Accurate modeling of high-repetition rate ultrashort pulse amplification in optical fibers.

A numerical model for amplification of ultrashort pulses with high repetition rates in fiber amplifiers is presented. The pulse propagation is modeled by jointly solving the steady-state rate equations and the generalized nonlinear Schrödinger equation, which allows accurate treatment of nonlinear and dispersive effects whilst considering arbitrary spatial and spectral gain dependencies. Comparison of data acquired by using the developed model and experimental results prove to be in good agreement.

Tunable, high-power, continuous-wave dual-polarization Yb-fiber oscillator.

We demonstrate a high-power, dual-polarization Yb-fiber oscillator, by separately locking the two linear polarization states defined by slow and fast axis of a polarization-maintaining gain fiber with volume Bragg gratings. Dual-line lasing is achieved with a tunable wavelength separation from 0.03 to 2 THz, while exceeding output powers of 78 W over the entire tuning range, maintaining a high beam-quality with M(2)<1.

High-power, single-frequency, continuous-wave optical parametric oscillator employing a variable reflectivity volume Bragg grating.

A continuous-wave singly-resonant optical parametric oscillator (SRO) with an optimum extraction efficiency, that can be adjusted independent of the pump power, is demonstrated. The scheme employs a variable-reflectivity volume Bragg grating (VBG) as the output coupler of a ring cavity, omitting any additional intra-cavity elements. In this configuration, we obtained a 75%-efficient SRO with a combined signal (19 W @ 1.

Myths and realities about the recovery of L׳Aquila after the earthquake.

There is a set of myths which are linked to the recovery of L׳Aquila, such as: the L׳Aquila recovery has come to a halt, it is still in an early recovery phase, and there is economic stagnation. The objective of this paper is threefold: (a) to identify and develop a set of spatial indicators for the case of L׳Aquila, (b) to test the feasibility of a numerical assessment of these spatial indicators as a method to monitor the progress of a recovery process after an earthquake and (c) to answer the question whether the recovery process in L׳Aquila stagnates or not. We hypothesize that after an earthquake the spatial distribution of expert defined variables can constitute an index to assess the recovery process more objectively.

High-power continuous-wave frequency-doubling in KTiOAsO4.

High-power continuous-wave generation at 533 nm is demonstrated in bulk periodically poled KTiOAsO(4) (KTA) by single-pass frequency doubling of a VBG-locked Yb-doped fiber laser. Absorption characteristic and second harmonic generation (SHG) performance of different KTA samples are studied and compared. The best performing sample catered for 25%-efficient SHG of 13.

Femtosecond laser-induced apodized Bragg grating waveguides.

We report on the inscription of apodized Bragg grating waveguides (BGWs) in fused silica using a modulated high repetition rate fs laser system. Tailoring of the grating's coupling strength is facilitated by appropriately substructuring the modulation of the inscribing laser radiation. The proposed alteration delivers an unchanged constant mean refractive index entailing homogeneous guiding properties along the entire waveguide.

Efficient spectral control and tuning of a high-power narrow-linewidth Yb-doped fiber laser using a transversely chirped volume Bragg grating.

A transversely chirped volume Bragg grating (TCVBG) is used for flexible wavelength-tuning of a high-power (>100 W) tunable Yb-fiber laser oscillator. Continuous tuning over 2.5 THz of the narrow-band (13 GHz) signal was achieved by transversely translating the TCVBG during high-power operation without cavity realignment.

Laser-written waveguides in KTP for broadband Type II second harmonic generation.

Femto-second laser writing was used to fabricate waveguides in a z-cut KTP sample with losses below 0.8 dB/cm. They were used for efficient, broad bandwidth, Type II birefringent second harmonic generation to the green.

On the tunability of a narrow-linewidth Yb-fiber laser from three- to four-level lasing behaviour.

We report on a tunable multi-watt ytterbium-doped fiber laser bridging the gap from three-level lasing around 980 nm to true four-level lasing at 1100 nm. Wavelength-locking and -tuning was achieved by using an external volume-Bragg grating(VBG) as the cavity end mirror. The results are compared with detailed numerical calculations based on a spectrally resolved rate equation analysis, taking competing emission at other wavelengths into account.