Incident Laser Beam Research Articles

All-optical limiter photonic crystal with two-photon absorption.

We present in this paper an original theory, modeling, and numerical calculations to make an all-optical limiter based on a two-photon absorption (TPA) nonlinear 2D parallel cylinders upon a triangular geometry photonic crystal in the visible domain. The structure could be either broadband or narrowband and is quasi-invariant to the incidence angle. The parameters used for the cylinders were extracted from the literature (combination of TiO2 and nonlinear ZnO cylinders presenting TPA). This device could be useful, for instance, to protect photodetectors from an intense incident laser beam.

Laser-induced damage of an anti-resonant hollow-core fiber for high-power laser delivery at 1 µm.

We demonstrate high-power laser delivery exceeding 1 kilowatt through a 5-meter homemade anti-resonant hollow-core fiber (AR-HCF) at 1-µm wavelength. Laser-induced damage to the fiber coating and jacket glass is experimentally observed respectively for different incident laser powers from a few hundred watts up to nearly 1.5 kilowatts. The cladding microstructure of the AR-HCF is free of damage at the incident end when 80% of the 1.5-kW incident power is coupled in. The deviation of an incident laser beam from the core to the cladding causes no damage but only deterioration of the coupling efficiency. The potential of the AR-HCF for higher-power laser delivery is discussed.

Diffraction ring patterns of the acid blue 29 in different solvents

The spatial self-phase modulation effect was exploited to study the nonlinear optical parameters of the acid blue 29 dye solutions. The acid blue 29 dye was used as samples and it was dissolved in four different alcohols. The trend in these experiments to investigate the influence of solvent structure on the formation and the temporal evolution of the far field self-diffraction ring patterns of the Gaussian laser beam passing through the studied samples. The nonlinear refractive index (n2), birefringence (Δn2) and thermo-optic coefficient [dn/dT] were determined from the obtained self-diffraction ring patterns. Our results have indicated that the difference between the numbers of diffraction rings is attributed to the type of the solvents and to the incident laser beam intensity.

Incident Angle Dependence of the Waveform of the Polarization-Sensitive Photoresponse in CuSe/Se Thin Film

The results of studying the waveforms of longitudinal and transverse photocurrent pulses generated in thin, semitransparent CuSe/Se films as a function of the angle of incidence (α) of a femtosecond laser beam at linear and circular polarizations are presented. It has been established that the durations of unipolar longitudinal photocurrent pulses at linear and circular polarizations of laser pumping do not depend on the angle α. It is shown that the evolution of the temporal profile of the helicity-sensitive transverse photocurrent with a change in α strongly depends on polarization. At linear polarization, the shape of the unipolar pulses remains virtually constant; however, at circular polarization, the generation of unipolar and bipolar pulses is possible, with the waveforms strongly depending on the angle α. The influence of the incidence angle on the waveforms of transverse photocurrent pulses is explained by the transformation of linear and circular polarization into an elliptical upon the refraction of light at the air/semitransparent film interface and by the interplay of photocurrents arising due to linear and circular surface photogalvanic effects in the film. The presented findings can be utilized to develop polarization and incidence angle-sensitive photovoltaic devices.

Experimental Study of Transverse Trapping Forces of an Optothermal Trap Close to an Absorbing Reflective Film

The optothermal manipulation of micro-objects is significant for understanding and exploring the unknown in the microscale word, which has found many applications in colloidal science and life science. In this work, we study the transverse forces of an optothermal trap in front of a gold film, which is an absorbing reflective surface for the incident laser beam. It is demonstrated that optothermal forces can be divided into two parts: optical force of a standing-wave trap, and thermal force of a thermal trap. The optical force of the standing-wave trap can be obtained by measuring the optical trapping force close to a non-absorbing film with same reflectance. The thermal force can be obtained by subtracting the optical force of the standing-wave trap from the total trapping force of the optothermal trap close to the gold film. The results show that both optical and thermal trapping forces increase with laser power increasing. The optical trapping force is larger than the thermal trapping force, which is composed of convective drag force and thermophoretic force. Further experiment is run to study the composition of thermal force. The result shows that the convective flow is generated later than the thermophoretic flow. The results proposed here are useful for enabling users to optimize optothermal manipulation method for future applications.

