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Optics Letters

Eric Y Zhu, Cory Rewcastle, Raanan Gad, Li Qian, Ofer Levi
We demonstrate ultrasound detection with 500-μm-diameter photonic-crystal slab (PCS) sensors fabricated from CMOS-compatible technology. An ultrasound signal impinging a PCS sensor causes a local modulation of the refractive index (RI) of the medium (water) in which the PCS is immersed, resulting in a periodic spectral shift of the optical resonance of the PCS. The acoustic sensitivity is found to scale with the index sensitivity S and quality factor Q. A noise equivalent pressure (NEP) of 650 Pa with averaging (7...
May 15, 2019: Optics Letters
Zexi Zhao, Mengfan Cheng, Chenkun Luo, Lei Deng, Minming Zhang, Songnian Fu, Ming Tang, Ping Shum, Deming Liu
An analog-digital hybrid optical chaos source and a corresponding secure key distribution (SKD) scheme are proposed. An analog-digital hybrid electro-optic feedback loop is introduced to enhance the robustness of the chaotic semiconductor lasers. The source, which can adopt robust digital synchronization strategies, could generate a broadband analog optical chaotic signal of high dynamical complexity. Furthermore, the source reduces the requirement on the processing speed of digital components and simplifies the hybrid system structure markedly...
May 15, 2019: Optics Letters
Popowicz Adam
In the paper, we propose a simple algorithm that improves the quality with which the displacements between images registered in the sub-apertures of a a Shack-Hartmann (SH) wavefront sensor can be determined. Instead of measuring shifts between a given sub-aperture and a reference image, the method transforms a matrix of all relative displacements between sub-apertures into a vector of final shifts estimated with significantly increased accuracy. The method can be applied to any observations employing an SH wavefront sensor, especially if a scene evolves rapidly and a reference, high-fidelity image cannot be obtained...
May 15, 2019: Optics Letters
Shoichiro Fukushima, Masaaki Shimatani, Satoshi Okuda, Shinpei Ogawa, Yasushi Kanai, Takao Ono, Koichi Inoue, Kazuhiko Matsumoto
Low dark current, high-responsivity middle-wavelength infrared (IR) graphene photodetectors using photo-gating amplification of injected photo-carriers are demonstrated. A graphene/p-indium antimonide (InSb) heterojunction and graphene/insulator region were formed. The injected photo-carriers from InSb to graphene were amplified by photo-gating induced in the graphene/tetraethyl orthosilicate (TEOS) region, resulting in the high responsivity and low dark current performance. A responsivity of 14.9 A/W and an ON/OFF ratio of 2...
May 15, 2019: Optics Letters
Haley Kerrigan, Shermineh Rostami Fairchild, Martin Richardson
Laser filaments can project intensities sufficient to ablate materials at long ranges, but the clamping of a filament's intensity to ∼1014   W/cm2 limits the effective ablation of targets with which the laser pulses interact. We seek to identify regimes in which auxiliary radiation can be used to augment the ablation created by single filaments. In this work, the combination of an 800 nm, 50 fs beam at single filament intensity and a 1064 nm, 8 ns laser pulse is studied. The ablation of GaAs is quantitatively evaluated for varying interpulse delays...
May 15, 2019: Optics Letters
Soongho Park, Sunghwan Rim, Younggue Kim, Byeong Ha Lee
A noncontact photoacoustic imaging method based on optical quadrature detection is proposed. The photo-induced acoustic signal is detected by an optical method without contacting the specimen. By utilizing the intrinsic phase difference of a multiport optical interferometer, the quadrature signal of a conventional interferometric signal could be obtained. With this quadratic signal pair, we could reconstruct the photoacoustic signal without suffering from the initial phase drift that usually occurs in a conventional interferometric system...
May 15, 2019: Optics Letters
Ran Hao, Jianyao Jiao, Xiliang Peng, Zheng Zhen, Rakhatbek Dagarbek, Yijun Zou, Erping Li
In this Letter, we report a graphene-based hybrid plasmonic modulator (GHPM) realized by employing the electro-absorption effect of graphene. The simulation results show that the modulation efficiency of GHPM, i.e., extinction ratio per length, can be as large as 0.417 dB/μm, which is more than twice as much as that of recently presented graphene-on-silicon modulator. It was found that the improvement in modulation efficiency is mainly due to the enhancement of the overlap between graphene and the mode field in GHPM...
