Sub-50-fs Kerr-lens mode-locked Yb-doped fluoride laser with 44% optical efficiency.

Yb-doped fluoride has been demonstrated to be potential crystals for application in efficient ultrafast lasers. However, the trade-off between the shorter pulses with higher efficiencies is a challenge. In this work, using Y b,G d:C a S r F 2 crystal, we report on a sub-50-fs Kerr-lens mode-locked oscillator with an optical efficiency up to 44%. Pumped by a 976-nm diffraction-limited fiber laser and using chirped mirrors combined with prism pairs for the dispersion compensation, a pulse as short as 46 fs was obtained with 620-mW output power, corresponding to an optical efficiency more than 40%. Stable Kerr-lens mode-locking with RMS of output power lower than 0.3% and beam quality factors M 2<1.14 were achieved. Moreover, a maximum output power of 780 mW was obtained in continuous-wave operation with 55.3% optical efficiency. To the best of our knowledge, the results in this work represent the shortest pulses generated from Yb-doped fluoride lasers as well as the highest optical efficiencies ever reported in sub-100 fs Yb bulk lasers.

Sub-100-fs Kerr-lens mode-locked Yb:Lu2O3 laser with more than 60% optical efficiency.

Yb-doped sesquioxides represent one of the most excellent laser crystals applying for high-power ultrafast lasers owing to their very high thermal conductivities and broadband emission spectra. Pumped by a high-brightness Yb-fiber laser at 976 nm, the Yb:Lu2O3 laser delivers a maximum output power that amounts to 3.55 W in the continuous-wave regime with an optical efficiency of 75%. In the mode-locked regime, 90-fs pulses were generated via soft-aperture Kerr-lens mode-locking at 1080.6 nm with an average output power of 2.85 W, which corresponds to an optical efficiency of 60.3% and a slope efficiency of 68.8%. Average output power of the mode-locked Yb:Lu2O3 laser can be further scaled to 3.05 W at the expense of the pulse duration (178 fs), which corresponds to an optical efficiency as high as 64.5%. To the best of our knowledge, it is the highest optical efficiency ever reported from any solid-state Kerr-lens mode-locked Yb lasers.

Sub-60-fs ultralow threshold and efficient Kerr-lens mode-locked Yb,Gd:CaSrF2 laser.

In this Letter, using a Yb,Gd:CaSrF2 co-doping mixed crystal, an ultra-low threshold and efficient Kerr-lens mode-locked femtosecond oscillator is realized with a mode-locking threshold as low as 150 mW. With a 200-mW pump power, the shortest pulses are obtained with a pulse duration of 57 fs. A maximum mode-locked output power of 185 mW is observed under a 500-mW pump power, corresponding to an optical-to-optical efficiency of up to 37%. To the best of our knowledge, the 150-mW threshold is the lowest pump power to realize Kerr-lens mode-locking operation in Yb-doped bulk lasers. Furthermore, an optical efficiency of 37% is the highest efficiency in Yb-doped fluoride bulk lasers to date. Our results provide a new basis for high-efficiency and low-threshold Yb-doped ultrafast bulk lasers.

Performance analysis of an SMF-/MMF-based single/double/quadruple tapered optical fiber structure.

This paper primarily discusses the structural performance analysis of a single/double/quadruple tapered optical fiber (TOF) structure based on single-mode fiber (SMF) and multi-mode fiber (MMF). Furthermore, the TOF's performance, including its diameter distribution, transmitted intensity, and reproducibility, is also evaluated. According to the experimental results, it can be concluded that the quadruple TOF structure based on SMF has a higher density of evanescent waves (EWs) on the surface of the tapered area, which is essential for the fabrication of high-sensitivity optical fiber sensors. The structure proposed in this article is feasible, and it can be used for optical fiber sensing while offering significant practical and promising applications as well.

Feasibility analysis of an SMS-/MSM-/SMSMS-based optical fiber sensor structure.

The paper discusses the application of single-mode fiber (SMF) and multimode fiber (MMF) to the fabrication of a sensor structure based on the hetero-core optical fiber structure. The proposed structures are SMF-MMF-SMF (SMS), MMF-SMF-MMF (MSM), and SMF-MMF-SMF-MMF-SMF (SMSMS). The transmitted intensity of the probe is used to estimate the strength of the evanescent field. The results indicate that the SMSMS structure generates more evanescent waves that penetrate deeper into the sensing probe, increasing its sensitivity. As a result, the SMSMS structure has enormous development potential in the field of sensing.

17.8 fs broadband Kerr-lens mode-locked Yb:CALGO oscillator.

