Two kinds of supercontinuum (SC) sources are successfully generated by propagating 200-fs unamplified and amplified
pulses through a 0.85-m long nonlinear photonic crystal fiber (PCF), respectively. The spectra bandwidth of
amplified-femtosecond-pumped SC is about 870 nm spanning 480 nm to 1350 nm, which is flat to 1.2dB over 100 nm
spreading from 550nm to 650 nm. With the same PCF, SC spectra pumped by unamplified-femtosecond-pulses are
narrower and unevener. A detailed simulation is carried out to help us understand the mechanism of supercontinuum
evolution. For pump wavelength located at the zero dispersion wavelength of the PCF, spectra are broadened by the
interaction between SPM and higher-order dispersion at early stage. With increasing the pump power, the spectra are
broadened by fission of higher solitons and parametric four-wave mixing (FWM). When the peak power is up to
mega-watt, FWM plays a notable role in flattening and further broadening the supercontinuum spectra in short
wavelength side. An effective way to generate a flat SC laser source pumped by femtosecond pulses is also
demonstrated.
Growth of AlN single crystals is achieved by physical vapor transport (PVT) in the reverse cone tungsten crucible, which
is induction-heated, for obtaining proper sublimation rate and ensuring effective heat and mass transport. In the
experiment, there is a little hole at the center of crucible lid where the temperature is lower than the periphery, and there
is a tungsten cover on the lid. A self-seeded AlN single crystal is grown due to the anisotropic growth property of AlN
crystals and limitation of the hole. During the following growth, the crystal as a seed becomes a large size and high
quality single crystal. By modified PVT, separate AlN single crystals with diameters of larger than 2mm on the crucible
lid have been obtained successfully for the first time.
Microchip-laser-pumped supercontinuum (SC) is successfully generated through a 30-m long photonic crystal fiber
(PCF). The spectra bandwidth of SC is 850 nm spanning from 550 nm to 1300 nm. The -15dB-flat bandwidth is 400 nm
spanning from 600 nm to 1000 nm. It is easy to achieve a much more flat SC with the sacrifice of spectra bandwidth. A
detailed simulation is carried out to help us understand more about the supercontinuum generation process. The primary
mechanism of spectral broadening is identified as parametric four-wave mixing (FWM) combined with stimulated
Raman scattering (SRS). These findings also demonstrate an effective way to generate a flat supercontinuum laser source.
Temporal coherence property of supercontinuum (SC) generated in a polarization-maintaining photonic crystal fiber
(PM-PCF) pumped by Ti:sapphire fs laser was experimentally studied by using a modified Michelson interferometer.
The coherence length of supercontinuum light was measured to characterize the temporal coherence property. The
coherence lengths of supercontinuum and pump laser were measured to be 6.5 μm and 59.14 μm, respectively. The
shortened coherence length of supercontinuum output from the PM-PCF was due to the broadened spectrum. Moreover,
the interferogram evolution versus the supercontinuum spectra was also investigated. It was indicated that the flatter the
supercontinuum was, the better the interferogram was.
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