This PDF file contains the front matter associated with SPIE Proceedings Volume 12502 including the Title Page, Copyright information, Table of Contents, and Conference Committee Page.

The spectroscopic and laser characteristics of optically polished Cr:ZnSe single crystals in four different lengths of 2, 3, 5, and 10 mm were investigated when pumping with a laser diode generating radiation at the wavelength of ~1.69 μm. The optimization from the point of laser efficiency was done in dependence on the crystal samples active length, effect of antireflection (AR) coatings, pumping pulse duration, and repetition rate. As a result, a 3 mm thick anti-reflection coated Cr:ZnSe crystal pumped by a laser diode with a pulse length of 20 ms and repetition rate of 10 Hz was chosen as the optimal. Using a 0.8 mm thick MgF₂ birefringent filter the laser oscillations were continuously tunable from 2.1 μm up to 2.7 μm with the narrow spectral linewidth of ~5 nm and Gaussian beam profile. Maximum mean output power of ~0.35 W and maximum optical-to-optical slope efficiency of ~39% was obtained for 3 mm thick AR-coated sample which was ~28% and ~10% higher than that for uncoated sample of the same thickness, respectively. Continuously tunable laser oscillation wavelength was measured in the range of ∼2.1-2.7 µm with the mean output power of P ≥ 150 mW within a ∼5 nm linewidth. The absorption and fluorescence spectra as well as fluorescence lifetime were also measured. The Cr²⁺ fluorescence lifetime of ∼7.2 µs measured for the 1 ns pulse excitation at room temperature (RT) was constant within the whole absorption band of 1.35–2.25 µm.

Fluoride crystals (CaF₂, SrF₂) doped with neodymium Nd³⁺ and codoped with non-active ions such as Y³⁺, La³⁺, or Gd³⁺ for breaking clusters of active ions, have become interesting active media for diode-pumped mode-locked lasers. They posses broad emission spectra and longer fluorescence lifetime in comparison with widely used crystals such as Nd:YAG or Nd:YVO₄. The crystal fibers grown by several groups in recent years might be attractive for high power operation and possibility of beam guiding. We investigated Nd,Gd:CaF₂ cylinders 10 mm long with diameter of 1.9 mm end pumped by 790 nm LD. In free running regime the wavelength tunability of 41 nm (1040-1081nm) was achieved. In continuously passively mode-locked regime using SESAM the pulses 1.3 ps long at 1065 nm with 2 nm spectral width were generated. The average output power was 200 mW for pump power of 1.6 W. Comparison with operation of standard bulk Nd,Gd:CaF₂ active media is also presented.

The precise optical resonators represent a key tool for ultra-narrow linewidth laser frequency stabilisation. They can serve as references for lasers of optical clock systems, optical frequency combs locking, dissemination of precise time and frequencies over optical links, or laser interferometry. The critical properties of these resonators are determined by their design, used materials and environmental conditions where they are operated. This contribution describes the design and performance of the “kHz” linewidth optical cavity intended for spectral-narrowing of a 1541 nm fibre laser. The cylindrical-shaped Fabry-Perot resonator with optical mirrors and a spacer part made of ceramics with ultra-low thermal expansion coefficient is placed inside the multi-shielded vacuum and thermostated chamber. The optical setup employs the Pound-Drewer-Hall locking technique for laser locking, and the resonator’s performance is measured by the ring-down measurement.

Raman lasers based on stimulated Raman scattering are attractive sources of laser radiation in a visible and an infrared spectral range. Synchronously pumped crystalline Raman lasers present interesting possibility to obtain effective generation in picosecond or femtosecond time-scale. According to semiclassical theory, their dynamic process can be described by a system of partial differential equations for optical and phonons fields. In the case of picosecond or femtosecond regime the set of equations has to be solved numerically. This is especially valid for synchronous pumping. The formal form of formulas is very similar to the task of optical parametrical process. The optical parametrical process is described by coupling of three optical waves. In the case of stimulated Raman scattering coupling is between the two optical fields and phonon field. Otherwise, the sets of equations are analogous. For this reason, the behavior is the same and the output properties of synchronously pumped Raman lasers have similar characteristics as a synchronously pumped optical parametrical oscillator. In this contribution, the split-step methods for numerical solution of synchronously pumped crystalline Raman lasers are presented and compared. In addition, the fundamental behavior of these systems is described.

