*The Rayleigh Length, <math>\mathrm{Z_{R}}</math> is defined as the distance from the beam waist along the axis of propagation to the point where its cross section is doubled, <math>\mathrm\omega_{R}</math>. Taking <math>\mathrm\omega_{0}</math> as the beam waist, and using the <math>\mathrm{FWHM}</math> as its value we are looking for the point where | *The Rayleigh Length, <math>\mathrm{Z_{R}}</math> is defined as the distance from the beam waist along the axis of propagation to the point where its cross section is doubled, <math>\mathrm\omega_{R}</math>. Taking <math>\mathrm\omega_{0}</math> as the beam waist, and using the <math>\mathrm{FWHM}</math> as its value we are looking for the point where |