The driving force behind combining the nanoimprinting and photolithography is to effectively utilize the advantages of
both patterning techniques simultaneously. Conventional shadow-mask UV-lithography can be used to pattern micron-scale
structures uniformly over large areas, whereas nanoimprinting enables patterning of nanoscale features, which can
also be tilted or round-shaped. We present the work on direct patterning of micro-optical structures by combined
nanoimprinting and lithography using modified mask aligner, hybrid mask mold and directly patternable, UV-curable
materials. Patterning of structures is carried out in wafer-level fashion. Hybrid mask mold fabrication can be realized for
example by modifying conventional shadow-mask using focused ion beam (FIB) milling, or by patterning a mold area on
shadow-mask surface by nanoimprinting. One of the advantages of proposed fabrication method is that there is no need
for reactive ion etching (RIE) process steps. We present also near-field holography (NFH) as a method of grating mold
fabrication. Fabricated micro-optical structures include directly patterned waveguides with light coupling gratings, and
also pyramid-shaped gratings which show antireflection properties in the mid-infrared spectral region.
Broadband antireflection properties of material surfaces are of primary interest for a wide variety of applications: to
enhance the efficiency of photovoltaic cells, to increase the sensitivity of photodetectors, to improve the performance of
light emitting diodes, etc...
In the past, broadband antireflection multilayer coatings were widely used and recently very low refractive index
materials in thin film form have been fabricated by several groups. The research work presented in this paper aims at
modeling and fabricating bi-periodic micro-structured silicon surfaces exhibiting broadband antireflection properties in
the infrared range. These structures of pyramidal shape, which typical dimensions are smaller than the wavelength, are
not in the Effective Medium Theory (EMT) validity domain. The optimization of the optical properties of such patterned
surfaces needs a fully Finite Difference Time Domain (FDTD) rigorous description of light propagation phenomena. The
influence of various opto-geometrical parameters such as period, depth, shape of the pattern is examined. The
antireflective properties of such bi-periodic patterned surfaces is then discussed using the photonic crystal theory and
photonic band diagrams description. The structure is considered as a two dimensional periodic structure with a nonuniform
third dimension. Correlations between the density of Bloch modes, flatness of dispersion curves and the surface
reflectance are presented. The last part of this paper is devoted to the presentation of the fabrication and the
characterization of the structures. Low cost and large surface processing techniques are proposed using wet anisotropic
etching through a silica mask obtained by photolithography or nanoimprinting.
In order to control the technique of laser-induced forward transfer (LIFT) in ultrashort regimes, it is necessary to understand the different basic mechanisms involved during the three steps: ablation-transfer-deposition. Back ablation of Cr thin film has been studied and compared to the front ablation of the same film in the same conditions. Experiments have been performed using ultrashort laser pulses (800 nm, 100 fs). The dynamics of the plumes have been monitored with a gated intensified charge coupled device (ICCD) camera. Image analysis gave us indications on the velocity and the composition of the ejected material. A parametric study of the ablation thresholds and ablation dynamics has been carried out as a function of the incident laser fluence and the thickness of the metal layer. These results contribute to optimize a process of LIFT. Transfers of Cr on glass and Silicon were obtained with a good spatial resolution.
Experiments of laser-induced forward transfer (LIFT) have been performed using ultrashort laser pulses (800nm, 100fs). 40nm of Cr thin film have been transferred on glass and Silicon acceptor substrates in different conditions. The analysis of the deposits was carried out by optical and electronic scanning microscopy. An optimisation of the process has been carried out and a good resolution of the patterns was obtained. The dynamics of the plume has been monitored with a gated ICCD camera and the images analysis gave us indications on the transfer of the material.