Spatio-temporal instability of the fundamental mode in Yb 3+-doped few-mode PM fiber amplifiers w... more Spatio-temporal instability of the fundamental mode in Yb 3+-doped few-mode PM fiber amplifiers with a core diameter of 8.5 μm was registered at 2-30 Watts pump power. Both experimental and theoretical analysis revealed the nonlinear power transformation of the LP 01 fundamental mode into high-order modes. Numerical simulation revealed self-consistent growth of the higher-order mode and traveling electronic index grating accompanying the population grating induced by the mode interference field (due to different polarizability of the excited and unexcited Yb 3+ ions). Experimental results and numerical calculations showed the increase of the instability threshold along with an increase of the signal frequency bandwidth.
Spatio-temporal instability of the fundamental mode in Yb 3+-doped few-mode PM fiber amplifiers w... more Spatio-temporal instability of the fundamental mode in Yb 3+-doped few-mode PM fiber amplifiers with a core diameter of 8-10 μm was studied experimentally and theoretically. The mode instability threshold was registered at 1-100 Watts pump power. The threshold was found to decrease dramatically in the presence of a backward reflection of the signal from the output fiber end or an external counter-propagating beam; an increase of the signal bandwidth or input power resulted in the increase of the threshold. Numerical simulation revealed a self-consistent growth of the higher-order mode and a traveling electronic index grating accompanying the population grating induced by the mode interference field (due to different polarizability of the excited and unexcited Yb 3+ ions).
An influence of backward reflection on spatio-temporal instability of the fundamental mode in Yb ... more An influence of backward reflection on spatio-temporal instability of the fundamental mode in Yb 3+-doped few-mode polarization maintaining fiber amplifiers with a core diameter of 10 μm was studied experimentally and theoretically. The mode instability threshold was registered to decrease dramatically in the presence of a backward reflection of the signal from the output fiber end; an increase of the signal bandwidth or input power resulted in the increase of the threshold. Numerical simulation revealed a self-consistent growth of the higher-order mode LP 11 and a traveling index grating accompanying the population grating induced by the mode interference field (due to different polarizability of the excited and unexcited Yb 3+ ions). The presence of the backward-propagating wave resulted in four-wave mixing on the common index grating induced by the interference field of pairs of the fundamental LP 01 and LP 11 modes.
Highly efficient laser oscillations at 2 μm were investigated in Tm:Lu 2 O 3 ceramics in-band pum... more Highly efficient laser oscillations at 2 μm were investigated in Tm:Lu 2 O 3 ceramics in-band pumped at 1670 nm by a Raman-shifted erbium fiber laser. Both 23 W CW and 15 W active Q-switched oscillations with 40 ns pulse duration and 15-30 kHz repetition rate were achieved in a high-quality beam. The evolution of two generated waves at 1966 and 2064 nm in dependence on pump power was studied.
A novel concept of a booster amplifier for a pulsed Tm fiber laser at 1940 nm based on Tm:Lu 2 O ... more A novel concept of a booster amplifier for a pulsed Tm fiber laser at 1940 nm based on Tm:Lu 2 O 3 ceramics and implementing fiber-combined signal and pump was examined. The pumping emission of the ceramics at 1678 nm was obtained from Raman-shifted Er fiber laser radiation. The hybrid fiber–ceramics amplifier with a gain factor of up to 6 dB and a pulse energy of more than 650 μJ with single-mode output was demonstrated.
In this paper we summarize the fundamentals of nonlinear refractive index change (RIC) in single-... more In this paper we summarize the fundamentals of nonlinear refractive index change (RIC) in single-mode ytterbium-doped optical fibers induced by optical pulses at 980 nm and derive the general rate equation describing the RIC evolution. The induced RIC dynamics is shown to follow the dynamics of the population of the excited/unexcited ion states with a factor proportional to their polarizability difference. An implicit expression is derived for this factor for the case of single-mode Yb-doped optical fibers and three different fiber core doped area profiles.
We develop a theoretical framework to analyze the mechanism of refractive index changes (RIC) in ... more We develop a theoretical framework to analyze the mechanism of refractive index changes (RIC) in double-clad Yb 3+ doped optical fibers under resonant core or clad pumping, and with signal amplification. The model describes and compares thermal and electronic contributions to the phase shifts induced on the amplified signal at 1064 nm and the probe signal at 1550 nm, i.e. located inside and outside of the fiber amplification band, respectively. The ratio between the thermal and electronic phase shifts is evaluated as a function of the pump pulse duration, the gain saturation, the amplified beam power and for a variety of fiber parameters.
