Exploiting the short wavelength gain of silica-based thulium-doped fiber amplifiers.

Short wavelength operation (1650-1800 nm) of silica-based thulium-doped fiber amplifiers (TDFAs) is investigated. We report the first demonstration of in-band diode-pumped silica-based TDFAs working in the 1700-1800 nm waveband. Up to 29 dB of small-signal gain is achieved in this spectral region, with an operation wavelength accessible by diode pumping as short as 1710 nm. Further gain extension toward shorter wavelengths is realized in a fiber laser pumped configuration. A silica-based TDFA working in the 1650-1700 nm range with up to 29 dB small-signal gain and noise figure as low as 6.5 dB is presented.

First demonstration of a 2µm few-mode TDFA for mode division multiplexing.

We report the first demonstration of an inline few-mode thulium doped fiber amplifier (TDFA) operating at 2µm for mode division multiplexed transmission. Similar gain and noise figure performance for both the LP(01) and LP(11) modes are obtained in a cladding pumped 2-mode group TDFA. A maximum gain of 18.3dB was measured at 1970nm with a 3dB gain bandwidth of 75nm while the average noise figure was measured to be between 7 and 8dB for wavelengths longer than 1970nm.

Pulse control in a Q-switched Nd:YVO4 bounce geometry laser using a secondary cavity.

A novel technique for obtaining enhanced control of pulsing parameters in a laser is described and implemented for the first time in a 1.1%Nd:YVO4 bounce geometry laser. The method uses a secondary laser cavity to control the gain in a Q-switched primary laser cavity and has enabled clean single-pulse Q-switched operation to be obtained across a repetition rate range of 1-800 kHz, where previously laser breakthrough had occurred below 150 kHz. Control of the pulse energy from the Q-switched laser is also demonstrated at a fixed repetition rate of 100 kHz by this technique.

100 kW peak power picosecond thulium-doped fiber amplifier system seeded by a gain-switched diode laser at 2 µm.

We report on the generation of picosecond pulses at 2 µm directly from a gain-switched discrete-mode diode laser and their amplification in a multistage thulium-doped fiber amplifier chain. The system is capable of operating at repetition rates in the range of 2 MHz-1.5 GHz without change of configuration, delivering high-quality 33 ps pulses with up to 3.5 µJ energy and 100 kW peak power, as well as up to 18 W of average power. These results represent a major technological advance and a 1 order of magnitude increase in peak power and pulse energy compared to existing picosecond sources at 2 µm.

Phase conjugate self-organized coherent beam combination: a passive technique for laser power scaling.

In this Letter, a first (to our knowledge) demonstration of phase conjugate self-organized coherent beam combination is reported. A demonstration involving combination of two self-adaptive gain grating holographic laser resonators is presented. Output powers of up to 27 W, with a combination efficiency of 94%, are demonstrated. This technique coherently combines individual phase conjugate laser modules, which do not have predefined spectral or spatial modes. This removes the problem of finding shared resonator modes, which should allow coherent beam combination of much larger laser arrays than standard self-organized coherent beam combination.

High-power near-diffraction-limited solid-state amplified spontaneous emission laser devices.

We present investigations into high-power scaling of solid-state amplified spontaneous emission (ASE) laser sources by use of two high-gain (~10(4)) Nd:YVO(4) bounce amplifiers. The sources deliver high power with a high-quality spatial output, but unlike a laser they have a high misalignment tolerance and do not require a precisely aligned cavity. In one system with two amplifiers, we demonstrate an ASE source with 24.5W of output power with good spatial quality, M(2)<2.5 in the horizontal and M(2)<1.2 in the vertical. In a more sophisticated setup, the two amplifiers are arranged in a loop configuration producing 30W of ASE output with near-diffraction-limited spatial quality, with M(2)<1.3 in the horizontal and M(2)<1.2 in the vertical, at an ~38% optical-to-optical conversion efficiency.

The disposition of gemifloxacin, a new fluoroquinolone antibiotic, in rats and dogs.

Gemifloxacin is a fluoroquinolone antibacterial compound with enhanced affinity for bacterial topoisomerase IV and is being developed for the treatment of respiratory and urinary tract infections. The disposition and metabolic fate of this antibiotic was studied in the rat and the dog, the animal species used in its toxicological evaluation. The investigations were carried out following oral and intravenous administration of gemifloxacin mesylate. Gemifloxacin is a racemic compound; therefore, the pharmacokinetics of its individual (+) and (-) enantiomers were characterized using a chiral high-performance liquid chromatography/tandem mass spectrometry assay. In both rat and dog, the pharmacokinetic profiles of the (+) and (-) enantiomers were essentially identical. The enantiomers were rapidly absorbed following oral administration of racemic gemifloxacin mesylate. They distributed rapidly beyond total body water, and their blood clearance values were approximately equal to one quarter of the hepatic blood flow in each species. Terminal phase elimination half-lives were ca. 2 h in the rat and 5 h in the dog. Gemifloxacin was metabolized to a limited extent following oral and intravenous administration of [14C]gemifloxacin mesylate, and all metabolites formed were relatively minor. The principal metabolites formed were the E-isomer (4-6% of dose) and the acyl glucuronide of gemifloxacin (2-6% of dose) in both species and N-acetyl gemifloxacin (2-5% of dose) in the rat. Data obtained following intravenous administration indicated that gemifloxacin-related material is eliminated from the body via urinary excretion, biliary secretion, and gastrointestinal secretion. Material was eliminated approximately equally by the three routes in the dog, whereas a slightly higher proportion of the dose was eliminated in the urine (46%) and a lower proportion in the bile (12%) of rats.

Metabolism and disposition of 14C-granisetron in rat, dog and man after intravenous and oral dosing.

1. The disposition and metabolic fate of 14C-granisetron, a novel 5-HT3 antagonist, was studied in rat, dog, and male human volunteers after intravenous and oral administration. 2. Complete absorption occurred from the gastrointestinal tract following oral dosing, but bioavailability was reduced by first-pass metabolism in all three species. 3. There were no sex-specific differences observed in radiometabolite patterns in rat or dog and there was no appreciable change in disposition with dose between 0.25 and 5 mg/kg in rat and 0.25 and 10 mg/kg in dog. Additionally, there were no large differences in disposition associated with route of administration in rat, dog and man. 4. In rat and dog, 35-41% of the dose was excreted in urine and 52-62% in faeces, via the bile. Metabolites were largely present as glucuronide and sulphate conjugates, together with numerous minor polar metabolites. In man, about 60% of dosed radioactivity was excreted in urine and 36% in faeces after both intravenous and oral dosing. Unchanged granisetron was only excreted in urine (5-25% of dose). 5. The major metabolites were isolated and identified by MS spectroscopy and nmr. In rat, the dominant routes of biotransformation after both intravenous and oral dosing were 5-hydroxylation and N1-demethylation, followed by the formation of conjugates which were the major metabolites in urine, bile and plasma. In dog and man the major metabolite was 7-hydroxy-granisetron, with lesser quantities of the 6,7-dihydrodiol and/or their conjugates.