Optical-to-optical conversion efficiencies of as high as 32% with a slope efficiency of 44% were obtained with a novel diode-bar, side-pumped laser cavity design. A slab geometry with a single, high-angle-of-incidence reflection was used to extract gain from near the pump face of a Nd:YVO(4) bar that absorbed strongly at the pump wavelength. Small-signal gains of greater than 8 cm(-1) and pulse energies of as much as 3.2 mJ were obtained in an almost TEM(00) mode. Aperturing effects by the laser rod were found to limit the effects of nonuniform gain on the laser mode.

A High Efficiency Diode-Pumped Nd:YVO 4 Slab Laser

This work presents a review on the effect of transverse mode instability in high-power fiber laser systems and the corresponding investigations led worldwide over the past decade. This paper includes a description of the experimental observations and the physical origin of this effect, as well as some of the proposed mitigation strategies.

Transverse mode instability

Recent progress in the development of high power fibre lasers will be reviewed, and the prospects for scaling output powers to well beyond the hundred watt level, whilst maintaining diffraction-limited beam quality will be discussed

High power fibre lasers

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

We quantify the refractive index changes (RIC) in single-mode ytterbium-doped optical fibers induced by optical pulses at 980 nm and, for the first time, report details of the effect dynamics. The RIC dynamics is shown to follow that of the population of the excited/unexcited ion states with a factor proportional to their polarizability difference (PD). The absolute PD value is evaluated in the spectral range of 1460-1620 nm for different fiber samples and is found to be independent on the fiber geometry and on the ion concentration. The PD dispersion profile indicates to a predominant far-resonance UV rather than near-resonant IR transitions contribution to the RIC.

Dynamics of pump-induced refractive index changes in single-mode Yb-doped optical fibers

An overview on current trends in stimulated Brillouin scattering and optical phase conjugation is given. This report is based on the results of the “Second International Workshop on stimulated Brillouin scattering and phase conjugation” held in Potsdam/Germany in September 2007. The properties of stimulated Brillouin scattering are presented for the compensation of phase distortions in combination with novel laser technology like ceramics materials but also for e.g., phase stabilization, beam combination, and slow light. Photorefractive nonlinear mirrors and resonant refractive index gratings are addressed as phase conjugating mirrors in addition.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/8305A06ED0CA6FD9A9145EF40CBD06B6/S0263034608000335a.pdf/div-class-title-trends-in-stimulated-brillouin-scattering-and-optical-phase-conjugation-div.pdf

Trends in stimulated Brillouin scattering and optical phase conjugation

Refractive index changes accompanying changes in population of electron levels of Nd/sup 3+/ ions in a Nd:YAG laser crystal under intensive diode and laser pumping have been studied using a highly sensitive polarization interferometer. An electronic change of the index due to population of the /sup 4/F/sub 3/2/ level is measured to be high (comparable with the thermal component) in the crystal under QCW diode-stack pumping (at 808 nm). The electronic component increased dramatically under pumping by an additional laser (at 266 nm) due to population of a higher-lying level /sup 2/F(2)/sub 5/2/. Analytical estimation reveals a predominating contribution of the well-allowed 4f-5d inter-shell transitions in polarizability of the excited levels /sup 4/F/sub 3/2/ and /sup 2/F(2)/sub 5/2/ both at a testing wavelength of 633 nm and at a wavelength of the strongest laser transition 1064.2 nm.

Electronic changes of refractive index in intensively pumped Nd:YAG laser crystals

We develop a theoretical framework to analyze the mechanism of refractive index changes (RIC) in double-clad Yb3+ 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.

Electronic and thermal refractive index changes in Ytterbium-doped fiber amplifiers

Rate Equation for the Nonlinear Phase Shift in Yb-Doped Optical Fibers Under Resonant Diode-Laser Pumping

We present an overview of theoretical analysis and experimental observation of the spatio-temporal transverse mode instability in polarization-maintaining high-gain fiber amplifiers with a high concentration of Yb3+ ions and core diameters of 8-10 μm. The nonlinear power transformation of the LP01 fundamental mode into the high-order modes is explained by a traveling refractive index grating accompanying a population grating induced by the mode interference field. The origin of the refractive index gratings is discussed. The threshold power for the transverse mode instability is found to depend on the fiber core diameter, numerical aperture, dopant concentration and the signal bandwidth. The threshold power is observed to decrease dramatically in the presence of a backward reflection of a signal from the output fiber facet.

Maxim S. Kuznetsov

Papers

Trends in stimulated Brillouin scattering and optical phase conjugation

Electronic changes of refractive index in intensively pumped Nd:YAG laser crystals

Electronic and thermal refractive index changes in Ytterbium-doped fiber amplifiers

Rate Equation for the Nonlinear Phase Shift in Yb-Doped Optical Fibers Under Resonant Diode-Laser Pumping

Low-threshold mode instability in few-mode Yb3+-doped fiber amplifiers: an overview of recent results