We discuss a radioactivity sensing based on monitoring of color centers formation in Yb-doped fib... more We discuss a radioactivity sensing based on monitoring of color centers formation in Yb-doped fiber under gamma irradiation. New method exploits the dynamic effect of refractive index changes (RIC) induced by laser pumping into the fiber absorption band. In our experiment four identical samples of the single-mode aluminum silicate Yb-doped optical fiber have been γ–irradiated with different doses from a 60 Co source. All fibers passed the test in the intereferometric setup for the purpose of the pump induced RIC effect. During the test the phase shifts induced in the fiber by 1-ms-square pump pulses at 980 nm were recorded with a probe signal at eleven different wavelengths ranging from ~1.46 to ~1.61 μm. The phase traces have been normalized to their maximum values and averaged over 100 traces for each probe wavelength and also over all probe wavelengths. The averaged phase traces highlight the differences in their growing and decaying parts in respect to the case of non-irradiated fibers. These differences are found to be in correlation with the fiber irradiation dose. For non-irradiated fibers decay parts are perfectly fitted by one exponential function with the relaxation time constant equal to the Yb-ion excited state lifetime ~750 μs, to be the same for all fiber samples. However, for irradiated fibers the similar fitting gives a triple exponential decay with time constants estimated as ~750, ~500 and 40μs. For higher irradiation dose the difference with one exponential fitting is more pronounced. Having in mind that the obtained difference in phase shift dynamics could be associated with excitation of some color centers induced in the fiber matrix by gamma irradiation, we represent the normalized phase shifts as a superposition of two contributions. The first contribution is due to excitation of Yb-ion, the same for all fiber samples. The second is due to excitation of color centers. The amplitude of the second part highlights a degree of fiber degradation under gamma radiation and is directly proportional to the concentration of the excited color centers that, in its turn, linearly grows with the irradiation dose. Therefore, new method is regarded as a good candidate for potential applications in fiber dosimeters.
Spatio-temporal instability of the fundamental mode in Yb 3+-doped few-mode PM fiber amplifiers w... more Spatio-temporal instability of the fundamental mode in Yb 3+-doped few-mode PM fiber amplifiers with a core diameter of 8.5 μm was registered at 2-30 Watts pump power. Both experimental and theoretical analysis revealed the nonlinear power transformation of the LP 01 fundamental mode into high-order modes. Numerical simulation revealed self-consistent growth of the higher-order mode and traveling electronic index grating accompanying the population grating induced by the mode interference field (due to different polarizability of the excited and unexcited Yb 3+ ions). Experimental results and numerical calculations showed the increase of the instability threshold along with an increase of the signal frequency bandwidth.
Spatio-temporal instability of the fundamental mode in Yb 3+-doped few-mode PM fiber amplifiers w... more Spatio-temporal instability of the fundamental mode in Yb 3+-doped few-mode PM fiber amplifiers with a core diameter of 8-10 μm was studied experimentally and theoretically. The mode instability threshold was registered at 1-100 Watts pump power. The threshold was found to decrease dramatically in the presence of a backward reflection of the signal from the output fiber end or an external counter-propagating beam; an increase of the signal bandwidth or input power resulted in the increase of the threshold. Numerical simulation revealed a self-consistent growth of the higher-order mode and a traveling electronic index grating accompanying the population grating induced by the mode interference field (due to different polarizability of the excited and unexcited Yb 3+ ions).
An influence of backward reflection on spatio-temporal instability of the fundamental mode in Yb ... more An influence of backward reflection on spatio-temporal instability of the fundamental mode in Yb 3+-doped few-mode polarization maintaining fiber amplifiers with a core diameter of 10 μm was studied experimentally and theoretically. The mode instability threshold was registered to decrease dramatically in the presence of a backward reflection of the signal from the output fiber end; an increase of the signal bandwidth or input power resulted in the increase of the threshold. Numerical simulation revealed a self-consistent growth of the higher-order mode LP 11 and a traveling index grating accompanying the population grating induced by the mode interference field (due to different polarizability of the excited and unexcited Yb 3+ ions). The presence of the backward-propagating wave resulted in four-wave mixing on the common index grating induced by the interference field of pairs of the fundamental LP 01 and LP 11 modes.
