Oleg L. Antipov

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

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.

Broadly tunable femtosecond Tm:Lu 2 O 3 ceramic laser operating around 2070 nm

Femtosecond mode locking of a Tm-doped Lu2O3 ceramic laser is reported. Transform-limited pulses as short as 180 fs are generated at 2076 nm with an average output power of 400 mW and a pulse repetition frequency of 121.2 MHz. An output power up to 750 mW can be reached at the somewhat longer pulse duration of 382 fs. Femtosecond pulse generation is realized in the 2030-2100 nm spectral range. Passive mode locking was achieved using an ion-implanted InGaAsSb quantum-well-based SESAM.

Detailed characterization of pump-induced refractive index changes observed in Nd:YVO(4), Nd:GdVO(4) and Nd:KGW.

The refractive index changes which can be induced in the Nd:YVO(4), Nd:GdVO(4) and Nd:KGW high gain laser crystals, when their Nd(3+) laser active ions are pumped from their ground- to excited- energy levels, have been carefully measured and characterized. By using two complementary optical techniques based on pump-probe interferometry and transient diffraction grating, the electronic and thermal contributions to the observed refractive index variations have been accurately determined and successfully exploited to derive various parameters such as polarizability changes, thermo-optic coefficients and thermal diffusivities.

All-fiber coherent combining of Er-doped amplifiers through refractive index control in Yb-doped fibers

We propose a simple all-fiber solution for coherent beam combining of Er-doped fiber amplifiers. This method, which we believe to be a new method, employs the effect of refractive index changes in Yb-doped fibers induced at approximately 1.55 microm by optical pumping at approximately 980 nm, which is performed for an active phase control in the fiber configuration. An algorithm based on population inversion in a two-level system supports the straightforward implementation of the effect into a feedback loop. Combining two 500 mW Er-doped amplifiers in a single-mode fiber is successfully demonstrated with control by approximately 120 mW laser diode. The method is shown to operate against the acoustic phase noise within the range of approximately pi rad and with a rate of approximately 2.6 pi rad/ms that potentially serves combining of at least 50 amplifiers similar to those used in practical work.

Electronic mechanism for refractive-index changes in intensively pumped Yb:YAG laser crystals

Refractive-index changes accompanying changes in population of electronic levels of Yb3+ ions in a Yb:YAG laser disk under intense diode and laser pumping have been studied by use of both a highly sensitive polarization interferometer and transient grating testing at 633 nm. The electronic change of the index that is due to excitation of the Yb3+ ions (which have different polarizability of ground state 2F7/2 and excited level 2F5/2) is strongly predominant over the thermal component. The polarizability differences are deltap (1.9 +/- 0.8) x 10(-26) and (1.95 +/- 0.25) x 10(-26) cm3 as measured at 633 nm in interferometric and transient grating experiments, respectively.

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

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.

Trends in stimulated Brillouin scattering and optical phase conjugation

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.

Optical properties and efficient laser oscillation at 2066 nm of novel Tm:Lu 2 O 3 ceramics

Structural, optical, and spectroscopic properties of novel Tm3+:Lu2O3 ceramics are studied. The average grain size is determined to be ~0.54-0.56 μm. The absorption spectra show good opportunities for diode pumping at 796 nm and 811 nm. The ceramics have high mid-IR transmittance of up to 7 μm. Strong luminescence lines are measured at 1942 nm, 1965 nm, and 2066 nm. CW laser operation at 2066 nm with an output power of up to 26 W and a slope efficiency of 42% is obtained. Q-switched operation with a pulse duration of 100-150 ns and a repetition rate of 5-10 kHz is achieved.

Diode-pumped Nd:YAG laser with reciprocal dynamic holographic cavity

A self-organizing laser based on a single diode-pumped Nd:YAG slab with reciprocal cavity completed by dynamic holographic gratings was created. The temporal dynamics, frequency spectrum and spatial characteristics of the generated beam were examined. A single-transverse-mode beam with up to 10 mJ pulse energy and 15% optical-to-optical efficiency was generated.

250-W average-power Nd:YAG laser with self-adaptive cavity completed by dynamic refractive-index gratings

A high average power laser oscillator with a cavity completed by a nonlinear mirror formed by refractive index gratings which accompany population gratings induced in Nd:YAG laser crystals by generating beams themselves is investigated numerically and experimentally. The role of different noise sources at the initial stage of nonlinear cavity formation is studied. The adaptation of the cavity formed by nonlinear dynamic mirrors to intracavity distortions is demonstrated. The generation of beams with average power up to 250 W, near-diffraction-limited divergence, and long coherence length has been achieved.