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.
KEYWORDS: Ions, Magnetism, Luminescence, Photons, Signal to noise ratio, Modulation, Magnetic sensors, Electromagnetism, Motion measurement, Frequency combs
Trapped ions, as one of the pillars of progress in frequency metrology and quantum optics, require a complex experimental environment with well-defined conditions. We present that a feature called dark resonance, provided by the trapped ion itself, can be used as a versatile sensor for enhanced in-situ analysis of interacting fields. The dark resonance is formed in the lambda-type energy level scheme of a laser cooled 40Ca+ ion and corresponds to a fluorescence quenching. The method uses an analysis of the detection times of photons emitted from the upper energy level, which is excited via two optical dipole transitions. The two excitation lasers are phase locked to an optical frequency comb to reduce their linewidths and for precise control of their optical frequencies within the dark resonance. The amplitudes of interacting fields are obtained using the Fourier transform of the ion fluorescence or photon correlation measurements. This paper shows that the method can be applied for sensing of electric, magnetic and electromagnetic fields. Firstly, we present the potential for frequency analysis of the secular motion of a few-ion Coulomb crystal, which corresponds to the axial static electric field of a linear ion trap. Secondly, we demonstrate the optical frequency analysis of the employed lasers driving the two transitions. In the last case we show the analysis of an alternating magnetic field at the position of single ion.
KEYWORDS: Calibration, Interferometers, Field programmable gate arrays, Interferometry, Sensors, Monte Carlo methods, Homodyne detection, Distance measurement, Signal processing, Signal detection, Laser interferometry
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 have addressed the challenge to carry out the angular tilt stabilization of a laser guiding mirror which is intended to route a laser beam with a high energy density. Such an application requires good angular accuracy as well as large operating range, long term stability and absolute positioning. We have designed an instrument for such a high precision angular tilt measurement based on a triangulation method where a laser beam with Gaussian profile is reflected off the stabilized mirror and detected by an image sensor. As the angular deflection of the mirror causes a change of the beam spot position, the principal task is to measure the position on the image chip surface. We have employed a numerical analysis of the Gaussian intensity pattern which uses the nonlinear regression algorithm. The feasibility and performance of the method were tested by numeric modeling as well as experimentally. The experimental results indicate that the assembled instrument achieves a measurement error of 0.13 microradian in the range ±0.65 degrees over the period of one hour. This corresponds to the dynamic range of 1:170 000.
In scanning probe microscopy laser interferometers are usually used for measuring the position of the probe tip with a
metrological traceability. As the most of the AFM setups are designed to work under standard atmospheric conditions
the changes of the refractive index of air have an influence to measured values of the length with 1.0exp(-4) relatively.
In order to achieve better accuracies the refractive index of air has to be monitored continuously and its instantaneous
value has to be used for compensating the lengths measured by all of the interferometric axes. In the presented work we
developed a new concept of an electronic unit which is able to monitor the refractive index of air on basis of
measurement of ambient atmospheric conditions: temperature, humidity, pressure of the air and the CO2 concentration. The data processing is based on Ciddor equation for calculating the refractive index of air. The important advantage of the unit is a very low power consumption of the electronics so the unit causes only negligible temperature effects to the
measured environment. The accuracy of the indirect measuring method employed by the unit was verified. We tested
the accuracy in comparison with a direct method of measuring refractive index of air based on an evacuatable cell
placed at the measuring arm of a laser interferometer. An experimental setup used for verification is presented together with a set of measurements describing the performance. The resulting accuracy of the electronic unit falls to the 4.1 exp(-7) relatively.
Although the laser interferometry represents the most precise class of techniques in the field of precise measurement of geometrical quantities, its wide use in measurement systems is still accompanied by many unresolved challenges. One of these challenges is the complexity of underlying optical systems. We present a novel approach to the interference phase detection - fringe subdivision - in the homodyne laser interferometry that aims at reduction of the optical complexity while the resolution is preserved. Our method employs a series of computational steps to infer a pair of signals in quadrature that allows to determine the interference phase with a sub-nanometre resolution from an interference signal from a non-polarising interferometer sampled by a single photodetector. The complexity trade-off is the use of laser beam with frequency modulation capability. The method was experimentally evaluated on a Michelson interferometer-based free-space setup and its performance has been compared to a traditional homodyne detection method. The results indicate the method is a feasible al
ternative for the traditional homodyne detection since it performs with comparable accuracy (< 0.5nm standard
deviation), especially where the optical setup complexity is principal issue and the modulation of laser beam is not a heavy burden, for instance in multi-axis measurement systems or laser diode based systems.