The PolFEL free electron laser, currently under construction at the National Centre for Nuclear Research in Poland, will generate a beam of coherent electromagnetic radiation in the ultraviolet (UV) spectral range with a wavelength of about 150 nm to 300 nm, in the form of several hundred fs pulses, energy up to 50 μJ, and repetition rate of 50 kHz. Vacuum ultraviolet (VUV) radiation beam in the wavelength range from 50 nm to 100 nm will be obtained by selecting the third harmonic using an absorption filter. The optical system of the UV/VUV beamline consists of two plane M1 and M2 mirrors and one focusing ellipsoidal M3 mirror. The radiation produced in the laser hits on the M1 mirror at a grazing incidence angle of 5°. After reflection from the M1 mirror, the beam falls on the M2 mirror at an angle of 17°, which directs the beam to the ellipsoidal M3 mirror, focusing the beam at the image plane at the second focal point of the ellipsoid. The M1 mirror is placed behind the 3 m-thick concrete wall in a hutch separated from the experimental hall by a 1.6 m-thick concrete wall. The optical properties of the beamline were tested by ray-tracing simulations using the RAY-UI software, the results of which are presented in the paper.

Optical coherence tomography (OCT) is a well-established non-destructive imaging technique providing high-resolution cross-sectional views of objects. The axial resolution of OCT is limited to single micrometers when using infrared and optical wavelengths. Recently, optical coherence tomography using broadband soft X-rays and extreme ultraviolet has been proposed to improve axial resolution. This variant of OCT, known as X-ray coherent tomography (XCT), enables axial resolution of a few nanometers. The paper presents OCT with the use of extreme ultraviolet in the wavelength range of 10–20 nm generated using a compact laser-produced plasma (LPP) source based on a double-stream gas puff target. The use of a gas puff target enables efficient extreme ultraviolet emission without producing target debris by laser ablation from a solid target. Two axisymmetric ellipsoidal grazing-incidence mirrors were used to focus the radiation from the source to the sample, and then to focus the radiation reflected from the sample to the spectrometer. We also present measurements on Silver/Zirconium multilayer periodic structures with a periodicity of 60 nm.

Terahertz waves have found many applications, including imaging, security, high-capacity telecommunications, and quality inspections. Moreover, sample characterization using the terahertz time-domain (THz-TDS) gives us information about both amplitude and phase, which is a significant advantage over other conventional spectroscopic methods. Several sources and detectors, such as photoconductive antennas, nonlinear crystals, or photo-Dember sources, can be used for these mentioned applications. However, they are often low-energy, limited by threshold or narrow spectrum. In our experimental setup, we generate the THz field using dual-color plasma. The generation process resides in the mixing of the first and second harmonics providing substantial conversion efficiency, excellent signal-to-noise ratio, and a broad spectrum ranging from 0,1 THz to 4 THz. Furthermore, we enhance our measurement technique by implementing ZnTe polarization-sensitive detection. Here we experimentally demonstrate plasma polarization response. Our multipurpose configuration is employed in various experimental arrangements such as transmission, reflection, or attenuated total reflection (ATR). It offers a complete sample analysis of thickness, dielectric functions, birefringence, and optical activity.

Recently, the terahertz family of sources increased by newly-developed terahertz spintronic emitter (STE), which competes with the traditional in many ways. This 30THz-broadband gapless source is versatile due to its low-cost, easy implementation, frequency-independent excitation, and perpendicularly-given polarization to the STE’s magnetization. Nowadays, the polarization control of STEs was demonstrated by rotating and multipolar magnets, a twisted magnetic field, or cascades of STEs. The methods suffer from mechanical stability, realization difficulties, and limited polarization control. We introduce here our new approach to control the emitted polarization following Stoner-Wohlfarth magnetization rotation within our FeCo/TbCo₂/FeCo-based STE exploiting magnetic anisotropy. The varying magnetic field along the hard magnetic axis induces the magnetization rotation, performing the polarization control. We present full-360-degree linear polarization control, not needing mechanically rotating components. This technique guarantees higher stability for polarimetry applications. We prove the whole terahertz spectrum follows the polarization control, preserving even the phase of sub-picosecond terahertz emission. It offers easy polarization calibration of the emitter for terahertz experimental setups. Moreover, we provide models to explain magnetic hysteresis defining the polarization behaviour. We predict that the polarization-controlled STEs will find many applications covering terahertz time-domain polarimetry and ellipsometry, medical imaging and security detection.

