Ultrashort Laser Research Articles

Generation of ultrashort cylindrical vector beams from a Mamyshev oscillator.

Cylindrical vector beams (CVBs), characterized by their spatially non-uniform but rotationally symmetric polarization distributions, have garnered considerable attention due to their unique properties. In this Letter, we demonstrate the generation of cylindrical vector beams directly from a Yb-doped Mamyshev oscillator (MO). Both the radially and azimuthally polarized vector beams are achieved with a pulse duration of 3.6 ps and a pulse energy of 8.2 nJ at the repetition rate of 15.25 MHz. We also find that the filtered linearly polarized beam from the output CVBs can be homogeneously dechirped to 114 fs using the external grating pairs, indicating the potential intracavity pulse compression capability for the output CVBs. Simultaneously, ultrafast scalar Gaussian beams can also be obtained from another arm. These results can give insights into the experimental design and realization of high-energy and high-power structured (CVB or vortex) ultrashort lasers.

Nonexistence of solutions to quasilinear Schrödinger equations with a parameter

This paper is concerned with the class of quasilinear Schrödinger equations: which models the self‐channeling of a high‐power ultra short laser in matter provided , where is a parameter, and . Under some appropriate assumptions on , we establish the nonexistence of solutions for the above problem.

Octave‐Spanning Second‐Harmonic Generation in Dispersion‐Engineered Lithium Niobate‐on‐Insulator Microwaveguide

Broadband lasers, e.g., ultrashort lasers, optical supercontinuum, and frequency combs, are revolutionary coherent light sources, which enable a plethora of state‐of‐the‐art applications ranging from precision spectroscopy to optical clocks. However, the spectral broadening of these coherent light sources mainly relies on the third‐order nonlinearity () and is difficult to extend to the visible or shorter wavelength regime. Second‐order nonlinearity (), which is orders of magnitude larger than , becomes a powerful tool for the frequency translation if its broadband operation is well addressed. Herein, an octave‐spanning second‐harmonic generation scheme is experimentally demonstrated beyond an extremely large frequency range of 135 THz and high conversion efficiency of 1% for sub‐100 pJ for the near‐infrared picosecond supercontinuum in a fiber–waveguide–fiber configuration. The process relies on ultrabroadband birefringence phase matching in the dispersion‐engineered lithium niobate‐on‐insulator ridge microwaveguide. The mode area of microwaveguide well matches with single‐mode lens fiber, reducing coupling loss and ensuring easy packaging. The method provides a new approach to span the wavelength range of coherent light with ‐based wavelength translation for supercontinuum or frequency combs into the visible regime. The result would find applications in spectroscopy, astrophysics, atomic optics, optical synthesis, etc.

An advanced methodology for the development of highly accurate two temperature models (TTMs) to describe the material irradiation by an ultrashort laser

Ultrashort lasers are an evolving field in both the researching and industrial world, mainly due to their ability to give very small Heat Affected Zones (HAZ) during the irradiation of a material, making them efficient for micro- and nanostructuring. Two Temperature Models (TTMs) are widely used in literature to simulate the irradiation of a material by an ultrashort laser, however, still now, they have some significant limitations, such as boundary conditions and mesh size dependency and low accuracy in predicting ablation depth and crater diameter. The novelty of the current paper is that it proposes an advanced methodology for the development of heat transfer-only TTMs, with boundary conditions and mesh size independency, that are able to predict ablation depth and crater diameter with very high accuracy, as they take into consideration phenomena such as spallation, explosive boiling and Kerr effect. As an example, this methodology has been applied on the ultrashort laser irradiation of Au.

