1,963 research outputs found
A mode-locked diode laser frequency comb for ultracold atomic physics experiments
No full textThis thesis is concerned with the development and characterisation of an actively mode locked diode laser system for the provision of a stable optical frequency comb spanning approximately 1 nm around the D2 spectroscopic line of Rubidium. Through large signal sinusoidal modulation of the laser DC injection current at around 3 GHz, Gaussian pulses of 21 ps are achieved with an associated spectral bandwidth in excess of 1 nm, generating pulses of optimal time-bandwidth product 13. An in-house built air-bearing Michelson interferometer is used to confirm the comb-like structure of the optical emission and a modulation frequency detuning range of 10 MHz is determined.Through a proof of principle investigation of CW injection locking of the frequency comb, phase coherence of the CW master laser with the modes of the frequency comb is demonstrated over at least 36 GHz. Via CW injection locking, sidemode suppression of 20.6 dB is achieved resulting in an 18% rise in the pulse temporal width and a concomitant reduction in the time-bandwidth product to 1.44, as well as a power dependant phase locking detuning range of up to 370 MHz. In the closing chapters, two CW lasers are shown to be stabilised to the frequency comb via Optical Phase-Locked Loops, a temperature stabilised fibre Mach-Zehnder interferometer is demonstrated for carrier frequency removal from a phase modulated laser, and a novel intra-cavity trace water vapour detection method is introduced
Cw ion lasers pumped by electron beams
No full textWe have obtained cw laser radiation from singly ionized Hg, I, Cd, Se, and As by exciting He metal-vapor mixtures with a dc electron beam. The beam is generated by glow discharge electron guns located apart from the active medium. This is the first time that cw ion laser action has been obtained using electron beam excitation
CW laser action in atomic fluorine
No full textWe have obtained CW laser action on four transitions in the doublet system of atomic fluorine for the first time. All previously reported laser action was on a pulsed basis only. CW laser radiation was obtained when F2 or AgF was used as a fluorine donor in an electron beam pumped helium plasma. A multiline output power of 200 mW was obtained
CW silver ion laser with electron beam excitation
No full textA CW laser power of 140 mW was obtained in the 840.39 nm transition of Ag II by electron beam excitation. This electron beam excited metal vapor ion laser is capable of operating using metals with high vaporization temperatures and is of interest for generation of CW coherent radiation in the 220-260 nm spectral region
B-hemolytic Streptococci as a cause of infectious endocarditis. Report from the ICE prospective cohort study
No full textAcanthamoeba castellanii activates murine macrophages in a MyD88 dependent, TRIF and PAR2 independent manner.
No full textAcanthamoeba castellanii is an opportunistic, facultative parasitic protozoan, known to be the agent of a
serious, painful, potentially blinding keratitis and fatal encephalitis in humans. Acanthamoeba keratitis is
most prevalent in contact lens wearers where it affects 1 in 30,000. Acanthamoeba are ubiquitous in
nature, and consequently, although individuals are regularly exposed to these amoebae, very few cases
of clinical infection occur, suggesting that the innate immune response is normally effective.
Macrophages and neutrophils are predominantly present at the site of infection, implicating them in the
resolution of the disease. Herein, macrophage interactions with trophozoites of Acanthamoeba
castellanii are investigated in vitro using bone marrow derived macrophages. The role of TLRs and
PARs in the recognition and response to Acanthamoeba are also examined using syngeneic mice
deficient in MyD88, TRIF or PAR 2 genes. Results demonstrated that Acanthamoeba castellanii
stimulated TNF- a , IL-6 and IL-12 production by murine macrophages in a MyD88-dependent, but
TRIF-independent manner. Acanthamoeba secreted proteases were able to stimulate the production of
pro-inflammatory cytokines by a PAR 2 independent mechanism. In addition, arginase activity was
significantly increased in murine macrophages after stimulation with trophozoites, whereas NO
production was below detection limits. Taken together, these results suggest that TLR-associated
signaling pathways play an important role in initiating the innate immune response to Acanthamoeba
castellanii with the ensuing production of pro-inflammatory cytokines and arginase activity
1-W cw Zn ion laser
No full textWe have obtained 1.2W of cw laser power on the 4911.6- and 4924.0-Å transitions of Zn II by exciting a He-Zn gas mixture with a dc glow discharge electron beam. In addition, 0.25-W output power has been obtained on the 6149.9-Å line of Hg+ using the same excitation scheme. The combination of electron beam ionization of rare gas atoms and subsequent charge transfer excitation to metal ion levels is shown to have the potential of significantly increasing the efficiency of ion lasers. cw multiwatt visible and ultraviolet ion lasers operating at efficiencies > 10-3 appear feasible using this excitation scheme
Stabilization as a CW approximation
No full textAbstractThis paper describes a peculiar property of the category of S-modules constructed by the author, Kriz, Mandell, and May: the full subcategory of suspension spectra (all of which are S-modules) forms a precise copy of the category of topological spaces. Consequently, the “classical” homotopy category of S-modules with morphisms the actual homotopy classes of maps contains a copy of unstable homotopy theory. Stabilization and stable homotopy are induced by CW approximation as S-modules. One consequence is that CW complexes whose suspension spectra are CW S-modules must be contractible
Cw iodine ion laser excited by an electron beam
No full textCW laser oscillation has been obtained on the 5760.7 and6127.5 Å transitions of singly ionized iodine in an He-I2 plasma excited by a dc electron beam
A closed manifold is a fat CW complex
No full textIn this paper, we introduce a notion of a fat CW complex to show that a
closed manifold is a regular CW complex, while it is not always the case if we
discuss about a smooth CW structure, introduced by the first author, instead of
a fat CW structure. We also verify that de Rham theorem holds for a fat CW
complex and that a regular CW complex is reflexive in the sense of Y.~Karshon,
J.~Watts and P.~I-Zemmour. Further, any topological CW complex is topologically
homotopy equivalent to a fat CW complex. It implies that there are lots of
non-manifold examples supporting de Rham theorem.Comment: 17 page
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