Passively Q-switched erbium-doped fiber laser using evanescent field interaction with gold-nanosphere based saturable absorber

Role of carrier-transfer in the optical nonlinearity of graphene/Bi2Te3 heterojunctions

Two-dimensional (2D) topological insulators (TIs) have attracted a lot of attention owing to their striking optical nonlinearity. However, the ultra-low saturable intensity (SI) of TIs resulting from the bulk conduction band limits their applications, such as in mode-locking solid-state lasers. In this work, through fabricating a graphene/Bi₂Te₃ heterojunction which combines monolayer graphene and a Bi₂Te₃ nanoplate, the optical nonlinearities are analyzed. Moreover, the thickness-dependent characteristics are also investigated by varying the thickness of the Bi₂Te₃ when synthesizing the heterojunctions. Furthermore, with the aid of the estimated junction electron escape time, a model of the photo-excited carrier-transfer mechanism is proposed and used to describe the phenomena of depression of ultra-low saturable absorption (SA) from the Bi₂Te₃ bulk band. The increased modulation depth of the graphene/Bi₂Te₃ heterojunction can accordingly be realized in more detail. In addition, a Q-switched solid-state laser operating at 1064 nm with heterojunction saturable absorbers is built up and characterized for validating the proposed model. The laser performance with varied Bi₂Te₃ thickness, such as pulse duration and repetition rate, agrees quite well with our proposed model. Our work demonstrates the functionality of optical nonlinear engineering by tuning the thickness of the graphene/Bi₂Te₃ heterojunction and demonstrates its potential for applications.

Tellurium as the saturable absorber for the passively Q-switched laser at 1.34 µm

The novel two-dimensional (2D) elementary tellurium is currently of great interest in optoelectronic and photonic applications. In this contribution, 2D tellurium nanosheets were successfully created by using the liquid-phase exfoliation method. With the as-prepared tellurium nanosheets as the saturable absorber (SA), we realized a passively $ Q $Q-switched ${\rm Nd} \text:{{\rm YVO}_4}$Nd:YVO₄ laser operating at 1342 nm with a pulse width of 947 ns and single pulse energy of 2.25 µJ. Our work indicated the tellurium SA could be an efficient $ Q $Q-switcher for a near-infrared solid-state laser.

Q-switched ytterbium-doped fiber laser based on evanescent field interaction with lutetium oxide

We demonstrated lutetium oxide (${\textrm{Lu}_2}{\textrm{O}_3}$Lu₂O₃) deposited onto D-shaped fiber producing Q-switched ytterbium-doped fiber laser (YDFL) with an operating wavelength of 1037 nm. D-shaped fiber ${\textrm{Lu}_2}{\textrm{O}_3}$Lu₂O₃ as a saturable absorber (SA) was prepared using a polishing-wheel technique by polishing 2 times to establish an excellent evanescent field interaction between material and light on the surface of the polished region. The SA was deployed into a YDFL to generate Q-switching. The proposed D-shaped fiber ${\textrm{Lu}_2}{\textrm{O}_3}$Lu₂O₃ initiated pulses as short as 3.6 µs, with the highest repetition rate of 65.8 kHz. Stability of the SA is proven, as it produced stable pulses within the pump power of 99 to 133 mW with an SNR of 62.13 dB. Q-switched YDFL generates pulses with an output power of 0.93 to 1.99 mW and pulse energy of 17 to 30 nJ. We obtained a laser cavity with the optical-to-optical efficiency of 3.33%, which was the highest among D-shaped fiber-deposited SA materials in YDFL. Therefore, ${\textrm{Lu}_2}{\textrm{O}_3}$Lu₂O₃ deposited onto D-shaped fiber can be deployed as an SA in YDFL for a portable Q-switched laser source.

Emerging transparent conducting oxides material: 2-dimensional plasmonic Zn doped CuGaO2 nanoplates for Q-switched fiber laser

A passively Q-switched Er³⁺ doped fiber laser has been realized by using Zn doped hexagonal CuGaO₂ (CGZO) nanoplates (NPs) as a saturable absorber (SA) for the first time. The CGZO NPs SA film exhibits strong saturable absorption property, meanwhile with a small nonsaturable loss of 5.179%, and the modulation depth is up to 40.821%. A stable passively Q-switched laser, which was centered at 1559.75 nm, was achieved, and the threshold was as low as 42 mW. With an increase of the pump power from 42mW to 361mW, the pulse duration decreases from 36 μs to 1.71 μs, and the maximum output power of 12.1 mW is achieved. Particularly, the optical-optical conversion efficiency of the Q-Switched laser based on CGZO NPs reached 3.76%. Due to whispering-gallery-mode (WGM) resonance in CGZO NPs, the nonlinear optical response of CGZO NPs has been enhancement. These findings demonstrate that CGZO NPs are promising SA for fabricating high-efficiency and low-threshold pulse lasers.

Gold nanostars as the saturable absorber for a Q-switched visible solid-state laser

We demonstrated a passively Q-switched visible Pr:YLF laser using the gold nanostars (GNSs) as the saturable absorber (SA). The nonlinear saturable absorption properties at 639 nm were measured, and the modulation and saturable fluence were calculated to be 3% and 0.3  GW/cm², respectively. With the GNSs SA, the efficient passively Q-switched lasers were obtained at 639 nm and 721 nm, respectively. The maximum output powers and shortest pulse widths were (256 mW, 168 ns) at 639 nm and (238 mW, 198 ns) for 721 nm. To the best of our knowledge, this is the first time there has been a visible bulk pulse laser using the GNSs as the SA. Our work indicates the GNSs could be excellent and promising optoelectronic devices in the visible domain.

