This PDF file contains the front matter associated with SPIE Proceedings Volume 11385, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

The problem of process monitoring is one of the most critical aspects of control in laser material processing. Chromatic sensors, which are characterized by high resolution, relatively large measurement range and good repeatability, may be used for measuring and adjusting the distance between laser head and the substrate. In this paper we propose a new solution of chromatic sensor integrated with optical laser head via an available standard monitoring port.

Optical components of laser heads are fabricated from materials characterized by high Abbe number (low range of longitudinal chromatic aberration). Therefore, for sensors application, the resulting chromatic aberration of the overall optical system should be enhanced by implementation the sets of lens described by a low value of Abbe. The numerical analysis were carried out in order to design an optical system of proposed solution, which will be described by wide measurement range, low attenuation and narrow characteristic spectral peak. The results obtained by WinLens software solutions were presented. The numerical tool whose principle of operation is based on geometric optics equations, was chosen for rapid prototyping because of its simplicity in implementation of optical components. The results from the numerical analysis were afterwards confirmed by the experiment on real optical system.

Risley prisms are utilized in a variety of applications, including precision pointing and scanning, interferometry, holography, polarimetry, and light attenuation. Laser scanning with such systems is fast, but the generated scan patterns are complicated. Analytical methods to determine them are rather difficult, while approximate methods do not provide exact patterns. While we point out these issues, the present study is built on a new, graphical method that, to our knowledge, we have introduced [V.-F. Duma, A. Schitea, Laser scanners with rotational Risley prisms: Exact scan patterns, Proc. of the Romanian Acad. Series A 19, 53-60, 2018] to obtain scan patterns produced by Risley prisms. A commercially available mechanical design program, CATIA V5R20 (Dassault Systèmes, Paris, France) has been used to perform the ray tracing, using the prisms equations, for all four possible configurations of laser scanners with a pair of rotational Risley prisms. One of these four configurations is considered in this study, to present the developed method. A deviation angle of 2° for the optical wedges is considered in this study. A brief comparison between the obtained exact scan patterns is made for different values of the parameter M (introduced by Marshall), which represents the ratio of the rotational speeds of the two prisms. The study also presents the cartesian coordinates of the points which define the trajectory of the laser spot on a scanned plane. Advantages of using the graphical method as well as its perspectives are pointed out.

Nowadays in dentistry a correct diagnosis is given only after a clinical and radiological evaluation. Radiographs are also required for treatment assessments. The aim of this study is to present results obtained on evaluating dental cavities in a dental clinic in Western Romania, using both X-ray radiography and Optical Coherence Tomography (OCT). The most common methods for daily-basis clinical imaging are utilized, i.e. panoramic radiography and three-dimensional (3D) cone beam computed tomography (CBCT). Advantages of OCT as an imaging method in dentistry are discussed: it avoids exposing the patient to X-ray radiation, and image resolution of OCT is superior. This led us to test this technique for dental assessments and see how it can work in conjunction with radiography. The study also provides upsides and downsides of both medical imaging techniques. Panoramic radiographs and 3D CBCT to several extracted teeth are performed. Dedicated toolbars from Romexis software (Planmeca, Helsinki, Finland) are analyzed with regard to their capability to make precise measurements. Processing of images are made to obtain a high-quality; measurements are done and data are collected. The same teeth are scanned with an in-house developed SS-OCT system. Images from both investigations are presented, and clinical conclusions are drawn. For dental issues (i.e., cavities) that appear on the surface of the teeth, OCT proves to be more suitable than radiographs; it is also more accurate and radiation-free.

A penetration laser welding mode characterized by formation of keyhole is often used. A small portion of the laser beam is reflected back from the keyhole and returned to the laser through the optical system of the welding head and optical fiber. The reflected radiation is monitored in the laser for the safety of the optical resonator and its signal can be read and used for process monitoring. The experiment was conducted to relate the intensity of the back-reflected radiation with depth and width of the weld for the variable focal position. The experiments were performed for two variants of the optical focusing system and materials with different thermo-physical properties - carbon steel and stainless steel. Furthermore, a mathematical model for back-reflected radiation was created using ray tracing. The shape of the keyhole was approximated as an inclined conical cavity. The results of the simulation were compared with experimentally measured data and it was found that the proposed model is most suitable for the description of stainless steel.

