Beta-distributed oscillator model as an empirical extension to the Lorentzian oscillator model: physical interpretation of the ${\beta \_{{\rm do}}}$ß_do model parameters.

The physical sense of the free parameters of the beta-distributed oscillator (${\beta \_{{\rm do}}}$ß_do) dispersion model is discussed. It is shown that the set of six model parameters provides information on central wavenumber, oscillator strength, absorption edge position, asymmetry, as well as homogeneous and inhomogeneous linewidth of a complicated absorption feature. For materials satisfying the Moss rule, the number of independent ${\beta \_{{\rm do}}}$ß_do parameters decreases down to five. We also show that the Cody absorption edge shape essentially represents a special case of the ${\beta \_{{\rm do}}}$ß_do approach. By making use of the generalized Miller rule, we propose a generalization of the ${\beta \_{{\rm do}}}$ß_do model to nonlinear refractive indices and absorption coefficients.

Theoretical study of multilayer coatingreflection taking into account third-order optical nonlinearities.

A theoretical approach is presented that allows calculating the reflectance of dielectric multilayer coatings taking third-order optical nonlinearities into account. The description is based on third-order optical susceptibility so that nonlinear refraction and two-photon absorption processes are automatically considered in terms of the real and imaginary parts of the susceptibility. Two model systems are calculated in order to demonstrate the physical validity of the approach: a mirror that is optimized for maximum reflectance at a given wavelength and a given incident intensity and a mirror that provides a rather flat dependence of the reflected intensity on the incident one. Model calculations are performed for laser wavelength values of 1064 nm, 800 nm, and 532 nm.

Simplified expression for estimating the nonlinear refractive index of typical optical coating materials.

A semiempirical equation is derived that allows estimating the electronic contribution to the nonlinear refractive index of an optical material from knowledge of the linear one. The approach is restricted to practically loss-free media at low frequencies. In contrast to other approaches, no explicit data on the optical gap or Abbe number are required. A comparison with experimental data from typical oxide and fluoride materials reveals an excellent agreement between experiment and theoretical estimation.

Analytical elimination of substrate backside reflections from reflectance measurements.

An analytical approach to eliminate substrate backside reflections from measured reflectance of an unknown optical coating has been deducted. Thereby, measured transmittance, reflectance, and backside reflectance of the coating and transmittance and reflectance of the uncoated substrate at the desired angle of incidence and polarization state are required as input data. In the underlying theory, layer and substrate materials may be absorbing.

Effect of oxygen vacancies on the laser-induced damage resistance of Y0.26Hf0.74Ox thin films.

The influence of the oxygen sub-stoichiometry on the femtosecond laser-induced damage resistance of Y0.26Hf0.74Ox films was investigated in this work. Photoluminescence (PL) spectroscopy was applied to analyze the various states of oxygen vacancies (V(O)), and laser-induced damage measurement was performed using a single 500 fs pulse laser at a wavelength of 1030 nm. Based on the PL spectra, a probable band gap structure with different defect energy levels was obtained, which is significant in explaining an observed inverse correlation between the laser-induced damage threshold (LIDT) and the concentration of V(O). The crystallization and the refractive index, which were previously found to be crucial factors in laser-induced damage resistance of optical thin films, are also closely dependent on the amount of induced oxygen vacancies.

Postdeposition treatment of IBS coatings for UV applications with optimized thin-film stress properties.

Ion-beam-sputtering (IBS) single-layer and multilayer coating designs for UV applications were examined after the deposition process as well as after a defined postdeposition treatment. High internal compressive film stress as well as moderate absorption losses in the UV spectral range were measured at the as-deposited thin films. Due to a controlled postdeposition treatment process, the absorption losses and the high compressive stress can be reduced significantly. We show that the remaining thin-film stress of SiO2 and HfO2 multilayer designs can be specifically manipulated by the parameters of the postdeposition treatment. Even zero and tensile stress can be achieved for complex multilayer coatings.

Manufacture and characterization of optical coatings with incorporated copper island films.

Copper island films have been prepared by thermal evaporation in vacuum and characterized by in situ as well as ex situ spectrophotometry. The parallel investigation of the island morphology by means of transmission electron microscopy allowed us to establish a clear correlation between film structure and optical properties. The effective optical constants of the copper island films could be determined by means of a fit of their ex situ transmission and reflection spectra. The effective optical constants have been used for designing and preparing optical multilayer coatings applicable for attenuator or color filter specifications. Measured characteristics of the multilayer coatings are in very good agreement with the calculated spectra.

Plasma-assisted deposition of metal fluoride coatings and modeling the extinction coefficient of as-deposited single layers.

We realized metal fluoride coatings with a high packing density and a low extinction coefficient by plasma (ion)-assisted deposition. The densification can be performed by different types of plasma sources, e.g., by a Leybold LION source and a Leybold APSpro, respectively. But the as-deposited coatings show a characteristic absorption behavior, whereas the absorption losses can be reduced in a postdeposition UV treatment step. We show experimental results of the plasma-assisted metal fluorides before and after the UV treatment and present a new model that allows us to describe and calculate the characteristic absorption losses of LaF3, MgF2, and AlF3.

Combined in situ and ex situ optical data analysis of magnesium fluoride coatings deposited by plasma ion assisted deposition.

The combination of in situ spectrophotometry during film deposition and ex situ spectrophotometry allows insight into the depth distribution of optical losses in plasma ion assisted deposition coatings. An adapted optical characterization strategy for absorbing coatings using only in situ transmittance data has been developed and is exemplified in application to magnesium fluoride coatings. Measurements and simulation results strongly indicate an increased absorption caused by local understoichiometry of the fluoride material close to the fused silica substrate.

