Highly scalable femtosecond coherent beam combining demonstrated with 19 fibers.

Coherent beam combining in the femtosecond regime of a record number of 19 fibers is demonstrated. The interferometric phase measurement technique, particularly well suited to phase-lock a very large number of fibers, is successfully demonstrated in the femtosecond regime. A servo loop is implemented to control piezoelectric fiber stretchers for both phase and delay variation compensation. The residual phase errors are below λ/60 rms. Nearly 50% of the total energy is contained in the far-field central lobe. After compression, we obtain a combined pulse width of 300 fs identical to the master oscillator pulse width.

Longwave infrared, single-frequency, tunable, pulsed optical parametric oscillator based on orientation-patterned GaAs for gas sensing.

We demonstrate a nanosecond single-frequency nested cavity optical parametric oscillator (NesCOPO) based on orientation-patterned GaAs (OP-GaAs). Its low threshold energy of 10 µJ enables to pump it with a pulsed single-frequency Tm:YAP microlaser. Stable single-longitudinal-mode emission is obtained owing to Vernier spectral filtering provided by the dual-cavity doubly-resonant NesCOPO scheme. Crystal temperature tuning covers the 10.3-10.9 µm range with a quasi-phase-matching period of 72.6 µm. A first step toward the implementation of this device in a differential absorption lidar is demonstrated by carrying out short-range standoff detection of ammonia vapor around 10.4 µm. Owing to the single-frequency emission, interferences due to absorption by atmospheric water vapor can be discriminated from the analyte signal.

Passive coherent beam combining of quantum-cascade lasers with a Dammann grating.

An external cavity using a binary phase grating has been developed to achieve coherent combining of five quantum-cascade lasers emitting at 4.65 µm. The grating phase profile is designed to combine five beams of equal intensities into a single beam with a good efficiency (~75%). The performances of this cavity concerning output power, stability, combining efficiency and beam quality are detailed. We report a CW combining efficiency of 66% corresponding to an output power of ~0.5 W with a good beam quality (M(2)<1.6).

High-efficiency 20-50 kHz mid-infrared orientation-patterned GaAs optical parametric oscillator pumped by a 2 microm holmium laser.

We report on what are, to our knowledge, the best results obtained with an orientation-patterned GaAs optical parametric oscillator (OPO) pumped by a Q-switched 2 microm Ho:YAG laser. Up to 2.85 W are obtained for 6.1 W of pump power, corresponding to an optical-to-optical conversion efficiency of 46.5% with a threshold of 1 W. Optical damage occurred at a fluence of about 2 J/cm2. The thickness of the crystal limited the pump power. Slope efficiencies are of the same order as those obtained with ZnGeP2 OPOs pumped with the same Ho:YAG laser.

High energy, single-mode, narrow-linewidth fiber laser source using stimulated Brillouin scattering beam cleanup.

We propose an original nonlinear beam cleaning fiber laser architecture to obtain high energy pulses with a good beam quality and a narrow linewidth. The output beam of a large core Er:Yb co-doped multimode fiber amplifier (M(2) approximately 6, 220 microJ) is converted into a near diffraction limited beam (M(2) = 1.6) through a stimulated Brillouin scattering injection seeded beam cleanup process. We report in this experiment a multimode to single mode conversion efficiency of 50% while preserving the master oscillator linewidth.

Beam cleanup in a self-aligned gradient-index Brillouin cavity for high-power multimode fiber amplifiers.

We propose a beam cleanup setup to convert a multimode beam into a single-mode beam by use of the Brillouin effect in a multimode gradient-index (GI) fiber. Phase conjugation and beam cleanup regimes in highly multimode fibers are discussed, and the self-aligned GI fiber Brillouin cavity is presented. We report a preliminary conversion from an M2=6.5 beam into an M2=1.3 beam with 31% efficiency.

Optical parametric oscillation in quasi-phase-matched GaAs.

We demonstrate an optical parametric oscillator (OPO) based on GaAs. The OPO utilizes an all-epitaxially-grown orientation-patterned GaAs crystal that is 0.5 mm thick, 5 mm wide, and 11 mm long, with a domain reversal period of 61.2 microm. Tuning either the near-IR pump wavelength between 1.8 and 2 microm or the temperature of the GaAs crystal allows the mid-IR output to be tuned between 2.28 and 9.14 microm, which is limited only by the spectral range of the OPO mirrors. The pump threshold of the singly resonant OPO is 16 microJ for the 6-ns pump pulses, and the photon conversion slope efficiency reaches 54%. We also show experimentally the possibility of pump-polarization-independent frequency conversion in GaAs.

Diffraction-limited polarized emission from a multimode ytterbium fiber amplifier after a nonlinear beam converter.

The multimode and depolarized output beam of a highly multimode diode-pumped Yb-doped fiber amplifier is converted to a diffraction-limited, linearly polarized beam by a self-referencing two-wave-mixing process in an infrared-sensitive photorefractive crystal (Rh:BaTiO3). As much as 11.6 W of single-mode output is achieved with a 78% multimode-to-single-mode photorefractive conversion efficiency.

Measurement of the nonlinear coefficient of orientation-patterned GaAs and demonstration of highly efficient second-harmonic generation.

