Cw Laser Radiation Research Articles

Laser-Induced Interference to Infrared Detector Using Continuous Wave and Short-Pulse Lasers.

The response of a DPbS3200 infrared detector irradiated by a nanosecond pulsed laser and CW laser has been investigated to study laser-induced interference. A laser interference experiment system was constructed to measure the time-varying response signal. A nanosecond pulsed laser and a CW laser of 10 Hz were used, with a 1064 nm wavelength and a millimeter-scale irradiation spot diameter. Firstly, the characteristics of transient interference signals induced by pulsed lasers were analyzed. Then, the characteristics of response signal interference by both CW laser and pulsed laser irradiation were further investigated. The results showed that the pulsed laser only produced transient interference. However, the CW laser led to a significant amplitude reduction of the response signal, which could continuously interfere in the operating time. For transient interferences, the amplitude of the interference signal increased linearly with the laser fluence. The relation between the pulse repetition rate of the incident laser and the operating frequency of the detector determined the numbers of transient interference signals in one response period; for the interference induced by both the CW laser and pulsed laser, CW laser interference played a leading role when CW laser power density increased to 4.1 W/cm2 or more. As the CW laser fluence reached 6.1 W/cm2, the PbS infrared detector was no longer able to detect any signal, which caused temporary blindness. In the end, a probit model was used to determine the interference threshold.

Probing the cw-Laser-Induced Fluorescence Enhancement in CsPbBr3 Nanocrystal Thin Films: An Interplay between Photo and Thermal Activation.

Perovskite nanocrystals hold significant promise for a wide range of applications, including solar cells, LEDs, photocatalysts, humidity and temperature sensors, memory devices, and low-cost photodetectors. Such technological potential stems from their exceptional quantum efficiency and charge carrier conduction capability. Nevertheless, the underlying mechanisms of photoexcitation, such as phase segregation, annealing, and ionic diffusion, remain insufficiently understood. In this context, we harnessed hyperspectral fluorescence microspectroscopy to advance our comprehension of fluorescence enhancement triggered by UV continuous-wave (cw) laser irradiation of CsPbBr3 colloidal nanocrystal thin films. Initially, we explored the kinetics of fluorescence enhancement and observed that its efficiency (φph) correlates with the laser power (P), following the relationship φph = 7.7⟨P⟩0.47±0.02. Subsequently, we estimated the local temperature induced by the laser, utilizing the finite-difference method framework, and calculated the activation energy (Ea) required for fluorescence enhancement to occur. Our findings revealed a very low activation energy, Ea ∼ 9 kJ/mol. Moreover, we mapped the fluorescence photoenhancement by spatial scanning and real-time static mode to determine its microscale length. Below a laser power of 60 μW, the photothermal diffusion length exhibited nearly constant values of approximately (22 ± 5) μm, while a significant increase was observed at higher laser power levels. These results were ascribed to the formation of nanocrystal superclusters within the film, which involves the interparticle spacing reduction, creating the so-called quantum dot solid configuration along with laser-induced annealing for higher laser powers.

NaSr3Be3B3O9F4 crystal growth and continuous-wave laser generation at 266 nm

In this paper, we have grown a large NaSr3Be3B3O9F4 (NSBBF) crystal with a top-seeded solution method and generated a continuous-wave (cw) laser radiation at 266 nm with a Brewster-cut NSBBF. With a high-power cw 532 nm and a frequency doubling stage, up to 120 mW cw UV laser was generated at 266 nm. A high stability at 50 mW was obtained more than 10 h. This cw UV laser source is applicable for self-calibrating solar irradiators.

Fs Laser Patterning of Amorphous As2S3 Thin Films.

This study investigates the morphological changes induced by femtosecond (fs) laser pulses in arsenic trisulfide (As2S3) thin films and gold-arsenic trisulfide (Au\As2S3) heterostructures, grown by pulsed laser deposition (PLD). By means of a direct laser writing experimental setup, the films were systematically irradiated at various laser power and irradiation times to observe their effects on surface modifications. AFM was employed for morphological and topological characterization. Our results reveal a clear transition threshold between photoexpansion and photoevaporation phenomena under different femtosecond laser power regimes, occurring between 1 and 1.5 mW, irrespective of exposure time. Notably, the presence of a gold layer in the heterostructure minimally influenced this threshold. A maximum photoexpansion of 5.2% was obtained in As2S3 films, while the Au\As2S3 heterostructure exhibited a peak photoexpansion of 0.8%. The study also includes a comparative analysis of continuous-wave (cw) laser irradiation, confirming the efficiency of fs laser pulses in inducing photoexpansion effects.

