Stress compensated back side coated chirped mirror with high negative dispersion

Abstract Back-side coated (BASIC) chirped mirror is characterized by very smooth group delay dispersion (GDD) curve over extremely wide spectral bandwidth. However, these optical elements suffer from poor flatness since they combine as thin as possible substrate and highly stressed sputtered coating. Several stress compensating techniques may be combined to produce fully stress-compensated BASIC chirped mirror. Ion beam sputtering technology was used to deposit BASIC chirped mirror based on Nb2O5/SiO2 mixtures and post-deposition annealing was implemented to compensate coating stress and fabricate optical element with sufficient flatness. Chirped mirror for 150 nm wavelength range and −300 fs average GDD was deposited on 0.35 mm thickness substrate. Final optical element featured initial flatness of uncoated substrate and close to maximum achievable GDD, considering coating thickness and wavelength range.