cutting?

Eye surgery Signup and view all the answers

What is the necessary condition for light amplification in lasers?

Population inversion Signup and view all the answers

Which of the following methods is used to obtain population inversion in Ruby lasers?

Optical pumping using Xenon flash lamp Signup and view all the answers

What type of laser uses a PN junction diode as the active medium?

Semiconductor laser Signup and view all the answers

What is the characteristic of lasers that maintain a population inversion indefinitely?

Continuous output Signup and view all the answers

Which type of laser uses macromolecules to produce different laser light from a single medium?

Dye laser Signup and view all the answers

What is the term for the delivery of energy to produce a population inversion?

Pumping Signup and view all the answers

Which of the following lasers is an example of a three-level laser?

Ruby laser Signup and view all the answers

What is the characteristic of lasers that have a short-lived population inversion?

Pulsed output Signup and view all the answers

What is the main principle for amplifying light in a Laser system?

Stimulated emission Signup and view all the answers

What is the condition for laser operation?

N1 < N2 Signup and view all the answers

What is the term for the state of the medium in which there are a larger number of atoms in the higher energy state as compared to the lower energy state?

Population inversion Signup and view all the answers

What is the characteristic of laser light that refers to the constant phase relationship between emitted photons?

Coherent Signup and view all the answers

Who is credited with the concept of stimulated emission?

Albert Einstein Signup and view all the answers

What is the term for the number of upward transitions due to absorption?

N1 P12 Signup and view all the answers

What is the relation between the Einstein coefficients B12 and B21?

B12 = B21 Signup and view all the answers

What is the purpose of the metastable state in a laser system?

To enhance the probability of population inversion Signup and view all the answers

What is the characteristic of laser light that refers to its high intensity?

Intense Signup and view all the answers

Who built the first laser using the concept of stimulated emission?

Theodore H. Maiman Signup and view all the answers

Study Notes

Flashtubes

A flashtube is an electric arc lamp designed to produce extremely intense, incoherent, full-spectrum white light for very short durations.
Made of a length of glass tubing with electrodes at either end.

Drawbacks of Ruby Laser

Requires high pumping power.
Efficiency of ruby laser is small.
Laser output is not continuous, occurs in form of pulses of microsecond duration.

Gas Lasers

Used for continuous laser beam.
Vapor metal ions are employed as active media.
Main advantage: exceptionally high monochromaticity, most pure spectrum, and high stability of frequency.
Output of gas lasers is moderate but inferior to that of crystal lasers.

He-Ne Laser

First gaseous laser to be developed.
Developed in 1961 by Ali Javan and associates.
A four-level laser.
Emits a wavelength of 6328A.

Comparison of Ruby and He-Ne Lasers

Ruby laser: solid-state laser, three-level laser, pulsed laser, optical pumping, coolant required, output power of 10kW, operation duration of a few hours.
He-Ne laser: gaseous laser, four-level laser, CW laser, electrical pumping, no coolant required, output power of 0.5 to 5mW, operation duration of ~10,000 hours.

Applications of Lasers

Welding, cutting of materials.
Eye surgery, treatment of dental decay, and skin diseases.
Barcode scanners in libraries and supermarkets.
Laser printers.
Nuclear Fusion.
CD/DVD players.
Holography.

LASERS

Light Amplification by Stimulated Emission of Radiations.
Concept of Stimulated Emission given by Albert Einstein in 1917.
Charles H. Townes utilized the concept to build MASER in 1953.
Extension to optical region: Theodore H. Maiman built the first Laser in 1960.

Properties of Laser Light

Monochromaticity: high degree of monochromaticity.
Coherent: all emitted photons bear a constant phase relationship with each other in both time and phase.
Directional: a very well-collimated beam that travels long distances with very little spread.
Intense: a very highly intense beam.

Interaction of Radiation with Matter

Absorption: probability of absorption, B12 is the Einstein coefficient of absorption.
Spontaneous Emission: probability of spontaneous emission, A21 is the Einstein coefficient of spontaneous emission.
Stimulated Emission: probability of stimulated emission, B21 is the Einstein coefficient of stimulated emission.

Relation Between Einstein Coefficients

In thermal equilibrium, total upward transition equals total downward transitions.
Substituting for probabilities, we get: A21 = B21 * B12 * N1 / N2.

Principle of Laser Action

The main principle for amplifying light in a laser system is the stimulated emission.

Concept of Population Inversion and Metastable States

State of the medium in which there are larger numbers of atoms in higher energy state as compared to the lower energy state.
The existence of metastable state enhances the probability of population inversion.

Condition for Laser Operation

If N1 > N2, radiation is mostly absorbed, spontaneous radiation dominates.
If N2 >> N1, population inversion occurs, most electrons occupy level E2, weak absorption, stimulated emission prevails, and light is amplified.

Population Inversion

Situation in which the number of electrons in the higher state exceeds that in the lower state (N2 > N1).
Methods to obtain population inversion: supply energy from outside, optical pumping, electrical pumping, chemical pumping, and laser pumping.

Types of Lasers

Solid-state lasers: active medium is solid crystal (e.g., Ruby, Nd:YAG).
Gaseous lasers: active medium is gaseous (e.g., He-Ne, Co2).
Dye lasers: macromolecules used for different laser light from a single medium.
Semiconductor lasers: PN junction diode used for producing LASER.

Studying That Suits You

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

Description

This quiz covers various types of lasers, including flashtubes, ruby lasers, and gas lasers, and their characteristics.