54 research outputs found
Trajectory and smooth attractors for Cahn-Hilliard equations with inertial term
The paper is devoted to a modification of the classical Cahn-Hilliard
equation proposed by some physicists. This modification is obtained by adding
the second time derivative of the order parameter multiplied by an inertial
coefficient which is usually small in comparison to the other physical
constants. The main feature of this equation is the fact that even a globally
bounded nonlinearity is "supercritical" in the case of two and three space
dimensions. Thus the standard methods used for studying semilinear hyperbolic
equations are not very effective in the present case. Nevertheless, we have
recently proven the global existence and dissipativity of strong solutions in
the 2D case (with a cubic controlled growth nonlinearity) and for the 3D case
with small inertial coefficient and arbitrary growth rate of the nonlinearity.
The present contribution studies the long-time behavior of rather weak (energy)
solutions of that equation and it is a natural complement of the results of our
previous papers. Namely, we prove here that the attractors for energy and
strong solutions coincide for both the cases mentioned above. Thus, the energy
solutions are asymptotically smooth. In addition, we show that the non-smooth
part of any energy solution decays exponentially in time and deduce that the
(smooth) exponential attractor for the strong solutions constructed previously
is simultaneously the exponential attractor for the energy solutions as well
High-efficiency generation in a short random fiber laser
We demonstrate a high-efficiency random lasing in a 850 m span of a phosphosilicate fiber. Random distributed feedback owing to the Rayleigh backscattering in the fiber enables narrowband generation with output power of up to 7.3 W at the Stokes wavelength Ξ»S = 1308 nm from 11 Wof the pump power at Ξ»P = 1115 nm. The laser demonstrates unique generation efficiency. Near the generation threshold, more than 2 W of output power is generated from only 0.5 W of pump power excess over the generation threshold. At high pump power, the quantum conversion efficiency defined as a ratio of generated and pump photons at the laser output exceeds 100%. Itis explained by the fact that every pump photon is converted into the Stokes photon far from the output fiber end, while the Stokes photons have lower attenuation than the pump photons
