Adrian down May01,2006 1 Longitudinal modes of a laser cavity 1.1 Resonant modes For the moment, imagine a laser cavity as a set of plane mirrors separated by a distance d. We will return to the specific properties of the cavity later Resonant modes of the laser cavity are those that are capable of producin standing waves. These modes occur at the wavelengths An that satisfy 入 The possible resonant frequencies of the cavity are The resonant frequencies of the cavity are equally spaced 1.2 Laser gain parameter In considering the output of a laser, we defined the laser gain parameter, hyB1(△N2-△N) where AN1,,2 is the concentration of particles in the state with energy E1.2 in the frequency range Av, and Ay is the range of frequencies in the beam output by the laserAdrian Down May 01, 2006 1 Longitudinal modes of a laser cavity 1.1 Resonant modes For the moment, imagine a laser cavity as a set of plane mirrors separated by a distance d. We will return to the specific properties of the cavity later. Resonant modes of the laser cavity are those that are capable of producing standing waves. These modes occur at the wavelengths λn that satisfy 2d = nλn The possible resonant frequencies of the cavity are νn = c λn = nc 2d The resonant frequencies of the cavity are equally spaced, νn+1 − νn = c 2d 1.2 Laser gain parameter In considering the output of a laser, we defined the laser gain parameter, αν = h c ν ∆ν B21 (∆N2 − ∆N1) where ∆N1,2 is the concentration of particles in the state with energy E1,2 in the frequency range ∆ν, and ∆ν is the range of frequencies in the beam output by the laser. 1