| 1. |
- Andersen, Torben, et al.
(författare)
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Neural networks for image-based wavefront sensing for astronomy
- 2019
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Ingår i: Optics Letters. - : Optical Society of America. - 0146-9592 .- 1539-4794. ; 44:18, s. 4618-4621
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Tidskriftsartikel (refereegranskat)abstract
- We study the possibility of using convolutional neural networks for wavefront sensing from a guide star image in astronomical telescopes. We generated a large number of artificial atmospheric wavefront screens and determined associated best-fit Zernike polynomials. We also generated in-focus and out-of-focus point-spread functions. We trained the well-known “Inception” network using the artificial data sets and found that although the accuracy does not permit diffraction-limited correction, the potential improvement in the residual phase error is promising for a telescope in the 2–4 m class.
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| 2. |
- Arwin, Hans, et al.
(författare)
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Structural circular birefringence and dichroism quantified by differential decomposition of spectroscopic transmission Mueller matrices from Cetonia aurata
- 2016
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Ingår i: Optics Letters. - : OPTICAL SOC AMER. - 0146-9592 .- 1539-4794. ; 41:14, s. 3293-3296
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Tidskriftsartikel (refereegranskat)abstract
- Transmission Mueller-matrix spectroscopic ellipsometry is applied to the cuticle of the beetle Cetonia aurata in the spectral range 300-1000 nm. The cuticle is optically reciprocal and exhibits circular Bragg filter features for green light. By using differential decomposition of the Mueller matrix, the circular and linear birefringence as well as dichroism of the beetle cuticle are quantified. A maximum value of structural optical activity of 560 degrees/mm is found. (C) 2016 Optical Society of America
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| 3. |
- Boyko, Andrey A., et al.
(författare)
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Rb:PPKTP optical parametric oscillator with intracavity difference-frequency generation in AgGaSe2
- 2016
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Ingår i: Optics Letters. - : Optical Society of America. - 0146-9592 .- 1539-4794. ; 41:12, s. 2791-2794
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Tidskriftsartikel (refereegranskat)abstract
- A 1.064 mu m pumped Rb:PPKTP optical parametric oscillator (OPO) generates mid-IR radiation by intracavity mixing the resonant signal and idler waves in AgGaSe2. The similar to 6 ns pulses at similar to 7 mu m have an energy of 670 mu J at 100 Hz, equivalent to an average power of 67 mW. The overall quantum conversion efficiency from 1.064 mu m amounts to 8%, and the power conversion efficiency is 1.2%.
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| 4. |
- Camacho, Miguel, et al.
(författare)
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Designer surface plasmon dispersion on a one-dimensional periodic slot metasurface with glide symmetry
- 2017
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Ingår i: Optics Letters. - : Optical Society of America. - 0146-9592 .- 1539-4794. ; 42:17, s. 3375-3378
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Tidskriftsartikel (refereegranskat)abstract
- In this Letter, we explore the dispersion of spoof surface plasmons supported by a single-layer glide-symmetric structure. This structure consists of an infinitely long double-notched slot perforated in a metal layer. The presence of a degeneracy of the two lowest-order modes at the Brillouin zone boundary, which have non-zero group velocity is explained and experimentally demonstrated. Further, the dependence of the band structure when glide-symmetric configuration is broken is also explored.
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| 5. |
- Carpenter, J., et al.
(författare)
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Complete spatiotemporal characterization and optical transfer matrix inversion of a 420 mode fiber
- 2016
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 41:23, s. 5580-5583
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Tidskriftsartikel (refereegranskat)abstract
- © 2016 Optical Society of America. The ability to measure a scattering medium's optical transfer matrix, the mapping between any spatial input and output, has enabled applications such as imaging to be performed through media which would otherwise be opaque due to scattering. However, the scattering of light occurs not just in space, but also in time. We complete the characterization of scatter by extending optical transfer matrix methods into the time domain, allowing any spatiotemporal input state at one end to be mapped directly to its corresponding spatiotemporal output state. We have measured the optical transfer function of a multimode fiber in its entirety; it consists of 420 modes in/out at 32768 wavelengths, the most detailed complete characterization of multimode waveguide light propagation to date, to the best of our knowledge. We then demonstrate the ability to generate any spatial/polarization state at the output of the fiber at any wavelength, as well as predict the temporal response of any spatial/polarization input state.
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| 6. |
- Chi, Kequn, et al.