Therapeutic processes for eradicating cancerous or benign tumours by laser beams using the excitonic approach of peptide groups

The aim of the present study was to develop a protocol for the treatment of cancerous or benign tumours making use of laser rays, also demonstrating that the destruction process remains exclusively confined in the defective organ. Thermal effects of lasers on biological tissue have been elucidated using vibrational excitations approach of peptide groups (PGs). It was proposed a Hamiltonian which integrate excitations induced by laser pulses and it was shown that the system is governed by a nonlinear equation with strong nonlinearity. It was also exactly described what happens in polypeptide chain once the unwanted organ is irradiated by the Neodymium-doped yttrium aluminium garnet, chosen as incident laser. It was shown that, the advent of incident laser beams contributes to a sudden reinforcement of the vibrational excitations of PGs frequencies and amplitudes. It was also demonstrated that the heating process leads to transverse and longitudinal deformation of the polypeptide chain and these sudden changes lead to the denaturation and subsequently to the destruction of the bulky organ. The drawn curves make it possible to estimate the spatial expansion of the denaturation, in order to effectively control the spread of the heat. Laser irradiation leads to a drastic increase in the vibration amplitudes of the PGs and subsequently results in the destruction of the undesirable tissue. An appropriate choice of the laser can make it possible to circumscribe the destruction only in the defective zone and to protect healthy cells.

Phase Matching via Plasmonic Modal Dispersion for Third Harmonic Generation.

The overall effectiveness of nonlinear optical processes along extended nonlinear media highly depends on the fulfillment of the phase‐matching condition for pump and generated fields. This is traditionally accomplished by exploiting the birefringence of nonlinear crystals requiring long interaction lengths (cm‐scale). For nonbirefringent media and integrated photonic devices, modal phase matching can compensate the index mismatch. Here, the various interacting waves propagate in transverse modes with appropriate phase velocities, but they suffer from a low refractive index contrast and cm‐scale interaction lengths. This work harnesses modal phase matching for third‐harmonic generation (THG) in plasmonic waveguides using an organic polymer (poly[3‐hexylthiophene‐2,5‐diyl]) as the nonlinear medium. One demonstrates experimentally an effective interaction area as small as ≈ 0.11 µm2 and the phase‐matched modal dispersion results in THG efficiency as high as ≈ 10–3 W‐2 within an effective length scale of ≈ 4.3 µm. THG also shows a strong correlation with the polarization of the incident laser beam, corresponding to the excitation of the antisymmetric plasmonic modes, corroborating that plasmonic modal phase matching is achieved. This large reduction in device area of orders of magnitude is interesting for various applications where space is critical (e.g., device integration or on‐chip applications).

Centrifugal atomization of stainless-steel rotating rods melted by a high-power LASER beam

316L grade stainless steel powders were produced by centrifugal atomization during the melting of a rotating rod heated by a high-power LASER beam. The feasibility has been demonstrated by atomizing a range of stainless steel rods. The atomization process has been observed via high-speed imaging and fragmentation regimes have been identified according to a literature review on the rotating electrode process (REP). Results were compared with literature data and an existing prediction model for such a process. High-speed observation can monitor the present process and it is shown that a solidified layer of metal is formed at the edge of the rod during the process inducing metal flake ejection due to the centrifugal stresses. Effects of incident LASER beam power density, ejection speed and oxygen content of the surrounding atmosphere on the particle size distribution and the sample surface have been studied and compared with literature data on classical REP atomizers. The study focuses on the production of irregular particles during the atomization process and highlights the influence of the oxygen content in the surrounding atmosphere on the fragmentation regime and the resulting particle size distribution.

Integrated optical system design for large-field-of-view and broad-spectrum laser warning.

