Femtosecond Laser Direct Writing Research Articles

Carbon Dot Synthesis in CYTOP Optical Fiber Using IR Femtosecond Laser Direct Writing and Its Luminescence Properties

Carbon Dot Synthesis in CYTOP Optical Fiber Using IR Femtosecond Laser Direct Writing and Its Luminescence Properties

Three-Dimensional Directional Assembly of Liquid Crystal Molecules.

The precise construction of hierarchically long-range ordered structures using molecules as fundamental building blocks can fully harness their anisotropy and potential. However, the three-dimensional (3D), high-precision, and single-step directional assembly of molecules is a long-pending challenge. Here, we propose a 3D directional molecular assembly strategy via femtosecond laser direct writing (FsLDW) and demonstrate the feasibility of this approach using liquid crystal (LC) molecules as an illustrative example. The physical mechanism for femtosecond (fs) laser-induced assembly of LC molecules has been investigated, and precise 3D arbitrary assembly of LC molecules has been achieved by defining the discretized laser scanning pathway. Additionally, an LC-based Fresnel zone plate array with polarization selection and colorization imaging functions has been fabricated to further illustrate the potential of this method. This study not only introduces a 3D high-resolution alignment method for LC-based functional devices but also establishes a universal protocol for the precise 3D directional assembly of anisotropic molecules. This article is protected by copyright. All rights reserved.

1.94 & 2.04 µm dual-band four-wavelength-switchable single-frequency narrow linewidth fiber laser using a novel fs-laser direct-written polarization-dependent four-channel filter

We present a dual-band four-wavelength-switchable single-frequency thulium-holmium co-doped fiber laser (THDFL) utilizing a novel band-switchable polarization-dependent four-channel filter (BS-PDFCF). The filter incorporates two high-birefringence fiber Bragg gratings (HB-FBGs) and an electrical-controlled optical switch (EC-OS). Specifically designed for operation in the 1.94 μm and 2.04 μm bands, two HB-FBGs are fabricated using femtosecond (fs) laser direct-writing technology in two segments of polarization-maintaining fibers via a point-by-point method. Each HB-FBG features two narrow-band reflection channels with perpendicular polarization directions. The EC-OS switches the operation band of the BS-PDFCF. A 1.2 m long dynamic ultra-narrow-band filter is employed in the THDFL to achieve single-longitudinal-mode oscillation. The THDFL achieves exceptional output performance, including four single-wavelength and two dual-wavelength operations, spectral wavelength and power fluctuations of ≤0.012 nm and ≤0.386 dB, respectively, OSNRs of >76 dB, RINs of ≤−142.48 dB/Hz@≥5 MHz, linewidths of ≤3.59 kHz@1.94 μm band and ≤5.46 kHz@2.04 μm band, and output power fluctuations of ≤0.109 dB in a measurement time span of 30 min.

Light-Triggered Transmittance Control in Thermoresponsive Hydrogels by Femtosecond Laser Direct Writing

Light-Triggered Transmittance Control in Thermoresponsive Hydrogels by Femtosecond Laser Direct Writing

Surface-Enhanced Raman Scattering Based on Sb2S3 Microstructures via Femtosecond Laser Direct Writing.

The noble-metal-free surface-enhanced Raman scattering (SERS) substrates have gained significant attention due to their abundant sources, signal uniformity, biocompatibility, and chemical stability. However, the lack of controllable synthesis and fabrication methods for high-SERS-activity noble-metal-free substrates hinders their practical applications. In this study, we demonstrate the use of a femtosecond laser direct writing technique to precisely manipulate and modify microstructures, resulting in enhanced SERS signals from Sb2S3 nonmetal-oxide semiconductor materials. Compared with unpatterned Sb2S3 samples, the Sb2S3 microstructures exhibited up to a 16-fold increase in Raman scattering intensity. Interestingly, our results indicate that the femtosecond laser can induce a transformation in the crystalline state of Sb2S3 and significantly enhance the Raman spectrum signal within the Sb2S3 microstructures. This enhancement is also highly dependent on the period and depth of the microstructures, possibly due to the cavity effects, resulting in a stronger local field enhancement.

Second harmonic generation of visible vortex laser based on a waveguide-grating emitter in LBO.

In this work, we propose a practical solution to visible vortex laser emission at 532 nm based on second harmonic generation (SHG) in a well-designed waveguide-grating structure. Such an integrated structure is fabricated by femtosecond laser direct writing (FsLDW) in an LBO crystal. Confocal micro-Raman spectroscopy is employed for detailed analysis of FsLDW-induced localized crystalline damage. By optical excitation at 1064 nm, the guiding properties, SHG performance, as well as vortex laser generation of the waveguide-grating hybrid structure are systematically studied. Our results indicate that FsLDW waveguide-grating emitter is a reliable design holding great promise for nonlinear vortex beam generation in integrated optics.

