Absorption Of Laser Light Research Articles

Photo-activated raster scanning thermal imaging at sub-diffraction resolution

Active thermal imaging is a valuable tool for the nondestructive characterization of the morphological properties and the functional state of biological tissues and synthetic materials. However, state-of-the-art techniques do not typically combine the required high spatial resolution over extended fields of view with the quantification of temperature variations. Here, we demonstrate quantitative far-infrared photo-thermal imaging at sub-diffraction resolution over millimeter-sized fields of view. Our approach combines the sample absorption of modulated raster-scanned laser light with the automated localization of the laser-induced temperature variations imaged by a thermal camera. With temperature increments ∼0.5–5 °C, we achieve a six-time gain with respect to our 350-μm diffraction-limited resolution with proof-of-principle experiments on synthetic samples. We finally demonstrate the biological relevance of sub-diffraction thermal imaging by retrieving temperature-based super-resolution maps of the distribution of Prussian blue nanocubes across explanted murine skin biopsies.

Calculation of Direct Drive Targets for Megajoule Laser Facilities with Radiation in the Second and Third Harmonics of Nd Laser

The numerical results for cryogenic direct drive targets of megajoule facilities with radiation in the second and third harmonics of a Nd laser are presented. The calculations were performed with the 1D radiation hydrodynamics code ERA with the laser light absorption model that takes into account stimulated Brillouin scattering (SBS), generation of fast electrons in the processes of two-plasmon decay (TPD), and stimulated Raman scattering (SRS). The verification of the developed models was carried out on the basis of the comparison with experiments performed at the OMEGA and NIF facilities. The ignition margin (WQ) of nonuniform fusion targets with an allowance for energy losses due to radiation transfer and heat conduction from the hot spot was the objective of the target optimization. The calculations showed that SBS and target heating by fast electrons generated in TPD and SRS fatally reduce WQ of targets with a CH ablator for the megajoule laser with wavelength λ = 0.53 µm. The possibilities of decreasing these effects by replacing a CH ablator with a glass ablator and reducing the laser intensity upon increasing the target aspect ratio are considered. However, in both cases, WQ remains substantially below unity for the laser with wavelength λ = 0.53 µm. The ignition margin increases by a factor of ∼2 upon transition from the second to the third harmonic of a Nd laser. A glass ablator almost eliminates fast electrons in calculation with the laser wavelength λ = 0.35 µm. In this case, if SBS is reduced by a factor of 3–4 via shifting the laser emission lines in the neighboring channels by Δμ ≈ 10–20 A, the ignition margin WQ ∼ 2 and a fusion energy yield of ∼50 MJ are obtained in the 1D calculation for a laser energy of ∼2 MJ and the third harmonic of a Nd laser.

Investigating the effect of gold nanoparticles on hydatid cyst protoscolices under low-power green laser irradiation.

Various scolicidal agents are applied for the destruction of protoscolices in cysts media. Undesirable complications of the scolicidal agents limit the techniques to treat the cyst disease. Therefore, new non-toxic scolicidal agents are needed. Upon laser light irradiation, the photothermal gold nanoparticles (AuNPs) convert the absorbed laser light into heat through photothermal effect which kills the surrounding protoscolices by rising the temperature of the cysts media. In this study, we introduced biocompatible AuNPs as a non-toxic scolicidal agent to cure liver hydatid cysts. The protoscoleces were collected from the livers of naturally infected sheeps. In each experimental group, 1.5 mL suspensions of hydatid liquid containing protoscolices were added to test tubes. The test tubes were divided into five groups. Control, AuNPs only, Green laser only, High-dose AuNPs + laser and Low-dose AuNPs + laser groups. Two concentrations (0.4 and 0.8 mL) of AuNPs and three laser powers (30, 50, 150 mW) were applied for 30, 60 and 120 minutes to the groups. Then the ciysts liquid assessed under a light microscope and determined the viability of protoscoleces. Protoscolices in high-dose AuNPs group were destructed up to 89.30% deaths under 150 mW laser power for 120 minutes. However, negligible cell deaths were observed in cases where only AuNPs added or only laser irradiated groups. Increasing the dose of AuNPs or laser power or duration of aplication increased the protoscolosidal death rate. In the study, we have successfully demonstrated that the AuNPs are an effective therapeutic and scolicidal agent to cure hydatid cyst disease under laser irradiation.

