Laser Calibration Research Articles

Test of candidate light distributors for the muon [formula omitted] laser calibration system

The new muon (g−2) experiment E989 at Fermilab will be equipped with a laser calibration system for all the 1296 channels of the calorimeters. An integrating sphere and an alternative system based on an engineered diffuser have been considered as possible light distributors for the experiment. We present here a detailed comparison of the two based on temporal response, spatial uniformity, transmittance and time stability.

On-line wavelength calibration of pulsed laser for CO2 DIAL sensing

Accurate on-line wavelength calibration is a crucial procedure for sensing atmospheric CO2 using the DIAL technique. Drastic fluctuations in the intensity of a pulsed laser pose a great challenge for accurate on-line wavelength determination and stabilization, resulting in CO2 retrievals lacking the desired accuracy for global climate change and carbon cycle research. To tackle this problem, a two-stage wavelength calibration method based on Voigt fitting was proposed in this work. Simulation analysis demonstrated that the proposed method is superior to the conventional method and provides wavelength calibration results with an accuracy of 0.1 pm when the noise level does not exceed than 5 %. This conclusion was confirmed through experiments with real signals. Furthermore, simulation analysis revealed that the proposed method could yield results with an accuracy of 0.1 pm by increasing the number of sample points, even for signals with noise levels of up to 20 %. This is a promising feature that could facilitate the development of DIAL systems without gas cells.

Performance of a fire detector based on a compact laser spectroscopic carbon monoxide sensor.

In this paper we show the suitability of a miniaturized tunable diode laser spectroscopy (TDLS)-based carbon-monoxide (CO) sensor for fire detection applications. The sensor utilizes a vertical-cavity surface-emitting laser (VCSEL) and inherent calibration scheme with reference gas filled in the photodetector housing. The fire-detection experiments are carried out under realistic conditions as described in the European standard EN54. The CO generation of all class C fires (according to EN54) could be well resolved. The cross-sensitivity to other substances was found to be very low: the maximum CO false response from cigarette smoke, hairspray and general aerosols reaches a low value of a few μL/L and only if the substance is directly applied into the sensor gas inlet. Therefore this sensor overcomes the disadvantage of high false alarm rate given by smoke detectors and is also in small size which is suitable for household and industrial applications. Hence, the VCSEL-based TDLS sensor is shown to have sufficient performance for fire-detection. It has advantages such as capability for fail-safe operation and, low cross-sensitivities as compared to existing point fire detector technology which is presently limited by these factors.

ONE STEP MOBILE MAPPING LASER AND CAMERA DATA ORIENTATION AND CALIBRATION

Abstract. Modern mobile mapping systems include one or several laser scanners and cameras. The main outputs of these systems are oriented camera images and 3D point clouds. These point clouds can be derived from pairs of overlapping images or using the laser raw data together with platform trajectory. A mobile mapping campaign may include several overlapping areas, generally, the derived point clouds of the same area are not properly registered, due to partial or total GNSS occlusions, multipath and inertial drift and noise. Nowadays, the standard procedure for co-registration between laser and laser and between camera and laser, includes several steps. The first ones are the system calibration where the lever arm and boresight between laser and IMU, and between camera and IMU must be determined. After the calibration steps, a camera and LiDAR point cloud can be derived. Then, a co-registration between LIDAR points clouds and between camera point cloud and LiDAR point cloud are computed. In contrast to the standard approach, in this paper we propose to solve the orientation and calibration of laser and camera data in a single, combined adjustment. Solving the orientation and calibration allows us to implicitly deal with the co-registration problem. The proposed method is based on the identification of common tie features between images and point clouds and their use in a combined adjustment. This common tie features are straight line segments. The preliminary results indicate the feasibility and the potential of the approach.