Passively Q-switched Yb-doped dual-wavelength fiber laser based on a gold-nanocage saturable absorber

In this paper, we demonstrate a passively Q-switched Yb-doped dual-wavelength fiber laser using gold nanocages (GNCs) as a saturable absorber. The GNCs are prepared by the seed-mediated method with modulation depth of 5.3% and saturable intensity of 0.16  MW/cm². A simultaneous dual-wavelength operation is achieved at 1059.9 and 1060.5 nm with 3 dB bandwidths of 0.05 and 0.04 nm, respectively. A maximum average output power of 6.03 mW with minimum pulse width of 2.06 μs and maximum repetition rate of 134.9 kHz is obtained at a pump power of 385 mW, corresponding to optical-to-optical conversion efficiency of 1.57% and slope efficiency of 2.75%.

Passively Q-switched mid-infrared laser pulse generation with gold nanospheres as a saturable absorber

High-quality gold (Au) nanospheres (Au-NPs) with a diameter of 52 nm were prepared by the seeded growth method. The mid-infrared (MIR) nonlinear saturable absorption properties were measured by a balanced twin-detector measurement technique. With the as-prepared Au-NPs saturable absorber (SA), an efficient passively Q-switched laser was realized at 2.95 μm for the first time, to the best of our knowledge. Under an absorbed pump power of 4.0 W, a maximum output power of 268 mW was obtained with the shortest pulse width of 734 ns and repetition rate of 91 kHz, corresponding to the pulse energy up to 2.95 μJ. The results indicate that Au-NPs are promising candidates as SAs for MIR laser pulse generation.

Stable nanosecond passively Q-switched all-fiber erbium-doped laser with a 45° tilted fiber grating

Nanosecond passive Q-switching generation from an all-fiber erbium-doped laser with a UV inscribed 45° tilted fiber grating (TFG) is systematically demonstrated. The 45° TFG is employed as a polarizer together with two polarization controllers (PCs) to realize nonlinear polarization rotation (NPR). Because of the NPR effect, stable Q-switched pulses with an average output power of 17.5 mW, a single pulse energy of 72.7 nJ, a repetition rate of 241 kHz, a pulse width of 466 ns, and a signal to noise ratio (SNR) of 58.8 dB are obtained with 600 mW pump power. To the best of our knowledge, the SNR is the highest among all-fiber passively Q-switched erbium-doped laser. The stability of this erbium-doped fiber laser (EDFL) is also examined by monitoring the laser consecutively for 5 h under laboratory conditions.

Gold nanobipyramid Q-switched Nd:LGGG eye-safe laser operating at 1423.4 nm

The performance of a laser-diode-pumped passively Q-switched Nd:LGGG laser at 1423.2 nm with gold nanobipyramids (Au-NBPs) as a saturable absorber was demonstrated. An average output power of 125 mW was obtained at a pump power of 12.2 W, corresponding to an optical-to-optical conversion efficiency of 1.36% and a slope efficiency of 1.78%. A minimum pulse width of 514 ns at a pulse repetition rate of 98.6 kHz was obtained at a pump power of 12.2 W. To the best of our knowledge, this is the first report focusing on the application of Au-NBPs as a saturable absorber for pulse laser operation in the eye-safe region.

Gold nanorods as the saturable absorber for a diode-pumped nanosecond Q-switched 2 μm solid-state laser

Gold nanorods (GNRs) with an average aspect ratio of 15 were experimentally exploited as the 2 μm saturable absorber in a laser diode pumped Tm:YAG laser for the first time, to the best of our knowledge. Q-switched pulses with a maximum average output power of 380 mW, a minimum pulse width of 796 ns, and a pulse repetition rate of 77 kHz were achieved under the LD pump power of 6.2 W. Our results indicate that GNRs with a large aspect ratio are promising saturable absorbers in the 2 μm wavelength region.

Pulsed Lasers Employing Solution-Processed Plasmonic Cu3- x P Colloidal Nanocrystals

A new approach to synthesize self-doped colloidal Cu3-x P NCs with controlled size and localized surface plasmon resonance absorption is reported. These Cu3-x P NCs show ultrafast exciton dynamics and huge optical nonlinearities due to plasmonic resonances, which afford the first demonstration of plasmonic Cu3-x P NCs as simple, effective, and solution-processed nonlinear absorbers for high-energy Q-switched fiber laser.

Gold nanobipyramids as saturable absorbers for passively Q-switched laser generation in the 1.1 μm region

We demonstrated that gold nanobipyramids (Au-NBPs) can be used as saturable absorbers for ultrafast pulsed-laser application, for the first time. Au-NBPs are prepared through a seed-mediated growth method, and performance is investigated in a passively Q-switched Nd:YVO4 laser. In the Q-switched operation the maximum average output power that can be achieved is 151 mW. The minimum pulse width is 396 ns at a pulse repetition rate of 90.6 kHz.

Anisotropically Enhanced Nonlinear Optical Properties of Ensembles of Gold Nanorods Electrospun in Polymer Nanofiber Film

Polymeric nanofibers containing gold nanorods (GNRs) are aligned in a uniform orientation through electrospinning. The dispersive and absorptive parts of the third-order optical nonlinear optical refractive index of the composite film measured by polarization dependent z-scan method are demonstrated to be anisotropically enhanced. Anisotropic optical response of the aligned GNRs and its connection with the ultrafast electron dynamics are discussed in light of the results of resonant femtosecond pump-probe experiments. The significant appearance of anisotropic nonlinear optical properties of ensembles of GNRs is attributed to the sensitive excitation of longitudinal surface plasmon resonance (LSPR) of highly aligned GNRs. For the macroscopic applications of ensembles of GNRs, such as passive mode-locking and all-optical switching, the experimental results demonstrate that the alignment of GNRs through electrospinning should be very high efficient, and economic.