Design, Fabrication and Laser Damage Comparisons of Low-Dispersive Mirrors

Low dispersive with broad bandwidth mirrors serve as indispensable elements in ultrafast laser systems. We report on three coatings, quarter-wave high reflection mirror, metal-dielectric mirror and ternary composite mirror, which are suitable for broad bandwidth high reflection (BBHR) with 800nm center wavelength. Mirrors based on quarter-wave Ta2O5/SiO2 layers are designed and fabricated. By depositing the quarter-wave HfO2/SiO2 layers on the metallic material, we have achieved the mirror with lager low-dispersive bandwidth, this design takes advantage of broad high reflection bandwidth of metal and high laser induced damage threshold (LIDT) of HfO2. Moreover, we have deposited HfO2/SiO2 layers on Ta2O5/SiO2 layers, since HfO2 demonstrates higher damage threshold than Ta2O5, such combination reach an ideal trade-off between the low-dispersive bandwidth and high LIDT comparing with traditional quarter-wave Ta2O5/SiO2 layers. Our BBHR mirrors are produced by means of dual-ion-beam sputtering technique. The designs afford low group delay dispersion (GDD) for reflected light over the broad bandwidth in order to minimize temporal broadening of the fs pulses. The design's GDD behaves in a smooth way, and its electric field intensities show promise for high LIDTs. Reflectivity and GDD measurements indicate good performance of the BBHR design. LIDTs of the produced BBHR mirrors are also tested and compared.