Absorption Of Laser Light Research Articles

Influence of excitation wavelength on LIBS (1064 nm vs 266 nm) for multi-element mortar analysis

The influence of laser parameters, such as the excitation wavelength, on the emission signal obtained by laser-induced breakdown spectroscopy (LIBS), has been studied since the beginning of the technique’s applications, until today. Choosing the best wavelength for a given sample, or a unique emission line, is always a challenge for researchers. This work evaluates the influence of excitation wavelength for the analyse of a full-width LIBS spectrum range. Particularly, eight different mortar samples were used in this study. Firstly, the average spectra obtained with the two excitations (266 and 1064 nm) were evaluated by superimposing the two acquired spectra, and, a trend of different behavior was observed, depending on the emission spectral region. Excitation using the 1064 nm laser was favorable for the spectral range of 180–310 nm, on the other hand, the 266 nm was for the range of 312 nm − 1000 nm. The intensities of the C I, Si I, Zr III, Sb I, Fe II, Mg I, Mg II, Ca I, Ca II, Li I, K I, and, Na I emission lines were evaluated individually, and the results followed the same behavior. The size of the crater was assessed for both lasers and showed more effectiveness for 266 nm than 1064 nm. It is observed that the temperature or ablated size was not exclusively determined for the emission signal. A competition of physical phenomena must be contributing to this. For 1064 nm excitation, the inverse Bremsstrahlung (IB) phenomenon and higher temperature caused by the greater absorption of laser light at this wavelength favored emission in the UV region of the spectrum. On the other hand, the spectra obtained by 266 nm excitation, where Photoionization (PI) effect prevail the temperature achieved in this case is more favorable for filling the levels involved in transitions in the visible and IR range.

Photothermal Depth Profiling of Gelatin-Stabilised Gold Nanorods-Trastuzumab Conjugate as a Potential Breast Cancer Photothermal Agent

AbstractGold nanorods (AuNRs) are powerful photothermal agents (PTAs) in cancer treatment due to their near-infrared laser light absorption ability. However, the cytotoxicity of AuNRs caused by the presence of cationic surfactants often used and their lack of specificity affect their application in photothermal therapy. Thus, we herein developed a bioconjugate obtained from the functionalisation of AuNRs to gelatin (Gel@AuNRs), followed by the conjugation of the as-synthesised material to a breast cancer antibody, trastuzumab (Trast-Gel@AuNRs) to address these issues. The optical and structural characterization of the as-synthesized indicated no significant changes in the optical properties of AuNRs after their functionalisation with gelatin and conjugation with the antibody. The photothermal profiling of the as-synthesised materials showed that AuNRs still have an excellent photothermal conversion efficiency (PCE) after their functionalisation (20%) and their conjugation to an antibody (19%). In addition, the In vitro photothermal depth response showed that Trast-Gel@AuNRs is a promising photothermal agent for HER2-positive breast cancer treatment. Graphical Abstract

Effect of absorption of laser light in mirrors on Fabry-Pérot based refractometry.

This work models and experimentally assesses the influence of absorption of laser light in mirrors in Fabry-Pérot based refractometers used for realization of pressure. Model parameters are assessed by experimental characterizations. Characterizations of two refractometers agree well with the predictions of the model. It is shown that, when pressures are assessed in the viscous region, the absorption of laser light in mirrors will give rise to a small alteration in the proportional response and a pressure-independent offset, where the latter is significant for He but considerably smaller for Ar and N2.

Enhancing tumor's skin photothermal therapy using Gold nanoparticles : a Monte Carlo simulation.

The aim of this study is to investigate how the introduction of Gold nanoparticles GNPs into a skin tumor affects the ability to absorb laser light during multicolor laser exposure. The Monte Carlo Geant4 technique was used to construct a cubic geometry simulating human skin, and a 5mm tumor spheroid was implanted at an adjustable depth x. Our findings show that injecting a very low concentration of 0.01% GNPs into a tumor located 1cm below the skin's surface causes significant laser absorption of up to 25%, particularly in the 900nm to 1200nm range, resulting in a temperature increase of approximately 20%. It is an effective way to raise a tumor's temperature and cause cell death while preserving healthy cells. The addition of GNPs to a tumor during polychromatic laser exposure with a wavelength ranging from 900nm to 1200nm increases laser absorption and thus temperature while preserving areas without GNPs.

