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Laser-Induced Periodic Surface Structures (LIPSS) manufacturing is a convenient laser direct-writing technique for the fabrication ofnanostructureswith adaptable characteristics on the surface of virtually any material. In this paper, we study the influence of 1D laser wavefront curvature on nanoripples spatial regularity, by irradiating stainless steel with a line-focused ultrafastlaser beamemitting 120fs pulses at a wavelength of 800nm and with 1kHz repetition rate. We find high correlation between the spatial regularity of the fabricated nanostructures and the wavefront characteristics of the laser beam, with higher regularity being found with quasi-plane-wave illumination. Our results provide insight regarding the control of LIPSS regularity, which is essential for industrial applications involving the LIPSS generation technique.

We describe a theoretical approach based on Müller and tensor calculus for predicting the polarization state and gain of cascaded Stokes orders produced under coherent Raman scattering regime conditions. The formulation follows a Markovian-style implementation for F2g-type modes in Raman cubic crystals. The theoretical model is supported by experimental results that corroborate that the polarization and power of the cascaded Stokes orders can be effectively predicted using sequential calculus. We extend these results to a variety of crystal propagation directions, with the aim of facilitating the design of advanced solid-state Raman lasers.

We demonstrate a continuously tunable, multi-Stokes Raman laser operating in the visible range (420 - 600 nm). Full spectral coverage was achieved by efficiently cascading the Raman shifted output of a tunable, frequency-doubled Ti:Sapphire laser. Using an optimized hemi-spherical external Raman cavity composed only of a diamond crystal and a single reflecting mirror, producing high power output at high conversion efficiency (>60 % from pump to Stokes) for a broad range of wavelengths across the visible. Enhancement of the cascading was achieved by controlling the polarization state of the pump and Stokes orders. The Stokes outputs exhibited a linewidth of 11 ± 1 GHz for each order, resembling the pump laser linewidth, enabling its use for the intended spectroscopic applications. Furthermore, the Raman laser performance was demonstrated by applying it for the resonance excitation of atomic transitions in calcium.

The control of the interaction between materials and biological tissues is a key factor to optimize the overall performance of implants and prostheses integrated into the body. With this objective in mind, biomimetic hierarchical one- and two-dimensional surface patterns textured at the micro and nano scales were fabricated on titanium alloys using femtosecond laser processing. The experimental results show that laser irradiation promotes surface oxidation together with a polarization-dependent nano-ripple formation. Human mesenchymal stem cells were subsequently cultured on different surface patterns aiming at determining their response to the underlying micro and nano structures. The ripple topography was demonstrated to induce a nonfouling behavior, which could be exploited in the fabrication of biomimetic hierarchical surface patterns to develop cell-trapping modules, The authors are grateful for funding provided by Ministerio de Economía y Competitividad (Spain), under project reference numbers MAT2014-54826-C2-1-R and MAT2014-54826-C2-2-R and NanoNeuroDev (Grant No. 2017/EEUU/11) from Santander-Universidad

A fast and reliable method for the fabrication of polarization modifying devices using femtosecond laser is reported. A setup based on line focusing is used for the generation of LIPSS on stainless steel, processing at different speeds between 0.8 and 2.4mm/s with constant energy per pulse of 1.4mJ. SEM and AFM characterizations of the LIPSS show a progressive increase in period as the processing speed increases, while height remains approximately constant in the studied range. Optical characterization of the devices shows an induced change in the polarization of the reflected beam that varies with the processing speed, which allows a controlled fabrication of these devices.

We study theoretically and experimentally the spectral and polarization effects occurring when cascading stimulated Raman scattering processes in diamond. We demonstrate an efficient, few-GHz linewidth, broadly tunable, multi-Stokes comb for spectroscopic applications.

We demonstrate a Raman laser continuously tunable in the visible range, capable of performing element-selective photo-ionization. The Stokes outputs exhibited a linewidth of 11.0 ± 1.0 GHz with a conversion efficiency of more than 60%. © 2020 The Authors

We demonstrate a rapid, accurate, and convenient method for tailoring the optical properties of diamond surfaces by employing laser induced periodic surface structuring (LIPSSs). The characteristics of the fabricated photonic surfaces were adjusted by tuning the laser wavelength, number of impinging pulses, angle of incidence and polarization state. Using Finite Difference Time Domain (FDTD) modeling, the optical transmissivity and bandwidth was calculated for each fabricated LIPSSs morphology. The highest transmission of ~99.5% was obtained in the near-IR for LIPSSs structures with aspect ratios of the order of ~0.65. The present technique enabled us to identify the main laser parameters involved in the machining process, and to control it with a high degree of accuracy in terms of structure periodicity, morphology and aspect ratio. We also demonstrate and study the conditions for fabricating spatially coherent nanostructures over large areas maintaining a high degree of nanostructure repeatability and optical performance. While our experimental demonstrations have been mainly focused on diamond anti-reflection coatings and gratings, the technique can be easily extended to other materials and applications, such as integrated photonic devices, high power diamond optics, or the construction of photonic surfaces with tailored characteristics in general.