KEYWORDS: Global Positioning System, Transmitters, Antennas, Data acquisition, Data transmission, Frequency shift keying, Animal model studies, Receivers, Satellites, Modulation
The radio telemetry is a well-known technique used within zoological research to exploit the behaviour of animal
species. A usage of GPS for a frequent and precise position recording gives interesting possibility for a further
enhancement of this method. We present our proposal of an architecture and design concepts of telemetry
transmitter with GPS module, called GTAG, that is suited for study of the Egyptian fruit bat (Rousettus
aegyptiacus). The model group we study set particular constrains, especially the weight limit (9 g) and prevention
of any power resources recharging technique. We discuss the aspect of physical realization and the energyconsumption
issues. We have developed a reference implementation that has been already deployed during
telemetry sessions and we evaluate the experience and compare the estimated performance of our device to a
real data.
In construction of highly mechanically stable measuring devices like AFM microscopes or nano-comparators the use of low expansion materials is very necessary. We can find Zerodur ceramics or ULE glasses used as a frame or basement of these devices. The expansion coefficient of such low-expansion materials is lower than 0.01 x 10-6 m•K-1. For example in case of a frame or basement 20 cm long it leads to a dilatation approximately 4 nm per 1 K. For calculation of the total uncertainty of the mentioned measuring devices the knowledge of the thermal expansion coefficient of the frame or basement is necessary. In this work we present a method, where small distance changes are transformed into rf-frequency signal. The frequency of this signal is detected by a counter which measures the value of the frequency with respect to an ultra-stable time-base. This method uses a Fabry-Perot cavity as a distance measuring tool. The spacer of the optical resonator is made from the investigated low-expansion material. It is placed into a vacuum chamber where the inside temperature is controlled. A selected mode of the femtosecond frequency of the femtosecond comb which represent the distance changes of the optical resonator. The frequency is measured by the rf-counter which is synchronized by a time-base signal from an atomic clock. The first results show the resolution of the method in the 0.1 nm order. Therefore the method has a potential in characterisation of materials in the nanoworld.
The depth of penetration is probably the most important factor that influences the quality of a laser weld. The
depth strongly depends on the focus of the welding beam. The sublimating material forms plasma vapors, that
act as a lens and defocus the laser beam. Our contribution presents a method to compensate this phenomenon
using an adaptive mirror - a mirror with flexible surface that can adjust the shape of the welding beam. The
mirror is regulated by a feedback control loop so that the focus of the laser beam and the penetration depth
remain in an optimal range. Since the only possibility to state the penetration depth is to monitor outer effects
to estimate desired parameters. a sensor unit is used to monitor the optical emissions of the plasma vapors
and the measured data are inputs to an algorithm that estimates the penetration depth. We have done several
experiments that study the relation of the adaptive mirror focus and the laser beam shape and how it influences
the penetration depth. The estimation results are compared with material samples from test welds. On the basis
of these experiments, a preliminary version of a control system was developed and a tested. The tests has shown
that the implementation of the control system has positive influence on the quality of the resulting weld.
Frequency doubled Nd:YAG lasers are often the option with stabilization to the saturated absorption in molecular iodine
featuring good signal-to-noise ratio at the 532 nm. Purity of iodine in the absorption cell is one of the most important
factor how to achieve results in optical frequencies corresponding to theoretical values. We present results of
measurement of purity of sets of iodine cells made at our institute. The purity was tested by improved method based on
measurement of induced fluorescence and evaluation by the
Stern-Volmer formula. Frequency-doubled Nd:YAG lasers
stabilized with these cells were compared to evaluate their frequency shifts. The absolute frequencies of selected iodine
hyperfine transitions were measured in direct laser frequency comparison with the reproducibility well below the kHz
level. The results indicating the iodine cell purity are presented with relation to the absolute frequency shifts. This not
only highlights the influence of iodine cell quality onto the stability and absolute frequency of lasers etalons but also
shows the way towards improvements of the iodine cell manufacturing technology.
We present methods of improvement of wavelength stability and tuneability of semiconductor laser diodes in fiber laser interferometers by fiber Bragg gratings (FBGs). We developed simulation method to calculation of arbitrary fiber grating (apodized, chirp etc.) with high precision by combination of methods based on layered dielectric media (LDM) and transfer matrix. On the basis of our simulations and measurements of the commercially available fiber gratings we designed a special 100 mm long fiber Bragg grating with apodization. We expect the application of the FBG to improvement of the linewidth and mode-hop free tuning range of semiconductor lasers at the wavelength 760 nm to increase resolution of fiber laser interferometer based on these diodes. We built the absolute fiber laser interferometer with Vertical Cavity Surface Emitting Laser (VCSEL) to easy employ FBG to stabilize wavelength and control the tuning range. First set up is presented.
