Subfemtosecond accuracy measurement of chirped mirrors

Summary form only given.Measuring dispersions with subfemtosecond accuracy has been a long standing problem. With the advent of chirped mirrors, which control the group delay on reflection on a femtosecond scale, this problem has become even more acute. However, chirped mirrors are complex dielectric stacks, and deposition errors can cause the actual dispersion to move away from the design goal. It is then essential to have an apparatus that can measure the group delay with the best possible accuracy. The most widespread apparatus used for measuring the dispersion of mirrors or other samples is white-light interferometric cross-correlation. This is basically a Michelson interferometer with one scanning mirror.