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Optics Letters

Mushegh Rafayelyan, Etienne Brasselet
We propose space-variant uniaxial flat optical elements designed to generate pure Laguerre-Gaussian modes with arbitrary azimuthal and radial indices l and p from an incident Gaussian beam. This is done via the combined use of the dynamic and the geometric phases. Optimal design protocol for the mode conversion efficiency is derived, and the corresponding characteristics are given for -6≤l≤6 and 0≤p≤5. The obtained "modal q-plates" may find many applications whenever the radial degree of freedom of a light field is at play...
May 15, 2017: Optics Letters
Evgenij Zubko, Alycia J Weinberger, Nataliya Zubko, Yuriy Shkuratov, Gorden Videen
The Umov effect manifests itself as an inverse correlation between the light-scattering maximum of positive polarization P<sub>max</sub> and the geometric albedo A of the target. In logarithmic scales, P<sub>max</sub> is linearly dependent on A. This effect has been long known in the optics of particulate surfaces and, recently, it was extended for the case of single-scattering dust particles whose size is comparable to the wavelength of the incident light. In this work, we investigate the effect of irregular shape on the Umov effect in single-scattering particles...
May 15, 2017: Optics Letters
Xia-Li Ou, Jing Feng, Ming Xu, Hong-Bo Sun
We have fabricated semitransparent and flexible indium-free perovskite solar cells (PeSCs) with high visible transmittance employing two kinds of composite ultrathin metallic electrodes, MoO<sub>3</sub>/Au and MoO<sub>3</sub>/Au/Ag/MoO<sub>3</sub>/Alq<sub>3</sub>, as the bottom and top electrodes, respectively. These electrodes show superb electrical conductivity, excellent mechanical robustness, and high optical transparency which are quite suitable for semitransparent and flexible PeSCs...
May 15, 2017: Optics Letters
Farzad Zangeneh-Nejad, Amin Khavasi
In this contribution a new approach to perform spatial integration is presented using a dielectric slab. Our approach is indeed based on the fact that the transmission coefficient of a simple dielectric slab at its mode excitation angle matches the Fourier-Green's function of first-order integration. Inspired by the mentioned dielectric-based integrator, we further demonstrate its graphene-based counterpart. The latter is not only reconfigurable but also highly miniaturized in contrast to the previously reported designs [Opt...
May 15, 2017: Optics Letters
Yun Gao, Wen Zhou, Xiankai Sun, Hon Ki Tsang, Chester Shu
Cavity-enhanced thermo-optic bistability is studied in a graphene-on-Si<sub>3</sub>N<sub>4</sub> ring resonator. By engineering the coverage of the monolayer graphene on top of the Si<sub>3</sub>N<sub>4</sub> ring resonator, we observed a two-fold enhancement in the thermo-optically induced resonance shift rate and an 18-fold increase in the effective thermal nonlinear refractive index compared with the devices without graphene. The thermo-optic hysteresis loop was also characterized in this hybrid structure, where the experimental results agree well with the theoretical calculations...
May 15, 2017: Optics Letters
Ke Huang, Mani Hossein-Zadeh
We demonstrate a simple and effective technique for stabilizing the oscillation amplitude of a radiation pressure driven RF optomechanical oscillator (OMO). By controlling the optomechanical gain through a feedback loop that uses the oscillation amplitude itself as the feedback parameter, we have been able to suppress the amplitude fluctuations and drift. In contrast to more complex techniques that only lock the relative wavelength detuning, the proposed technique isolates the oscillation amplitude not only from laser wavelength variations, but also from laser power variations, ambient temperature variations, and coupling gap variations...
May 15, 2017: Optics Letters
Seongjin Hong, Woohyun Jung, Tavakol Nazari, Sanggwon Song, Taeoh Kim, Chai Quan, Kyunghwan Oh
We report unique thermo-optical characteristics of DNA-Cetyl tri-methyl ammonium (DNA-CTMA) thin solid film with a large negative thermo-optical coefficient of -3.4×10<sup>-4</sup>/°C in the temperature range from 20°C to 70°C without any observable thermal hysteresis. By combining this thermo-optic DNA film and fiber optic multimode interference (MMI) device, we experimentally demonstrated a highly sensitive compact temperature sensor with a large spectral shift of 0.15 nm/°C. The fiber optic MMI device was a concatenated structure with single-mode fiber (SMF)-coreless silica fiber (CSF)-single mode fiber (SMF) and the DNA-CTMA film was deposited on the CSF...
