Laser Beam Spot Research Articles

Property and Quality Optimization of Laser Welded Rheo-Cast F357 Aluminum Alloy

F357, a hypo-eutectic Al-7%Si-0.6%Mg alloy without beryllium, was processed with CSIR-Rheo technology to the Semi-Solid Metal (SSM) state and cast in plates by means of High Pressure Die Casting. The castings were either left in the as-cast (F) condition or subjected to T4 or T6 heat treatments prior to autogenous Nd:YAG laser welding. A welding operating window was established and within this window, the weld porosity and undercut were minimised. Butt welds complying with ISO 13919-2: 2001 could be produced by means of the optimum parameters of 3.8 kW laser power and a welding speed of 4 m/min with a twin spot laser beam configuration. The mechanical properties of age-hardenable Al-Si-Mg alloys are dependent on the rate at which the alloy is cooled after the solution heat treatment. The low heat input provided by the laser welding process resulted in high enough cooling rates to ensure that both the fusion zone and HAZ were in the T4 condition after welding. Tensile properties equivalent to the parent metal in T6 condition were obtained after subjecting welded T4 plates to conventional artificial ageing treatment.

Fabrication of microfluidic hemicylindrical lenses for light scanning of laser sheet

A light scanning device with two microfluidic hemicylindrical lenses was demonstrated for adjustable laser sheet beam scanning applications. An elastomeric hemicylindrical lens, whose focal length can be adjusted by control of the applied fluidic pressure, was fabricated by application of the pressurized casting process on polydimethylsiloxane (PDMS) obtained from a prepared microsized mold. The hemicylindrical lens consisted of a thin membrane, a liquid chamber and a microchannel. The applied fluidic pressure deformed the lens membrane and changed the lens shape. The change of the lens shape allowed beam shape transformation or beam scanning according to the relative size of the beam to the lens. By orthogonally placing two microfluidic lenses of different sizes, 1 mm × 5 mm and 3 mm × 15 mm, respectively, a spot laser beam from a 200μm-large pinhole was transformed into laser sheet, and then the laser sheet was scanned. The relationship between the lens properties, including lens curvature and laser beam shaping according to different applied pressures on the lens, were systematically investigated. Laser beam scanning properties of the microfluidic light scanning device were also characterized for various applied pressures and offset distances.

Laser irradiation affects enzymatic antioxidant system of streptozotocin-induced diabetic rats

The aim of the present study was to analyze the effect of low-power laser irradiation in the antioxidant enzymatic system of submandibular (SMG) and parotid (PG) salivary glands of streptozotocin-induced diabetic rats. The animals were randomly divided into six groups: three diabetic groups (D0, D5, and D20) and three non-diabetic groups (C0, C5, and C20), according to laser dose received (0, 5, and 20 J/cm(2), respectively). Areas of approximately 1 cm(2) were demarcated in the salivary glands (each parotid and both submandibular glands) and after irradiated according to Simões et.al. (Lasers Med Sci 24:202-208, 2009). A diode laser (660 nm/100 mW) was used, with laser beam spot of 0.0177 cm(2). The group treated with 5 J/cm(2) laser dose was subjected to irradiation for 1 min and 4 s (total irradiation time) and the group treated with 20 J/cm(2) laser dose was subjected to irradiation for 4 min and 16 s. Twenty-four hours after irradiation the animals were euthanized and the salivary glands were removed for biochemical analysis. The total antioxidant values (TA), the activity of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase enzymes were determined. SOD and CAT activities, as well as TA were higher in SMG of irradiated diabetic rats. However, in SMG of non-diabetic rats, laser irradiation decreased TA values and led to an increase in the CAT activity. In addition, there was a decrease in the activity of CAT in PG of diabetic and non-diabetic animals after laser irradiation. According to the results of the present study, low-power laser irradiation can affect the enzymatic antioxidant system of salivary glands of streptozotocin-induced diabetic rats.

Fabrication of sub-spot-size microchannel of microfluidic chip using CO 2 laser processing with metal-film protection

CO2 laser ablation has been a popular technique for microfluidic chip fabrication but it always suffers some problems such as bulges, clogging, re-solidification and large heat-affected zone around the rim of channels and holes. In this Letter, a simple effective method for diminishing the defects has been proposed using a metal-film protection for CO2 laser ablation. Polymethylmethancrylate (PMMA) was used as a substrate to demonstrate the fabricated microfluidic channels without clogging as well as bulges reduced. The feature size of the microchannel can also distinctly be decreased from 268 µm in air to around 58 µm with metal-film-protection method, which is smaller than the laser-beam spot size. The bulge height was reduced to less than 0.2 µm and clogging effect in the channel junction was not occurred. ANSYS simulation was also used to analyse the temperature distribution on PMMA substrate during laser ablation in air and with metal-film protection. The method presented here is suitable for microfluidic device production while overcoming the bad surface quality and low-resolution limit of CO2 laser ablation in air.