ZnO thin film sputtered on alumina substrate is processed by Direct Laser Interference Patterning (DLIP). The heat transfer equation has been simulated for interference patterns with a period of 730 nm and two different fluences (85 mJ/cm2 and 165 mJ/cm2). A thermal threshold of 900 K, where crystal modification occurs has been calculated, indicating a lateral and depth processing around 173 nm and 140 nm, respectively. The experimentally reproduced samples have been analyzed from the structural and composition point of view and compared to conventional thermal treatments at three different temperatures (600 °C, 700 °C and 800 °C). Promising properties have been observed for the laser treated samples, such as low influence on the thin film/substrate interface, an improvement of the crystallographic structure, as well as a decrease of the oxygen content from O/Zn = 2.10 to 1.38 for the highest fluence, getting closer to the stoichiometry. The DLIP characteristics could be suitable for the replacement of annealing process in the case of substrates that cannot achieve high temperatures as most of flexible substrates.

Waveplates modify polarization by generating a phase change. Laser Induced Periodic Surface Structures (LIPSS) have recently started to be studied as waveplates due to the birefringence in-duced by the nanoripples, easily fabricated in a one-step process by laser, where LIPSS morphology is defined by the characteristics of the laser process parameters and the substrate material. The optical properties of these waveplates are defined by LIPSS parameters such as period, depth or width of the ripples. In this work we have deposited thin film coatings on stainless steel samples containing LIPSS for different coating thickness and composition. Results show that thin film coatings are a good candidate for the tunability of LIPSS birefringence since the coating modifies the induced polarization change and reflectivity of the sample depending on coating thickness and composition, as expected from numerical simulations.

In this work we have developed hierarchical structures that consist of micro-patterned surfaces covered by nanostructures with a femtosecond laser. The first part of this work is a study to determine the microscale modifications produced on a stainless steel alloy (AISI304) surface at high pulse energy, different velocities, and number of overscans in order to obtain microstructures with a selected depth of around 10 μm and line widths of 20 μm. The second part of the work is focused on finding the optimal irradiation parameters to obtain the nanostructure pattern. Nanostructures have been defined by means of Laser Induced Periodical Surface Structures (LIPSS) around 250 nm high and a period of 580 nm, which constitute the nanostructure pattern. Finally, dual scale gratings of 50 mm 2 were fabricated with different geometries and their effect on the measured contact angle. Combining the micro-pattern with the LIPSS nano-pattern, highly hydrophobic surfaces have been developed with measured static contact angles higher than 150° on a stainless steel alloy.

We demonstrate an effective method for fabricating large area periodic two-dimensional semiconductor nanostructures by means of single-pulse laser interference. Utilizing a pulsed nanosecond laser with a wavelength of 355 nm, precisely ordered square arrays of nanoholes with a periodicity of 300 nm were successfully obtained on UV photoresist and also directly via a resist-free process onto semiconductor wafers. We show improved uniformity using a beam-shaping system consisting of cylindrical lenses with which we can demonstrate highly regular arrays over hundreds of square micrometers. We propose that our novel observation of direct pattern transfer to GaAs is due to local congruent evaporation and subsequent droplet etching of the surface. The results show that single-pulse interference can provide a rapid and highly efficient route for the realization of wide-area periodic nanostructures on semiconductors and potentially on other engineering materials.

A diffractive optical element was fabricated by monolithically integrating two volume phase-gratings (VPGs) in the bulk of a single-piece transparent material. A computer model of the diffraction generated by the double volume phase-grating (DVPG) was made with a rigorous coupled wave analysis simulator. Simulations and experiments show that the diffractive behavior of a DVPG can be controlled by arranging the relative displacement and the distance between the VPGs according to Talbot self-imaging planes. In order to diffract the total incident light, the phase accumulation in the VPGs has to be π/2, which was achieved by single-scan femtosecond laser processing of a nanocrystal doped glass as the substrate material. Ex situ microscope images of the cross-sections are presented for laser processed lines in the form of VPGs and DVPGs. The far-field diffraction of DVPGs formed by selectively located VPGs was characterized with a monochromatic 633 nm and a supercontinuum white light. Functional designs of high diffraction efficiency with potential applications in photonics were successfully fabricated in a one-step and free of chemicals process.

