Group delay dispersion monitoring for computational manufacturing of dispersive mirrors.

We present a computational manufacturing program for monitoring group delay dispersion (GDD). Two kinds of dispersive mirrors computational manufactured by GDD, broadband, and time monitoring simulator are compared. The results revealed the particular advantages of GDD monitoring in dispersive mirror deposition simulations. The self-compensation effect of GDD monitoring is discussed. GDD monitoring can improve the precision of layer termination techniques, it may become a possible approach to manufacture other optical coatings.

Third and fifth order nonlinear susceptibilities in thin HfO2 layers.

Third harmonic generation (THG) from dielectric layers is investigated. By forming a thin gradient of HfO2 with continuously increasing thickness, we are able to study this process in detail. This technique allows us to elucidate the influence of the substrate and to quantify the layered materials third χ(3)(3ω: ω, ω, ω) and even fifth order χ(5)(3ω: ω, ω, ω, ω, - ω) nonlinear susceptibility at the fundamental wavelength of 1030 nm. This is to the best of our knowledge the first measurement of the fifth order nonlinear susceptibility in thin dielectric layers.

Ultrafast switching with nonlinear optics in thin films.

We demonstrate a novel, to the best of our knowledge, concept for an all-optical switch based on the optical Kerr effect in optical interference coatings. The utilization of the internal intensity enhancement in thin film coatings as well as the integration of highly nonlinear materials enable a novel approach for self-induced optical switching. The paper gives insight into the design of the layer stack, suitable materials, and the characterization of the switching behavior of the manufactured components. A modulation depth of 30% could be achieved, which prepares the way for later applications in mode locking.

Optical interference coatings: measurement problem 2022 [Invited].

The 2022 Optical Interference Measurement Problem comprised the determination of the refractive index of a thin tantalum pentoxide film at a wavelength of 532 nm and the characterization of the UV band edge as an optional task.

Reduction of nanoparticles in optical thin films through ion etching.

Contaminating particles in optical thin films can lead to the formation of nodules and reduction of laser induced damage threshold (LIDT). This work investigates the suitability of ion etching of the substrates to reduce the impact of nanoparticles. Initial investigations suggest that ion etching can remove nanoparticles from the sample surface; however, doing so introduces texturing to the surface of the substrate. This texturing leads to an increase in optical scattering loss, though LIDT measurements show no significant reduction in the durability of the substrate.

Substrate-free miniaturized thin-film filters for single-element coarse wavelength division multiplexing fibers.

We have created high-precision, miniaturized, substrate-free filters, based on ion beam sputtering on a sacrificial substrate. The sacrificial layer is cost efficient and environmentally friendly and can be dissolved using only water. We demonstrate an improved performance compared to filters on thin polymer layers from the same coating run. With these filters, a single-element coarse wavelength division multiplexing transmitting device for telecommunication applications can be realized by inserting the filter between fiber ends.

Enabling rotary atomic layer deposition for optical applications.

Atomic layer deposition (ALD) has been proven as an excellent method for depositing high-quality optical coatings due to its outstanding film quality and precise process control. Unfortunately, batch ALD requires time-consuming purge steps, which leads to low deposition rates and highly time-intensive processes for complex multilayer coatings. Recently, rotary ALD has been proposed for optical applications. In this, to the best of our knowledge, novel concept, each process step takes place in a separate part of the reactor divided by pressure and nitrogen curtains. To be coated, substrates are rotated through these zones. During each rotation, an ALD cycle is completed, and the deposition rate depends primarily on the rotation speed. In this work, the performance of a novel rotary ALD coating tool for optical applications is investigated and characterized with S i O 2 and T a 2 O 5 layers. Low absorption levels of <3.1p p m and <6.0p p m are demonstrated at 1064 nm for around 186.2 nm thick single layers of T a 2 O 5 and 1032 nm S i O 2, respectively. Growth rates up to 0.18 nm/s on fused silica substrates were achieved. Furthermore, excellent non-uniformity is also demonstrated, with values reaching as low as ±0.53% and ±1.07% over an area of 135×60m m for T a 2 O 5 and S i O 2, respectively.

Prevention of laser damage precursors in spaceborne ultraviolet antireflection coatings.