May 15, 2017: Optics Letters
Junying Ru, Qijie Xie, Chaoran Huang, Bofang Zheng, Chester Shu
We have demonstrated a new approach to enhance the uniformity of conversion efficiency in serial-to-parallel data conversion via time lens processing. In our approach, Raman amplification is applied to enhance four-wave mixing in a highly nonlinear fiber. By carefully selecting the pump wavelength, the Raman gain profile can be exploited to compensate the roll-off in conversion efficiency resulted from the varying phase mismatch between the linearly chirped pump and the signal. With Raman amplification, improvement of sensitivity up to 6...
May 15, 2017: Optics Letters
Sarper Ozharar, Alphan Sennaroglu
We present a novel multi-pass cavity design based on the use of a rotationally symmetric end mirror having a specifically designed spherical aberration so that its focal length varies inversely as the ray height from the optical axis. We provide a detailed discussion of how ray tracing can be done for this system and show with numerical simulations that a very rich set of exotic spot patterns can be formed on the end mirrors. We further show a specific q-preserving configuration where the q-parameters of the input and output beams remain the same...
May 15, 2017: Optics Letters
J Haase, S Bagiante, H Sigg, J A van Bokhoven
We report the enhancement of infrared absorption of chemisorbed carbon monoxide on platinum in the gap of plasmonic nanoantennas. Our method is based on the self-assembled formation of platinum nanoislands on nanoscopic dipole antenna arrays manufactured via electron beam lithography. We employ systematic variations of the plasmonic antenna resonance to precisely couple to the molecular stretch vibration of carbon monoxide adsorbed on the platinum nanoislands. Ultimately, we reach more than 1500-fold infrared absorption enhancements, allowing for an ultrasensitive detection of a monolayer of chemisorbed carbon monoxide...
May 15, 2017: Optics Letters
C Burcklen, S de Rossi, E Meltchakov, D Dennetière, B Capitanio, F Polack, F Delmotte
We present an experimental comparison of several Sc-based short period multilayer mirrors including Cr/Sc with B<sub>4</sub>C barrier layers and CrN<sub>x</sub>/Sc, and we propose a new material combination that provides high reflectance in the water window domain. Multilayer samples with period thickness in the range 1.5-1.7 nm have been deposited by magnetron sputtering and characterized by x-ray reflectometry with a Cu-Kα source and with synchrotron radiation near the Sc-L<sub>2,3</sub> edge...
May 15, 2017: Optics Letters
Wu Liu, Jintao Fan, Chen Xie, Youjian Song, Chenlin Gu, Lu Chai, Chingyue Wang, Minglie Hu
A digital micromirror device (DMD)-based arbitrary spectrum amplitude shaper is incorporated into a large-mode-area photonic crystal fiber laser cavity. The shaper acts as an in-cavity programmable filter and provides large tunable dispersion from normal to anomalous. As a result, mode-locking is achieved in different dispersion regimes with watt-level high output power. By programming different filter profiles on the DMD, the laser generates femtosecond pulse with a tunable central wavelength and controllable bandwidth...
May 15, 2017: Optics Letters
Soroush Shabahang, Nicholas S Nye, Christos Markos, Demetrios N Christodoulides, Ayman F Abouraddy
In the absence of suitable deposition processes, the fabrication of graded-index chalcogenide waveguides or fibers remains an outstanding challenge. Here, by exploiting the strong thermo-optic effect present in chalcogenide glasses, we experimentally demonstrate non-permanent optically-induced waveguides in bulk As<sub>2</sub>Se<sub>3</sub> rods using a 1.55 μm wavelength laser. This single-step process can be used not only to self-trap the writing beam, but also to guide another optical beam at a different wavelength in the opto-thermally inscribed waveguide channel...