The GRIN rod lenses are favorable optical elements for the image transmission in applications where transverse dimensions of the optical system are limited such as rigid borescopes or endoscopes. Flexible versions of these instruments usually use imaging bundles of optical fibers to assure both the mechanical elasticity and the optical transmission. The image resolution of this solution suffers from being limited by minimum fiber core diameter allowable for imaging and total number of fibers in a given cross-section area. GRIN rod lens allows for a higher image resolution for small diameters. While the optical properties of the GRIN rod lens are well known, there is no information about its allowed mechanical stress. In this paper we present a simple system for load and deformation measurement of a GRIN rod lens aimed to be used for a miniature endoscope for eye surgery operation. The system allows for loading force measurement with a deformation strain gauge cell and deformation measurement with an optical triangulation sensor. The paper presents deformation limits of the tested GRIN rod lens loaded by a three-point bending test. We also evaluated the Young modulus of the GRIN rod lens material from the measured data. Our data shows that tested GRIN lenses can be statically deformed by bending down to minimum radius 105 mm without braking.

Metals can break either in a ductile or brittle manner if a static or dynamic load is applied to the same material. This depends on a variety of factors, such as the manner in which the load is applied, the shape of the mechanical part, the operating conditions, the nature and structure of the metallic material, and the working temperature. If subjected to variable loads, metallic materials break due to what is called fatigue. The microscopic analysis of fracture surfaces is currently carried out by using scanning electron microscopy (SEM). We have proposed, for the first time to our knowledge, a new method to analyze fracture surfaces, using a low coherence interferometry technique, Optical Coherence Tomography (OCT) [Gh. Hutiu, V.-F. Duma, et al., Surface imaging of metallic material fractures using optical coherence tomography, Appl. Opt. 53, 5912-5916 (2014); Gh. Hutiu, V.-F. Duma, et al., Assessment of ductile, brittle, and fatigue fractures of metals using optical coherence tomography, Metals 8, 117 (2018)]. The present paper presents the way we have demonstrated that OCT can replace the gold standard in such assessments, i.e. SEM, despite the fact that OCT has a resolution of 20 to 4 μm (in our investigations), while the SEM we employed has a 4 to 2 nm resolution. A few examples are given in this respect–for different types of fractures. The advantages of OCT versus SEM are discussed. This development opens the way for in situ investigations, for example in forensic sciences, where OCT can be applied (including with handheld scanning probes. as we have developed). In contrast, SEM, TEM, and AFM are lab-based techniques, more expensive, and they require trained operators.

Ion Beam Figuring (IBF) has been used for nearly 20 years by several laboratories and companies as a highly deterministic method of final processing of ultra-precision optical elements. Nowadays, requirements for high precision optics demand to have full control over the ion beam, which includes both the ion beam profile and intensity. Electrostatic focusing using an Einzel lens setup provides a simple option to control the ion beam shape by changing voltage. This experimental study investigates the early stage development of an Einzel lens used to control an RF40 ion source. First results demonstrate the possibility to use an Einzel lens to control the ion beam profile and indicate possible future challenges this technology has to overcome when used in IBF machines.

Chemically reactive Plasma Jet Machining (PJM) is a contactless and efficient surface machining technique increasingly applied to the surface shape generation and error correction of various optical elements. However, the application of fluorine-based PJM to surface machining of N-BK7® is challenging since the chemical interaction between reactive plasma species and metal components of N-BK7 induces a residual layer in the contact zone and surrounding of the plasma-treated area. It was noticed that a residual layer degrades the ability of obtaining the prerequisite surface profile and causes a nonlinear and hardly predictable removal behavior with respect to the etching time. In this paper, extensive studies are conducted for relaxing constraints in applying the fluorine-based PJM to the surface machining of N-BK7, particularly regarding to the manufacture of freeform optical elements. In this regard, the chemical composition of residual layer is evaluated by using SEM/EDX analysis aiming at clarifying the chemical kinetics between plasma generated active particles and the N-BK7 surface atoms. Furthermore, the etching behavior of N-BK7 is compared with Fused Silica to verify the optimality of obtained results. Finally, the area machining is tested at different plasma dwell times to evaluate the predictability and regularity of results.

