OUTPUT  CHARACTERISTICS

    The output from an unrestricted ruby laser employing broadband optics is somewhat wide, spectrally speaking, spanning a range of 0.5 nm. Use of an etalon in the cavity (like that employed in the previous example) can reduce the spectral width drastically into the region 20 to 40 MHz, increasing the coherence length to up to 10 m in length. Like many other lasers, ruby lasers tend to operate in high-order transverse modes which can extract the highest powers from the rod. Restricting the mode by using an intracavity aperture can yield a TEM₀₀ mode with minimal divergence for optimal beam quality, but energy extraction is not as efficient, so power output is decreased. Q-switching decreases the energy available in a single pulse, in some cases by a factor of 100, but the peak power available is increased drastically. Where a non-Q-switched laser produces pulses of about 1 ms, pulses as short as 10 ns are possible when Q-switching is employed. Peak powers of 100 MW to over 1 GW are possible, especially when a separate amplifier is used.