Quantizing nanolaminates are under development for use as materials with optimized properties for optical interference coatings. The optical dispersion needs a different description compared with simply mixing the basic materials because of the band gap shift. Although quantizing nanolaminates consist of alternating high- and low-index materials, representing them as a conventional layer stack can be questionable due to their extremely thin-often nanometer-scale-layers. This work gives an overview of Si-SiO2 layer stacks over a large range of different thickness combinations. The samples range from an almost pure SiO2 single layer to an almost standard interference stack of both materials. By treating all samples as single layers and fitting their dispersions to an arbitrary function, we examined which combinations show a shift in the absorption edge and can be described with sufficient accuracy that they are suitable for production.

Quantizing nanolaminates are under development for use as materials with optimized properties for optical interference coatings. The optical dispersion needs another description than simply mixing the basic materials because of the bandgap shift.

Layer materials combination Ta 2 O 5 /SiO 2 is widely used for production of optical coatings in the broadband spectral ranges. Optical properties of PARMS produced monolayers were characterized based on spectral and ellipsometric data using two software tools.

Multilayer structures incorporating silver and gold metal-island films in two different embedding materials are designed to achieve the reflectance of three distinct colors. The designs are specially adjusted for micro and nanoarray fabrication to involve the least number of deposition runs. The designs were generated taking into account feasibility restrictions. However, it was found that color combinations are reduced, i.e., not all the combinations can be obtained using the investigated approach and the materials used.

Reliable substrate characterization approach is proposed. Four widely used substrates SK-1300, MgF2, ZnSe, and Si were characterized in a broadband spectral range from 250-4200 nm based on multi-angle measurements. Refractive index accuracy was estimated.

The design problems for OIC 2025 involve a Design for Production challenge (Problem A) and an Immersed, Polarizing Notch Filter challenge (Problem B).

Electro-optic sampling of infrared electric fields has set sensitivity and dynamic-range records in broadband molecular vibrational spectroscopy. Yet, in these works, the 1-second-scale single-trace acquisition time leads to intra-scan noise accumulation and restricts the throughput in measurements of multiple samples and of dynamic processes. We present a dual-laser-oscillator approach capturing 2800 mid-infrared waveforms per second by scanning the relative delay between the sampled waveform and the gate pulses using a modulated repetition-frequency lock. The new technique of electro-optic delay tracking (EODT) provides delay calibration with down to few-attosecond precision and provides a general route to high-precision dual-oscillator spectroscopy with picosecond delay ranges. Our work has immediate applications in, e.g., precision electric-field metrology and high-speed biosensing.

Accurate knowledge of the substrate optical properties is crucial for the theoretical designing and monitoring of optical coatings and characterization of produced optical coatings. Typically, substrate characterization is performed based on reflectance and transmittance data in the relevant spectral range. Measurement errors (offsets of spectral characteristics and noise) are inevitable. Neglecting scattering and assuming transparent spectral ranges, offset values of experimental data can be estimated as a difference between 100% and the sum of the measured transmittance and reflectance. It doesn't provide insights into which spectral characteristic(s), reflectance, transmittance, or both, contribute to the offset or to what extent. We suggest an approach that allows one to estimate the offset values in reflectance and transmittance separately, estimate the effect of these offsets on the determination of substrate optical constants and characterize the substrates reliably. We demonstrate the approach characterizing various substrates in the range 220-1700 nm based on PHOTON RT measurements (EssentOptics).

Development of modern mid-infrared laser applications requires high-quality optical elements operating in the broadband spectral ranges from visible to 15 um. ZnS/YbF3 coatings on ZnSe substrates are perspective candidates for such elements since these thin-film materials and the substrate are transparent in this region and provide sufficient refractive index contrast. Experiments demonstrate that spectra of ZnS/YbF3 multilayers on ZnSe and glass substrates are shifted with respect to each other significantly. This issue plays a key role in the monitoring concept of YbF3/ZnS-coatings since typically the monitoring is conducted on a glass, and the final optical elements are on the ZnSe substrates. The study reports sophisticated experiments on the deposition of ZnS layers, its in-depth analysis on different substrates, and innovative reverse engineering of double-sided ZnS/YbF3 optical elements in the spectral ranges from 400 nm to 12 um. The results can be interesting for optical coating and laser engineers.

