A Chirped Mirror is a subcategory of a dispersive mirror consisting of alternating layers of dielectric materials with varying thicknesses used to introduce a negative Group Delay Dispersion (GDD) optimized for ultrafast/femtosecond lasers. Chirped mirrors eliminate the pulse broadening effect (“compress” the pulse length) of ultrafast laser pulses when the pulses are stretched while propagating through optics. 

A chirped mirror can be classified as a type of dispersive mirror, but not all dispersive mirrors can be called chirped. The distinct characteristic of chirped mirrors arises from their unique coating structure. The coating of a chirped mirror is constructed by alternating layers of dielectric materials with spatially non-uniform thicknesses. For ultrafast pulse control, the design ensures smooth reflectance and minimal oscillations in dispersion curves. The result is optimal mirror GDD compensation.

When femtosecond lasers or ultrafast pulsed lasers are transmitted through optical media, the laser pulse, consisting of spectral components of the pulse does not propagate at the same speed, causing the pulse to become stretched (dispersed). The concept of chirping is to make the Group Delay Dispersion (GDD) of longer wavelengths greater than shorter wavelengths. One can regard an ultrafast chirped mirror as a special Bragg mirror consisting of layers of gradually changing thicknesses, so that shorter wavelengths reflect from shallower layers, while longer wavelengths reflect from deeper layers, resulting in a negative net GDD value. Chirped mirrors of negative GDD can work as an excellent and indispensable type of ultrafast dispersion compensation mirror, compensating the pulse widening, reducing pulse durations, and helping to maintain the beam profile for femtosecond and ultrafast laser beams.

Primarily utilized in femtosecond laser systems, chirped mirror lasers act to preserve the temporal profile of pulses, which are vital for applications requiring high peak power and minimal distortion. Chirped mirrors also can be integrated into ultrafast pulse compressors, ensuring that ultrafast pulses maintain their high peak power and compressing the pulses during light propagation.

Shanghai North Optics offers Custom Chirped Mirrors Optimized for Femtosecond and Ultrafast Lasers. North Optics’s chirped mirrors feature a very low negative group delay dispersion (GDD), minimized phase distortion and third-order distortion, and high reflectance. In our factory, North Optics utilizes accurate and up-to-date GDD measuring equipment to ensure the precise dispersion characteristics of our optical components which guarantees that our products meet the highest standards for pulse compression, dispersion compensation, and other ultrafast optical requirements.

North Optics provides narrowband and broadband ultrafast chirped mirrors of diverse central wavelengths, some typical examples include 266nm(240-270nm), 515nm(430-660nm), 800nm(500-1000nm), and 1030nm(600-1300nm), whereas other custom wavelength ranges are also available. The diverse wavelength ranges of our chirped mirrors accommodate various femto laser systems, such as Ti: sapphire or fiber-based ultrafast lasers. The substrate sizes can be as compact as 12.7mm at minimum but also as large as 80x35mm at maximum, with a maximum aperture size reaching 3 inches. The combined usage of two or more chirped mirrors allows the tuning of the compensation intensities. 

Besides, North Optics also offers Chirped Mirror Pairs.