Ultra-broadband substrate-compensated low-dispersion mirror

We report an ultra-broadband, highly reflective substrate-compensated low-dispersion mirror (SC LDM) operating in the wavelength range of 700-1050 nm. Conventional low-dispersion mirrors have difficulty meeting the bandwidth requirements of next-generation femtosecond lasers. We propose a design strategy that enables the substrate to participate in dispersion management, where the positive dispersion of the substrate is compensated by a negative-dispersion mirror coated on the rear surface, thereby achieving zero dispersion across an ultra-broad spectral range. The incident light passes through the substrate and then interacts with the negative-dispersion mirror. The laser-induced damage threshold of SC LDM was measured in a 16.4 fs ultrafast laser system, and the cause of damage was explained using a multi-wavelength electric field model. This study introduces a novel design approach for low-dispersion mirrors with extended operating bandwidth and measures the damage threshold of a pre-substrate dispersive element for the first time, laying the foundation for the advancement of ultrafast laser systems with wider spectral range.