Study on multi-scale ablation behavior of C/SiC composites under high-energy CW laser irradiation

This work conducts ablation experiments and multi-scale numerical simulations of C/SiC composite materials under CW laser action. The highest surface temperature, macroscopic and microscopic ablation morphology, and approximate ablation threshold for C/SiC composites at different power densities were obtained. A multi-scale ablation calculation method for C/SiC composite materials under CW laser action was established using the level-set method. At the meso-scale, a macro-mesoscopic cross-scale surface ablation model was established, taking into account factors such as solid heat transfer, heat exchange of chemical reactions, differential temperature rise process between internal fibers and matrix, and differences in ablation behavior of two-dimensional plain weave fabrics. The experimental and microscale simulation results indicate that different ablation behaviors (oxidation and sublimation) occur in different regions, resulting in “shoot tip” fibers and residual matrix pore morphology. This work can provide theoretical and experimental basis for the design and precision machining of C/SiC materials.

Silver(I)-induced anisotropy in the plasmon-driven growth of nanoscale gold

ABSTRACT The plasmon-mediated synthesis of anisotropic gold nanoparticles (AuNPs) has only recently been investigated and achieved. This process typically utilizes the surface plasmon resonances (SPRs) of the nanoparticles themselves to drive metal deposition and growth. Many of the traditional methods for shape control, including use of functional surfactants and etchants, have yet to be utilized within the context of light-driven synthesis. Here, the underpotential deposition of Ag(I) is utilized as a shape-controlling strategy in a hot electron-driven photochemical synthesis to grow anisotropic gold nanoparticles. The strategy also relies on L-pyroglutamic acid, a natural amino acid metabolite, as a photochemical relay aiding in the transport and localization of plasmon-generated hot electrons. By carefully adjusting reagent concentrations, the morphologies of the resulting nanoparticles can be facilely tuned from spheres to nanostars and nanoflowers. The high extinction in the NIR region of the ‘ideal’ gold nanostars synthesized advocates their use as photothermal therapy agents, supported by a sufficient photothermal conversion efficiency (η = 30.8%) under 808 nm CW laser irradiation. This contribution expands the repertoire of gold nanostructures accessible to visible-light-driven plasmonic photochemistry. Different gold nanoparticle shapes have been accessed using a plasmon-mediated growth technique. Ag(I) ions induce symmetry breaking, yielding nano-sized gold spheres, stars, and flowers. A specialized photoreactor, equipped with 505 nm LED illumination, facilitates the transfer of hot electrons from a pre-made gold nanocube seed surface. Gold reduction and deposition occur, and anisotropic structures grow with the aid of L-pyroglutamic acid and Triton X-100 as coordinating and shape-directing agents.

Laser Surface Texturing of Metals Using Dynamic Melt Expulsion by Application of Fast Modulated CW-Laser Radiation

Laser Surface Texturing of Metals Using Dynamic Melt Expulsion by Application of Fast Modulated CW-Laser Radiation

Photobleaching Kinetics and Effect of Solvent in the Photophysical Properties of Indocyanine Green for Photodynamic Therapy.

Indocyanine green is an attractive molecule for photodynamic therapy due to its near infrared absorption, resulting in a higher tissue penetration. However, its quantum yields of the triplet and singlet state have been reported to be low and then, reactive oxygen species are unlikely to be formed. Aiming to understand the ICG role in photodynamic response, its photobleaching behavior in solution has been studied under distinct conditions of CW laser irradiation at 780 and 808 nm, oxygen saturations and solvents. Sensitizer bleaching and photoproduct formation were measured by absorption spectroscopy and analyzed using the PDT bleaching macroscopic model to extract physical parameters. ICG photobleaching occurs even at lower oxygen concentrations, indicating that the molecule presents more than one way of degradation. Photoproducts were produced even in solution of less than 4 % oxygen saturation for both solvents and excitation wavelengths. Also, the amplitude of absorption related to J-dimers was increased during irradiation, but only in 50 % PBS solution. The formation of photoproducts was enhanced in the presence of J-type dimers under low oxygen concentration, and the quantum yields of triplet and singlet states were one order of magnitude and two times higher, respectively, when compared to ICG in distilled H2 O.

Challenges in the development of a reliable cw-LIDT measurement routine

The characterization of continuous-wave (cw) laser-induced damage threshold (LIDT) requires a suitable measurement routine to obtain reliable results. In this study, we show that the existing measurement protocols are of limited use for cw-LIDT measurements. On the basis of testing several mirrors with varied distance and number of spots on the samples an adapted protocol for the damage behavior under cw laser irradiation is proposed. We observed a significant effect governed by debris and induced stress of induced damages on the damage behavior of subsequent irradiation spots. Finally, we performed a parametric study on the optical properties of mirror designs consisting of a metal and a dielectric multilayer film and demonstrated the LIDT dependence on the thermal conductivity of the substrate and the absorption of the components.

