850900 800 750 700
850900 800 750 700
technique with subsequent constrained optimization gives the final design structure
presented in Figure 2(b). Color coordinates
of the final design are shown in the chro-
maticity color diagram seen in Figure 2(c).
Integral transmittance of the final design
in the visible spectral range is 56%. A series of similar designs based on gold (Au)
with different combinations of reflected
and back-reflected colors has been successfully produced by Vesna Janicki and Jordi
Sancho-Parramon of the Institut Ruđer
Bošković (IRB; Zagreb, Croatia).
Ultra-fast laser coatings
The use of ultrafast optics is rapidly growing in physics.
Dispersive dielectric multilayer mirrors are the key elements
controlling group-delay dispersion (GDD) of high-intensity fem-
tosecond laser pulses. They allow generating sub-5-fs pulses directly from the cavity of a titanium:sapphire (Ti:sapphire) laser.
At the current state of the art, typical highly dispersive mir-
rors contain 70 to 120 layers. Production of such coatings is a
challenge for optical coating engineers because dispersive mir-
rors are extremely sensitive to deposition errors. The usage of
magnetron-sputtering and ion-beam-sputtering deposition pro-
cesses providing high-density coating layers and stable deposi-
tion rates makes possible accurate time control of layer thick-
nesses during mirror deposition.
Some errors in layer thicknesses are still inevitable in the
course of coating production. We have developed software that
can decrease the sensitivity of dispersive mirrors to errors by
including design stability into the formulation of the design
problem. The robust synthesis method produces stable final
designs without using special starting designs.
The key robust design parameters are: ( 1) a level of absolute
(or relative) errors σ and ( 2) the number of designs in a cloud
FIGURE 3. Reflectance and group-delay dispersion (GDD) are shown for conventional (a)
and robust (b) designs. The gray areas indicate corridors of GDD errors.