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In this work, submicro and nanostructures self-formed on the surface of Platinum thin films under femtosecond laser-pulse irradiation are investigated. A Ti:Sapphire laser system was used to linearly scan 15 mm lines with 100 fs pulses at a central wavelength of 800 nm with a 1 kHz repetition rate. The resulting structures were characterized by scanning electron microscopy (SEM) and 2D-Fast Fourier Transform (2D-FFT) analysis. This analysis of images revealed different types of structures depending on the laser irradiation parameters: random nanostructures, low spatial frequency LIPSS (LSFL) with a periodicity from about 450 to 600 nm, and high spatial frequency LIPSS (HSFL) with a periodicity from about 80 to 200 nm. Two different modifications regimes have been established for the formation of nanostructures: (a) a high-fluence regime in which random nanostructures and LSFL are obtained and (b) a low-fluence regime in which HSFL and LSFL are obtained.

We study the fabrication of photonic surface structures in single crystal diamond by means of highly controllable direct femtosecond UV laser induced periodic surface structuring. By appropriately selecting the excitation wavelength, intensity, number of impinging pulses and their polarization state, we demonstrate emerging high quality and fidelity diamond grating structures with surface roughness below 1.4 nm. We characterize their optical properties and study their potential for the fabrication of photonic structure anti-reflection coatings for diamond Raman lasers in the near-IR.

ZnO thin film on alumina has been deposited by RF sputtering and processed by two dimensional direct laser interference patterning (DLIP) using a nanosecond laser (λ=355nm). The thermodynamic and structural properties have been investigated. Morphological characterization has shown a line-pattern structure with small alterations depending on the fluence of the laser (85 mJ/cm 2 or 165 mJ/cm 2 ). In order to understand these modifications, a simulation has been carried out to model the transient temperature during the DLIP to study the temperature reached by the ZnO surface for the different fluences. Moreover, a comparison with a non-interference energy distribution pulse is also simulated to corroborate the model. For samples processed by DLIP, a thermal annealing effect has been noticed when temperatures at the surface are between 1000K and 1800K. Due to the slow cooling process, a possible recrystallization of the material similar to a thermal treatment is obtained. For temperatures close or higher than 1800K, the material starts to ablate.

Volume-phase gratings (VPGs) were fabricated in CdS x Se1−x quantum-dot-doped borosilicate glass at a low repetition rate (800 nm, 140 fs, 1 kHz). The VPGs were designed based on rigorous coupled wave analysis simulations. Results indicate that the inscribed thickness (L) is the key parameter to maximize the diffraction efficiency at order 1. Microscope images of the cross sections and diffraction efficiency measurements were taken in order to characterize the modification of the material at different laser-inscription parameters. A maximum VPG diffraction efficiency of 67% (at order 1) was achieved. Also, a refractive index change of Δn=2.25·10−3 is estimated from these VPG diffraction efficiency measurements. The measurements regarding polarization-insensitive diffraction efficiency showed that the birefringence produced in the substrate is negligible.

The precise control over the interaction between cells and the surface of materials plays a crucial role in optimizing the integration of implanted biomaterials. In this regard, material surface with controlled topographic features at the micro- and nano-scales has been proved to affect the overall cell behavior and therefore the final osseointegration of implants. Within this context, femtosecond (fs) laser micro/nano machining technology was used in this work to modify the surface structure of stainless steel aiming at controlling cell adhesion and migration. The experimental results show that cells tend to attach and preferentially align to the laser-induced nanopatterns oriented in a specific direction. Accordingly, the laser-based fabrication method here described constitutes a simple, clean, and scalable technique which allows a precise control of the surface nano-patterning process and, subsequently, enables the control of cell adhesion, migration, and polarization. Moreover, since our surface-patterning approach does not involve any chemical treatments and is performed in a single step process, it could in principle be applied to most metallic materials.

