Department of Physics, Unit Catalogue 2007/08 |
PH30032 Laser physics |
| Credits: 6 |
| Level: Honours |
| Semester: 2 |
| Assessment: EX100 |
| Requisites: |
| Before taking this unit you must (take PH20013 or take PH20060) and (take PH20014 or take PH20061) and take PH20020 |
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Aims: The aim of this unit is to outline the main physical principles underlying the generation and manipulation of laser radiation.
Learning Outcomes: After taking this unit the student should be able to: * design simple resonant cavities and analyse their main features; * describe and analyse the interactions between light and matter that lead to spontaneous emission and lasing in 3- and 4-level systems; * treat cw, mode-locked and Q-switched laser operation and describe the resulting temporal, spectral and power characteristics; * outline the effects of group velocity dispersion and self-phase modulation on short pulses; * relate the fringe visibility to the degree of coherence of the source; * analyse the propagation of Gaussian beams. Skills: Numeracy T/F A, Problem Solving T/F A. Content: Optical beams and resonators (5 hours): Gaussian beams; Rayleigh length, beam waist, phase front curvature. Q-factor, parallel mirror resonator, three-dimensional resonators. Resonators with curved mirrors; stability criterion. Mode density in resonators. Losses in resonators. Emission and absorption of radiation (2 hours): Spontaneous emission; lineshape and broadening mechanisms. Stimulated emission. Einstein relations. Absorption and amplification. Gain saturation. Complex susceptibility of laser medium. The Fabry-Perot laser (3 hours): Amplitude and phase conditions for oscillation, population inversion at threshold, frequency of oscillation, cavity lifetime and Q-factor. Three- and four-level lasers. Critical fluorescence power. Output power in lasers above threshold. Types of gain medium (4 hours): Linewidth and coherence. Examples of specific 3- and 4-level lasers and pumping mechanisms: gas lasers, Nd3+:YAG, semiconductor and fibre lasers. Pulsed lasers (8 hours): Q-switching. Mode-locking; time-bandwidth product for pulses, active and passive mode-locking. Examples of mode-locked lasers. Dispersion; group velocity dispersion, Gaussian pulse spreading caused by GVD, dispersion of optical fibres, frequency chirp. Coherence; partial coherence and fringe visibility. Autocorrelation. Frequency conversion; second-harmonic generation, phase-matching. |