Characterization of Visible Range Gain in Praseodymium Doped Fiber Amplifier

In the optical (380-700 nm) region, a simulation study was conducted to assess the low-signal gain, power conversion efficiency (PCE), and optical output power of a praseodymium-doped fiber optic amplifier (PDFA). The PDFA performance was assessed using the optimized Pr3+ fiber length, Pr3+ ion concentration, and pump power. Additionally, the effects of input signal voltage and amplifier gain on amplified spontaneous emission (ASE) were investigated. A lower peak signal of roughly 1 dB at 635 nm was obtained with a shorter 5 m Pr3 + doped fiber and a higher pump power of 300 mW. The impact of wavelength and pump power variations on the amplifier's optical output power's spontaneous enhanced emission (EEM) is examined. Finally, the ionic interaction (general-purpose conversion effect) in the low-power amplifier signal is analyzed by taking into account various values of the upconversion factor. Keywords: Praseodymium doped fibre amplifier, Small-signal gain, Pump power, Ultrashort laser.

Analysis of the Principles and Applications of Ultra-intensity and Ultrashort Laser

With the development of laser technology, how to improve the output performance and peak power of lasers has become one of the hot directions of current research. This study analyzes the principles and applications of ultra-intensity and ultrashort pulse laser. It firstly outlines the development history of laser technology and the basic definition of ultra-intensity and ultrashort pulse laser. It also mentions the realization methods for generating ultra-intensity and ultrashort pulse lasers, such as mode-locked femtosecond oscillators and CPA-based femtosecond amplifiers. The paper describes the principles of CPA technique and emphasizes its importance in realizing high power ultrashort pulses. The paper discusses various applications of ultra-intensity and ultrashort pulsed laser and summarizes and discusses the major bottlenecks facing current and future ultra-intensity and ultrashort pulsed lasers and their possible solutions. The technical review in this paper aims to enhance the understanding of ultra-intensity and ultrashort pulsed laser and provide insights into the next phase of research exploration in ultra-intensity and ultrashort pulsed lasers.

Single-shot optical imaging with spectrum circuit bridging timescales in high-speed photography.

Single-shot optical imaging based on ultrashort lasers has revealed nonrepetitive processes in subnanosecond timescales beyond the recording range of conventional high-speed cameras. However, nanosecond photography without sacrificing short exposure time and image quality is still missing because of the gap in recordable timescales between ultrafast optical imaging and high-speed electronic cameras. Here, we demonstrate nanosecond photography and ultrawide time-range high-speed photography using a spectrum circuit that produces interval-tunable pulse trains while keeping short pulse durations. We capture a shock wave propagating through a biological cell with a 1.5-ns frame interval and 44-ps exposure time while suppressing image blur. Furthermore, we observe femtosecond laser processing over multiple timescales (25-ps, 2.0-ns, and 1-ms frame intervals), showing that the plasma generated at the picosecond timescale affects subsequent shock wave formation at the nanosecond timescale. Our technique contributes to accumulating data of various fast processes for analysis and to analyzing multi-timescale phenomena as a series of physical processes.

Open-Air Testing of Dual-Comb Time-of-Flight Measurement.

We configured a long-distance ranging apparatus to test the principle of dual-comb time-of-flight measurement using ultrashort lasers. Emphasis was given to the evaluation of open-air performance quantitatively in terms of the measurement resolution and stability. The test results revealed that our dual-comb asynchronous optical pulse sampling permits micrometer-resolved ranging with a repeatability of 2.05 μm over a 648 m distance in dry weather conditions. Further atmospheric effects were evaluated in three different weather conditions with corresponding Allan deviations. Finally, the capability of simultaneous determination of multiple targets was verified with the potential of advanced industrial applications, such as manufacturing, surveying, metrology, and geodesy.