Printing 3D Metallic Structures in Porous Matrix.

The fabrication of metallic micro/nanostructures has great potential for advancing optoelectronic microdevices. Over the past decade, femtosecond laser direct writing (FsLDW) technology has played a crucial role in driving progress in this field. In this study, silica gel glass is used as a supporting medium, and FsLDW is employed to reduce gold and palladium ions using 7-Diethylamino-3-thenoylcoumarin (DETC) as a two-photon sensitizer, enabling the printing of conductive multilayered and 3D metallic structures. How the pore size of the silica gel glass affects the electrical conductivity of printed metal wires is systematically examined. This 3D printing method is versatile and offers expanded opportunities for applying metallic micro/nanostructures in optoelectronic devices.

Femtosecond laser one-step direct-writing high quality volume Bragg grating.

Volume Bragg grating is one-step fabricated with femtosecond laser direct-writing technology inside a high nonlinearity chalcogenide glass of As2S3. As the generated femtosecond laser filamentation effect could combined with the cylindrical lens focusing method, a two-dimensional refractive index change interface could spontaneously grow along the incident direction with either the laser pulse energy or number increasing. A number of two-dimensional refractive index change interfaces are periodically arranged to stack into a volume Bragg grating. Through periodically moving the sample stage, a grating of 2 mm × 2 mm × 1.7 mm can be fabricated in 15 minutes. And the maximum diffraction efficiency of grating reached 95.49% under the optimal parameters. This study provides a new processing strategy for femtosecond laser direct-writing volume Bragg grating with high processing efficiency and excellent structural performance.

Femtosecond Laser Direct Writing of Flexible Electronic Devices: A Mini Review.

By virtue of its narrow pulse width and high peak power, the femtosecond pulsed laser can achieve high-precision material modification, material additive or subtractive, and other forms of processing. With additional good material adaptability and process compatibility, femtosecond laser-induced application has achieved significant progress in flexible electronics in recent years. These advancements in the femtosecond laser fabrication of flexible electronic devices are comprehensively summarized here. This review first briefly introduces the physical mechanism and characteristics of the femtosecond laser fabrication of various electronic microdevices. It then focuses on effective methods of improving processing efficiency, resolution, and size. It further highlights the typical progress of applications, including flexible energy storage devices, nanogenerators, flexible sensors, and detectors, etc. Finally, it discusses the development tendency of ultrashort pulse laser processing. This review should facilitate the precision manufacturing of flexible electronics using a femtosecond laser.

Femtosecond Laser Direct-Writing Optical Waveguide Amplifiers and Lasers (Invited)

Femtosecond Laser Direct-Writing Optical Waveguide Amplifiers and Lasers (Invited)

Monolithic ultrashort-cavity DBR gain-switched thulium doped fiber laser made by high-precision femtosecond laser direct-writing

We demonstrate a novel monolithic ultrashort-cavity distributed Bragg reflector (DBR) gain-switched thulium doped silica fiber laser. Commercial heavily thulium doped non-polarization-maintaining silica fiber was selected as the gain medium. Monolithic linear laser resonator, which includes a pair of uniform fiber Bragg gratings (FBGs) with a space of 1.0-mm inbetween, was inscribed in the thulium fiber by femtosecond-laser point-by-point (PbP) writing method. The reflectivity of either FBG is close to 100 % and the effective cavity length is calculated to be 3.5 mm. Such an ultrashort-DBR-cavity fiber laser exhibited high Q factor and low cavity loss, allowing the efficient utilization of pump power within the millimeter-long cavity. Single-longitudinal, linearly polarized, gain-switched TDFL at 2003 nm, with a recorded shortest pulse duration of 4.3 ns, a repetition rate of 50 kHz, a maximum peak power of 500 W, and single pulse energy of 2.14 μJ, has been realized, benefitted from the ultrashort cavity length.

Bragg gratings with novel waveguide models fabricated in bulk glass via fs-laser writing and their slow-light effects.

