We report on developing, characterizing, and verifying a compact, monolithic laser interferometric assembly designed for high-precision two- and three-axis displacement measurements in coordinate positioning systems. The design targets OEM integration into advanced precision motion platforms, including nanometrology instruments, semiconductor manufacturing equipment, and ultra-high vacuum (UHV) environments. Using a single laser source, the assembly integrates multiple interferometers into a monolithic L-shaped base frame, enabling sub-nanometer periodic error in X-Y motion systems while minimizing geometric and thermal instabilities. The pre-aligned and pre-adjusted architecture simplifies integration, enhances long-term stability, and ensures consistent metrological performance. The system's verification protocol employs quadrature phase analysis and systematic error metrics to characterize performance and optimise assembly. The results indicate sub-nanometer measurement capability and suggest the system's suitability for scalable implementation in advanced coordinate metrology applications.

The contribution reviews actual trends in the design of molecular iodine reference cells intended for laser standards operated in space-related applications and which were recently developed at ISI CAS. The need for the optical setup compactness and robustness introduced multipass arrangements, leading to reduced system weight and volume while maintaining long laser beam–absorber interaction lengths. The resilience to harsh environmental conditions, especially during the mission launch, and system reliability for the whole mission lifetime led to the investigation of novel approaches in reference cells development and performance evaluation.

Our research efforts in displacement measurement interferometry focused on long-term drifts initiated an extended experimental investigation in the interferometric assemblies of our design. We aimed to analyze, characterize and tackle the long-term measurement stability, expressed as the zero-drift, with particular attention to the thermal effects. For the experimentation, we developed a thermostatic chamber equipped with active temperature regulation, an array of sensors and control electronics. With either the finely stabilized temperature or with the thermal cycling, we can carry out a range of investigations: verification of modified design or prototype interferometers, testing of production pieces, characterization of integrated assemblies and units in terms of the zero drift and the susceptibility to thermal effects -- the temperature sensitivity dL/dT, expressed in nm/K. With these experimental studies, we demonstrate the potential of the zero drift studies to contribute to the development and broader expansion of interferometric instrumentation.

One of the limiting factors for GNSS geolocation capabilities is the clock technology deployed on the satellites and the knowledge of the satellite position. Consequently, there are numerous ongoing efforts to improve the stability of space-deployable clocks for next-generation GNSS. The COMPASSO mission is a German Aerospace Center (DLR) project to demonstrate high-performance quantum optical technologies in space with two laser-based absolute frequency references, a frequency comb and a laser communication and ranging terminal establishing a link with the ground station located in Oberpfaffenhofen, Germany. A successful mission will strongly improve the timing stability of space-deployable clocks, demonstrate time transfer between different clocks and allow for ranging in the mm-range. Thus, the technology is a strong candidate for future GNSS satellite clocks and offers possibilities for novel satellite system architectures and can improve the performance of scientific instruments as well. The COMPASSO payload will be delivered to the international space station in 2025 for a mission time of 2 years. In this article, we will highlight the key systems and functionalities of COMPASSO, with the focus set to the absolute frequency references.

Laser interferometers have served as the workhorses in the metrology of length for several decades. Their broader application brings further challenges, especially for longer measurement time-frames or outside the laboratory environment with strictly controlled conditions. As a part of our team’s activities aiming at characterizing and eliminating the effects of unstable temperature on interferometric length measurements, we report on successfully remodelling a differential interferometer’s optical arrangement focused on increasing resilience against temperature changes. The experimental characterization under constant temperature and subsequently under thermal load proved a tenfold decrease in short-term fluctuations and reduced sensitivity to temperature changes by a factor of 100.

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.

We report on an instrument for calibration of the 8-mm length gauges, currently being developed and finalised at ISI. The design and construction were focused on elimination and compensation of the typical error sources associated with laser interferometric length measurement. The state-of-art four beam double-path differential plane interferometer with the common-path arrangement (with co-planar beams and co-axial arms) has its z-axis coincident with that of the calibrated gauge so that the system preserves Abbé principle. The differential arrangement efficiently reduces the metrological loop as the reference mirror of the interferometer is mounted on the preloaded grip holder of the tested sensor and the object (measurement) mirror simultaneously loading the measuring tip of the calibrated gauge. The latter is carried with a two-stage positioning comprising a precise linear ball bearing guide actuated with a DC motor (75 mm range, 2,6 mm/s velocity), and a triplet of piezoelectric elements that allow for a micro-positioning (0,015 mm range) and tilting of the object mirror. The displacement readout, compensated for the refractive index of air fluctuations using temperature, pressure and humidity sensors, provides feedback for the stabilisation of the object mirror position in the z-axis (to a nanometre). The interferometer also features a facility for detecting the lateral displacement of the beam in the measurement arm, providing feedback for the closed-loop stabilisation of the object mirror tilts that reduces the guidance-induced cosine error. With the series of test-run calibration of an optical ruler, we achieved the precision below 12 nm (k = 2) and accuracy below 34 nm (k = 2) over 25 mm range. A zero-drift test revealed the coincidence at a static position below 2,3 nm (k = 2) over six hours. Finally, the instrument is designed for automated operation with telemetry data collection compatible with the advanced manufacturing and Industry 4.0 demands.