Analysis of impact of atmospheric attenuation and measurement uncertainties on laser hazard distances in navigable airspace for visible cw laser radiation

Analysis of impact of atmospheric attenuation and measurement uncertainties on laser hazard distances in navigable airspace for visible cw laser radiation

Generation of Short Pulses by Filtering Phase-Modulated CW Laser Radiation

A method for generating short pulses with a high repetition rate is proposed. It is based on periodic modulation of the radiation phase of a CW laser and subsequent filtering through a narrow-band frequency filter. At the output of the filter, a sequence of short pulses is generated with a period equal to half the modulation period. In the case of a resonant filter using atoms, ions or molecules with a narrow absorption line, the appearance of pulses can be explained by constructive interference of the incident radiation with radiation coherently scattered by resonant particles. An alternative explanation of the pulse generation in the general case, when frequency filters operating on other principles are used, is based on the interference of the spectral components remaining after filtering. The method can be applied for time division multiplexing to transmit digital information through a single channel at high speed. The advantage of the proposed method is the use of phase modulation (not strictly periodic), integrated with frequency filtering to generate pulses and encode information simultaneously in one circuit, while in other known methods, information is introduced into a sequence of regularly generated pulses using additional amplitude modulation.

Melt flow and ripple formation induced by continuous wave laser irradiating of copper foil at 10 Pa

Continuous wave laser (CW laser) ablation morphology of copper foil in low pressure environment is very different from that in atmospheric environment. In low pressure environment, there are few splashes on the surface of molten region. Ring ripples are also observed on the surfaces of molten region after laser irradiation. A 2D axisymmetric model considering temperature dependent surface tension and condensation coefficient is established to investigate the molten flow behavior in molten pool during laser ablation in the environment of 10 Pa. The results show that Marangoni effect caused by temperature gradient is the main driver of fluid flow during laser irradiation. Ring ripples are formed by Marangoni effect and capillary force during cooling process. Compared with those in atmospheric environment, the recoil pressure in 101 Pa environment is smaller and the evaporation rate is higher at the same temperature. For foils with different thicknesses, the differences in temperature gradient make the distribution of ripples different. The mechanisms of the ripple formation on metal foil induced by CW laser irradiation are revealed for the first time.

Research on High Power Laser Damage Resistant Optically Addressable Spatial Light Modulator

Liquid crystal spatial light modulators (LC-SLMs) are devices that can accurately adjust the parameters of beam amplitude, phase, wavefront and polarization. However, due to the limitation of laser damage resistance of component materials, LC-SLMs still have difficulty meeting the application and development needs of a high-average power laser system. Here, we proposed an optically addressable spatial light modulator (OASLM) based on a sapphire substrate. Due to the good thermal conductivity of sapphire, the laser damage resistance of the device was greatly improved. The thermal distribution of OASLM based on the sapphire substrate and the K9 substrate is analyzed by a laser-induced temperature rise model. The experimental results also show the excellent performance of sapphire OASLM under high-power CW laser irradiation, its laser power density is increased from 10 W/cm2 to 75 W/cm2, and the working time is more than 30 min. By bonding sapphire to the other side, the laser power density can be increased to 100 W/cm2, and these are completed without active heat dissipation. This method provides a feasible path for high-average-power SLMs.

Comparative photocrystallographic study using CW and pulsed laser irradiation on a photo-switchable ruthenium nitrosyl complex

Comparative photocrystallographic study using CW and pulsed laser irradiation on a photo-switchable ruthenium nitrosyl complex

Studying IR Photohyperthermia Sensitized by Titanium Nitride Nanoparticles Using Tissue-Equivalent Phantoms

Purpose: To use tissue-equivalent phantom for studies of thermal fields in biological tissues during IR photo hyperthermia with plasmonic titanium nitride nanoparticles (TiN NPs). Material and methods: Gel phantom based on polyacrylamide (PAA) with addition of naphtol green dye and intralipid 10% was created. Optical properties (reduced scattering coefficient) of phantom ingredients were determined using added absorber technique. Thermal field distribution was studied with IR thermal imaging technique. 50 nm plasmonic TiN NPs, synthetized by laser ablation in liquids, were used as sensitizers of photothermic action. Photothermal experiments were performed using two phantoms: a phantom with homogeneous optical parameters, which are relevant to biological tissues (absorption coefficient µa=0.35 сm-1, reduced scattering coefficient µ's=30 сm-1), and a phantom containing 0.02 mg/ml of TiN NPs, which increased absorption coefficient by Dµa=0.65 сm-1. The part of phantom with the NPs was located under 5 mm layer of NPs-free phantom. Photothermal effect was excited by CW laser irradiation of 830 nm wavelength and 16 W/cm2 intensity (900 mW, beam diameter: 1.3 mm) for 2 min. Thermal field distribution inside the phantom was measured by IR thermal camera. Results: A tissue-equivalent gel phantom with independently tunable absorption and scattering coefficients was designed. The phantom had cubic shape with 30 30 30 mm size. Results of photothermal experiments showed that the use of TiN NPs as sensitizers IR photohyperthermia leads to a significant increase in tissue temperature (up to 5 degrees Celsius) at distances up to 15 mm under the phantom surface. In addition, a simple experimental setup for measuring scattering coefficient of a liquid phantom ingredients was described. Conclusion: A simple method for preparation of PAA phantom for modelling photothermal heating of biological tissues and studying thermal fields distributions was described. The phantom is handy and allows one to quickly experimentally simulate the photothermal response of biological tissues, including tissues containing various spatial distributions of photosensitive NPs. TiN NPs experimentally confirmed to be an effective sensitizer of IR photothermal effect.

