Femtosecond Laser Direct Writing Research Articles

Dual-wavelength self-Q-switched mode-locked waveguide lasers based on Nd:LGGG cladding waveguides

We report a self-Q-switched mode-locked Nd:LGGG waveguide laser with tunable dual-wavelength emission fabricated by femtosecond laser direct writing (FsLDW). The waveguide laser delivers pulses with a minimum temporal duration of approximately 30 ps at a fundamental repetition rate of up to 8.03 GHz, without using any modulation element. The maximum output power is determined to be 226 mW with a slope efficiency of 25.38%. This work indicates the promising applications of waveguide lasers based on mixed crystals for integrated optics.

Guided-Wave Up-Conversion Luminescence in Er3+/Yb3+ Co-doped Phosphate Glass Waveguide Produced by Direct Femtosecond Laser Writing

We report on guided-wave up-conversion luminescence in femtosecond laser writing cladding waveguides in Er3+/Yb3+ co-doped phosphate glass. The waveguides were fabricated with 30-μm- and 100-μm-diameter of the guiding cores. The guiding properties of waveguides have been investigated at 633 nm by end face coupling of free space light and physical contact of fibers. The experimental and calculated results of propagating modal profiles and losses have proved favorable performances suitable to Gaussian mode field and multi-mode applications. Under the optical pump laser at 980 nm, the guided-wave up-conversion luminescence at visible light range has been realized through the waveguides.

Rapid In-Situ Synthesis and Patterning of Edge-Unsaturated MoS2 by Femtosecond Laser-Induced Photo-Chemical Reaction

Molybdenum disulfide (MoS2) is a representative transition metal sulfide that is widely used in gas and biological detection, energy storage, and integrated electronic devices due to its unique optoelectrical and chemical characteristics. To advance toward the miniaturization and on-chip integration of functional devices, it is strategically important to develop a high-precision and cost-effective method for the synthesis and integration of MoS2 patterns and functional devices. Traditional methods require multiple steps and time-consuming processes such as material synthesis, transfer, and photolithography to fabricate MoS2 patterns at the desired region on the substrate, significantly increasing the difficulty of manufacturing micro/nanodevices. In this work, we propose a single-step femtosecond laser-induced photochemical method which can realize the fabrication of arbitrary two-dimensional edge-unsaturated MoS2 patterns with high efficiency in microscale. Based on this method, MoS2 can be synthesized at a rate of 150 μm/s, 2 orders of magnitude faster than existing laser-based thermal decomposition methods without sacrificing the resolution and quality. The morphology and roughness of the MoS2 pattern can be controlled by adjusting the laser parameters. Furthermore, the femtosecond laser direct writing (FLDW) method was used to fabricate microscale MoS2-based gas detectors that can detect a variety of toxic gases with high sensitivity up to 0.5 ppm at room temperature. This FLDW method is not only applicable to the fabrication of high-precision MoS2 patterns and integrated functional devices, it also provides an effective route for the development of other micro/nanodevices based on a broad range of transition metal sulfides and other functional materials.

Narrow-linewidth diamond single-photon sources prepared via femtosecond laser

Nitrogen-vacancy (NV) color centers in diamonds with narrow optical linewidths are commonly used as solid-state single-photon sources that emit indistinguishable photons. However, NV color centers prepared using ion implantation typically have large optical linewidths of over 100 MHz. Herein, we used the femtosecond laser direct writing (FsLDW) technique to prepare single NV color centers in diamond with a narrow optical linewidth of 13.05 ± 0.2 MHz and a long decoherence time of 445 ± 27.6 μs. In addition, the density functional theory was adopted to establish calculation models and illustrate why single NV color centers prepared by FsLDW have narrower linewidths compared to those of the ion implantation method. Thus, this study provides an effective reference for the preparation of narrow-linewidth single-color centers in diamonds and other wide-gap crystals.

Fabrication of LIG/RuO2 Composite Electrode by Femtosecond Laser Direct Writing

Fabrication of LIG/RuO2 Composite Electrode by Femtosecond Laser Direct Writing

Femtosecond Laser Direct Writing for Eternal Data Storage: Advances and Challenges

Femtosecond Laser Direct Writing for Eternal Data Storage: Advances and Challenges

Femtosecond Laser Direct Writing of Copper Microstructures with High Efficiency via Thermal Effect of Nanoparticles

Femtosecond Laser Direct Writing of Copper Microstructures with High Efficiency via Thermal Effect of Nanoparticles

Programmable fabrication of a miniaturized photodetector with thermal stability via femtosecond laser direct writing

With the ever-increasing sophistication of integration of electronic devices, the problem of heat accumulation has become ever more serious. Here, a miniaturized photodetector with thermal stability was fabricated by combining the excellent characteristics of femtosecond laser direct writing (FsLDW) and silicon (Si). The sensing part of the photodetector is a Si microwire composed of Si nanoparticles and the sensing area is only 300 μm2. As a result, the photodetector can work stably at a temperature as high as 100°C and the response speed of the photodetector becomes notably faster at high temperatures. Furthermore, an image sensor was successfully fabricated by integrating 16 photodetectors and the image sensor can also work stably at high temperatures. This work demonstrates the potential for application of photodetectors based on Si microwires prepared by FsLDW under harsh conditions.

