A He-Ne laser has a cavity length of 20 cm, a gain tube radius of 1 mm, and has mirror reflectivities of 0.99 (output co

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A He Ne Laser Has A Cavity Length Of 20 Cm A Gain Tube Radius Of 1 Mm And Has Mirror Reflectivities Of 0 99 Output Co 1 (48.89 KiB) Viewed 40 times

A He-Ne laser has a cavity length of 20 cm, a gain tube radius of 1 mm, and has mirror reflectivities of 0.99 (output coupler) and 0.998 (high reflector). The absorption loss in the cavity is negligible. Important parameters of the gain medium is extracted from a laser handbook, as shown below. Laser He-Ne Gas partial pressures (torr) 2.5 He 0.5 Ne Concentration of active gas molecules (10¹4 cm ³) 120 Emission wavelength (μm) 0.6328 Peak emission o (10-14 cm²) 30 Excited state lifetime T (ns) ~100 Transition linewidth Av (GHz) 1.5 (a) Find the threshold population inversion. What fraction of the available Ne atoms need to be in the upper laser state for lasing? (b) Find the number of atoms that must be pumped into the upper level per unit time to achieve lasing. (c) The upper laser level is ~ 20 eV above the ground state. What is the minimum pump power required to achieve lasing?