1,551 research outputs found
From Nonlinear Integrated Optics to Microresonator Frequency Combs
No full textPerhaps one of the most spectacular current applications of nonlinear integrated optics, a field
which was pioneered by George Stegeman more than thirty years ago [1], is that of nonlinear
microresonator based optical frequency comb light sources. Optical frequency comb sources are
characterized by a spectrum comprising many equally spaced components [2], and have a wide
range of scientific and technological applications. Although commercial comb generators are based
on mode-locked lasers and fiber supercontinuum generation, nonlinear integrated optics provides a
low-cost and chip-scale alternative, based on a low-power cw laser coupled into a high-Q
microresonator [3]. So far microresonator frequency combs have exploited the third order “Kerr”
nonlinearity, which permits to generate successive comb lines with a spacing equal to the resonator
free-spectral range via cascaded four-wave mixing [4-5]. Modeling of microresonator frequency
combs can be greatly simplified by a single partial differential equation approach [4-6], analogous
to the case of other coherently driven Kerr spatially diffractive [7] or temporally dispersive [8-9]
nonlinear cavities. In order to lower the threshold power and extend the spectral range of frequency
comb generation, for example into the visible or mid-infrared, while still using near-infrared cw
laser pumps, quadratic nonlinear cavities can be exploited [10]. These quadratic microresonator
frequency comb sources operate close to the phase-matching condition for the underlying quadratic
processes, and not in the cascading regime that reduces the dynamics to the Kerr case [11]. Quite
remarkably, a single time domain partial differential equation with an effective delayed third-order
nonlinearity was derived to describe with excellent accuracy the dynamics of quadratic frequency
comb generation [12-13]. In situations where multiple processes are present, and the frequency
combs generated around the interacting waves over multiple octaves overlap, we carried out
numerical modeling based on a single envelope equation approach [14].
References
[1] G.I. Stegeman, E.M. Wright, N. Finlayson, R. Zanoni, and C.T. Seaton, J. Lightwave Technology 6, 953 (1988).
[2] T. Udem, R. Holzwarth, and T. W. Hänsch, Nature 416, 233 (2002).
[3] P. Del’Haye, A. Schliesser, O. Arcizet, T. Wilken, R. Holzwarth, and T. J. Kippenberg, Nature 450, 1214 (2007).
[4] S. Coen, H. G. Randle, T. Sylvestre, and M. Erkintalo, Opt. Lett. 38, 37 (2013).
[5] T. Hansson, D. Modotto, and S. Wabnitz, Phys. Rev. A 88, 023819 (2013).
[6] T. Hansson, D. Modotto, and S.Wabnitz, Opt. Comm. 312, 134 (2014).
[7] L. A. Lugiato and R. Lefever, Phys. Rev. Lett. 58, 2209 (1987).
[8] M. Haelterman, S. Trillo, and S. Wabnitz, Opt. Commun. 91, 401 (1992).
[9] F. Leo, S. Coen, P. Kockaert, S.-P. Gorza, P. Emplit, and M. Haelterman, Nature Photon. 4, 471 (2010).
[10] I. Ricciardi, S. Mosca, M. Parisi, P. Maddaloni, L. Santamaria, P. De Natale, and M. De Rosa, Phys. Rev. A 91,
063839 (2015).
[11] G. I. Stegeman, D. J. Hagan, and L. Torner, Optical and Quantum Electronics 28, 1691 (1996).
[12] F. Leo, T. Hansson, I. Ricciardi, M. De Rosa, S. Coen, S. Wabnitz, and M. Erkintalo, Phys. Rev. Lett. 116, 033901
(2016).
[13] F. Leo, T. Hansson, I. Ricciardi, M. De Rosa, S. Coen, S. Wabnitz, and M. Erkintalo, Phys. Rev. A 93 (2016).
[14] T. Hansson, F. Leo, M. Erkintalo, J. Anthony, S. Coen, I. Ricciardi, M. De Rosa, and S. Wabnitz, J. Opt. Soc. Am.
B 33, 1207 (2016)
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
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
Electron beam pumped cw Se II laser
No full textWe have observed cw laser action in 15 transitions of singly ionized selenium using an electron beam to excite a He-Se mixture. The variation of the laser output power as a function of the electron beam discharge parameters is reported
Circulating ceramides are inversely associated with cardiorespiratory fitness in participants aged 54-96 years from the Baltiore Longitudinal Study of Aging.
No full textCardiorespiratory fitness (VO2 peak) declines with age and is an independent risk factor for morbidity and mortality in older adults. Identifying biomarkers of low fitness may provide insight for why some individuals experience an accelerated decline of aerobic capacity and may serve as clinically valuable prognostic indicators of cardiovascular health. We investigated the relationship between circulating ceramides and VO2 peak in 443 men and women (mean age of 69) enrolled in the Baltimore Longitudinal Study of Aging (BLSA). Individual species of ceramide were quantified by HPLC-tandem mass spectrometry. VO2 peak was measured by a graded treadmill test. We applied multiple regression models to test the associations between ceramide species and VO2 peak, while adjusting for age, sex, blood pressure, serum LDL, HDL, triglycerides, and other covariates. We found that higher levels of circulating C18:0, C20:0, C24:1 ceramides and C20:0 dihydroceramides were strongly associated with lower aerobic capacity (P < 0.001, P < 0.001, P = 0.018, and P < 0.001, respectively). The associations held true for both sexes (with men having a stronger association than women, P value for sex interaction <0.05) and were unchanged after adjusting for confounders and multiple comparison correction. Interestingly, no significant association was found for C16:0, C22:0, C24:0, C26:0, and C22:1 ceramide species, C24:0 dihydroceramide, or total ceramides. Our analysis reveals that specific long-chain ceramides strongly associate with low cardiovascular fitness in older adults and may be implicated in the pathogenesis of low fitness with aging. Longitudinal studies are needed to further validate these associations and investigate the relationship between ceramides and health outcomes
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