| 401. |
- Legall, H., et al.
(författare)
-
Compact X-ray microscope for the water window based on a high brightness laser plasma source
- 2012
-
Ingår i: Optics Express. - 1094-4087. ; 20:16, s. 18362-18369
-
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.
|
|
| 402. |
- Lehmuskero, Anni, et al.
(författare)
-
Plasmonic particles set into fast orbital motion by an optical vortex beam
- 2014
-
Ingår i: Optics express. - : The Optical Society. - 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 ħl per photon.
|
|
| 403. |
- Lehmuskero, Anni, 1982, et al.
(författare)
-
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
|
|
| 404. |
- Levenius, Martin, et al.
(författare)
-
Ultra-broadband optical parametric generation in periodically poled stoichiometric LiTaO(3)
- 2011
-
Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 19:5, s. 4121-4128
-
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.
|
|
| 405. |
- Levitz, D, et al.
(författare)
-
Determination of optical scattering properties of highly-scattering media in optical coherence tomography images
- 2004
-
Ingår i: Optics Express. - 1094-4087. ; 12:2, s. 249-259
-
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.
|
|
| 406. |
- Lewander, Märta, et al.
(författare)
-
Clinical system for non-invasive in situ monitoring of gases in the human paranasal sinuses
- 2009
-
Ingår i: Optics Express. - 1094-4087. ; 17:13, s. 10849-10863
-
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
|
|
| 407. |
- Li, Bo, et al.
(författare)
-
Comprehensive CO detection in flames using femtosecond two-photon laser-induced fluorescence
- 2017
-
Ingår i: Optics Express. - 1094-4087. ; 25:21, s. 25809-25818
-
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.
|
|
| 408. |
- Li, Bo, et al.
(författare)
-
Filamentary anemometry using femtosecond laser-extended electric discharge - FALED
- 2018
-
Ingår i: Optics Express. - 1094-4087. ; 26:16, s. 21132-21140
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a non-contact spatiotemporally resolved comprehensive method for gas flow velocity field measurement: Filamentary Anemometry using femtosecond Laser-extended Electric Discharge (FALED). A faint thin plasma channel was generated in ambient air by focusing an 800-nm laser beam of 45 fs, which was used to ignite a pulsed electric discharge between two electrodes separated over 10 mm. The power supplier provided a maximum voltage up to 5 kV and was operated at a burst mode with a current duration of less than 20 ns and a pulse-to-pulse separation of 40 μs. The laser-guided thin filamentary discharge plasma column was blowing up perpendicularly by an air jet placed beneath in-between the two electrodes. Although the discharge pulse was short, the conductivity of the plasma channel was observed to sustain much longer, so that a sequence of discharge filaments was generated as the plasma channel being blown up by the jet flow. The sequential bright thin discharge filaments can be photographed using a household camera to calculate the flow velocity distribution of the jet flow. For a direct comparison, a flow field measurement using FLEET [Michael, Appl. Opt. 50, 5158 (2011)] was also performed. The results indicate that the FALED technique can provide instantaneous nonintrusive flow field velocity measurement with good accuracy.
|
|
| 409. |
- Li, Jianqiang, 1983, et al.
(författare)
-
Building up low-complexity spectrally-efficient Terabit superchannels by receiver-side duobinary shaping
- 2012
-
Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 20:9, s. 10271-10282
-
Tidskriftsartikel (refereegranskat)abstract
- Recently, an increasing interest has been put on spectrally-efficient multi-carrier superchannels for beyond 100G. Apart from orthogonal frequency-division multiplexing (OFDM) and Nyquist wavelength-division multiplexing (WDM), another low-complexity WDM approach based on transmitter-side pre-filtering and receiver-side duobinary shaping is proposed to build up multi-carrier superchannels. This approach is referred to as receiver-side duobinary-shaped WDM (RS-DBS-WDM). Generation and transmission of a 1.232-Tbit/s 11-carrier superchannel is experimentally demonstrated. The superchannel signal can be well fit inside the passband of multiple 300-GHz reconfigurable optical add and drop multiplexers (ROADMs). In the superchannel scenario, the proposed RS-DBS-WDM is qualitatively compared with OFDM and Nyquist-WDM in terms of implementation complexity. In sum, the proposed RS-DBS-WDM approach features high transceiver analog-bandwidth efficiency, high spectral-efficiency, the absence of specific spectral manipulation, compatibility with conventional WDM technologies and coherent detection algorithms, and comparable implementation penalty.
|
|
| 410. |
- Li, Jingjing, et al.
(författare)
-
Optical magnetic plasma in artificial flowers
- 2009
-
Ingår i: Optics Express. - 1094-4087. ; 17:13, s. 10800-10805
-
Tidskriftsartikel (refereegranskat)abstract
- We report the design of an artificial flower-like structure that supports a magnetic plasma in the optical domain. The structure is composed of alternating "petals" of conventional dielectrics (epsilon > 0) and plasmonic materials (Re(epsilon) < 0). The induced effective magnetic current on such a structure possesses a phase lag with respect to the incident TE-mode magnetic field, similar to the phase lag between the induced electric current and the incident TM-mode electric field on a metal wire. An analogy is thus drawn with an artificial electric plasma composed of metal wires driven by a radio frequency excitation. The effective medium of an array of flowers has a negative permeability within a certain wavelength range, thus behaving as a magnetic plasma.
|
|
