| 341. |
- Kahnt, Maik, et al.
(författare)
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Complete alignment of a KB-mirror system guided by ptychography
- 2022
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Ingår i: Optics Express. - 1094-4087. ; 30:23, s. 42308-42322
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate how the individual mirrors of a high-quality Kirkpatrick-Baez (KB) mirror system can be aligned to each other to create an optimally focused beam, through minimizing aberrations in the phase of the ptychographically reconstructed pupil function. Different sources of misalignment and the distinctive phase artifacts they create are presented via experimental results from the alignment of the KB mirrors at the NanoMAX diffraction endstation. The catalog of aberration artifacts can be used to easily identify which parameter requires further tuning in the alignment of any KB mirror system.
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| 342. |
- Kakande, Joseph, et al.
(författare)
-
Detailed characterization of a
fiber-optic parametric amplifier in phase-sensitive and phase-insensitive operation
- 2010
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 18:5, s. 4130-4137
-
Tidskriftsartikel (refereegranskat)abstract
- We experimentally demonstrate a single-pumped, non-degenerate phase-sensitive parametric amplifier with a precise control of phase and amplitude of the in-going waves and investigate in detail its gain, attenuation and saturation properties in comparison with operation in phase insensitive amplifier (PIA) mode. We experimentally observe the variation of the gain and attenuation as a function of the relative phase, pump power and the signal-idler power ratio. The phase sensitive gain spectrum is studied over a 24 nm symmetrical bandwidth and we achieve a maximum phase sensitive amplification (PSA) gain of 33 dB. A departure from the theoretical maximum attenuation as the gain increases is observed and explained.
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| 343. |
- Kakkar, Aditya, et al.
(författare)
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Impact of local oscillator frequency noise on coherent optical systems with electronic dispersion compensation
- 2015
-
Ingår i: Optics Express. - 1094-4087. ; 23:9, s. 11221-11226
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical investigation of the equalization-enhanced phase noise (EEPN) and its mitigation is presented. We show with a frequency domain analysis that the EEPN results from the non-linear inter-mixing between the sidebands of the dispersed signal and the noise sidebands of the local oscillator. It is further shown and validated with system simulations that the transmission penalty is mainly due to the slow optical frequency fluctuations of the local oscillator. Hence, elimination of the frequency noise below a certain cut-off frequency significantly reduces the transmission penalty, even when frequency noise would otherwise cause an error floor. The required cut-off frequency increases linearly with the white frequency noise level and hence the linewidth of the local oscillator laser, but is virtually independent of the symbol rate and the accumulated dispersion.
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| 344. |
- Kaldvee, Billy, et al.
(författare)
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Highly range-resolved ammonia detection using near-field picosecond differential absorption lidar
- 2012
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Ingår i: Optics Express. - 1094-4087. ; 20:18, s. 20688-20697
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Tidskriftsartikel (refereegranskat)abstract
- Ammonia detection is highly relevant for combustion in boilers and furnaces since NH3 is able to suppress nitric oxide levels by catalytic as well as non-catalytic reduction. The mixing of ammonia with flue gases is an important parameter to obtain efficient non-catalytic reduction. In this paper picosecond DIAL was used for range-resolved, single ended, NH3 detection, utilizing a tunable picosecond laser source. The absorption spectrum of the A(v(2) = 1)-> X(v(2) = 0) band was recorded and 212.2 and 214.5 nm was selected as the on-and off-resonance wavelength, respectively. One-dimensional concentration profiles with various NH3 concentration distributions are presented. The detection limit was found to be 40 ppm with a spatial resolution of 16 cm. (C) 2012 Optical Society of America
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| 345. |
- Kamran, Faisal, et al.
(författare)
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Computationally effective solution of the inverse problem in time-of-flight spectroscopy
- 2015
-
Ingår i: Optics Express. - 1094-4087. ; 23:5, s. 6937-6945
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Tidskriftsartikel (refereegranskat)abstract
- Photon time-of-flight (PTOF) spectroscopy enables the estimation of absorption and reduced scattering coefficients of turbid media by measuring the propagation time of short light pulses through turbid medium. The present investigation provides a comparison of the assessed absorption and reduced scattering coefficients from PTOF measurements of intralipid 20% and India ink-based optical phantoms covering a wide range of optical properties relevant for biological tissues and dairy products. Three different models are used to obtain the optical properties by fitting to measured temporal profiles: the Liemert-Kienle model (LKM), the diffusion model (DM) and a white Monte-Carlo (WMC) simulation-based algorithm. For the infinite space geometry, a very good agreement is found between the LKM and WMC, while the results obtained by the DM differ, indicating that the LKM can provide accurate estimation of the optical parameters beyond the limits of the diffusion approximation in a computational effective and accurate manner. This result increases the potential range of applications for PTOF spectroscopy within industrial and biomedical applications. (C) 2015 Optical Society of America
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| 346. |
- Kanngiesser, Franz, 1992, et al.
