Laser Power Measurements Research Articles

Terahertz Laser Power Measurement Comparison

A comparison of terahertz (THz) laser power measurements was undertaken among three national metrology institutes. At two laser frequencies, 2.52 THz (119 μm) and 0.762 THz (394 μm), a power level of approximately 3 mW was compared at one place at one time by means of national standard THz detectors, which had been calibrated by each participant at their own metrology institute beforehand. The measurements took advantage of the power stability and Gaussian beam profile of the THz radiation source, consisting of a molecular gas laser pumped with a line-tunable CO2 laser at the THz detector calibration facility of Physikalisch-Technische Bundesanstalt. A reference value was determined as weighted average of the measurement results with a maximum weight obtained from the arithmetic mean of the uncertainties stated by the participants. All measurement results agreed with the reference value and to each other within the stated expanded uncertainties.

A New Remote Monitoring System Application in Laser Power Based on LabVIEW

In this paper, a new remote monitoring system based on LabVIEW was proposed to measure laser power automatically and remotely. This system consists of four basic components: an DH-JG2 optical power meter, a NI-USB 6008 data acquisition card, a personal computer (PC), and HP laserJet 1020 Plus printer. Since power output of laser is generally so unstable that abnormal work situation could not retroaction to inspectors right away, new system was designed to solve this problem. The detection system realized function of remote control by TCP protocol and mobile phone. Laser power curve that is measured by detection system demonstrated that the design has a good performance in real-time detection and operability.

Sensors for Terahertz Spectroscopy and Quantum Cascade Lasers

AbstractHigh‐precision laser power measurement plays a crucial role in many laser applications, be it in the lab or in industrial settings. Only if the power of a laser can be measured precisely, the laser can be used correctly. The precise measurement of infrared lasers, for example quantum cascade lasers, and terahertz radiation used to be challenging because of a lack of adequate measurement tools. A novel measurement solution developed by Thorlabs GmbH now closes this gap. In collaboration with greenTEG AG, an ETH Zurich spin‐off, Thorlabs developed a measurement head, which detects the power in the low μW‐range independently of the wavelength of the laser. A low rise time of less than a second guarantees fast measurement results.

Formation and characterisation of copper oxide coating for absolute radiant laser power measurement absorbing cavity

The aim of this work is to optimise the different parameters for realisation of an absorbing cavity to measure the incident absolute laser energy. Electrochemical oxidation is the background process that allowed the copper blackening. A study of the blackened surface quality was undertaken using atomic force microscopy (AFM) analysis and ultraviolet-visible-infrared spectrophotometry using a Shimadzu spectrophotometer. A two-dimensional and three-dimensional microscopy of the formed oxide coating made by AFM shows that the copper surfaces became porous after electrochemical etching with different roughnesses. This aspect becomes more and more important with decreasing current density anodisation. In a 2 mol.L−1 NaOH solution at a temperature of 90°C and using a 16 mA/cm² constant density current, copper oxide formed has a reflectivity of around 5% in the spectral range between 300 nm and 1800 nm. Using 'mirage effect' technique, the obtained Cu2O diffusivity and thermal conductivity are, respectively, equal to (11.5 ± 0.5) 10−7 m2s−1 and (350 ± 20) Wm−1K−1. This allows us to consider that our Cu2O coating is a good thermal conductor. The results of optical and thermal study dictate the choice of the cavity design. The absorbing cavity is a hollow cylinder machined to its base at an angle of 30°. If the included angle of the plan is 30° and the interior surface gives specular reflection, an incoming ray parallel to the axis will undergo six reflections before exiting the device. So, the absorption of the surface becomes closely near 0.999999.

1.5 kW, near-diffraction-limited, high-efficiency, single-end-pumped all-fiber-integrated laser oscillator.

We report a monolithic single-end-pumped all-fiber laser oscillator with 1.5 kW power output operating at 1070 nm. The laser scheme design and fiber parameter selection are based on our theoretical analysis through one rate equation model consisting of changing pump wavelengths. The laser oscillator is pumped by 49 fiber-pigtailed 915 nm laser diodes with power of 50 W each through two stage combiners. The measured laser power is 1520 W at the pump power of 2054 W, and the corresponding optical-to-optical efficiency is 74%, in agreement with numerical simulation. Stimulated Raman scattering is observed when the laser power reaches 1030 W and the power ratio of Raman power is 4% at maximum output power. The experimental results show that the beam qualities represented by the M(2) factor are less than 1.2 at all pump power levels.

Focus on sensors and detectors

Focus on sensors and detectors

Laser Compensation for Ceramics Accuracy Improvement of Selective Laser Sintering

This research developed a feedback control system of laser compensation for the rapid prototyping (RP) machine using layer-wise slurry deposition and selective laser sintering (SLS). The slurry was prepared by silica power and silica sol with 60 and 40 wt.% with suitable rheological properties for 0.1 mm layer deposition. Four ceramics for comparison of the formability of fabricated ceramic green parts with/without the feedback control system of laser energy density for models were designed With this laser feedback control, batter quality ceramic green parts can be manufactured and the rapid prototyping machine with steady laser energy radiated on slurry layer was achieved. Experimental results validate the well performance of the measuring laser power and feedback control system.