Besides the environmental fluctuations, the typical sources of significant uncertainty in the laser interferometry systems are the geometrical errors. These are stemming, among others, from the misalignment of measurement axes, the thermo-mechanical influences of the system components and the mounting, guidance errors of the translation mechanism that carries the measurement mirror or vibrations. We report on a compact double-pass differential plane interferometer that features an original optical arrangement with four parallel and coplanar beams, where the beam pairs in the two arms are coaxial. The differential arrangement minimizes the dead path and shortens the metrological loop so that the sensitivity to thermal drifts and vibrations is reduced. The arm symmetry allows for the preservation of the Abbe principle, and the common path mitigates the influences of the environmental disturbances. The interferometer optics is designed as a self-contained single-piece assembly made using optical contacting from the low-expansion materials. The interferometer system integrates the homodyne receiver (even though the optical arrangement is well-suited for heterodyne detection too) and also a tilt-detection electronics that allows for detection of pitch and roll of the interferometer mirror so that the parasitic movement of the measuring mirror could be compensated for. The experimental characterization revealed a good optical performance of the interferometer with sub-nanometre cyclic error and the resolution of tilt detection in order of a few microradians.

We present a novel design of hollow-core photonic ciystal fiber based spectroscopic references purposed for laser frequency stabilization and spectroscopic analysis with low optical losses and mini-invasive approach of gas media filling.

In this work, we demonstrate the simple fabrication process of AlN-based piezoelectric energy harvesters (PEH), which are made of cantilevers consisting of a multilayer ion beam-assisted deposition. The preferentially (001) orientated AlN thin films possess exceptionally high piezoelectric coefficients d33 of (7.33 ± 0.08) pC∙N−1. The fabrication of PEH was completed using just three lithography steps, conventional silicon substrate with full control of the cantilever thickness, in addition to the thickness of the proof mass. As the AlN deposition was conducted at a temperature of ≈330 °C, the process can be implemented into standard complementary metal oxide semiconductor (CMOS) technology, as well as the CMOS wafer post-processing. The PEH cantilever deflection and efficiency were characterized using both laser interferometry, and a vibration shaker, respectively. This technology could become a core feature for future CMOS-based energy harvesters.

We compare three focus sensors designed for the optical topography measurement of rough surface specimens with submicron accuracy. The laser beam was modulated by three specific computer-generated holograms displayed on a spatial light modulator.

In this contribution, we investigate the properties of antireflective coatings on iodine-filled absorption cell windows. These coatings are subject to high temperatures during the cell production process and are in direct contact with the absorption medium, which influences their optical performance. We tested the thermal resistance of TiO2- and Ta2O5- based coatings produced using conventional electron beam evaporation (e-beam) and ion-assisted deposition (PIAD). We prepared a set of iodine-filled absorption cells that were used to test the coatings' resistance to iodine vapors. We show that the choice of coating materials, coating methods, and a well-chosen bakeout procedure can mitigate any unwanted effects, such as temperature-induced spectral shifts and optical losses inhomogeneities or settling of the absorption medium in the coating.

We present an experimental study of the method using a spatial light modulator for correction of the wavefront reflected from the optically rough surface. This method is based on the detection of the mutual phase differences between different regions of the wavefront that correspond to the constructive interference. We study the capabilities of this method from the metrological point of view for the ground glass samples characterized by several different levels of roughness. The resulting wavefront correction is tested in dependence on the measurement parameters settings and is verified by analyzing two specific patterns generated by the spatial light modulator.

We report on a traceable calibration system for a 3500mm-long console that carries a measurement system for inspecting the diameter of a circular reactor chassis. The system uses two single-pass laser interferometers with homodyne fringe detection for measurement in two degrees of freedom. The hybrid FPGA-microcontroller control module carries out the fringe detection together with the application-specific scale linearization approach and the compensation of environmental influences such as thermal elongation and the refractive index of air fluctuations. We demonstrated the system feasibility with an accuracy of a few microns and translation velocity higher than 0:1 metre per second.

