The rapid development of additive manufacturing has fueled a revolution in various research fields and industrial applications. Among the myriad of advanced 3D printing techniques, two-photon polymerization lithography (TPL) uniquely offers a significant advantage in nanoscale print resolution, and has been widely employed in diverse fields, for example, life sciences, materials sciences, mechanics, and microfluidics. More recently, by virtue of the optical transparency of most of the resins used, TPL is finding new applications in optics and photonics, with nanometer to millimeter feature dimensions. It enables the minimization of optical elements and systems, and exploration of light-matter interactions with new degrees of freedom, never possible before. To review the recent progress in the TPL related optical research, it starts with the fundamentals of TPL and material formulation, then discusses novel fabrication methods, and a wide range of optical applications. These applications notably include diffractive, topological, quantum, and color optics. With a panoramic view of the development, it is concluded with insights and perspectives of the future development of TPL and related potential optical applications.

In this article, we review the development and the state-of-the-art of edge-emitting modelocked QD lasers. We start with a brief introduction on QD active media and their uses in lasers, amplifiers, and saturable absorbers. We further discuss the basic principles of mode-locking in QD lasers, including theory of nonlinear phenomena in QD waveguides, ultrafast carrier dynamics, and mode-locking methods. Different types of mode-locked QD laser systems, such as monolithic one- and two-section devices, external-cavity setups, two-wavelength operation, and master-oscillator power-amplifier systems, are discussed and compared. After presenting the recent trends and results in the field of mode-locked QD lasers, we briefly discuss the application areas.

Fiber laser technology has been demonstrated as a versatile and reliable approach to laser source manufacturing with a wide range of applicability in various fields ranging from science to industry. The power/energy scaling of single-fiber laser systems has faced several fundamental limitations. To overcome them and to boost the power/energy level even further, combining the output powers of multiple lasers has become the primary approach. Among various combining techniques, the coherent beam combining of fiber amplification channels is the most promising approach, instrumenting ultra-high-power/energy lasers with near-diffraction-limited beam quality. This paper provides a comprehensive review of the progress of coherent beam combining for both continuous-wave and ultrafast fiber lasers. The concept of coherent beam combining from basic notions to specific details of methods, requirements, and challenges is discussed, along with reporting some practical architectures for both continuous and ultrafast fiber lasers.

By employing both frequency shifting and nonlinear polarization rotation mechanisms in a Yb-doped fiber laser, similariton operation regime is demonstrated. Directly generated pulses from an oscillator has a duration of 7.8 ps with 20.5 nm spectrum width and average output power of 7.4 mW with a repetition rate of 26.4 MHz. The pulses can be externally dechirped to be 140 fs. Through numerical simulations we illustrate the details of similariton pulse formation under the simultaneous action of two mode-locking techniques and advantages of hybrid mode-locking approach.

Here, we report on the preparation of a series of organic–inorganic hybrid photoresists that exhibit enhanced
laser-induced damage threshold. These photoresists showed to be candidates for the fabrication ofmicro-optical elements (MOEs) using three-dimensional multiphoton lithography.
Moreover, they demonstrate pattern ability by nanoimprint lithography, making them suitable for future mass production of MOEs.

We study numerically the possibility of using various gain-switched seed laser pulse parameters and fibers for a low-cost, all-fiber Mamyshev regenerator scheme. We find that for increasing pulse durations, sufficient spectral broadening will be difficult to achieve in practice and careful design of the system parameters is required for the regenerator to function. Furthermore, an optimal input peak power level can be defined for a given fiber and pulse duration that results from a balance of competing Kerr effect and stimulated Raman scattering. We also demonstrate experimental results of 3 ps pulse generation seeded by an 80 ps gain-switched diode. Our results pave the way for designing pulse-on-demand picosecond scale fiber sources for applications.

Multiphoton lithography allows the high resolution, free-form 3D printing of structures such as micro-optical elements and 3D scaffolds for Tissue Engineering. A major obstacle in its application in these fields is material and structure autofluorescence. Existing photoresists promise near zero fluorescent in expense of poor mechanical properties, and low printing efficiency. Sudan Black B is a molecular quencher used as a dye for biological studies and as means of decreasing the autofluorescence of polymers. In our study we report the use of Sudan Black B as both a photoinitiator and as a post-fabrication treatment step, using the zirconium silicate SZ2080TM for the development of a non-fluorescent composite. We use this material for
the 3D printing of micro-optical elements, and meso-scale scaffolds for Mesenchymal Stem Cell cultures. Our results show the hybrid, made photosensitive with Sudan Black B, can be used for the fabrication of high resolution, highly transparent, autofluorescence-free microstructures.

A breakthrough concept in high-power industrial lasers. Laser technology continues to have an almost unlimited number of applications. Following widespread developments using continuous-wave lasers, breakthroughs in high-power short-pulsed lasers were recently recognised by the Nobel Prize in Physics 2018 to Gérard Mourou and Donna Strickland for their method of generating high-intensity, ultra-short optical pulses. Although, a relatively short time ago, the femtosecond laser was a tool consigned to the laboratory; now these systems have developed the reliability necessary for use in industry. Ultrafast pulsed lasers have seen exponential growth with the number of filed patents increasing five-fold from
about 100 to 500 per year (Mottay, 2013). Several advanced niche applications have benefited from fs-laser processing including in photonics (Misawa and Juodkazis, 2006), microelectronics (Rizvi, Karnakis and Gower, 2001), MEMS (Bellouard, 2011) and many other markets.

We demonstrate a compact picosecond master-oscillator power-amplifier (MOPA) system based on an Yb-doped polarization-maintaining double-clad tapered fiber (T-DCF) delivering pulses with over 1.26 MW peak power and average output power up to 200 W preserving near diffraction limited beam quality. The unique properties of an active tapered fiber enable to amplify the seed pulses directly with no need for applying of additional stretching technique. This simplified laser system can find the practical implementation in industrial micromachining.

We show that light spiraling like a tornado can be generated by superimposing abruptly auto-focusing ring-Airy beams that carry orbital angular momentum of opposite handedness. With different parabolic propagation trajectories, the superimposing ring-Airy beams are tailored to abruptly auto-focus at overlapping focal regions. This results in a complex wave with intense lobes that twist and shrink in an accelerating fashion along propagation. By achieving angular acceleration values that exceed 295  rad/mm2, these tornado waves can find numerous applications in laser trapping, direct laser writing, and high-harmonic generation.

Passively mode-locked electrically-pumped (EP) VECSELs are compact, low-cost sources of picosecond laser pulses. Since the first demonstration of passive mode-locking in 2003, several different EP-VECSEL designs and mode-locking methods have been investigated. Mode-locking has enabled the generation of output pulses with durations of few picoseconds and peak powers of several Watts. In this publication, we review the state-of-the-art and ongoing research in the field of mode-locked EP-VECSEL. An overview of operation states, laser performance, and output pulse characteristics will be presented. Additionally, we will discuss laser designs, mode-locking techniques, and nonlinear pulse dynamics in mode-locked EP-VECSEL.

We demonstrated, for the first time to our best knowledge, an active tapered double clad fiber with circular birefringence and 35 μm core diameter. The output radiation had perfect beam quality (M2=1.18/1.1) and linearly polarized light with 15 dB of PER. The developed double clad active fiber was investigated for amplification of picosecond pulses in allfiber MOPA system. The MOPA system delivered 50 ps pulses with 55 W of the average power revealed 34.4 dB gain of the booster amplifier.

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