Raman scattering as a candidate for photon-pair generation is explored recently both theoretically and experimentally. Here, we systematically analyze the Stokes–anti-Stokes photon-pair generation in Raman scattering, akin signal–idler photon-pair emission in the spontaneous parametric down conversion, to obtain suitable conditions for photon-pair generation. Non-zero mean phonon number and losses in the phonon mode are observed to be relevant parameters in this context in addition to the Raman active material properties and pump power. Specifically, the Raman active materials with stronger anti-Stokes coupling compared to the Stokes coupling constant are suitable for photon-pair generation. Ideal Stokes–anti-Stokes photon-pair generation is possible even for non-zero thermal phonons provided that the phonon losses are negligible. Here, we characterized the performance of photon-pair generation using noise-reduction parameter in detail. We also discuss the effect of phonon losses on the observed non-classical features.

We discuss a system of two coupled anharmonic Kerr-type quantum oscillators. The oscillators are continuously driven, and the strength of excitation changes periodically. We show that such a system can be a source of strongly entangled states, and the degree of entanglement between two subsystems depends on the period of changes in excitation’s strength.

A bifunctional system for nondestructive characterization of fiber optic preforms in transverse illumination is presented. It allows for measurements of geometrical parameters of the preform core as well as the distribution of stress-induced birefringence. The system measures the core thicknesses versus its angular orientation and by numerical fitting of the experimental data, the core orientation, its ellipticity and dimensions of ellipse axis are determined. After inserting the polarizer into the illuminating beam, the system is capable of measuring the preform birefringence induced by thermal stress. Maps of retardation distributions are obtained simultaneously at RGB channels of the CMOS camera with the use of the rotating polarizer method. This allows to determine the exact value of the stress-related retardation without interference order unambiguity and finally to calculate the stress-induced birefringence and axial stress distribution using inverse Abel transformation. Sample measurements for step index preform with nominally circular core are presented.

Numerical modeling of many optical-fiber-based devices' operation requires an exact knowledge of fiber's parameters like core diameter and dopant, usually GeO₂, concentration. While diameters are typically specified in the fiber's data sheet, material composition, including dopant in the core, is rarely available. We present a procedure utilizing a reverse engineering approach to find GeO₂ concentration in single-mode step-index optical fiber. Our method consists of several stages. First, we measured the numerical aperture NA for several commercially available fibers employing a onedimensional far-field scan. The far-filed mode intensity was acquired by a Ge detector placed on a rotation stage with a stepper motor for fiber end-face positioned on the motor's axis of rotation. We calculated NA for the angular detector position when the light intensity reached 13.5%, 5%, and 1% of its maximum value. Then, taking the corresponding values of core and cladding diameters and using the Sellmeier formula for pure (cladding) and GeO₂ doped (core) silica glass, we found the concentration of GeO₂ numerically matching calculated NA to the experimental data. We found that dopant concentration equals 9.0, 18.0, 34.0, 34.5, and 39.8 mol% for the fibers, respectively, 980-HP, UHNA1, UHNA3, UHNA4 and UHNA7 produced by Coherent. To verify the correctness of our method, we performed this procedure for several fibers with a known level of GeO₂ concentration in the core fabricated by the Laboratory of Optical Fiber Technology, Maria Curie-Sklodowska University. The results of this simulation coincide with expectations with great accuracy.

In recent years the novel active glass materials for optical fibers with broadband emission are of great interest due to potential application in spectroscopy, environmental monitoring or medicine. Development of that kind materials is based on elaborating the glass matrix co-doped with different rare earth ions, e.g. Er, Yb, Ho, Tm. Glasses doped with multiple rare earths characterize with a high number of spectroscopic parameters, due to the presence of energy transfer phenomena between those different rare earth ions. Nonlinear nature of that phenomena varying with the dopants concentration levels, makes the design and development of optical fibers made of glass doped with several active ions not trivial. In this work, we present the nanostructured material composed of several separated glass areas with subwavelength size with individually designed parameters. As a proof-of-concept, we propose the active phosphate fiber with the core consisted of two types of glasses doped with Yb³⁺ and Er ³⁺ ions, which exhibit independent performance. The presented phosphate fiber laser operates simultaneously at dual wavelengths at 1.04 μm and 1.535 μm with very good beam quality of M²=1.14 and slope efficiency of 23.0% and 9.8%, respectively. To our knowledge, this kind of fiber has not been demonstrated previously