In order to enhance the reliability and performance of space-based Lidar systems, it is desirable to increase the damage resistance of ultraviolet antireflective coatings. For laser pulses with nanosecond pulse duration, laser-induced damage is known to be triggered by nano-sized defects embedded in the optical coating. In this work, we demonstrate the mitigation of damage precursors during the manufacturing of ion-beam sputtered (IBS) coatings using two approaches: ion bombardment with a secondary ion source and laser irradiation with a nanosecond-pulsed laser. Optical coatings produced with both technologies show a significantly increased damage threshold when tested in large-area raster scans.

2019 Topical Meeting on Optical Interference Coatings: introduction.

This feature issue of Applied Optics is dedicated to the fourteenth Topical Meeting on Optical Interference Coatings held 2-7 June 2019, in Santa Ana Pueblo, New Mexico, USA. The conference, taking place every three years, is a focal point for global technical interchange in the field of optical interference coatings and provides premier opportunities for people working in the field to present their new advances in research and development. Papers presented at the meeting covered a broad range of topics ranging from fundamental research on coating design theory, new materials, and deposition and characterization technologies, to the vast and growing number of applications in electronic displays, communication, optical instruments, consumer electronics, high power and ultra-fast lasers, solar cells, space missions, gravitational wave detection, and many others.

Optical interference coatings measurement problem 2019 [Invited].

The 2019 Optical Interference Coatings measurement problem comprised the determination of the total backscattering, forward scattering, reflectance, and transmittance spectra of a multilayer system.

Quantizing nanolaminates as versatile materials for optical interference coatings.

In this paper, the theoretical foundation of quantizing nanolaminates is explained, and the dependence of the optical band gap on quantum-well thickness is demonstrated. The production is investigated by applying molecular dynamics growth simulation and by correlating the results with layers deposited by ion beam sputtering and atomic layer deposition. The properties of manufactured nanolaminates are then compared to the theoretical behavior, and good agreement is found.

Upconversion Nanocrystal Doped Polymer Fiber Thermometer.

In recent years, lanthanide-doped nanothermometers have been mainly used in thin films or dispersed in organic solvents. However, both approaches have disadvantages such as the short interaction lengths of the active material with the pump beam or complicated handling, which can directly affect the achievable temperature resolution. We investigated the usability of a polymer fiber doped with upconversion nanocrystals as a thermometer. The fiber was excited with a wavelength stabilized diode laser at a wavelength of 976 nm. Emission spectra were recorded in a temperature range from 10 to 35 ∘C and the thermal emission changes were measured. Additionally, the pump power was varied to study the effect of self-induced heating on the thermometer specifications. Our fiber sensor shows a maximal thermal sensitivity of 1.45%/K and the minimal thermal resolution is below 20 mK. These results demonstrate that polymer fibers doped with nanocrystals constitute an attractive alternative to conventional fluorescence thermometers, as they add a long pump interaction length while also being insensitive to strong electrical fields or inert to bio-chemical environments.

Towards Highly Efficient Polymer Fiber Laser Sources for Integrated Photonic Sensors.

Lab-on-a-Chip (LoC) devices combining microfluidic analyte provision with integrated optical analysis are highly desirable for several applications in biological or medical sciences. While the microfluidic approach is already broadly addressed, some work needs to be done regarding the integrated optics, especially provision of highly integrable laser sources. Polymer optical fiber (POF) lasers represent an alignment-free, rugged, and flexible technology platform. Additionally, POFs are intrinsically compatible to polymer microfluidic devices. Home-made Rhodamine B (RB)-doped POFs were characterized with experimental and numerical parameter studies on their lasing potential. High output energies of 1.65 mJ, high slope efficiencies of 56 % , and 50 % -lifetimes of ≥900 k shots were extracted from RB:POFs. Furthermore, RB:POFs show broad spectral tunability over several tens of nanometers. A route to optimize polymer fiber lasers is revealed, providing functionality for a broad range of LoC devices. Spectral tunability, high efficiencies, and output energies enable a broad field of LoC applications.

Correlation of structural and optical properties using virtual materials analysis.

Thin film growth of ${\textrm{TiO}}_2$TiO2 by physical vapor deposition processes is simulated in the Virtual Coater framework resulting in virtual thin films. The simulations are carried out for artificial, simplified deposition conditions as well as for conditions representing a real coating process. The study focuses on porous films which exhibit a significant anisotropy regarding the atomistic structure and consequently, to the index of refraction. A method how to determine the effective anisotropic index of refraction of virtual thin films by the effective medium theory is developed. The simulation applies both, classical molecular dynamics as well as kinetic Monte Carlo calculations, and finally the properties of the virtual films are compared to experimentally grown films especially analyzing the birefringence in the evaluation.