Improvement on Infrared Imaging Video Bolometer by Laser Calibration Method

Improvement on Infrared Imaging Video Bolometer by Laser Calibration Method

Functional Evaluation and Performance Improvement of a Gantry IR’s NC Axes

The paper presents main results obtained from experimental works performed for functional performances evaluation of a gantry robot, used for ultrasonic flaw detection (NDT Automation standard-duty ULTRA PAC Ultrasonic immersion model). The functional status of the robot has been evaluated by mean of a RENISHAW LASER ML 10 interferometer measuring system, from the point of view of positioning accuracy and repeatability in position as well as geometric errors of each gantry IR's NC axes. The research stages are referring to: individual NC axis functional evaluation (experimental determination of IRs X, Y, and Z axis positioning accuracy and repeatability in position), overall IRs NC axes functional evaluation (identifying of the partially geometric errors induced by inaccurate mounting of IRs joints / links or inappropriate technical solutions adopted for assembling different structural elements / joints of the studied gantry robot), as well as IRs X NC axis functional improvement (X NC axis positioning accuracy optimization) by mean of software errors compensation. The experimental setup included the analyzed gantry robot and the laser calibration system associated with different mountings of the laser measurement optics system (interferometers linear reflectors) for each measurement procedure. The final results and conclusions relieve means to functionally improve both, individual NC axes' as well as overall IRs performances.

Calibration of a planar laser induced fluorescence technique for use in large scale water facilities

A calibration process for planar laser induced fluorescence (PLIF) is presented and employed to investigate the mixing field of a co-flowing jet in a water channel flow. The calibration technique uses individual calibration curves for each pixel in the image array that correct for the non-uniformities of the laser sheet, optics and digital sensor and account for parameters that affect fluorescence efficiency of the dye. A unique commercial optic is introduced into the optical train to generate a thin laser sheet with an approximately uniform laser intensity distribution. The performance of the calibration procedure is investigated by analysis of the calibration data and through the investigation of a co-flowing jet. The results compare well with the results documented in the literature for this flow field. The work shows that the simple approach designed specifically for application in large-scale facilities is suitable for calibration of PLIF style techniques.

Simulation of space-charge effects in an ungated GEM-based TPC

A fundamental limit to the application of Time Projection Chambers (TPCs) in high-rate experiments is the accumulation of slowly drifting ions in the active gas volume, which compromises the homogeneity of the drift field and hence the detector resolution. Conventionally, this problem is overcome by the use of ion-gating structures. This method, however, introduces large dead times and restricts trigger rates to a few hundred per second. The ion gate can be eliminated from the setup by the use of Gas Electron Multiplier (GEM) foils for gas amplification, which intrinsically suppress the backflow of ions. This makes the continuous operation of a TPC at high rates feasible.In this work, Monte Carlo simulations of the buildup of ion space charge in a GEM-based TPC and the correction of the resulting drift distortions are discussed, based on realistic numbers for the ion backflow in a triple-GEM amplification stack. A TPC in the future p¯anda experiment at FAIR serves as an example for the experimental environment. The simulations show that space charge densities up to 65fCcm−3 are reached, leading to electron drift distortions of up to 10mm. The application of a laser calibration system to correct these distortions is investigated. Based on full simulations of the detector physics and response, we show that it is possible to correct for the drift distortions and to maintain the good momentum resolution of the GEM-TPC.

Stepping robotic system based on cellular grid map

In order to meet the demand of providing varieties of physical services in the intelligent space, this paper designed and implemented a stepping robotic system based on cellular grid map, from both hardware implementation and software algorithm aspects. In the hardware aspect, the paper designed and implemented an omni-directional wheels structure and the mobile platform, stepping robot driving system and sensing detection system. Among them, the designing of the mechanical structure of the entire stepping robot body has greatly improved the effectiveness and reliability of the hardware system. The major innovative work includes analysing and modelling the omni-directional mobile platform with six wheels in mechanics, kinematics and dynamics, the designing and implementation of optical odometer by using FPGA to parse PS/2 protocol, and the laser calibration system. In terms of software algorithms, the paper mainly focused on four contents, consisting of multi-sensor data fusion, creating of a cellular grid map, local path planning and global path planning of the stepping robot based on the map. The main innovative work in the software algorithm includes the achievement of multi-dimensional sensor data fusion algorithm by introducing Mahalanobis distance, six-direction local path planning with the solution of the Dead Angle phenomenon and the Dead Circle phenomenon, as well as extending TSP optimisation problem based on Genetic Algorithm to the state of the cellular grid map. The issues mentioned above have been realised on the simulation platform. In the field test, the precision of the stepping robotic system can reach the millimeter scale.