Bacteriophage-mediated identification of bacteria using photoacoustic flow cytometry.

.Infection with resistant bacteria has become an ever increasing problem in modern medical practice. Currently, broad spectrum antibiotics are prescribed until bacteria can be identified through blood cultures, a process that can take two to three days and is unable to provide quantitative information. To detect and quantify bacteria rapidly in blood samples, we designed a method using labeled bacteriophage in conjunction with photoacoustic flow cytometry (PAFC). PAFC is the generation of ultrasonic waves created by the absorption of laser light in particles under flow. Bacteriophage is a virus that infects bacteria and possesses the ability to discriminate bacterial surface antigens, allowing the bacteriophage to bind only to their target bacteria. Bacteria can be tagged with dyed phage and processed through a photoacoustic flow cytometer where they are detected by the acoustic response. We demonstrate that E. coli can be detected and discriminated from Salmonella using this method. Our goal is to develop a method to determine bacterial content in blood samples. We hope to develop this technology into future clinical use and decrease the time required to identify bacterial species from 3 to 4 days to less than 1 hour.

Controlling energy distribution of fast ions and X-ray emission via target reliefs in ultrafast and relativistic laser plasma interaction

Secondary emission from laser produced plasma is governed by the electron distribution function. Therefore, its control is of utmost importance to steer the emission, e.g., of ultrashort bursts of high energy photons and ions for decisive application. Maximum gain is achieved if the laser light absorption by plasma is also maximized. In our theoretical analysis including comparison to recent experiments, we follow this route and study how the energy is transferred from a short laser pulse to the energy of fast ions and X-rays. We make use of ion and K-α emissions, which respond differently to branches of the electron distribution function when we optimize the laser light absorption via structuring of the target surface. Our investigation comprises laser intensities up to 5 × 1020 W/cm2 produced with femtosecond near infrared laser pulses and titanium foil targets of a few micrometer thicknesses. In particular, we reveal an energy relaxation process of hot electrons, which determines the observed laser intensity dependence of secondary emission and points to the benefit of target surface structuring in different optimization scenarios.

Photochemical reduction of carbonyl group of polyimide by 450 nm diode laser

In this article, we report directly patterned graphene nanoribbons by laser irradiation. The transformation of polymer into graphene nanostructure by breaking oxygen bonding and followed by graphitization of carbon atoms has been employed by using the photochemical technique. The scalable and fast growth of graphene nanoribbon was carried out by irradiating 450 nm diode laser directly onto polyimide polymer. Patterned graphene was characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and Field emission scanning electron microscopy (FESEM). The ability of polyimide to absorb laser light in the near-ultraviolet region contribute to the tailoring of graphene nanoribbon which reduces oxygen bonding as well as paves way for the development of optoelectronics applications.

Soft X-ray spectral analysis of laser produced molybdenum plasmas using the fundamental and second harmonics of a Nd:YAG laser.

Our measurement of the soft X-ray emission of Mo plasmas produced by picosecond Nd:YAG lasers emitting on the fundamental (1064 nm, 150 ps) and second (532 nm, 130 ps) harmonics is presented. The contrast in intensity between spectral peaks and the intensity outside them is lower for the second harmonic produced plasmas probably due to the presence more intense satellite emission and higher optical thickness. The measured spectra are absolutely calibrated and the observed output photon flux was (7 - 9) × 1013 photons/sr in the water-window (2.3 - 4.4 nm) spectral range for a laser energy of 160 mJ independent of laser wavelength. However, in the short wavelength range 1.5 - 2 nm, the emission using the second harmonic is strongly enhanced and is even higher than for the maximum energy of 220 mJ of the fundamental wavelength, so despite inevitable energy losses, laser wavelength conversion may lead to emission enhancement in certain spectral ranges. This enhancement is attributed to higher absorption of short wavelength laser light and higher charge state generation in denser plasmas.

