## Overview This topic covers the process of stimulated emission and how this leads to coherent light emission. The structure of lasers is studied, including how a population inversion is attained. The advantages and disadvantages of different types of laser are compared. ## Working Scientifically Questions set on this unit will assess learner’s abilities to apply scientific knowledge to practical contexts; to process and analyse data using appropriate mathematical skills; to present data in appropriate ways. ## Mathematical Skills There are a number of opportunities for the development of mathematical skills in this unit. These include; visualising and representing 2D and 3D forms including 2D representations of 3D objects. ## How Science Works There are opportunities within this topic for learners to communicate information and ideas in appropriate ways using appropriate terminology; to consider applications and implications of science and evaluate their associated benefits and risks. ### Learners should be able to demonstrate and apply their knowledge and understanding of: 
 (a) the process of stimulated emission and how this process leads to light emission that is coherent (b) the idea that a population inversion (N2 > N1) is necessary for a laser to operate (c) the idea that a population inversion is not (usually) possible with a 2-level energy system (d) how a population inversion is attained in 3 and 4-level energy systems (e) the process of pumping and its purpose (f) the structure of a typical laser i.e. an amplifying medium between two mirrors, one of which partially transmits light (g) the advantages and uses of a semiconductor laser i.e. small, cheap, far more efficient than other types of laser, and it is used for CDs, DVDs, telecommunication etc