Tapered depressed-cladding waveguide lasers modulated by Ag nanoparticles embedded in SiO2

We report on fabrication of tapered circular depressed-cladding waveguides in Nd:YAG crystal by femtosecond laser direct writing (FsLDW). Based on the fabricated waveguides, for the first time to the best of our knowledge, efficient Q-switched mode-locked (QML) lasers are realized by employing silver nanoparticles (NPs) embedded in fused silica as saturable absorber (SA) element. Laser pulses as short as 25 ps with a repetition rate of 7.7 GHz are generated at a wavelength of 1064 nm. We systematically explore the influence of incident-output facet and the reduction factors on guiding properties and laser performance by conducting a comparative study of different tapers, and it has been found that the waveguides with tapered structures can suppress multi-mode guiding while ensure fundamental-mode output for waveguide lasers. Our work paves a new way toward developing three-dimensional (3D) waveguide for applications in on-chip ultrafast laser sources.

Femtosecond laser direct writing continuous phase vortex gratings with proportionally distributed diffraction energy

In this Letter, we propose a type of continuous phase vortex gratings (CPVGs), which are able to generate a series of vortex beams with equal or proportional diffracted energies and different topological charges (TCs). A set of CPVGs with dimensions (60 × 60 × 1.1 μm3) are directly designed by mathematical equations, which avoids the use of iterative algorithms. The CPVGs are fabricated by femtosecond laser direct writing (FsLDW) with photoresist, and the experimentally generated vortex beams are in good agreement with the theoretical designs, exhibiting high optical efficiencies. In addition, we realized a CPVG onto the tip of a composite fiber for integrated optical systems. Our work paves the way for applications in optical communications, optical manipulations, and high-performance integrated optics.

Femtosecond Laser Micromachining of Cladding Waveguides in KTiOAsO4 Crystal for Second‐Harmonic Generation

Second‐harmonic generation (SHG) of green lasers generated in KTiOAsO4 (KTA) cladding waveguides fabricated by femtosecond laser direct writing (FsLDW) is reported. The minimum propagation loss of the fabricated waveguides is determined to be 2.39 ± 0.24 dB cm−1 at 1064 nm. The SHG performance is characterized by utilizing a 1064 nm pulsed laser. The maximum SHG conversion efficiency reaches 13.67%. This work suggests potential applications of KTA crystals and FsLDW technology in definition of compact waveguide devices for integrated nonlinear optics.

Photonic-lattice-like guiding microstructures in Nd:YVO4 waveguides: Fabrication, 3D splitting, and lasing

We report femtosecond laser direct writing (FsLDW) of three-dimensional (3D) photonic-lattice-like microstructures in Nd:YVO4 crystal. These structures are capable of simultaneously realizing optical waveguiding and beam splitting under both passive and active operations. Integrated further with the Ag nanoparticles (NPs) embedded in SiO2 crystal as saturable absorber (SA), these photonic-lattice-like microstructures have been used for generation of Q-switched mode-locked lasers with tailored optical modes. This work indicates the promising application of FsLDW in constructing complex 3D structures in functional dielectric crystals and their excellent performance as well as small footprints for on-chip integration in compact and robust packages.

Femtosecond laser direct writing of Nd:YLF cladding waveguides for efficient 1047-nm laser emission

In this work, to the best of our knowledge, the first demonstration of 1047-nm Q-switched mode-locked Nd:YLF cladding waveguide lasers fabricated by femtosecond laser direct writing (FsLDW) is reported. Modulated by Gr-ReS2-Gr heterostructure film, the fabricated waveguide laser delivers laser pulses with a pulse duration of as short as 31 ps at a fundamental repetition rate of up to 9.55 GHz. The maximum output power under the pulsed regime is determined to be 300 mW with a slope efficiency of 31.77%. The result in this work indicates promising applications of Gr-ReS2-Gr heterostructure film for modulation of ultrafast pulsed laser and compact Nd:YLF waveguide lasers for integrated photonics.

Beam Splitters Fabricated by Nonlinear Focusing of Femtosecond Laser Writing in Pure YAG Crystal

We report on the fabrication of waveguides and beam splitters in pure YAG crystals by femtosecond laser direct writing (FLDW). During the femtosecond laser writing process, a positive refractive index is induced through the nonlinear focusing above the focus position, resulting in an unusual guiding cross-sectional configuration. The supported guiding modes at 632.8 nm are measured and analyzed using the end–face coupling system. The propagation loss can be as low as 1.9 dB/cm for the single-line waveguide. Different from the geometry of the traditional fs-laser modified area, this novel structure might offer a new approach in the quest toward integrated photonics.

Laser digital manufacturing of high-performance photodetectors based on a semiconductor microwire.

