Design and Fabrication of Chirped Mirror

Chirped mirrors (CMs) are designed and manufactured. The optimized CM provides a group delay dispersion (GDD) of around -60 fs² and average reflectivity of 99.4% with bandwidth 200nm at a central wavelength of 800nm. The CM structure consists of 52 layers of alternating high refractive index Ta₂O₅ and low refractive index SiO₂. Measurement results show that the control of CM manufacturing accuracy can meet our requirement through time control with ion beam sputtering. Because the GDD of CMs is highly sensitive to small discrepancies between the layer thickness of calculated design and those of the manufactured mirror, we analyze the error sources which result in thickness errors and refractive index inhomogeneities in film manufacture.