(författare)
-
Coating material-dependent differences in modelled lidar-measurable quantities for heavily coated soot particles
- 2019
-
Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 27:25, s. 36368-36387
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Tidskriftsartikel (refereegranskat)abstract
- The optical properties of thickly coated soot particles are sensitive to the chemical composition, thus to the refractive index of the coating material. For 58 differently sized coated soot aggregates the extinction-to-backscatter ratio (lidar ratio) and the depolarisation ratio are computed at a wavelength of 355 nm, 532 nm and 1064 nm for two different coating materials: a toluene-based coating and a sulphate coating. Additionally the Ångström exponents between 355 nm and 532 nm as well as between 532 nm and 1064 nm are calculated. The extinction-to-backscatter ratio is found to allow a distinction between the coating materials at all three wavelengths, and the depolarisation ratio allows for a distinction at 355 and 532 nm.
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| 347. |
- Kanngiesser, Franz, 1992, et al.
(författare)
-
Optical properties of water-coated sea salt model particles
- 2021
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 29:22, s. 34926-34950
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the optical properties of marine aerosol in dependence of the water content. To this end we develop a model geometry that realistically mimics the morphological changes as the salt particles take up more water. The results are compared to morphologically simpler models, namely, homogeneous and inhomogeneous superellipsoids, as well as cube-sphere hybrids. The reference model yields depolarization ratios, depending on size and water uptake, in the range from 0 to 0.36 ± 0.12. Overall, the simple models can reproduce optical properties of the reference model. The overall nonsphericity, as well as inhomogeneity are identified as key morphological parameter, while rounding of edges only has a minor impact on optical properties.
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| 348. |
- Karlsson, Hanna, et al.
(författare)
-
Inverse Monte Carlo for estimation of scattering and absorption in liquid optical phantoms
- 2012
-
Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 20:11, s. 12233-12246
-
Tidskriftsartikel (refereegranskat)abstract
- A spectroscopic probe with multiple detecting fibers was used for quantifying absorption and scattering in liquid optical phantoms. The phantoms were mixtures of Intralipid and red and blue food dyes. Intensity calibration for the detecting fibers was undertaken using either a microsphere suspension (absolute calibration) or a uniform detector illumination (relative calibration between detectors). Two different scattering phase functions were used in an inverse Monte Carlo algorithm. Data were evaluated for residual spectra (systematic deviations and magnitude) and accuracy in estimation of scattering and absorption. Spectral fitting was improved by allowing for a 10% intensity relaxation in the optimization algorithm. For a multi-detector setup, non-systematic residual spectrum was only found using the more complex Gegenbauer-kernel phase function. However, the choice of phase function did not influence the accuracy in the estimation of absorption and scattering. Similar estimation accuracy as in the multi-detector setup was also obtained using either two relative calibrated detectors or one absolute calibrated detector at a fiber separation of 0.46 mm.
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| 349. |
- Karlsson, Mikael, et al.
(författare)
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Diamond micro-optics: microlenses and antireflection structured surfaces for the infrared spectral region
- 2003
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Ingår i: Optics Express. - 1094-4087. ; 11:5, s. 502-507
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Tidskriftsartikel (refereegranskat)abstract
- Fabrication and evaluation of a subwavelength grating in diamond, designed to reduce the Fresnel reflection, is demonstrated. The antireflection (AR) structures are designed to reduce the surface reflection at an illuminating wavelength of 10.6 µm. With this AR-treatment, where no other material is introduced (i.e., no thin film coating), the unique properties of diamond can be fully used. The fabricated AR structures were optically evaluated with a spectrophotometer. The transmission through a diamond substrate with AR structures on both sides was increased from 71% to 97%, with a theoretical value of 99%. Microlenses in diamond are also demonstrated. The lenses are evaluated with interferometers and show good performance. The micro-optical structures were fabricated by electron-beam lithography or photolithographic methods followed by plasma etching.
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| 350. |
- Karlsson, Mikael, et al.
(författare)
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Fabrication and evaluation of a diamond diffractive fan-out element for high power lasers
- 2003
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Ingår i: Optics Express. - 1094-4087. ; 11:3, s. 191-198
-
Tidskriftsartikel (refereegranskat)abstract
- Fabrication and evaluation of diamond binary diffractive fan-out elements is demonstrated. The diffractive optical elements (DOEs) are designed for two different wavelengths, 633 nm and 10.6 µm. The DOE splits an incident beam into 16 spots that form a ring pattern. The surface reliefs were fabricated by photolithographic methods followed by plasma etching, which produced well-defined patterns with smooth surfaces. One DOE was optically evaluated with a HeNe laser, operating at a wavelength of 633 nm, and showed good performance. The DOE designed for a wavelength at 10.6 µm was tested together with a carbon dioxide laser. The light pattern was used to microstructure a 10 mm thick PMMA piece with very good results.
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