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Ytterbium Doped Fiber Lasers for spontaneous emission

Ytterbium doped fiber lasers spontaneous emissionA team of researchers presents a new random noise pulsed regime provided by a ytterbium doped fiber laser. Herewith, the output of the ytterbium laser complies with the photon statistics common to narrowband amplified spontaneous emission resulting in the noise pulsing in terms of probability density and autocorrelation functions. The new fiber laser technique demonstrates that the increase of ytterbium doped laser leads to a prominent decrease in the regime’s coherence time (from few ns to tens ps).

Fiber laser systems are regarded as highly promising tools that have a wide range of commercial applications. Fiber lasers are used as light sources in fully fiberized optical schemes with no free-space components. Herein, they offer a high level of optical and electrical to optical conversion efficiency. Additionally, fiber laser systems have various operating regimes, “characterized by narrow (from a tens Hz) to a very large optical band, in continuous-wave (CW) and pulsed regimes including Q-switched, mode-locking and soliton operations where the pulse width is ranged from hundreds of nanoseconds down to tens of femtoseconds”.

Ytterbium doped fiber lasers are considered to have such a benefit as an excellent power budget thanks to the absence of excited-state absorption. Nevertheless, ytterbium doped lasers have a disadvantage that influences their efficiency: there is a specific broadening of the laser line in the case when the cavity of fiber laser is made from FBG couplers. Thus, the partial leakage of fiber laser power occurs on highly reflective fiber Bragg gratings.
The output power of ytterbium doped fiber lasers may vary from several watts to tens kW or even a few hundred kW depending on single-mode and multimode operations. It should be noted that the low cavity Q-factor of ytterbium lasers causes high fiber laser gain, and the regime of the laser system is changed on random kW pulses resulting in Brillouin scattering.

The researchers confirm that the operation of ytterbium doped lasers happens in a noise pulse regime with random magnitudes and widths (not in the CW regime). Moreover, there is a dependence between the fiber laser photon statistics and laser beam power (and hence on laser linewidth), thus, its behavior seems similar to narrowband ASE. For instance, several high-amplitude noise events with low probability achieve powers more than the mean laser beam power.

Finally, the developed laser system has been already tested. It shows that the laser spectrum’s width becomes higher with increasing output power. While the rate of the ytterbium laser process at lower output powers is lower than at higher one. Taking into consideration the fact that the nonlinear optical fiber length is considerably shorter than the cavity one.

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