There are still types of lenses that should to be glued on holder for polishing in the latter-day optical production. A negative effect during this process is a deformation of the optical surface caused by a different thermal expansion of the holder, glass and blocking pitch. This paper presents a numerical simulation of deformation of hemispheric lens which was verified by a series of experiments. A new segmented lens holder, which significantly suppresses mutual tension and therefore an amplitude of a surface deformation was designed based on the results. The lens holder reduces the surface deformation by approximately 30 times compared to standard holders. The most beneficial part of this work is a development of the precise simulation method that allows designing and optimizing the lens holder for an application before its realization.

Laser beam distribution system is a complex system allowing safe and precise delivery of laser beams. The new generation of HiLASE high energy diode-pumped solid state laser systems with high repetition rates requires advanced approach, which makes design of the distribution system a state-of-the-art challenge. The distribution system delivers four different laser beams multiway from laboratories to several experimental stations. We report results in design and testing of a distribution system for high-power laser beam delivery developed within the HiLASE project of the IOP in the Czech Republic. We use modular framing that allows gradual modification and flexible change of the distribution according to current laboratory needs. The system is extendable and has already proven performance.

Solid-state lasers are broadly used in various applications. The most common gain medium is neodymium-doped yttrium aluminum garnet (Nd:YAG). Very important parameters are angle between polished face surfaces and result wave-front deformation. These parameters are usually measured with two different methods. The paper presents a procedure for measurements of the parameters in a single measurement sequence using Fourier transform phase-shifting interferometry. The results are figures of both optical surfaces, and their mutual position, wave-front deformation, and homogeneity of refractive index. Based on the knowledge of these parameters can be done precise correction of resulted wave-front and of the wedge by polishing of face surfaces. The presented method reduces manipulation with the elements is non-sensitive to the operator and allows more precise wavefront correction thanks to the knowledge of inhomogeneity of material.

Laser Induced Damage Threshold (LIDT) is an important property of laser system components. It is obtained as a statistical value from controlled experiments and defines the maximum optical intensity, which does not cause damage to certain components. Correlation between maximum optical intensity, beam pulse length and focal spot size provides a unique characterization of a specimen. Some specimen requires conditions or environment unreachable in stationary setup, therefore a lighten, portable, version of testing setup may be used with proper source and surroundings. The advantage of the mobile LIDT station is access to different laser systems with variety of beam properties (repetition rate, pulse length, etc). In following paper were investigated accuracy of measurements done by the mobile LIDT station and copared to stationary, ISO compliant LIDT station measurements as reference.

Coherence scanning interferometry (CSI) is a precise and versatile method to measure the shape of objects with rough and smooth surface. However, this method requires a large amount of raw data. The demands on increasing measurement speed and camera resolution require to reduce the number of camera frames. We present an evaluation technique that allows a direct reconstruction of the interferograms envelope. An octadical wave plate is inserted into the reference arm of the interferometer. Thus two signals arise, each for one polarization state, that are shifted by 90 degrees to each other. From the two signals, a direct reconstruction of the interferograms envelope is possible.

We report photometric measurements of selected exoplanet transits from the archive of the TOPTEC telescope, operated by our team at an observatory Horní Halže, near Klášterec nad Ohří, Czech Republic. We have compared measured geometry with catalogue geometry of selected exoplanetary systems. We have found a candidate for potential system with new non-transiting planet with the help of an archive TRESCA.

The shape of the tympanic membrane (TM) plays an important role in sound transmission through the ear for hearing. Previously we developed a high-speed holographic system employing tunable wavelength laser for rapid TM shape measurement. However, the tunable laser illumination is not sufficient to measure the shape of the unpainted TM due to semi-transparency of the TM and short exposure time of the camera. This paper presents a new multiple angle illumination technique that allows us to use a single wavelength higher power laser to perform the shape measurement on the unpainted TM. We successfully applied the new shape measurement method on a fresh postmortem human TM without any paint.