Enhancement of the damage resistance of ultra-fast optics by novel design approaches.

Dielectric components are essential for laser applications. Chirped mirrors are applied to compress the temporal pulse broadening crucial in the femtosecond regime. However, the design sensitivity and the electric field distribution of chirped mirrors is complex often resulting in low laser induced damage resistances. An approach is presented to increase the damage resistance of pulse compressing mirrors up to 190% in the NIR spectral range. Layers with critical high field intensity of a binary mirror design are substituted by ternary composites and quantized nanolaminates, respectively. The deposition process is improved by an in situ technique monitoring the phase of reflectance.

Tunable optical properties of amorphous Tantala layers in a quantizing structure.

Plasma deposition techniques like ion-beam-sputtering (IBS) are state of the art to manufacture high quality optical components for laser applications. Besides the well optimized process and monitoring systems, the coating material selection is integral to achieve optimum optical performances. Applying the IBS technology, an approach is presented to create novel materials by the direct application of binary oxides in a quantizing structure. By reducing the physical thickness of the high refractive index material to a few nm, within a classical high-low index stack, the electron confinement can be changed. Optical characterizations of the manufactured samples with decreasing quantum well thicknesses result in an increasing blue shift of the absorption gap and offer a method to approximate the effective mass of the high refractive index material in conjunction with theoretical models. Laser-induced damage threshold tests of coating samples prepared with different well thicknesses indicate an increase of the measured threshold values with optical gap energy.

The Optical Society's 2016 topical meeting on optical interference coatings: introduction.

This feature issue of Applied Optics is dedicated to the 13th Topical Meeting on Optical Interference Coatings, which was held June 19-24, 2016, in Tucson, Arizona, USA. The conference, taking place every three years, is a focal point for global technical interchange in the field of optical interference coatings and provides premier opportunities for people working in the field to present their new advances in research and development. Papers presented at the meeting covered a broad range of topics, including fundamental research on coating design theory, new materials, and deposition and characterization technologies, as well as the vast and growing number of applications in electronic displays, communication, optical instruments, high power and ultra-fast lasers, solar cells, space missions, gravitational wave detection, and many others.

Fourier-transform spectral interferometry for in situ group delay dispersion monitoring of thin film coating processes.

A fast Fourier-based measurement system to determine phase, group delay, and group delay dispersion during optical coating processes is proposed. The in situ method is based on a Michelson interferometer with a broad band light source and a very fast spectrometer. To our knowledge, group delay dispersion measurements directly on the moving substrates during a deposition process for complex interference coatings have been demonstrated for the first time. Especially for the very precise production of chirped mirrors it is advantageous to get information about the phase properties of the grown layer stack to react on errors and retrieve more information about the coating process.

Dual wavelength laser-induced damage threshold measurements of alumina/silica and hafnia/silica ultraviolet antireflective coatings.

An approach for the measurement of the laser-induced damage threshold with two wavelengths combined was made while testing antireflective coatings for the wavelengths 266 and 532 nm. Samples were made of Al2O3/SiO2 and HfO2/SiO2 ion beam sputtered films. The results show that adding radiation of a second wavelength might lead to a significant reduction of the threshold. The damage morphology of single and dual wavelength tests is very similar and does not suggest an altered damage mechanism. Further investigations indicated that the dual wavelength threshold is a function of the temporal delay of the two pulses.

Frequency tripling mirror.

A frequency tripling mirror (FTM) is designed, fabricated and demonstrated. The mirror consists of an aperiodic sequence of metal oxide layers on a fused silica substrate tailored to produce the third harmonic in reflection. An optimized 25-layer structure is predicted to increase the reflected TH by more than five orders of magnitude compared to a single hafnia layer, which is a result of global compensation of the phase mismatch of TH and fundamental, field enhancement and design favoring reflection. Single pulse conversion efficiencies approaching one percent have been observed with the 25-layer stack for fundamental wavelengths in the near infrared and 55 fs pulse duration. The FTM is scalable to higher conversion, larger bandwidths and other wavelength regions making it an attractive novel nonlinear optical component based on optical interference coatings.