This paper describes two different designs of 1×8 passive optical splitters. The first splitter consists of cascade arranged directional waveguide branches (Y-branch splitter) with (0.8×0.16) µm² waveguide cross-section. The second splitter is based on multimode interference occurring in a large MMI coupler, which uses a self-imaging effect for beam propagation, exhibiting the same waveguide core size as a Y-branch splitter. The waveguide channel profile, used in both approaches, is based on a silicon nitride material platform, with a refractive index of core being n_c = 1.925 and a refractive index of cladding n_cl = 1.4575. The splitters are designed as a planar structure for a medical operating wavelength 850 nm. Design, simulation, and optimization of passive optical components are performed by a commercial photonic software tool BeamPROP simulation engine by RSoft Photonics Suite tool, employing beam propagation method. This work aims to find the minimum physical dimensions of the designed splitters with the satisfactory optical performance. According to the minimum insertion loss and minimum non-uniformity, the optimum length of the splitters is determined. Finally, the optical properties of splitters for both approaches are discussed and compared with each other.

The main goal of this study is to explore possibilities of using cavities with dielectric or semiconductor grating as a main building block of spin-injected vertical-cavity surface-emitting lasers (spin-VCSELs) for ultrafast data transfer up to hundreds of Gb/s. Spin-VCSELs allow direct control of emitted polarization by means of electron spin injection. Compared to intensity-modulated VCSELs, the information is encoded into polarization state of light. Shorter response time is offered as a result of introducing anisotropy, in this case via periodic grating, which couples circularly-polarized photons, emitted in spin-polarized quantum wells. Precise modeling of the lasing regime is essential and based upon theory developed in our previous work. Eigenmodes of cavity with periodic structures are extracted using effective medium theory implemented in the transfer matrix formalism. Mathematical tools allow us to calculate optimal parameters of birefringent grating and consequently to design the cavities with required functionality. Particular focus is put on calculation of photon lifetimes, generalized confinement factors and frequencies of eigenmodes, which are necessary for studying dynamical performance of grating-based spin-VCSELs. According to the numerical model, desired gratings and grating-based cavities can be fabricated using PVD deposition of dielectric material sophisticated by lithographic techniques along with sample etching.

We present 256-channel, 25-GHz AWG designed for ultra-dense wavelength division multiplexing. For the design two in-house developed tools were used: AWG-Parameters tool for the calculation of input design parameters and AWGAnalyser tool, used to evaluate the simulated transmission characteristics. The AWG structure was designed for AWG central wavelength of 1550 nm and simulated with PHASAR tool from Optiwave. To keep the size of AWG structure as small as possible the number of waveguides in the phased array was tested. The simulations show that there is a certain minimum number of phased array waveguides necessary to reach sufficient AWG performance. After optimization, the AWG structure reached 10 cm x 11 cm in size and satisfying optical properties.

The fiber infrastructure in buildings can pose a security risk. Using interferometric measurement techniques, a fibre installed in a room can be turned into a sensitive microphone and thus misused for eavesdropping. In our contribution we are investigating the transfer of mechanical vibrations to the fiber in the audible frequency band. An installation of optical fiber connecting two buildings of the institute was measured using a heterodyne interferometric system. The phase changes of an ultra-narrow C-band laser working at 1540.5nm wavelength transmitted through the fiber were detected and converted to an audio signal. The power spectral density of the interference phase for audible Fourier frequencies was analyzed over a period of several working and non-working days. A practical example of post-processing the measured data for speech eavesdropping is discussed.

The paper presents the result of an experimental investigation of the effect of a magnetic field on the transmittance of a magnetic fluid placed between two crossed linear polarizers and illuminated by light from a supercontinuum light source. The change of the optical signal in the visible region detected behind the output polarizer depending on the magnetic flux density shows that the magnetic fluid becomes optically anisotropic, and the change of the optical signal is the consequence of the so-called birefringence induced by a magnetic field oriented perpendicular to the direction of the light beam passing the magnetic fluid sample. The phenomenon was observed on samples of magnetic fluid with Fe₃O₄ nanoparticles dispersed in ITO100 oil and thicknesses from 25μm to 380μm in static fields with values of magnetic flux density up to 60mT. The dependence of birefringence on wavelength, magnetic flux density, and sample thickness is evident from the measured dependencies.

