Problem - The cavity of a Kr+-laser is stimulated to emit at 413.1 nm. If the cavity has a length of 0.75 m calculates:
1) The axial mode number nearest to the line centre.
2) The frequency spacing between axial modes.
3) The maximum length to which the cavity would have to be altered to ensure that only one axial mode could oscillate within the full width half maximum (1.2 GHz) of the 413.1 nm line.