May 15, 2017: Optics Letters
Simone Vadilonga, Ivo Zizak, Dmitry Roshchupkin, Andrei Petsiuk, Igor Dolbnya, Kawal Sawhney, Alexei Erko
A functional test for a pulse picker for synchrotron radiation was performed at Diamond Light Source. The purpose of a pulse picker is to select which pulse from the synchrotron hybrid-mode bunch pattern reaches the experiment. In the present work, the Bragg reflection on a Si/B<sub>4</sub>C multilayer was modified using surface acoustic wave (SAW) trains. Diffraction on the SAW alters the direction of the x rays and it can be used to modulate the intensity of the x rays that reach the experimental chamber...
May 15, 2017: Optics Letters
Alessio Gambetta, Edoardo Vicentini, Yuchen Wang, Nicola Coluccelli, Eugenio Fasci, Livio Gianfrani, Antonio Castrillo, Valentina Di Sarno, Luigi Santamaria, Pasquale Maddaloni, Paolo De Natale, Paolo Laporta, Gianluca Galzerano
We report on absolute measurements of saturated-absorption line-center frequencies of room-temperature trifluoromethane using a quantum cascade laser at 8.6 μm and the frequency modulation spectroscopy method. Absolute calibration of the laser frequency is obtained by direct comparison with a mid-infrared optical frequency comb synthesizer referenced to a radio-frequency Rb standard. Several sub-Doppler transitions falling in the υ<sub>5</sub> vibrational band are investigated at around 1158.9  cm<sup>-1</sup> with a fractional frequency precision of 8...
May 15, 2017: Optics Letters
Ying Zhang, Wenfeng Sun, Xinke Wang, Jiasheng Ye, Shengfei Feng, Peng Han, Yan Zhang
A simple and energy-saving method has been proposed to actively modulate the spectra of terahertz (THz) waves radiated from two serial plasmas, which uses the background light to generate one plasma to make full use of the energy of the femtosecond laser. With this method, the modulation of the central frequency, spectral bandwidth, and spectral profile of the output THz waves have been observed. The shifting of the amplitude dip has been manipulated by changing the distance of the two serial plasmas. The manipulation results agree with the ones simulated by the transition-Cherenkov model...
May 15, 2017: Optics Letters
Alejandro Dominguez-Lopez, Marcelo A Soto, Sonia Martin-Lopez, Luc Thevenaz, Miguel Gonzalez-Herraez
A differential pulse-width pair (DPP) Brillouin distributed fiber sensor is implemented to achieve centimetric spatial resolution over distances of several kilometers. The presented scheme uses a scanning method in which the spectral separation between the two probe sidebands is kept constant, while the optical frequency of the pump is swept to scan the Brillouin spectral response. Experimental results show that this method avoids detrimental temporal distortions of the pump pulses, which in a standard implementation prevent the DPP method from operating over mid-to-long distances...
May 15, 2017: Optics Letters
François Goudail
Estimation of the Stokes vector from N>4 intensity measurements is usually performed with the pseudo-inverse (PI) estimator, which is optimal when the noise that corrupts the measurements is additive and Gaussian. In the presence of Poisson shot noise, the maximum-likelihood (ML) estimator is different from the PI estimator, but is more complex to implement since it is not closed-form. We compare in this Letter the precisions obtained with the ML and the PI estimators in the presence of Poisson noise when using measurement structures based on spherical designs...
May 15, 2017: Optics Letters
Yanqi Qiao, Yajun Peng, Yuanlin Zheng, Fangwei Ye, Xianfeng Chen
Scattering has usually been considered detrimental for optical focusing or imaging. Recently, more and more research has shown that strongly scattering materials can be utilized to focus coherent light by controlling or shaping the incident light. Here, purposeful focusing of second-harmonic waves, which are generated and scattered from nonlinear turbid media via feedback-based wavefront shaping, is presented. This Letter shows a flexible manipulation of both disordered linear and nonlinear scattering signals, indicating more controllable degrees of freedom for the description of turbid media...
May 15, 2017: Optics Letters
Kequn Chi, Liu Yang, Zhaolang Liu, PingQi Gao, Jichun Ye, Sailing He
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...
May 15, 2017: Optics Letters
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