Pulses as short as 17.8 fs with a spectral bandwidth of 145 nm and central wavelength of 1118 nm have been generated from a Kerr-lens mode-locked Yb:CALGO oscillator. The oscillator operating at an average power of 26 mW and a repetition rate of 95.9 MHz is pumped by a cost-effective single-mode fiber coupled laser diode emitting 800 mW at 976 nm. The dispersion is compensated using a prism pair combined with broadband chirp mirrors. To the best of our knowledge, the pulse durations corresponding to approximately 4.8 optical cycle pulses are the shortest achieved durations through a Yb-doped bulk oscillator.

Bismuth quantum dots as an optical saturable absorber for a 1.3 µm Q-switched solid-state laser.

Two-dimensional bismuth has attracted extensive attention for its unique properties, such as a moderate bandgap, high carrier mobility, and high stability. In this work, a uniform bismuth quantum dots saturable absorber (BiQDs-SA) was successfully fabricated by the liquid-phase exfoliation method. It was successfully employed in a passively Q-switched bulk laser operating at the telecommunication wavelength of 1.3 µm. The as-fabricated BiQDs-SA-based 1.3 µm Q-switched laser not only exhibits low timing jitter but also shows long-term stability for several days. The maximum average output power of 125 mW was obtained with the shortest pulse width of 510 ns and repetition rate of 135 kHz, corresponding to single-pulse energy and pulse peak power of 0.9 µJ and 1.8 W, respectively. The results indicate that BiQDs-SA is a potential optical modulator for passively Q-switched solid-state lasers.

Biaxial crystal ß-BaTeMo2O9: theoretical analysis and the feasibility as high-efficiency acousto-optic Q-switch.

The high efficiency acousto-optic modulators become indispensable in photonics and optoelectronics for the pulse generation and signal modulation in optical display and telecommunications. In this paper, the validity and feasibility of the biaxial crystals as acousto-optic mediums have been theoretically analyzed and confirmed by experiments using a biaxial crystal of ß-BaTeMo2O9. The diffraction angle and diffraction efficiency of the ß-BaTeMo2O9 acousto-optic Q-switch are determined to be 1.420° and 78.1%, which are comparable with that of TeO2 acousto-optic modulator at the identical operating wavelength of 1064 nm and 100 MHz, respectively. The minimum of the modulated pulse width can be achieved to be 6 ns at 5 kHz with Nd:YVO4 as the gain medium. The results not only provide an excellent acousto-optic medium, but also explore the field of biaxial acousto-optic medium for device fabrications.

Passively mode-locked 1.34 µm bulk laser based on few-layer black phosphorus saturable absorber.

By using few-layer black phosphorus (BP) as saturable absorber, an efficient mode-locked Nd:GdVO4 bulk laser operating at 1.34 µm was realized. An average output power of 350 mW was achieved with a slope efficiency of 15%. The corresponding mode-locking pulse repetition rate, pulse duration and pulse energy were 58.14 MHz, 9.24 ps and 3.0 nJ, respectively. To the best of our knowledge, the pulse width is the shortest among the mode-locked 1.34 µm neodymium lasers ever obtained with other two-dimensional materials saturable absorber. The results clearly indicate the few-layered BP is a kind of promising saturable absorber for ultrafast 1.34 µm lasers.

Few-layered ReS2 as saturable absorber for 2.8 µm solid state laser.

A novel two-dimensional (2D) material member in the transition metal dichalcogenides family, few-layered rhenium disulfide (ReS2) was prepared by liquid phase method successfully. By using the open-aperture Z-scan method, the saturable absorption properties at 2.8 µm were characterized with a saturable fluence of 22.6 µJ/cm2 and a modulation depth of 9.7%. A passively Q-switched solid-state laser at 2.8 µm was demonstrated by using the as-prepared ReS2 saturable absorber successfully. Under an absorbed pump power of 920 mW, a maximum output power of 104 mW was obtained with a pulse width of 324 ns and a repetition rate of 126 kHz. To the best of our knowledge, this is the first demonstration of applying ReS2 in an all-solid-state laser. Moreover, this represents the shortest pulses in Q-switched MIR lasers based on a 2D material as the saturable absorber, which demonstrated the superiority of ReS2 acting as an optical modulator for generating short-pulsed lasers. The results well prove that 2D ReS2 is a reliable optical modulator for MIR solid-state lasers.

759 fs pulse generation with Nd3+-doped CNGS ordered crystal based on a semiconductor saturable absorber mirror.

