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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., 7 pages, 4 figures; SPIE Photonics Europe, 2014, Brussels, Belgium

We present an investigation of iodine cell purity and influence of contaminations upon frequency shifts of iodine-stabilized frequency-doubled Nd : YAG lasers. The study combines measurements of laser-induced fluorescence and evaluation through the Stern–Volmer formula, with direct measurement of frequency shifts referenced by means of an optical comb to a radiofrequency clock etalon. These indirect and direct approaches are compared and provide feedback on the cell manufacturing procedure. Significant improvement of the apparatus for the measurement of induced fluorescence is reported, leading to better repeatability of the results. The ultimate precision that can be achieved in measurements of the absolute frequency of a stabilized laser is discussed in terms of the cell quality. (Some figures in this article are in colour only in the electronic version)

An international comparison of eight 127I2-stabilized semiconductor laser systems (DLs) has been carried out. Five of the DLs were extended-cavity lasers (ECLs) using extra-cavity saturation spectroscopy; another was a microlens-mounted diode modified to have weak optical feedback, stabilized using the same technique; the seventh ECL was stabilized using frequency-modulated spectroscopy. The final DL was a simple laser diode at 635 nm locked with a digital system on a linear absorption of iodine. The P(33) 6-3 transition of iodine was first used to compare the first seven DLs with a He-Ne laser stabilized on the R(127) 11-5 transition of iodine. The relative frequency stability of these lasers was between 5 parts in 1011 and 7 parts in 1012 for a sampling time of 1 s, with the best results less than 2 parts in 1013 over 1000 s. The frequency repeatability measured during one week was of the order of a few tens of kilohertz. This large fluctuation was caused by poor adjustment of the electronic offset of two of the lasers. For the well-corrected lasers, the repeatability was within a few kilohertz. A study of stabilization on the strong absorption group of transitions R(60) 8-4, R(125) 9-4 and P(54) 8-4, located about -12 GHz from the R(127) 11-5 transition, was also carried out. For the first time, a short-term frequency stability better than that of the classical He-Ne laser around 633 nm has been achieved with a relative frequency stability of 4 parts in 1012 for 1 s.

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.

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 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.

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.

We present a technology of iodine cell preparation and an arrangement for the fluorescence purity investigation of the iodine following the cell manufacturing process, iodine purification and filling. The quality of the cells is evaluated by means of Stern-Vollmer formula from the fluorescence measurement and compared to direct frequency shift comparison using Nd:YAG lasers.

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 effectively reduced by monitoring the fluorescence in a second, reference iodine cell and together with monitoring of the laser power enables cancellation 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.

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.

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.

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.

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 2 P 1/2 - 2 P 3/2 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.

With the iodine-stabilized He-Ne laser at 633 nm remaining the key etalon of length and a standard for comparisons ofstabilized lasers as stated in the report of the 9th meeting of the Consultative Committee for the Definition of the Metre2there are also new optical frequencies and new laser sources being introduced into the metrological practice. The Revisionof the practical realization of the definition of the metre adopted by the by the Comite International des Poids et Mesures3recommends introduction of new standard radiations. It follows the development in laser technology and also the demandfor standardization arising from the new laser applications. Beside the Nd:YAG lasers the semiconductor lasers seem to beof growing metrological significance in these days due to their dynamic development and growing range of applications.Laser diodes became the most widespread lasers and now are available in a broad spectrum of wavelengths rangingfrom infrared to the visible region. The low power ones mainly those with the quantum well structure and gain or indexguided configuration perform a narrow linewidth and soon became a favourite tool for interferometry and spectroscopy.An effort to reduce the linewidth even further and to suppress the mode instability soon followed. The broad gain spectral

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.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We present a stabilized semiconductor laser system designed to operate as a fiber-optic front-end master oscillator of a pulsed high-power iodine laser Prague Asterix Laser System (PALS). The replacement of the PALS master oscillator is a part of a broader effort to rebuild PALS into a laser generating shorter pulses with higher pulse power by the technique of optical parametric chirped pulse amplification. With an operating wavelength of 1315.15nm the stabilized laser master oscillator is based on a telecommunication single-frequency distributed feedback diode. The frequency stabilization is derived from transitions in thermally dissociated iodine. Locking to the selected transition is fully automatic and the control system employs a unique combination of control loops derived from temperature and absorption to overcome the problem of narrow locking range of a single absorption line.

We present a tunable extended-cavity semiconductor laser, based on the Littman configuration, which has been frequency-stabilized to Doppler-free hyperfine transitions in I2. The stability was measured compared with the reference He-Ne-I2 laser system, whereas the semiconductor laser was locked on components of the P(33) 6-3 transition close enough to the reference R(127) 11-5 line to allow beat frequency counting. A relative stability of 4 x 10(-12) over a 100-s integration time was achieved. The laser configuration allowed mode-hop-free tuning over a range including the P(33) 6-3 transition and the group of strong overlapping transitions R(60) 8-4, R(125) 9-4, and P(54) 8-4 with higher signal-to-noise ratio than the P(33) 6-3 located approximately 13 GHz toward lower optical frequencies.

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.