Laser Research Articles

Profiling atmosphere temperature from space using lidar with a Mach−Zehnder interferometer: principle and assessment

The Mach Zehnder interferometer is an effective device for characterizing coherence of light. By the interference signals of the four channels for the Mach Zehnder interferometer, the interference contrast of Rayleigh Brillouin (RB) backscattering from atmospheric molecules to the laser beam is obtained. This interference contrast is related to the width of the RB backscattering spectrum, which is proportional to the average speed of irregular thermal motion of molecules. This average velocity is directly related to the temperature of the atmosphere at the backscattering point. The interference contrast of RB backscatter at different altitudes can vertically profile temperature. Using a Mach Zehnder interferometer with significant optical path difference, the ultraviolet spaceborne lidar can approach accuracy (random 1 K), vertical resolution (500 m), and horizontal resolution (50 km) of temperature in the troposphere.

High-speed pulsing circuit for continuous wave laser beams

Abstract Tunable continuous wave (CW) lasers produce the highest optical resolution for pumping and probing atomic and molecular transitions. These lasers adopt sophisticated electronic control of optical components within the cavity to set the wavelength and ensure a narrow bandwidth. The low-cost circuit described here gates a CW laser beam on and off for high resolution timing experiments, using an electro-optic modulator that acts as a switchable waveplate between linear polarizers. The switch can operate at rates of up to 100 kHz with a minimum pulse width of 650 ns, or it can be configured to deliver laser pulses with widths ⩾ 35 ns at lower rates. Multiple laser pulses of equal or non-equal widths can also be delivered within each repetition cycle.

Dynamics of spatial frequency modulation of $${\varvec{q}}$$-Gaussian laser beams in preformed radially inhomogeneous collisional plasma channels: effect of self-focusing

Dynamics of spatial frequency modulation of $${\varvec{q}}$$-Gaussian laser beams in preformed radially inhomogeneous collisional plasma channels: effect of self-focusing

Gouy phase shift of Bessel Gauss laser beams in plasmas with axial temperature ramp: effect of self focusing

Gouy phase shift of Bessel Gauss laser beams in plasmas with axial temperature ramp: effect of self focusing

Quality assurance via a cyber physical system of a PBF-LB/M machine

Abstract Powder Bed Fusion with Laser Beam of Metals (PBF-LB/M) faces challenges in reproducibility and quality assurance, even for widely applied alloys like AlSi10Mg. This work introduces a digital provenance framework for PBF-LB/M, showcased through the EOS M 300–4 multi-laser machine. An Extract, Transform, Load (ETL) pipeline autonomously captures machine data, including scan vectors as well as process signals, and organizes them into a Digital Shadow (DS). The DS is further extended by external data sources, such as Melt Pool Monitoring (MPM), to enable comprehensive analysis and root cause identification. This approach ensures continuous data representation and facilitates the development of new quality metrics. Moreover, the framework enhances quality assurance and traceability, supports compliance with industry standards, and improves productivity. It also enables more precise cost calculations and predictive maintenance. By addressing these challenges, the framework is essential for advancing PBF-LB/M in industrial applications, achieving greater consistency and scalability in production.

Fabrication of Silicon Surface Microstructures via Vortex Femtosecond Laser Irradiation for Reusable Substrates in SERS Applications.

Surface-enhanced Raman spectroscopy (SERS) is a key technique in analytical chemistry because of its exceptional sensitivity and specificity for detecting a broad spectrum of substances. Herein, a silicon (Si) substrate fabricated using vortex femtosecond laser beams in ambient air is proposed as an innovative, highly sensitive, and reusable platform for advanced SERS applications. The substrate has composite nanostructures adorned with bush-like formations on top of the elongated structures, which is a direct consequence of the orbital angular momentum of the vortex beam. Simulations conducted using COMSOL provide valuable insights into the distribution of hot spots and electromagnetic field across the substrate surface after gold nanoparticles deposition, underscoring the superior SERS detection capabilities of the fabricated substrate using vortex beams as compared to those processed by Gaussian beams. The vortex-fabricated substrate possesses remarkable reusability, stability, and time-resistance. It exhibited outstanding detection performance for malachite green and microcystin-LR, achieving limits of detection values of 3.91 pM and 2.69 pg·mL-1, respectively. Therefore, the Si substrates fabricated using a vortex femtosecond laser beam is an ideal candidate for advancing SERS sensors to new heights.

