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Lasers & Atom-light Interactions - PHY00013M

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  • Department: Physics
  • Module co-ordinator: Dr. Erik Wagenaars
  • Credit value: 10 credits
  • Credit level: M
  • Academic year of delivery: 2022-23

Module will run

Occurrence Teaching cycle
A Spring Term 2022-23

Module aims

An introduction of the basic features of lasers is first given leading to a more general discussion on the interaction of light with atoms. The properties of laser cavities are investigated, leading to a description of the stable operating range for cavities and the associated mode structures. The quantum mechanics of the atom-radiation interaction are considered in the semi-classical limit (treating the radiation field classically) to determine transition probabilities. Some of the spectroscopic background for the description of plasma emission processes important in astrophysical and laboratory plasmas is presented.

Module learning outcomes

  • describe the basic components of a laser and the principles of laser operation.
  • describe and apply matrix methods to establish stability requirements for laser cavities.
  • describe beam propagation in a laser cavity in terms of solutions of Maxwell’s equations.
  • derive Planck’s radiation law from a consideration of radiation modes in a cavity.
  • determine the relationship between Einstein’s A and B coefficients.
  • determine a general formula for laser gain
  • by applying perturbation theory to the problem of light interacting with an atom in the semi-classical limit, determine in a general way the selection rules for radiative transitions.
  • determine line shape formula for radiative and Doppler line broadening.
  • describe how collisional-radiative processes control light emission from plasmas.
  • describe the physics behind selected (laser-based) plasma diagnostics

Module content

Lasers and light in laser cavities

Simple laser cavity parameters – gain, threshold gain, longitudinal modes.

Matrix methods for paraxial optics. Stability criterion for laser cavities.

Directionality and spreading of an electromagnetic beam. Beam propagation. The cylindrically symmetric solution. Transverse modes.

Gaussian beams in a cavity. The ‘ABCD’ rule. Cavity mode frequencies.

Density of modes in a three-dimensional cavity. Quantisation of the field energy. Planck’s law.

The Einstein A and B coefficients. Lines shapes and laser gain. Rate equations for a four level laser.


Interaction of electromagnetic radiation with atoms or molecules

The effect of electromagnetic radiation on an atom or molecule.

The interaction Hamiltonian in the semi-classical limit.

Transition probabilities and selection rules.

The macroscopic theory of absorption. 

Collisional radiative processes in plasmas. The Saha equation. Coronal equilibrium.


Task Length % of module mark
Online Exam - 24 hrs (Centrally scheduled)
Lasers & Atom-light Interactions Exam
8 hours 100

Special assessment rules



Task Length % of module mark
Online Exam - 24 hrs (Centrally scheduled)
Lasers & Atom-light Interactions Exam
8 hours 100

Module feedback

Our policy on how you receive feedback for formative and summative purposes is contained in our Department Handbook.

Indicative reading

Loudon R: The quantum theory of light (Oxford Science) **

Verdeyen J T: Laser electronics (Prentice Hall)**

Tallents, G.J.  An Introduction to the atomic and radiation physics of plasmas (CUP)

The information on this page is indicative of the module that is currently on offer. The University is constantly exploring ways to enhance and improve its degree programmes and therefore reserves the right to make variations to the content and method of delivery of modules, and to discontinue modules, if such action is reasonably considered to be necessary by the University. Where appropriate, the University will notify and consult with affected students in advance about any changes that are required in line with the University's policy on the Approval of Modifications to Existing Taught Programmes of Study.