Broadly tunable high-power random fibre laser
As shown recently, a long telecommunication fibre may be treated as a natural one-dimensional random system, where lasing is possible due to a combination of random distributed feedback via Rayleigh scattering by natural refractive index inhomogeneities and distributed amplification through the Raman effect. Here we present a new type of a random fibre laser with a narrow (βΌ1 nm) spectrum tunable over a broad wavelength range (1535-1570 nm) with a uniquely flat (βΌ0.1 dB) and high (>2 W) output power and prominent (>40 %) differential efficiency, which outperforms traditional fibre lasers of the same category, e.g. a conventional Raman laser with a linear cavity formed in the same fibre by adding point reflectors. Analytical model is proposed that explains quantitatively the higher efficiency and the flatter tuning curve of the random fiber laser compared to conventional one. The other important features of the random fibre laser like "modeless" spectrum of specific shape and corresponding intensity fluctuations as well as the techniques of controlling its output characteristics are discussed. Outstanding characteristics defined by new underlying physics and the simplicity of the scheme implemented in standard telecom fibre make the demonstrated tunable random fibre laser a very attractive light source both for fundamental science and practical applications such as optical communication, sensing and secure transmission
Mode decomposition of Kerr self-cleaned beams by phase only SLM
Graded-index multimode optical bers have recently attracted a renewed attention, thanks to the discovery
of new nonlinear eects, such as Kerr beam self-cleaning. In essence, Kerr self-cleaning involves a
ow of
the propagating beam energy into the fundamental mode of the ber, accompanied by a redistribution of the
remaining energy among high-order modes. Increasing the fundamental mode energy leads to a signicant
improvement of the output beam quality. A standard method to determine beam quality is to measure the M2
parameter. However, since self-cleaning involves the nonlinear redistribution of energy among a large number of