We introduce an integrated large-field-of-view optical system, including a diffraction grating and a multiband narrowband filter, for laser detection. Simulation of the system in the ZEMAX optical design software package indicated that it was capable of detecting laser radiation in the visible light to near-infrared spectral range (500-1700 nm) from azimuth angles up to 120°, and pitch angles up to 96°. In practical experiments conducted at typical laser wavelengths (532 nm, 1064 nm, 1550 nm), the angle error in the full field of view was better than 0.5°, while the laser center wavelength detection accuracy was better than 7 nm, confirming the system's ability to identify the angle of incidence and wavelength of an incoming laser beam.

Emittance in nonlinear Thomson scattering

Inverse Compton scattering sources are finding increasing use as intense sources of high-energy photons. When operated at high field strength, ponderomotive detuning of the scattered emission can lead to decreased source performance. Up to now, the calculations of spectra for such nonlinear Thomson scattering have been done assuming a perfectly aligned electron interacts with the incident laser beam and several authors have investigated whether pondermotive detuning may be mitigated or cured by suitable incident laser chirping prescriptions. In order to determine if these chirping prescriptions are suitable in real beams with nonzero emittance, it is necessary to include misaligned boundary conditions in the electron motion and calculate the resulting spectra from the exact motion. In this paper we provide the exact solution for the electron equations of motion in the case of a misaligned electron passing through a laser pulse of high field strength. This solution is then used to calculate the scattered radiation distribution and we determine the emittance limits for the simplest chirping prescription.

An Atmospheric Turbulence Compensation Algorithm Based on FSM-DM Cascaded AO Architecture for FSO Communications

Free-space optics (FSO) communication enjoys desirable modulation rates at unexploited frequency bands, however, its application is hindered by atmospheric turbulence which causes phase shifting in laser links. Although a single deformable mirror (DM) adaptive optics (AO) system is a good solution, its performance remains unsatisfactory as the proportion of tilts aberrations becomes relatively high. This condition happens when the incident angle of the laser beam for the optical receiver dynamically shifts. To tackle this problem, we introduce a fast steering mirror (FSM), DM cascaded AO architecture, based upon which we also propose an atmospheric turbulence compensation algorithm. In this paper, we compare the compensation ability of FSM and DM towards tilts aberrations. Furthermore, we gain model matrices for FSM and DM from testbed and simulatively verify the effectiveness of our work. For a Kolmogorov theory-based atmospheric turbulence disturbed incident laser beam where the tilt components take up 80% of the total proportion of wavefront aberrations, our proposed architecture compensates the input wavefront to a residual wavefront root mean square (RMS) of 116 wavelength, compared to 16 wavelength for single DM architecture. The study intends to overcome atmospheric turbulence and has the potential to guide the development of future FSO communications.

A facile fabrication of ultrahigh haze optical diffuser using nematic liquid crystal encapsulated by cellulose acetate biopolymer

Polymer dispersed liquid crystals (PDLCs) are materials for next-generation optoelectronic devices. In this work, free-standing optical diffusers based on PDLC are formed by liquid crystals (LCs) and cellulose acetate polymer network. The micron and submicron-sized liquid crystal droplets embedded in the matrix of cellulose acetate biopolymer act as scattering particles, leading to an efficient diffused transmission of the incident laser beam. By optimizing the concentration of LC and polymer, the optical characterizations of the fabricated PDLC films reveal an ultrahigh haze value (99 %) and broad angular distribution of transmitted light with the full width of half maxima up to 114°. The film fabricated with 55 wt % LC results in a light transmitted profile similar to the ideal light diffusing surface with Lambertian distribution. Furthermore, the technique employed to develop the films offers a straightforward and inexpensive fabrication process of light-diffusing films for a high-performance foldable optoelectronic device.

Multi-conformational Luminescence and Phosphorescence of Few Phenazine 1,2,3-triazole Molecules.