Quantitative investigation on the effects of eyeball geometry, blood perfusion and natural convection in retinal laser surgery

The photothermal effects of laser on tissue are widely used in ophthalmology to treat retinal diseases. The accurate modelling of retinal laser surgery will prove valuable guidance for clinic treatment. There are several important issues should be carefully evaluated during retinal laser surgery modelling, including the eye geometry (whole eye or fundus only, retinal pigment epithelium layer incorporated or not), blood perfusion and natural convection. In previous publications, the existence of the anterior part of eyeball and retinal pigment epithelium layer is neglected to simply the eye geometry due to low laser light absorption (anterior part of eyeball) or small volume occupation (retinal pigment epithelium layer), respectively. However, the justification of this treatment has not been conducted. In this study, we will quantitatively investigate these factors systemically in a large pulse duration range that covers all the retinal laser surgery used in clinic. To do this, we present a bioheat transfer model for the simulation of the thermal response of the eye to laser irradiation. In the simulation, the 3D whole-eye geometry is considered. The Pennes bioheat transfer equation is adopted for the whole-eye temperature modelling. Simultaneously, we treat the fundus as a multilayered medium that all primary components, including RPE layer, are considered for first time in whole eye modelling. Our model calculates the thermal responses of the eye during laser retinal surgery with the pulse duration from nanosecond to tens of second. The effects of eye geometry, blood perfusion and natural convection are clearly clarified based on the laser pulse duration and incident energy used. The results show that neglecting the anterior part of eyeball will introduce the computational error more than 27 %. The existence of the retinal pigment epithelium layer should always be considered in retinal laser surgery modelling in all pulse durations used in clinic, otherwise more than 20 % computational error will be generated. When the pulse duration is longer than 10s, the effect of blood perfusion and natural convection in vitreous body should both be considered.

Influence of environmental pressure on the energy coupling and droplet transition behavior in laser welding with filler wire

The influence of environmental pressure on droplet behavior and weld formation in laser welding with filler wire for 304 stainless steel was investigated and the energy coupling behavior was analyzed. As ambient pressure increases from 5 kPa to 700 kPa, the weld depth decreases by 77 %, the variance of the weld width increases approximately 5 times, and the continuity of the weld surface formation deteriorates. During the welding process, a high-speed camera was employed to observe the melt pool, plasma, and melt drop transition behavior. With an increase in the ambient pressure followed by an increase in the metal evaporation temperature, the effects of shielding of the plasma and its internal metal vapor particles on the laser beam lead to a reduction in the depth of the melt. The inverse bremsstrahlung absorption of laser by plasma increased by approximately 36.3 times at 700 kPa compared with that at atmospheric pressure. The number of metal vapor particles at 700 kPa is approximately 3.58 times higher than that at 101 kPa, and the average particle diameter is approximately 0.4 times higher, causing enhanced absorption of laser light by the metal vapor particles. An increase in gas density at elevated ambient pressures resulted in a significant increase in the resistance to droplet descent and decrease in the drive force, leading to an increase in the droplet transition period. This change shifts from a liquid bridge transition to a particle transition, which is the main cause of the deterioration of weld surface formation at high pressures.

3D camera based on laser light absorption by atmospheric oxygen at 761 nm.

A 3D camera based on laser light absorption of atmospheric oxygen at 761 nm is presented. The camera uses a current-tunable single frequency distributed feedback laser for active illumination and a silicon-based image sensor as a receiver. This simple combination enables capturing 3D images with a compact and mass producible set-up. The 3D camera is validated in indoor environments. Distance accuracy of better than 4 cm is demonstrated between 4 m and 10 m distances. Future potential and improvements are discussed.