Photonics has become recently an intensively evolving area, where the possibilities of photonic structures or crystals (PhC) for integrated optoelectronics were found. An employment of three dimensional (3D) laser technology with combination of stable polymer resin enable printing of micro-optical and nano-optical components or other type diffractive structures for optoelectronic applications. In this paper, we demonstrate possibilities of 3D laser technology based on two photon polymerization for application in optoelectronics. We prepared two types of 3D polymer photonic structures, which was proposed for direct application on light emitting diode chip. We designed and fabricated Kagome and square lattice structures in 3D arrangement and we analyzed their properties in scanning electron microscope and by diffraction measurements.

In this paper, we will focus on the quality of polymer mirror interfaces prepared by high-precise 3D laser lithography. Using this technique, it is possible to create various optical elements, such as interferometers, resonators, and sensors. For these elements to function properly, it is necessary to achieve the best possible surface roughness parameters of the mirror interfaces. The polymer mirror surfaces can be post-treated with a focused ion beam, but our goal will be to achieve acceptable polymer surfaces in a one-step lithography process. By changing of printing parameters, we can achieve different surface roughness. We will focus on optimizing the laser printing process, for elements working in the infrared region, near to telecommunication wavelength of 1550 nm. For measurements we will use the optical spectrum analyzer and LED source, where reflection on IP-Dip polymer will be investigated.

Various types of nano- and micro-structures, such as security holograms and diffractive optical elements, can be prepared directly into a photoresist using a direct-write optical lithography. Precise knowledge of photoresist properties, parameters of exposure, and photoresist development time are essential. We have characterized and optimised exposure of the positive binary sensitive photoresist ma-P 1200 series. Complex optical functions were obtained using Mueller matrix spectroscopic ellipsometry. True thickness profile of linearly exposed photoresist was studied by confocal microscopy and strong non-linearity was observed. In this paper we propose exposure correction to compensate this non-linearity.

Conventional fiber-based metal coated aperture near-field probes offer a technologically easily reproducible and costfriendly option to achieve substantially good resolution in near-field imaging and lithography techniques, however the limiting mechanism behind the performance of these probes is the shape and the dimensions of the aperture. Hyperbolic metamaterials (HMM) have enabled the possibility to directly influence the propagation of highly-localized evanescent optical modes due to their extreme anisotropic properties. Implementation of such anisotropic metamaterial onto the tapered metal-coated probes offers a novel possibility to fabricate a probe capable of achieving the /7 resolution and better. This paper deals with a design and numerical characterization of plasmonic near-field probe consisting of tapered optical fiber coated with aluminium upon which a hyperbolic metamaterial is placed. The hyperbolic dispersive medium enables a directional propagation and interference of the highly-localized near-field waves.

The paper shows concepts of optical splitting based on three dimensional (3D) optical splitters based on multimode interference principle. This paper is focused on the design, fabrication and characterization of 3D MMI splitter with formed output waveguides based on IP-Dip polymer for direct application on optical fiber. The MMI optical splitter was simulated and fabricated using direct laser writing process. Output characteristics were characterized by highly resolved near-field scanning optical microscope (NSOM) and compared with 3D MMI splitter without output waveguides.

In this paper, we present inverted pyramids patterned in the surface of IP-Dip polymer that can be used as a SERS substrate. Inverted pyramids are prepared using direct laser writing lithography and they are metal-coated in the next step. Prepared SERS structure consists of field of 40x40 pyramids with base of 3 μm and two depths – 2 and 3 μm. Afterwards, an Au layer with 4 different thicknesses (10 nm, 20 nm, 30 nm and 40 nm) is evaporated. Transmission spectra were simulated and measured for characterization of prepared structures. The micro-Raman measurements using Rhodamine 6G in aqueous solution at concentration of 10-2 M as the probe molecule were performed.

We proposed, simulated and fabricated a new type of three-dimensional (3D) optical splitter based on multimode interference (MMI). Splitter was designed for the wavelength of 1550 nm and the input signal is divided into 9 outputs. The multimode waveguide part of the splitter was designed as a block with square basis of cross-section of 26 x 26 μm² and length of 211 μm. We used the IP-Dip polymer as a standard material for 3D laser lithography. We present the design, simulated and measured optical field distribution in the output of the MMI splitter and its direct integration on the single mode optical fiber.