Dropcast films produced from blends solutions of phenazine 1,2,3-triazole molecules in very lowconcentrations in a 1,3-Bis (N-carbazolyl) benzene (mCP) matrix were investigated at room tem-perature. The mCP acts as an optically inert matrix, having no influence on the emission propertiesof the guest molecules. Its conductive properties ensure the blend films as completely organic active layers. The fluorescent and phosphorescent emissions of the guest molecules in blue, green, red and also in white are relatively intense, without the need to mix different organic materials. The excitation of the system occurs directly by the incident laser beam on the films. The steady-state spectroscopy for the blue monomer and green dimer singlet fluorescence emissions were investigated. The analysis of their temporal decays was done using a different approach based on the Exponentially Modified Gaussian function. The phosphorescent emissions of the triplet steady-states, in the orange or in the red wavelength regions, were observed to be correlated, respectively, to the formation of guest monomers or to the guest dimers singlet states.

Two-Color Grating Magneto-Optical Trap for Narrow-Line Laser Cooling

We demonstrate the two-color cooling and trapping of alkaline-earth atoms in a grating magneto-optical trap (GMOT). The trap is formed by a single incident laser beam together with four secondary beams that are generated via diffraction from a nanostructured wafer. A grating structure for a GMOT operating with strontium atoms is optimized and fabricated. We trap ${10}^{6}{\phantom{\rule{0.2em}{0ex}}}^{88}\mathrm{Sr}$ atoms on the ${}^{1}{S}_{0}{\ensuremath{\rightarrow}}^{1}{P}_{1}$ transition at $461\phantom{\rule{0.2em}{0ex}}\mathrm{nm}$ and transfer 25% of these atoms to the second cooling stage on the narrower ${}^{1}{S}_{0}{\ensuremath{\rightarrow}}^{3}{P}_{1}$ intercombination transition at $689\phantom{\rule{0.2em}{0ex}}\mathrm{nm}$, preparing a sample of $2.5\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms at $5\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{K}$. These results demonstrate the applicability of the GMOT technology in conjunction with two widely differing wavelengths and enable the continued miniaturization of alkaline-earth-based quantum technologies like optical atomic clocks.

Writing and reading with the longitudinal component of light using carbazole-containing azopolymer thin films

It is well known that azobenzene-containing polymers (azopolymers) are sensitive to the polarization orientation of the illuminating radiation, with the resulting photoisomerization inducing material transfer at both the meso- and macroscale. As a result, azopolymers are efficient and versatile photonic materials, for example, they are used for the fabrication of linear diffraction gratings, including subwavelength gratings, microlens arrays, and spectral filters. Here we propose to use carbazole-containing azopolymer thin films to directly visualize the longitudinal component of the incident laser beam, a crucial task for the realization of 3D structured light yet remaining experimentally challenging. We demonstrate the approach on both scalar and vectorial states of structured light, including higher-order and hybrid cylindrical vector beams. In addition to detection, our results confirm that carbazole-containing azopolymers are a powerful tool material engineering with the longitudinal component of the electric field, particularly to fabricate microstructures with unusual morphologies that differentiate from the total intensity distribution of the writing laser beam.

New Generation Free-Space Optical Communication Systems With Advanced Optical Beam Stabilizer

In this paper, we introduce a novel concept and design of a full-duplex and all-optical FSO transceiver and evaluate its transmission performance in 200 m outdoor environment. Our transceiver enables a reliable fiber-to-fiber FSO link with intelligent lens-based optical-beam-stabilization (OBS) by utilizing miniaturized and cost-effective 3-axis voice-coil motors (VCMs) actuators. The VCM-based moving lens that is widely used in smartphone cameras for auto-focus and optical-image-stabilization is customized and optimized for our designed transceiver to expand the transmitter and receiver field-of-view, control both the transmitted and incident laser beam alignment, suppress the effects of random beam angle-of-arrival fluctuations induced by the atmospheric turbulence and pointing errors and maintain efficient direct coupling to the fiber core at the receiver. Unlike the 2-axis fast-steering-mirrors, the use of 3-axis VCM lenses can not only maintain the beam alignment, but also control the beam collimation and adjust the difference between the lens focal plane and projection plane for a higher fiber coupling efficiency. Using our developed FSO transceivers, we demonstrate an error-free transmission of the standard signals 10 GbE LAN and common public radio interface (LTE-CPRI) over 200 m links. We also performed a continuous 24-h transmission evaluation in a clear weather day, with only occasional burst errors were recorded and a total 24-h BER of 3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\times 10^{-10}$</tex-math></inline-formula> . The obtained results demonstrate the potential of our proposed FSO transceiver to ensure high-capacity communication links and facilitate the adoption of the FSO system as a viable candidate to address the main requirements of B5G/6G networks.