Thermodynamic perspective of ion acoustic wave excitation by self focused Bessel Gauss laser beams in axially inhomogeneous plasmas

Thermodynamic perspective of ion acoustic wave excitation by self focused Bessel Gauss laser beams in axially inhomogeneous plasmas

Perceived Brightness and Resolution of Holographic Augmented Reality Retinal Scan Glasses

Augmented reality display performance depends strongly on features of the human visual system. This is especially true for retinal scan glasses, which use laser beam scanning and transparent holographic optical combiners. Human-centered approaches allow us to go beyond conventional optical metrology and evaluate display performance as it is perceived in actual augmented reality use cases. Here, we first present a theoretical formula for the retinal scan luminance and ambient contrast ratio calculated from optical powers, wavelengths, field of view, and human pupil diameter. As a promising insight, we found that the pupil diameter dependence is beneficial in assimilating the virtual image luminance to the ambient luminance. Second, we designed and performed a psychophysical experiment to assess perceived resolution in augmented reality settings using a fully functional retinal scan glasses prototype. We present the results of the trials and illustrate how this approach can be used in the further development of augmented reality smart glasses.

The influence of symmetry breaking on the Inner Core of a Structured Laser Beam

The influence of symmetry breaking on the Inner Core of a Structured Laser Beam

Microstructure tailoring for crack mitigation in CM247LC manufactured by powder bed fusion – Laser beam

Microstructure tailoring for crack mitigation in CM247LC manufactured by powder bed fusion – Laser beam

On the influence of optically controlled thermocapillary flow during vertical convective assembly: Origin of remora disk-like patterns

Vertical convective assembly, a cost-effective and efficient colloidal assembly strategy, has garnered interest from a wide range of disciplines, including photonics and sensors. In this work, we reveal the role of nonuniform temperature distribution at the three-phase contact line (TPCL) during the vertical lifting of the substrate from the colloidal suspension. Conventionally, vertical assembly is performed under isothermal conditions, and the possible outcomes are uniform particle deposits and discrete lines based on stick-slip behavior. We demonstrate that exposing the TPCL with a nearly Gaussian-type temperature profile under an optimal lifting speed of 0.8–5 μm/s results in a new kind of particle pattern, which we call remora disk-like assembly, with periodic central thick regions and lamella-kind structures on either side. We generate the required temperature gradient by irradiating the TPCL with a laser beam, whose emission wavelength matches the plasmonic excitation of the nanoparticles used (λ = 532 nm). The nonuniform temperature distribution at the TPCL (ΔT = 13 °C) generates a corresponding thermocapillary flow, which drives the particles toward the TPCL in a gradient manner. We develop a physical model to explain the particle deposition mechanism, the nature of the remora disk assembly, and the asymmetric depinning behavior of the meniscus. Furthermore, by varying the lifting speed, we could tune the morphology and spacing of the patterns. We believe the new insights on the particle dynamics under optically controlled thermocapillary flow could significantly contribute to the fundamental understanding as well as enriching the applied aspects of the vertical lifting-based colloidal lithography.

Rotation of polarization plane of a laser beam by fluid vorticity

The polarization plane of a beam of light experiences angular drag when it traverses a medium rotating about an axis parallel to the direction of the beam. Here, fluid vorticity in a horizontal Rijke tube is used to cause rotation in the polarization plane of a continuous laser beam. The vorticity distribution and acoustic pressure history in the tube have been predicted numerically. The thermo-acoustic phenomenon in the tube has been found to generate the vorticity. A suitable optical arrangement has been used to capture the light intensity variation due to the rotation of the plane of polarization of the beam, and up to 4° of rotation has been observed.

Enhanced plasma wave excitation in a tapered plasma channel through chirped laser beatwaves

The excitation of plasma waves by the beatwave of two-color laser beams within a tapered plasma channel has been investigated both analytically and through particle-in-cell (PIC) simulations. This study presents a promising approach for beatwave accelerators. The design aims to achieve a more stable and enhanced plasma wave amplitude, even under non-resonant conditions, compared to untapered channels. For the analytical description, we solved the plasma wave equation generated by two beating laser beams propagating through a tapered channel with a linear radial density profile. The study further validates its results by comparing the analytical predictions with PIC simulations of the beatwave phenomenon in the tapered channel. The findings confirm that this design significantly enhances plasma wave amplitude compared to untapered channels. In addition, we demonstrated that employing a chirped laser pulse with a fast rise time can significantly increase the strength of the plasma wave.