May 15, 2019: Optics Letters
Yanwen Sun, Nan Wang, Sanghoon Song, Peihao Sun, Matthieu Chollet, Takahiro Sato, Tim B van Driel, Silke Nelson, Rajan Plumley, Jordi Montana-Lopez, Samuel W Teitelbaum, Johann Haber, Jerome B Hastings, Alfred Q R Baron, Mark Sutton, Paul H Fuoss, Aymeric Robert, Diling Zhu
We present the concept and a prototypical implementation of a compact x-ray split-delay system that is capable of performing continuous on-the-fly delay scans over a range of ∼10  ps with sub-100 nanoradian pointing stability. The system consists of four channel-cut silicon crystals, two of which have gradually varying gap sizes from intentional 5 deg asymmetric cuts. The delay adjustment is realized by linear motions of these two monolithic varying-gap channel cuts, where the x-ray beam experiences pairs of anti-parallel reflections, and thus becomes less sensitive in output beam pointing to motion imperfections of the translation stages...
May 15, 2019: Optics Letters
Nezam Uddin, Guigen Liu, Qiwen Sheng, Ming Han
We demonstrate the constant temperature (CT) operation of a fiber-optic anemometer based on a laser-heated silicon Fabry-Perot interferometer (FPI), where the temperature of the FPI is kept constant by adjusting the heating laser power through a feedback control loop and the output signal is the heating laser power. We show that the CT operation can dramatically improve the frequency response over the commonly used constant power (CP) operation, where the laser heating power is kept constant and the output signal is the temperature of the FPI...
May 15, 2019: Optics Letters
Kari Remes, Antti Järvenpää, Tapio Fabritius
Testing and characterization techniques intended for traditional electronics production are rarely compatible with modern large-area, thin film electronics manufacturing processes such as roll-to-roll fabrication. Online quality monitoring of conductive thin films is necessary for upscaling and maintaining high-yield production. Thermography has already shown its usefulness in these kinds of applications, but has suffered from the lack of proper non-contact electrical heating. Now a fully contactless quality inspection technique based on thermal imaging and induction heating is implemented and evaluated...
May 15, 2019: Optics Letters
Hang Chen, Leimin Deng, Jun Duan, Xiaoyan Zeng
A welding method that utilizes a picosecond laser with a small-scale rapid oscillating scan is presented in this Letter to achieve the welding of glasses with natural stacking contact (gap≈10  μm). The rapid oscillating scan of the laser not only creates enough molten material to fill the gap, but also releases the internal thermal pressure during the welding process. The contraction created by condensation of the welding area can reduce the gap to less than 3 μm, which provides necessary conditions for realizing continuous welding...
May 15, 2019: Optics Letters
Qing Wang, Jinwei Zhang, Alexander Kessel, Nathalie Nagl, Vladimir Pervak, Oleg Pronin, Ka Fai Mak
A myriad of existing and emerging applications could benefit from coherent and broadband mid-infrared (MIR) light. Yet, existing tabletop sources are often complex or sensitive to interferometric optical misalignment. Here we demonstrate a significantly simplified scheme of broadband MIR generation by cascading the intra-pulse difference-frequency generation process in a specific nonlinear crystal. This allows pulses generated directly from mode-locked lasers to be used without further nonlinear temporal compression...
May 15, 2019: Optics Letters
Lien Hu, Chuantao Zheng, Jie Zheng, Yiding Wang, Frank K Tittel
In order to achieve a high acoustic coupling strength and detection sensitivity and to simplify the assembly and alignment process in quartz-enhanced photoacoustic spectroscopy (QEPAS) technique, a novel quartz tuning fork (QTF) embedded off-beam QEPAS (E-OB-QEPAS) spectrophone was proposed. The structural parameters of the acoustic micro-resonator of the E-OB-QEPAS spectrophone were optimized for enhancing the signal-to-noise ratio gain based on experimental investigation. Compared with the on-beam configuration using a bare QTF, a detection sensitivity enhancement by a factor of ∼25 was achieved by embedding the QTF in one resonant tube...
