| 391. |
- Lee, Kwang Jo, et al.
(författare)
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Analysis of acceptable spectral windows of quadratic cascaded nonlinear processes in a periodically poled lithium niobate waveguide
- 2011
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 19:9, s. 8327-8335
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Tidskriftsartikel (refereegranskat)abstract
- We report a systematic and comparative study of the acceptance bandwidths of two cascaded quadratic nonlinear processes in periodically poled lithium niobate waveguides, namely cascaded second-harmonic generation and difference-frequency generation (cSHG/DFG) and cascaded sum-frequency generation and difference-frequency generation (cSFG/DFG). We first theoretically and experimentally study the acceptance bandwidths of both the individual second-harmonic generation (SHG) and sum-frequency generation (SFG) processes in the continuous wave (CW) and pulsed-pump regimes. Our results show that the SHG bandwidth is approximately half that of the SFG process in the CW regime, whereas the SHG acceptance bandwidth can approach the CW SFG bandwidth limit when pulsed-pump is used. As a consequence we conclude that the tuning bandwidths of both cascaded processes should be similar in the pulsed pump regime once the pump pulse bandwidths approach that of SFG (i.e. the cSHG/DFG bandwidth is not limited by the CW SHG bandwidth). We confirm that this is the case experimentally.
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| 392. |
- Lee, Kwang Jo, et al.
(författare)
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OTDM to WDM format conversion based on quadratic cascading in a periodically poled lithium niobate waveguide
- 2010
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Ingår i: Optics Express. - 1094-4087. ; 18:10, s. 10282-10288
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Tidskriftsartikel (refereegranskat)abstract
- We propose and demonstrate error-free conversion of a 40 Gbit/s optical time division multiplexed signal to 4 x 10 Gbit/s wavelength division multiplexed channels based on cascaded second harmonic and difference frequency generation in a periodically poled lithium niobate waveguide. The technique relies on the generation of spectrally (and temporally) flat linearly chirped pulses which are then optically switched with short data pulses in the nonlinear waveguide. Error-free operation was obtained for all channels with a power penalty below 2dB.
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| 393. |
- Lee, Kwang Jo, et al.
(författare)
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Phase sensitive amplification based on quadratic cascading in a periodically poled lithium niobate waveguide
- 2009
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Ingår i: Optics Express. - 1094-4087. ; 17:22, s. 20393-20400
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Tidskriftsartikel (refereegranskat)abstract
- We propose and demonstrate phase-sensitive amplification based on cascaded second harmonic generation and difference frequency generation within a periodically poled lithium niobate waveguide. Excellent agreement between our numerical simulations and proof-of-principle experiments using a 3-cm waveguide device operating at wavelengths around 1550 nm is obtained. Our experiments confirm the validity and practicality of the approach and illustrate the broad gain bandwidths achievable. Additional simulation results show that the maximum gain/attenuation factor increases quadratically with input pump power, reaching a value of +/- 19.0dB at input pump powers of 33 dBm for a 3 cm-long waveguide. Increased gains/reduced powers for a fixed gain could be achieved using longer crystals.
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| 394. |
- Legall, H., et al.
(författare)
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Compact X-ray microscope for the water window based on a high brightness laser plasma source
- 2012
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Ingår i: Optics Express. - 1094-4087. ; 20:16, s. 18362-18369
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Tidskriftsartikel (refereegranskat)abstract
- We present a laser plasma based x-ray microscope for the water window employing a high-average power laser system for plasma generation. At 90 W laser power a brightness of 7.4 x 10(11) photons/(s x sr x mu m(2)) was measured for the nitrogen Ly alpha line emission at 2.478 nm. Using a multilayer condenser mirror with 0.3 % reflectivity 10(6) photons/(mu m(2) x s) were obtained in the object plane. Microscopy performed at a laser power of 60 W resolves 40 nm lines with an exposure time of 60 s. The exposure time can be further reduced to 20 s by the use of new multilayer condenser optics and operating the laser at its full power of 130 W.
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| 395. |
- Lehmuskero, Anni, et al.
(författare)
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Plasmonic particles set into fast orbital motion by an optical vortex beam
- 2014
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Ingår i: Optics express. - : The Optical Society. - 1094-4087. ; 22:4, s. 4349-4356
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Tidskriftsartikel (refereegranskat)abstract
- We optically trap plasmonic gold particles in two dimensions and set them into circular motion around the optical axis using a helically phased vortex laser beam. The orbiting frequency of the particles reaches 86 Hz, which corresponds to a particle velocity of the order 1 mm per second, for an incident laser power of a few tens of milliwatts. The experimentally determined orbiting frequencies are found to be well in line with the notion that the beam carries an orbital angular momentum of ħl per photon.
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| 396. |
- Lehmuskero, Anni, 1982, et al.