The impact of laser lift-off with sub-ps pulses on the electrical and optical properties of InGaN/GaN light-emitting diodes

Laser lift-off (LLO) is an important step in the processing chain of nitride-based light-emitting diodes (LEDs), as it enables the transfer of LEDs from the growth substrate to a more suitable carrier. A distinctive feature of LLO with ultrashort pulses is the ability to use either above- or below-bandgap radiation, since nonlinear absorption becomes relevant for ultrashort pulses. This study addresses the differences in the absorption scheme for below- and above-bandgap radiation and investigates the electrical and optical properties of InGaN/GaN LEDs before and after LLO with 347 and 520 nm laser light via current–voltage and power- as well as temperature-dependent photoluminescence measurements. LLO could be successfully realized with both wavelengths. The threshold fluence required for LLO is about a factor of two larger for 520 nm compared to that for 347 nm. Furthermore, an increase in leakage current by several orders of magnitude and a significant decrease in efficiency with laser fluence are observed for below-bandgap radiation. In contrast, leakage current hardly increases and efficiency is less dependent on the laser fluence for samples lifted with 347 nm. This degradation is ascribed to the absorption of laser light in the active region, which facilitates a modification of the local defect landscape. The effect is more severe for below-bandgap radiation, as more laser light penetrates deep into the structure and reaches the active region. Ultimately, we show that LEDs lifted with ultrashort laser pulses can exhibit good quality, making ultrashort pulse LLO a viable alternative to conventional LLO with nanosecond pulses.

Laser Frequency Modulation and PM-to-AM Noise Conversion in Atomic Clocks.

Laser wavelength stability is a necessity in present-day chip-scale atomic clocks (CSACs), in next-generation atomic clocks planned for Global Navigation Satellite Systems (GNSSs), and in many other atomic devices that generate their signals with lasers. Routinely, this is accomplished by modulating the laser's frequency about an atomic or molecular resonance, which in turn induces modulated laser-light absorption. The modulated absorption then generates a correction signal that stabilizes the laser wavelength. However, in addition to creating absorption modulation for laser wavelength stabilization, the modulated laser frequency can produce a time-dependent variance in transmitted laser intensity noise because of laser phase-noise (PM) to transmitted laser intensity-noise (AM) conversion. Here, we show that the time-varying PM-to-AM conversion can have a significant influence on the short-term frequency stability of vapor-cell atomic clocks. If diode-laser enabled vapor-cell atomic clocks are to break into the [Formula: see text] frequency-stability range, the amplitude of laser frequency modulation for wavelength stabilization will need to be chosen judiciously.

Hybrid ultrasound and single wavelength optoacoustic imaging reveals muscle degeneration in peripheral artery disease

Peripheral arterial disease (PAD) leads to chronic vascular occlusion and results in end organ damage in critically perfused limbs. There are currently no clinical methods available to determine the muscular damage induced by chronic mal-perfusion. This monocentric prospective cross-sectional study investigated n = 193 adults, healthy to severe PAD, in order to quantify the degree of calf muscle degeneration caused by PAD using a non-invasive hybrid ultrasound and single wavelength optoacoustic imaging (US/SWL-OAI) approach. While US provides morphologic information, SWL-OAI visualizes the absorption of pulsed laser light and the resulting sound waves from molecules undergoing thermoelastic expansion. US/SWL-OAI was compared to multispectral data, clinical disease severity, angiographic findings, phantom experiments, and histological examinations from calf muscle biopsies. We were able to show that synergistic use of US/SWL-OAI is most likely to map clinical degeneration of the muscle and progressive PAD.

The Application of Bacteriophage and Photoacoustic Flow Cytometry in Bacterial Identification.