Femtosecond laser micromachining has progressed considerably in the last decade due to the increasing interest in glass microsystems. In this work, we present a systematic study of the femtosecond laser ablation rate of soda-lime glass as a function of the deposited energy and pulse overlapping parameters. Experimental results demonstrate that the incubation effect reported by other authors can be neglected for particular process conditions and a constant ablation rate can be obtained, thus enhancing the depth control of the fabricated features.

This work presents the fabrication of hollow-core metallic structures with a complete laser interference lithography (LIL) process. A negative photoresist is used as sacrificial layer. It is exposed to the pattern resulting from the interference of two laser beams, which produces a structure of photoresist lines with a period of 600 nm. After development of the resist, platinum is deposited on the samples by DC sputtering and the resist is removed with acetone. The resulting metallic structures consist in a continuous platinum film that replicates the photoresist relief with a hollow core. The cross section of the channels is up to 0.1 μm 2 . The fabricated samples are characterized by FESEM and FIB. This last tool helps to provide a clear picture of the shape and size of the channels. Conveniently dimensioned, this array of metallic submicrometric channels can be used in microfluidic or IC cooling applications.

The production of periodic structures in silicon wafers by four-beam is presented. Because laser interference ablation is a single-step and cost-effective process, there is a great technological interest in the fabrication of these structures for their use as antireflection surfaces. Three different laser fluences are used to modify the silicon surface (0.8 J cm−2, 1.3 J cm−2, 2.0 J cm−2) creating bumps in the rim of the irradiated area. Laser induced periodic surface structures (LIPSS), in particular micro and nano-ripples, are also observed. Measurements of the reflectivity show a decrease in the reflectance for the samples processed with a laser fluence of 2.0 J cm−2, probably caused by the appearance of the nano-ripples in the structured area, while bumps start to deteriorate.

Periodic structures are of increasing interest in many fields such as nanotechnology and biotechnology among others. Laser Interference Lithography (LIL) has been widely studied for the fabrication of periodic structures. However, a LIL tool for the nanoscale structuring of materials that can scale beyond laboratory prototypes into cost effective industrial processes is not yet defined. In this work, we describe a versatile and automatic high-power multiple beam interference lithography system design capable of overcoming the limitations of manual setups. Using this system, we have successfully processed photoresist samples on the whole surface of 3in. silicon wafers, demonstrating the applicability of this prototype to a wide range of device fabrication.

High throughput and low cost fabrication techniques in the sub-micrometer scale are attractive for the industry. Laser interference lithography (LIL) is a promising technique that can produce one, two and three-dimensional periodical patterns over large areas. In this work, two- and four-beam laser interference lithography systems are implemented to produce respectively one- and two-dimensional periodical patterns. A high-power single pulse of ∼8 ns is used as exposure process. The optimum exposure dose for a good feature patterning in a 600 nm layer of AZ-1505 photoresist deposited on silicon wafers is studied. The best aspect ratio is found for a laser fluence of 20 mJ/cm2. A method to control the width of the sub-micrometer structures based on controlling the resist thickness and the laser fluence is proposed.

We have investigated the temperature and carrier density dependence of the carrier capture time of two optically pumped InGaN/GaN multiple quantum well laser structures by subpicosecond time-resolved differential transmission spectroscopy. We find that the carrier capture time varies significantly with both the temperature and the carrier density. The carrier density dependence is consistent with screening of piezoelectric fields, in agreement with theoretical predictions. The sample with the lower threshold for stimulated emission has a faster carrier capture rate, which highlights the importance of carrier capture for the lasing process. At room temperature the capture time is less than 1.2 ps in both samples.

We present a novel method to fabricate low bend loss femtosecond-laser written waveguides that exploits the differential thermal stabilities of laser induced refractive index modifications. The technique consists of a two-step process; the first involves fabricating large multimode waveguides, while the second step consists of a thermal post-annealing process, which erases the outer ring of the refractive index profile, enabling single mode operation in the C-band. By using this procedure we report waveguides with sharp bends (down to 16.6 mm radius) and high (80%) normalized throughputs. This procedure was used to fabricate an efficient 3D, photonic device known as a pupil-remapper with negligible bend losses for the first time. The process will also allow for complex chips, based on 10's - 100's of waveguides to be realized in a compact foot print with short fabrication times., 9 pages, 6 figures

This paper introduces the quality inspection of nanoscale patterns produced by the Laser Interference Lithography (LIL) technology using image analysis techniques. In this paper, patterns of two-beam and four-beam interferences are considered. Image analysis techniques based on the Hough transform (HT) and Maximum Likelihood Estimation (MLE) have been applied to detect and estimate various quality parameters for the two types of textures. The HT and a modified grey-scaled HT are introduced as a global approach for the analysis of the two-beam interference patterns. Surface parameters, such as the period, depth, and their uniformities, can be obtained directly without a priori knowledge of the textures. Due to different pattern structures and strong noise effects, the four-beam patterns are dealt with a different approach, using a statistical method based on the likelihood function to estimate each circle's center and shape. Taking into consideration of noises and defects, another further rejection step is introduced to filter out noises and defects. Results from experimental samples are presented.