Multilayer optical coatings operating across broad spectral ranges from visible to mid-infrared play a crucial role in numerous industrial and scientific applications. MgF2, YF3, and Al2O3 are promising low-index materials within this range, Ge and Si can be harnessed as high-index materials. One of the key prerequisites to producing high-quality optical components is accurate knowledge of optical constants of thin-film materials as well as their environmental properties, which are dependent on deposition technology and process parameters. The present study reports characterization of monolayer samples of Ge, Si, YF3, Al2O3, and MgF2 on Silicon and Fused Silica substrates produced by e-beam evaporation with ion assistance technology. Deposition of the samples was performed at ORTUS-700 vacuum coater (IPhotonics). Reflectance and transmittance were measured using Photon RT spectrophotometer (Essent Optics) in the range 300-5000 nm. The samples were numerically characterized using advanced algorithms of OTF Studio software; layer optical constants were reliably determined.

The monitoring of thickness evolution during the deposition of optical interference coatings is widely performed by transmittance measurements and continuous comparison with theoretical models. The fitted thickness of the actual layer is influenced by the quality of the signal. Effects from light path, substrate and spectrometers result in deviations because these are often not part of the models. We show an implementation of these unmodeled effects in the fitting algorithms. The outcome of different configurations while coating the same optical filter design is compared. Additionally, the time consumption of these strategies is investigated to verify their suitability for production.

Field-resolved infrared spectroscopy (FRS) of impulsively excited molecular vibrations can surpass the sensitivity of conventional time-integrating spectroscopies, owing to a temporal separation of the molecular signal from the noisy excitation. However, the resonant response carrying the molecular signal of interest depends on both the amplitude and phase of the excitation, which can vary over time and across different instruments. To date, this has compromised the accuracy with which FRS measurements could be compared, which is a crucial factor for practical applications. Here, we utilize a data processing procedure that overcomes this shortcoming while preserving the sensitivity of FRS. We validate the approach for aqueous solutions of molecules. The employed approach is compatible with established processing and evaluation methods for the analysis of infrared spectra and can be applied to existing spectra from databases, facilitating the spread of FRS to new molecular analytical applications.

Narrow bandpass filters featuring broadband blocking ranges find extensive applications in spectroscopy, imaging, illumination, distance measurements, remote sensing, space and earth observations. The interest in bandpass filters with low angular shift is permanently growing [1, 2, 3]; but as narrow filter width and large angular fields are inherently conflicting requirements, researchers explore various approaches to reduce this shift. We develop immersed bandpass filters exhibiting (i) a narrow high transmittance range at 825-875 nm, (ii) blocking ranges at 200-780 nm and 900-1100 nm, and (iii) low blue shift for angles of incidence up to 25 degrees. However, the design solution should also allow for the possibility of shifting the transmission range further into the visible or near-infrared regions. Due to the immersed nature of the filter, it is difficult to effectively address such a complex task using two materials only; at least three materials should compose the coating. To provide an ultra-broadband blocking range, absorbing thin film materials should be involved. At the same time, these materials should be transparent outside of this range to maintain the high transmittance. Therefore, in the design process, a balanced compromise should be found. Not all theoretical solutions or/and materials combinations can be realized due to limitations of the production tools. The monitoring concept as well as design robustness should be considered; the number of layers cannot be very high. Double-sided optical elements composed as front side filter and back side blocker hold promise in this regard. The solutions are oriented at Ion Beam Sputtering deposition technique, not equipped with load lock solution.