Quasi-phase-matched (QPM) GaAs structures, 0.5 mm thick, 10 mm long, and with 61-mum grating periods, were grown by a combination of molecular-beam epitaxy and hydride vapor phase epitaxy. These were characterized by use of mid-IR second-harmonic generation (SHG) with a ZnGeP(2) (ZGP) optical parametric oscillator as a pump source. The SHG efficiencies of QPM GaAs and QPM LiNbO(3) were directly compared, and a ratio of nonlinear coefficients d(14)(GaAs)/d(33) (LiNbO(3))=5.01+/-0.3 was found at 4.1-mum fundamental wavelength. For input pulse energies as low as 50muJ and approximately 60-ns pulse duration, an internal SHG conversion efficiency of 33% was measured in QPM GaAs.

Self-optical parametric oscillation in periodically poled neodymium-doped lithium niobate.

Self-optical parametric oscillation is demonstrated for the first time to our knowledge in a periodically poled neodymium-doped lithium niobate (Nd:PPLN) crystal. The crystal is pumped by a cw Ti:sapphire laser at 813.5 nm. The Nd(3+) ions absorb the 813.5-nm radiation to generate 1084-nm laser oscillation. The internally Q switched 1084-nm radiation pumps the periodically poled lithium niobate host matrix to generate optical parametric oscillation at 1.55 and 3.6 microm . Up to 24% conversion efficiency from laser to signal is observed.

Difference frequency generation of 8-microm radiation in orientation- patterned GaAs.

First-order quasi-phase-matched difference frequency generation of narrowband tunable mid-infrared light is demonstrated in orientation-patterned GaAs. The all-epitaxial orientation-patterned crystal is fabricated by a combination of molecular beam epitaxy and hydride vapor phase epitaxy. Lasers at 1.3 and 1.55 microm were mixed to give an idler output at 8 microm, with power and wavelength tuning consistent with theoretical estimates, indicating excellent material uniformity over the 19-mm-long and 500-microm-thick device.

Synthesis, structure-activity relationships, and pharmacological profile of 9-amino-4-oxo-1-phenyl-3,4,6,7-tetrahydro[1,4]diazepino[6, 7,1-hi]indoles: discovery of potent, selective phosphodiesterase type 4 inhibitors.

The synthesis, structure-activity relationships, and biological properties of a novel series of potent and selective phosphodiesterase type 4 (PDE4) inhibitors are described. These new aminodiazepinoindoles displayed in vitro PDE4 activity with submicromolar IC(50) values and PDE4 selectivity vs PDE1, -3, and -5. Specifically, one compound (CI-1044, 10e) provided efficient in vitro inhibition of TNFalpha release from hPBMC and hWB with IC(50) values of 0.34 and 0.84 microM, respectively. This compound was found to exhibit potent in vivo activity in antigen-induced eosinophil recruitment in Brown-Norway rats (ED(50) = 3.2 mg/kg po) and in production of TNFalpha in Wistar rats (ED(50) = 2.8 mg/kg po). No emetic side effects at therapeutic doses were observed in ferrets.

Cascaded second-harmonic and sum-frequency generation of a CO2 laser by use of a single quasi-phase-matched GaAs crystal.

Cascaded second-harmonic and sum-frequency generation were used to obtain the third harmonic of a CO(2) laser in a single quasi-phase-matched GaAs crystal. Both continuous-wave and pulsed regimes with a single-pass configuration were studied. The continuous case confirmed the good capability of the GaAs stack to bear high average power density. In the pulsed regime a 0.66% peak power conversion efficiency was achieved for the third harmonic when the laser was pumping at 8.2 MW/cm(2) , in fair agreement with theoretical predictions.

Efficient second-harmonic generation of a CO2 laser with a quasi-phase-matched GaAs crystal.

We report on the fabrication and characterization of 5-mm-long quasi-phase-matched diffusion-bonded GaAs crystals designed for frequency doubling of a CO(2) laser. Second-harmonic generation of a pulsed laser yielded up to 24% peak power efficiency at 20 MW/cm(2) . Tunability and laser damage threshold are also investigated.

Fabrication parameter optimization of a low-threshold high-efficiency proton-exchanged waveguide laser in Nd:LiTaO(3).

Knowing the correlation between the Nd(3+) excited-state lifetime in proton-exchanged waveguides and the phase diagram of the H(x)Li(1-x)TaO(3) compound permits optimized waveguide fabrication parameters to be found. These have been used to produce a Nd:LiTaO(3) waveguide laser with a threshold of 2.9 mW and a slope efficiency of 33%, in good agreement with the best predicted values. Nevertheless this component suffers from instabilities because of the photorefractive effect.

Rare-earth-doped glass and LiNbO(3) waveguide lasers and optical amplifiers.

Recently there has been considerable interest in the field of rare-earth-doped integrated optics because of their potential use in compact and efficient monolithic devices combining the rare-earth laser gain and the large range of integrated optical functions already demonstrated. Recent developments in Nd(3+)-doped and Er(3+)-doped glass and LiNbO(3) waveguide lasers and optical amplifiers, their application, and future prospects are reviewed briefly.

Nd:MgO:LiNbO(3) waveguide laser and amplifier.

We report efficient operation of a channel waveguide laser and a channel waveguide amplifier in Nd:MgO:LiNbO(3). For the laser a cw output power of 2.9 mW was obtained for 23.6 mW of absorbed pump power. The absorbed pump power at threshold was 1.5 mW, and a slope efficiency of 13% was achieved. For the amplifier a small-signal gain of 7.5 dB was achieved for 22 mW of coupled pump power.