Precise Time and Frequency dissemination and its essential infrastructure on national or even international level are being focused recently. We present here the situation in Czechia, our strategy and approach to contribute with experience of non–commercial solution, open activity utilizing optical networks shared with other data traffic. The cost efficient solution of accurate time and very stable frequency is realized, and operated within shared spectrum of CESNET network infrastructure; the costs are under control then. We are focused on future developments, plans, upgrades concerning wavelength bands and geographic solutions and extensions. Bidirectional dark channels on various wavebands, we do realize them to utilize shared leased fibers, bidirectional compensation of the fiber losses is the benefit or must for these solutions. When operating precise Time and Frequency, single path with bidirectional amplification performed by optical amplifiers is preferred, however it is sensitive to feedbacks by fiber line, caused mainly by back scattering, reflections, and potential to cause unwanted oscillations. The interference with parallel data transmissions is the issue being carefully solved. Within this paper, we also briefly mention CLONETS Design Study project where we share the experience, and the consortium is about to plan and realize the coherent Pan-European Time and Frequency dissemination network to interconnect national research network, and to provide various Time and Frequency services for a wide range of users, research, non-commercial and commercial as well.

Dissemination of precise time and frequencies and its corresponding infrastructure has become a key tool for many scientific and industrial applications (optical clocks comparisons, global navigation and positioning systems, security). Although most of these transfers use optical fibre networks, free-space photonic links represent an essential supplement in cases where the fibres cannot be utilised. This work presents pilot experimental results of free-space optical (FSO) link phase noise measurement, an initial requirement for further intended phase-coherent transfer of precise time and frequency. The measurement setup consists of a 30 m long unidirectional FSO (DUT) supplied by an ultra-narrow 1540 nm fibre laser (locked to the ultra-stable optical cavity), and it is supplemented with parallel phase-noise stabilised optical fibre delivering the reference beam to the beat-note with the signal obtained from the FSO receiver.

In this paper, the design and preparation of polymer based monolithic high-contrast grating (MHCG) structures and their Talbot self-imaging effect are presented. For the preparation of MHCG structures to IP-Dip negative photoresist material, 3D laser lithography was used. The shape and morphological properties of the prepared MHCG structure were investigated by scanning electron microscope (SEM). Finally, the highly resolved near-field scanning optical microscope (NSOM) for the vertical optical field distribution over the grating structure was used. The demonstration of the Talbot effect for different wavelengths in a diffraction and a subwavelength regime is presented theoretically and experimentally from NSOM measurements.

Optical nano-printing provides a versatile platform to print various nanoparticles into arbitrary configurations. Optical printing, the use of light to direct the formation of a desired structure, has been of significant interest in the last two decades. For particles much smaller than the laser wavelength, optical forces can be well described in the dipole approximation. For a focused laser beam, two main optical force components are identified: the gradient force, which attracts particles toward the high-intensity focal spot, and the scattering force, which tends to push particles along the beam propagation direction. When the wavelength light is close to the particle localized surface plasmons resonance, a scattering force is dominant and can be used to efficiently push nanoparticles along the beam optical axis onto a substrate. In this context, optical forces can be applied to optically print nanoparticles into patterns aggregated on surfaces such as glass. Here, we report on use optical nanoprinting of plasmonic nanoparticles to create an active aggregate in a solution containing dyes or nanoplastics. The active aggregate, produced by optical forces, serves as a sensitive sensor which is used to detect dyes in concentrations below the limit of detection for Raman spectroscopy and/or to detection of plastic nanoparticles.

The work is aimed at the development of the experimental device to study of the motion of different colloidal objects in the combined force field composed of the optical-trapping force originating in the light-intensity gradient and the thermophoretic force caused by the temperature gradient in aqueous solvents. Polystyrene microscopic beads of submicrometer diameters are used as a simple model of the optical tweezers calibration. The methods of generating temperature gradient are under development. A dual optical trap is used as a tool for the investigation of the thermophoretic force acting on the observed particles. Also, the generated optical trap's force constant is calculated by various methods, including Fast Fourier Transform, and the influence of differences in the sample environment and light intensity is compared. Results of these experiments should contribute to the theory of the optical trapping effect, so far not understood in detail, and should open a way for developing novel methods of the investigation of thermophoretic phenomena in a water environment.