May 15, 2019: Optics Letters
Quimey Pears Stefano, Lorena Rebón, Silvia Ledesma, Claudio Iemmi
We present a tomographic method which requires only 4d-3 measurement outcomes to reconstruct any pure quantum state of arbitrary dimension d. Using the proposed scheme, we have experimentally reconstructed a large number of pure states of dimension d=7, obtaining a mean fidelity of 0.94. Moreover, we performed numerical simulations of the reconstruction process, verifying the feasibility of the method for higher dimensions. In addition, the a priori assumption of purity can be certified within the same set of measurements, which represents an improvement with respect to other similar methods and contributes to answering the question of how many observables are needed to uniquely determine any pure state...
May 15, 2019: Optics Letters
Junoh Kim, Jooho Lee, Yong Hyub Won
Focus-tunable liquid lens arrays have been used to improve depth in glass-free three-dimensional devices where high fill factor is required. For high fill factors, polygonal apertures should be used, but due to the difficulty of controlling aberrations during focus tuning, polygonal aperture focus-tunable lenses have rarely been studied. This Letter proposes a new structure with walls at the lens boundaries using a square parabolic lens model to control the quadrafoil aberration induced by the square aperture...
May 15, 2019: Optics Letters
Ekaterina Migal, Andrey Pushkin, Boris Bravy, Vyacheslav Gordienko, Nikita Minaev, Anatoly Sirotkin, Fedor Potemkin
We report on entering a new era of mid-IR femtosecond lasers based on amplification in a relatively new gain chalcogenide medium, Fe:ZnSe. Our hybrid all-solid-state laser system is based on direct pulse amplification of femtosecond seed from three-stage AGS-based-optical parametric amplification (OPA) in a Fe:ZnSe laser crystal optically pumped by a Cr:Yb:Ho:YSGG Q-switched nanosecond laser. The development of the pump source with output energy up to 90 mJ operating at a 10 Hz repetition rate regime and highly efficient grating compressor (80%) provides 3...
May 15, 2019: Optics Letters
Tae-Jung Ahn, Sucbei Moon
We present an optically tunable fiber Bragg grating (FBG) based on a photo-mechanical tuning mechanism. Azobenzene containing polymer was utilized as a photo-mechanical tuning agent coated over a bare section of FBG. Controlled by ultraviolet (UV) irradiation, the polymer coating acts as a micro-actuator that deforms the fiber structure. Reversible tunability was obtained by the coating locally stretching the embedded FBG fiber by the intensity and the spatial distribution of the UV light. We found that our tunable FBG could linearly tune its center wavelength as large as 2...
May 15, 2019: Optics Letters
Khos-Ochir Tsogvoo, Baatarchuluun Tsermaa, Byung Kwan Yang, Kim Myung-Whun
We measured time- and frequency-resolved phase changes owing to two-photon absorption induced by ultrashort (10 fs) pulses transmitted through a transparent material (ZnSe crystal), using femtosecond two-photon phase change spectroscopy. The maximal phase change was 0.02 rad when a pulse with the energy density of 1.5 nJ was focused with the focus diameter of 100 μm. The maximal phase change occurred when a probe pulse was delayed with respect to a pump pulse by 64 fs. A calculation assuming two-photon absorption by noninteracting atomic gases was consistent with the experimental observations, which supported the observed phase change of the pulse that is due to the two-photon absorption...
May 15, 2019: Optics Letters
Miguel A Porras
We describe the effects of the coupling between the orbital angular momentum (OAM) and the temporal degrees of freedom in pulsed Laguerre-Gauss beams as a significant increase of the duration of few-cycle pulses when the OAM carried by the pulse is large, and as an enhancement to other previously known spatiotemporal couplings as radial red- and blue-shift of the mean frequency. In contrast to other detrimental, but retrievable, effects in the generation and propagation of ultrashort vortices such as spatial, group velocity, and topological charge dispersions, the OAM-temporal coupling effect is unavoidable and, therefore, has an impact on applications such as OAM-based optical communications, or on the generation of vortex-carrying attosecond pulses...
May 15, 2019: Optics Letters
V B Gildenburg, I A Pavlichenko
The evolution of optical discharge induced in the volume of transparent dielectric by a focused fs laser pulse is studied under condition of ionization instability that results in deep small-scale periodic modulation of breakdown plasma parameters in the direction of laser polarization. Laser pulse intensity range is found where the instability evolving from very small seed perturbations leads to formation of the contrast subwavelength periodic structure containing narrow zones with overcritical plasma density and enhanced energy deposition...
May 15, 2019: Optics Letters
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