Precise measurement of laser power using an optomechanical system

This paper shows a novel method to precisely measure the laser power using an optomechanical system. By measuring a mirror displacement caused by the reflection of an amplitude modulated laser beam, the number of photons in the incident continuous-wave laser can be precisely measured. We have demonstrated this principle by means of a prototype experiment uses a suspended 25 mg mirror as an mechanical oscillator coupled with the radiation pressure and a Michelson interferometer as the displacement sensor. A measurement of the laser power with an uncertainty of less than one percent (1σ) is achievable.

Array detector for high energy laser based on diffuse transmission sampling

In order to improve the ability and accuracy of measuring the temporal-spatial distribution of the intensity of a large-size, high-energy laser beam, a novel array detecting method based on diffuse transmission sampling is proposed. The measurement principle and the design of the sampling and attenuating unit are presented. High-temperature-resistant diffuse transmission material is used to sample and attenuate a high energy laser beam. Pure copper, whose surface is first sand-blasted and then gold-plated, is applied to scatter the incident high-energy laser beam. The formula for the attenuation ratio was derived in detail. We developed two large-aperture array detectors with spatial resolution of 5 mm, spatial duty ratio of 20%, and useable angle range of ±30° without varying the responsivity, the non-uniformity in the laser profile measurement is below 1%, and the repeatability error in the laser power measurement is approximately 1%. The maximal energy density that the array detector can endure is more than 10 kJ/cm(2).

Influence of Welding Current and Focal Position on the Resonant Absorption of Laser Radiation in a TIG Welding Arc

Abstract The work presents the influence of welding current and focal position on the resonant absorption of diode laser radiation in a TIG welding arc. The laser beam is guided perpendicular to the electrical arc to avoid an interaction with the electrodes. Laser power measurements have shown a reduction of the measured laser power up to 18% after passing the electrical arc. This reduction results from the interaction of argon shielding gas atoms and laser radiation at 810.4 nm and 811.5 nm. The interaction is strongly affected by the adjusted welding current and the adjustment of the laser beam and the electrical arc. Lowering the welding current or shifting the laser beam out of the centerline of the electrical arc reduces the ionization probability. An increased ionization is necessary to decrease the resistance of the electrical arc.

Same-wavelength cascaded-transition quantum cascade laser

Conventional Quantum Cascade (QC) lasers are based on intersubband transitions in repeated stages of precisely engineered quantum wells, with one electron emitting at most one photon in each stage. Here, we report on a same-wavelength cascaded-transition (SWCT) QC structure, with two subsequent optical transitions emitting at the same wavelength (λ ∼ 14.2 μm) in each stage. This SWCT QC gain medium was inserted between two conventional QC stacks, also at ∼14.2 μm. The measured laser power shows a quasi-saturation region with a 46% increase in slope efficiency after it. This quasi-saturation region is attributed to different current injection mechanisms.

Thermal modelling of RLCYC 75: a 2kW electrically calibrated laser calorimeter designed for Laser MegaJoule diagnostics calibration

RLCYC 75 is a new electrically calibrated laser calorimeter especially manufactured by Laser Métrologie to calibrate energy diagnostics of Laser MegaJoule (LMJ). It consists of an optical cavity cooled by a hydraulic system. The system is designed to provide laser power measurements with uncertainty less than 1% at 2kW and traceability to the International System of Units (SI) thanks to electrical calibrations. In this paper, a 3D thermal model is developed to study the thermal equivalence between electrical calibration and optical measurement. The simulation results are crossed with PT100 measurements in order to validate the model. The thermal modelling of the RLCYC 75 calorimeter is a key point to analyse the calorimeter efficiency, thus this work validates the geometrical design of RLCYC 75 calorimeter.

High accuracy measurement of the quantum efficiency using radiation pressure

Preliminary investigations of a novel method to measure the laser power accurately using the radiation pressure are reported here. We aim to measure the laser power within one percent error to then obtain an accurate quantum efficiency (QE) of a photodiode. Since the typical error of QE is still a few percent due to the uncertainty of measured laser power, an accurate measurement of the laser power contributes a precise estimation of the QE. Our experimental setup is a suspended Michelson interferometer, where one of the pendulums is small, consisting of a 20-mg mirror and 10-um fiber. The motion of this small mirror is very sensitive to changes in radiation pressure. Due to this, the number of photons in the incident (intensity modulated) laser beam can be counted accurately by measuring displacement of the mirror. We set up the apparatus, and have found a suitable frequency band for the accurate measurement. Displacement caused by the radiation pressure was observed using the feedback signal.

Power and Energy Measurement

Recently, lasers are remarkably in use under various circumstances. The measurement of laser power and energy is the most fundamental one, and to know it quantitatively is very important for laser optimization by alignment, daily check as well as the min-max setting and the feedback system control in laser processing application, which leads to better quality control. So the interest in laser measurement is increasing more and more. In this paper I will pick up power meter and explain the principle, how to use and things to remember.

