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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Temporal Ghost Imaging with Wavelength Conversion
摘要： Ghost imaging is a non-direct measurement technique that uses the correlation between multiple probing patterns and the integrated signal measured after transmission (or reflection) through an object. [1] The resolution of the technique is determined by the characteristic length scale of the probing patterns fluctuations and/or the resolution with which they can be measured. Originally demonstrated in the spatial domain to reconstruct images of real physical objects, ghost imaging has been recently extended to the time-domain to measure ultrafast signals at telecom wavelengths [2]. In this work, we experimentally demonstrate ultrafast ghost imaging in the time-domain where the correlated intensities have completely different wavelengths. This wavelength-conversion temporal ghost-imaging scheme exploits fully the benefit of ghost imaging opening up new possibilities for ultrafast imaging in spectral regions where sensitive and/or fast detectors are not available and in particular the mid-infrared or THz range.
关键词： temporal domain,mid-infrared,ultrafast imaging,Ghost imaging,wavelength conversion,THz range
更新于2025-09-12 10:27:22
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Development of an optical pressure measurement system using an external cavity diode laser with a wide tunable frequency range
摘要： Optical pressure measurement systems can precisely measure pressure from vacuum to high pressure with a single apparatus. However, the continuously measurable range without interrupting measurement is limited to less than 1 kPa. In this study, an optical pressure measurement system with a wide continuous measurable range was developed. The optical system can continuously measure a pressure range of 18 kPa when using nitrogen gas by using a Littrow external cavity diode laser as its light source. First, discrete pressure points from vacuum to atmospheric pressure were measured. The repeatability and non-linearity of the differences between the measured values had standard deviations of 0.1 Pa and 0.5 Pa, respectively. Next, a pressure range from 91 kPa to 109 kPa was continuously measured. The results showed that the linearity characteristics of gauges as a function of pressure can be evaluated precisely using our optical pressure measurement system.
关键词： optical pressure measurement,external cavity diode laser,refractive index,wide tunable frequency range,Fabry-Perot cavity
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Generation of Ultrabroadband Phase-Locked Pulse Pairs in the Ultraviolet by Achromatic SHG
摘要： Two-dimensional electronic spectroscopy (2DES) is a powerful spectroscopic technique for the study of dynamics in coupled multi-chromophore systems, which has been successfully applied in the visible and infrared ranges. Its extension to the UV range (2DUV) is extremely promising for the study of biomolecules but poses several technical challenges: (i) the requirement of phase-locked pulse pairs; (ii) generation of extremely broadband UV pulses; (iii) dispersion management for the UV range. Here we present a setup able to generate ultrabroad phase-locked UV pump pulses with bandwidth from 260 to 310 nm. The UV pump pulse pairs are generated by Achromatic Second Harmonic Generation (ASHG) of a phase-locked, visible pulse pair (Fig. 1(a)). A non-collinear optical parametric amplifier (NOPA) produces 10-μJ, <6-fs-pulses in the 500-640 nm range. Two delayed, phase-locked replicas of the visible pulses are then generated by TWINS [1], a compact ultrastable interferometer consisting of a sequence of β-BBO birefringent wedges that allows varying with extreme accuracy and up to 1 ps the delay between the two replicas. The broadband visible replicas are subsequently chirped in a 45-mm block of SF57 and frequency doubled to the UV range by ASHG [2]. In this scheme, the visible pulse is dispersed by a fused silica (FS) prism and the angular dispersion is converted to a lateral dispersion by a second prism. The resulting collimated beam is focused into a 300-μm β-BBO crystal for SHG. By suitably choosing the prism separation (152 cm) and the focal length (35 mm) we match the propagation direction of each component with its SHG phase-matching angle.
关键词： ultrabroadband UV pulses,UV range,Two-dimensional electronic spectroscopy,Achromatic Second Harmonic Generation,phase-locked pulse pairs
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Long Length Fibre Fabry-Perot Interferometers and their Applications in Fibre Characterization and Temperature Sensing
摘要： Since the free spectral range (FSR) of a fibre Fabry-Perot (f-FP) is the reciprocal of the time delay inside the interferometer, it can be used for the precise measurement of fibre properties (chromatic dispersion when measured as a function of wavelength, birefringence, etc.) or for the measurement of environmental changes (such as temperature, pressure, stress, etc.) which alter the fibre’s parameters. Here we propose a method to precisely measure the FSR of long-length f-FP based on an incoherent optical source and RF beat signal analysis. We built a 7-m long f-FP made of a single mode fibre (SMF) and investigated the use of several algorithms to evaluate the FSR. When measuring over time, we achieved an excellent accuracy down to 2.4 Hz (corresponding to a relative error of 1.5× 10??). To demonstrate its use in sensing application, we varied the f-FP temperature and monitored the associated FSR. We achieved a sensitivity of 345 Hz/K, leading to an excellent temperature resolution below 10 mK. Additionally, the achieved high accuracy in the measured FSR can also be used to measure fibre’s properties very precisely (e.g., zero chromatic dispersion wavelength) or to determine their temperature dependence. The method requires no alignment and requires only a few off-the-shelf components and instruments.