We present results of measurement of purity of a set of iodine cells made at our institute. The purity was tested by
improved method based on measurement of induced fluorescence and evaluation by the Stern-Volmer formula. The
reproducibility of the fluorescence detection system was improved by introducing of additional compensation for the
pumping laser spectral and power instabilities. Frequency-doubled Nd:YAG lasers stabilized with these cells were
compared to evaluate their frequency shifts. The absolute frequencies of selected iodine hyperfine transitions were
measured in direct laser frequency comparison with the reproducibility well below the kHz level. The results indicating
the iodine cell purity are presented with relation to the absolute frequency shifts. This not only highlights the influence of
iodine cell quality onto the stability and absolute frequency of laser etalons but also shows the way towards
improvements of the iodine cell manufacturing technology.
We present an improved technique for detection of trace impurities in iodine-filled absorption cells for laser frequency
stabilization. The results of purity investigation are compared to frequency shifts measured with a set of two iodine
stabilized Nd:YAG lasers. The setup for direct fluorescence measurement with an Argon-ion laser operating at 502 nm
wavelength is equipped with compensation for laser power and spectral instabilities.
KEYWORDS: Iodine cells, Iodine, Nd:YAG lasers, Luminescence, Laser stabilization, Signal detection, Absorption, Photodetectors, Modulation, Signal to noise ratio
We present an improved technique for detection of trace impurities in iodine-filled absorption cells for laser frequency
stabilization. The results of purity investigation are compared to frequency shifts measured with a set of two iodine
stabilized Nd:YAG lasers. The setup for direct fluorescence measurement with an Argon-ion laser operating at 502 nm
wavelength is equipped with compensation for laser power and spectral instabilities.
In the contribution we present a system for measurement of iodine purity by means excitation of a selected strong
transition, measurement of induced fluorescence and evaluation by the Stern-Volmer formula. The arrangement is based
on a pumping Ar-ion laser tuned to the transition of interest but its linewidth far exceeds the transition. Frequency noise
of the laser is effectivelly reduced by monitoring the fluorescence in a second, reference iodine cell and together with
monitoring of the laser power enables cancelation of the frequency noise influence which generates errors by
demodulating on the absorption profile. The level of the scattered light is subtracted as well. All the measured data are
digitally processed and the experiment is fully computer controlled.
KEYWORDS: Absorption, Semiconductor lasers, Laser stabilization, Pulsed laser operation, Iodine, Modulation, Laser systems engineering, Signal detection, Digital signal processing, Oscillators
We present a fully digital stabilized semiconductor laser system designed to operate as a fiber-optic front-end o
a pulsed power laser PALS (Prague Asterix Laser System). With an operating wavelength of 1315.15 nm the
stabilized laser is based on a telecommunication single-frequency DFB (Distributed FeedBack) diode. The lines
are detected by means of linear absorption in a heated cell filled with thermally dissociated iodine. The detection
scheme is based on a derivative spectroscopy with a current frequency modulation and thermal wavelength
control. The detection chain together with stabilization servo loop is fully digital represented by signal-processing
single-chip controllers. The operation of the controllers can be monitored by PC via CAN (Control Area Network)
bus. The algorithm of the absorption spectrum scanning, line selection and locking makes it possible to operate
the laser in a maintenance-free regime, monitored only by a "ready" signal from a control panel of the PALS.
Mechanical construction of the fiber absolute laser interferometer is presented in this article. The unique system is based on the VCSEL laser diode (wavelength 760 nm) and uses single-mode fibers. Optical setup consists of new E2000/APC connectors and fiber optic isolator to minimize the back-reflection to the laser diode. The whole system is placed on the massive duralumin plate to minimize mechanical influences. Base plate is placed on the rack with control electronics to create compact unit. The whole system is developed for industrial applications.
In the contribution we present briefly the manufacturing technology of the cells and the filling process and an
experimental attempt to determine the iodine purity of the finished and sealed cell by an independent method. The data
from manufacturing of a first sample cell are compared with the purity measurement and also with measurement of the
absolute optical frequency of laser stabilized to hyperfine transitions in iodine in this sample cell. The main goal of this
effort is to recognize the limits of the absolute precision of the optical frequency of iodine transitions and look for
further improvements in the iodine cell manufacturing technology that may lead to even smaller frequency shifts.
