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.
The generation of optical pulses with parabolic time intensity profiles is experimentally demonstrated. A Mode Locked Laser
(MLL) that generates near transform limited pulses with a gaussian optical spectrum are temporally stretched using a linearly
chirped fiber Bragg grating. The temporal intensity profile of the stretched pulses matches the optical spectrum of the laser
due to frequency-to-time mapping. An amplitude modulator is driven by a carefully designed voltage signal to result in
parabolic pulses. Experimental results of pulse shaping with a MLL input source are presented, and show good agreement
with modeling results. Parabolic pulse generation using a CW laser source is also demonstrated and a deviation of less than
3% from an ideal parabola is observed.
We demonstrate a chirped-pulse amplification system generating 25 μJ compressed pulses at a center wavelength of
1552.5 nm. The seed module and the amplifier chain are all in-fiber (with a few small fiber-pigtailed free-space
components), followed by a free-space diffraction grating pulse compressor. The amplifier chain contains a pre-amplifier
and a booster whose gain fibers are 45/125 μm core/cladding-diameter, core-pumped Er-doped fibers. The pump lasers
for both amplifiers are single-mode 1480 nm Raman lasers capable of up to 8 W output. The seed module generates up
to 2 ns chirped pulses that are amplified and subsequently compressed to <800 fs duration. At a repetition rate of 50 kHz,
the 2 ns pulses from the seed module were amplified to 72 μJ, resulting in 25 μJ after pulse compression. The
corresponding peak power levels after the amplifier chain and compressor were 36 kW and 31 MW, respectively.