This paper informs about a construction of an all-spherical Cassegrain telescope with a two lens Volosov corrector. The entrance doublet of the Volosov corrector radically corrects the residual optical aberrations of the system and makes possible the attainment of high quality of images across the field of view of up to 2˚ within the whole visual spectral branch. One optical set of the system was manufactured in the IPP AV CR v.v.i – TOPTEC Center in Turnov in 2005. Its entrance diameter was 280 mm and focal length approximately 2450 mm.

Measurement of large or aspheric optical surfaces shape as single aperture using interferometry is problematic due multiple reasons. Typical problem is numerical aperture limitation of the interferometer transmission element. Aspheric surfaces are also problematic due a significant shape deviation from the illumination wavefront. This deviation typically causes vignetting and spatial aliasing on the camera. A solution is sub-aperture measurement and subsequent subaperture stitching. A stitching algorithm in principle uses overlaps between sub-apertures to eliminate aberrations of each sub-aperture to obtain a full-aperture for further analysis. This process is computation time demanding and an optimization has to be implemented in order to obtain result in reasonable time. In this paper, descriptions of considered aberrations using Zernike polynomials are presented and the stitching method based on linear equation system is proposed and it is mathematically described. The method was practically tested with real data measured on spherical surfaces using QED ASI and the results are presented. Stitching quality was quantified for results and compared to other stitching methods.

Today, aspherical elements have become an indispensable part of modern high-precision optical assemblies. Several kinds of defects arise during their manufacture. As far as very precise aspherical surfaces are concerned, mid-spatial frequencies are probably the most important issue. This type of imperfection fills the gap between shape (low-spatial frequencies) and microroughness (high-spatial frequencies).

A smaller part of these defects arise during polishing; however, more of them are generated during the grinding process. Due to the interference of different controlling frequencies in the machine and imperfections in the constructional solution of the grinding machine, defects occur on the optical surface, which deform it. The periods of these defects usually lie in an interval of 0.5 to 10 mm, depending on the parameters of the machining process. To prevent the generation of these structures, a comprehensive measurement of the sources and transmission of vibrations was realised using the measuring device VibXpert II. The measurement was made on the grinding machine Optotech MCG 100 CNC. Several simulations of different types of processes were realised and the measurement was also subsequently performed during a real grinding process of aspherical optical surfaces. The data acquired from the measurement of vibrations were mathematically processed in frequency space. The experiment revealed several reasons for these defects.

Lutetium oxide (Lu₂O₃) is an interesting host material for scintillating applications due to its properties, including high density (9.4 g/cm3), high effective atomic number (Z_eff = 67), chemical and mechanical stability. Although it exhibits some intrinsic luminescent properties, its emission can be tuned to better suit the specific needs of individual applications by doping with lanthanide elements. However, the extremely high melting point of Lu₂O₃ (~2490 °C) makes the fabrication of a single crystal both difficult and costly. Lu₂O₃ is therefore commonly studied in the form of polycrystalline powder and thin films, or highly transparent dense ceramics.

In this work, the fabrication of europium-doped Lu₂O₃ transparent ceramics is presented. First, a powder precursor was prepared using a reverse co-precipitation and characterized utilizing X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Powder was then compacted into dense transparent ceramics by spark-plasmasintering. Photoluminescence, radioluminescence and transmittance spectra, as well as scanning electron microscopy pictures, of sintered Eu:Lu2O3 samples are presented.

Demonstrator of remote sensing system based on an uncooled LWIR hyperspectral imager was designed. This paper describes design of its optical part which is a hyperspectral imager in a spectral range of 7.5-12 um with a 40°×20° field of view. The hyperspectral imaging system is push-broom type based on an imaging spectrometer with transmission grating. Emphasis during design of optical subsystem was placed on future commercial production and usability in the field, thus focused on manufacturability, robustness and reduction of complexity. The optical subsystem was reduced down to 6 aspherical elements, of which one caries the spherical diffraction grating. The use of spherical grating improved manufacturability but introduced aberrations, which were not fully compensated by limited amount of optical elements. The final optomechanical design has an envelope of a 230×80×80 mm. A length of the optical subsystem is 160 mm.

A new approach for measurement of small and thin lenses is introduced, based on the combination of long and short coherence interferometrical point probe systems in one measurement device. The basic working principle, as well as first results, are presented, and the benefits of this approach are highlighted.