Hybrid surface-relief/volume one dimensional holographic gratings D.E. Lucchetta a,⇑ , P. Spegni a , A. Di Donato b , F. Simoni a , R. Castagna c,⇑ a Dipartimento SIMAU, Università Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona, Italy b Dipartimento DII, Università Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona, Italy c NEST, Istituto Nanoscienze – CNR, Scuola Normale Superiore di Pisa, Piazza San Silvestro 12, 56127 Pisa, Italy article info Article history: Received 24 September 2014 Received in revised form 9 January 2015 Accepted 12 January 2015 Available online xxxx Keywords: Optical holography Acrylates Free radical photopolymerization Bragg gratings Surface relief gratings Morphological analysis abstract Many one dimensional optically patterned photopolymers exist as surface relief or volume phase grat- ings. However, as far as we know, holographically recorded acrylate-based gratings in which both config- urations are present are not described in literature. In this work we report a two steps fabrication process in which a large-area high-resolution hybrid volume/surface relief grating phase gratings is created in a thin film of multiacrylate material spinned on a proper designed substrate. Optical and morphological investigations, made on the optically patterned area, confirm the presence of a one dimensional double (surface relief and Bragg volume phase) periodic structure. Ó 2015 Elsevier B.V. All rights reserved. 1. Introduction High resolution thin periodic structures known also as surface relief gratings (SRGs) are currently used in many research fields including nanophotonics [1], biophotonics [2], integrated optics [3] and plasmonics [4]. Some of those applications [5] require large-area, high resolution structures made in thin layers (a few micrometers) of material. Optical interferometry in principle, gives the possibility of writing such structures in photo-polymers in a cheap and fast way. One of the most used materials for optical pat- terning and nano-imprinting is the photopolymer SU-8 [6], an epoxy-based and viscous negative photo-resist. SU-8 is usually spinned on flat surfaces with thickness ranging from below 1 lm up to above 300 lm and an aspect ratio of 1:10 when periodically patterned. However, thin layers of patterned photopolymers can be obtained also in different ways. In Ref. [7] for example, it has been shown how the fabrication of such gratings is possible in materials characterized by linear chains doped with azo-benzene structures. It is worth noting how in some situations these periodically pat- terned structures derive from self-assembling processes and how, once settled, are sensitive to the polarization state of an impinging light [8]. Following this well established technological path, in this work we show the possibility of recording double structured large area thin and stable polymeric gratings in a simple mixture mainly based on a pure multiacrylate monomer. The recording process is fast and simple and requires only a two step procedure to be accomplished. The so recorded gratings are characterized by high resolution, high optical contrast and thickness in the range 0.05– 2.0 lm. More in general, depending on the ratio between grating pitch and grating depth, from an optical point of view, these struc- ture can be distinguished into SRG or volume phase gratings. In particular, Klein and Cook [9] introduced a parameter Q, defined as Q =2pk 0 L=K 2 n 0 (where L is the grating thickness, k 0 is the vac- uum wavelength of light, K is the grating pitch, and n 0 is the mean refractive index of the structure) to discriminate the two situa- tions. Values of Q < 1, i.e., thin gratings, were believed to give Raman–Nath operation whereas large values of Q (Q > 10), i.e., thick gratings, were believed to give Bragg regime operation. 2. Experimental details 2.1. Materials Di-pentaerythritol-penta/hexa acrylate (DPPHA), N-Vinyl- Pirrolidone (NVP), (1R,4S)-1,7,7-trimethylbicyclo[2.2.1]heptane- 2,3-dione (Camphorequinone, CQ) from SIGMA–Aldrich, Bis-(tri- methyl-phenyl) phosphine oxide (Irgacure 819) from CIBA Specialty Chemicals are used in this work. http://dx.doi.org/10.1016/j.optmat.2015.01.028 0925-3467/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding authors. Tel.: +39 0712204222 (D.E. Lucchetta). Tel.: +39 050509848 (R. Castagna). E-mail addresses: d.e.lucchetta@univpm.it (D.E. Lucchetta), riccardo.castagna@ nano.cnr.it, riccardo.castagna@sns.it (R. Castagna). Optical Materials xxx (2015) xxx–xxx Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat Please cite this article in press as: D.E. Lucchetta et al., Opt. Mater. (2015), http://dx.doi.org/10.1016/j.optmat.2015.01.028