Laser Calibration Research Articles

The Fermilab Muon g-2 experiment: laser calibration system

The anomalous muon dipole magnetic moment can be measured (and calculated) with great precision thus providing insight on the Standard Model and new physics. Currently an experiment is under construction at Fermilab (U.S.A.) which is expected to measure the anomalous muon dipole magnetic moment with unprecedented precision. One of the improvements with respect to the previous experiments is expected to come from the laser calibration system which has been designed and constructed by the Italian part of the collaboration (INFN). An emphasis of this paper will be on the calibration system that is in the final stages of construction as well as the experiment which is expected to start data taking this year.

Geometric contributions to chopper wheel optical attenuation uncertainty

Calibrated optical choppers are used in high-power laser calibration services at the National Institute of Standards and Technology for beam power reduction due to their advantages in performance and safety over wedges and semi-transparent materials. While the design, operation, and calibration of such choppers is generally straightforward, fabrication tolerances and edge geometry must be taken into account for low transmission (<5%) choppers now required to accommodate the increased powers (upwards of 10 kW) available for the calibration service. The slit edge is presented to the beam at non-zero angles of incidence and for edge thicknesses on order of 10% of the slit width, the relative error from design transmission can exceed 2% (depending on beam diameter and angle of incidence). Both slit edge presentation at non-zero angles of incidence and displacement of the slit edges due to minor variation in fabrication or coating yield significant changes in transmission with radial displacement of the beam over the chopper face. While diffraction effects play a smaller role under typical setup conditions, they become an appreciable factor for detectors having small entrance apertures or located far from the chopper wheel. Here we demonstrate a close agreement between the calculated and measured transmission ratio for two optical choppers when considering these three effects.

The Laser Control System for a Calibration Facility of a Light-Based Detector

Laser calibration facilities play a key role in the study and characterization of detectors like electromagnetic or hadronic calorimeters. They can be operated both during physics data taking and off runs. Typically, these facilities are based on a laser source which delivers light to each detector element via a light distribution system. The laser control (LC) system typically manages the interface between the experiment and the laser source, allowing the generation of light pulses according to specific needs such as detector calibration, study of detector performance in running conditions, and evaluation of data acquisition performance. Any specific implementation depends on hardware features. As an example, light pulses could be generated according to a physics distribution during physics runs or real data taking. In this case, light pulses should be generated according to a pattern that follows a programmable function and changes on a statistical base event by event. In this paper, we present a LC system for calibration of a calorimeter. It is a custom solution based on a hybrid platform hosting a field-programmable gate array and an ARM processor. We present the system architecture and the performances of a preliminary implementation. This system, in a more specific and specialized version, will be used in the Muon g-2 experiment (E989) at Fermilab.

Geant4 simulations of the lead fluoride calorimeter

In this paper we simulate the charged particle interaction with complex structures, including the emission, with help of Geant4. We take into account Cherenkov radiation, transition radiation, bremsstrahlung, pair production and other accompanying processes. As an application we investigate the full size electromagnetic calorimeter for the muon g-2 experiment at Fermilab. A calorimeter module consists of a Delrin front panel for installation of the laser calibration system, 54 PbF2 Cherenkov crystals wrapped by black Tedlar paper, and silicon photo-multiplier sensors. We report here on results of a simulation of the radiation from positrons striking the calorimeter system. The Cherenkov radiation expansion when a positron moves down through the calorimeter at the arbitrary angle of incidence has been considered. Both spectral and angular distributions of Cherenkov optical photons in different parts of the calorimeter system was evaluated as well as the transition radiation and pre-shower distributions from both the Delrin panel and the Al vacuum chamber of the g-2 storage ring.

The laser calibration system of the TOP detector

The TOP detector of the Belle II Experiment at KEK is a particle identification detector, devoted mainly to the separation of charged pions and kaons. The Cherenkov photons produced in fused silica bars are detected by an array of micro-cannel plate photomultipliers, and the position and time of arrival of the photoelectrons are used to identify the particle. In order to achieve a time resolution of less than 100ps, the performance of electronics and PMTs must be continuously monitored by a high resolution laser calibration system. Here we report about the design, characterization, construction and installation of this light distribution system consisting of a picosecond laser source, a printed light circuit (PLC), long single mode fibers coupled to bundles of multimode fibers terminated with graded index microlenses, to provide illumination of all the PMT pixels with time jitter less than 50ps.

