Cavity ring down (CRD) measurements are suitable to measure reflectivities of e.g. high quality optical layer systems. Therefore, the laser beam is coupled into an optical resonator (cavity) for a large number of round-trips. Losses of a layer or layer system can be calculated from the decay time (cavity ring down time) of the laser beam.

measured intensity                I_T = I_o e^-(1/τ)t

ring down time                      τ = d/[c((1-R_G)+αd)]
                                            R_G = √(R₁R₂) 

» high accuracy reflectivity measurements of dielectric mirrors
» measurement of losses in coated and uncoated substrates
» availability of different wavelengths (300 nm to 900 nm)
» in-situ measurements and data reduction
» development of customized CRD set-ups