We present method for the improvement of the measurement accuracy in the optical frequency spectra measurements based on tunable optical filters. The optical filter was used during the design and realization of the measurement system for the inspection of the fiber Bragg gratings. The system incorporates a reference block for the compensation of environmental influences, an interferometric verification subsystem and a PC - based control software implemented in LabView. The preliminary experimental verification of the measurement principle and the measurement system functionality were carried out on a testing rig with a specially prepared concrete console in the UJV Řež. The presented system is the laboratory version of the special nuclear power plant containment shape deformation measurement system which was installed in the power plant Temelin during last year. On the base of this research we started with preparation other optical fiber sensors to nuclear power plants measurement. These sensors will be based on the microstructured and polarization maintaining optical fibers. We started with development of new methods and techniques of the splicing and shaping optical fibers. We are able to made optical tapers from ultra-short called adiabatic with length around 400 um up to long tapers with length up to 6 millimeters. We developed new techniques of splicing standard Single Mode (SM) and Multimode (MM) optical fibers and splicing of optical fibers with different diameters in the wavelength range from 532 to 1550 nm. Together with development these techniques we prepared other techniques to splicing and shaping special optical fibers like as Polarization-Maintaining (PM) or hollow core Photonic Crystal Fiber (PCF) and theirs cross splicing methods with focus to minimalize backreflection and attenuation. The splicing special optical fibers especially PCF fibers with standard telecommunication and other SM fibers can be done by our developed techniques. Adjustment of the splicing process has to be prepared for any new optical fibers and new fibers combinations. The splicing of the same types of fibers from different manufacturers can be adjusted by several tested changes in the splicing process. We are able to splice PCF with standard telecommunication fiber with attenuation up to 2 dB. The method is also presented. Development of these new techniques and methods of the optical fibers splicing are made with respect to using these fibers to another research and development in the field of optical fibers sensors, laser frequency stabilization and laser interferometry based on optical fibers. Especially for the field of laser frequency stabilization we developed and present new techniques to closing microstructured fibers with gases inside.

This article deals with the evaluation of the chemical purity of iodine-filled absorption cells and the optical frequency references used for the frequency locking of laser standards. We summarize the recent trends and progress in absorption cell technology and we focus on methods for iodine cell purity testing. We compare two independent experimental systems based on the laser-induced fluorescence method, showing an improvement of measurement uncertainty by introducing a compensation system reducing unwanted influences. We show the advantages of this technique, which is relatively simple and does not require extensive hardware equipment. As an alternative to the traditionally used methods we propose an approach of hyperfine transitions' spectral linewidth measurement. The key characteristic of this method is demonstrated on a set of testing iodine cells. The relationship between laser-induced fluorescence and transition linewidth methods will be presented as well as a summary of the advantages and disadvantages of the proposed technique (in comparison with traditional measurement approaches).

We present the design of an interferometric position measuring system for the control of the sample-carrying translation stage in an e-beam writer with reproducibility of the position on nanometre level and resolution below nanometre. We introduced differential configuration of the interferometer where the position is measured with respect to a central reference point to eliminate deformations caused by thermal and pressure effects on the vacuum chamber. The reference is here the electron gun of the writer. The interferometer is designed to operate at infrared telecommunication wavelength due to the risk of interference of stray light with sensitive photodetectors in the chamber. The laser source used is a narrow-linewidth DFB laser diode with a custom-developed electronics that allows for high precision and stability of the laser diode chip temperature and the injection current, very low-noise, EMI protection and high-frequency modulation capability. Detection of the interferometric signal relies on a technique using a high frequency modulation of the laser’s optical frequency and the single-detector phase-sensitive detection.

The absorption cells represent an unique tool for the laser frequency stabilization. They serve as irreplaceable optical frequency references in realization of high-stable laser standards and laser sources for different brands of optical measurements, including the most precise frequency and dimensional measurement systems. One of the most often used absorption media covering visible and near IR spectral range is molecular iodine. It offers rich atlas of very strong and narrow spectral transitions which allow realization of laser systems with ultimate frequency stabilities in or below 10-14 order level. One of the most often disccussed disadvantage of the iodine cells is iodine’s corrosivity and sensitivity to presence of foreign substances. The impurities react with absorption media and cause spectral shifts of absorption spectra, spectral broadening of the transitions and decrease achievable signal-to-noise ratio of the detected spectra. All of these unwanted effects directly influence frequency stability of the realized laser standard and due to this fact, the quality of iodine cells must be precisely controlled. We present a comparison of traditionally used method of laser induced fluorescence (LIF) with novel technique based on hyperfine transitions linewidths measurement. The results summarize advantages and drawbacks of these techniques and give a recommendation for their practical usage.

We present a new self-referenced interferometer for the form measurement of hollow cylindrical tubes that provides the accuracy in the micrometer range. It is based on a simple and robust setup where the reference and object waves are represented by the central and peripheral parts, respectively, of the conical wave generated by a single axicon. The inteferogram is characterized by a closed-fringe pattern with a circular carrier which allows for the interference phase demodulation using spatial synchronous detection. The misalignment aberrations are corrected by an iterative computational procedure. The measurement capabilities of the interferometer are experimentally tested for the glass and stainless steel tubes with lengths from 220 mm to 600 mm.