Design of a polymer-based cladding mode stripper with a distributed temperature profile.

An optimized polymer-based fiber cladding mode stripper (CMS) is presented experimentally. A unique partial fiber stripping method is introduced in CMS fabrication to enable distributed power extraction and temperature along the length of the CMS. The designed CMS based on a 400 µm double-clad fiber (DCF) extracts 300 W of inner cladding power, with an attenuation coefficient of 18.

Ex vivo testing of air-cooled CW/modulated 30 W thulium fiber laser for lithotripsy.

A diode-pumped, air-cooled, all-fiber, quasi-continuous-wave thulium laser at an operating wavelength of 1.94 μm has been designed to study the performance of the laser parameter on the rate of fragmentation and its dependence on stone composition, fragmented particle size, as well as the retropulsion effect. The optimized laser cavity with an active fiber core/cladding diameter of 10/130 μm under a counter-propagating pump provides a stable laser power of 30 W at a slope efficiency of 50% and wall plug efficiency of 17%.

Hybrid pumped gain-switched thulium fiber laser at a high repetition rate.

A gain-switched all-fiber thulium laser at 2 μm with high repetition rate has been demonstrated under a hybrid pumping scheme combined of a pulsed pump at 1.56 μm and CW pump at 793 nm. The in-band pulsed pump at 1.

Diverse mode of operation of an all-normal-dispersion mode-locked fiber laser employing two nonlinear loop mirrors.

In this paper, we propose an all-normal-dispersion ytterbium-fiber laser with a novel ring cavity architecture having two nonlinear amplifying loop mirrors (NALM) as saturable absorbers, capable of delivering distinctly different pulses with adjustable features. By optimizing the loop lengths of the individual NALMs, the cavity can be operated to deliver Q-switched mode-locked (Q-ML) pulse bunches with adjustable repetition rates, mode-locked pulses in dissipative soliton resonance (DSR) regime or noise-like pulse (NLP) regime with tunable pulse width. The DSR pulses exhibit characteristic narrowband spectrum, while the NLPs exhibit large broadband spectrum.

High repetition rate gain-switched 1.94 μm fiber laser pumped by 1.56 μm dissipative soliton resonance fiber laser.

A dissipative soliton resonance (DSR) mode-locked Er:Yb fiber laser has been used to pump a thulium fiber laser to generate gain-switched pulses at high repetition rates. Here 412 ns long DSR pulses with a center wavelength of around 1.56 μm at a repetition rate of 410 kHz have been fed to a thulium fiber laser, resulting in generation of gain-switched pulses at 1.

Continuous-wave and quasi-continuous wave thulium-doped all-fiber laser: implementation on kidney stone fragmentations.

A continuous-wave (CW) as well as quasi-continuous wave (QCW) thulium-doped all-fiber laser at 1.94 μm has been designed for targeting applications in urology. The thulium-doped active fiber with an octagonal-shaped inner cladding is pumped at 793 nm to achieve stable CW laser power of 10 W with 32% lasing efficiency (against launched pump power).

"All-fiber" tunable laser in the 2 μm region, designed for CO2 detection.

A stable and tunable thulium-doped "all-fiber" laser offering a narrow linewidth has been created specifically to act as a compact and simple laser source for gaseous CO(2) detection. This has been done through a careful design to match the laser output wavelengths to the CO(2) absorption lines at 1.875 and 1.

Ytterbium-sensitized Thulium-doped fiber laser in the near-IR with 980 nm pumping.

The use of an unidirectional auxiliary pump at approximately 1600 nm in conjunction with a 980 nm primary pump for Ytterbium (Yb(3+))-sensitized-Thulium (Tm(3+))-doped single mode silica fiber (YTDF) is found to be very effective to activate the most significant resonance energy transfer from Yb(3+) to Tm(3+), in order to obtain significant emission in the near-infrared. The resulting laser performance of the YTDF at 1874 nm is reported here. The influence of the Tm(3+)/Yb(3+) concentration, their relative proportions and the host glass composition on the lasing efficiency has also been investigated to optimize the fiber parameters for maximum laser output power.

Generation of supercontinuum and its theoretical study in three-ring silica microstructured optical fibers.

We report supercontinuum generation in nonlinear microstructured optical fibers (MOFs) especially fabricated in a two-step stack and draw process having three rings of airholes. High air-filling fraction (>0.9) is obtained in a simple and straightforward way during the drawing process which is essential to enhance nonlinearity.

RecA-mediated cleavage of lambda cI repressor accepts repressor dimers: probable role of prolyl cis-trans isomerization and catalytic involvement of H163, K177, and K232 of RecA.

The lambda cI repressor is found to be cleaved in the presence of activated RecA in its DNA-bound dimeric form at a rate similar to that in the absence of operator DNA in contrast to previous studies inferring repressor monomer as a preferred substrate. Though activated RecA does not possess any measurable isomerase activity against a standard peptide substrate, prolyl isomerase inhibitors cyclosporin A and rapamycin do inhibit RecA-mediated cleavage. Histidine and lysine to a smaller extent, are shown to cleave cI repressor in a non-enzymatic fashion whereas arginine and glutamate do not.

Digestion of the lambda cI repressor with various serine proteases and correlation with its three dimensional structure.

Partial proteolysis of the lambda cI repressor has been carried out systematically with trypsin, chymotrypsin, elastase, endoproteinase Glu-C, kallikrein, and thrombin. The cleavage sites have been determined by (i) comparison of fragments produced and observed in SDS-polyacrylamide gel with known fragments and plots of distance migrated versus log (molecular weight of fragment), (ii) partial Edman sequencing of the stable C-terminal fragments to identify cleavage points, and (iii) electrospray mass spectrometry of fragments produced. Most cleavage points are found to occur in the region 86-137, saving some in the N-terminal domain observed for trypsin and Glu-C.

The mechanism of rare earth incorporation in solution doping process.

The mechanism involved during solution doping process has been systematically investigated by correlating the soot characteristics and solution parameters with the amount of rare earth (RE) incorporated in the core of optical fiber. Experiments show that the amount of RE incorporation may be controlled with better precision by adjusting Al ion concentration in the soaking solution. A model has been developed on the basis of cooperative adsorption mechanism correlating different parameters in the overall process.

Improved model of a LexA repressor dimer bound to recA operator.

A complete three dimensional model for the LexA repressor dimer bound to the recA operator site consistent with relevant biochemical and biophysical data for the repressor was proposed from our laboratory when no crystal structure of LexA was available. Subsequently, the crystal structures of four LexA mutants Delta(1-67) S119A, S119A, G85D and Delta(1-67) quadruple mutant in the absence of operator were reported. It is examined in this paper to what extent our previous model was correct and how, using the crystal structure of the operator-free LexA dimer we can predict an improved model of LexA dimer bound to recA operator.

pH-dependent autocleavage of lambda repressor occurs in the operator-bound form: characterization of lambda repressor autocleavage.

The first-order rate constants for the RecA-independent, spontaneous, pH-dependent autocleavage of the lambda cI repressor was measured in the present study at pH 10.6 at 27, 37 and 42 degrees C respectively. Autocleavage of the repressor occurs also at pH 9 and 8, although at progressively slower rates.