Evolution of autoresonant plasma wave excitation in two-dimensional particle-in-cell simulations

The generation of an autoresonantly phase-locked high-amplitude plasma waves to the chirped beat frequency of two driving lasers is studied in two dimensions using particle-in-cell simulations. The two-dimensional plasma and laser parameters correspond to those that optimized the plasma wave amplitude in one-dimensional simulations. Near the start of autoresonant locking, the two-dimensional simulations appear similar to one-dimensional particle-in-cell results (Luo et al., Phys. Rev. Res., vol. 6, 2024, p. 013338) with plasma wave amplitudes above the Rosenbluth–Liu limit. Later, just below wave breaking, the two-dimensional simulation exhibits a Weibel-like instability and eventually laser beam filamentation. These limit the coherence of the plasma oscillation after the peak plasma wave field is obtained. In spite of the reduction of spatial coherence of the accelerating density structure, the acceleration of self-injected electrons in the case studied remains at $70\,\%$ to $80\,\%$ of that observed in one dimension. Other effects such as plasma wave bowing are discussed.

High-Peak-Power Sub-Nanosecond Laser Pulse Sources Based on Hetero-Integrated “Heterothyristor–Laser Diode” Vertical Stack

Compact high-power sub-nanosecond laser pulse sources with a wavelength of 940 nm are developed and studied. A design for laser pulse sources based on a vertical stack is proposed, which includes a semiconductor laser chip and a current switch chip. To create a compact high-speed current switch, a three-electrode heterothyristor is developed. It is found that the use of heterothyristor-based current switches allows the creation of a low-loss pump current circuit, generating short current pulses and operating the semiconductor laser in gain-switching mode. For the semiconductor laser chip, an asymmetric semiconductor heterostructure with a quantum-well active region is designed. The design of the emitting aperture of the laser chip is optimized to improve the operating characteristics of the laser beam when generating sub-ns optical pulses. It is shown that the transition to a monolithic emitting aperture design reduces the laser pulse turn-on spatial inhomogeneity, which is 90 ps over the entire range of optical powers studied. It is also demonstrated that by increasing the emitting aperture width to 400 μm, laser pulses with a peak power of 39.5 W and a pulse width at full width at half maximum (FWHM) of 120 ps can be generated.

Solidification of a quaternary X5CrNi18-10 alloy during laser beam welding using CALPHAD data in a phase-field approach

Solidification of a quaternary X5CrNi18-10 alloy during laser beam welding using CALPHAD data in a phase-field approach

Relativistic self-focusing of Laguerre–Gaussian laser beam in density-rippled cold quantum plasma

Relativistic self-focusing of Laguerre–Gaussian laser beam in density-rippled cold quantum plasma

Exploring the thermal-induced optical nonlinearity of crude oil via spatial self-phase modulation technique

This study aims to investigate the nonlinear optical (NLO) characteristics of diluted crude oil samples from the Ramshir, Rag-e-Sefid, and Ahwaz-20 reservoir fields in the southwest region of Iran. Utilizing spatial self-phase modulation (SSPM) techniques, we measured the nonlinear refractive index () by observing the intensity-dependent number of diffraction rings with continuous-wave laser beams at and wavelengths. This study focused on examining the ratios of different sample concentrations to identify the role of thermal effects in the observed NLO responses. Our findings indicate a direct correlation between the concentration of crude oil in the samples and their NLO properties, with thermal effects significantly influencing the changes in NLO responses. In the thermal region, the nonlinear refractive index was approximately determined to be . Additionally, the study explores the collapse of diffraction rings to further understand how the relative nonlinear refractive index varies with the sample concentration and incident intensity at both wavelengths. The results suggest that crude oil possesses promising NLO properties, making it potentially suitable for the development of new photonic devices and applications, especially in areas where thermal nonlinearities are crucial, such as sensing and all-optical technologies.

Two-photon excited fluorescence with shaped laser pulses for refractive beams

We report two-photon excited fluorescence of dyes for refracted laser beams by utilizing tailored laser pulses. A fluorescence contrast difference due to phase shaping could be achieved between different coumarin dyes. Particularly, an increased contrast difference is obtained for configurations close to the Brewster angle. Furthermore, by using a subsequent deformable phase plate for spatial shaping it was possible to precisely adjust the laser beam for controlled refraction at the liquid dye surface. A polarization-dependent refraction was observed when directing the shaped laser beam on the curved liquid adhesion meniscus close to the cuvette wall. This results in a refraction-dependent contrast difference. The presented method could be utilized for surface-sensitive biophotonic imaging applications.Graphic abstract

Dynamics of self modulation of axial phase of $$q$$-Gaussian laser beams in relativistic plasma channels

Dynamics of self modulation of axial phase of $$q$$-Gaussian laser beams in relativistic plasma channels