Design and fabrication of broadband chirped mirror pairs with group delay dispersion of -100fs2 and -200fs2

The dispersive mirrors (DMs) offer high reflectivity and precise control of dispersion compensation, making them essential elements in ultrashort pulse systems. With the development of ultrashort pulse technology, the dispersion oscillations of the DMs become more stronger with the increase of the dispersion compensation bandwidth and target group delay dispersion (GDD) value. To reduce the GDD oscillation of DMs, two pairs of chirped mirror with a central wavelength of 800 nm and a bandwidth of about 200 nm were designed and fabricated, which provide about -100fs² and -200fs² GDD respectively in the wavelength range of 700-900 nm. The GDD oscillation is reduced from ±100 fs² for a single chirped mirror to nearly 0 fs² using chirped mirror pairs. The chirped mirror pairs were fabricated by dual-ion beam sputtering deposition, and their GDD was tested with a white light interferometer. To verify the compression performance, we simulated the propagation of a Gaussian pulse through our chirped mirrors. We added +1200 fs² of positive dispersion to a Gaussian pulse at the Fourier transform limit and reflected it 12 times on a pair of fabricated chirped mirrors with a GDD of -100 fs². The simulated results showed that the fabricated chirped mirror pairs closely match the design specifications and effectively reduce the oscillation of GDD.