Single-step Laser Plastic Deposition (LPD) using a near-infrared Thulium fiber-laser

Additive Manufacturing of thermoplastic polymers is typically carried out using techniques such as Selective Laser Sintering (SLS) or Fused Layer Modeling (FLM), both of which require the use of support structures that have to be removed after the production process. The laser welding of thermoplastic polymers using laser sources with a wavelength of around 1 μm and thus also Direct Selective Laser Melting (SLM) in the same wavelength spectrum requires the admixing of additives such as carbon black in order to improve the absorption of laser light within the polymer and hence poses an additional process step that has to be performed. Laser sources like Thulium fiber-lasers with a wavelength of around 2 μm enable the absorber-free welding of thermoplastic polymers and therefore promise to be a new source for the SLM of thermoplastic polymers as well as a possible adaption of the known Laser Metal Deposition (LMD) to plastics, the so called „Laser Plastic Deposition“ (LPD).In the present paper, the feasibility of a single-step LPD process using irradiation of a 1,94 μm Thulium fiber-laser is investigated through the manual deposition of unfilled and absorber-free polyamide-12 powder on polyamide-6 substrates. Powder material and the created structures are characterized by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). In addition to that, optical microscopy and computer tomography analysis (CT) are carried out and discussed for the created LPD structures. From the experiments, it is to be concluded that a single-step LPD process can be carried out using a 2 μm Thulium fiber-laser.

Effects and side effects of plasmonic photothermal therapy in brain tissue

BackgroundHeat generated from plasmonic nanoparticles can be utilized in plasmonic photothermal therapy. A combination of near-infrared laser and plasmonic nanoparticles is compelling for the treatment of brain cancer, due to the efficient light-to-heat conversion and bio-compatibility. However, one of the challenges of plasmonic photothermal therapy is to minimize the damage of the surrounding brain tissue. The adjacent tissue can be damaged as a result of either absorption of laser light, thermal conductivity, nanoparticles diffusing from the tumor, or a combination hereof. Hence, we still lack the full understanding of the light–tissue interaction and, in particular, the thermal response.ResultsWe tested the temperature change in three different porcine cerebral tissues, i.e., the stem, the cerebrum, and the cerebellum, under laser treatment. We find that the different tissues have differential optical and thermal properties and confirm the enhancement of heating from adding plasmonic nanoparticles. Furthermore, we measure the loss of laser intensity through the different cerebral tissues and stress the importance of correct analysis of the local environment of a brain tumor.ConclusionsOur results stress the conclusion that a personalized analysis of the local environment is needed to balance the effect and side effects prior to plasmonic photothermal therapy.

Using Polymers and Pigments to Produce Laser Interference Rings

When a laser of sufficient intensity is shined into a pigmented transparent medium, the partially absorbed laser light can heat and change the refractive index of the medium in the path of the beam. This altered medium will in turn cause the transmitted laser light to thermally defocus into a series of concentric rings. Some solvents such as 2-propanol and a variety of polymers such as polystyrene, polyethylene terephthalate, and polydimethylsiloxane can be pigmented with a variety of colors. Samples of various colors can be used to spectacularly demonstrate characteristics of light absorption. For example, a 2-propanol solution containing methyl red in red acidic form will absorb a green laser and produce interference rings, but a solution of methyl red in yellow basic form will not. As another example, a red laser beam will pass unaffected through a red pigmented film, but the beam will heat a green film (e.g., from a green pigmented polyethylene terephthalate soda bottle) to produce interference rings. Additionally, since the pattern produced is based on the interference of light waves, these demonstrations reinforce concepts associated with the wave nature of light.

