A He-Ne laser cavity has a cylindrical geometry with length 30cm and diameter 0:5cm. The laser transition is at 633nm, with a frequency width of 10nm. (a) Determine the number of modes in the laser cavity that are within the laser transition linewidth. (b) A power meter is then placed at the cavity output coupler for 1 minute. The reading is constant at 1mW. Determine the average number of photons per cavity mode.