Laser interference lithography (LIL) is concerned with the use of interference patterns generated from two or several coherent beams of laser radiation for the structuring of materials. This paper presents the work on the processes based on resists and direct writing with laser interference lithography. In the work, a four-beam laser interference system was used as a submicrometer structuring tool in which a high-energy pulsed, frequency-tripled and TM polarized Nd:YAG laser (355 nm) with a coherent length of 3 m, energy power up to 320 mJ/cm2, pulse duration of 8 ns and 10 Hz repetition rate was used as a light source. The experimental results were achieved with 2-beam and 4-beam interference patterning. The processes can be used to define submicron surface relieves in large areas for use in the field of MEMS.

This paper presents a system requirement analysis of multi-beam laser interference nanolithography for nanoscale structuring of materials including seven sections: introduction, formation of multi-beam laser interference patterns, user requirements, system architecture, experiments, discussions and conclusions. Analytical expressions were obtained for the spatial distribution of radiation of the interfering beams as a function of their amplitudes, phases, angles of incidence on the sample, and polarization planes with computer simulation and experimental results. The environmental effect and technological potential were also discussed.

Multi-beam laser interference lithography (MB-LIL) is a rapid and cost-effective maskless optical lithography technique to parallelly pattern periodic or quasi- periodic micro/nano-structured material over large areas more than square centimetres. An interference pattern between two or more coherent laser beams is set up and recorded in a recording material of substrate. This interference pattern consists of a periodic series of geometries representing intensity minima and maxima. The patterns that can be formed depend on the number and configuration of laser beams. This review introduces the development and application of MB-LIL system for fabrication of micro/nano-structured material. At first, it surveys various types of MB-LIL methods by classifying different beam configurations. Then the paper shows some application results for fabrication 2D/3D micro/nano structure arrays by means of interference patterns with multi-exposed or directly ablation technique. The patterend micro/nano-structure arrays include crossed diffraction grating array in photoresist, 3D pattern in polymetric photonic crystals, and magnetic nanoarrays in thin film. Finally, an innovative four-beam LIL system is introduced, which is being developed within the EC-granted project DELILA.

Nanoscale periodic and quasiperiodic relieves on fused quartz are of interest for the creation of a variety of optical and electronic devices such as phase masks, one- and two-dimensional stamps for nanoimprint and wide-band antireflection structures. The authors of this paper have developed a method of interference lithography to pattern nanoscale relief on quartz with a high-power pulsed XeCl laser with high-quality output radiation at wavelength 308nm. One of the advantages of the proposed technique is the significantly smaller influence of mechanical oscillations in an optical setup on the results of nanoscale modification. The relief on quartz was formed with the use of a complete cycle of lithography. As the mask, a two-layer structure of a copper film of 50nm in thickness and a photoresist of 400nm in thickness were employed. The mask pattern was formed by exposure of a photoresist by two radiation beams of a XeCl laser with energy density ~ 30mJ/cm 2 , aqueous-alkali development of a photoresist, and copper etching by the ion beam (Ar + ). Quartz was etched by the method of ion-beam reactive etching in a flow of CF 4 - O 2 (20%) gas mixture, with etching rate 30nm/min.

This paper presents a theoretical analysis of formation of 4-beam laser interference patterns for nanolithography. Parameters of 4-beam interference patterns including the pattern amplitude, period, orientation and uniformity were discussed. Analytical expressions were obtained for the spatial distribution of radiation of the interfering beams as a function of their amplitudes, phases, angles of incidence on the sample, and polarization planes with computer simulation and experimental results.

