7,618 research outputs found
Interplay of Kerr and Raman beam cleaning with a multimode microstructure fiber
We experimentally study the competition between Kerr beam self-cleaning and
Raman beam cleanup in a multimode air-silica microstructure optical fiber. Kerr
beam self-cleaning of the pump is observed for a certain range of input powers
only. Raman Stokes beam generation and cleanup lead to both depletion and
degradation of beam quality for the pump. The interplay of modal four-wave
mixing and Raman scattering in the infrared domain lead to the generation of a
multimode supercontinuum ranging from 500 nm up to 1800 nm
Ge-Doped microstructured multicorefiber for customizable supercontinuum generation
Supercontinuum generation in a multicore fiber in which several uncoupled cores
were doped with dissimilar concentrations of germanium was studied experimentally.
Germanium doping provided control over the separation between the zero-dispersion
wavelength and the 1064-nm wavelength of a Q-switched Nd:YAG pump laser. Supercontinua
generated independently in each core of the same piece of fiber displayed clear
and repeatable differences due to the influence of germanium doping on refractive index and
four-wave mixing. The spectral evolution of the subnanosecond pump pulses injected into
the different cores was accurately reproduced by numerical simulations
A multiwavelength study of the remnant of nova GK Persei
We present new observations of the nebular remnant of the old nova GK Persei
1901, in the optical using the 2m HCT and at low radio frequencies using the
GMRT. The evolution of the nova remnant indicates shock interaction with the
ambient medium, especially in the southwest quadrant. Application of a simple
model for the shock and its evolution to determine the time dependence of the
radius of the shell in the southwest quadrant indicates that the shell is now
expanding into an ambient medium that has a lower density compared to the
density of the ambient medium ahead of the shock in 1987.There are indications
of a recent interaction of the nova remnant with the ambient medium in the
northeast quadrant also. The nova remnant of GK Per is detected at all the
observed radio frequencies and is of similar extent as the optical remnant.
Putting together our radio observations with VLA archival data on GK Per from
1997, we obtain three interesting results: 1. The spectrum above 1.4 GHz
follows a power law with an index -0.7 and below 1.4 GHz follows a power law
with an index ~ -0.85. This could be due to the presence of at least two
populations of electrons dominating the global emission at different
frequencies. 2. We record an annual secular decrease of 2.1% in the flux
density of the nova remnant at 1.4 and 4.9 GHz between 1984 and 1997 which has
left the spectral index unchanged at -0.7. No such decrease is observed in the
flux densities below 1 GHz. 3. We record an increase in the flux density at
0.33 GHz compared to the previous estimate in 1987. We conclude that the
remnant of nova GK Per is similar to supernova remnants and in particular, to
the young supernova remnant Cas A.Comment: 10 pages; uses A&A style; figures 1, 2 & 6 are in JPEG format.
Accepted for publication in Astronomy & Astrophysics. Full paper including
Figures 1, 2 & 6 may be downloaded from
http://www.iiap.res.in/personnel/gca/gca.htm
Control of near-infrared supercontinuum bandwidth by adjusting pump pulse duration
We experimentally and numerically investigated the impact of input pump pulse duration on the near-infrared bandwidth of supercontinuum generation in a photonic crystal fiber. We continuously stretched the temporal duration of the input pump laser (centered at 1030 nm) pulses from 500 fs up to 10 ps, while keeping fixed the pump peak power. We observed that the long-wavelength edge of the supercontinuum spectrum is increased by 200 nm as the pump pulse duration grows from 500 fs to 10 ps. We provide a quantitative fit of the experimental results by means of numerical simulations. Moreover, we have explained the observed spectral broadening enhancement induced by pump pulse energy by developing an approximate yet fully analytical model for soliton energy exchange through a series of collisions in the presence of stimulated Raman scattering
Spatiotemporal Characterization of Supercontinuum Extending from the Visible to the Mid-Infrared in Multimode Graded-Index Optical Fiber
We experimentally demonstrate that pumping a graded-index multimode fiber
with sub-ns pulses from a microchip Nd:YAG laser leads to spectrally flat
supercontinuum generation with a uniform bell-shaped spatial beam profile
extending from the visible to the mid-infrared at 2500\,nm. We study the
development of the supercontinuum along the multimode fiber by the cut-back
method, which permits us to analyze the competition between the Kerr-induced
geometric parametric instability and stimulated Raman scattering. We also
performed a spectrally resolved temporal analysis of the supercontinuum
emission.Comment: 5 pages 7 figure
Ge-Doped microstructured multicorefiber for customizable supercontinuum generation
Supercontinuum generation in a multicore fiber in which several uncoupled cores
were doped with dissimilar concentrations of germanium was studied experimentally.
Germanium doping provided control over the separation between the zero-dispersion
wavelength and the 1064-nm wavelength of a Q-switched Nd:YAG pump laser. Supercontinua
generated independently in each core of the same piece of fiber displayed clear
and repeatable differences due to the influence of germanium doping on refractive index and
four-wave mixing. The spectral evolution of the subnanosecond pump pulses injected into
the different cores was accurately reproduced by numerical simulations
Spatial beam self-cleaning and supercontinuum generation with Yb-doped multimode graded-index fiber taper based on accelerating self-imaging and dissipative landscape
We experimentally demonstrate spatial beam self-cleaning and supercontinuum generation in a tapered Ytterbium-doped multimode optical fiber with parabolic core refractive index profile when 1064 nm pulsed beams propagate from wider (122 µm) into smaller (37 µm) diameter. In the passive mode, increasing the input beam peak power above 20 kW leads to a bell-shaped output beam profile. In the active configuration, gain from the pump laser diode permits to combine beam self-cleaning with supercontinuum generation between 520-2600 nm. By taper cut-back, we observed that the dissipative landscape, i.e., a non-monotonic variation of the average beam power along the MMF, leads to modal transitions of self-cleaned beams along the taper length
Spatio-temporal beam dynamics in multimode nonlinear optical fibers
ABSTRACT
We overview recent advances in the spatio-temporal nonlinear dynamics of optical pulses propagating in multimode optical fibers. The Kerr effect leads to spatial beam self-cleaning in a graded-index multimode optical fiber, followed by sideband series generation spanning multiple octaves. Effectively single mode supercontinuum spanning from the visible to the mid-infrared was also demonstrated. Enhancement of Kerr beam self-cleaning was observed in active fiber with quasi-step index profile. Moreover, mutual self-cleaning was recently reported for both the fundamental and the second harmonic beams in optically poled multimode fibers with cubic and quadratic nonlinearity
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