High reflective coatings for 193nm wavelength and 45° incidence were developed which combines the advantages of all-oxide
and all-fluorides layer stacks. Using plasma-assisted evaporation very smooth and dense Al2O3/ SiO2 multilayers showing small light scatter were deposited onto fused silica substrates. In the same coating process followed metal
fluoride stacks, which could reduce the resulting coating absorption at 193nm. The non-polarized reflectance of
combined stacks at 193nm is R>98.5% at 45° and R>98.0% for an angle range of 42°-48°. As the number of fluoride
layers could be drastically reduced compared to all-fluoride coatings any formation of micro-cracks could be avoided.
The stress of the oxide/fluoride stacks was less than 40MPa.
This paper discusses improvements in manufacturing of coated infrared optical components. Such components often have key functions in defence, security or space applications and must withstand severe environmental conditions. Therefore, very durable coatings are desired. As a consequence of its radioactivity the formerly used low refractive index material thorium fluoride is substituted. Examples for beam splitter cubes contacted with novel infrared transparent cement, interference filters, mirrors and AR coatings are presented.
The presented work is embedded in the research network “Integrative Ion Processes for Modern Optics”, called IntIon, consisting of 12 partners from the German optics industry and two research institutes. The main target of the IntIon network is the development of new process concepts on the basis of ion assisted deposition (IAD) for the industrial production of optical thin film components. Besides an improvement in efficiency, a major aim is concentrated on the optical characteristics for selected application fields with high economical potential. In this network, different ion and plasma sources are compared with regard to their qualification for ion assisted deposition processes. This work includes the characterization of the ion energy and ion current using Faraday-cup measurements. The selection of investigated coating materials includes a broad variety of standard and non-standard oxides. First results of the network will be presented for adapted deposition materials and different operation characteristics of ion sources.
In the past 10 years improvements in micro-lithography have generated increasing demands on the performance of optical components in lithography machines and inspection devices as well. At this time typically used illumination sources are 248nm and 193nm lasers (KrF and ArF excimer lasers). Systems with 157nm (F2) excimer lasers are in a launching phase. Inspection with 266nm solid state laser (4th harmonic of Nd: YAG) or 193nm excimer laser is getting increasing interest too. First approaches to DUV or VUV coatings were focussed on realising useful windows, output couplers and folding or end mirrors with acceptable high transmission or reflection, respectively. In addition the laser induced damage threshold (LIDT) of the coated elements should be as high as possible when tested in so called 1-on-1 or 1-on-N tests (1 or N high-power laser pulses focussed on one point of an elements surface). After fulfilling these fundamental requirements the elements must meet additional specifications defined also for user-optimised component applications. In detail there are typical demands related to long-term and climatic stability, component lifetime during application, shift behaviour of the optical function, hardness of coating surfaces and resistance against chemical solvents together with a possibility of careful cleaning contaminated surfaces. Also mechanical film stress got more and more interest as a reason for deformation of ultra-precise finished optical surfaces and related wavefront distortions. Furthermore, the optical functions of UV components have become more complicated. Now the DUV and VUV filters, polarisers or attenuators show similar or more sophisticated optical performances compared to those components used for applications in the visible range. In this paper there will be presented some examples for improvements of component properties
An example of a multilayer component for 248-nm excimer laser applications is explained in this contribution. By means of a polarizing beam splitter the potential of plasma- assisted deposition is shown. Such a coating shows a high reflecting and a high transmitting function for different polarization at a certain angle of incidence. High reflection requires a considerable number of layer pairs with a large total optical film thickness. Despite large film thickness, the optical absorption can be minimized and high transmission can be obtained. The laser induced damage threshold of such a coating is in the order of 2.5 J/cm2 for single shot measurements at 20 ns pulse length. The life time is greater than 5X109 shots at a fluence of 10mJ/cm2. Very stable deposition conditions must be maintained to produce these coatings within small tolerance of the optical function. It was found that plasma-assisted deposition is a more reliable technology for producing these coatings compared to classical evaporation.
SiO2, Ta2O5 and MgF2 have been deposited by electron beam evaporation under bombardment of ions generated by three different ion or plasma sources. Multilayer systems containing 5 to 12 layers have been designed and realized. The maximum reflectance R of a glass/air interface can be reduced down to R < 0.5 percent in a spectral region of 400 nm to 700 nm with each of such AR coatings mostly exceeds that of all-oxide system in the shorter wavelength region. With scanning scratch test the scratch resistance of the coatings have been determined relative to each other.
The structure evolution characteristics of single and stratified NdF3 optical thin films on amorphous quartz substrates have been investigated by cross sectional transmission electron microscopy, x-ray diffractometer measurements and atomic force microscopy. The films were deposited by physical vapor deposition under ultra high vacuum conditions. The morphology changes with substrate temperature from V shaped columnar (Zone T) to a columnar morphology corresponding to zone II. The zone boundary falls in the range above 300 °C. The surface roughness of the single films is lowest at 300 °C substrate temperature. The main texture components are <111<, <1 13< and <001< respectively for the three single films of increasing substrate temperature. The surface roughness is decreased by the stratification. The grain size is increased by stratification with CaF2 and decreased by stratification with MgF2 compared to the grain size ofthe single film at the same substrate temperature. Keywords: thin film, stratification, morphology, texture, surface roughness, extinction
The structure evolution characteristics of MgF2 and NdF3 optical thin films on CaF2 (111) substrates have been investigated by cross sectional transmission electron microscopy and atomic force microscopy and were related to their extinction coefficient. The films were deposited by physical vapor deposition under ultra high vacuum conditions. A series of experiments have been carried out at various substrate temperatures at 300 nm thickness and by the stratification of the two fluoride materials. The structure evolution of single and stratified films was investigated and discussed in relation to the structure zone models. The effect of stratification on the structure and extinction coefficients is discussed in comparison to the effect of segregating impurities. The development of morphology of stratified films is analyzed in relation to the thickness of the interlayers and temperature. The optimum conditions for preparing films of low extinction coefficients are found at parameters corresponding both to the transition between zone T and zone II growth and to the formation of nanocrystalline structures.
Optical coatings for the ultraviolet spectral region consisting of fluorides have been made by molecular beam deposition in ultrahigh vacuum. The laser induced damage threshold at (lambda) equals 248 nm of the NdF3 single layers has been improved by means of reactive deposition. It was found that the threshold of fluoride antireflection coatings for 248 nm is significantly lower than that of single layers and does not show significant dependence on reactive gas conditions. A surface smoothing has been obtained due to an interrupted growth of very thin sublayers crystallizing in different crystal lattices. The damage threshold of interrupted grown antireflection coatings is somewhat higher than that of a conventional one.
A new technique for the fabrication of optical interference layers is being introduced. MgF2 and NdF3 have been evaporated by molecular beam deposition (MBD) in an ultrahigh vacuum system. The fluoride films are used in optical interference coatings for optical components of high power excimer lasers. The growth conditions were varied by changing the remaining gas composition, variation of the substrate temperature from 50 degree(s)C to 300 degree(s)C, and interruption of grain growth. The optical losses of the films were measured by transmission spectroscopy and laser calorimetry, and the film morphology was investigated by transmission electron microscopy. It was shown, that a stratification of very thin (1 nm - 10 nm) layers of two different fluorides can avoid the growth of large grains and wide columns, and gives rise to smoother surfaces. The packing density of MBD-films is higher in comparison with fluoride films deposited under conventional high vacuum conditions.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.