Seam Tracking Monitoring Based on Molten Pool Infrared Images

Visual sensors can be used for monitoring the welding seam and seam tracking, but it is difficult to acquire the deviations between the laser beam spot and the weld seam from the images because of the strong disturbances caused by spatters and plume. An extraction method was developed to detect the deviations between the laser beam spot and the weld seam during high power fiber laser welding. Laser welding experimental results showed that the deviations could be detected accurately, and the proposed method can be used to monitor the seam tracking status.

New Laser-Scan Exposure System for Delineating Precise Helical Patterns onto Sub-50-µm Wires

A new laser-scan exposure system for patterning onto fine wires and pipes with diameters as small as 40 µm was developed. New schemes for vertically holding specimens were adopted, and improved optics of imaging and in situ observation were used. In addition, specially contrived half-vacuum support guides were attached, and a short-wavelength violet laser with a wavelength of 408 nm was also attached. Because the laser beam spot was kept steady at a constant size by the improved half-vacuum support guide with triple narrow slits, patterns with homogeneous widths of approximately 20 µm were constantly delineated suppressing the width fluctuations to less than ±2 µm. In addition, owing to the short-wavelength laser, exposure time was greatly decreased to approximately 1/10 compared with the previous system. The new exposure system will be applicable to development of fine microcomponents such as microcoils useful for very fine probe pins of semiconductor device testers.

The Influence of Input Variability on the Compressive Residual Stresses in 30CrMnSiNi2A via Laser Shock Processing

The laser shock processing(LSP) is a new surface treatment technique that induce a significant compressive residual stress field on the metal and alloys. The developed compressive stress field is beneficial to improve surface properties such as fatigue, wear, and corrosion. To improve the understanding of the shock process, investigation into the physical processes and its variability involved is necessary. This work examines the effect of LSP at different input variability to induce its compressive stress. Various factors that affect the compressive stress of the LSP are tested with a serial experimental using 30CrMnSiNi2A as workpiece. It was found that the in-depth residual stress induced by LSP were a function of laser power density,laser beam spot size, laser pulse width and pulse repetition.

Laser absorption of aluminium alloy in high brightness and high power fibre laser welding

Laser welding of aluminium alloys is difficult because of their high reflectivity and heat conductivity. However, high brightness and high power lasers such as fiber laser or disk laser can produce narrow and deep penetration welds, when highly-efficient laser absorption is expected. The objective of this research is to measure laser absorption in bead-on-plate welding of A5052 aluminium alloy with a 200 μm fine laser beam spot under a wide range of conditions such as fiber laser powers of 2–10 kW or welding speeds of 17–250 mm/s by water-calori-metric method. Furthermore, the relationship between the laser absorption and the keyhole geometry was investigated by using X-ray transmission in-site observation system or high-speed video camera with diode-laser illumination. It was found that the absorption at 10 kW laser power and 17 mm/s welding speed was 93% high. Compared with focusing feature of the incident fiber laser beam, X-ray images of the keyhole shape demonstrated that the centre part of the incident beam with a bell-shape profile could be delivered directly to the tip of a keyhole. Moreover, the increase in the welding speeds from 17 to 250 mm/s reduced the absorption from 93 to 72%. The high-speed observation pictures showed that the incident fiber laser beam was partly shot on the molten pool in front of the keyhole inlet at higher welding speeds, which might be the chief cause of the decrease in the laser absorption. Consequently, the tightly-focused high-power fiber laser welding was confirmed to be a highly-efficiency process of 93–72% in laser absorption.

Ultra-short ultra-intense laser guiding and its influence on electron acceleration

Simulations and analyses of ultra-short ultra-intense laser propagting in plasmas with uniform and parabolic density profiles, as well as the electron injection into the wake field and the electron spectra in the stable transmission state are performed by using a particle-in-cell code. Fixing the incident laser focal spot size but changing the plasma density in a range of (0.42)1019/cm3, comparative analyses are carried out of the evolutions of the laser beam spot during the propagation of the laser pulse in the plasmas with aforementioned two density profiles, with the normalized laser intensity ranging from 1 to 6. The results show that a plasma channel with a parabolic density profile can realize a good guiding of an ultra-short ultra-intense pulse, which is beneficial for high energy electron acceleration. However, at higher densities, self-guiding can be realized by relativistic self-focusing in uniform plasma, which is conducive to simplifying the experiment and to producing more accelerated electrons.