Infection with resistant bacteria has become an ever-increasing problem in modern medical practice. Bacteremia is a serious and potentially lethal condition that can lead to sepsis without early intervention. Currently, broad-spectrum antibiotics are prescribed until bacteria can be identified through blood cultures, a process that can take 2-3 days and is unable to provide quantitative information. Staphylococcus aureus (S. aureus) is a leading cause of bacteremia, and methicillin-resistant S. aureus (MRSA) accounts for more than a third of the cases. Other bacteria such as Clostridium difficile, Acinetobacter baumannii, and Carbapenem-resistant Enterobacteriaceae are becoming more prevalent and antibiotic-resistant. Rapid diagnostics for each of these superbugs has been a priority for health organizations around the world. Bacteriophages have evolved for millions of years to develop exquisite specificity in target binding using their host attachment proteins. Bacteriophages are viruses that infect bacteria. Bacteriophages use tail spikes, specialized attachment proteins, to bind specifically to their target bacterial cell surface proteins. We use bacteriophages and parts of bacteriophages as specific tags coupled with photoacoustic flow cytometry for the detection and quantification of bacteria. In photoacoustic flow cytometry, laser light is absorbed by particles under flow, and the ultrasound waves generated on the release of the energy are detected. Photoacoustics involves the detection of ultrasound waves resulting from laser irradiation. In photoacoustic flow cytometry, pulsed laser light is delivered to a sample flowing past a focused transducer, and particles that absorb laser light create a photoacoustic response. Bacteria can be tagged with dyed bacteriophage and processed through a photoacoustic flow cytometer where they are detected by the acoustic response. In this chapter, we describe the procedure and methods used to accomplish this. Often the limiting factor for the treatment of patients is the time spent waiting for results. It is our hope that the work presented in this chapter can be a foundation for future work and provide an ability to detect bacterial pathogens in blood cultures. Bacterial plate cultures and Gram staining are nineteenth-century technologies that have been the gold standards for decades, but current trends in resistant bacteria have necessitated a move toward more rapid and quantifiable diagnostic tools.

Laser light absorption of high-temperature metal surfaces

Laser beam absorption is the basic effect to enable many high-temperature applications and processes. However, high temperature absorption data of metals is often not available or based on theoretical assumptions. In this work, using a newly developed experimental arrangement to measure laser light absorption on liquid metal surfaces even above boiling temperature enabled the derivation of absorption values in those regimes. Results indicate that interband absorption must be considered even at such high temperatures against common theoretical predictions. It is shown that the simulated nearly constant absorption depth and absorption values between melting and boiling temperatures indicate that the increased atom distance due to thermal expansion, denoting a reduced absorption volume, is counterbalanced by the increased statistical availability of conduction electrons due to Fermi band broadening.

Direct femtosecond laser writing of nanochannels by carbon allotrope transformation

Existing approaches for creating durable nanochannels are complex, expensive, and time-consuming. Here, a novel approach is presented in which a femtosecond laser is used to directly write optically accessible nanochannels with arbitrary lengths. Their cross-sections resemble slits and have dimensions that differ by two orders of magnitude. These nanochannels form between an ultra-thin nanocrystalline diamond film and a glass substrate, and their cross-sectional dimensions can be tuned via laser pulse energy. Microscopic investigations show that the laser writing process converts a portion of the sample into a nanostrip, and dedicated experiments indicate that this originates from laser light absorption in the NCD film. The nanostrip is flanked by two nanochannels formed through the delamination of the film. Within the nanostrip, there is non-diamond carbon that plays a vital role in supporting the delaminated portions of the film. This non-diamond carbon is produced when diamond changes into a different carbon allotrope. Besides investigating the mechanism underlying nanostrip formation in depth, film patterning through laser writing is also presented. To demonstrate the applicability of the laser-written nanochannels, a nanofluidic device is fabricated. The nanochannels of the device fill with water via capillary action, as supported by reflectance measurements and simulations. By bypassing complex fabrication techniques and utilizing a durable material system, this work opens doors to manufacturing affordable devices reliant on durable nanochannels, thereby offering promising prospects for future applications.