Mixed oxide coatings for optics.

Material mixtures offer new possibilities for synthesizing coating materials with tailored optical and mechanical properties. We present experimental results on mixtures of HfO2, ZrO2, and Al2O3, pursuing applications in UV coating technology, while the mixtures are prepared by magnetron sputtering, ion beam sputtering, plasma ion-assisted deposition (PIAD), and electron beam evaporation without assistance. The properties investigated include the refractive index, optical gap, thermal shift, and mechanical stress. The first high reflectors for UV applications have been deposited by PIAD.

All-oxide broadband antireflection coatings by plasma ion assisted deposition: design, simulation, manufacturing and re-optimization.

A new all-oxide design for broadband antireflection coatings with significantly reduced impact of deposition errors to the final reflectance is presented. Computational manufacturing including re-optimization during deposition has been used in the design work to account for maximum insensibility of the design with respect to deposition errors typical for plasma ion assisted deposition PIAD. Repeated deposition runs with the deducted monitoring and re-optimization strategy verify the validity of the simulations and the stability of the derived design solution.

Computational manufacturing of optical interference coatings: method, simulation results, and comparison with experiment.

Virtual deposition runs have been performed to estimate the production yield of selected oxide optical interference coatings when plasma ion-assisted deposition with an advanced plasma source is applied. Thereby, deposition of each layer can be terminated either by broadband optical monitoring or quartz crystal monitoring. Numerous deposition runs of single-layer coatings have been performed to investigate the reproducibility of coating properties and to quantify deposition errors for the simulation. Variations of the following parameters are considered in the simulation: refractive index, extinction coefficient, and film thickness. The refractive index and the extinction coefficient are simulated in terms of the oscillator model. The parameters are varied using an apodized normal distribution with known mean value and standard deviation. Simulation of variations in the film thickness is performed specific to the selected monitoring strategy. Several deposition runs of the selected oxide interference coatings have been performed to verify the simulation results by experimental data.

In situ optical characterization and reengineering of interference coatings.

A new optical monitoring system has been developed that allows recording of transmission spectra in the wavelength range between 400 and 920 nm of a growing optical coating during deposition. Several kinds of thin film sample have been prepared by use of a hybrid monitoring strategy that is essentially based on a combination of quartz monitoring and in situ transmission spectra measurements. We demonstrate and discuss the applicability of our system for reengineering procedures of high-low stacks and measurements of small vacuum or thermal shifts of optical coatings.

Optical characterization of hybrid antireflective coatings using spectrophotometric and ellipsometric measurements.

A hybrid antireflective coating combining homogeneous layers and linear gradient refractive index layers has been deposited using different techniques. The samples were analyzed optically based on spectrophotometric and spectroscopic ellipsometry measurements under different angles of incidence in order to precisely characterize the coatings. The Lorentz-Lorenz model has been used to calculate the refractive index of material mixtures in gradient and constant index layers of the coating. The obtained refractive index profiles have been compared with the targeted ones to detect errors in processes of deposition.

Broadband antireflective surface-relief structure for THz optics.

The requirements for a broadband antireflective structure in the THz spectral region are derived. Optimized structural parameters for a surface-relief grating adapted to the spectrum of an intended THz pulse are deduced. The effect of a structure fabricated into Topas((R)) by a single-point diamond-turning process is demonstrated.

New optimization algorithm for the synthesis of rugate optical coatings.

A model of a rugate coating that takes into account production potentialities of the Leybold Syrus Pro 1100 deposition system is presented. An efficient algorithm for the synthesis of rugate coatings is proposed. Numerical results are also presented.

Putrescine N-methyltransferase in Solanum tuberosum L., a calystegine-forming plant.

Putrescine N-methyltransferase (PMT, EC 2.1.1.53) catalyses the first specific step in the biosynthesis of tropane and nicotine alkaloids. Potato (Solanum tuberosum L.) contains neither nicotine nor the medicinal tropane alkaloids hyoscyamine or scopolamine, but calystegines. They are nortropane alkaloids with glycosidase inhibitory activity. Based on the assumption of calystegine formation by the tropane alkaloid pathway, PMT genes and enzymes were investigated in potato. Sprouting tubers contained both N-methylputrescine and PMT activity. Two cDNA clones coding for PMTs were obtained together with a cDNA clone for spermidine synthase (SPDS, EC 2.5.1.16). The pmt sequences resemble those from Nicotiana tabacum (85% identity) and those from tropane alkaloid plants, Atropa belladonna (80% identity) and Hyoscyamus niger (79% identity). They are less similar to SPDS of S. tuberosum (66% identity). Expression of pmt1 and spds cDNA in Escherichia coli yielded active enzymes, while pmt2 expression resulted in insoluble protein. Chimera proteins obtained by fusion of fragments of S. tuberosum pmt2 and H. niger pmt were active as PMT, if the initial part of pmt2 was used, indicating that a mutation in the terminal part of the gene caused insolubility of the enzyme. PMT1 was purified after expression in E. coli and proved to be an active N-methyltransferase without SPDS activity. The enzyme was specific for putrescine (K (M) 250 microM) and inhibited by n-butylamine and cadaverine. While spds was transcribed in all plant organs, pmt transcripts were found in small tuber sprouts only. The results confirm that in potato genes and enzymes specific for the tropane alkaloid metabolism are expressed and active.