Axially magnetized electron–positron and electron plasma competition on the self focusing of intense laser beam

The spot-size evolution of circularly polarized intense laser beam propagating through the axially magnetized electron–positron (EP) and electron plasmas is discussed, in mildly relativistic and weakly non-linear ( a 2 ≪ 1) regime. The non-linear current density source terms are obtained by making used of the perturbative technique. The variational principle approach method is applied to the solution of the non-linear Schrodinger wave equation. It is shown that the laser beam spot size decreases for the left and increases for the right handed polarized beams with increasing the external magnetic field, owing to the beam passages inside the electron plasma. Furthermore, it is revealed that the self focusing property strongly enhanced in the EP plasma in comparison to the electron plasma. Moreover, self focusing of linearly polarized laser beam is investigated for EP plasma by superposition of the right and left circularly polarized beams.

Spatial Filtering Collimator for Optimized Laser Indicator and Laser Range Finder

A novel spatial filtering collimator is developed for the laser indication application. The mass produced, inexpensive, red and blue semiconductor laser modulars can easily be optimized as fine line laser indicator source. We have theoretically investigated the results, simulated the designs, and measure the laser beam spots and the laser fine lines. The spatial filtering collimator is designed and optimized for practical used and the results are very satisfactory.

Multi-wavelength laser sensor for intruder detection and discrimination

An intruder detection and discrimination sensor with improved optical design is developed using lasers of different wavelengths to demonstrate the concept of discrimination over a distance of 6 m. A distinctive feature of optics is used to provide additional transverse laser beam scanning. The sample objects used to demonstrate the concept of discrimination over a distance of 6 m are leaf, bark, black fabric, PVC, wood and camouflage material. A camouflage material is chosen to illustrate the discrimination capability of the sensor. The sensor utilizes a five-wavelength laser combination module, which sequentially emits identically-polarized laser light beams along one optical path. A cylindrical quasi-optical cavity with improved optical design generates multiple laser light beams for each laser. The intensities of the reflected light beams from the different spots are detected using a high speed area scan image sensor. Object discrimination and detection is based on analyzing the Gaussian profile of reflected light at the different wavelengths. The discrimination between selected objects is accomplished by calculating four different slopes from the objects' reflectance spectra at the wavelengths 473 nm, 532 nm, 635 nm, 670 nm and 785 nm. Furthermore, the camouflage material, which has complex patterns within a single sample, is also detected and discriminated over a 6 m range by scanning the laser beam spots along the transverse direction.

Periodic adjustment of the position of a laser beam spot on a semiconductor saturable absorber mirror in a passively mode-locked solid-state laser

A laser diode end-pumped passively mode-locked Nd:YVO4 solid-state laser with a semiconductor saturable absorber mirror (SESAM), in which the intracavity laser beam spot on the SESAM can be adjusted periodically, is investigated. Inserting a rectangular prism (RP) into the laser cavity is a promising approach towards the goal of periodically moving the position of the focus spot of the intracavity pulse on the SESAM surface to avoid the long-time irradiation of the laser beam on the same position, thereby solving a series of problems caused by damage to the SESAM and greatly prolonging its usage life. The adjustment of the rectangular prism in the laser cavity does not break the stable continuous wave (CW) mode-locked condition. The laser generates a stable picosecond pulse sequence at 1064 nm with an output power of 3.6 W and a pulse width of 14 ps. The instabilities of the output power and the pulse width are 1.77% and 4.5%, respectively.

Laser treatment of silicon at nitrogen ambient: thermal stress analysis

Laser control melting of silicon surface is carried out at nitrogen gas environment and temperature rise as well as thermal stress developed in the irradiated region is simulated using the finite element method. The residual stress developed in the surface region after the laser treatment is measured using the XRD technique and the measurement results are compared with the predictions. The fracture toughness of the laser treated surface is also measured using the indentation tests. The structural and morphological changes in the laser irradiated region are examined using the scanning electron microscope. It is found that β phase silicon nitride was formed in the surface region of the laser treated workpiece. The temperature gradient close to the laser beam spot attains significantly high values due to the high heating and cooling rates. This, in turn, results in high stress levels in this region during the laser treatment process. The laser treated surface was free from the defects including microcracks, voids and cavitations.

Active control over nanofocusing with nanorod plasmonic antennas

Active control over light nanofocusing in a nanorod plasmonic antenna coupled to a photonic crystal cavity is proposed and demonstrated by means of full-vectorial 3D simulations. By varying the excitation of the cavity with laser beam spot size allows us to achieve a gradual control over light nanofocusing at the tip of the nanoantenna. The demonstrated control mechanism eliminates the need for nonlinear effects or mechanical reconfiguration and represents a step towards the implementation of reliable tunable subwavelength light sources.