We present a fully digital stabilized semiconductor laser system designed to operate as a fiber-optic front-end of a pulsed power laser PALS (Prague Asterix Laser System). The replacement of the PALS master oscillator is a part of a broader effort to rebuild PLAS into a laser generating shorter pulses with higher pulse power by the technique of optical parametric chirped pulse amplification. With an operating wavelength of 1315.15 nm the stabilized laser is based on a telecommunication single-frequency DFB diode. The frequency stabilization is derived from the same transitions in dissociated iodine as those employed in the following power amplifiers. The lines are detected by means of linear absorption in a heated cell filled with thermally dissociated iodine. The technique of laser frequency stabilization folows the demands of a fully automated self-contained system operated by a remote control. The detection scheme is based on a derivative spectroscopy with a current frequency modulation and thermal wavelength control. The detection chain together with stabilization servo loop is fully digital represented by two signal-processing single-chip controllers.
We present an experimental arrangement for the investigation of the spectra of a iodine in the spectral region around 1315 nm. The work was motivated by the need to assemble a stabilized laser system emitting at the wavelength matching with the transition used in iodine laser optical amplifiers where the laser frequency stability
is limited by the linewidth of this 2P1/2-2P3/2 hyperfine transition. This stabilized laser system followed by an electro-optic Q-switch and fibre-optic preemplifiers will serve as a master oscillator for a pulsed high-power laser Asterix IV in the PALS facility.
Laser diodes became the most widespread lasers and now are available in a broad spectrum of wavelengths ranging from infrared to the visible region. The low power ones mainly those with the quantum well structure and gain or index guided configuration perform a narrow linewidth and soon became a favourite tool for interferometry and spectroscopy. The need for continuous tuning range led to the development Extended Cavity Laser systems (ECL) and Vertical Cavity Surface Emitting Lasers (VCSEL). Both systems seem to be promising laser sources for design of optical frequency standards or interferometric distance measurement devices. We present design of these laser systems and their applications in metrology of length.
We present the design of several types of extended-cavity lasers (ECL) based on the Littman1 configuration and an arrangement for an external stabilizating scheme employing Doppler-free saturation spectroscopy in the molecular iodine. The ECLs followed the requirements of metrological applications where the stress has been put to mechanical stability, thermal control, narrow linewidth and a mode-hop free tuning range. We developed the technique of antireflection coatings of the laser diodes front facets which proved to be a crucial step towards the internal cavity suppression and propper operation of the ECL. To control the laser optical frequency an electronics consisting of a precise thermal control and a current source with a protective circuitry was designed.
We present a tunable extended-cavity semiconductor laser system based on the Littman configuration emitting in the visible region of spectra with the wavelength close to the 633 nm of He-Ne lasers. It has been frequency stabilized to Doppler free hyperfine transmission in molecular iodine. The stability was measured compared to the reference He-Ne-I2 laser system, the present most commonly used laser primary standard. While the semiconductor laser was locked on components of the P(33) 6-3 transmission close enough to the reference R(127) 11-5 line to arrange a beat frequency counting. A relative stability of 4 by 10-12 over a 100 s integration time was achieved. The laser configuration allowed a mode-hop free tuning over a range including a group of strong overlapping transitions R(60) 8-4, R(125) 9- 4 and P(54) 8-4 with higher signal-to-noise ratio.
For a fundamental etalon of optical frequency based on the external-cavity semiconductor laser (ECL), not only the long-term frequency stability but also the linewidth seems to be an important parameter. The linewidth broadening is dominated by fluctuations of the optical frequency. Parameters of these fluctuations and their spectral characteristics are crucial information for their suppression. We present an experimental setup for the frequency noise measurements designed for a free running 633 nm ECL with a stabilized reference He-Ne laser. We observed the corner frequency of the 1/f noise of the ECL of approximately 10 MHz. No significant spectral components over the 1/f noise corner frequency were found.
In this article we describe a system which enables creation of several optical traps by splitting the laser beam in two parts and by using an acoustooptical deflector in one of these parts. This system is combined with a UV pulse laser so that a complex apparatus for optical trapping and cutting is obtained. Movable lenses ensure independent 3D positioning of a beam focus of the trapping and cutting beam without power losses at the back objective aperture. We present several applications of this system.
This contribution presents a design of the circuitry for operation of a high stability and high coherence laser diode emitting in the visible region of spectra. The laser diode is used in a laser system with an external cavity with a large mode-hop free tuning range. This system can be used in spectroscopic and interferometric applications. The laser diode instrumentation consists of a low noise and high stability current source, high frequency modulation circuitry and electromagnetic interference protection. Special attention is paid to the protection against fast transients induced from the outside or generated by switching leading to the degradation of the laser diode active channel or its damage. Details concerning stability, noise and interference shielding are presented.
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