Design and study of dielectric double chirped mirrors in ultra short femtosecond pulse lasers

All recent research deal with Nanotechnology. Our research deals with Femtotechnology, which is very advanced in laser and fiber optics technology. Where: Nanotechnology = 10^-9 seconds, but, Femtotechnology = 10^-15 seconds. Where in femtosecond lasers: lasers emitting pulses with durations between a few femtoseconds and hundreds of femtoseconds. The generation of ultrashort pulses, that is pulses in the order of picoseconds an femtosecond lasers involves optical coatings as important functional elements, e.g. high reflectors (HR), output couplers (OC) and antireflection (AR) coatings. These optical elements are based on the interference phenomenon of light. Their theoretical analysis generally relies on the well known scattering matrix formalism derived from the Maxwell equations. Laser performance strongly depends on the quality of optical coatings: reflectance of high reflectors should approach the ideal 100% value at the operation wavelengths in order to minimize laser inter cavity losses and output coupling has to be set to specific values to ensure optimal operation. This paper reports a theoretical design of double-chirped mirror (DCM) to achieve high reflectivity and dispersion compensation over a broad bandwidth. Analytic expressions for reflectivity (R), group delay (GD) and group delay dispersion (GDD) are used. The aim is to compress the limits of pulse duration to reach femtosecond scale. The mirror consists of 53 layers: 37 layers from dielectric materials SiO₂/TiO₂, arranged, as periodic stacks have been used to design chirped mirrors using the FusedSilica as a substrate and 16 layers from tow dielectric materials SiO₂/Ta₂O₅ have been used to design AR-coating. We demonstrate a double chirped dielectric multilayer mirror with controlled reflectivity and dispersion in the wavelength range 650-900nm, it exhibits a reflectivity of >;99.9995%.