Laser Ablation Mechanism and Performance of Carbon Fiber-Reinforced Poly Aryl Ether Ketone (PAEK) Composites

The ablation mechanism and performance of carbon fiber (CF)-reinforced poly aryl ether ketone (PAEK) thermoplastic composites were studied in this paper. The results show that the ablation damaged area is controlled by the irradiation energy, while the mass loss rate is controlled by the irradiation power density. In the ablation center, the PAEK resin and CFs underwent decomposition and sublimation in an anaerobic environment. In the transition zone, the resin experienced decomposition and remelting in an aerobic environment, and massive char leaves were present in the cross section. In the heat-affected zone, only remelting of the resin was observed. The fusion and decomposition of the resin caused delamination and pores in the composites. Moreover, oxygen appeared crucial to the ablation morphology of CFs. In an aerobic environment, a regular cross section formed, while in an anaerobic environment, a cortex–core structure formed. The cortex–core structure of CF inside the ablation pit was caused by the inhomogeneity of fibers along the radial direction and the residual carbon layer generated by resin decomposition in an anoxic environment. The description of the ablation mechanism presented in this study broadens our understanding of damage evolution in thermoplastic composites subjected to high-energy CW laser irradiation.

Calculation and analysis of laser hazard distances in navigable airspace for multi-beam visible CW laser radiation

Abstract The article describes the way to calculate the distances, defined by the U.S. Federal Aviation Administration in the AC 70-1B document, essential for the flight safety in the case of illumination of aircraft pilots by laser radiation. FAA’s calculations and presented examples are simplified for the most common cases of a single circular beam, or circular beams sharing the same power, divergence and aperture. Proposed in this article calculation method was extended to multi-beam radiation sources characterized by different wavelengths, different divergences in two perpendicular planes and different powers. The impact of ellipticity of the beams on the calculated distances was shown. The presented analysis may be a supplement to the AC 70-1B document and may serve as a sample approach for those who need to deal with such laser sources. Laser pointers characterized by powers of up to 50 W as well as these with typical powers of several mW were considered. It was shown that even typical 1 mW laser pointers may still distract the aircraft pilots during landing or take-off which may have adverse consequences.

Development of a novel probe for measuring emissivity and temperature during Raman spectroscopy

Abstract In this work, an innovative tool to perform real-time measurements of emissivity and temperature of a given material surface under CW laser irradiation was developed. In the radiative energy balance, the emissivity represents the complementary component of the reflectance, thus, its measurement can be exploited to calculate the temperature at the target surface from infrared emission measurements provided by a suitable sensor. A miniaturized photothermal sensing line was designed as an accessory of Raman probes for driving thermal control loops in order to prevent overheating during the spectroscopic acquisition. To demonstrate its effectiveness and reliability, it was integrated with in a home-made Raman instrument (exc. 1064 nm) and associated software to achieve an automated online thermal control. Temperature rise during Raman spectroscopy can induce chemical alterations of the material under analysis and seriously affect its original spectral features. In several applications, such photothermal side effects can represent a serious problem to be carefully controlled in order to safeguard the integrity of the material and its spectral fingerprint. A thorough experimentation of the novel tool was carried out on photothermally sensitive materials such as red lead and massicot powders, traditionally used as pigments since ancient times. Finally, the compactness of the components and the fast response time made this system particularly suitable for nondestructive in-situ investigations.

Perforation effect of CW laser irradiation on aluminum alloy under subsonic flow

Perforation effect of CW laser irradiation on aluminum alloy under subsonic flow

On the initial stage of the evolution of hydrodynamic parameters during deep penetration of metals by high-power laser radiation

A qualitative analysis of changes in hydrodynamic parameters during keyhole formation by thermocapillary melt removal under the point action of CW laser radiation is presented. It is established that rapid surface deformation leads to adhesion of the viscous sublayer to the melting boundary and creation the shear structure of thermocapillary flow which stimulates acceleration of keyhole growth. Keywords: keyhole formation, laser radiation, thermocapillary effect, shear flow, viscous sublayer, sticking.