Doubling the spot size will increase the effective volume by a factor of eight.A larger spot size usually enables faster and more effective treatment in dermatologic applications such as treatment of vascular lesions, laser hair removal, etc.However, more photons must be supplied by more complex and expensive power supplies, components, and delivery devices.As a general rule, doubling the spot size and halving the fluence will yield an equivalent effective fluence at a given depth. The rest of the energy is transmitted by the material. Thank you. There is reasonable correlation between the experimental data and the simulated results. Here’s how to turn an everyday power meter into a laser power density meter: Step 1: Take an ordinary power sensor that’s a good fit for your laser power, energy, intensity, wavelength, etc. However, the plastically affected depth associated with the compressive residual stress is difficult to define properly from the simulation. 7.14(a) show that the residual stress profiles are clearly changed when using the different peak pressures. As the plasma is trapped between the material and transparent overlay, the magnitude and duration of plasma can be increased by a factor of 10 for the peak pressure and by a factor of 3 for the duration, respectively, compared with the direct ablation mode (Peyre et al., 1998a). Clauer (1996) reported this phenomenon for LSP on a 1.5 mm thick 4340 steel sheet and it was found that the tensile residual stress at the mid-plane of the section was higher after five shots. Laser power density and interaction time show major effects on the extent of thermal damages in laser processing. K. Ding, L. Ye, in Laser Shock Peening, 2006. Some people prefer using other percentages of a beam’s maximum intensity to define its width. From these you can calculate the divergence (actually convergence) angle by common trigonometry. For a perfect Gaussian beam with no noise in the measurement system, the measured diameters in 1/e2 definition and D4σ are identical. How to measure the peak power of a pulsed laser? However, in optical sciences the terms are typically used to describe a two-dimensional area, unless described as “volumetric.” Power density, energy density, fluence, and irradiance are often used interchangeably in the optics industry, which can be completely inaccurate, especially if it is not clear if the metric is a two- or three-dimensional value. Energy per unit area, also known as fluence. ScienceDirect ® is a registered trademark of Elsevier B.V. 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URL: https://www.sciencedirect.com/science/article/pii/B9780857090300500114, URL: https://www.sciencedirect.com/science/article/pii/B9781855739291500020, URL: https://www.sciencedirect.com/science/article/pii/B9781855739291500068, URL: https://www.sciencedirect.com/science/article/pii/B9781855739291500044, URL: https://www.sciencedirect.com/science/article/pii/B9781782420774000024, URL: https://www.sciencedirect.com/science/article/pii/B978185573929150007X, URL: https://www.sciencedirect.com/science/article/pii/B9781855739291500056, URL: https://www.sciencedirect.com/science/article/pii/B9781845696924500171, URL: https://www.sciencedirect.com/science/article/pii/B9781855739291500032, URL: https://www.sciencedirect.com/science/article/pii/B978085709264950012X, Laser machining of fibre-reinforced polymeric composite materials, Machining Technology for Composite Materials, Physical and mechanical mechanisms of laser shock peening, Two-dimensional simulation of two-sided laser shock peening on thin sections, As discussed in previous chapters, increasing the, Two-dimensional simulation of single and multiple laser shock peening, The plasma pressure pulse induced by LSP is a function of, Surface modification of magnesium and its alloys for biomedical applications, T.S.N. Root porosity may occur under defocused minus (−) conditions (of a focal point under the plate surface) or in the case of the existence of interaction between a laser beam and induced plume or plasma in high power CO2, fiber or disk laser welding. can quickly and easily be interchanged to optimize printing for all application types. The last parameter you will need to check is what laser power density hits your sensor. By simply calculating the area of a beam using the radius in cm and dividing the beam’s power by that area the power density in units of W/cm2 is easily obtained. Your Map to Laser Beam Profiling Accessories:Which Cameras Do They Work With? Unlike LED light which is not collimated or focused. Distribution of residual stresses with respect to different peak pressures for single LSP. For processing over today’s ranges of laser power it is important to be able to control power density. Sankara Narayanan, ... Min-Ho Lee, in, Surface Modification of Magnesium and its Alloys for Biomedical Applications, Banas, Elsayed-Ali, Lawrence, & Rigsbee, 1990; Banas, Lawrence, Rigsbee, & Elsayed-Ali, 1990, Simulation of laser shock peening on a curved surface, The residual stress field with respect to changes in impact pressure was also evaluated by 3D FE analyses. We are happy to know you find our blog post relevant and efficient. France a été enregistré. Example: A 4 Watt continuous wave laser would deliver 240 Joules in one minute. Thus, power density as a function of diameter can be expressed as the power density of a 1 mm beam divided by d2: This formula assumes the beam is a flat top beam where the beam power density is uniform. You can change this selection at any time, but products in your cart, saved lists, or quote may be removed if they are unavailable in the new shipping country/region. Required fields are marked *. However, the magnitude of the residual stress is obviously increased in the depth with an increase of almost 15% in the plastically affected depth, shown in Fig. In Eq. CO2Energy SensorsExcimerFiber LaserHigh Power DensityIndustrialIRLaser DiodeLEDMedicalMetersOEMPC