ber modes, measuring a single beam quality parameter is not sucient to characterize the eect. A properly
informative approach requires performing the mode decomposition of the output beam. Mode decomposition
permits to evaluate the energy distribution among all of the excited ber modes, which enables investigations
of nonlinear mode coupling processes at a qualitatively new level. In this work, we demonstrate an eciency
mode decomposition method based on holography, which is suitable for analyzing the self-cleaning eect. In
a theoretical study, we describe the solution of the mode decomposition problem for the modes of the gradedindex
multimode ber. In an experimental investigation, we demonstrate the decomposition of both low-power
(speckled) and self-cleaned beams, involving more than 80 modes
Π ΠΠ‘Π¨ΠΠ ΠΠΠΠ ΠΠΠΠΠΠΠ§ΠΠ‘ΠΠΠΠ ΠΠΠΠΠΠΠΠΠ ΠΠΠΠΠΠΠΠ’ΠΠ ΠΠ ΠΠΠΠ‘ ΠΠ ΠΠ‘ΠΠΠΠ ΠΠΠΠΠΠ Π€ΠΠ’ΠΠΠΠ’ΠΠΠ’ΠΠ ΠΠ ΠΠΠΠ-2000 Π ΠΠΠΠ-4000
One trend in the development of integral atomic emission spectral analysis with low spectral background excitation sources, such as inductively coupled or microwave plasma, is to increase the dynamic range of spectrum recording systems based on photodetector arrays. To achieve low detection limits, it is necessary to use photodetector arrays with low reading noise. The dynamic range of a single readout of such photodetector arrays usually does not exceed four orders of magnitude. The dynamic range increase due to the accumulation of spectra from multiple acquisition leads to a quadratic increase in the measurement time. This method does not allow one to cover the entire dynamic range of spectral line intensities of inductively coupled or microwave plasma (which can reach seven orders of magnitude) while maintaining an acceptable total measurement time of a sample spectrum. As an alternative, it is proposed to increase the dynamic range toward higher line intensities by using two different alternating accumulation times during measurement. The objective of this study is to implement the proposed recording mode in MAES analyzers based on BLPP-2000 and BLPP-4000 photodetector arrays in order to increase the dynamic range of recorded spectral lines. Dependences of the signal-to-noise ratio and the dynamic range of spectral lines