Highly nonlinear optic nucleic acid thin-solid film to generate short pulse laser.

Using aqueous precursors, we report successfully fabricating thin-solid films of two nucleic acids, ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). We investigated the potential of these films deposited on a fiber optic platform as all-fiber integrated saturable absorbers (SAs) for ultrafast nonlinear optics. RNA-SA performances were comparable to those of DNA-SA in terms of its nonlinear transmission, modulation depth, and saturation intensity. Upon insertion of these devices into an Erbium-doped fiber ring-laser cavity, both RNA and DNA SAs enabled efficient passive Q-switching operation. RNA-SA application further facilitated robust mode-locking and generated a transform-limited soliton pulse, exhibiting a pulse duration of 633 femtoseconds. A detailed analysis of these pulsed laser characteristics compared RNA and DNA fiber optic SAs with other nonlinear optic materials. The findings of this research establish the feasibility of utilizing RNA as a saturable absorber in ultrafast laser systems with an equal or higher potential as DNA, which presents novel possibilities for the nonlinear photonic applications of nucleic acid thin solid films.

Ultrafast Fiber Lasers with Low-Dimensional Saturable Absorbers: Status and Prospects.

Wide-spectral saturable absorption (SA) in low-dimensional (LD) nanomaterials such as zero-, one-, and two-dimensional materials has been proven experimentally with outstanding results, including low saturation intensity, deep modulation depth, and fast carrier recovery time. LD nanomaterials can therefore be used as SAs for mode-locking or Q-switching to generate ultrafast fiber laser pulses with a high repetition rate and short duration in the visible, near-infrared, and mid-infrared wavelength regions. Here, we review the recent development of emerging LD nanomaterials as SAs for ultrafast mode-locked fiber laser applications in different dispersion regimes such as anomalous and normal dispersion regimes of the laser cavity operating in the near-infrared region, especially at ~1550 nm. The preparation methods, nonlinear optical properties of LD SAs, and various integration schemes for incorporating LD SAs into fiber laser systems are introduced. In addition to these, externally (electrically or optically) controlled pulsed fiber laser behavior and other characteristics of various LD SAs are summarized. Finally, the perspectives and challenges facing LD SA-based mode-locked ultrafast fiber lasers are highlighted.

Sensitivity-tuned CO gas sensors with tailored Ga-doping in ZnO nanowires.

Sensitivity-customization of zinc oxide (ZnO) nanowire (NW) gas sensors has been demonstrated by controlling Ga-doping, thereby tuning the resistance of the NWs. Both un-doped and 5 weight% Ga-doped ZnO (GZO) NWs are synthesized for the highly sensitive sensing within a narrow detection window and a less sensitive one within an expanded window, respectively. We have employed hot-walled pulsed laser deposition (HW-PLD) for the NW synthesis. With CO gas injection, the resistance reduction of NWs is detected and analyzed in a self-designed gas chamber that guarantees the precise control of gas flow and, gas concentration, as well as temperature. NW sensitivity is proportional to the sensing temperature and inversely proportional to the doping concentration resulting in widening the sensing window up to 230 times by the 5 wt.% Ga-doping.

Characterizations of Ga-doped ZnO nanowires depending on growth temperature and target-substrate distance in hot-walled pulsed laser deposition.

Using a hot-walled pulsed laser deposition (HW-PLD), nanowires (NWs) comprising 3 weight% Ga-doped ZnO (3GZO) have been successfully grown on a sapphire substrate. The structural and optical properties of 3GZO nanostructures have also been systematically investigated with respect to the target-substrate (T-S) distance and the growth temperature. The morphology transformations of nanostructures such as nano-horns, NWs, and clusters are strongly affected by growth temperatures due to different thermal energy. Also, the morphologies of nanostructures--including length, diameter, and density--are strongly affected by the T-S distance, illustrating a close correlation between the growth kinetics and the position in the plume formed by the particles from the GZO target. Also, the exciton that is bound to the neutral donor (D(0)X) peak of the 3GZO nanostructures is found at the low temperature PL spectra, indicating successful Ga-doping into ZnO NWs.

Effects of silver impurity on the structural, electrical, and optical properties of ZnO nanowires.

1, 3, and 5 wt.% silver-doped ZnO (SZO) nanowires (NWs) are grown by hot-walled pulsed laser deposition. After silver-doping process, SZO NWs show some change behaviors, including structural, electrical, and optical properties. In case of structural property, the primary growth plane of SZO NWs is switched from (002) to (103) plane, and the electrical properties of SZO NWs are variously measured to be about 4.26 × 106, 1.34 × 106, and 3.04 × 105 Ω for 1, 3, and 5 SZO NWs, respectively. In other words, the electrical properties of SZO NWs depend on different Ag ratios resulting in controlling the carrier concentration. Finally, the optical properties of SZO NWs are investigated to confirm p-type semiconductor by observing the exciton bound to a neutral acceptor (A0X). Also, Ag presence in ZnO NWs is directly detected by both X-ray photoelectron spectroscopy and energy dispersive spectroscopy. These results imply that Ag doping facilitates the possibility of changing the properties in ZnO NWs by the atomic substitution of Ag with Zn in the lattice.