Corneal stromal ablation with femtosecond ultraviolet pulses in rabbits

To determine the effectiveness of femtosecond ultraviolet (UV) pulses in ablating corneal stroma in a rabbit model and to compare the healing response between eyes treated with femtosecond UV pulses and eyes treated with standard excimer photorefractive keratectomy. Laser Research Center, Vilnius University, Vilnius, Lithuania. Experimental study. Myopic photoablation using a femtosecond UV solid-state laser system was applied to corneas of pigmented rabbits. Experiments in 16 eyes were performed for optimization of the laser system parameters (fluence, spot size, pulse repetition rate) and calibration of ablation rate. In 7 rabbits, deep femtosecond UV ablation (∼130 μm) in 1 eye and shallow ablation (∼30 μm) in the contralateral eye were performed. Nine rabbits received an approximately 30 μm ablation with femtosecond UV pulses in 1 eye and with a conventional excimer system in the contralateral eye. Two eyes were used as controls. The ablation process and surface-temperature dynamics were monitored and recorded. Surface quality and haze development were evaluated. Rabbits were humanely killed 0 to 6 months after surgery, and eyes were enucleated for histological examination. Rabbit corneas ablated with femtosecond UV pulses or excimer laser radiation were similar in terms of the corneal wound-healing process, surface quality, and histology. The experiments indicate the feasibility of clinical application of femtosecond UV lasers for stromal ablation. The ability to switch between laser harmonics allows fast changeover from infrared to the UV mode, implying that a wide range of ophthalmic procedures can be performed using a single solid-state laser device. Ms. Gabryte and Mr. Danielius are paid employees of Light Conversion Ltd. Mr. Danielius is a shareholder of Light Conversion Ltd. No other author has a financial or proprietary interest in any material or method mentioned.

A laser calibration system for in situ dynamic characterization of temperature sensors

Dynamic calibration of temperature sensors is of crucial importance in many applications where temperature changes quickly. Response time qualification testing of sensors is usually performed by sensor manufacturers by plunge tests into flowing water. “Loop Current Step Response” (LCSR) technique, self-heating index and noise analysis techniques are the current methods used for in situ dynamic characterization of temperature sensors. The dynamic calibration technique using laser as an excitation source has been developed for many applications. Here, a portable dynamic calibration system for in situ calibration is proposed. A high brilliance laser diode heating system is used to generate both step change and ramp change in temperature so as to measure the dynamic response of the sensor. Laboratory tests performed in different environments show the reliability and the advantages of the proposed system. The laser calibration performed with the new portable device gave good results with accuracy levels in comparison with currently available techniques.

Initial Surface Temperature of PMMA Plates Used for Daily Laser Calibration Affects the Predictability of Corneal Refractive Surgery

To investigate the relevance of initial temperature of the polymethylmethacrylate (PMMA) plates used as a target for photoablation during calibration of excimer lasers performed in daily clinical routine. An experimental argon fluoride excimer laser with a repetition rate of 1050 Hz, a radiant exposure of 500 mJ/cm², and single pulse energy of 2.1 mJ was used for photoablation of PMMA plates. The initial plate temperature varied from 10.1°C to 75.7°C. The initial temperature was measured with an infrared camera and the central ablation depth of a myopic ablation of -9.00 diopters (D) with an optical zone of 6.5 mm was measured by means of a surface profiling system. The ablation depth increased linearly from 73.9 to 96.3 μm within a temperature increase from 10.1°C to 75.7°C (increase rate of 0.3192 μm/K). The linear correlation was found to be significant (P<.05) with a coefficient of determination of R²=0.95. Based on these results and assuming a standard room temperature of 20°C, optimal plate temperature was calculated to be 15°C to 25°C to maintain an ablation within 0.25 D. The temperature of PMMA plates for clinical laser calibration should be controlled ideally within a range of approximately ±5°C, to avoid visually significant refractive error due to calibration error. Further experimental investigations are required to determine the influence of different initial corneal temperatures on the refractive outcome.