InterfacesPower MeasurementPower SensorsResearchSoftware (Power Measurement)THzUVVisible LightYAG, « Using COM to integrate Ophir Meters into your own PC-based Photonics Application, Reference to your article “A Shorcut for Calculating Power Density of a laser beam”. W/cm 2: Peak Irradiance In micromachining applications, users will not be able to discern the problem by simply measuring irradiance or fluence. Intensity [Watts/cm2] = Laser peak power (W)/ Effective focal spot area (cm2) Laser fluence (Laser energy density) defined as the energy which is delivered per region or active area. From singlet, doublet, or triplet lens designs to achromatic, aspheric, cylinder, ball, or fresnel, we have thousands of choices for the UV, visible, or IR spectrum. The Calculation of power density is straightforward. Albuquerque, NM 87109 - (505) 761-8250. Usually power density is expressed in terms of W/cm2. In most scientific disciplines, including chemistry and electrical engineering, “power density” and “energy density” typically describe a three-dimensional volume. Both power and energy densities are volumetric amounts, so the resulting cut made by the laser may not be as accurate and could be off-center. Nowadays with technical advancements in lasers and processing capabilities, coupled with industry’s desire to process larger and larger parts at faster rates, Optomec LENS systems have increased available laser power ranges in their systems from 500 W to 1 kW, 2 kW, and now even 3 kW systems, making higher-powered laser capability available to all users. – Part 1, http://www.sonicator.com/literature/faq.shtml#powerintensity. If you include you beam … With increasing laser powers introduced into its systems, Optomec faced the challenge of how to keep a consistent power density and thus a stable conductive process over a wide range of laser powers. A common one is 13.5%, which leads us to our next beam diameter definition: 1/e2. 12.13. If the average power is above 1 W, you will have to sample your beam before using attenuation filters. Let’s look at each one and why I ask them. We recommend a sensor size of at least 3 times the largest diameter. No other device has this advantage. Simply that e, Euler’s constant, is approximately equal to 2.71828, so 1/e^2 = 0.13534! 6.8. 4.16(b) and Fig. It seems more relevant to your question. When a high-energy laser pulse is focused onto a metal surface, passing through a transparent overlay and striking the opaque overlay of a surface, the heated zone on the surface is vaporised, reaching temperatures up to 10 000 °C and then is transformed into plasma by ionisation. Both the American National Standard and the Federal Aviation Administration use this definition for laser safety calculations. Figure 6.8 shows the residual stress profiles in the depth of a section (at r = 1.5 mm) corresponding to three different peak pressures, 3.5, 4.0 and 5.0GPa, when the pulse duration of 100 ns and laser spot size of r0 = 3 mm were kept the same. In a similar fashion, the lack of variability in power density during DED processing could have a deleterious effect on the part build. Learn the correct definitions and usage. Copyright © 2020 Elsevier B.V. or its licensors or contributors. 3.1. They have no pulses by definition, therefore peak irradiance cannot be applied. The predicted increase in the plastically affected depth correlates well with the experimental observation on aluminium alloys that the compressive residual stress could be driven deeper below the surface by increasing the pulse pressure (Clauer, 1996; Peyre et al., 1996). Linear distribution of a flat top beam’s power describing the laser-induced damage threshold (LIDT) of continuous wave (CW) lasers through total power divided by 1/e. Residual stresses at r = 1.5 mm in the depth of section for different peak pressures. If you need to measure a laser beam spot size to comply with these laser safety regulations, you will have to use the 1/e2 definition. 27 When fibres and matrix exhibit only slightly different vaporisation times (e.g. The full width at half-maximum, also called half-power beam width, is measured from the distribution curve of the beam’s intensity along a pre-defined axis, passing through the beam’s center, which is also usually its point of maximum intensity. Instead, the beam profile will need to be carefully monitored. 4.16. Without the context of what someone wishes to achieve with a measurement, it is easy to get lost in translation. When someone asks me how to measure the spot size of their laser beam, I often answer with a few questions, because this type of measurement is not as simple as it can appear at first glance, especially if you want to do it with precision and rigor. This, together with the high thermal conductivity of carbon fibres, leads to poorer cut quality of glass and carbon fibre composites as compared to aramid fibre composites.28. For effective penetration, light needs to avoid scattering and surface absorption. However, what if a customer wanted to carry out DED processing over a wide range of laser powers? Optimisation of plasma pressure on material surface can play an important role in achieving the best treatment results (Masse and Barreau, 1995a; Montross et al., 2002; Fabbro et al., 1998). The value is actually closer to 255, not 250, but this difference is trivial, introducing only ~2% error. In any case, the discussion in our blog was focused on a quick calculation for when you know the diameter and the power – a very common situation of course, since those 2 parameters are often the ones that are directly measured. In Eq. The specimen surface was coated with black paint and the plasma was confined by a water overlay. Calculating the power density at the focal spot is possible, but there is not a simple formula for it. By definition, power density is power per unit area which is usually expressed in terms of W/cm2.
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