A diode-pumped passively continuous wave mode-locked laser at 1064.2 nm based on an ordered Nd:CNGS crystal has been experimentally investigated (for the first time, to our knowledge). Stable mode-locked pulses with a duration of 759 fs were produced at a repetition rate of 43.2 MHz. It is the shortest pulse generation of mode-locked lasers based on Nd3+-doped ordered crystal, as far as we know. A maximum average mode-locked output power of 133 mW was obtained at the absorbed pumped power of 6.7 W, and corresponding single-pulse energy and peak power were determined to be 3.1 nJ and 4.1 kW, respectively. The results indicate that the Nd:CNGS as an ordered crystal is indeed a potential candidate as a femtosecond laser gain medium.

Femtosecond solid-state laser based on a few-layered black phosphorus saturable absorber.

In this Letter, a high-quality, few-layered black phosphorus (BP) saturable absorber (SA) was fabricated successfully, and a femtosecond solid-state laser modulated by BP-SA was experimentally demonstrated for the first time, to the best of our knowledge. Pulses as short as 272 fs were achieved with an average output power of 0.82 W, corresponding to the pulse energy of 6.48 nJ and peak power of 23.8 MW. So far, these represent the shortest pulse duration and highest output power ever obtained with a BP-based mode-locked solid-state laser. The results indicate the promising potential of few-layered BP-SA for applications in solid-state femtosecond mode-locked lasers.

Multi-layered black phosphorus as saturable absorber for pulsed Cr:ZnSe laser at 2.4 µm.

A high-quality black phosphorus (BP) saturable-absorber mirror (SAM) was successfully fabricated with the multi-layered BP, prepared by liquid-phase exfoliation (LPE) method. The modulation depth and saturation power intensity of BP absorber were measured to be 10.7% and 0.96 MW/cm(2), respectively. Using the BP-SAM, we experimentally demonstrated the mid-infrared (mid-IR) pulse generation from a BP Q-switched Cr:ZnSe laser for the first time to our best knowledge. Stable Q-switched pulse as short as 189 ns with an average output power of 36 mW was realized at 2.4 µm, corresponding to a repetition rate of 176 kHz and a single pulse energy of 205 nJ. Our work sufficiently validated that multi-layer BP could be used as an optical modulator for mid-IR pulse laser sources.

760 fs diode-pumped mode-locked laser with Yb:LuAG crystal at 1032 nm.

In this study, we experimentally demonstrate the generation of 760 fs pulse duration from a diode-pumped Yb:LuAG mode-locked laser at 1032 nm. At the repetition rate of 58.6 MHz, the maximum average power of 1.07 W was obtained, corresponding to the peak power of 24 kW. To our knowledge, these results represent the shortest pulse duration and highest peak power ever obtained for a 1032 nm mode-locked laser with Yb:LuAG crystal.

Exfoliated layers of black phosphorus as saturable absorber for ultrafast solid-state laser.

High-quality black phosphorus (BP) saturable absorber mirror (SAM) was successfully fabricated with few-layered BP (phosphorene). By employing the prepared phosphorene SAM, we have demonstrated ultrafast pulse generation from a BP mode-locked bulk laser for the first time to our best knowledge. Pulses as short as 6.1 ps with an average power of 460 mW were obtained at the central wavelength of 1064.1 nm. Considering the direct and flexible band gap for different layers of phosphorene, this work may provide a possible method for fabricating BP SAM to achieve ultrafast solid-state lasers in IR and mid-IR wavelength region.

High-power passively mode-locked laser at 1062.4 nm based on Nd:LaGGG disordered crystal.

A diode-pumped passively continuous-wave mode-locked Nd:(La(x)Gd(1-x))3Ga5O12 (Nd:LaGGG) laser at 1062.4 nm with a semiconductor saturable absorber mirror was demonstrated for the first time, to the best of our knowledge. Pulses with duration of 12.78 ps were produced at a repetition rate of 59.8 MHz. A maximum average mode-locked output power of 3.18 W was obtained at the absorbed pumped power of 10.12 W, corresponding to a slope efficiency of 35.7% and a peak power of 4.2 kW. As far as we know, this is the highest power obtained in the passively mode-locking operation with Nd3+-doped disordered garnet crystals.

Passively Q-switched 2 µm Tm:YAP laser based on graphene saturable absorber mirror.

Using high-quality single-layer graphene as a saturable absorber, Tm:YAlO3 (Tm:YAP) crystal as the gain medium, we demonstrated a laser-diode-pumped, compact, passively Q-switched (PQS) solid-state laser in the 2 µm region. The maximum average output power was 362 mW, with the corresponding largest pulse repetition rate and pulse energy of 42.4 kHz and 8.5 µJ, respectively. Under the same pump power, the pulse width of 735 ns was obtained, which is, to our best knowledge, the shortest pulse width among Tm-doped solid-state PQS lasers using graphene saturable absorber mirrors.