关键词： fibre characterization,temperature sensing,RF beat signal analysis,free spectral range,fibre Fabry-Perot interferometers
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - GaSb-Based Swept-Wavelength Lasers for Spectroscopic Sensing Applications in the 1.7–2.5 Micron Spectral Range
摘要： 1.7-2.5 micron spectral region is particularly interesting for spectroscopic sensing due to the presence of strong and molecule-specific ro-vibrational absorption bands. These absorption bands correspond to the first overtone of the C-H stretching vibrations and the combination of stretching and bending vibrations of C-H, N-H and O-H bonds, acting as a unique molecular fingerprint for sensing applications and can be read by means of direct photon-phonon (target molecule vibration) interaction [1]. This provides an opportunity for laser based spectroscopic sensing for both gases and liquids. In the field of biomedical application, laser-based sensing of critical biomolecules such as glucose, lactate, urea, serum albumin as they provide key insights into the person’s metabolism as well as allow tracking patient’s condition in case of difficult chronic diseases such as diabetes, chronic renal failure or act as an important marker in case sepsis. In this work, we provide our recent results in developing fast, miniature and potentially low-cost swept-wavelength laser technology based on GaSb type-I gain-chips embedded in external cavity. We demonstrate excellent performance in the entire 1.7-2.5 micron spectral band both in terms of output power, bandwidth and speed [2]. From the application provide experimental data for realizing swept-laser based spectroscopic sensor for sensing the main critical biomolecules both in-vitro and in-vivo in the entire physiologically relevant concentration level range. Moreover we present a pathway to transfer this technology for volume manufacturing, opening opportunity to the consumer and personalized healthcare markets.
关键词： GaSb-based,1.7-2.5 micron Spectral Range,Swept-Wavelength Lasers,Spectroscopic Sensing
更新于2025-09-12 10:27:22
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Ferromagnetism in quantum dot plaquettes
摘要： Following recent experimental progress concerning Nagaoka ferromagnetism in finite-size quantum dot plaquettes, a general theoretical analysis is warranted in order to ascertain in rather generic terms which arrangements of a small number of quantum dots can produce saturated ferromagnetic ground states and under which constraints on interaction and interdot tunneling in the plaquette. This is particularly necessary since Nagaoka ferromagnetism is fragile and arises only under rather special conditions. We test the robustness of ground state ferromagnetism in the presence of a long-range Coulomb interaction and long-range as well as short-range interdot hopping by modeling a wide range of different plaquette geometries accessible by arranging a few (～4) quantum dots in a controlled manner. We find that ferromagnetism is robust to the presence of long-range Coulomb interactions, and we develop conditions constraining the tunneling strength such that the ground state is ferromagnetic. Additionally, we predict the presence of a partially spin-polarized ferromagnetic state for 4 electrons in a Y-shaped 4-quantum-dot plaquette. Finally, we consider 4 electrons in a ring of 5 dots. This does not satisfy the Nagaoka condition; however, we show that the ground state is spin 1 for strong, but not infinite, on-site interaction. Thus, even though Nagaoka’s theorem does not apply, the ground state for the finite system with one hole in a ring of 5 dots is partially ferromagnetic. We provide detailed fully analytical results for the existence or not of ferromagnetic ground states in several quantum dot geometries which can be studied in currently available coupled quantum dot systems.
关键词： long-range Coulomb interactions,Nagaoka ferromagnetism,interdot tunneling,ferromagnetic ground states,quantum dot plaquettes
更新于2025-09-12 10:27:22
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[IEEE 2019 IEEE 2nd Ukraine Conference on Electrical and Computer Engineering (UKRCON) - Lviv, Ukraine (2019.7.2-2019.7.6)] 2019 IEEE 2nd Ukraine Conference on Electrical and Computer Engineering (UKRCON) - Surface and Bulk Wave Modes of Two Dimensional Photonic Crystal Waveguide
摘要： Electrodynamical characteristics of the two-dimensional photonic crystal waveguide are considered. Effect of the width of hollow waveguide channel on the dispersion characteristics and spatial distribution of electric field is analyzed. Slow wave localized modes with phase velocity less than speed of light are supported by photonic crystal waveguide and can be used for synchronization with linear electron beams in the terahertz beam-wave systems. Widening of the waveguide hollow channel does not result in significant decrease of the electric field intensity on the axis of waveguide as occur in metallic slow-wave systems.
关键词： spatial harmonics,dispersion characteristics,two-dimensional photonic crystal waveguide,terahertz range,slow wave modes
更新于2025-09-11 14:15:04
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Flexible Pressure Sensors with Wide Linearity Range and High Sensitivity Based on Selective Laser Sintering 3D Printing
摘要： To achieve practical applications of flexible pressure sensors, good performance and scalable manufacturing processes are both desired. Here, flexible pressure sensors with excellent performance are fabricated via selective laser sintering (SLS). Having benefitted from the irregular microstructures generated in the powder sintering process, the sensors exhibit high sensitivity of 55 kPa?1 in a wide linearity range of 100 kPa, and they maintain decent sensitivity (>10 kPa?1) over a high-pressure range (100–400 kPa), which is among the best results for flexible pressure sensors. The working mechanism of the sensor is finely revealed combining in situ observations and electrical simulations. The results demonstrate that electrical saturation (due to parasitic resistance) greatly affects the linearity range except for the geometric saturation of the microstructure. As a proof of concept, tactile, pulse, muscle stiffness, and plantar pressure tests are performed. The fast and stable responses of the sensor show its great potential for electronic skin, human–machine interface, and healthcare monitoring. Besides its excellent performance, the fabrication processes via SLS are compatible with fab-scale production and flexible customization, which pave new paths for the mass manufacturing and diversified applications of flexible pressure sensors in the future.