Optical regime diagram of the shock tube/pulsed laser-induced fluorescence imaging technique

A laser-induced fluorescence (LIF) model has been employed to characterize the shock tube/pulsed laser-induced fluorescence imaging method. The LIF model was first validated using experimental data for the reactions of H-abstraction by OH on benzene and toluene. The model was then employed to establish optical regime diagrams. Three regimes were distinguished: (i) the optically-thin regime, in which the rate constant obtained is not much affected by laser light absorption; (ii) the optically-thick regime, in which the laser absorption induces a significant error on the rate constant; and (iii) the so-called “non-physical” regime, in which the rate constant is negative.

Pre-processing of hematite-doped alumina granules for Selective Laser Melting

Abstract Structure and composition evolution of α-Fe2O3 doped alumina granules during calcination is investigated by means of synchrotron X-ray powder diffraction. The α-Fe2O3 nanoparticles are added to increase the absorption of laser light, however, they also play a significant role in transition kinetics of alumina. It is shown that calcination in air leads to implementation of Fe3+ ions in corundum structure, while calcination in reducing atmosphere leads to creation of metallic iron. Moreover, it is demonstrated that for alumina granules consisting of a mixture of micron-size α-alumina, submicron α-alumina and nano-size γ−/δ--alumina, it is possible to obtain a system composed of two corundum-type structures with different Fe doping levels and the ratio of these two phases can be controlled by calcination temperature.

Iron Oxide Doped Spray Dried Aluminum Oxide Granules for Selective Laser Sintering and Melting of Ceramic Parts

Powder bed density, flowability, and laser light absorption of the powder strongly influence the quality and performance of aluminum oxide parts processed by selective laser sintering and melting. By means of spray drying, highly dense granules with a good flowability are manufactured. An ultrasonic atomizer and a co‐current droplet air mixing are used to spray aqueous slurries consisting of either bimodal or trimodal distributions of aluminum oxide. Nano‐iron oxide improves the interaction with the green pulsed laser. The improved absorption of the green laser light is verified by means of an Ulbricht sphere. The appropriate amount of dispersant for consecutive water‐based spray granulation is determined by Zeta Potential measurements. Dibasic ammonium citrate is found to be the most suitable dispersant. A final uniform distribution of the iron oxide within the spray dried granules is confirmed by X‐ray μ‐beam fluorescence tomography. The powder quality is characterized by apparent density, tapped density, Hausner ratio, moisture content, and particle size distribution. Powders with a tapped density of almost 50% of the theoretical density and an absorbance of 69% (green laser light) lead to maximum densities of the laser processed parts of around 96%.

Beyond the conventional collisional absorption of laser light in under-dense plasma: A particle-in-cell simulation study

Collisional absorption of laser light in an under-dense plasma is studied by particle-in-cell (PIC) simulation with Monte Carlo binary Coulomb collisions between charge particles. For a given plasma thickness of a few times the wavelength of 800 nm laser, fractional absorption ( $$\alpha $$ ) of the laser light due to Coulomb collisions (mainly between electrons and ions) is calculated at different electron temperature $$T_\mathrm {e}$$ with a total velocity $$v = ({ v}_\mathrm {th}^2 + { v}_0^2/2)^{1/2}$$ dependent Coulomb logarithm $$\ln \Lambda (v)$$ , where $${ v}_\mathrm {th}$$ and $${ v}_0$$ are thermal and ponderomotive velocity of an electron. In the low-temperature regime ( $$T_\mathrm {e}\lesssim 15$$ eV), it is found that $$\alpha $$ increases with increasing laser intensity $$I_0$$ up to a maximum corresponding to an intensity $$I_c$$ , and then it drops (approximately) obeying the conventional scaling of $$\alpha \propto I_0^{-3/2}$$ when $$I_0>I_c$$ . Such a non-conventional increase of $$\alpha $$ with $$I_0$$ in the low-intensity regime was demonstrated earlier in experiments, and recently explained by classical and quantum models [Phys. Plasmas 21, 13302 (2014); Phys. Rev. E 91, 043102 (2015)]. Here, for the first time, we report this non-conventional collisional laser absorption by PIC simulation, thus bridging the gap between models, simulations, and experimental findings. Moreover, electron energy distributions naturally emanating during the laser interaction (in PIC simulations) are found to be anisotropic and non-Maxwellian in nature, leading to some deviations from the earlier analytical predictions.