Fabrication of BiCuOS nanoflowers acting as nanoarrays on photonic nanoparticles for chemo-photothermal therapy

In recent years, 3D flower shaped nanostructures with an ability to improve internal photo reflections and absorptions is gaining popularity for the development of photo-thermal heat generating materials for cancer therapy. The use of bimetallic oxysulfide materials as photo-thermal agent is especially interesting as it is not only resulting in heat generation by absorbing laser light in the biological window but also participates in reactive oxygen species generation in tumor environment. In this work, we have reported a novel flower shaped BiCuOS nanostructures made of CuS base structures with vertical nanoarrays of bismuth oxide nanoplates for synergistic chemo-photothermal cancer therapy. Notably, 2D nanoplates (∼150 ± 50 nm in length and thickness of about ∼25 nm) could be seen grown in the form of nanoflowers (NFs) of 800 ± 100 nm in size on CuS base structures. The electronic structure, density of states, bond angle, bond length and thermal stability of formed NFs were investigated by density functional theory and molecular dynamic studies. The photo-thermal conversion efficiency was increased as a function of NF concentration. The percentage of doxorubicin released was estimated to be only ∼4% even after one day of incubation at pH 7.4 which increased to 38 and 45% at pH 5.5 without and with near infra-red light exposure, respectively. The cell viability experiments with fibroblast cells and red blood cells exhibited excellent biocompatibility of BiCuOS NFs. The synthesized BiCuOS NFs showed excellent anticancer activity against Hep-2 cells. Hence, the BiCuOS NFs reported here have huge potential for use as novel dual performing chemo-and-photothermal agent for advanced cancer therapy.

In Vivo Laser-Induced Vasoactive Microenvironmental Setting via a Stimuli-Responsive Microstructured Depot.

A stimuli-responsive polymeric three-dimensional microstructured film (PTMF) is a 3D structure with an array of sealed chambers on its external surface. In this work, we demonstrate the use of PTMF as a laser-triggered stimulus-response system for local in vivo targeted blood vessels stimulation by vasoactive substances. The native vascular networks of the mouse mesentery were used as model tissues. Epinephrine and KCl were used as vasoactive agents that were sealed into individual chambers upon precipitation in the amount of pictograms. We demonstrated the method for non-damaged one-by-one chamber activation using a focused 532 nm laser light passed through biological tissues. To avoid laser-induced photothermal damage to biological tissues, the PTMF was functionalized with Nile Red dye, which effectively absorbs laser light. Chemically stimulated blood vessel fluctuations were analyzed using digital image processing methods. Hemodynamics changes were measured and visualized using the particle image velocimetry approach.

Laser light absorption and Brewster angle on liquid metal

Laser light absorption occurs in all laser-based processes and is, therefore, of importance for process simulation input, parameter optimization, and understanding of the occurring phenomena, such as melt pool flow or vaporization effects. Theoretical models were successful in predicting metal absorption for certain cases but often fail in high-temperature situations due to unknown impacts of occurring effects, such as surface irregularities or contaminations. Measuring absorption at high temperatures is challenging, and there are limited literature data available on values further above melting temperatures of metals. In this work, a radiometric measurement method is used to derive absorption values at high temperatures. The results show shifted values from Fresnel predictions and absorption peaks at comparably low incident angles. The decreasing absorption tendency at low incident angles was shown to be possibly induced by multi-interface absorption effects caused by surface layering and Knudsen layer effects. Surface layering was seen to be able to induce a very low Brewster angle comparable to the observations in the measurements and is, therefore, seen as a possible dominant factor in absorption at elevated temperatures.

Laser–tissue interaction simulation considering skin-specific data to predict photothermal damage lesions during laser irradiation

Abstract This study aimed to develop a simulation model that accounts for skin-specific properties in order to predict photothermal damage during skin laser treatment. To construct a computational model, surface geometry information was obtained from an optical coherence tomography image, and the absorption coefficient of the skin was determined through spectrophotometry. The distribution of the internal light dose inside the skin medium was calculated using the light propagation model based on the Monte Carlo method. The photothermal response due to the absorption of laser light was modeled by a finite difference time domain model to solve the bio-heat transfer equation. The predicted depth and area of the damaged lesions from the simulation model were compared to those measured in ex vivo porcine skin. The present simulation model gave acceptable predictions with differences of approximately ∼10% in both depth and area.