978 Nm All-Polarization-Maintaining Mode-Locked Fiber Laser Based on Phase-Biased Nonlinear Amplifying Loop Mirror

Terahertz (THz) wave generation based on ultrafast laser are one of the most predominant and popular technologies. In particular, for THz generation by photoconductor antenna and optical rectification, higher optical to THz conversion efficiency usually requires ultrafast laser excitation into semiconductor or nonlinear crystal, therefore it is of great desire to develop ultrafast laser with high performance. CW Yb-doped lasers at 980 nm have been applied to generate THz wave range from 0.5 to 6 THz by DFG technique. To meet the demand of some THz wave generation (e.g. BNA crystal, gold nanoplasma), 980 nm ultrafast fiber laser are ideal pump sources and in desire to be developed. Here we demonstrate a 978 nm robust all-polarization-maintaining (PM) picosecond fiber laser mode- locked by phase-biased nonlinear amplifying loop mirror (PB- NALM). By introducing a nonreciprocal - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pi$</tex-math></inline-formula> /2 phase shifter into the fiber loop, a self-starting stable mode-locking is obtained with the center wavelength of 978.14 nm and a 3-dB bandwidth of 0.43 nm. The pulse duration is 8.1 ps corresponding to the time bandwidth product (TBP) of 1.09. The maximum average output power is 14.5 mW with a repetition rate of 45.438 MHz. After a master oscillator power amplification system, the 978 nm average output power reaches 2.12 W, which is then injected into a PPLN crystal for second harmonic generation and 52 mW 489 nm ultrashort lasers is obtained. This is, to the best of our knowledge, the first report of PB-NALM-based mode-locked fiber laser at 978 nm. The 978 nm ultrafast fiber laser and SHG to 489 nm have great potential in terahertz emission by shorter NIR and blue light.

Elastic, thermal and spectral properties of Yb3+:CaSrAl2SiO7 laser crystal

Elastic and thermal properties of CaSrAl2SiO7 crystal have been simulated theoretically. Mechanical and thermal properties of the crystal have been found better than those of Ca2Al2SiO7 with the same crystal structure. An Yb3+:CaSrAl2SiO7 single crystal has been grown by the micro-pulling-down method. Detailed spectral properties of the Yb3+:CaSrAl2SiO7 have been investigated. All the results indicate that the Yb3+:CaSrAl2SiO7 is a potential material for Yb3+ laser, especially for tunable and ultrashort lasers.

Surface Quality and Material Removal Rate in Fabricating Microtexture on Tungsten Carbide via Femtosecond Laser.

Tungsten carbide is currently the most widely used tool material for machining difficult-to-machine materials, such as titanium alloys and nickel-based super alloys. In order to improve the performance of tungsten carbide tools, surface microtexturing, a novel technology that can effectively reduce cutting forces and cutting temperatures and improve wear resistance, has been applied in metalworking processes. However, when fabricating the micro-textures such as micro-grooves or micro-holes on tool surfaces, the significant decrease in material removal rate is a major obstacle. In this study, a straight-groove-array microtexture was fabricated on the surface of tungsten carbide tools via a femtosecond laser with different machining parameters including laser power, laser frequency, and scanning speed. The material removal rate, surface roughness, and the laser-induced periodic surface structure were analyzed. It was found that the increase in the scanning speed decreased the material removal rate, whereas increasing the laser power and laser frequency had the opposite effects on the material removal rate. The laser-induced periodic surface structure was found to have a significant influence on the material removal rate, and the destruction of the laser-induced periodic surface structure was the reason for the reduction in the material removal rate. The results of the study revealed the fundamental mechanisms of the efficient machining method for the fabrication of microtextures on ultrahard materials with an ultrashort laser.

Photonic Lanterns, 3-D Waveguides, Multiplane Light Conversion, and Other Components That Enable Space-Division Multiplexing

Four-mode multiplexing and manipulation technologies are reviewed in the context of space-division multiplexing (SDM) optical communication systems. These are multiplane light conversion (MPLC), fused fiber devices, such as photonic lanterns and tapered fiber bundles, 3-D waveguides fabricated using ultrafast laser inscription, and free-space imaging systems. Each device has its unique strengths and use cases. MPLC can create very complex transformations between two arbitrary sets of spatial modes and leverages mature gray-scale lithographic techniques. Photonic lanterns and tapered fiber bundles are all-fiber devices that can convert beams on single-mode fiber inputs into spatial modes. The all-fiber construction leads to very low losses and high-power handling. 3-D waveguides are inscribed into a glass block using ultrashort lasers and can arbitrarily route light in 3-D. Finally, free-space systems using lenses can also relay many multicore and multimode beams through a single free-space device, such as a thin film filter or an optical isolator. These four technologies have enabled hero transmission experiments in the multimode, multicore, and multimode fiber.