The influence of oxide layer pattern size created on the surface of C45 steel on laser light absorption during laser quenching procedure

An increase in surface absorptivity can be helpful with a number of laser heat treatment processes. This study examines the relationship between the surface condition and its influence on interaction with a laser beam. The aim of this paper is to examine the effect of the oxide layer pattern size on the absorption of IR radiation and the influence of the ambient atmosphere. The process was carried with inert gas shielding. The oxide layers are created by the controlled heating method. The controlled heating method uses a scanning laser system to create oxide layers of different thickness on steel EN 10083-2: C45. Subsequently, the absorbency of the formed oxide layer was measured, depending on the irradiation energy emitted into the surface. According to recent experiments has been found that the higher the thickness of the oxide layer increases absorption. These results have shown that the use of surface oxidation increases the coupling of laser energy to material surface in the order of tens of percent. The thickness and hardness of the laser hardened layer were considered. That paper describes possibilities of precise laser quenching of the oxidized C45 material surface.

Energy transfer between lasers in low-gas-fill-density hohlraums

We investigate cross-beam energy transfer (CBET), where power is transferred from one laser beam to another via a shared ion acoustic wave in hohlraums with low-gas-fill density as a tool for late-time symmetry control for long-pulse (greater than $10\phantom{\rule{0.28em}{0ex}}\mathrm{ns}$) inertial confinement fusion (ICF) and laboratory astrophysics experiments. We show that the radiation drive symmetry can be controlled and accurately predicted during the foot of the pulse (until the rise to peak power), which is important for mitigating areal density variations in the compressed fuel in ICF implosions. We also show that the effective inner-beam drive after CBET is much greater than observed in previous high-gas-filled-hohlraum experiments, which is thought to be a result of less inverse bremsstrahlung absorption of the incident laser light and reduced (by more than 10 times) stimulated Raman scattering (and Langmuir wave heating). With the inferred level of inner-beam drive after transfer, we estimate that more than $1.25$ times larger plastic capsules could be fielded in this platform with sufficient laser-beam propagation to the waist of the hohlraum. We also estimate that a full-scale plastic capsule, $1100\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$ in capsule radius, would require $\ensuremath{\sim}1--2\phantom{\rule{0.16em}{0ex}}\AA{}$ of $1\ensuremath{\omega}$ wavelength separation between the outer and inner beams to achieve a symmetric implosion in this platform.

Design of fuzzy radial basis function neural network classifier based on information data preprocessing for recycling black plastic wastes: comparative studies of ATR FT-IR and Raman spectroscopy

As large amounts of plastics are widely used in diverse areas of industry, the amount of plastic waste, including black plastics, continues to increase. In this situation, the necessity of useful recycling having limited resources gradually increases. The design of plastic classification systems for plastics recycling becomes more important to effectively address recycling activities. Until now, conventional sorting systems based on the near infrared ray technology have been used to classify plastic wastes. However, the classification of black plastic waste still remains a challenge because such materials do not reflect sufficient signals due to the absorption of laser light coming from the NIR spectrometer. In order to solve such problems, this research is focused on an efficient way to identify black plastics. Attenuated Total Reflectance (ATR) Fourier Transform Infrared Radiation (FT-IR) and a Raman spectrometer are used to carry out qualitative and quantitative analysis for the effective as well as efficient classification of black plastic wastes. In this study, to effectively classify the black plastic waste, data processing and Fuzzy Transform (F-Transform) as well as PCA-based Fuzzy Radial Basis Function Neural Networks (FRBFNNs) classifier is proposed. Input variables extracted on a basis of chemical characteristic peaks as well as interval range positioned near the chemical characteristic peaks were exploited as a way to improve the classification performance of the FRBFNN classifier. In order to evaluate the performance of the classifier, a suite of techniques including F-Transform-based as well as Principal Component Analysis (PCA)-based FRBFNNs classifier designed with the aid of Particle Swam Optimization are developed to analyze and classify black plastics.

