Michael Helgert

Max Planck Institute of Microstructure Physics, Halle-on-the-Saale, Saxony-Anhalt, Germany

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Publications (18)52.01 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We fabricated stochastic antireflective structures (ARS) and analyzed their stability against high power laser irradiation and high temperature annealing. For 8 ps pulse duration and 1030 nm wavelength we experimentally determined their laser induced damage threshold to 4.9 (±0.3) J/cm<sup>2</sup>, which is nearly as high as bulk fused silica with 5.6 (±0.3) J/cm<sup>2</sup>. A commercial layer stack reached 2.0 (±0.2) J/cm<sup>2</sup>. An annealing process removed adsorbed organics, as shown by XPS measurements, and significantly increased the transmission of the ARS. Because of their monolithic build the ARS endure such high temperature treatments. For more sensitive samples an UV irradiation proved to be capable. It decreased the absorbed light and reinforced the transmission.
    Optics Express 07/2012; 20(16):18348-55. · 3.53 Impact Factor
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    ABSTRACT: In this paper, we present a broadband wire grid polarizer with a spectral working range down to a wavelength of 193 nm. Tungsten is chosen as grating material because it provides a high extinction ratio and transmission compared with other common grating materials. The fabrication of the grating with 100 nm period was accomplished using a spatial frequency doubling approach based on ultrafast electron beam lithography and a sophisticated deposition technique. At a wavelength of 193 nm, a transmission of about 44% and an extinction ratio of 20 was measured.
    Applied Optics 06/2012; 51(16):3224-7. · 1.69 Impact Factor
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    ABSTRACT: Antireflective subwavelength structures (ARS) resembling nanostructures found on the cornea of night-active insects reduce the reflection of light by providing a gradual change in the refractive index at the interface. These artificial ARS have mainly been fabricated by a combination of conventional lithography and reactive ion etching, which constrains their application to planar substrates. We report on the fabrication of ARS using three different techniques including bottom-up and top-down methods as well as their combination on microlens arrays (MLAs) made of fused silica. The optical performance of the resulting ARS on the MLAs is as good as ARS fabricated on planar substrates with increased transmission of up to 96% at certain wavelengths.
    Applied Optics 01/2012; 51(1):8-14. · 1.69 Impact Factor
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    ABSTRACT: We present transmission increased fused silica lenses produced by using self-organized antireflective structures for which we developed an efficient manufacturing process. The spectral transmission measured over the whole lens aperture shows a significant transmission enhancement of up to 3.5% in the UV range. Local measurements on the lens's surface reveal a strongly reduced reflection of below 0.1% for 300 nm wavelength, which is homogeneous over the whole lens. Further, the lenses show a broadband spectral antireflection behavior. For 600 nm wavelength the reflection was measured at about 1%.
    Optics Letters 10/2011; 36(19):3924-6. · 3.39 Impact Factor
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    ABSTRACT: We present a cheap and versatile method to fabricate antireflective moth-eye structures on various substrates. This method consists of a mask created by a self-assembly technique (block copoplymer micelle nanolithography - BCML) and a subsequent reactive ion etching step. Contrary to most other methods this technique also allows for the creation of moth-eye structures on non-flat substrates. We demonstrate the superiority of this technique on a diffraction grating and on different lenses. Electron micrographs show that almost the whole surface area is homogenously covered with these antireflective nanostructures. Transmittance and reflectance measurements support these findings.
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    ABSTRACT: A flexible, nondestructive, and cost-effective replication technique for nanostructures is presented. The advantages of the process are: 1) it allows for tailoring structural parameters of the replica (e.g., line width) nearly independent of the structural geometry of the master; 2) it allows for replication of high-aspect-ratio structures also in polymer materials from solution (especially noncurable polymers) such as polystyrene and polymethylmethacrylate; 3) it includes an easy separation process, thus preserving the master for repeated use. Linear grating replicas with line widths ranging from 88 to 300 nm are obtained using a single nanostructured master. Nanofibers and complex nanopatterned replicas are achievable. The presented technique and its flexibility show that atomic layer deposition is a unique tool for the preparation of high-efficiency polarizer diffractive optics, photonics, electronics, and catalysts.
    Small 11/2010; 6(23):2701-7. · 7.51 Impact Factor
