High-performance cavity-dumped Q-switched Alexandrite laser CW diode-pumped in double-pass configuration.

We present a high-performance Alexandrite laser for LIDAR applications with repetition rates up to 20 kHz in cavity-dumped Q-switched operation continuous-wave diode-pumped in the red spectral region. With a double-pass pump configuration, short pulses with 2.8 ns duration at repetition frequencies ranging from 1 kHz to 20 kHz could be demonstrated. At 5 kHz a - to our knowledge - record pulse energy of over 500 µJ could be achieved at 755 nm in TEM00. Furthermore, a stability measurement at an energy of around 350 µJ with 5 kHz showed no degradation over 150 Mega-shots. The influence of the crystal temperature on the laser performance is also investigated, first in continuous-wave and secondly in cavity-dumped Q-switched operation.

Experimental and numerical study of interlock requirements for high-power EYDFAs.

In this work, we studied the interlock requirements in a seed failure scenario for Er3+:Yb3+ doped fiber amplifiers (EYDFAs) pumped with high intensities in the MWcm-2 range at 9XX nm. We fed a time-dependent FEM-tool with the data from backwards directed amplified spontaneous emission (ASE) transients of different commercially available core-pumped single-mode fibers. In the FEM-tool, the Er3+:Yb3+ system is defined as a bi-directional energy transfer process and described by the corresponding rate equations. The power evolution of the pump, seed, and ASE signal is computed by differential equations taking into account the transient population densities of the relevant energy levels. With the model, we computed the temporal evolution of the corresponding energy levels after a seeder failure to take place within tens to hundreds of µs and calculated the associated gain. The fibers under test provide a critical total gain of 30 dB after ∼ 80 µs within the Yb3+ band and after ∼300 µs within the Er3+ band. This time decreases with increasing pump power and doping concentration. The results can be extrapolated to high-power cladding-pumped EYDFAs to meet the challenging requirements of engineering-level systems.

Gain dynamics in Raman fiber lasers and passive pump-to-Stokes RIN suppression.

We report on theoretical and experimental investigations of gain dynamics in Raman fiber lasers in the frequency range of 1 Hz-1 MHz. An analytical solution of the problem is due to the nonlinear nature of the Raman effect not feasible. Thus, we used a numerical simulation to gain general insights. Experimentally and numerically obtained results for a Raman fiber laser emitting at 1180 nm show good qualitative agreement. We also present a potential physical interpretation of the observed dynamical properties. In addition, we report on an experimental proof-of-principle of a passive pump-to-Stokes RIN suppression scheme for the main Stokes order in cascaded Raman fiber lasers utilizing an additional parasitic Stokes order. Again, results from numerical and experimental studies of a cascaded Raman fiber laser at 1180 nm and 1240 nm show good agreement and confirm the passive pump-to-Stokes RIN suppression at 1180 nm. The dependencies between the resonator design and the parameters of the noise suppression are investigated. In addition, it is shown that the scheme can also be applied to cascaded Raman fiber lasers with more then two Stokes shifts. This opens the possibility to design for example low-noise Raman fiber lasers at 1480 nm to pump low-noise Er(3+) doped fiber amplifiers.

Gain dynamics in Er(3+):Yb(+) co-doped fiber amplifiers.

Understanding the gain dynamics of fiber amplifiers is essential for the implementation and active stabilization of low noise amplifiers or for coherent beam combining schemes. The gain dynamics of purely Er3+ or Yb3+ doped fiber amplifiers are well studied, whereas no analysis for co-doped systems, especially for Er3+:Yb3+ co-doped fiber amplifiers has been performed, so far. Here, we analyze for the first time the gain dynamics of Er3+:Yb3+ co-doped fiber amplifiers theoretically and experimentally. It is shown that due to the energy transfer between the Yb3+ and Er3+ ions a full analytical solution is not possible. Thus, we used numerical simulations to gain further insights. Comparison of experimental and numerical results shows good qualitative agreement. In addition, we were able to determine the Yb3+-Er3+ transfer function of the energy transfer experimentally.

Co-seeded Er3+:Yb3+ single frequency fiber amplifier with 60 W output power and over 90% TEM(00) content.

We report on the design and fabrication of an Er(3+):Yb(3+) triple clad fiber and on the power scaling of a single frequency fiber amplifier at 1.5 µm based on that fiber. In addition, we report on mode content measurements in order to reveal the overlap of the amplifier output with the TEM(00) mode. The triple clad design was used to enable high output power levels, a good slope efficiency and an excellent beam quality. A maximum single frequency output power of 61 W at 1.5 µm could be achieved with the aid of the co-seeding method, which was used to suppress parasitic processes at 1.0 µm. With a scanning ring cavity the mode content of the amplifier output was analyzed with respect to the TEM modes. For all output power levels the TEM(00) content was above 90%.

Ultrafast double-slab regenerative amplifier with combined gain spectra and intracavity dispersion compensation.

We report on a diode-pumped double-slab Yb:KYW regenerative amplifier with combined gain spectra and intracavity dispersion compensation. At repetition rates > 20 kHz an average power of up to 5 W after compression was generated, resulting in a maximum pulse energy of 250 µJ. Pulse durations of around 190 fs were achieved by using a GRISM compressor with a transmission efficiency of 90%.

Differential phase-noise properties of a ytterbium-doped fiber amplifier for the Laser Interferometer Space Antenna.

The interferometric gravitational-wave detector Laser Interferometer Space Antenna (LISA) needs to transfer clock information among its three spacecraft in the form of phase-modulation sidebands. For this reason phase noise introduced by the optical chain between the carrier and a sideband must be low. We have measured this differential phase noise for a ytterbium-doped fiber amplifier emitting up to 2 W. For 1 W of output power as required for LISA, the measured differential phase noise was within its requirement. For 2 W output power the amplifier exhibited stimulated Brillouin scattering and showed a differential phase-noise factor of up to 15 higher. Dependencies on operating parameters and optical length noise of the amplifier were also measured.