The surface morphology of a Niobium sample, irradiated in air by a femtosecond laser with a wavelength of 800 nm and pulse duration of 100 fs, was examined. The period of the micro/nanostructures, parallel and perpendicularly oriented to the linearly polarized fs-laser beam, was studied by means of 2D Fast Fourier Transform analysis. The observed Laser-Induced Periodic Surface Structures (LIPSS) were classified as Low Spatial Frequency LIPSS (periods about 600 nm) and High Spatial Frequency LIPSS, showing a periodicity around 300 nm, both of them perpendicularly oriented to the polarization of the incident laser wave. Moreover, parallel high spatial frequency LIPSS were observed with periods around 100 nm located at the peripheral areas of the laser fingerprint and overwritten on the perpendicular periodic gratings. The results indicate that this method of micro/nanostructuring allows controlling the Niobium grating period by the number of pulses applied, so the scan speed and not the fluence is the key parameter of control. A discussion on the mechanism of the surface topology evolution was also introduced.

We present a novel process to fabricate high index contrast waveguides in boro- aluminosilicate glass based on differential thermal post-annealing. Firstly, large high index contrast multimode waveguides are inscribed and subsequently annealed to achieve single-mode operation. We applied this technique to significantly increase the throughput of 3D astrophotonic devices and to demonstrate anti-resonant (ARROW) guiding in a laser written structure for the first time.

Atomic-scale manipulation of carbon based surfaces, such as diamond, has an enormous potential for the construction of future nano-scale, photonic and optoelectronic devices. Diamond, when compared to other group IV covalent semiconductors, is particularly interesting; not only its tightly packed and strongly bound crystal lattice is an ideal environment for extreme physics, but it also offers advantages in terms of heat conductivity, hardness and transparency for multitude of applications. The development of diamond transistors [1], single photon sources for quantum computation based on diamond [2] or high power diamond optics and lasers [3] have benefited from developments on high precision diamond processing greatly.

By modelling time resolved emission spectra of 3 and 4 nm In0.07Ga0.93N quantum wells we show that injected carriers reduce the internal field to only 70% of its unscreened value at typical laser thresholds

An accurate method to define three-dimensional (3D) microstructures is the electrochemically controlled etching (ECE) process of an epitaxial silicon wafer in anisotropic etchants. In this paper, a study of the temperature and concentration influence of the anisotropic etchant (KOH) on the passivation potential (PP) and passivation current density (jpass) is presented. The dependence of jleak through the reverse biased junction between the epilayer and the substrate on the resistor diffusion depth has been studied. The results have been applied to optimize a three-electrode ECE process. In this way, 15 μm thick membranes have been obtained with 3 μm depth previously diffused resistors.

The discovery of the formation of nanogratings when irradiating fused silica glass with ultrashort laser pulses in 2003 may have opened a new generation of compact and long life time optical devices. 3D-writing, thermal stability up to 1000 oC and virtually unlimited lifetime at room temperature make optics based on nanogratings of great potential for compact sensors or devices that work in adverse environmental conditions [1]. In addition, nanogratings behave as subwavelength structures in the visible and NIR spectrum, so that they allow micro-sized waveplates with controllable retardance and fast-axis orientation and, thus, they are expected to allow the fabrication of almost any design of polarization device in glass [2]. In this work we study volume polarization gratings (VPOG) in glass with special focus on the self-imaging of the grating produced by the Talbot effect. The experimental results are compared with the theoretical planar polarization gratings described by Scalar Diffraction Theory.

Since the first refractive index modification of transparent materials was achieved via femtosecond laser micromachining [1], the fabrication of bulk inscribed 3D optical elements has been insistently pursued. This method has been extensively used to generate a variety of photonic devices such as waveguides, couplers or amplifiers, which enabled a large number of technological breakthroughs [2]. In particular, the fabrication of glass embedded volume-phase gratings (VPG) has been studied in detail by many authors [3]. Currently, the process for manufacturing VPGs involves the use of dichromated gelatin hologram recording, which is accomplished sealing the gelatin between two layers of glass. Using femtosecond laser inscribing technique, VPGs can be fabricated in a more direct, robust and environmental friendly way.

Comparative X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) characterisation of nanocrystalline tin oxide prepared by sputtering and liquid pyrolysis was carried out taking into account the main procedure steps for each of these technological approaches. Results of morphological and structural characterisation show high similarity between these two technologies concerning structural parameters such as grain size and tin and oxygen binding energies and their modification with the calcination process. Nevertheless, some significant discrepancy remains after high-temperature treatments. Sputtered samples present residual lattice distortions that seem to be related to the layer compactness. Likewise, the role played by the oxygen vacancy concentration in the distortion evolution with the thermal treatments is discussed.