Quantitative measurement of temperature in oxygen enriched CH4/O2/N2 premixed flames using Laser Induced Thermal Grating Spectroscopy (LITGS) up to 1.0 MPa

The application of laser diagnostics to high pressure combustion phenomena is particularly challenging, especially in practical combustors such as rocket motors. In this study, temperature measurements using Laser Induced Thermal Grating Spectroscopy (LITGS) are demonstrated in oxygen enriched CH4/O2/N2 premixed laminar flames at pressures up to 1.0 MPa. We use a previously developed OH absorption LITGS technique to determine product gas temperatures from 0.3 to 1.0 MPa, for both high temperature oxygen-enriched and pure-oxygen flames, for measurements up to 3000 K. Further, we demonstrate how it is necessary to correct the measurements for the local absorption of laser light to obtain accurate temperatures, and offer a technique for producing the correction by using different laser energies. Once the correction is applied, we demonstrate that the measurements at 0.5 MPa are within 1.6% of the adiabatic non-strained flame temperatures, with a standard deviation of about 160 K, thus offering a competitive method for the challenging conditions at high pressures and temperatures. The values obtained at derived temperatures at 1.0 MPa were lower than the adiabatic unstrained flame temperatures, which could possibly be attributed to loss mechanisms.

An experimental study of the effects of surface roughness and coating of Cr2O3 layer on the laser-forming process

Today, laser is widely used in various applications including cutting, welding, surface operations (heat-treatment, coating, and cleaning), rapid prototyping, and forming. In these processes, since energy is not transmitted merely through radiation, the ability of a material to absorb the laser beam energy and control the level of this energy is of great importance. The present paper was aimed to investigate the effects of two factors, i.e. surface roughness and Cr2O3 oxide layer created on the AISI 304-stainless steel sheet, on the absorptivity and formability of the samples in the laser-forming (LF) process with ytterbium fiber laser beam. Various levels of surface roughness were created by hand sandpapers and EDM (electric discharge machining). Furthermore, the Cr2O3 layer with different thicknesses was deposited on the samples using the sol-gel dip-coating process. Through the absorption spectroscopy and the bending angle created during the LF process, the mathematical models of absorption and bending angle were obtained. Increasing the surface roughness and thickness of the Cr2O3 layer led to a significant increase in the samples’ absorptivity and bending angle in the LF process. By roughening the samples’ surface from Ra = 0.04 μm to Ra = 1.9 μm without coating and via depositing up to 6 μm without roughening, the absorptivity at the laser wavelength of 1064 nm and the bending angle were increased, respectively, by 2.3 and 1.8 times and 2.1 and 1.5 times in the LF process. Eventually, multi-objective optimization was conducted to determine the optimal process parameters that could enhance the laser light absorption and maximize the bending angle in the LF process. The validation test confirmed that the predicted value was in good agreement with the actual value.

Revealing the 3-dimensional shape of atom probe tips by atomic force microscopy

For the very first time, atomic force microscopy is used to determine quantitatively the 3-dimensional shape of an atom probe tip, which is key towards improved accuracy and understanding of artefacts in atom probe tomography. We have successfully measured by atomic force microscopy the apex and shank region of 3 different atom probe tips, of which two show (severe) deviations from a hemisphere due to either non-uniform laser light absorption or the presence of two different materials. Clearly, our method which overcomes the challenge of aligning two very sharp tips on top of each other, offers new pathways to study physical mechanisms in (laser-assisted) atom probe. It represents an important step towards improved reconstruction algorithms as the image formation in atom probe tomography is based on the intricate link between the tip shape (down to the atomic level), the electric field distribution and the ions’ flight path towards the detector. Further on, present reconstruction algorithms solely account for a hemispherical tip shape, which does not hold true for most applications and results in complex artefacts. Therefore our method is an attractive novel approach to assess the 3D tip shape.