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Lecture : Laser- I. Part-I. Objectives. In this lecture you will learn the following. Maser. Rate Equations for a Two Level System. Three Level Laser. Rate Equations for a Three Level System. Four Level Laser. Rate Equations for a Four Level System. Fabry - Perot Cavity and Laser Oscillation. Gain Saturation. Properties of
As seen in Figure 3 above, there is four energy levels, with energies E1, E2, E3, E4 with populations of N1, N2, N3, N4 respectively. There energies increase for each level so that E1 < E2 < E3 < E4. In this system, optical pumping from the ground state (E1) into the pump band (E4) excites the atoms. From this level the
four-level system Laser gain with a much lower excitation level is possible in a four-level system, such as Nd:YAG. Here, the lower level of the laser transition is somewhat above the ground state, and a rapid (most often nonradiative) transfer from there to the ground state keeps the population of the lower laser level very
12 Feb 2015 Three-level laser. ? . . ? 1 ? 2 ? . Difference between three and four-level systems, and why four-level systems are superior. Saturation intensity is independent of the pumping-rate "i.e. The signal intensity needed to reduce the pop. Inv. To half its initial value doesn't depend on
7.2.1 Three and Four Level Laser Media. As we discussed before inversion can not be achieved in a two level system by optical pumping. The coherent regime is typically inaccesible by typcial optical pump sources. Inversion by optical pumping can only be achieved when using a three or four-level system, see Figures 7.5
Lasers based on number of energy levels. Three-level laser. • No lasing action in two level system : no population inversion. • Three level system: lasing possible but require high pump energy than four level system. • Example: Ruby Laser (three level)
PHYS20312 Wave Optics -? Section 5: Lasers But these three processes operate at the same time, hence the total rate equation for level 2: ? ?. 12. 1 . levels than this. A real material is often chosen as 'good' gain medium because it forms a '4- level laser system', as illustrated in Fig 4. Figure 4 A four-level laser system.
to as three-level lasers and four-level lasers [ERN10b]. A sketch of the pumping and lasing transitions of these systems is shown in Fig. 2.2. The advantage of involving additional states for the electrons are easy to un- derstand: While an optically driven two-level system can never reach population inversion through optical
below laser threshold, atoms in level 2 predominantly return to the ground state by spontaneous emission. terminal level of the laser transition is the highly populated ground state, a very high population must be The Four-Level System. The four-level laser system, which is characteristic of the rare earth ions in glass.
Figure 1.1 Energy level diagram for (a) three- and (b) four level laser systems. N1 to achieve the condition of population inversion between E2 and E1 at moderate pumping. 1.1.5. Threshold Gain Coefficient for Lasing. Laser beam undergoes multiple oscillations (through active medium) between pair of mirrors to achieve
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