High-power 0.4-mJ picosecond CPA system based on an extra-large-mode-area triple-clad fiber.

A high-average-power, high-pulse-energy picosecond chirped pulse amplification (CPA) laser system based on an extra-large-mode-area (XLMA) triple-clad fiber (TCF) was demonstrated. The ultrashort pulses, generated from all-fiber mode-locked oscillator, stretched and then were pre-amplified to 10 W through a series of fiber power amplifiers. Subsequently, the average output power was amplified to 620 W corresponding to a pulse energy of 0.62 mJ via XLMA TCF. Additionally, the amplified pulses were compressed to a pulse duration of 7.6 ps with an average power of 423 W and a compression efficiency of 68.2%. The ultrashort laser is a promising light source for application of water-guided laser processing, albeit with a beam quality factor of 20 and 21 along two orthogonal axes.

Yttrium Oxide (Y2O3) as a Pulse Initiator in a Mode-Locking Erbium-Doped Fiber Laser

Mode-locking is an ultra-short pulse laser generation technique. The range of pulse duration may vary from picoseconds to femtoseconds. Yttrium Oxide (Y2O3) based saturable absorber (SA) was appropriately revealed in the mode-locked method within the 1.55-micron regime. Y2O3 is perfect for strength, melting point, and chemical stability and can be used as a laminated insulator due to its properties. Moreover, Y2O3 also owns broadband service, switching speed, and engineering features. The Y2O3-PVA film was produced by combining the 50 mg Y2O3 powder into a 50 mL polyvinyl alcohol (PVA) solution and stirring it at room temperature for about 24 h. A mode-locked pulse was recorded with the integrated Y2O3-PVA SA in the erbium-doped fiber laser (EDFL) cavity, and the output spectrum optical spectrum analyzer displayed was around 1560.66 nm. In addition to the sustained mode-locked pulse, a nearly constant repetition rate of 1.01 MHz at a specific pump power begins from 175.87 mW to 228.04 mW while the pulse duration is 4.15 ps. Lastly, the mode-locked pulse had been evaluated, which showed the peak power started from 4.94 kW to 6.07 kW.

Gamma ray and Electron- positron pairs generation based on ultra-intensity and ultra-short laser

With the rapid development of the ultra-short and ultra-intensity laser techniques, the intensity of laser has reached 1023W/cm2, which offers a tool to investigate the laser matter interaction in QED regime. On this basis, it is feasible to generate gamma rays and electron positron pairs in terms of strong field laser plasma interaction. In this paper, the state-of-art configuration and schemes for above particles generation are discussed. Besides, the limitations as well as future direction are also analysed. These results shed light on further exploration of laser-plasma phenomena in strong field physics.

Single-Step Process for Titanium Surface Micro- and Nano-Structuring and In Situ Silver Nanoparticles Formation by Ultra-Short Laser Patterning

Ultra-short laser (USL)-induced surface structuring combined with nanoparticles synthesis by multiphoton photoreduction represents a novel single-step approach for commercially pure titanium (cp-Ti) surface enhancement. Such a combination leads to the formation of distinct topographical features covered by nanoparticles. The USL processing of cp-Ti in an aqueous solution of silver nitrate (AgNO3) induces the formation of micron-sized spikes surmounted by silver nanoparticles (AgNPs). The proposed approach combines the structuring and oxidation of the Ti surface and the synthesis of AgNPs in a one-step process, without the use of additional chemicals or a complex apparatus. Such a process is easy to implement, versatile and sustainable compared to alternative methodologies capable of obtaining comparable results. Antimicrobial surfaces on medical devices (e.g., surgical tools or implants), for which titanium is widely used, can be realized due to the simultaneous presence of AgNPs and micro/nano-structured surface topography. The processed surfaces were examined by means of a scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM) and Raman spectroscopy. The surface morphology and the oxidation, quality and quantity of AgNPs were analyzed in relation to process parameters (laser scanning speed and AgNO3 concentration), as well as the effect of AgNPs on the Raman signal of Titanium oxide.