recorded in integral atomic emission spectrometry on the accumulation time, the total measurement time, the spectral background level, and the photodetector array parameters are obtained. It is shown theoretically that the use of the recording mode with alternating different accumulation times should increase the dynamic range of BLPP-2000 and BLPP-4000 photodetector arrays by two orders of magnitude. The dynamic range of spectral line intensities of a hollow-cathode lamp is shown experimentally to increase by two orders of magnitude (to five orders of magnitude).Keywords: atomic emission spectrometry, inductively coupled plasma, microwave plasma, spectrum analyzer, MAES, photodetector arrays, extended dynamic range, alternating exposureΒ DOI: http://dx.doi.org/10.15826/analitika.2021.25.4.011Sergey A. Babin1,2, Vladimir A. Labusov1,2,3, Denis O. Selyunin1,2, and OlegΒ V.Β Pelipasov1,21Institute of Automation and Electrometry, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga, 1, Novosibirsk, 630090, Russian Federation2VMK-Optoelektronika, pr. Akademika Koptyuga, 1, Novosibirsk, 630090,Russian Federation3Novosibirsk State Technical University, pr. K. Marksa, 20, Novosibirsk,630073, Russian FederationΠΠ΄Π½ΠΎ ΠΈΠ· Π½Π°ΠΏΡΠ°Π²Π»Π΅Π½ΠΈΠΉ ΡΠ°Π·Π²ΠΈΡΠΈΡ ΠΌΠ΅ΡΠΎΠ΄Π° Π°ΡΠΎΠΌΠ½ΠΎ-ΡΠΌΠΈΡΡΠΈΠΎΠ½Π½ΠΎΠ³ΠΎ ΡΠΏΠ΅ΠΊΡΡΠ°Π»ΡΠ½ΠΎΠ³ΠΎ Π°Π½Π°Π»ΠΈΠ·Π° Ρ ΠΈΡΡΠΎΡΠ½ΠΈΠΊΠ°ΠΌΠΈ Π²ΠΎΠ·Π±ΡΠΆΠ΄Π΅Π½ΠΈΡ ΡΠΏΠ΅ΠΊΡΡΠΎΠ², ΠΈΠΌΠ΅ΡΡΠΈΠΌΠΈ Π½ΠΈΠ·ΠΊΡΡ ΠΈΠ½ΡΠ΅Π½ΡΠΈΠ²Π½ΠΎΡΡΡ ΡΡΠΎΠ²Π½Ρ ΡΠΏΠ΅ΠΊΡΡΠ°Π»ΡΠ½ΠΎΠ³ΠΎ ΡΠΎΠ½Π°, ΡΠ°ΠΊΠΈΡ
ΠΊΠ°ΠΊ ΠΈΠ½Π΄ΡΠΊΡΠΈΠ²Π½ΠΎ ΡΠ²ΡΠ·Π°Π½Π½Π°Ρ ΠΈΠ»ΠΈ ΠΌΠΈΠΊΡΠΎΠ²ΠΎΠ»Π½ΠΎΠ²Π°Ρ ΠΏΠ»Π°Π·ΠΌΠ°, ΡΠ²Π»ΡΠ΅ΡΡΡ ΡΠ²Π΅Π»ΠΈΡΠ΅Π½ΠΈΠ΅ Π΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ Π΄ΠΈΠ°ΠΏΠ°Π·ΠΎΠ½Π° ΡΠΈΡΡΠ΅ΠΌ ΡΠ΅Π³ΠΈΡΡΡΠ°ΡΠΈΠΈ ΡΠΏΠ΅ΠΊΡΡΠΎΠ² Π½Π° ΠΎΡΠ½ΠΎΠ²Π΅ Π»ΠΈΠ½Π΅Π΅ΠΊ ΡΠΎΡΠΎΠ΄Π΅ΡΠ΅ΠΊΡΠΎΡΠΎΠ². ΠΠ»Ρ Π΄ΠΎΡΡΠΈΠΆΠ΅Π½ΠΈΡ Π½ΠΈΠ·ΠΊΠΈΡ
ΠΏΡΠ΅Π΄Π΅Π»ΠΎΠ² ΠΎΠ±Π½Π°ΡΡΠΆΠ΅Π½ΠΈΡ Π½Π΅ΠΎΠ±Ρ
ΠΎΠ΄ΠΈΠΌΠΎ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°ΡΡ Π»ΠΈΠ½Π΅ΠΉΠΊΠΈ Ρ ΠΌΠ°Π»ΡΠΌ Π·Π½Π°ΡΠ΅Π½ΠΈΠ΅ΠΌ Π‘ΠΠ ΡΡΠΌΠ° ΡΡΠ΅Π½ΠΈΡ. ΠΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΈΠΉ Π΄ΠΈΠ°ΠΏΠ°Π·ΠΎΠ½ ΠΎΠ΄ΠΈΠ½ΠΎΡΠ½ΠΎΠ³ΠΎ ΡΡΠ΅Π½ΠΈΡ ΡΠ°ΠΊΠΈΡ
Π»ΠΈΠ½Π΅Π΅ΠΊ ΡΠΎΡΠΎΠ΄Π΅ΡΠ΅ΠΊΡΠΎΡΠΎΠ² ΠΎΠ±ΡΡΠ½ΠΎ Π½Π΅ ΠΏΡΠ΅Π²ΡΡΠ°Π΅Ρ ΡΠ΅ΡΡΡΠ΅Ρ
