We describe unprecedented performance level from a femtosecond fiber laser system optimized for precision industrial micro-machining. The monolithic fiber chirped pulse amplifier chain enables system output of 215 μJ pulse energy, ~510 fs pulse duration and 16 W average power. We reveal the critical enabling technology to reach this unprecedented pulse energy level, the salient operating principles for the full chirped pulse amplification system, and the key experimental performance data for the laser system.
We report on recent design and fabrication of Kagome type hollow-core photonic crystal fiber (HC-PCF) for the
purpose of high power fast laser beam transportation. The fabricated seven-cell three-ring hypocycloid-shaped large
core fiber exhibits an up-to-date lowest attenuation (among all Kagome fibers) of 40dB/km over a broadband
transmission centered at 1500nm. We show that the large core size, low attenuation, broadband transmission, single
modedness, low dispersion and relatively low banding loss makes it an ideal host for high power laser beam
transportation. By filling the fiber with helium gas, a 74μJ, 850fs and 40kHz repetition rate ultra-short pulse at
1550nm has been faithfully delivered with little propagation pulse distortion. Compression of a 105μJ laser pulse
from 850fs to 300fs has been achieved by operating the fiber in ambient air.
Leakage channel fibers, where several air holes form a core, can be precisely engineered to create large leakage loss for
higher order modes, while maintain negligible transmission loss for the fundamental mode. This unique property can be
used for designing optical fibers with large effective mode area, which supports robust fundamental mode propagation.
The large air holes in the design also enable the optical fibers to be bend-resistant. The principles of design and operation
regime are outlined in this paper. Performance of an ytterbium-doped double clad leakage channel fiber and an
ytterbium-doped polarization-maintaining (PM) double clad leakage channel fiber with ~50&mgr;m core diameter is also
discussed.
We report on the temperature dependence of L-band laser emission of fiber-taper-coupled Er3+-doped tellurite glass microsphere. Pumping at 1480 nm instead of 975nm was used to enhance the coupling efficiency, reduce the internal thermal effect, and increase the output laser emission. The microsphere laser emission threshold increased and the emitted laser wavelength shifted with temperature. The experimental results are explained with a quasi-four-level model, showing that a significant reduction of laser threshold can be achieved at lower temperatures and higher Q values of this microsphere laser.
A fiber-taper-coupled L-band microsphere laser was proposed and demonstrated. Er3+-doped tellurite glass was used to fabricate the microspheres. The microspheres were made by a novel spin method. The pump and emission light were coupled in and out of the microsphere modes with a tapered fiber. 975nm pumped L-band single/multi-mode microsphere lasers were demonstrated. The laser can be tuned in L-band. We call Er3+-doped microsphere laser as EDML.
Microstructure resonators have attracted considerable attention because of their versatility for signal processing applications. We use our Er3+ doped telluride glass to fabricate Er3+ glass microsphere. The excitation of whispering-gallery modes is realized by coupling from an angle-polished single-mode optical fiber tip to an optical microsphere cavity. In the experimental setup, one fiber was used as an input coupler and the other fiber was used as an output coupler. 975nm fiber pigtailed laser diode was used to side pump the microspheres. Very nice whispering-gallery modes (WGM's) near 1.5mm were observed successfully. Signal enhancement was observed in this Er3+ doped telluride glass microsphere with a radius around 50mm. The best enhancement of this Er3+ doped telluride glass microsphere reaches 12dB.
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