INSTITUTE OF APPLIED PHYSICS - Antireflective surfaces

Antireflective surfaces

Antireflective surfaces have been fundamental for numerous optical applications for decades. They can be found in many consumer products (e.g. eyeglass lenses, camera objectives) as well as in lab systems and highly specialised optics. One method to reduce surface reflections are antireflective structures (ARS), also called moth eye structures. In contrast to inference coatings, these ARS have a wide angular and spectral behaviour which is determined by the depth and lateral size of the structures. They provide high damage threshold and temperature stability due to their monolithic build [1].
Fabrication techniques have been developed to create ARS on silicon (so-called black silicon) and fused silica for broad spectral and angular applications in the UV, VIS, and IR band. To fabricate deterministically ordered ARS high-end electron beam lithography to (see Fig.1) have been used. Also stochastic structures by a so-called self-masking etching process (see Fig.2) are created. Both methods provide high performance ARS, the latter being faster and more cost-efficient. The implementation options of silicon or fused silica ARS are manifold. They can be used in high efficient solar cells, metrology systems, objectives, high power applications, etc. Recently, the IAP fabricated highly transmission enhanced ARS lenses for the UV range [2].

Antireflective surfaces_TKB_Schulze_1
Fig.1: Deterministically ordered antireflective structures (ARS). Left: Antireflective silicon surface for a
        THz application. The structure depth in approx. 500 µm and the pillar width about 35 µm.
        Right: ARS in fused silica for antireflection in the IR range. Structure depth and period are 3 µm
        and 500 nm, respectively.

Antireflective surfaces_TKB_Schulze_2
Fig.2: Stochastic antireflective structures on silicon (left) and on fused silica (right).

[1] M. Schulze, M. Damm, M. Helgert, E.-B. Kley, S. Nolte, and A. Tünnermann:
     Durability of stochastic antireflective structures - analyses on damage thresholds
     and adsorbate elimination, Opt. Express 20 (16), 18348-18355 (2012).

[2] M. Schulze, D. Lehr, M. Helgert, E.-B. Kley, and A. Tünnermann: Transmission
     enhanced optical lenses with self-organized antireflective subwavelength
     structures for the UV range, Opt. Lett. 36 (19), 3924-3926 (2011).