ΠΏΠΎΡΡΠ΄ΠΊΠΎΠ². Π£Π²Π΅Π»ΠΈΡΠ΅Π½ΠΈΠ΅ Π΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ Π΄ΠΈΠ°ΠΏΠ°Π·ΠΎΠ½Π° Π·Π° ΡΡΠ΅Ρ ΠΌΠ½ΠΎΠ³ΠΎΠΊΡΠ°ΡΠ½ΠΎΠΉ ΡΠ΅Π³ΠΈΡΡΡΠ°ΡΠΈΠΈ ΠΈ Π½Π°ΠΊΠΎΠΏΠ»Π΅Π½ΠΈΡ ΡΠΏΠ΅ΠΊΡΡΠΎΠ² ΠΏΡΠΈΠ²ΠΎΠ΄ΠΈΡ ΠΊ ΠΊΠ²Π°Π΄ΡΠ°ΡΠΈΡΠ½ΠΎΠΌΡ ΡΠΎΡΡΡ Π²ΡΠ΅ΠΌΠ΅Π½ΠΈ ΠΈΠ·ΠΌΠ΅ΡΠ΅Π½ΠΈΡ. Π’Π°ΠΊΠΎΠΉ ΡΠΏΠΎΡΠΎΠ± Π½Π΅ ΠΏΠΎΠ·Π²ΠΎΠ»ΡΠ΅Ρ ΠΏΠ΅ΡΠ΅ΠΊΡΡΡΡ Π²Π΅ΡΡ Π΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΈΠΉ Π΄ΠΈΠ°ΠΏΠ°Π·ΠΎΠ½ ΠΈΠ½ΡΠ΅Π½ΡΠΈΠ²Π½ΠΎΡΡΠ΅ΠΉ ΡΠΏΠ΅ΠΊΡΡΠ°Π»ΡΠ½ΡΡ
Π»ΠΈΠ½ΠΈΠΉ ΠΈΠ½Π΄ΡΠΊΡΠΈΠ²Π½ΠΎ ΡΠ²ΡΠ·Π°Π½Π½ΠΎΠΉ ΠΈ ΠΌΠΈΠΊΡΠΎΠ²ΠΎΠ»Π½ΠΎΠ²ΠΎΠΉ ΠΏΠ»Π°Π·ΠΌΡ, ΠΊΠΎΡΠΎΡΡΠΉ ΠΌΠΎΠΆΠ΅Ρ Π΄ΠΎΡΡΠΈΠ³Π°ΡΡ 7 ΠΏΠΎΡΡΠ΄ΠΊΠΎΠ², ΠΏΡΠΈ ΡΠΎΡ
ΡΠ°Π½Π΅Π½ΠΈΠΈ ΠΏΡΠΈΠ΅ΠΌΠ»Π΅ΠΌΠΎΠ³ΠΎ ΠΏΠΎΠ»Π½ΠΎΠ³ΠΎ Π²ΡΠ΅ΠΌΠ΅Π½ΠΈ ΡΠ΅Π³ΠΈΡΡΡΠ°ΡΠΈΠΈ ΡΠΏΠ΅ΠΊΡΡΠ° ΠΎΠ±ΡΠ°Π·ΡΠ°. Π ΠΊΠ°ΡΠ΅ΡΡΠ²Π΅ Π°Π»ΡΡΠ΅ΡΠ½Π°ΡΠΈΠ²Ρ ΠΏΡΠ΅Π΄Π»ΠΎΠΆΠ΅Π½ΠΎ ΡΠ²Π΅Π»ΠΈΡΠ΅Π½ΠΈΠ΅ Π΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ Π΄ΠΈΠ°ΠΏΠ°Π·ΠΎΠ½Π° Π² ΡΡΠΎΡΠΎΠ½Ρ ΡΠ΅Π³ΠΈΡΡΡΠ°ΡΠΈΠΈ Π±α½ΉΠ»ΡΡΠΈΡ
ΠΈΠ½ΡΠ΅Π½ΡΠΈΠ²Π½ΠΎΡΡΠ΅ΠΉ Π»ΠΈΠ½ΠΈΠΉ Π·Π° ΡΡΡΡ ΡΠ΅Π³ΠΈΡΡΡΠ°ΡΠΈΠΈ ΡΠΏΠ΅ΠΊΡΡΠΎΠ² Π² ΡΠ΅ΡΠ΅Π½ΠΈΠ΅ Π²ΡΠ΅ΠΌΠ΅Π½ΠΈ ΠΈΠ·ΠΌΠ΅ΡΠ΅Π½ΠΈΡ Ρ ΠΏΠΎΠΏΠ΅ΡΠ΅ΠΌΠ΅Π½Π½ΡΠΌ ΡΠ΅ΡΠ΅Π΄ΠΎΠ²Π°Π½ΠΈΠ΅ΠΌ Π½Π°ΠΊΠΎΠΏΠ»Π΅Π½ΠΈΠΉ Π΄Π²ΡΡ
ΡΠ°Π·Π»ΠΈΡΠ½ΡΡ
ΠΏΡΠΎΠ΄ΠΎΠ»ΠΆΠΈΡΠ΅Π»ΡΠ½ΠΎΡΡΠ΅ΠΉ. Π¦Π΅Π»Ρ ΡΠ°Π±ΠΎΡΡ β Π²Π½Π΅Π΄ΡΠ΅Π½ΠΈΠ΅ ΠΏΡΠ΅Π΄Π»ΠΎΠΆΠ΅Π½Π½ΠΎΠ³ΠΎ ΡΠ΅ΠΆΠΈΠΌΠ° Π² Π°Π½Π°Π»ΠΈΠ·Π°ΡΠΎΡΡ ΠΠΠΠ‘ Ρ Π»ΠΈΠ½Π΅ΠΉΠΊΠ°ΠΌΠΈ ΡΠΎΡΠΎΠ΄Π΅ΡΠ΅ΠΊΡΠΎΡΠΎΠ² ΠΠΠΠβ2000 ΠΈ ΠΠΠΠβ4000 Π΄Π»Ρ ΡΠ²Π΅Π»ΠΈΡΠ΅Π½ΠΈΡ Π΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ Π΄ΠΈΠ°ΠΏΠ°Π·ΠΎΠ½Π° ΡΠ΅Π³ΠΈΡΡΡΠΈΡΡΠ΅ΠΌΡΡ
ΡΠΏΠ΅ΠΊΡΡΠ°Π»ΡΠ½ΡΡ
Π»ΠΈΠ½ΠΈΠΉ. Π ΡΠ°Π±ΠΎΡΠ΅ ΠΏΠΎΠ»ΡΡΠ΅Π½Ρ ΡΠΎΡΠΌΡΠ»Ρ Π·Π°Π²ΠΈΡΠΈΠΌΠΎΡΡΠΈ ΠΎΡΠ½ΠΎΡΠ΅Π½ΠΈΡ ΡΠΈΠ³Π½Π°Π»-ΡΡΠΌ ΠΈ Π΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ Π΄ΠΈΠ°ΠΏΠ°Π·ΠΎΠ½Π° ΡΠ΅Π³ΠΈΡΡΡΠ°ΡΠΈΠΈ ΡΠΏΠ΅ΠΊΡΡΠ°Π»ΡΠ½ΡΡ
Π»ΠΈΠ½ΠΈΠΉ Π² ΠΈΠ½ΡΠ΅Π³ΡΠ°Π»ΡΠ½ΠΎΠΉ Π°ΡΠΎΠΌΠ½ΠΎ-ΡΠΌΠΈΡΡΠΈΠΎΠ½Π½ΠΎΠΉ ΡΠΏΠ΅ΠΊΡΡΠΎΠΌΠ΅ΡΡΠΈΠΈ Π² Π·Π°Π²ΠΈΡΠΈΠΌΠΎΡΡΠΈ ΠΎΡ ΠΏΡΠΎΠ΄ΠΎΠ»ΠΆΠΈΡΠ΅Π»ΡΠ½ΠΎΡΡΠΈ Π½Π°ΠΊΠΎΠΏΠ»Π΅Π½ΠΈΡ, ΠΏΠΎΠ»Π½ΠΎΠ³ΠΎ Π²ΡΠ΅ΠΌΠ΅Π½ΠΈ ΠΈΠ·ΠΌΠ΅ΡΠ΅Π½ΠΈΡ, ΡΡΠΎΠ²Π½Ρ ΡΠΏΠ΅ΠΊΡΡΠ°Π»ΡΠ½ΠΎΠ³ΠΎ ΡΠΎΠ½Π° ΠΈ ΠΏΠ°ΡΠ°ΠΌΠ΅ΡΡΠΎΠ² Π»ΠΈΠ½Π΅Π΅ΠΊ. Π’Π΅ΠΎΡΠ΅ΡΠΈΡΠ΅ΡΠΊΠΈ ΠΏΠΎΠΊΠ°Π·Π°Π½ΠΎ, ΡΡΠΎ ΠΏΡΠΈΠΌΠ΅Π½Π΅Π½ΠΈΠ΅ ΡΠ΅ΠΆΠΈΠΌΠ° ΡΠ΅Π³ΠΈΡΡΡΠ°ΡΠΈΠΈ Ρ ΡΠ΅ΡΠ΅Π΄ΠΎΠ²Π°Π½ΠΈΠ΅ΠΌ Π½Π°ΠΊΠΎΠΏΠ»Π΅Π½ΠΈΠΉ ΡΠ°Π·Π»ΠΈΡΠ½ΠΎΠΉ ΠΏΡΠΎΠ΄ΠΎΠ»ΠΆΠΈΡΠ΅Π»ΡΠ½ΠΎΡΡΠΈ Π΄ΠΎΠ»ΠΆΠ½ΠΎ ΡΠ²Π΅Π»ΠΈΡΠΈΡΡ Π΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΈΠΉ Π΄ΠΈΠ°ΠΏΠ°Π·ΠΎΠ½ ΠΈΠ·ΠΌΠ΅ΡΠ΅Π½ΠΈΡ Π»ΠΈΠ½Π΅Π΅ΠΊ ΡΠΎΡΠΎΠ΄Π΅ΡΠ΅ΠΊΡΠΎΡΠΎΠ² ΠΠΠΠβ2000 ΠΈ ΠΠΠΠβ4000 Π½Π° Π΄Π²Π° ΠΏΠΎΡΡΠ΄ΠΊΠ°. ΠΠΊΡΠΏΠ΅ΡΠΈΠΌΠ΅Π½ΡΠ°Π»ΡΠ½ΠΎ ΠΏΠΎΠΊΠ°Π·Π°Π½ΠΎ ΡΠ²Π΅Π»ΠΈΡΠ΅Π½ΠΈΠ΅ Π΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ Π΄ΠΈΠ°ΠΏΠ°Π·ΠΎΠ½Π° ΠΈΠ·ΠΌΠ΅ΡΠ΅Π½ΠΈΡ ΠΈΠ½ΡΠ΅Π½ΡΠΈΠ²Π½ΠΎΡΡΠΈ ΡΠΏΠ΅ΠΊΡΡΠ°Π»ΡΠ½ΡΡ