We present the experimental realization of an innovative parallel partially overlapping waveguides (PO-WGs) model grounded in the thermal accumulated regime and fabricated using femtosecond (fs) laser direct-writing within low-iron bulk glass. The 75mm long novel PO-WGs model was made by partially overlapping the shell parts of two core-shell types of waveguides via a back-and-forth single pass fs-laser inscription. The detailed evolution of the PO-WGs model from inception to completion was offered, accompanying by a thorough characterization, which unveils a substantial refractive index (RI) change, on the order of 10-3, alongside low propagation loss (0.2 dB/cm) and distinctive features associated with the single mode and shell-guided light. Notably, the unsaturated performance of PO-WGs model after the primary inscription paves the way for potential applications in the successful creation of two distinctive types of Bragg gratings: first-order dot-Bragg grating and second-order line-Bragg grating. The 75 mm long dot-Bragg grating was written by a periodic dot array with a height of 6 µm atop the PO-WGs, and the birefringence was measured of 1.5 × 10-5 with a 16 pm birefringence-induced wavelength difference. The line-Bragg grating, which was inscribed with dual PO-WGs extending the line grating part to 40 mm in length along its period for increasing the transmission dip, exhibits a pronounced polarization dependence showcasing an effective birefringence of 4.2 × 10-4 at the birefringence-induced wavelength difference of 0.45 nm. We delved into the slow-light effects of the two Bragg gratings thoroughly, which the theoretical analysis revealed an effective group delay of 0.58 ns (group index 2.3) for the dot-Bragg grating. Similarly, the line-Bragg grating exhibited an effective group delay of 0.3 ns (group index 2.3), in good agreement with experimental measurements. These findings underscore the exciting potential of our gratings for creating optical slow-wave structures, particularly for future on-chip applications.

2 µm band four-wavelength-switchable narrow linewidth fiber laser enabled by fs-laser direct-written polarization-dependent parallel fiber Bragg gratings

We propose and experimentally demonstrate a four-wavelength-switchable single-longitudinal-mode (SLM) narrow linewidth thulium–holmium co-doped fiber laser (THDFL) using two polarization-dependent parallel fiber Bragg gratings (PD-PFBGs). The PD-PFBGs, fabricated using femtosecond (fs) laser direct-writing technology in a standard single-mode fiber (SMF) via a point-by-point method, are used as a four-channel reflection filter. Two FBGs are inscribed in parallel in the fiber core along the axial direction and are uniquely positioned symmetrically on either side of the centerline. This configuration enables polarization-dependent multi-channel filtering capability, which further allows for polarization-control-based four-wavelength-switchable operations of the THDFL. SLM lasing is accomplished by utilizing a simple dual-ring sub-cavity filter. An exceptional output performance of the THDFL is achieved, including an optical signal-to-noise ratio (SNR) of >72 dB, maximum power and wavelength fluctuations of 0.350 dB and 0.024 nm, respectively, and a linewidth of <2 kHz, for all four single-wavelength operations lasing at ∼2000 nm. These performance indicators suggest that the THDFL can be applied in free-space optical communication, atmospheric monitoring, and Lidar.

Monolithic 2-µm single-frequency linearly-polarized gain-switched distributed feedback fiber laser by femtosecond laser direct-writing.

We report a single-frequency, linearly polarized gain-switched, distributed feedback (DFB), 2-µm thulium doped silica fiber laser (TDFL), with an effective cavity length of 2.5 mm. The cavity is based on a heavily thulium doped non-polarization-maintaining silica fiber and composed of a π-phase-shifted fiber Bragg grating (FBG) with a total FBG length of 35 mm. The DFB FBG was written by femtosecond-laser point-by-point (PbP) method. In-band pumping scheme is chosen with a 1550 nm nanosecond pulsed erbium-doped silica fiber laser pump. Single-longitudinal, linearly polarized, gain-switched TDFL at 2002 nm, with a recorded shortest pulse duration of 4.7 ns, a repetition rate of 20 kHz, a maximum peak power of 170 W, and single pulse energy of 0.8 µJ, has been obtained, benefitting from the ultrashort DFB cavity made by the femtosecond laser direct-writing method.

Room-temperature laser operation at 1.8 μm in Tm:GdVO4 waveguides

We report on the first experimentally demonstrated Tm-doped gadolinium vanadate waveguide laser operating at 1.8 μm. Cladding waveguides with a diameter of 60 μm are fabricated by femtosecond laser direct writing (FsLDW) in 3 at. % Tm:GdVO4 crystal. A continuous-wave (CW) Ti:sapphire laser is used as the pump source for waveguide laser generation. The impacts of waveguide lengths and cavity conditions on the obtained lasing performance are well studied. For the Tm:GdVO4 waveguide with a total length of 2.8 mm, the laser output at 1812 nm is achieved with a lasing threshold of 116.6 mW and a slope efficiency of 23.2% when utilizing the π-polarized pump source at 799 nm. And the maximum output power of 179 mW is determined at a pump power of 932 mW, which corresponds to an overall optical-to-optical efficiency of 19.2%. The experimental results achieved in this work suggests that compact and low-threshold Tm:GdVO4 waveguide lasers can be very promising for applications in mid-infrared photonic devices with compact structures.