关键词： flexible pressure sensors,selective laser sintering 3D printing,linearity range,graphene,surface microstructures
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Rare-Earth Doped Oxide Glasses and Fibers for Lasers Emitting in the 2÷3 μm Spectral Range
摘要： The aim of this investigation is the search of novel promising materials for solid-state and fiber lasers emitting in the spectral range 2÷3 microns, i.e. out of the range where the well-developed rare-earth doped silica fibers can successfully operate. We have stopped our choice on tellurite and calcium aluminate glasses. In contrast to silica glasses, both these glass types can contain high (>1021 cm-3) amounts of rare earth dopants. In contrast to ZBLAN glass that is widely used for mid-infrared fiber lasers, both tellurite and aluminate glasses can be quite stable to air moisture. Furthermore, calcium aluminate glasses are prominent for their extraordinary mechanical properties (better than those of fused silica). Our spectral investigations have shown that deeply dehydrated tellurite glasses (TG) are very suitable hosts for 2.3 μm Tm3+ lasers and can be also used as a host for 2.7 μm Er3+ lasers. As for calcium aluminate glasses (CAG), their phonon spectrum is not suitable for 2.7 for μm lasers. But the emission properties of Tm3+ ions in this host show some unusual feature. Two-micron Tm3+ emission band in CAG is anomalously widened and red shifted so that it overlaps well with the 2.3μm emission band. Thus continuous tuning of Tm doped CAG fiber laser from ~2μm up to ~2.4μm is conceivable. Figures 1 and 2 give some examples of bulk Tm-doped TG and CAG lasing properties. Fig. 1 shows the 2.3μm lasing parameters of 30 mm long TG sample when pumped by a pulsed ruby laser. CAG in similar conditions showed cascade lasing at 2.3μm and 2.1μm. Fig. 2 shows the lasing parameters of a quasi CW diode-pumped CAG chip laser, operating at the wavelength of 2.1 μm. Surely most practical applications of such laser glasses require fiber configuration. We have developed the laboratory technology of TG multimode and single-mode double-cladding fibers fabrication. In Tm doped TG fibers laser action at 1.9 μm and 2.3 μm was successfully demonstrated. Er doped fibers were also manufactured but 2.7 μm laser action in them requires highly reflective fiber Bragg gratings to be made in them. Fabrication of CAG fibers is a very complicated technological task due to high tendency of CAG to devitrification. Nevertheless, using “rod-in-tube” method we have prepared an optical fiber starting from Tm-doped CAG rod in a silica tube. Unfortunately, the core of this fiber contained too much SiO2 diffused from the cladding. The choice of a suitable lower-melting cladding glass should solve the problem. Thus, the properties of deeply dehydrated rare-earth doped tellurite and calcium-aluminate glasses are shown to be quite pertinent for lasers emitting in the 2÷3 μm spectral range.
关键词： rare-earth doped oxide glasses,mid-infrared spectral range,fiber lasers,tellurite glasses,calcium aluminate glasses
更新于2025-09-11 14:15:04
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High-resolution ISAR imaging of fast rotating targets based on pattern-coupled Bayesian strategy for multiple measurement vectors
摘要： Very high resolution inverse synthetic aperture radar (ISAR) imaging of fast rotating targets is a complicated task. There may be insufficient pulses or may introduce migration through range cells (MTRC) during the coherent processing interval (CPI) when we use the conventional range Doppler (RD) ISAR technique. With compressed sensing (CS) technique, we can achieve the high-resolution ISAR imaging of a target with limited number of pulses. Sparse representation based method can achieve the super resolution ISAR imaging of a target with a short CPI, during which the target rotates only a small angle and the range migration of the scatterers is small. However, traditional CS-based ISAR imaging method generally faced with the problem of basis mismatch, which may degrade the ISAR image. To achieve the high resolution ISAR imaging of fast rotating targets, this paper proposed a pattern-coupled sparse Bayesian learning method for multiple measurement vectors, i.e. the PC-MSBL algorithm. A multi-channel pattern-coupled hierarchical Gaussian prior is proposed to model the pattern dependencies among neighboring range cells and correct the MTRC problem. The expectation-maximization (EM) algorithm is used to infer the maximum a posterior (MAP) estimate of the hyperparameters. Simulation results validate the effectiveness and superiority of the proposed algorithm.
关键词： Multiple measurement vectors (MMV),Fast rotating target,Inverse synthetic aperture radar (ISAR),Migration through range cells (MTRC),Pattern-coupled hierarchical model
更新于2025-09-11 14:15:04