The selector-free single-frequency operation of an Yb-doped fiber laser with scanning in the range of ?20?nm is demonstrated. The frequency and intensity evolution is shown to be driven by a self-induced phase grating in the active fiber defined by gain saturation in a standing-wave. A theory has been developed that describes well the main features of the experiment and provides possibilities for optimization of laser parameters. Perspectives for utilizing the self-scanned laser in fundamental studies and practical applications are discussed.

Self-scanned single-frequency operation of a fiber laser driven by a self-induced phase grating

The effect of broad-range (16 nm) self-sweeping of a narrow-line (less than 1 pm) Yb-doped fiber laser has been demonstrated experimentally. It is found that the effect arises from the self-sustained relaxation oscillations. As a result, the sweeping rate increases as square root of the laser power and decreases with increasing cavity length. Based on these results we propose a model describing dynamics of the laser frequency. The model takes into account the effects of gain saturation at the laser transition and spatial hole burning in the self-pulsing regime.

Broad-range self-sweeping of a narrow-line self-pulsing Yb-doped fiber laser

We present a brand-range self-sweeping Tm-Ho co-doped fiber laser experimentally. The laser’s center wavelength sweeps periodically around 1.9 μm with self-sweeping range of 4 nm ~17 nm, and the sweep rate can be changed in the range of 0.4 nm/s ~1.5 nm/s. The sweep range increases and the sweep rate declines when the pump power rises.

Tm-Ho co-doped all-fiber brand-range self-sweeping laser around 1.9 μm.

Self-swept erbium fiber laser emitting around 1.56 μm is reported in detail. Both sweep directions were registered: pointing toward longer and shorter wavelengths, redshift and blueshift sweeping, respectively. We describe method of determining the direction of the wavelength drift using the monochromator based optical spectrum analyzer. Possible root for this sweeping regime, i.e., the gain modulation along active fiber, is discussed with the help of a simple model calculating the overall cavity gain that can predict the direction of the laser wavelength sweeping.

Self-swept erbium fiber laser around 1.56 μm

Self-induced laser line sweeping of various regimes of sweep direction is reported for an experimental ytterbium fiber laser. The regimes involve sweeping from shorter to longer wavelengths ( nm)—so-called normal self-sweeping; from longer to shorter wavelengths ( nm)—so-called reverse self-sweeping; and a mixed regime in which a precarious balance of the normal and reverse sweeping exists and the sweep direction can change between consecutive sweeps. The regimes of sweeping were selected by changing the pump wavelength only. A detailed explanation of this sweep direction dynamics is presented based on a semi-empirical model. This model also provides a way to predict the sweep direction of fiber lasers based on other rare-earth-doped laser media.

https://iopscience.iop.org/article/10.1088/1612-202X/aa548d/pdf

Reverse spontaneous laser line sweeping in ytterbium fiber laser

The results of an experimental investigation were combined with the published work to show that undamped spikes in the output of multimode pulsed lasers were due to an inhomogeneous depletion of the inverted population in the bulk of an active rod. A quasicontinuous output was obtained from a ruby laser with plane mirrors. It was found that the mechanical and thermal distortions of the resonator, which could suppress the laser action, were essentially misalignments. A new feature of the stimulated emission, called inertia, was observed for a ruby laser with spherical mirrors when the spatial inhomogeneities of the population inversion were smoothed out.

Spike structure of the emission of solid-state lasers

A superregenerative amplification scheme was used to obtain unidirectional stimulated emission from a ruby ring laser under free-oscillation and Q-switched conditions. The duration of external control pulses was either tc > L/c or tc < L/c. The carrier frequency of giant pulses could be tuned within a range of 0.25 nm when the spectrum was 6×10–5 nm wide. Reproducible generation of short high-coherence light pulses was achieved.

Ruby ring laser subjected to an external signal

A theoretical and experimental investigation was made of the problem of controlling the mode structure of the spectra of giant pulses from actively Q-switched solid-state lasers by injection of external radiation at a frequency independent of the natural frequencies of the resonator. A marked difference was observed between the spectral kinetic characteristics of giant pulses from neodymium-glass and ruby lasers. On the basis of a comparison with previously established differences in the free-lasing dynamics, an explanation of this observation by nonlinear mode interaction is proposed and confirmed theoretically and experimentally. A method of improving the mode selection efficiency under giant pulse conditions using passive negative feedback is proposed and implemented experimentally using a neodymium-glass laser. Giant pulse generation with a spectral width of ≤ 5 × 10−4cm−1 and a power of 20 MW was obtained using an actively Q-switched neodymium-glass laser.

V S Pivtsov

Papers

Spike structure of the emission of solid-state lasers

Ruby ring laser subjected to an external signal

Fine structure of the spectra of giant pulses from actively Q-switched solid-state lasers with injection of external radiation