Digital manufacturing technology meets the needs of today's technological development. However, the post-processing is essential for some digital fabrication methods, such as annealing and ultraviolet (UV) exposure. Femtosecond laser direct writing (FsLDW) has gained considerable attention, because it is a non-photolithographic, non-vacuum, and no heat fabrication method. The photodetectors based on a semiconductor microwire were fabricated via FsLDW. Finally, the responsivity of the fabricated photodetectors based on zinc oxide (ZnO), titanium dioxide (TiO2), and tin oxide (SnO2) can reach 14.27, 1.3, and 81 A/W, respectively. The enhanced performance is attributed to the rough and porous surface of ZnO, TiO2, and SnO2 microwires. The whole preparation process is realized by the programmed control femtosecond laser scanning path. This Letter demonstrates that the fabrication method has potential in the digital manufacturing of high-performance UV photodetectors.

Cell‐Repellent Interfaces: Micropatterned Cell‐Repellent Interface Using Femtosecond Laser Direct Writing to Engineer Controlled Cell Organization (Adv. Mater. Technol. 7/2021)

Cell‐Repellent Interfaces: Micropatterned Cell‐Repellent Interface Using Femtosecond Laser Direct Writing to Engineer Controlled Cell Organization (Adv. Mater. Technol. 7/2021)

Direct Generation of Airy Beams at Designed Fourier Planes Using Integrated Airy Phase Plates

Featuring extraordinarily curved propagation trajectories, self-accelerating Airy beams have stimulated considerable interests from academic research to practical applications. However, generation of high-quality Airy beams using compact optical devices is still highly desirable. Here we present a design of integrated Airy phase plates (IAPPs) with a miniature size (60 μm × 60 μm × 1.1 μm). In addition, a phase-type Fresnel zone plate (FZP) is incorporated in the phase element to further reduce the system dimension, endowing the IAPPs the ability of directly generating Airy beams without introducing a bulky Fourier transform (FT) lens. The fabrication of IAPPs is facilitated by femtosecond direct laser writing (FsDLW), and the experimentally generated Airy beams are in good agreement with the numerical simulations. Furthermore, the flexible fabrication of IAPPs with different focal lengths is demonstrated, which results in the generation of Airy beams at different Fourier planes as desired. Our design strategy and fabrication methodology of the microscale three-dimensional (3D) phase plates can unfold new capacities of Airy beams for miniaturization applications in fiber optics and in on-chip photonics.

17-GHz waveguide lasers modulated by a heterostructure layered material

In this work, a thin-film MoS2/WS2/MoS2/WS2 heterostructure is employed as a saturable absorber (SA) material for efficient ultrafast pulsed laser operation, achieving a 17.54 GHz Q-switched mode-locked Nd:GGG waveguide laser fabricated by femtosecond laser direct-writing (FsLDW). The mode-locked pulse duration is measured to be as short as 31 ps. The maximum laser slope efficiency and the average output power are determined to be 29.27% and 310 mW, respectively. Such a high-performance compact pulsed laser exhibits promising applications of crystalline waveguide structures and layered heterostructures in ultrafast integrated photonics. This work represents the very first experimental demonstration of a pulsed laser based on FsLDW Nd:GGG waveguides and the very first demonstration of using a MoS2/WS2/MoS2/WS2 heterostructure as an efficient SA.

Micropatterned Cell‐Repellent Interface Using Femtosecond Laser Direct Writing to Engineer Controlled Cell Organization

AbstractCell‐repellent interfaces have various applications, including microfluidic devices, biosensors, and antibiofouling surfaces. Efficient cell repellency, long‐term stability, and ability to fabricate micropatterns with cell repellency are main optimal requirements for cell‐repellent interfaces. In this study, a flexible and practical method is proposed to construct a cell‐repellent interface and engineer controlled cell organization. Using femtosecond‐laser direct writing to pattern surfaces with microcraters, it is shown that micropatterned surfaces with physical and chemical changes have outstanding characteristics of super‐hydrophobicity. Furthermore, the cell adhesion is inhibited by these features and arbitrary cell patterns are achieved by selective cell adhesion induced by the distribution of the microcrater structures. These findings suggest a high potential for directing cell organization with desired shapes to analyze the fundamental mechanism of cell adhesion.

Whispering Gallery Mode Lasing from Perovskite Polygonal Microcavities via Femtosecond Laser Direct Writing.

Organic-inorganic halide perovskites have excellent intrinsic properties, such as long carrier lifetime, high photoluminescence quantum yield, and high gain, in whispering gallery mode (WGM) cavities by facile vapor self-assembly or solution process, which make them competitive for high-performance microlasers. However, the performance of perovskite-based microlasers is severely limited by the fabrication of microcavities, which results in poor reproducibility and uncontrolled morphology. Herein, we explore a reproducible method which combined thermal co-evaporation with femtosecond (fs) laser direct writing for formamidinium lead iodide (FAPbI3) perovskite polygon-shaped WGM microcavities. The microlasers pumped with the fs laser had a low threshold of 4.0-12.3 μJ/cm2 and narrow full width at half-maximum of 0.62-1.05 nm. Moreover, size- and shape-dependent WGM lasing performances are also investigated systematically. The results prove that FAPbI3 polygonal microcavities can serve as promising WGM lasers and have great potential for practical optoelectronic applications.