Investigation of the influence of optical nonlinearity on combining efficiency in ultrashort pulsed fiber laser coherent combining system

In this paper, the influence of optical nonlinearity on combining efficiency in ultrashort pulsed fiber laser coherent combining system is investigated theoretically and experimentally. In the theoretical work, a new theoretical algorithm for the coherent combining efficiency, which can be used to quantify the spectral coherence decay induced by optical nonlineary imbalance between the sub-beams, is presented. The spectral information of the sub-beam is obtained by numerically solving the nonlinear Schrödinger equation (NLSE) in this algorithm to ensure an accurate prediction. In the experimental work, the coherent combining of two all-fiber picosecond lasers is achieved, and the influence of imbalanced optical nonlinearity on the combining efficiency is studied, which agrees with the theoretical prediction. This paper reveals the physical mechanism for the influence of optical nonlinearity on the combining efficiency, which is valuable for the coherent combining of ultrashort pulsed fiber laser beams.

Laser Assisted Micro Grinding of Titanium

Laser assisted micro-grinding (LAMG) is an emerging area of research in the field of high-quality micro-job fabrication and performance improvement. Conventional micro grinding (CMG) by micro pencil grinding tool suffers drawbacks such as tool deflection, higher cutting force and poor surface finish. In the present work, authors have attempted to investigate the performance of LAMG and CMG in the fabrication of micro-channel on Titanium material. Surface of workpiece was structured with the help of air assisted nanosecond-pulsed fiber laser scanning prior to the CMG at the different values of laser power by keeping scanning velocity constant. During the study, the CMG forces were recorded and after the processes surface roughness of the fabricated microchannels was measured. Results have shown reduction in the magnitude of the normal and tangential force by 31 % and 44 %, respectively, in LAMG compared to the CMG. In addition to that better surface finish was observed in LAMG than CMG. The surface roughness of micro-channel and grinding forces were found to be dependent on the power density of laser. Increase in the laser power deteriorates the surface finish and reduces the magnitude of grinding forces. High grinding forces in the CMG led to the dynamic deflection of the grinding wheel which produced the vibration in the process. The excessive vibration in CMG processes exploited the surface finish of the micro-channel. Such vibration was not observed on the LAMG process; as a result, better dimensional accuracy and surface finish of the channel was found.

Ytterbium impulse laser for surface modification of tool steel with B4C-Al powders

The paper deals with a new application solution of Ytterbium Picosecond Pulsed Fiber Laser for surface modification of 3Kh2V8F hot-work tool steel (the analog of AISI H21 steel). Surface modification was conducted by B4C-Al powders from preplaced pastes followed by laser heating. The ratio of B4C-Al powders was taken as 5/1 by weight and the paste thickness was approximately 1 mm. Laser treatment was conducted according to the following parameters: 1070 nm of wavelength, 100 W of power, 1 mJ of pulse energy, 100 ns pulse duration, pulse frequency range from 50 kHz to 90 kHz. Several tracks with different widths were obtained as a result of treatment depending on velocity of the laser move. EDS analysis showed that B4C particles were not completely dissolved in the weld beads. However, an enhanced concentration of boron (8-12 wt.%) was revealed in the vicinity of B4C particles. The aluminum concentration was low (up to 0.79 wt.%) on the surface of the weld beads.

Highly efficient mode-locked and Q-switched Er3+-doped fiber lasers using a gold nanorod saturable absorber

Mode-locked and Q-switched pulsed fiber laser sources with wavelengths of 1.55 μm are widely used in various fields. Gold nanorods (GNRs) have been applied in biomedicine and optics owing to their biocompatibility, easy fabrication, and unique optical properties. This paper presents the analysis of a saturable absorber based on a colloidal gold nanorod (GNR) thin film for dual-function passively mode-locked and Q-switched 1.55-μm fiber lasers. The colloidal GNR thin film possesses superior properties such as a wide operating wavelength range, large nonlinear absorption coefficient, and a picosecond-order recovery time. Its modulation depth and saturation intensity at 1.55 μm are 7.8% and 6.55 MW/cm2, respectively. Passive mode-locked or Q-switched laser operation is achieved by changing the number of GNR thin-film layers. The advantages of these high-quality GNRs in mode-locked and Q-switched fiber lasers with record-high slope efficiency are verified by conducting comprehensive material and laser dynamic analyses. The self-starting mode-locked fiber laser with an efficiency as high as 24.91% and passively Q-switched fiber laser with the maximum energy of 0.403 μJ are successfully demonstrated. This paper presents the novel demonstration of reconfigurable mode-locked and Q-switched all-fiber lasers by incorporating colloidal GNR thin films.

A Parametric Study on Dissimilar Metal Welding of Aluminum and Copper using Pulsed Fiber Laser

Joining dissimilar metals is critically challenging due to the difference in properties of the metals themselves which leads to the formation of brittle intermetallic compounds (IMCs). Aluminum (Al) and copper (Cu) are well-known materials for electrical application as they attribute to various advantageous characteristics. In lithium-ion batteries, to obtain most of the features of the metals, combinations of these metals are highly recommended. However, with such high reflective metals and heat-sensitive characteristics in the battery, the joint of these metals needs to be processed with an advanced method. In this study, a pulsed fiber laser source that suits to process for heat-sensitive components is utilized to weld two overlap configurations of Al/Cu and Cu/Al, separately. Different ranges of laser power are designated for each welding configuration separately. Thus, the quality of the two welds is evaluated in terms of microstructure and mechanical properties. Consequently, it is found that the growth of IMCs with dendritic structure towards the Al side is observed in both cases. Moreover, the weld of Al/Cu shows a better connection strength as well as fewer imperfections than the weld of Cu/Al.

2-10 µm Mid-Infrared All-Fiber Supercontinuum Laser Source: Experiment and Simulation

Mid-infrared supercontinuum (SC) sources in the 2 to 20 µm molecular fingerprint region are in high demand for a wide range of applications including optical coherence tomography, remote sensing, molecular spectroscopy, and hyperspectral imaging. In this work, we investigate mid-IR SC generation in a cascaded silica-ZBLAN-chalcogenide fiber system directly pumped with a commercially available 460-ps pulsed fiber laser operating in the telecommunications window at 1.55 µm. This all-fiber system is shown to generate a flat broadband mid-IR SC covering the entire range from 2 to 10 µm with severaltens of mWof output power. This technique paves the way for cheaper, practical, and robust broadband SC sources in the mid-IR without the requirement of mid-infrared pump sources or Thulium-dopedfiber amplifiers. We also describe a fully realistic numerical model used to simulate the nonlinear pulse propagation through the cascaded fiber system and we use our numerical results to discuss the physical processes underlying the spectral broadening in the cascaded system. We conclude with recommendations to optimize the current cascaded systems based on our simulation results.