Femtosecond‐Laser‐Direct‐Writing Micro‐Scale Soft Actuators with Controllable Shape Morphing

AbstractMicro‐scale soft actuators with controllable shape‐morphing are the focus of advanced technological fields, ranging from advancing sensing, industrial robotics, and digital manufacturing to medical devices. Particularly, there is a growing interest in the scientific community to leverage liquid crystal polymers (LCPs) to fabricate such soft actuators, because LCPs can offer reversible, programmable deformations under external stimuli. However, pattern micromachining of LCPs into micro‐scale remains a daunting challenge. Herein, a femtosecond laser direct writing (FsLDW) method for cross‐linked LCP (CLCP) microstructure construction is reported that enables arbitrary pattern machining with a minimum size of 40 µm and average heat‐affected zone (HAZ) below 8 µm through optimization of processing parameters. Light‐driven behaviors of CLCP microstructures are systematically characterized through analyzing the effects of film thickness, length‐width ratio, light irradiation time, incident angle, light intensity, and cutting direction on bending and twisting behaviors. Finally, a light‐driven micromirror system is demonstrated, which can achieve not only a controllable swing but also a rotation of the mirror surface with a maximum scanning frequency of ≈2 Hz.

High performance flexible PVDF film pressure sensor fabricated by femtosecond laser

Flexible pressure sensors have shown great potential for applications in detection and medical fields due to their unique piezoelectricity and high sensitivity. In this paper, micro-nano-perforated structures with different periods and diameters are fabricated on the polyester (PET) films by femtosecond laser direct writing (FsLDW), and then the perforated structures are embossed on polyvinylidene fluoride (PVDF) films to form sensors with circular truncated cone (CTC) structures. The effect of period and diameter on the sensitivity of the sensor is studied numerically and experimentally. The results show that the high sensitivity of 8.98 mV/KPa can be achieved in a PVDF film pressure sensor with a period of 50 μm and a diameter of 30 μm, which is about 10.9 times that of the structureless sensor. This work not only provide a fast fabricated method for the pressure sensor based on the femtosecond laser and hot embossing, but also has potential applications in the detection of the micro-signals.

Superhydrophobic and Anti‐Icing Surface by Femtosecond Laser Direct Writing

Glass fiber‐reinforced polymer (GFRP) is formed with glass fiber as the reinforcing material and resin as the matrix. It is widely used in wind turbine blades because of its lightweight, high strength, and corrosion resistance properties. Herein, a method to prepare superhydrophobic GFRP surfaces by femtosecond laser direct writing combined with fluoroalkylsilane modification is demonstrated. The prepared GFRP surface has excellent superhydrophobicity with contact angle of 163.9° and sliding angle of 3.8°. In the ice resistance tests, the icing delay time is extended from 33 to 273 s at −5 °C. The ice adhesion strength is reduced from 217.4 to 40.3 kPa. The surface still has superhydrophobicity and ice adhesion strength of less than 100 kPa after ten cycles of the test. The laser exposure conditions are optimized for water/ice repelling and are at high intensity of 4 TW cm−2 pulse−1 and 2.5 m s−1 beam travel speed, which make the presented approach efficient for fabrication over industrially large areas.

Nd:YSAG waveguide-grating vortex laser: design and implementation

In this work, we fabricate a hybrid waveguide-grating vortex laser in Nd:YSAG by using femtosecond laser direct writing (FsLDW). The detailed parameters of the hybrid structure are fixed by optical simulation. In experiments, an efficient vortex beam is produced in the passive operation at 1064 nm. Under optical pumping at 808 nm, a dual-wavelength waveguide laser at 1060/1062 nm as well as a waveguide-grating vortex laser at 1060 nm are obtained. The laser performance and diffraction properties of the generated vortex laser are detailed, studied, and discussed, providing meaningful reference results toward the practical applications of FsLDW and waveguide-grating structures in integrated photonics.

Customized Micron-Scale Waveguide-Grating Structure for Vortex Laser Emission in Tm:YLF Processed by Femtosecond Laser Direct Writing

We report a micron-scale tailored waveguide-grating device designed for vortex laser generation in the Tm:YLF crystal inscribed by femtosecond laser direct writing (FLDW). The confocal micro-Raman measurement clarifies the microscopic mechanisms of the laser modification on the crystal lattice and the formation of the waveguide and the fork grating. The guiding performance and diffraction properties of the integrated generator are measured by the end-face coupling system with a 1064 nm continuous laser. A polarization-dependent vortex laser array at 1877 nm is pumped by the laser at 792.8 nm. Our results reveal that the hybrid structure combining waveguide and fork grating Tm:YLF crystal has great potential for the application of the vortex laser generator in the mid-infrared region.