Fiber based Mamyshev regenerators provide potentially a low cost, pulse-on-demand source with pulse durations down to the hundred femtosecond scale. Based on nonlinear broadening of gain switched diode laser pulses in fiber and consequent pulse shaping methods, these sources could provide an alternative for mode-locked systems. Here we study numerically the properties of such sources in terms of input pulse duration and power as well as various fibers. We show that an optimum operating region can be found for each input parameter combination, that is limited mainly by the onset of spontaneous Raman scattering and optical wave breaking.
Andrei Fedotov, Vasilii Ustimchik, Joona Rissanen, Teppo Noronen, Regina Gumenyuk, Yuri Chamorovskii, Alexander Kolosovskii, Victor Voloshin, Igor Vorob'ev, Valery Filippov
We developed ytterbium-doped double-clad large mode area (MFD = 30 μm) spun tapered fibers with low internal birefringence and perfect beam quality (M2 < 1.2). Picosecond MOPA system (95ps/100 MHz, 1064 nm) based on proposed active tapered fiber with output average power of 64 W (gain 32 dB) is demonstrated.
In this paper, we have developed Yb-doped fiber suitable for creation of all-fiber seed laser schemes operating near 977 nm. The fiber was based on a ring-doping design (cladding was partially doped with Yb-ions), which allowed us to fabricate a relatively small core and provide mode field diameter (MFD) of the active fiber comparable with standard fibers (to achieve small splicing losses with commercially available optical fibers) and, simultaneously, increase absorption from the cladding to keep a reasonably high lasing efficiency. So MFDx of the fiber was 12 μm, MFDy was 14 μm. Outer silica cladding of the active fiber was decreased to diameter of 80 μm and a special pump and signal combiner was used to inject pump and signal into the active fiber. Based on the developed Yb-doped fiber an all-fiber polarization maintaining mode-locked laser with central wavelength around 977 nm was demonstrated for the first time. SESAM was used as a saturable absorber. The laser was self-starting for pump powers above 4.6 W, with the output power of 3 mW. The autocorrelation was the best fitted with sech2 profile and pulse duration was estimated to be as long as 9.5 ps. The fundamental cavity frequency corresponded to the pulse repetition rate of 33.532 MHz. Signal-to-noise ratio measured in the radio frequency range was more than 50 dB, the line width was below 1 kHz, which indicate ultimate stability of the fabricated mode-lock laser.
We present a single-mode narrow band linear-polarized picosecond green fiber source delivered up to 146.4 kW of peak power. The laser architecture is composed of frequency-doubled all-fiber MOPA system operating at 1064 nm. The commercially available gain-switched semiconductor laser diode was used as a seed source delivered 77 ps pulses with the repetition rate between 100 kHz - 80 MHz. Two stages of pre-amplifiers based on the single-mode Yb-doped fibers were designed to amplify microwatt pulsed signal up to milliwatt level. A high-power amplification cascade comprised a double-clad polarization-maintaining tapered Yb3+-doped fiber as a gain medium. The frequency doubling was realized in a single-pass scheme with LBO crystal. The MOPA design with the active tapered fiber enabled to amplify effectively a narrowband picosecond IR radiation with relatively small spectral broadening. We obtained stable laser radiation with 77 ps pulses at repetition rate of 1 MHz, 290 pm spectral bandwidth with a central wavelength of 532 nm, the average power of 12 W corresponding to 12 μJ of pulse energy and 146.4 kW of peak power. The overall efficiency of secondharmonic generation reached 37 % in a single pass scheme. The obtained results showed advantages of the MOPA system based on a tapered amplifier in comparison with already published picosecond green laser systems exploited standard amplifiers based on cylindrical fixed-core fibers. The single-mode green laser with high peak power and narrow line are in high demand for a wide range of Raman spectroscopy applications.
We developed a highly efficient double-clad Yb-doped polarization-maintaining fiber to be implemented for small-signal amplification near 0.976 μm. The fiber was designed to have a relatively small mode field diameter compatible with standard step-index single-mode optical fibers. Another feature of the fiber was a small threshold for 0.976 μm signal amplification, which was achieved by a creation of a thin inner cladding (80 μm diameter). The unique design of the fiber allowed us to construct successfully an all-fiber picoseconds mode-locked laser at 0.98 μm for the first time to the best of our knowledge.
We demonstrated, for the first time to our best knowledge, an active tapered double clad fiber with circular birefringence and 35 μm core diameter. The output radiation had perfect beam quality (M2=1.18/1.1) and linearly polarized light with 15 dB of PER. The developed double clad active fiber was investigated for amplification of picosecond pulses in allfiber MOPA system. The MOPA system delivered 50 ps pulses with 55 W of the average power revealed 34.4 dB gain of the booster amplifier.
In the presented work, we investigated the optical and thermal stability of upconversion nanoparticles based on the three widely used matrices (NaYF4, Y2O3, LaF3). Analysis of the upconversion emission as a function of pump power density in a wide range revealed a multi-stage functional dependence. The stages of linear growing, saturation and degradation with both reversible and irreversible characters were discovered. For matrices of nanoparticles with low-temperature stability (NaYF4), the dependence proves to be irreversible that could cause by a change in the structure and chemical composition of the matrix. Reversible dependence occurs in matrices with high-temperature stability (Y2O3 and LaF3) and is caused by multiphonon nonradiative relaxation, which can be temperature-stimulated because of self-heating and low air-cooling of the crystal matrixes with low thermal conductivity.
Generation of ultrashort pulses with high average power and moderately high pulse energy generally requires a modelocked laser followed by several fiber amplifiers in a master-oscillator power-amplifier configuration. Recently, gainswitched diode lasers have emerged as a viable replacement to mode-locked oscillators as sources of sub-100 ps pulses in these systems, but the low output power available from the diodes necessitates the use of multiple costly amplifier stages. Here, we demonstrate the generation of 1.7 μJ pulses at 1030 nm, and 11.7 μJ pulses at 1064 nm from a gain-switched diode seeded compact MOPA with only two amplification stages. The final stage is a tapered fiber amplifier, whose geometry efficiently suppresses amplified spontaneous emission and allows reaching a gain of ~40 dB. This research work is still in progress, and further increase in pulse energy should be possible by optimizing the setup.
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