Π»ΠΈΠ½ΠΈΠΉ Π»Π°ΠΌΠΏΡ ΠΏΠΎΠ»ΠΎΠ³ΠΎ ΠΊΠ°ΡΠΎΠ΄Π° Π½Π° Π΄Π²Π° ΠΏΠΎΡΡΠ΄ΠΊΠ° Π΄ΠΎ 5 ΠΏΠΎΡΡΠ΄ΠΊΠΎΠ² Π²Π΅Π»ΠΈΡΠΈΠ½Ρ.ΠΠ»ΡΡΠ΅Π²ΡΠ΅ ΡΠ»ΠΎΠ²Π°: Π°ΡΠΎΠΌΠ½ΠΎ-ΡΠΌΠΈΡΡΠΈΠΎΠ½Π½Π°Ρ ΡΠΏΠ΅ΠΊΡΡΠΎΠΌΠ΅ΡΡΠΈΡ, ΠΈΠ½Π΄ΡΠΊΡΠΈΠ²Π½ΠΎ-ΡΠ²ΡΠ·Π°Π½Π½Π°Ρ ΠΏΠ»Π°Π·ΠΌΠ°, ΠΌΠΈΠΊΡΠΎΠ²ΠΎΠ»Π½ΠΎΠ²Π°Ρ ΠΏΠ»Π°Π·ΠΌΠ°, Π°Π½Π°Π»ΠΈΠ·Π°ΡΠΎΡ ΡΠΏΠ΅ΠΊΡΡΠΎΠ², ΠΠΠΠ‘, Π»ΠΈΠ½Π΅ΠΉΠΊΠΈ ΡΠΎΡΠΎΠ΄Π΅ΡΠ΅ΠΊΡΠΎΡΠΎΠ², ΡΠ°ΡΡΠΈΡΠ΅Π½Π½ΡΠΉ Π΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΈΠΉ Π΄ΠΈΠ°ΠΏΠ°Π·ΠΎΠ½, ΡΠ΅ΡΠ΅Π΄ΠΎΠ²Π°Π½ΠΈΠ΅ Π²ΡΠ΅ΠΌΡΠ½ ΡΠΊΡΠΏΠΎΠ·ΠΈΡΠΈΠΉDOI: http://dx.doi.org/10.15826/analitika.2021.25.4.01
Multicolour nonlinearly bound chirped dissipative solitons
The dissipative soliton regime is one of the most advanced ways to generate high-energy femtosecond pulses in mode-locked lasers. On the other hand, the stimulated Raman scattering in a fibre laser may convert the excess energy out of the coherent dissipative soliton to a noisy Raman pulse, thus limiting its energy. Here we demonstrate that intracavity feedback provided by re-injection of a Raman pulse into the laser cavity leads to formation of a coherent Raman dissipative soliton. Together, a dissipative soliton and a Raman dissipative soliton (of the first and second orders) form a two (three)-colour stable complex with higher total energy and broader spectrum than those of the dissipative soliton alone. Numerous applications can benefit from this approach, including frequency comb spectroscopy, transmission lines, seeding femtosecond parametric amplifiers, enhancement cavities and multiphoton fluorescence microscopy
All-fiber highly chirped dissipative soliton generation in the telecom range
A high-energy (0.93 nJ) all-fiber erbium femtosecond oscillator operating in the telecom spectral range is proposed and realized. The laser cavity, built of commercially available fibers and components, combines polarization maintaining (PM) and non-PM parts providing stable generation of highly chirped (chirp parameter 40) pulses compressed in an output piece of standard PM fiber to 165 fs. The results of the numerical simulation agree well with the experiment. The analyzed intracavity pulse dynamics enables the classification of the generated pulses as dissipative solitons