Wavelength calibration of narrowband ArF laser with iron hollow cathode lamp

Accurate and precise wavelength controlling of narrowband excimer lasers is essential for the lithography of an integrated circuit. High-precision wavelength tuning and calibration of a line-narrowed ArF laser are presented in this work. The laser spectrum is narrowed to a sub-picometer with a line narrowing system. Absolute wavelength calibration of the line-narrowed laser is performed based on the optogalvanic (OG) effect using iron hollow cathode discharge (HCD). An sccuracy of better than 0.1 pm for wavelength tuning and calibration is achieved with our homemade wavemeter.

The Laser calibration of the ATLAS Tile Calorimeter during the LHC run 1

This article describes the Laser calibration system of the ATLAS hadronic Tile Calorimeter that has been used during the run 1 of the LHC . First, the stability of the system associated readout electronics is studied. It is found to be stable with variations smaller than 0.6 %. Then, the method developed to compute the calibration constants, to correct for the variations of the gain of the calorimeter photomultipliers, is described. These constants were determined with a statistical uncertainty of 0.3 % and a systematic uncertainty of 0.2 % for the central part of the calorimeter and 0.5 % for the end-caps. Finally, the detection and correction of timing mis-configuration of the Tile Calorimeter using the Laser system are also presented.

High-precision radius measurement of ball indenter

Abstract To solve the problem of calibrating the radius of a ball indenter in a hardness tester, a laser confocal radius measurement and calibration method for the ball indenter is proposed without separating the ball from the body of the indenter. The laser confocal radius measurement and calibration method uses the maximum of the confocal axial intensity curve to precisely identify the cat’s eye and confocal position of the test ball indenter. The distance between these two positions is then measured to achieve high-precision radius measurement. The theoretical analyses and experimental results indicate that the radius measurement uncertainty of the ball indenter with a diameter of 1.5875 mm is within 0.12 μm.

Effect of the Femtosecond Laser on an Intracorneal Inlay for Surgical Compensation of Presbyopia during Cataract Surgery: Scanning Electron Microscope Imaging

ABSTRACTPurpose: To investigate the effect of the femtosecond laser-assisted cataract surgery (FLACS) on porcine eyes implanted with a Kamra corneal inlay and to describe how the inlay may change the effect of the femtosecond laser on the lens.Methods: FLACS was performed on six porcine eyes and a Kamra corneal inlay had been implanted, exploring the lens under the surgical microscope. Another Kamra corneal inlay was attached to the upper part of the transparent hemisphere used for calibration of the femtosecond laser. Capsulorhexis, arcuate incisions, and phacofragmentation were carried out. The Kamra corneal inlay was compared with a nontreated one using a scanning electron microscope (SEM), and the hemisphere was analyzed with a surgical microscope.Results: Capsulorhexis and phacofragmentation were completed in all the porcine eyes, although accuracy to determine the exact effect on the lens was not possible to achieve. The effect of the femtosecond laser on the PMMA hemisphere through the Kamra corneal inlay showed the capsulorhexis was placed outside the outer margin of the inlay and a sharply sculpted fragmentation pattern with a three-dimensional (donut-shaped) annulus untreated beneath it. SEM images of the nontreated and the treated inlays were comparable. No ultrastructural changes were found in the treated Kamra corneal inlay.Conclusions: FLACS can be performed with a Kamra corneal inlay for surgical compensation of presbyopia without the risk of damaging the inlay. The Kamra corneal inlay acts as a screen that avoids the laser to reach the areas beneath its shadow, but not the exposed areas of the lens.

ON-LINE WAVELENGTH CALIBRATION OF PULSED LASER FOR CO2 DIFFERENTIAL ABSORPTION LIDAR

Abstract. Differential absorption lidar (DIAL) remote sensing is a promising technology for atmospheric CO2 detection. However, stringent wavelength accuracy and stability are required in DIAL system. Accurate on-line wavelength calibration is a crucial procedure for retrieving atmospheric CO2 concentration using the DIAL, particularly when pulsed lasers are adopted in the system. Large fluctuations in the intensities of a pulsed laser pose a great challenge for accurate on-line wavelength calibration. In this paper, a wavelength calibration strategy based on multi-wavelength scanning (MWS) was proposed for accurate on-line wavelength calibration of a pulsed laser for CO2 detection. The MWS conducted segmented sampling across the CO2 absorption line with appropriate number of points and range of widths by using a tunable laser. Complete absorption line of CO2 can be obtained through a curve fitting. Then, the on-line wavelength can be easily found at the peak of the absorption line. Furthermore, another algorithm called the energy matching was introduced in the MWS to eliminate the backlash error of tunable lasers during the process of on-line wavelength calibration. Finally, a series of tests was conducted to elevate the calibration precision of MWS. Analysis of tests demonstrated that the MWS proposed in this paper could calibrate the on-line wavelength of pulsed laser accurately and steadily.

