With a homemade (1+1) side-pumped fiber and 1018 nm tandem-pumping strategy, we report an experimental demonstration of 17.4 kW power output, which is apparently a remarkable achievement. The (1+1) side-pumped fiber consists of an active core, highly doped with Ytterbium up to 2000 ppm, and a pump core to transport intensive pumping power through a homemade 5×1 combiner. Stimulated Raman scattering suppression ratio at maximum power is improved to 37.8 dB due to an array of connected tilted fiber Bragg gratings performance. So, the experimental result clarifies the feasibility of combining side- and tandem- pumping in ultra high power scale of tens of kilowatts.
A ytterbium-doped large-mode-area step-index fiber perform was fabricated by chelate precursor doping technique. For
the purpose of raising the threshold of nonlinear effects and transverse mode instability simultaneously, a long tapered
fiber was drew by changing the perform drawing speed. The core/cladding diameter of this tapered fiber was varied from
10/155 to 26/400 μm in 18m-long with the tapering ratio of 2.6. Using this fiber as a gain medium for a fiber laser in
amplifier, the beam quality factor M2 was ~1.2 when the output power obtained over 1.2kW with slope efficiency of
74.5%. The laser output spectrum was centered at 1063.8nm with narrow 3dB bandwidth of 0.26nm. The stimulated
Raman scattering suppression ratio was about ~34.7dB.
The 2.5-terahertz quantum cascade lasers (THz QCLs) based on first-order distributed feedback (DFB) Bragg grating are reported. The loss and threshold gain within different grating duty cycles are calculated according to the mode-coupling theory. The laser output power reaches up to record values of 34.1 mW in pulse mode and 23.4 mW in continuous wave mode at 15 K. The threshold current density is as low as 125 A / cm2. The single-mode emission is achieved, and the side-mode suppression ratio is 12 dB. In addition, the device is bonded together with the other two DFB THz QCLs (2.9 and 3.0 THz) on a copper chip. The simultaneous different wavelength emissions with single mode are successfully realized.
A key requirement to put terahertz (THz) imaging systems into applications is high resolution. Based on a self-developed THz quantum cascade laser (QCL), we demonstrate a THz inline digital holography imaging system with high lateral resolution. In our case, the lateral resolution of this holography imaging system is pushed to about 70 μm, which is close to the intrinsic resolution limit of this system. To the best of our knowledge, this is much smaller than what has been reported up to now. This is attributed to a series of improvements, such as shortening the QCL wavelength, increasing Nx and Ny by the synthetic aperture method, smoothing the source beam profile, and diminishing vibration due to the cryorefrigeration device. This kind of holography system with a resolution smaller than 100 μm opens the door for many imaging experiments. It will turn the THz imaging systems into applications.
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