阵列探测器对斜入射激光的功率测量不确定度

阵列探测器对斜入射激光的功率测量不确定度

Final report on supplementary comparison COOMET.PR-S4: Laser power responsivity (COOMET project 461/RU/090)

Physikalisch-Technische Bundesanstalt (PTB) and All-Russian Research Institute for Optical and Physical Measurements (VNIIOFI) agreed in December 2008 to conduct a bilateral comparison on laser power responsivity at wavelengths 532 nm/530.9 nm, 1.064 µm and 10.6 µm. The aim of this comparison was to assess the equivalence of laser power responsivity measurements between the two laboratories. The comparison was conducted within the COOMET regional metrological organization (COOMET project 461/RU/090) and was registered in the BIPM Key Comparison DataBase as a supplementary comparison with the identifier COOMET.PR-S4.The comparison was carried out using two detector heads for measuring laser power. One detector head was supplied by PTB (OPHIR 30A) and the other detector head by VNIIOFI (COHERENT PM10).The results of this comparison essentially demonstrated agreement between the results obtained at the two participating laboratories. Furthermore, linkage between the laser radiometry laboratory of VNIIOFI and the EUROMET.PR-S2 supplementary comparison reference value was established.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by COOMET, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The direct measurement of ablation pressure driven by 351-nm laser radiation

The instantaneous scaling of ablation pressure to laser intensity is directly inferred for ramp compression of diamond targets irradiated by 351-nm light. Continuously increasing pressure profiles from 100 to 970 GPa are produced by direct-drive laser ablation at intensities up to 7 × 1013 W/cm2. The free-surface velocity on the rear of the target is used to directly infer the instantaneous ablation-pressure profile at the front of the target. The laser intensity on target is determined by laser power measurements and fully characterized laser spots. The ablation pressure is found to depend on the laser intensity as P(GPa)=42(±3)[I(TW/cm2)]0.71(±0.01).

Continuous Wave Laser Irradiation of Explosives

AbstractQuantitative measurements of the levels of continuous wave (CW) laser light that can be safely applied to bare explosives during contact operations were obtained at 532 nm, 785 nm, and 1550 nm wavelengths. A thermal camera was used to record the temperature of explosive pressed pellets and single crystals while they were irradiated using a measured laser power and laser spot size. A visible light image of the sample surface was obtained before and after the laser irradiation. Laser irradiation thresholds were obtained for the onset of any visible change to the explosive sample and for the onset of any visible chemical reaction. Deflagration to detonation transitions were not observed using any of these CW laser wavelengths on single crystals or pressed pellets in the unconfined geometry tested. Except for the photochemistry of DAAF, TATB and PBX 9502, all reactions appeared to be thermal using a 532 nm wavelength laser. For a 1550 nm wavelength laser, no photochemistry was evident, but the laser power thresholds for thermal damage in some of the materials were significantly lower than for the 532 nm laser wavelength. No reactions were observed in any of the studied explosives using the available 300 mW laser at 785 nm wavelength. Tables of laser irradiance damage and reaction thresholds are presented for pressed pellets of PBX9501, PBX9502, Composition B, HMX, TATB, RDX, DAAF, PETN, and TNT and single crystals of RDX, HMX, and PETN for each of the laser wavelengths.

High-speed analog fiber-optic link for electromagnetic interference suppression in infrared power measurement

Electromagnetic interference (EMI) is a common problem in a high-power pulsed infrared laser measurement. In order to eliminate susceptibility to radiated EMI, we developed, tested and implemented an infrared power measurement system using a high-speed analog fiber-optic link. Key components are commercially available parts designed for high-speed digital data transmission, but can be operated in analog mode. We successfully utilized the system for time-resolved measurements of high-power transversely-excited atmospheric-pressure CO(2) lasers in amplifier and oscillator configurations. This paper presents experimental setup, testing results, and the details of the laser power measurements results.

Selective Ablation of Xe from Silicon Surfaces: Molecular Dynamics Simulations and Experimental Laser Patterning

The mechanism of laser-induced removal of Xe overlayers from a Si substrate has been investigated employing MD simulations and evaluated by buffer layer assisted laser patterning experiments. Two distinct regimes of overlayer removal are identified in the simulations of a uniform heating of the Si substrate by a 5 ns laser pulse: The intensive evaporation from the surface of the Xe overlayer and the detachment of the entire Xe overlayer driven by explosive boiling in the vicinity of the hot substrate. Simulations of selective heating of only a fraction of the silicon substrate suggest that the lateral heat transfer and bonding to the unheated, colder regions of the Xe overlayer is very efficient and suppresses the separation of a fraction of the overlayer from the substrate. Interaction with surrounding cold Xe is responsible for significant increase in the substrate temperature required for achieving the spatially selective ablation of the overlayer. The predictions of the MD simulations are found to be in a qualitative agreement with the results of experimental measurements of the threshold laser power required for the removal of Xe overlayers of different thickness and the shapes of metallic stripes generated by buffer-assisted laser patterning.