The paper introduces the fabrication, characterization and analysis of a novel graphene capacitor, which can be used as an effective saturable absorber modulator in a passive Q-switched system. The photoelectric interaction mechanism of the device is studied based on its electrical transmission and spectral absorption properties. Due to the change of Fermi level and carrier density, the absorption properties of graphene in the device can be adjusted by gate voltage without changing the properties of SA material. The output characteristics of all-solid-state pulse laser can be adjusted flexibly under ultra-low electric modulation power (~13 pA current and 1 nW power). It is applied to the Nd∶ YVO4 all solid state laser system, and the stable pulse output at 532.04 nm wavelength is achieved. The laser absorption pump power is kept constant, and the gate voltage is changed. The pulse duration of the Q-switched output can be compressed from 1.1 μs to 345 ns. This structure is expected to further promote the development of tunable pulse lasers from visible light to mid-infrared band. In particular, passive Q-switching/mode-locking devices based on graphene devices will be used in future applications such as infrared measurement, projection display, and optical modulation.
A novel method of stability analysis was proposed by threshold gain analysis based on a transfer matrix theory in this study. The results reveal that long coupling delays need weak coupling strength, whereas short coupling delays need strong coupling strength. To analyze the linewidth of mutually injection-locked semiconductor lasers under weak coupling, an analytical method based on noise correlation analysis is used. The results show that the coupling delay and coupling strength are the main factors affecting the linewidth; however, the phase difference has less influence on the linewidth, which can be used for fine adjustment.
In summary, we have demonstrated the design of a three-stage ultrafast mid-IR fiber laser system, which can directly deliver 10 W level average power, hundreds of nJ pulse energy, and hundreds of fs pulse duration. We believe that the design and analysis demonstrated here can provide useful information to the construction and optimization of real high-power, ultrafast, mid-IR fiber laser systems.
In summary, we have achieved a 4.5 W mid-infrared laser output at 3.1 μm in an acetylene-filled HCF, corresponding to an optical-to-optical conversion efficiency of 14%, which is the currently the maximum power of a fiber gas laser in the mid-infrared region. The experimental results show that fiber gas lasers have the potential to achieve high-power mid-infrared fiber laser outputs.
The BGSe crystal is a new type of wide-bandgap IR NLO material with unique advantages and good application prospects in mid-far IR laser output via the frequency down-conversion process. The future research direction of BGSe mainly focuses on improving the crystal quality, searching for the optimal phase-matching direction, and solving the matching problem between the different types of pump sources and the optical properties of BGSe.
In this study, high quality ZGP crystals with diameters of 3.85.0 cm have been grown by the ultralow gradient freezing technique in self-made furnaces with growth yields over 95%. The crystal growth efforts and post processing have resulted in ZGP OPO devices with an ultra-low absorption loss (0.015 cm-1 @2.09 μm) and a size of up to 30 mm×30 mm×40 mm. A high average output power (>100 W) ZGP OPO with only one low absorption ZGP device has been demonstrated, with no obvious limits to further scaling. The results indicate that the combination of large aperture and low absorption losses makes our ZGP crystals extremely attractive for high average power and high energy applications.
The GSA and ESA dual-wavelength pumped Tm: YAP laser emitting in the 2.3 μm region have been realized successfully. The Tm∶YAP crystal has a maximum output power of 2.28 W at 2.3 μm. To the best our knowledge, this is the highest CW output power obtained in a 2.3 μm Tm-doped solid-state laser. Making full use of the broadband emission spectrum of the 3H4→3H5 transition of the Tm∶YAP crystal, a watt-level LD-pumped 2.5 μm Tm∶YAP laser is achieved using the dual-wavelength pumping scheme. Our results show that GSA and ESA dual-wavelength pumping is an effective technical means to achieve a high power output of 2.3 μm Tm-doped laser.