ON-LINE WAVELENGTH CALIBRATION OF PULSED LASER FOR CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; DIFFERENTIAL ABSORPTION LIDAR

Differential absorption lidar (DIAL) remote sensing is a promising technology for atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; detection. However, stringent wavelength accuracy and stability are required in DIAL system. Accurate on-line wavelength calibration is a crucial procedure for retrieving atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; concentration using the DIAL, particularly when pulsed lasers are adopted in the system. Large fluctuations in the intensities of a pulsed laser pose a great challenge for accurate on-line wavelength calibration. In this paper, a wavelength calibration strategy based on multi-wavelength scanning (MWS) was proposed for accurate on-line wavelength calibration of a pulsed laser for CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; detection. The MWS conducted segmented sampling across the CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; absorption line with appropriate number of points and range of widths by using a tunable laser. Complete absorption line of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; can be obtained through a curve fitting. Then, the on-line wavelength can be easily found at the peak of the absorption line. Furthermore, another algorithm called the energy matching was introduced in the MWS to eliminate the backlash error of tunable lasers during the process of on-line wavelength calibration. Finally, a series of tests was conducted to elevate the calibration precision of MWS. Analysis of tests demonstrated that the MWS proposed in this paper could calibrate the on-line wavelength of pulsed laser accurately and steadily.

HYBRID ONLINE MOBILE LASER SCANNER CALIBRATION THROUGH IMAGE ALIGNMENT BY MUTUAL INFORMATION

Abstract. This paper proposes an hybrid online calibration method for a laser scanner mounted on a mobile platform also equipped with an imaging system. The method relies on finding the calibration parameters that best align the acquired points cloud to the images. The quality of this intermodal alignment is measured by Mutual information between image luminance and points reflectance. The main advantage and motivation is ensuring pixel accurate alignment of images and point clouds acquired simultaneously, but it is also much more flexible than traditional laser calibration methods.

HYBRID ONLINE MOBILE LASER SCANNER CALIBRATION THROUGH IMAGE ALIGNMENT BY MUTUAL INFORMATION

This paper proposes an hybrid online calibration method for a laser scanner mounted on a mobile platform also equipped with an imaging system. The method relies on finding the calibration parameters that best align the acquired points cloud to the images. The quality of this intermodal alignment is measured by Mutual information between image luminance and points reflectance. The main advantage and motivation is ensuring pixel accurate alignment of images and point clouds acquired simultaneously, but it is also much more flexible than traditional laser calibration methods.

Investigation of the accuracy of MV radiation isocentre calculations in the Elekta cone-beam CT software XVI

Accurate determination of the megavoltage (MV) radiation isocentre of a linear accelerator (linac) is an important task in radiotherapy. The localization of the MV radiation isocentre is crucial for correct calibration of the in-room lasers and the cone-beam CT scanner used for patient positioning prior to treatment. Linac manufacturers offer tools for MV radiation isocentre localization. As a user, there is no access to the documentation for the underlying method and calculation algorithm used in the commercial software. The idea of this work was to evaluate the accuracy of the software tool for MV radiation isocentre calculation as delivered by Elekta using independent software.The image acquisition was based on the scheme designed by the manufacturer. Eight MV images were acquired in each series of a ball-bearing (BB) phantom attached to the treatment couch. The images were recorded at cardinal angles of the gantry using the electronic portal imaging device (EPID). Eight Elekta linacs with three different types of multileaf collimators (MLCs) were included in the test. The influence of MLC orientation, x-ray energy, and phantom modifications were examined. The acquired images were analysed using the Elekta x-ray volume imaging (XVI) software and in-house developed (IHD) MATLAB code.Results from the two different software were compared. A discrepancy in the longitudinal direction of the isocentre localization was found averaging 0.23 mm up to a maximum of 0.75 mm. The MLC orientation or the phantom asymmetry in the longitudinal direction do not appear to cause the discrepancy.The main cause of the differences could not be clearly identified. However, it is our opinion that the commercial software delivered by the linac manufacturer should be improved to reach better stability and precise results in the MV radiation isocentre calculations.

Upgrade of the Laser calibration system for the ATLAS hadronic calorimeter TileCal

We present in this contribution the new system for Laser calibration of the ATLAS hadronic calorimeter TileCal. The Laser system is a part of the three stage calibration apparatus designed to compute the calibration factors of the individual cells of TileCal. The Laser system is mainly used to correct for short term drifts of the readout of the individual cells. A sub-percent accuracy in the control of the calibration factors is required. To achieve this goal in the LHC Run2 conditions, a new Laser system was designed. The architecture of the system is described with details on the new optical line used to distribute Laser pulses in each individual detector module and on the new electronics used to drive the Laser, to read out optical monitors and to interface the system with the ATLAS readout, trigger and slow control. The LaserII system has been fully integrated into the framework used for measuring calibration factors and for monitoring data quality. First results on the Laser system performances studied are presented.