We present a design of a new compact vacuum chamber with an electrical trap for trapping and laser cooling of ⁴⁰Ca⁺ and ²⁷Al⁺ ions. The custom chamber was designed to a minimum dimension to achieve ultra-high vacuum environment and good optical access to trapped ions. Combining the shape of the electrical trap with intrinsic geometrical symmetry and the size of the viewports will allow maximum efficiency of fluorescence collection from ions. The setup is ready for ablation and loading of ⁴⁰Ca⁺ and ²⁷Al⁺ ions to deal with quantum logic experiments for optical clock operation. In combination with magnetic saddle coils, Helmholtz coil and external magnetic shielding made of mu-metal, we achieve a very homogeneous magnetic field in the ion trapping area. The main part of a chamber equipped with viewports is made of titanium to maintain this homogeneous magnetic field and suppress residual fields. The presented setup will allow quantum experiments with single ions and Coulomb crystals in a stable and homogeneous magnetic field, which is necessary for many-ions optical clock systems.

The problem of numerical simulations of the optical trap is widely discussed in literature for three regimes: geometrical optics for objects larger than wavelength of trapping laser, Lorenz-Mie regime for object’s size close to the wavelength and dipole approximation for trapped bead smaller than the wavelength [1]. Despite the abundance of articles in this field, the issue of comparison of numerical results with the experiment is omitted [2]. Here we show the compliance of numerical simulations with the experiment. By utilizing geometrical optics methods it is possible to numerically recreate behavior of beads for specific experimental setup. The parameters available in the simulation have their direct counterpart in the experimental system, which allows for comparison and verification of numerical simulations against the experiment. The data obtained from simulation and experiment is compared using statistical analysis of trajectory. Compliance of numerical simulations with experimental data proves useful for verification of methods of recording the object's trajectory in a trap.

Remote positioning by precise measurements of lateral displacements of laser beams at large distances is inevitably disturbed by the influence of atmospheric turbulences. We test numerically the use of various arrangements of four single optical vortices for this purpose. Our previous work shows that using the single or higher order vortex beam (topological charge 4) gives better results than vortex free laser beam. We consider arrangement of four separated vortices with different topological sign and show that some configuration leads to comparable results, but there are small differences which are discussed in this paper.

The paper demonstrates initial results of measuring the retardance of waveplates using a variable wavelength interferometer. The instrument utilizes a continuously variable interference bandpass filter placed in a specially designed intermediate image plane. The fringe field, created by the Wollaston prism, is processed and analysed only once, which speeds up the measuring procedure. In this application a reflected-light mode configuration is presented. The solution is suitable also for transmitted-light systems. The interferometer provides the user the spectral characteristic of retardance of the waveplate across the visible spectrum. The instrument is based on a classical microscope with the Kӧhler illumination system.

Chirality – the non-superimposability of an object on its mirror image – shows its twists at all scales, from giant stellar galaxies to the electronic structure of materials. It enters into nearly every aspect of everyone’s daily routine without acknowledging it. Yet, it governs the stereochemistry of all molecular processes in nature, making them life-forming or life-incompatible. It makes the knowledge of molecular spatial configuration essential in pharmacy, medicine, and biochemistry. Here, by combining spectroscopic Mueller matrix ellipsometry and suitable theory, we experimentally demonstrate and theoretically verify the advantage of the proposed method to determine dispersion characteristics of molecular chirality. We first show how the Mueller matrix relates to both macroscopic and microscopic physical quantities used commonly in description of molecular chirality. Next, we experimentally determine quantitative observables such as specific rotation (with sensitivity 0.001 rad) of limonene enantiomers. We believe that our findings may provide a deeper insight into the problematics and potentially extend the scope of the state-of-the-art Mueller matrix ellipsometry beyond the classical optics and photonics.

Using multiphoton microscopy, we can image the tissue with sub-cellular resolution at depths down to 1.5 mm. Beyond this reach, the light must be delivered to the target region by optical relay elements inserted into the tissue – the endoscopes. Focusing light through a step-index multimode optical fibre (MMF) using wave-front control enables minimally-invasive endoscopy. With fibre micro-endoscopes, we can reach any depth with negligible tissue disruption and keep the resolution below 1 micrometre, sufficient for in vivo microscopy. We designed a novel custom-terminated multimode fibre probe. This work will focus on optical fibre probe manufacturing methods (etching, polishing and coating) and their impact on imaging quality.