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    ABSTRACT: Laterally structured antireflective sub-wavelength structures show unique properties with respect to broadband performance, damage threshold and thermal stability. Thus they are superior to classical layer based antireflective coatings for a number of applications. Dependent on the selected fabrication technology the local topography of the periodic structure may deviate from the perfect repetition of a sub-wavelength unit cell. We used rigorous coupled-wave analysis (RCWA) to simulate the efficiency losses due to scattering effects based on height and displacement variations between the individual protuberances. In these simulations we chose conical and Super-Gaussian shapes to approximate the real profile of fabricated structures. The simulation results are in accordance with the experimentally determined optical properties of sub-wavelength structures over a broad wavelength range. Especially the transmittance reduction in the deep-UV could be ascribed to these variations in the sub-wavelength structures.
    Optics Express 11/2010; 18(23):23878-90. · 3.53 Impact Factor
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    ABSTRACT: Antireflective surfaces composed of biomimetic sub-wavelength structures that employ the 'moth eye principle' for reflectance reduction are highly desirable in many optical applications such as solar cells, photodetectors and laser optics. We report an efficient approach for the fabrication of antireflective surfaces based on a two-step process consisting of gold nanoparticle mask generation by micellar block copolymer nanolithography and a multi-step reactive ion etching process. Depending on the RIE process parameters nanostructured surfaces with tailored antireflective properties can easily be fabricated that show optimum performance for specific applications.
    Nanotechnology 10/2010; 21(42):425301. · 3.67 Impact Factor
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    ABSTRACT: The optical characteristics of shallow 2D nanostructured polycarbonate samples are presented. Tunable guided-mode resonance filters are experimentally demonstrated for the visible spectral range when functional coatings are applied to 2D nanostructures by means of atomic layer deposition. The wavelength position of the reflection peaks can be easily tuned in a broad range (>150 nm) through rotation of the optical element around the axis normal to the substrate without changing the rest of the optical setup. Rigorous coupled wave approach simulation of model systems is performed to obtain insight into the complexity of the optical properties of these systems. The photonic nanostructures presented here are promising optics for application in ultra-compact, portable, miniaturized optical systems.
    Advanced Functional Materials 07/2010; 20(13). · 10.44 Impact Factor
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    ABSTRACT: Imaging diffractive optical elements (DOEs), randomly distributed microlenses and sub-lambda-structures allow the improvement of the performance of Excimer-based imaging and illumination systems. Here we present the concept study of a hybrid imaging system for Excimer laser high power application at a working wavelength of 308 nm. In this hybrid approach a focus has to be put onto the impact of the non-desired diffraction orders to the optical performance and also to the amount of light remaining in the system and causing lens heating. Hereby the diffraction efficiency of the DOE is of enormous importance. Especially the influence of the passive facet of blazed transmission gratings has to be considered. For illumination systems we discuss the transfer of the uneven raw profile of an Excimer-laser into a Gaussian far-field distribution by introducing a microlens array with a 2-dimensional Voronoi-pattern. The holographic record of the microlens array allows additionally to influence the coherence parameters.
    Proceedings of SPIE - The International Society for Optical Engineering 07/2010; · 0.20 Impact Factor
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    ABSTRACT: Imaging DOEs, randomly distributed microlenses and sub-λ-structures allow the improvement of the performance of Excimer-based imaging and illumination systems. The potentials and the challenges are discussed especially with the focus on the local profile.
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    ABSTRACT: The paper discusses optical applications of atomic layer deposition. X-ray mirrors, antireflective coatings and bandpass filters were made for the visible spectral region. Coatings applied to two-dimensional shallow gratings produced tunable guided mode resonance filters.
    Advances in Optical Materials; 10/2009
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    ABSTRACT: Al(2)O(3) and TiO(2) thin films have been deposited on Si wafers, quartz, BK7 glass, and polycarbonate substrates by atomic layer deposition (ALD). The refractive indices and growth rates of the materials have been determined by spectroscopic ellipsometry and transmission electron microscopy. The influence of substrate temperature and precursor on the refractive indices has been investigated. The refractive index of TiO(2) significantly increases with temperature, whereas the Al(2)O(3) films are temperature insensitive. The films deposited using H(2)O(2) as oxygen source show a slightly higher refractive index than the films prepared with H(2)O. Multilayer narrow-bandpass filters and broadband antireflective coatings have been designed and produced by ALD.