Wavelet modulus maxima method for on-line wavelength location of pulsed lidar in CO_2 differential absorption lidar detection

Differential absorption lidar (DIAL) is an excellent technology for atmospheric CO2 detection. However, the accuracy and stability of a transmitted on-line wavelength are strictly required in a DIAL system. The fluctuation of a tunable pulsed laser system is relatively more serious than that of other laser sources, and this condition leads to a large measurement error for the lidar signal. These concerns pose a significant challenge in on-line wavelength calibration. This study proposes an alternative method based on wavelet modulus maxima for the accurate on-line wavelength calibration of a pulsed laser. Because of the different propagation characteristics of the wavelet transform modulus maxima between signal and noise, the singularities of a signal can be obtained by detection of the local modulus maxima in the wavelet transform maximum at fine scales. Simulated analysis shows that the method is more accurate than the general method such as quintic polynomial fitting and can steadily maintain high calibration precision at different signal-to-noise ratios (SNRs). Last, 16 groups of real experiments were conducted to verify the simulated analysis, which shows that the proposed method is an alternative for accurately calibrating an on-line wavelength. In addition, the proposed method is able to suppress noises in the process of wavelength calibration, which gives it an advantage in accurate on-line wavelength calibration with a low SNR.

Real-time dynamic calibration of a tunable frequency laser source using a Fabry-Pérot interferometer.

We report on a method for real-time dynamic calibration of a tunable external cavity diode laser by using a partially mode-matched plano-concave Fabry-Pérot interferometer in reflection geometry. Wide range laser frequency scanning is carried out by piezo-driven tilting of a diffractive grating playing the role of a frequency selective mirror in the laser cavity. The grating tilting system has a considerable mechanical inertness, so static laser frequency calibration leads to false results. The proposed real-time dynamic calibration based on the identification of primary- and Gouy-effect type secondary interference peaks with known frequency and temporal history can be used for a wide scanning range (from 0.2 GHz to more than 1 GHz). A concave spherical mirror with a radius of R = 100 cm and a plain 1% transmitting mirror was used as a Fabry-Pérot interferometer with various resonator lengths to investigate and demonstrate real-time calibration procedures for two kinds of laser frequency scanning functions.

The calibration system of the new g−2 experiment at Fermilab

The muon anomaly (g−2)μ/2 has been measured to 0.54 parts per million by E821 experiment at Brookhaven National Laboratory, and at present there is a 3–4 standard-deviation difference between the Standard Model prediction and the experimental value. A new muon g−2 experiment, E989, is being prepared at Fermilab that will improve the experimental error by a factor of four to clarify this difference. A central component to reach this fourfold improvement in accuracy is the high-precision laser calibration system which should monitor the gain fluctuations of the calorimeter photodetectors at 0.04% accuracy.

Investigating the ocular temperature rise during femtosecond laser lens fragmentation: an in vitro study.

To investigate the trend of temperature variation during lens fragmentation simulated by a femtosecond laser on an in vitro eye model. In our experimental study, a convex cylinder of gelatinous material, usually employed in femtosecond laser calibration, was used to simulate both an anterior segment and a crystalline lens during fragmentation performed with the Victus femtosecond laser (Technolas Perfect Vision GmbH, Germany; Bausch + Lomb Incorporated, USA). Two radiated energies (7000 nJ and 9000 nJ) and three cutting patterns (crosses, circles and cross + circle) were applied. Trends of temperature variation as a function of time were obtained using a T-type thermocouple. The maximum value of temperature rise during lens fragmentation ranged from 3.53 to 5.13°C; the rise was directly proportional to the intensity of the radiated energy (7000 nJ or 9000 nJ) and the cutting pattern performed. This behavior was experimentally represented by an asymmetric function with a characteristic bell curve shape, whereas it was mathematically described by a transport diffusive model. Since the temperature rise at the fragmentation volume base resulted to be around 5°C in our in vitro study, lens fragmentation performed using the Victus femtosecond laser might be considered safe form a thermal point of view.

Analytical/Numerical Modelling of Two Parallel Robots as Laser Calibration Instruments Controlled by Classical/Intelligent Schemes

Analytical/Numerical Modelling of Two Parallel Robots as Laser Calibration Instruments Controlled by Classical/Intelligent Schemes