Search

Diffractive optical elements (DOEs) play an important role in modern optical applications such as spectral and imaging systems, but it is challenging to balance the diffraction efficiency with the working bandwidth. The core issue is controlling the broadband dispersion of all phase units to achieve achromatic 2π-phase modulation in the broadband domain. Here, we demonstrate broadband DOEs utilizing multilayer subwavelength structures with different materials, making it possible to freely control the phase and phase dispersion of the structural units on a much larger scale than monolayer structures. The desired dispersion-control abilities arose due to a dispersion-cooperation mechanism and vertical mode-coupling effects between the top and bottom layers. An infrared design comprised of two vertically concatenated TiO2 and Si nanoantennas separated by a SiO2 dielectric spacer layer was demonstrated. It showed an average efficiency of over 70% in the three-octave bandwidth. This work shows enormous value for broadband optical systems with DOEs such as spectral imaging and augmented reality.

A comparative study was performed to investigate how etching methods and parameters affect the properties of

A comparative study was performed to investigate how etching methods and parameters affect the properties of S i O 2 and H f O 2 coatings. S i O 2 and H f O 2 single layers were prepared by electron-beam evaporation (EBE), ion-beam assisted deposition (IAD), and ion-beam sputtering (IBS). Then, ion-beam etching (IBE), reactive ion etching (RIE), and inductively coupled plasma etching (ICPE) were used to study the influence of ion bombardment energy and chemical reaction on the etching rates and properties of the prepared S i O 2 and H f O 2 single layers. For S i O 2 coatings, chemical reaction plays a dominant role in determining the etching rates, so ICPE that has the strongest C H F 3 plasma shows the highest etching rate. Moreover, all three etching methods have barely any influence on the properties of S i O 2 coatings. For H f O 2 coatings, the etching rates are more dependent on the ion bombardment energy, although the chemical reaction using C H F 3 plasma also helps to increase the etching rates to some extent. To our surprise, the ion bombardment with energy as high as 900 V does not change the amorphous microstructure or crystalline states of prepared H f O 2 coatings. However, the high-energy ion bombardment in IBE significantly increases the absorption of the H f O 2 coatings prepared by all deposition techniques and decreases their laser damage resistance to different extents.