Variable filters, which central wavelength of the bandpass shifts along one dimension of the component, is a promising way to simplify and to miniaturize imaging spectrophotometer systems for spatial observation. In fact, by combining a dispersive element and a variable filter, it is possible to realize a spectral and a spatial filtering based on pushbroom technique. While there were numerous methods developed in order to produce variable filters, at this date, there is no simple, reliable and repeatable method. In this paper, we present a new method for the fabrication of variable filters based on plasma assisted reactive magnetron sputtering (PARMS).
Variable filters are obtained upon the variation of the thickness of some or all the layers deposited on the substrate. The layers are deposited using a Bühler HELIOS machine in order to benefit from the high stability of the deposition process. To insure a non-uniformity of the deposited layers, adapted masks are placed in front of the targets for the low and high refractive index materials. The uniformity of these layers is measured via a custom set-up allowing a local measurement of the transmission to perform a mapping of the transmission over the whole component aperture.
In this paper, we present the fabrication of layers and filters with variable thickness. Various types of thickness gradients are presented.
Antireflection coatings are among the most common and spread optical coatings that are used in every optical system in order to decrease losses and prevent shadow images. For space applications, they are critical elements which specifications will highly influence the overall optical systems performances. Despite the very wide range of developments that have been carried out over the past thirty years, the production of broadband antireflection coatings for visible and infrared ranges remains a challenge. In this paper, we will present some recent results based on thin film technology for the production of antireflection coatings dedicated to visible, near-IR and mid-IR spectral ranges. We will first present broadband antireflection coatings for [400-1100] nm spectral range We will present two type of coatings, one for normal and one for oblique incidence. Experimental demonstration by plasma assisted reactive magnetron sputtering using a Bühler HELIOS machine will be presented. We will then show antireflection coatings covering the [1.5-15] μm range. Experimental demonstration and limitation will be presented.
We present hereafter the results on the fabrication of complex optical filters within the Institut Fresnel in close collaboration with CILAS. Bandpass optical filters dedicated to astronomy and space applications, with central wavelengths ranging from ultraviolet to near infrared, were deposited on both sides of glass substrates with performances in very good congruence with theoretical designs. For these applications, the required functions are particularly complex as they must present a very narrow bandwidth as well as a high level of rejection over a broad spectral range. In addition to those severe optical performances, insensitivity to environmental conditions is necessary. For this purpose, robust solutions with particularly stable performances have to be proposed.
With the aim to expand its capability to offer state-of-the-art space qualified multispectral optical filters assemblies, Sodern continues its effort to evaluate and incorporate new technologies in its designs. For many years, Sodern has been developing complex optical devices incorporating spectral filters.
Multispectral or hyperspectral images allow acquiring new information that could not be acquired using colored images and, for example, identifying chemical species on an observed scene using specific highly selective thin film filters. Those images are commonly used in numerous fields, e.g. in agriculture or homeland security and are of prime interest for imaging systems for onboard scientific applications (e.g. for planetology).
Today, the demand on flat optical components with specification on final surface flatness that must be smaller than ?/20 or ?/30 peak to valley, for various applications including linear accelerators [1,2], space applications …, needs an accurate knowledge on the mechanical stress induced in thin films. In order to design correctly stacks of thin films on both side of a substrate and achieve perfect stress compensation, it is thus obvious that the first step is to precisely characterize the stress in single layers.
We report on the sub-picosecond laser-induced damage of optical thin films of different thickness made by Magnetron sputtering, Ion assisted deposition and Ion plating, and submitted to single irradiation of the first and the third harmonics of an Ytterbium laser (1030 and 343nm). Using a single rate equation approach for free electron excitation coupled with calculation of the spatial and temporal distribution of the electric field, we investigate numerically the spatial density distribution of the absorbed energy and evaluate its capacity to describe damage phenomena especially damage threshold and morphologies (damage diameter, ablation deepness). Laser-induced damage thresholds are compared for different film thicknesses and different irradiation conditions.
We present hereafter the results on the fabrication of complex optical filters within the Institut Fresnel in close collaboration with CILAS. Bandpass optical interference filters, with central wavelengths ranging in near ultraviolet or in the near infrared, were deposited on both sides of glass substrates with a very good congruence with theoretical designs. For these applications, the required functions are particularly complex as they must present a very narrow bandwidth as well as a high level of rejection over a broad spectral range. Moreover, in order to satisfy more and more critical specifications on flatness of the component treated on both faces, the stress induced by the different layers has to be taken in account in the filter design.
All these components were manufactured using Plasma Assisted Reactive Magnetron Sputtering (PARMS) technics offered by the HELIOS machine and monitored in real time with an OMS5000 in-situ optical monitoring, both developed by BUHLER Optics.
Compressive mechanical stress of 364 MPa and 55 MPa respectively for SiO2 and Nb2O5 are measured, final sag of 326 nm and 13 nm, and uniformity from -0.05% to 0.10% and from -0.10% to 0.20% are obtained respectively for the two manufactured filters.
Due to market demand and technical progresses, a new generation of optical components requires much more sophisticated structures with a great number of layers. These complex structures enable to achieve severe optical performances but, at the same time, enhance light scattering processes.
For these reasons, it is essential to develop a metrological tool which provides an accurate quantification of the spectral and angular scattering losses behavior with sufficient angular and spectral resolutions.
In order to face this issue, new investigations were performed by our group at Institut Fresnel and led to the development of the new scatterometer SALSA (Spectral and Angular Light Scattering characterization Apparatus). The use of both a broad-band light source and a tunable filter allows to accurately select the illumination wavelength and the spectral bandwidth on the whole spectral range of CCD detectivity. In this paper we will present the performances of the setup and some experimental results.
This paper is devoted to the presentation of a new spectrophotometric system that allows us for the accurate measurement of the transmission of thin-film filters over an ultra-wide optical density range (from 0 to 11) between 400 nm and 1000 nm. After a detailed description of its structure, we define the transmission range reachable to this set-up and we quantify the influence of the spectral profile of the source on this critical feature. A qualification of this bench, including a determination of its noise floor, is performed on a dedicated band- pass filter manufactured by Institut Fresnel, and we conclude by the presentation of results of ultra-wide range transmission measurements achieved on commercially available filters (long-pass, short-pass, and notch).
We report on the laser-induced damage threshold at 500fs of optical films made by Magnetron Sputtering and
submitted to single and multiple irradiations at different harmonics of an Ytterbium laser (1030nm, 515nm
and 343nm). Single layers of SiO2, HfO2, and Nb2O5 as bare fused silica samples are under investigation.
A first generation of dielectric rib waveguides has been designed and shaped to support a monomode confinement by using organosilicon materials elaborated by plasma enhanced chemical vapor deposition (PECVD). Optical losses have been measured around 5.5dB.cm-1 and 11.5dB.cm-1 for TE00 and TM00 modes, respectively. Then, synthesis of titanium dioxide thin films by PECVD has been investigated to improve optical and propagation properties. The first results on these films exhibit a refractive index around 1.99 at a 633 nm wavelength with a 380 nm optical gap. When an rf bias is applied to the substrate, the refractive index reaches 2.36, from -5V, without significant optical gap variation.