(författare)
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Large-scale nanostructured low-temperature solar selective absorber
- 2017
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Ingår i: Optics Letters. - : Optical Society of America. - 0146-9592 .- 1539-4794. ; 42:10, s. 1891-1894
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Tidskriftsartikel (refereegranskat)abstract
- A large-scale nanostructured low-temperature solar selective absorber is demonstrated experimentally. It consists of a silicon dioxide thin film coating on a rough refractory tantalum substrate, fabricated based simply on self-assembled, closely packed polystyrene nanospheres. Because of the strong light harvesting of the surface nanopatterns and constructive interference within the top silicon dioxide coating, our absorber has a much higher solar absorption (0.84) than its planar counterpart (0.78). Though its absorption is lower than that of commercial black paint with ultra-broad absorption, the greatly suppressed absorption/emission in the long range still enables a superior heat accumulation. The working temperature is as high as 196.3 degrees C under 7-sun solar illumination in ambient conditions-much higher than those achieved by the two comparables.
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| 7. |
- Chi, Xiaoming, et al.
(författare)
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Fractal superconducting nanowire single-photon detectors with reduced polarization sensitivity
- 2018
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Ingår i: Optics Letters. - : OPTICAL SOC AMER. - 0146-9592 .- 1539-4794. ; 43:20, s. 5017-5020
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate superconducting nanowire single-photon detectors (SNSPDs) based on a fractal design of the nanowires to reduce the polarization sensitivity of detection efficiency. We patterned niobium titanium nitride thin films into Peano curves with a linewidth of 100 nm and integrated the nanowires with optical microcavities to enhance their optical absorption. At a base temperature of 2.6 K, the fractal SNSPD exhibited a polarization-maximum device efficiency of 67% and a polarization-minimum device efficiency of 61% at a wavelength of 1550 nm. Therefore, the polarization sensitivity, defined as their ratio, was 1.1, lower than the polarization sensitivity of the SNSPDs in the meander design. The reduced polarization sensitivity of the detector could be maintained for higher-order spatial modes in multimode optical fibers and could tolerate misalignment between the optical mode and the detector. This fractal design is applicable to both amorphous and polycrystalline materials that are commonly used for making SNSPDs.
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| 8. |
- De Luca, Eleonora, et al.
(författare)
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Gallium Indium Phosphide Microstructures with Suppressed Photoluminescence for Applications in Nonlinear Optics
- 2019
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Ingår i: Optics Letters. - : Optical Society of America. - 0146-9592 .- 1539-4794. ; 44:21
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Tidskriftsartikel (refereegranskat)abstract
- Gallium indium phosphide (Ga0.51In0.49P), lattice matched to gallium arsenide, shows remarkable second-order nonlinear properties, as well as strong photoluminescence due to its direct band gap. By measuring the second-harmonic generation from the GaInP microwaveguide (0.2 x 11 x 1300 μm) before and after stimulating intrinsic photobleaching, we demonstrate that the photoluminescence could be strongly suppressed (-34 dB), leaving the nonlinear properties unchanged, making it suitable for low-noise applications.
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| 9. |
- Dev Choudhury, Bikash, et al.
(författare)
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Surface second harmonic generation from silicon pillar arrays with strong geometrical dependence
- 2015
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 40:9, s. 2072-2075
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Tidskriftsartikel (refereegranskat)abstract
- We present experimental demonstration and analysis of enhanced surface second harmonic generation (SHG) from hexagonal arrays of silicon pillars. Three sets of Si pillar samples with truncated cone-shaped pillar arrays having periods of 500, 1000, and 2000 nm, and corresponding average diameters of 200, 585 and 1550 nm, respectively, are fabricated by colloidal lithography and plasma dry etching. We have observed strong dependence of SHG intensity on the pillar geometry. Pillar arrays with a 1000 nm period and a 585 nm average diameter give more than a one order of magnitude higher SHG signal compared to the other two samples. We theoretically verified the dependence of SHG intensity on pillar geometry by finite difference time domain simulations in terms of the surface normal E-field component. The enhanced surface SHG light can be useful for nonlinear silicon photonics, surface/interface characterization, and optical biosensing.
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| 10. |
- Durán Bosch, Vicente Andrés, 1977, et al.
(författare)
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Electro-optic dual-comb interferometry over 40-nm bandwidth
- 2016
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 41:18, s. 4190-4193
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Tidskriftsartikel (refereegranskat)abstract
- Dual-comb interferometry is a measurement technique that uses two laser frequency combs to retrieve complex spectra in a line-by-line basis. This technique can be implemented with electro-optic frequency combs, offering intrinsic mutual coherence, high acquisition speed and flexible repetition-rate operation. A challenge with the operation of this kind of frequency comb in dual-comb interferometry is its limited optical bandwidth. Here, we use coherent spectral broadening and demonstrate electro-optic dual-comb interferometry over the entire telecommunications C band (200 lines covering ~ 40 nm, measured within 10 microseconds at 100 signal-to-noise ratio per spectral line). These results offer new prospects for electro-optic dual-comb interferometry as a suitable technology for high-speed broadband metrology, for example in optical coherence tomography or coherent Raman microscopy.
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