WE-G-BRA-04: The Development of a Virtual Reality Dosimetry Training Platform for Physics Training.

Recently there has been a great deal of interest in the application of Simulation methodologies for training. We have previously developed a Virtual Environment for Radiotherapy Training, VERT, which simulates a fully interactive and functional Linac. Patient and plan data can be accessed across a DICOM interface, allowing the treatment process to be simulated. Here we present a newly developed range of Physics equipment, which allows the user to undertake realistic QC processes. Five devices are available: 1) scanning water phantom, 2) 'solid water' QC block/ion chamber, 3) light/ radiation field coincidence phantom, 4) laser alignment phantom and 5) water based calibration phantom with reference class and 'departmental' ion chamber. The devices were created to operate realistically and function as expected, each has an associated control screen which provides control and feedback information. The dosimetric devices respond appropriately to the beam qualities available on the Linac. Geometrical characteristics of the Linac, e.g. isocentre integrity, laser calibration and jaw calibrations can have random errors introduced in order to enable the user learn and observe fault conditions. In the calibration module appropriate factors for temperature and pressure must be set to correct for ambient, simulated, room conditions. The dosimetric devices can be used to characterise the Linac beams. Depth doses with Dmax of 15mm/29mm and d10 of 67%/77% respectively for 10cm square 6/15MV beams were measured. The Quality Indices (TPR20/10 ratios) can be measured as 0.668 and 0.761 respectively. At a simple level the tools can be used to demonstrate beam divergence or the effect of the inverse square law; They are also designed to be used to simulate the calibration of a new ion chamber. We have developed a novel set of tools that allow education of Physics processes via simulation training in our virtual environment. Both Authors are Founders and Directors of Vertual Ltd, a spin-out company that exists to commericalise the results of the research work presented in this abstract.

Performance Evaluation of Multi-Axis CNC Machine Tools by Interferometry Principle using Laser Calibration System

Advancement in digital electronics and microprocessors has made the manufacturing sector capable to generate complex components within small tolerance zone in nanometre range at one machining center. All motion control systems have some form of position feed back system fitted with the machine. But the systems are not perfectly accurate due to the errors in the positioning performance of the machine tools which will change over time to time due to wear, damage and environmental effect. The complex structure of multi-axis CNC machine tools produces an inaccuracy at the tool tip caused by kinematic parameter deviations resulting in manufacturing errors, assembly error and quasi-static errors. Analysis of these errors using a laser measurement system provides the user with a way to achieve better accuracy, and hence higher quality output from these processes. In this paper, characteristic of the positioning errors of the axes of multi-axis CNC machine tools and the technique to measure the errors by a laser interferometer calibration system have been discussed and the positioning accuracy of the machine each axis has been verified.

EXACTRACx-ray and beam isocenters-What's the difference?

