We report on the demonstration of a passively Q-switched 1.55 µm fiber laser utilizing a colloidal PbS quantum dot (QD) thin film as a saturable absorber. Colloidal PbS QD films have several features that are advantageous in passively Q-switched fiber laser operation, including a large operation wavelength range, cost-effectiveness, and a low saturable absorption intensity. We conducted thorough material and optical studies to verify the advantages of PbS QDs in Q-switched laser operation and successfully generated 801 nJ pulses with a 24.2 kHz repetition rate. To the best of our knowledge, the developed Q-switched fiber laser is the first based on colloidal PbS QDs.

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.

Utilising a pulse laser deposition technique, 1.0 wt.% tungsten-doped zinc oxide (WZO) films were fabricated under different growth temperatures (200–400 °C), and their structural, optical, morphological, and electrical properties were discussed. The crystalline structures of the WZO target and films were examined by X-ray diffraction (XRD) analysis, and preferred orientations along the strong c-axis (002) were strongly observed for all growth temperatures. All WZO films demonstrated transparencies above 75%, along with a wide spectral range (400–700 nm). Their bandgap values ranged between 3.21 and 3.35 eV and their optimised resistivity, which was significantly influenced by the growth temperature, was measured as 1.97 × 10⁻³ Ω cm. Further, the electrical characteristics of the WZO films were investigated under different W-doping amounts (1.0–9.0 wt.%) and a constant growth temperature (300 °C), and the results indicated that the carrier mobility showed an opposite tendency to the W-doping percentage. In addition, the elemental compositions of the WZO films and pristine ZnO films were comparatively studied in terms of Zn, O, and W contents, via X-ray photoelectron spectroscopy (XPS) analysis.

Purpose: A modified laser capture micro-dissection (LCM) system is developed to improve resolution to 400 nm, using a laser light (808 nm) transmitted by a near-field tip probe. Materials and methods: Using a 150-nm aperture to heat an ethylene vinyl acetate (EVA) film, melted spots on the average of 400 nm in diameter are generated on the underlying target composed of a 20-nm gold-particle monolayer. The near-field tip probe composed of fiber is set on a 2-D nanometer piezoactuator (PZT) for precise capturing of the monolayer of gold particles. The monolayer of gold particles under the target is bound to the EVA film using a laser, while the remaining EVA film stays on the monolayer. Results: The diameter of the melted spots as small as 400 nm are produced and details are provided that demonstrate the feasibility of the nano-operation of this new LCM system. Conclusion: The new LCM system successfully captures nanoparticles and improves resolution of micro-dissection to 400 nm. With this LCM system, the isolation of a single organelle or bacterium is possible.