Highly efficient laser oscillations at 2 μm were investigated in Tm:Lu 2 O 3 ceramics in-band pum... more Highly efficient laser oscillations at 2 μm were investigated in Tm:Lu 2 O 3 ceramics in-band pumped at 1670 nm by a Raman-shifted erbium fiber laser. Both 23 W CW and 15 W active Q-switched oscillations with 40 ns pulse duration and 15-30 kHz repetition rate were achieved in a high-quality beam. The evolution of two generated waves at 1966 and 2064 nm in dependence on pump power was studied.
A novel concept of a booster amplifier for a pulsed Tm fiber laser at 1940 nm based on Tm:Lu 2 O ... more A novel concept of a booster amplifier for a pulsed Tm fiber laser at 1940 nm based on Tm:Lu 2 O 3 ceramics and implementing fiber-combined signal and pump was examined. The pumping emission of the ceramics at 1678 nm was obtained from Raman-shifted Er fiber laser radiation. The hybrid fiber–ceramics amplifier with a gain factor of up to 6 dB and a pulse energy of more than 650 μJ with single-mode output was demonstrated.
In this paper we summarize the fundamentals of nonlinear refractive index change (RIC) in single-... more In this paper we summarize the fundamentals of nonlinear refractive index change (RIC) in single-mode ytterbium-doped optical fibers induced by optical pulses at 980 nm and derive the general rate equation describing the RIC evolution. The induced RIC dynamics is shown to follow the dynamics of the population of the excited/unexcited ion states with a factor proportional to their polarizability difference. An implicit expression is derived for this factor for the case of single-mode Yb-doped optical fibers and three different fiber core doped area profiles.
We develop a theoretical framework to analyze the mechanism of refractive index changes (RIC) in ... more We develop a theoretical framework to analyze the mechanism of refractive index changes (RIC) in double-clad Yb 3+ doped optical fibers under resonant core or clad pumping, and with signal amplification. The model describes and compares thermal and electronic contributions to the phase shifts induced on the amplified signal at 1064 nm and the probe signal at 1550 nm, i.e. located inside and outside of the fiber amplification band, respectively. The ratio between the thermal and electronic phase shifts is evaluated as a function of the pump pulse duration, the gain saturation, the amplified beam power and for a variety of fiber parameters.
We discuss a radioactivity sensing based on monitoring of color centers formation in Yb-doped fib... more We discuss a radioactivity sensing based on monitoring of color centers formation in Yb-doped fiber under gamma irradiation. New method exploits the dynamic effect of refractive index changes (RIC) induced by laser pumping into the fiber absorption band. In our experiment four identical samples of the single-mode aluminum silicate Yb-doped optical fiber have been γ–irradiated with different doses from a 60 Co source. All fibers passed the test in the intereferometric setup for the purpose of the pump induced RIC effect. During the test the phase shifts induced in the fiber by 1-ms-square pump pulses at 980 nm were recorded with a probe signal at eleven different wavelengths ranging from ~1.46 to ~1.61 μm. The phase traces have been normalized to their maximum values and averaged over 100 traces for each probe wavelength and also over all probe wavelengths. The averaged phase traces highlight the differences in their growing and decaying parts in respect to the case of non-irradiated fibers. These differences are found to be in correlation with the fiber irradiation dose. For non-irradiated fibers decay parts are perfectly fitted by one exponential function with the relaxation time constant equal to the Yb-ion excited state lifetime ~750 μs, to be the same for all fiber samples. However, for irradiated fibers the similar fitting gives a triple exponential decay with time constants estimated as ~750, ~500 and 40μs. For higher irradiation dose the difference with one exponential fitting is more pronounced. Having in mind that the obtained difference in phase shift dynamics could be associated with excitation of some color centers induced in the fiber matrix by gamma irradiation, we represent the normalized phase shifts as a superposition of two contributions. The first contribution is due to excitation of Yb-ion, the same for all fiber samples. The second is due to excitation of color centers. The amplitude of the second part highlights a degree of fiber degradation under gamma radiation and is directly proportional to the concentration of the excited color centers that, in its turn, linearly grows with the irradiation dose. Therefore, new method is regarded as a good candidate for potential applications in fiber dosimeters.
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Papers by Oleg L Antipov