Wave kinetics of random fibre lasers
Traditional wave kinetics describes the slow evolution of systems with many degrees of freedom to equilibrium via numerous weak non-linear interactions and fails for very important class of dissipative (active) optical systems with cyclic gain and losses, such as lasers with non-linear intracavity dynamics. Here we introduce a conceptually new class of cyclic wave systems, characterized by non-uniform double-scale dynamics with strong periodic changes of the energy spectrum and slow evolution from cycle to cycle to a statistically steady state. Taking a practically important exampleβrandom fibre laserβwe show that a model describing such a system is close to integrable non-linear SchrΓΆdinger equation and needs a new formalism of wave kinetics, developed here. We derive a non-linear kinetic theory of the laser spectrum, generalizing the seminal linear model of Schawlow and Townes. Experimental results agree with our theory. The work has implications for describing kinetics of cyclical systems beyond photonics
Experimental Method of Temperature and Strain Discrimination in Polymer Composite Material by Embedded Fiber-Optic Sensors Based on Femtosecond-Inscribed FBGs
Experimental method of temperature and strain discrimination with fiber Bragg gratings (FBGs) sensors embedded in carbon fiber-reinforced plastic is proposed. The method is based on two-fiber technique, when two FBGs inscribed in different fibers with different sensitivities to strain and/or temperature are placed close to each other and act as a single sensing element. The nonlinear polynomial approximation of Bragg wavelength shift as a function of temperature and strain is presented for this method. The FBGs were inscribed with femtosecond laser by point-by-point inscription technique through polymer cladding of the fiber. The comparison of linear and nonlinear approximation accuracies for array of embedded sensors is performed. It is shown that the use of nonlinear approximation gives 1.5β2 times better accuracy. The obtained accuracies of temperature and strain measurements are 2.6β3.8Β°C and 50β83βΞΌΞ΅ in temperature and strain range of 30β120Β°C and 0β400βΞΌΞ΅, respectively
- β¦