Quantum-limited noise performance of a femtosecond all-fiber ytterbium laser.

We report on quantum-limited noise performance of a mode-locked ytterbium all-fiber laser. The laser operates at a high normal net dispersion without dispersion compensation. We show that the naïve application of analytical models to such lasers leads to strongly underestimated timing jitter, whereas a numerical simulation is in reasonable agreement with measurements. The measured timing phase noise is found to be essentially limited by quantum noise influences and not by technical noise. Furthermore we show that the phase noise of different comb lines has a quasi-fix point at the center of the optical spectrum and that the jitter is translated into high carrier-envelope offset phase noise with a linewidth of around 3 MHz.

Ultrafast high power Yb:KLuW regenerative amplifier.

We report on an high power ultra-short pulse regenerative Yb:KLuW amplifier based on the thin disk concept. A maximum pulse energy of 571 microJ was extracted at a repetition rate of 20 kHz. Compression of the output pulses resulted in a pulse duration of 197 fs assuming a deconvolution factor of 2.16. At a repetition rate of 125 kHz a maximum average power of 17.9 W was measured in front of the compressor.

Sub-100 fs pulses from a low repetition rate Yb-doped fiber laser.

We report on a passively mode-locked ytterbium-doped fiber laser with a repetition rate of 1.8 MHz. The laser was hybridly mode-locked via nonlinear polarization evolution and a semiconductor saturable absorber mirror. It generated chirped 3.8 ps long pulses with a pulse energy of 1.0 nJ which could be dechirped to a pulse duration of 93 fs.

Impact of third-order dispersion on the generation of wave-breaking free pulses in ultrafast fiber lasers.

Wave-breaking free pulses generated in passively mode-locked fiber lasers can tolerate a certain cubic phase delay induced by third-order dispersion without losing pulse quality. We demonstrate that the spectral as well as the temporal profile of the pulses become asymmetric. The generated pulses had a pulse energy up to 3.5nJ and could be externally compressed down to 145fs. The fact that the pulses could always be dechirped within 10% of the Fourier limit points out the linearity of the chirp. The pulse asymmetry was also observed in the output coupling characteristic of the mode-locking mechanism.

Narrow-linewidth ytterbium-doped fiber amplifier system with 45 nm tuning range and 133 W of output power.

We report on a master-oscillator ytterbium-doped fiber amplifier system with up to 133 W of continuous-wave output power using a tunable narrow-linewidth external-cavity diode laser seed source. Stable tunable high-power operation was demonstrated from 1040 nm to 1085 nm with more than 12 dB suppression of amplified spontaneous emission.

Similariton fiber laser with a hollow-core photonic bandgap fiber for dispersion control.

We report on an ytterbium-doped similariton fiber ring laser with a hollow-core photonic bandgap fiber for intracavity dispersion control. The oscillator is hybrid mode locked with a saturable Bragg reflector and by nonlinear polarization evolution. This scheme allows for an exact adjustment of the transmission characteristic to avoid the formation of bunched noiselike pulses while the self-starting characteristic is preserved. The oscillator generates highly stretched similaritons at 1025 nm with a pulse energy above 1n J at a repetition rate of 21.9 MHz.

Dynamics of parabolic pulses in an ultrafast fiber laser.

We report experimental and numerical results on the dynamics and propagation of parabolic pulses in a passively mode-locked ytterbium-doped fiber laser. Experimental data and numerical simulations are shown to match. Particular importance is attached to the pulse-shaping process in the different sections of the resonator. The paramount role of the gain fiber and saturable absorber in the laser is explicated.

Vertical ridge augmentation using polylactic membranes in conjunction with immediate implants in periodontally compromised extraction sites: an experimental study in dogs.

Polylactic membranes were evaluated for vertical ridge augmentation around immediate implants in periodontally compromised extraction sites. Ligature-induced periodontitis was produced in 10 adult beagle dogs. The periodontium was allowed to heal for 6 weeks. All premolar teeth were extracted and three implants were placed immediately into the extraction sockets on either side of the mandible so that the polished cone extended above the alveolar bone level. On one side of the mandible, the implants were covered with a 0.2-mm-thick polylactic membrane (DL-lactide-co-trimethylene carbonate in a ratio of 7:3). Histologic and morphometric analyses performed after 3 and 5 months revealed that the membrane group did not exhibit significantly greater bone-implant contact than the controls. The occurrence of dehiscences correlated significantly with use of the membrane. Use of the membrane was associated with significantly less peri-implant bone height after 5 months. No remnants of the membrane material could be identified after 3 or 5 months, indicating rapid resorption during the first weeks of implantation. The tested membrane material did not fulfill the requirements of resorption kinetics and space maintenance for guided bone regeneration in vertical ridge augmentation.

[Effects of artificial light, distributed through long photophases, on the annual growth cycle of the crayfish Orconectes limosus (Raffinesque)]. / Effets de la lumière artificielle, dispensée en longues photophases, sur le cycle annuel de croissance de l'ecrevisse Orconectes limosus (Rafinesque)

A photophase of 18 hrs interrupts the annual anecdysis of Orconectes limosus, which does not constitute an irrefutable evidence of a photoperiodic control in the cessation of anecdysis, since molts are also induced during the annual rest by an abnormally high temperature after a stay at low temperature. On the contrary, long photophases (18 and 24 hrs), dispensed from the beginning of the molting period, do not inhibit the start of the anecdysis of adults on the express condition that the covers are reconstituted.