Terrestrial Laser Scanner Resolution: Numerical Simulations and Experiments on Spatial Sampling Optimization

An empirical approach is proposed in order to evaluate the largest spot spacing allowing the appropriate resolution to recognize the required surface details in a terrestrial laser scanner (TLS) survey. The suitable combination of laser beam divergence and spot spacing for the effective scanning angular resolution has been studied by numerical simulation experiments with an artificial target taken from distances between 25 m and 100 m, and observations of real surfaces. The tests have been performed by using the Optech ILRIS-3D instrument. Results show that the discrimination of elements smaller than a third of the beam divergence (D) is not possible and that the ratio between the used spot-spacing (ss) and the element size (TS) is linearly related to the acquisition range. The zero and first order parameters of this linear trend are computed and used to solve for the maximum efficient ss at defined ranges for a defined TS. Despite the fact that the parameters are obtained for the Optech ILRIS-3D scanner case, and depend on its specific technical data and performances, the proposed method has general validity and it can be used to estimate the corresponding parameters for other instruments. The obtained results allow the optimization of a TLS survey in terms of acquisition time and surface details recognition.

Optical probe for porosity defect detection on inner diameter surfaces of machined bores

We demonstrate an optical probe for detection of porosity inside spool bores of a transmission valve body with diameters down to 5 mm. The probe consists of a graded-index relay rod that focuses a laser beam spot onto the inner surface of the bore. Detectors, placed in the specular and grazing directions with respect to the incident beam, measure the change in scattered intensity when a surface defect is encountered. Based on the scattering signatures in the two directions, the system can also validate the depth of the defect and distinguish porosity from bump-type defects coming out of the metal surface. The system can detect porosity down to a 50-µm lateral dimension and ~40 µm in depth with >3-dB contrast over the background intensity fluctuations. Porosity detection systems currently use manual inspection techniques on the plant floor, and the demonstrated probe provides a noncontact technique that can help automotive manufacturers meet high-quality standards during production.

Research on Focusing Spot Shape of High Power CO<sub>2 </sub>Laser

In order to meet the requirements of laser processing technology and quality, the laser bean oblique incidence technique is put forward and focusing laser spots with different shape and incident direction are realized. The relation between the output laser beam spot shape and laser power of high power CO2 laser is studied through the organic glass sampling method. The result indicates that the laser beam cross-section shape presents rectangle and the long-axis length of laser beam has nothing to do with the laser power changes, but the short-axis width increases with the laser power improving. The two-dimension rotary laser head is designed and the laser bean tilt incidence is realized. The formula of the relation between focusing spot coordinate in the processing plane and laser head turn angle, also swinging angle is deduced. The relation between the focusing spot shape and the laser power, defocusing amount, laser head turn and swinging angles is researched through the single-side gummed paper sampling method. The result indicates that the focusing laser spot form is affected by the parameters of laser power, defocusing amount, laser head turn and swinging angles.

Effect of spot size on cone formation in a XeCl laser ablation of polyethersulfone films

Radiation from the UV excimer lasers, with the fluence above the ablation threshold, can etch the polymer surfaces by photoablation. In some cases different microstructures may appear on the surface during the laser ablation. In this paper the effect of the laser spot size on the cone formation on polyethersulfone films has been investigated. The experiments have been performed with a XeCl laser at the wavelength of 308 nm and at the fluences of 70 and 100 mJ/cm 2 at air. For the investigation of the effect of the laser spot size on cone formation, the samples were irradiated at two different laser spot sizes of w 1 and w 2 = 0.1 w 1. The morphology of the processed surface was studied by scanning electron microscopy (SEM). It has shown that the shape, size and density of cones change with the change of the laser spot size. Also, the number of pulses and the pulse repetition rate which are needed for threshold of cone formation are affected by the laser beam spot size on the surface.

Broadband optoacoustic measurements of ultrasound attenuation in severely plastically deformed nickel

Laser optoacoustics and immersion techniques allowed a broadband ultrasound spectroscopy which was used for measuring the attenuation of severely plastically deformed nickel. A disk shaped specimen of nickel of about 33 mm diameter and 2.5 mm thickness was prepared by the high pressure torsion method. The produced equivalent shear strain linearly increased from a minimum at the center up to 1000% at the edge, gradually refining the grain size distribution down to 200 nm. The metal water interface was illuminated by 5 ns laser pulses, generating longitudinal ultrasound pulses with a pronounced compression phase and a smooth spectrum covering the range from 0.1 up to 150 MHz. The laser beam spot diameter was 6 mm, yielding a maximum power density below 15 MW/cm2. The ultrasound passed through the sample thickness and a 2 mm layer of coupling water. The pulse was detected by a 25 μm thick piezoelectric foil transducer with a diameter of the sensitive area of 2 mm. The transient signals were locally measured at different radii of the specimen. The attenuation almost linearly increases with frequency while its absolute value decreases from the center to the edge of the specimen.