    Applied Optics 04/2009; 48(9):1727-32. · 1.69 Impact Factor
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    ABSTRACT: Refractive microlens arrays in quartz glass are manufactured in a simple room temperature sol–gel casting process. The complete element, lenslet structure and substrate, is fabricated simultaneously. In contrast to other sol–gel processes, further re-shaping steps such as exposure or reflow techniques are not required. The process includes an isotropic shrinkage step in which the element dimensions are reduced by a factor of 2. The results of the manufactured lenslet arrays in terms of global uniformity, mesoscopic profile accuracy and surface roughness are discussed. A form stability of the spherical calottes from replica to replica was found to be ±2%.
    Microelectronic Engineering 04/2009; 86:1173-1175. · 1.34 Impact Factor
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    ABSTRACT: We report an innovative approach for the fabrication of highly light transmissive, antireflective optical interfaces. This is possible due to the discovery that metallic nanoparticles may be used as a lithographic mask to etch nonstraightforward structures into fused silica, which results in a quasihexagonal pattern of hollow, pillar-like protuberances. The far reaching optical performance of these structures is demonstrated by reflection and transmission measurements at oblique angles of incidence over a broad spectral region ranging from deep-ultraviolet to infrared light.
    Nano Letters 06/2008; 8(5):1429-33. · 12.94 Impact Factor
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    ABSTRACT: Micro and nanostructured optical components are evolved over millions of years in nature and show a wide application range as microlens arrays, diffractive or subwavelength structures in manifold biological systems. In this contribution we discuss the advantages and challenges to transfer the concepts based on the nature models to increase the performance of high-end optical systems in applications such as beam shaping and imaging. Especially we discuss the application of sophisticated statistical microlens arrays and diffractive structures in different fields such as lithography, inspection or for medical instruments. Additionally we focus on anti-reflection coatings which are commonly used to suppress reflection of light from the surface of optical components in the visible range. We report an innovative approach for the fast and cost-efficient fabrication of highly UV transmissive, anti-reflective optical interfaces based on self assembled gold nanoparticles.
    Proceedings of SPIE - The International Society for Optical Engineering 01/2008; · 0.20 Impact Factor
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    ABSTRACT: We demonstrate the potential of interference lithography in the DUV by examples of two-dimensional patterns that have been obtained by multiple exposure techniques. Using immersion prisms we realized gratings with more than 10 000 lines/mm.
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    ABSTRACT: Diffractive optical elements (DOEs) have a great potential in the complete or partial substitution of refractive or reflective optical elements in imaging systems. The greater design flexibility compared to an all-refractive/reflective solution allows a more convenient realization of the optical systems and additionally opens up new possibilities for optimizing the performance or compactness. To demonstrate the opportunities of the hybrid optical concept we discuss different imaging systems for various applications. We present the lens design of a hybrid microscope objective which is especially applicable for wafer inspection technologies. Meeting the requirements for such a system used in the deep-UV regime (248 nm) is very challenging. The short wavelength limits the material selection and demands cement free optical groups. The additional requirement of an autofocus system, working at a wavelength in the near infrared region, is fulfilled by the special combination of two selected and adjusted DOEs. Furthermore, we discuss the opportunities of the hybrid concept c of a slit lamp used for ophthalmologic examinations. The DOEs are the basic elements of this hybrid concept. We demonstrate that holographic lithography is an appropriate technology to realize a wide variety of elements with different profile geometries. We address in particular the additional possibilities of an UV-laser system as an exposure tool. Additionally to the high spatial frequencies, the 266 nm exposure wavelength allows the use of novel photo resists with advantageous development behavior.
    SPIE Proc; 01/2003

Publication Stats

96 Citations
52.01 Total Impact Points


  • 2009
    • Max Planck Institute of Microstructure Physics
      • Experimental Department 2
      Halle-on-the-Saale, Saxony-Anhalt, Germany
  • 2008
    • Carl Zeiss AG
      Oberkochen, Baden-Württemberg, Germany
    • Universität Heidelberg
      Heidelburg, Baden-Württemberg, Germany