Engineering a better light sheet in an axicon-based system using a flattened Gaussian beam of low order.

Lasers are fundamental tools in research and development. The shape of an incident laser beam directly affects the results, when it propagates through complex structured meso-aspheric optical elements. In conic-based systems utilizing elements such as axicons, the impact of secondary lobes is mostly overlooked, although the intensity distributions at the central spot and the side-lobes directly affect the beam properties. We investigate the interaction of two axicons (160° and 170°) with incident beams approximated by Gaussian, high-order Flattened-Gaussian, and low-order Flattened-Gaussian functions. We demonstrate that replacing an incident Gaussian beam with a low-order Flattened-Gaussian beam reduces the secondary lobes and significantly improves the uniformity of the intensity profile. We practically applied this effect in engineering a conic-aspheric-based static light-sheet microscope producing markedly improved results.

Scattering of an intense laser beam by atomic systems

A nonrelativistic quantum approach is adopted to describe the scattering of an intense laser beam from a simple atomic system. Two forms of the corresponding transition amplitude (TA) are derived, one involving the kinetic momentum operator of the electron and the other involving the force operator. The spectral and angular distribution of the scattered radiation is expressed in terms of TA by a relation recalling the classical one. The formalism is applied to the scattering of radiation by an electron (free or bound) with the absorption of two photons from the incident laser beam. Analytic and numeric results are presented for the distributions of the emitted photons in the case of the nonlinear Compton scattering from a hydrogenic atom in the ground state.

Self-Stabilization of Light Sails by Damped Internal Degrees of Freedom

We consider the motion of a light sail that is accelerated by a powerful laser beam. We derive the equations of motion for two proof-of-concept sail designs with damped internal degrees of freedom. Using linear stability analysis, we show that perturbations of the sail movement in all lateral degrees of freedom can be damped passively: the sail is asymptotically stable. This analysis also shows complicated behavior akin to that associated with exceptional points in PT-symmetric systems in optics and quantum mechanics. We show that the excess heat that is produced by the damping mechanism is likely to be substantially smaller than the expected heating due to the partial absorption of the incident laser beam by the sail.

Assessment of ablation damage on quartz ceramics through experiment and 3D modelling considering a dynamic heat source

The effects of irradiation time (IT), laser power (LP), and spot diameter (SD) on the damage caused to quartz ceramics under continuous-wave laser irradiation were investigated through an orthogonal experiment. The experimental results show that the LP has the dominant effect on the depth of an ablation pit, while the SD has the greatest impact on the diameter of the ablation centre. The diameter and depth of the ablation pit were both positively correlated to the irradiation energy. The bubbles and molten silica transition layer affected the laser beam's reflection and transmission properties, leading to the incident laser beam scattering into the entire ablation pit and forming an elliptical ablation pit. Furthermore, a 3D finite element (FE) model considering a dynamic heat source was developed to simulate the laser damage process. The shape and dimension of the ablation pit predicted by the FE model were consistent with those obtained through the experiment, demonstrating the effectiveness and rationality of the model. The FE analysis results show that the different ablation rates in the radial and depth directions significantly influence the morphology of the ablation pits. The temperature gradient in the transition region increases while the thickness of the transition region decreases as the LP increases. This indicates that a large LP will lead to greater thermal stress in this area and result in more microcracks.