Bonding and Debonding of Zirconia Using Laser Approaches.

To describe the current findings regarding the use of lasers to enhance the bonding properties of zirconia and to enable its debonding. The PudMed database was searched for literature up to July 2021. The keywords used for zirconia surface treatment were: laser irradiation; zirconia; and bond strength. For ceramic laser debonding, the keywords were: laser irradiation; ceramic; and debonding. A total of 36 studies were included for zirconia surface treatment, and 12 for ceramic laser debonding. Nd:YAG, CO2, Er:YAG, Er,Cr:YSGG, and ultrashort lasers were used for surface treatment, whereas only Er:YAG and Er,Cr:YSGG lasers were applied to debond zirconia structures. The use of laser irradiation to improve the bonding properties of zirconia depends on the type of laser and the parameters used. Among the laser types included in this review, ultrashort lasers have shown the most promising results; however, more studies are needed to prove their superiority over the other lasers for enhancing zirconia bond strength. In terms of debonding, irradiation with different lasers was effective regardless of the ceramic type; however, well-established protocols (ie, laser irradiation time and motion, laser settings) are still needed for different thicknesses and material ceramic types.

Thermoelastic vibrations of microbeam resonator under pulsed laser heating

ABSTRACT In Ultra-short pulsed laser heat problems, two dominant effects are considered, the non-Fourier heat conduction and the coupling effect between temperature and strain rate. In the present study, the thermoelastic vibrations of the Euler-Bernoulli microbeam resonator under pulsed laser heating have been investigated by considering the effect of the length parameter based on the modified couple stress theory. The equation of motion of the system is extracted using Hamilton’s principle and the equations of thermal and vibration coupling are solved by combining the two methods of finite sine Fourier transform and Laplace transform. The obtained results have been compared with the results of continuous classical theory. Also, increasing the length scale in the modified couple stress theory reduces the temperature and increases the frequency of heatwave oscillations distributed in the resonator.

Progress in ultrafast spintronics research

Ultrafast spintronics is one of the most promising fields for information processing technology innovation. When compared with traditional electronic devices, new spin-based devices have advantages such as low power consumption, high speed, and nonvolatility. Exploring novel physical phenomena and mechanisms relating to electronic spins significantly promotes the development of next-generation spintronic devices. In this review, we outline a sequence of advances in the fields of ultrafast magnetics and spintronics. First, a quick overview of spintronics and the discovery of ultrafast demagnetization induced by a femtosecond laser is provided. The proposed physical mechanisms and theories of ultrafast spin dynamics are then summarized, including the phenomenological three-temperature model, computations based on the time-dependent density functional theory, the Elliott-Yafet spin-flip mechanism, and the nonlocal superdiffusive spin transport model. Following that, the most recent experimental and theoretical studies on all-optical switching of ferrimagnetic and ferromagnetic metals are thoroughly reviewed. Furthermore, the discovery of hot-electron spin transport induced by ultrashort lasers as well as its influence on ultrafast magnetization dynamics, ultrafast spin transfer torque, spin injection into semiconductors, and spin accumulation and dissipation in hot-electron transport are described. The advancements in the optimization and manipulation of spintronics-based terahertz emitters are reviewed and analyzed. Finally, we discuss the current challenges in ultrafast spintronics research as well as possible future studies.

Study of electron acceleration induced by ultrashort and ultraintense x-ray free electron laser pulse in the presence of uniform axial magnetic field

There is a great interest in the application of ultraintense and ultrashort lasers in the area of accelerator physics. Recent advances in attosecond pulsed lasers have generated a new possibility in the production of high quality and high energy electron beams. The present work investigates the attosecond laser induced electron acceleration in the presence of an external magnetic field. The electron dynamics is studied with the help of linearly and circularly polarized light in vacuum medium. A similar trend in electron trajectory is observed in both polarizations with relatively more energetic electrons in circular polarization. It is found that the external magnetic field plays an important role to confine the electron motion in the laser field and increase the energy of accelerating electrons considerably.