To evaluate the geometric accuracy of the isocenter of an image-guidance system, as implemented in the exactrac system from brainlab, relative to the linear accelerator radiation isocenter. Subsequently to correct the x-ray isocenter of the exactrac system for any geometric discrepancies between the two isocenters. Five Varian linear accelerators all equipped with electronic imaging devices and exactrac with robotics from brainlab were evaluated. A commercially available Winston-Lutz phantom and an in-house made adjustable base were used in the setup. The electronic portal imaging device of the linear accelerators was used to acquire MV-images at various gantry angles. Stereoscopic pairs of x-ray images were acquired using the exactrac system. The deviation between the position of the external laser isocenter and the exactrac isocenter was evaluated using the commercial software of the exactrac system. In-house produced software was used to analyze the MV-images and evaluate the deviation between the external laser isocenter and the radiation isocenter of the linear accelerator. Subsequently, the deviation between the radiation isocenter and the isocenter of the exactrac system was calculated. A new method of calibrating the isocenter of the exactrac system was applied to reduce the deviations between the radiation isocenter and the exactrac isocenter. To evaluate the geometric accuracy a 3D deviation vector was calculated for each relative isocenter position. The 3D deviation between the external laser isocenter and the isocenter of the exactrac system varied from 0.21 to 0.42 mm. The 3D deviation between the external laser isocenter and the linac radiation isocenter ranged from 0.37 to 0.83 mm. The 3D deviation between the radiation isocenter and the isocenter of the exactrac system ranged from 0.31 to 1.07 mm. Using the new method of calibrating the exactrac isocenter the 3D deviation of one linac was reduced from 0.90 to 0.23 mm. The results were complicated due to routine maintenance of the linac, including laser calibration. It was necessary to repeat the measurements in order to perform the calibration of the exactrac isocenter. The deviations between the linac radiation isocenter and the exactrac isocenter were of an order that may have clinical relevance. An alternative method of calibrating the isocenter of the exactrac system was applied and reduced the deviations between the two isocenters.

A study on reliability enhancement for laser and camera calibration

The laser and camera calibration problem has been the primary issue in the subject of fusion of 3D space and 2D image information. While the solution for the calibration is mathematically well defined as closed-form by least squares techniques, reliability of the solution can be degraded by uncertainties in measurements. To enhance the reliability of calibration results, we adopted the EM (Expectation-Maximization) algorithm as a noise removal process in the sensor system. The simulation and real experimental results show the effectiveness of our approaches.

A method for temperature inversion in middle-upper atmosphere using FPI without laser calibration and its observational data preliminary analysis

In this paper we present a method, by which the temperature inversion is carried our without the calibration of the laser under the FPI observations. On the basis of 630 nm and 557.7 nm observational data are obtained by Wuhan University FPI atmospheric temperature measurement system, using the above method. The results of temperature inversion show that the method doesnot require the calibration of the laser, and can be used for FPI temperature inversion with different wavelengths.

Rapid High-Precision In Situ Wavelength Calibration for Tunable Lasers Using an Athermal AWG and a PD Array

This letter presents a simple and rapid high-precision in situ calibration technique for tunable superstructure grating distributed Bragg reflector (SSG-DBR) lasers using a laser driver board with an athermal arrayed waveguide grating (AWG) and a photodetector (PD) array. The experiment demonstrates laser calibration for seven wavelength channels completed in 23 s with a precision of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\pm$</tex> </formula> 0.015 nm. This letter describes the details of the system calibration method, the mode competition detection technique, and the calibration time analyses. The presented technique can also apply to other tunable lasers with suitable modification in the laser driver interfaces. <?Pub _bookmark="" Command="[Quick Mark]"?>

The TileCal Laser Calibration System

Abstract TileCal is the central hadronic calorimeter of the ATLAS detector operating at LHC. It is a sampling calorimeter whose active material is made of scintillating plastic tiles. Scintillation light is read by photomultipliers. A Laser system is used to monitor their gain stability. During dedicated calibration runs the Laser system sends via long optical fibers, a monitored amount of light simultaneously to all the ≈10000 photomultipliers of TileCal. This note describes two complementary methods to measure the stability of the photomultipliers gain using the Laser calibration runs. The results of validation tests are presented for both methods and theirrespective performances and limitations are discussed.

Vacuum wavelength calibration of frequency-stabilized He-Ne lasers used in commercial laser interferometers

We report on the calibration results of the wavelength of the lasers used in commercial laser interferometers, including the vacuum wavelength deviation from its nominal value, the vacuum wavelength stability, the repeatability of stabilized wavelength, and the secular change of these properties, by analyzing the calibration data accumulated for more than two decades. We present an experimental method of calibrating the frequency of laser interferometers. We also propose a proper time interval and an appropriate uncertainty expression for the vacuum wavelength calibration of the laser interferometers.