(författare)
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Plasmonic particles set into fast orbital motion by an optical vortex beam WARI SC, 1992, JOURNAL OF MODERN OPTICS, V39, P1097
- 2014
-
Ingår i: Optics Express. - : The Optical Society. - 1094-4087 .- 1094-4087. ; 22:4, s. 4349-4356
-
Tidskriftsartikel (refereegranskat)abstract
- We optically trap plasmonic gold particles in two dimensions and set them into circular motion around the optical axis using a helically phased vortex laser beam. The orbiting frequency of the particles reaches 86 Hz, which corresponds to a particle velocity of the order 1 mm per second, for an incident laser power of a few tens of milliwatts. The experimentally determined orbiting frequencies are found to be well in line with the notion that the beam carries an orbital angular momentum of hl per photon. (C) 2014 Optical Society of America
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| 397. |
- Levenius, Martin, et al.
(författare)
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Ultra-broadband optical parametric generation in periodically poled stoichiometric LiTaO(3)
- 2011
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 19:5, s. 4121-4128
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Tidskriftsartikel (refereegranskat)abstract
- We report on broadband gain in an optical parametric generator based on periodically poled 1 mol% magnesium-doped stoichiometric LiTaO(3) (PPMg:SLT). More than an octave-spanning parametric gain, stretching from near to mid-infrared, is generated by pumping the crystals close to the point where, at parametric degeneracy, the waves experience zero group-velocity dispersion. Using a picosecond Ti:sapphire source, we measured the broadest parametric gain bandwidths, 180 THz at 10 dB, in PPMg: SLT gratings with a period of 25 mu m pumped at 860 nm.
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| 398. |
- Levitz, D, et al.
(författare)
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Determination of optical scattering properties of highly-scattering media in optical coherence tomography images
- 2004
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Ingår i: Optics Express. - 1094-4087. ; 12:2, s. 249-259
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Tidskriftsartikel (refereegranskat)abstract
- We developed a new algorithm that fits optical coherence tomography (OCT) signals as a function of depth to a general theoretical OCT model which takes into account multiple scattering effects. With use of this algorithm, it was possible to extract both the scattering coefficient and anisotropy factor from a particular region of interest in an OCT image. The extraction algorithm was evaluated against measurements from an integrating sphere on a set of tissue phantoms and yielded valid results. Finally, a preliminary ex vivo OCT investigation on human aortic specimen indicated that the algorithm may contribute importantly to differentiation between normal and atherosclerotic arteries. We conclude that this algorithm may facilitate tissue characterization by OCT. (C) 2004 Optical Society of America.
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| 399. |
- Lewander, Märta, et al.
(författare)
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Clinical system for non-invasive in situ monitoring of gases in the human paranasal sinuses
- 2009
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Ingår i: Optics Express. - 1094-4087. ; 17:13, s. 10849-10863
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Tidskriftsartikel (refereegranskat)abstract
- We present a portable system for non-invasive, simultaneous sensing of molecular oxygen (O-2) and water vapor (H2O) in the human paranasal cavities. The system is based on high-resolution tunable diode laser spectroscopy (TDLAS) and digital wavelength modulation spectroscopy (dWMS). Since optical interference and non-ideal tuning of the diode lasers render signal processing complex, we focus on Fourier analysis of dWMS signals and procedures for removal of background signals. Clinical data are presented, and exhibit a significant improvement in signal-to-noise with respect to earlier work. The in situ detection limit, in terms of absorption fraction, is about 5 x 10(-5) for oxygen and 5 x 10(-4) for water vapor, but varies between patients due to differences in light attenuation. In addition, we discuss the use of water vapor as a reference in quantification of in situ oxygen concentration in detail. In particular, light propagation aspects are investigated by employing photon time-of-flight spectroscopy. (C) 2009 Optical Society of America
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| 400. |
- Li, Bo, et al.
(författare)
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Comprehensive CO detection in flames using femtosecond two-photon laser-induced fluorescence
- 2017
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Ingår i: Optics Express. - 1094-4087. ; 25:21, s. 25809-25818
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a femtosecond two-photon laser-induced fluorescence (fs-TPLIF) technique for sensitive CO detection, using a 230 nm pulse of 9 µJ and 45 fs. The advantages of fs-TPLIF in excitation of molecular species were analyzed. Spectra of CO fs-TPLIF were recorded in stable laminar flames spatially resolved across the flame front. A hot band (1, n) together with the conventional band (0, n) of the B→A transitions were observed in the burned zone and attributed to the broadband nature of the fs excitation. The CO fs-TPLIF signal recorded across the focal point of the excitation beam shows a relatively flat intensity distribution despite of the steep laser intensity variation, which is beneficial for CO imaging in contrast to nanosecond and picosecond TPLIF. This phenomenon can be explained by photoionization, which over the short pulse duration dominates the population depletion of the excited B state due to the high peak power, but only contributes in total a negligible X state depletion due to the low pulse energy. Single-shot CO fs-TPLIF images in methane/air flames were recorded by imaging the broadband fluorescence. The results indicate that fs-TPLIF is a promising tool for CO imaging in flames.
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