3,934 research outputs found
Generation of tunable q-switched erbium-doped fiber laser based on graphite flakes saturable absorber
Pulsed fiber laser has tremendous application in laser processing and laser sensor.
The key element to produce a passively Q-switched fiber laser is by using a saturable
absorber (SA). Passively Q-switched fiber laser is the most desirable pulse in laser
technology due to its ability to generate optical pulses in microsecond and
nanosecond. The aim of this study is to construct a single ring erbium-doped fiber
(EDF) laser based on graphite flakes SA to produce short pulse laser. Graphite flakes
SA were prepared by mechanical exfoliation techniques and was transferred onto a
fiber ferrule tip. The saturable absorption property of the graphite was measured
using twin detector method which resulted in a modulation depth of 23.82% with a
saturation intensity of 0.031 MW/cm2. Surface morphology, elemental analysis and
absorbance characteristics of the graphite flakes were analyzed by the field emission
scanning electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDX)
and ultraviolet visible spectroscopy (UV-VIS). The result showed that the carbon
element on the SA has a very strong peak intensity. The two different EDF
coefficient of 6.43 dB/m and 18.93 dB/m (EDF M-5 and EDF I-12) showed a
repetition rate of 41.62 kHz and 60.00 kHz with a pulse width of 6.45 μs and 3.38 μs,
respectively at a pump power of 268.8 mW. The wavelength tunability of passively
Q-switched fiber laser for EDF M-5 and EDF I-12 were optimized at fixed pump
power where the tuning range of EDF M-5 occurred between 1544 nm to 1560 nm
and 1552 nm to 1570 nm for EDF I-12. The passively Q-switched fiber laser with
different EDF coefficients were successfully constructed in a single ring
configuration with more selection of wavelength that is up to L band by using higher
EDF coefficient
Termination of Electron Acceleration in Thundercloud by Intra/Inter-cloud Discharge
An on-ground observation program for high energy atmospheric phenomena in
winter thunderstorms along Japan Sea has been performed via measurements of
gamma-ray radiation, atmospheric electric field and low-frequency radio band.
On February 11, 2017, the radiation detectors recorded gamma-ray emission
lasting for 75 sec. The gamma-ray spectrum extended up to 20 MeV and was
reproduced by a cutoff power-law model with a photon index of
, being consistent with a Bremsstrahlung radiation from a
thundercloud (as known as a gamma-ray glow and a thunderstorm ground
enhancement). Then the gamma-ray glow was abruptly terminated with a nearby
lightning discharge. The low-frequency radio monitors, installed 50 km
away from the gamma-ray observation site recorded leader development of an
intra/inter-cloud discharge spreading over 60 km area with a 300 ms
duration. The timing of the gamma-ray termination coincided with the moment
when the leader development of the intra/inter-cloud discharge passed 0.7 km
horizontally away from the radiation monitors. The intra/inter-cloud discharge
started 15 km away from the gamma-ray observation site. Therefore, the
glow was terminated by the leader development, while it did not trigger the
lightning discharge in the present case.Comment: 12 pages, 4 figures, accepted for publication in Geophysical Research
Letter
Ping-Pong Diplomacy and its Legacy in the American Foreign Policy
The aim of the paper is to investigate ping-pong diplomacy between
the Unites States and China, which was used by both countries as a diplomatic
tool, aimed at achieving political rapprochement despite ideological dissonance
and conflict over Taiwan. Both governments were seeking a way to establish
closer relations but the circumstances prevented them from traditional diplomatic
contacts. Sports exchange proved to be a convenient solution. In the
paper the Author attempts to verify a hypothesis on a subsequent legacy of
the ping-pong diplomacy in American foreign policy. The study allowed to
determine reasons for the need to employ sport in order to establish closer relations
between two hostile actors of international relations. It is an attempt to
answer a question concerning the intentional or coincidental character of the
analysed sports exchange. The paper is an empirical case study on one of the
prime examples of positive sports diplomacy and was conducted with the use
of decision-making.The project has been financed by National Science Centre (Poland), grant no. 2015/19/D/
HS5/00513
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