The study focuses on reliable reverse engineering of electron-beam deposited TiO2/SiO2 coatings. It is known that optical constants of evaporated TiO2 films are dependent on deposition conditions and may vary from layer to layer. Also, the nominal optical constants, used during the theoretical designing, may differ from the actual optical constants of coating layers, determined based on characterization of thicker single layers. Typically, post-production characterization of e-beam evaporated coatings is based on spectral photometric or/and ellipsometric data measured ex-situ. The study reports a new reliable algorithm that allows reliable estimation of layer thicknesses and optical constants based on ex-situ measurements. The reliability of the results is verified using a specially produced unique set of samples including single layers identical to the ones included in the multilayer sample. The obtained results, based on the photometric and ellipsometric data, are in correspondence with each other. The algorithm delivers practical results and avoids overfitting.

The design problems for the Optical Interference Coating (OIC) 2022 Topical Meeting include black box coatings to reverse engineer and a pair of white-balanced, multi-bandpass filters for three-dimensional cinema projection in cold and hot outdoor environments. There were 14 designers from China, France, Germany, Japan, Russia, and the United States, submitting 32 total designs for problems A and B. The design problems and the submitted solutions are described and evaluated.

A post-production characterization approach based on spectral photometric and ellipsometric data related to a specially prepared set of samples is proposed. Single-layer (SL) and multilayer (ML) sets of samples presenting building blocks of the final sample were measured ex-situ, and reliable thicknesses and refractive indices of the final ML were determined. Different characterization strategies based on ex-situ measurements of the final ML sample were tried, reliability of their results was compared, and the best characterization approach for practical use, when preparation of the mentioned set of samples would be a luxury, is proposed.

Field-resolved infrared spectroscopy (FRS) with electro-optic sampling (EOS) has evolved as a powerful alternative to conventional intensity-based infrared absorption measurements [1]. It allows to capture the response field of a molecular sample emitted upon vibrational excitation with an ultrashort infrared pulse, directly in the time domain. The temporal separation of excitation and molecular response enables background-free detection of the sample-specific signal via temporal filtering. In order to additionally reduce the influence of low- frequency noise of the mid-infrared (mid-IR) excitation, ultra-rapid EOS detection at multi-kHz scan rates has been implemented with mechanical [2] and dual-oscillator [3] approaches. Here, we present a dual-oscillator FRS instrument, recording broadband mid- IR EOS traces simultaneously in sample and reference channels, at a scan rate of 4.2 kHz. With full spectroscopic referencing on the individual-scan basis, the system can correct sample measurements for fast fluctuations and long-term drifts of the mid- IR excitation pulses.

The determination of the effective optical constants of metal island films is an essential step towards the practical incorporation of this kind of films in optical coatings. In this work, the optical properties of aluminium island films deposited by electron beam evaporation on quartz substrates are investigated using different approaches employed by three research groups. The effective optical constants of the island films are inferred from optical measurements (spectrophotometry and spectroscopic ellipsometry) using: (i) a parameter-free dispersion model, (ii) a multiple oscillator model based on Gaussian line-shapes and (iii) the β distributed oscillator model. All the used approaches provide similar physical insights, i.e., an increase in the effective thickness of the metal island film, a red-shift and broadening of the plasmon resonance and an enhancement of the infrared absorption as the amount of deposited material increases. However, the optimal values of the effective optical constants and thickness significantly depend on the employed model and the experimental data used for data fitting.

The study reports practically important and interesting results on designing dispersive mirrors (DMs) operating in the mid-infrared spectral range from 3 to 18 µm. The admissible domains of the most important design specifications, the mirror bandwidth and group delay variation, were constructed. Estimations of the required total coating thickness, thickness of the thickest layer, and expected number of layers are obtained. The results are confirmed by an analysis of several hundreds of DM design solutions.

We demonstrate rapid electro-optic sampling of broadband mid-infrared waveforms using a dual-oscillator setup employing a narrowband, waveform-stable calibration signal obtained by intra-pulse difference frequency mixing. Sub-attosecond waveform jitter is obtained for 1-s integration time.