We investigate the optical performance of anti-reflective coatings subject to high temperatures and the presence of iodine gas to determine the most suitable technological process for iodine-filled absorption cell production. Two unwanted effects need to be avoided or mitigated. One is the settling of iodine gas in the coating structure, which reduces the transmittance of the cell windows. The other is the thermally induced spectral shift which limits the effect of the antireflective coating. We investigate the thermal resistance of TiO₂ and Ta₂O₅ based coatings produced by electron beam evaporation (e-beam) and plasma ion-assisted deposition (PIAD). We prepared sets of quartz samples subject to a range of temperatures and the presence of iodine gas. We show that the choice of the coating technique and annealing procedure can mitigate the aforementioned effects.

The definition of both meter and second relies on precisely measured frequency. The convenient sources of such frequencies are lasers stabilized by molecular vapours. The He-Ne lasers stabilized by iodine vapours represent the cornerstone sources in the visible spectrum. On the other hand, the infrared spectrum (particularly 1550 nm C-band) is of metrological interest thanks to its cost-effective, readily available components. The widely used absorption media at 1550nm has been two acetylene isotopes (¹²C₂H₂, ¹³C₂H₂), while H¹³C¹⁴N represents an alternative covering a broader spectrum well corresponding to the telecommunication C-band.

This paper describes an idea of creating a liquid analyte sensor based on a one-dimensional (1D) photonic crystal - dielectric mirror - integrated on the optical fiber end face and creating a resonant cavity with the reversed structure. This geometry produces the evident resonances within the photonic band gap spectral region which are sensitive to refractive index changes inside the resonant cavity. The main idea is to use this arrangement as a sensor in Lab-on-a-chip (LOC) device with two single mode optical fibers (SMFs). An inlet and outlet is proposed for different liquid analyte delivery and in-situ monitoring of the refractive index change of the analyte.

Two-photon vision relies on the perception of pulsed near-infrared laser beams as having colors like their half-wavelength counterparts. The phenomenon is due to two-photon absorption occurring in visual pigments [1]. This study is focused on methods to determine the contrast sensitivity function (CSF) for two-photon vision, which has not yet been investigated. CSF was measured for eight spatial frequencies using the tumbling E letter optotype. The optotype was projected on a white background by fast scanning the retina with a pulsed 1040 nm or 520 nm laser beam, both perceived as green. The contrast threshold was determined for the power of the beam corresponding to a minimum stimulus brightness for which the subject was able to state the correct letter orientation. Because a luminance curve for the two-photon stimulus is not available, expressing the brightness of the infrared stimulus in photometric units required finding a suitable method. Three approaches for determining contrast sensitivity for two-photon stimulus were proposed and tested to overcome this problem. The threshold contrast values, defined as Weber contrast, differ substantially between normal and two-photon vision mechanisms. Each tested method allowed qualitative comparison of the obtained contrast sensitivities. The results show that the two-photon CSF has a significantly broader range than the one-photon CSF. Determining the CSF for twophoton vision will help assess the applicability of this phenomenon to augmented reality displays.

Twisted nematic liquid crystals (TNLCs) are an interesting alternative to the linear liquid crystal variable retarders commonly used in polarimetric systems. The first and last molecules are anchored on the bounding surface of the liquid crystal cell at 90° angles to each other. As a result of the application of an electric field, there is a change in the polarization properties of the eigenvectors of the TNLC and the phase difference introduced by them. Theoretical analysis indicates that the use of TNLC can generate and analyze an infinite number of polarization states. Nevertheless, their practical applicability is limited and depends on the physical parameters of the liquid crystal cell. Therefore, this work presents the polarimetric characteristics (azimuth angle, ellipticity angle and phase difference) measured as a function of applied voltage of two TNLCs manufactured by Thorlabs®. The study aims to test whether it is possible to achieve a phase difference greater than 4π by using TNLC, which is desirable for optimization reasons. The polarization states that can be produced and analyzed with the examined TNLCs are represented on the Poincaré sphere. This provides a base for selecting the optimal practically possible polariscope configurations in the future.