An extended Vlasov–Fokker–Planck approach for kinetic simulations of laser plasmas

Vlasov–Fokker–Planck simulation codes occupy an important niche in modeling laser-produced plasmas, since they are well suited to studying the effect of collisions on electron kinetic phenomena, especially energy transport. One of the most important elements of energy transport is the absorption of laser light by the plasma; however, simulating this in detail requires resolving oscillations of the laser light, whose characteristic timescale is orders of magnitude shorter than the simulation time needed to study transport physics. For this reason, most Vlasov–Fokker–Planck codes used to study electron transport in laser plasmas rely on simplified models of the laser–plasma coupling. Their underlying assumptions nominally preclude their use for modeling laser light having short-scale structure in space or time, such as broadband lasers. In this work, we derive a more general computational framework suitable for arbitrarily structured laser fields. Our approach is based on an extended set of Vlasov–Fokker–Planck equations that separately solve for the low- and high-frequency plasma response. We implement these extended Vlasov–Fokker–Planck equations in the spherical harmonic code K2 and demonstrate the performance of the method on several laser absorption test problems, with particular attention to the judicious selection of time steps, time integrators, and spherical harmonic truncation, according to the intensity and spectrum of the laser light under consideration. Comparison with the widely used Langdon absorption operator shows the Langdon operator performs remarkably well for predicting laser heating in the simple cases considered here, even in situations that would seem to violate its underlying assumptions.

Application of Planar Laser-Induced Fluorescence for Interfacial Transfer Phenomena

The present review describes the current achievements in the applications of a planar laser-induced fluorescence (PLIF) method for the diagnostics of liquid films, bubbles, individual droplets, and sprays. Such flows are related with strongly curved interphases, which often results in additional high errors during the PLIF data quantification because of laser light reflection, refraction, and absorption. The present review demonstrates that a two-color PLIF approach and a PLIF modification for regularly structured illumination resolves the reflection- and refraction-caused errors. The latter modification ensures proper phase separation in the measurement cross-section and visualization of the interface dynamics. The former approach provides the accurate evaluation of the local temperature and concentration both in liquid and gaseous phases even in the case of strong variations of the laser sheet intensity. With intensified cameras, the PLIF method is used for multi-parameter diagnostics of the two-phase combustion of sprays in combustion chambers with optical access. It visualizes and quantifies the liquid fuel evaporation and mixing, to measure temperature in the gas and liquid phases and to reveal the regions of pollutant formation. The PLIF technique can also be easily combined with a particle image (or tracking) velocimetry method, to evaluate local heat and mass transfer.

Optical spin-wave detection beyond the diffraction limit

Spin waves are proposed as information carriers for next-generation computing devices because of their low power consumption. Moreover, their wave-like nature allows for novel computing paradigms. Conventional methods to detect propagating spin waves are based either on electrical induction, limiting the downscaling and efficiency complicating eventual implementation, or on light scattering, where the minimum detectable spin-wave wavelength is set by the wavelength of the laser unless near-field techniques are used. In this article, we demonstrate the magneto-optical detection of spin waves beyond the diffraction limit using a metallic grating that selectively absorbs laser light. Specifically, we demonstrate the detection of propagating spin waves with a wavelength of 700nm in 20nm thick Ni80Fe20 strips using a diffraction-limited laser spot with a diameter of 10μm. Additionally, we show that this grating is selective to the wavelength of the spin wave, providing phase-sensitive, wavevector-selective spin-wave detection in the time domain, thus providing a complementary approach to existing techniques such as Brillouin light scattering. This should open up new avenues toward the integration of the burgeoning fields of photonics and magnonics and aid in the optical detection of spin waves in the short-wavelength exchange regime for fundamental research.