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- 实验方案
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Site-selective Atomic Layer Precision Thinning of MoS2 via Laser-Assisted Anisotropic Chemical Etching
摘要： Various exotic optoelectronic properties of two-dimensional (2D) transition metal dichalcogenides (TMDCs) strongly depend on their number of layers, and typically manifest in ultra-thin few- or mono-layer formats. Thus, precise manipulation of thickness and shape is essential to fully access their potential in optoelectronic applications. Here, we demonstrate site-selective atomic layer precision thinning of exfoliated MoS2 flake by laser. The oxidation mediated anisotropic chemical etching initiated from edge defects and progressed by controlled scanning of the laser beam. Thereby, the top-most layer can be preferentially removed in designed patterns without damaging the bottom flake. In addition, we could monitor the deceleration of the thinning by in-situ reflectance measurement. The apparent slow-down of the thinning rate is attributed to the sharp reduction in the temperature of the flake due to thickness dependent optical properties. Fabrication of monolayer stripes by laser thinning suggests potential applications in non-linear optical gratings. The proposed thinning method would offer a unique and rather straightforward way to obtain arbitrary shape and thickness of TMDCs flake for various optoelectronic applications.
关键词： Laser Thinning,Single layer precision thinning,Non-linear optical grating,Anisotropic chemical etching,TMDCs,MoS2
更新于2025-09-12 10:27:22
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Encyclopedia of Maritime and Offshore Engineering || Optical Fiber Sensors for Marine Structural Condition Monitoring
摘要： Effective structural condition monitoring, and the action from it, is likely to result in significant economic savings from a better determination of structural integrity and use of the structure itself. It is also essential for the enhanced prediction of structural service lifetimes based on real-time measurement data obtained. Fiber optic-based sensors have shown real promise for structural condition monitoring, due to the attractive features they possess, such as small size, geometric versatility, multiplexing capability, and resistance to corrosive and hazardous environments. As a result, these sensors have been explored widely for monitoring a wide range of structural materials, including composites, concrete, limestones, carbon/aluminum, and metals (Scott et al., 2013; Sun et al., 2012; Nguyen et al., 2014; Kerrouche et al., 2009a), and the key parameters that have been measured include temperature, strain, vibration, relative humidity, pH, and chlorides, and so on.
关键词： Moisture Ingress Sensor,pH Sensor,Fiber Bragg Grating,Optical Fiber Sensors,Vibration Sensors,Marine Structural Condition Monitoring
更新于2025-09-12 10:27:22
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All fiber mode-locked thulium-doped fiber laser using a novel femtosecond-laser-inscribed 45°-plane-by-plane-tilted fiber grating
摘要： Using the novel 45°-plane-by-plane-tilted fiber grating inscribed by a femtosecond laser as an in-line fiber polarizer, we demonstrate an all-fiber passively mode-locked thulium-doped fiber laser. We characterize the grating for polarization-dependent loss, indicating high contrast and broad operating wavelength. The 45°-tilted fiber grating together with polarization controller act as an artificial saturable absorber suitable for mode-locking through nonlinear polarization rotation. By properly pre-adjusting the polarization controller, stable mode-locking is achieved for a pump power in the range of 300 mW–400 mW at 1565 nm. Owing to the net anomalous dispersion, a stable mode-locked soliton pulse centered at 1870 nm with a pulse width of 862 fs is reported at a fundamental repetition rate of 22.34 MHz. A long-term stability test reveals that the laser is quite stable for 24 h under laboratory conditions, confirming the capabilities of the 45°-tilted fiber grating for stable laser operation.
关键词： fibre lasers,tilted fiber Bragg grating,dissipative soliton,thulium doped fibre,soliton mode-locking
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) - Ring Interband Cascade Lasers for Environmental Monitoring
摘要： Interband cascade lasers (ICLs) combine the concept of quantum cascade lasers (QCLs) and conventional photodiodes, because they rely on the voltage-efficient in-series connection of multiple active regions as in QCLs as well as the long upper-level recombination lifetimes of photodiodes. The distinctive low power consumption of ICLs makes them especially attractive for mobile applications in the mid-infrared, such as process control, medical applications and spectroscopy. As a first proof of principle we present ICLs fabricated into ring-shaped cavities. A second order distributed feedback (DFB) grating is used for the light outcoupling of our ring ICLs, in vertical direction through the GaSb substrate. The first demonstrated devices with a waveguide width of 10 μm and 400 μm outer diameter show light emission at a wavelength of ~3.7 μm. A pulsed threshold current density <1 kA/cm2 is measured at 20°C. We are currently working on the second generation of such ring ICLs with smaller waveguides for better suppression of higher order lateral modes and larger outer diameter (e.g. 800 μm) for increased optical output power. The newly developed devices are used in a project for trace gas sensing via the principle of photothermal interferometry.
关键词： Interband cascade lasers,trace gas sensing,distributed feedback grating,photothermal interferometry,ring-shaped cavities
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) - Thin-Disk Laser Emitting Beams with 980 W of CW-Output Power and Radial Polarization
摘要： Within the past decade, a variety of scientific groups have demonstrated the potential of radially and azimuthally polarized laser beams in many applications [1-3]. Experimental investigations in high-power operation indicate additional beneficial properties for material processing, such as drilling and deep-penetration-welding, which have been demonstrated to lead to an increase of the process efficiency by using such a polarization state. Cutting of metal sheets with radially polarized beams at 1 micron wavelength have been reported recently to increase the process efficiency [4]. In the present work, we report on the generation of radially polarized laser beams in cw operation by using grating-waveguide mirror (GWM) [5]. The grating design is based on the leaky-mode coupling mechanism, which allows for sufficient reduction of the reflectivity of the polarization state (azimuthal or radial) to be suppressed in the resonator. It consists of a circular sub-wavelength diffraction grating integrated into a highly or partially reflective dielectric multilayer mirror. At the central wavelength of the Yb:LuAG TDL, i.e., at 1030 nm, the absolute values of the reflectivities for the TE- and TM-polarized light were measured to be (55.2 ± 0.2)% and (99.8 ± 0.2)%, respectively. This corresponds to a reflectivity difference of approximately 45%. At wavelengths of 1023, 1042, and 1059 nm, the reflectivity of the TE-polarized beam was measured to be <1%, making the grating attractive for other applications with lasers operating within this wavelength range. The grating was implemented as cavity end mirror in an Yb:LuAG thin-disk laser setup, pumped at its “zero-phonon” line, i.e. λ = 969 nm. The implementation of the GWM led to the extraction of a radially polarized beam with an output power of 980 W and an optical efficiency of 50.5%. Single transversal mode operation of a radially polarized LG01 mode was sustained for the whole output power range with beam quality factors of Mx2 = 2.0 and My2 = 2.3. Figure 1(a) shows a photograph of the GWM. In Fig. 1(b), the performance of the laser and the far field intensity distribution of the emitted laser beam is shown. A qualitative analysis of the polarization was carried out by recording the intensity distributions transmitted through a rotating polarizer at different orientations of its transmission axis. Furthermore, the purity of polarization (degree of polarization) was measured with a custom-made camera-based 2D Stokes-polarimeter. An average degree of radial polarization of 95% was measured.
关键词： grating-waveguide mirror,high-power operation,radially polarized laser beams,material processing,Yb:LuAG thin-disk laser
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) - Tunable Narrowband Tm:YAP Laser using a Transversally Chirped Volume Bragg Grating
摘要： Tunable long wave infrared (LWIR) coherent sources emitting between 8 and 12 μm can be used for versatile remote gas sensing. In ref [1] we implemented a parametric oscillator in which wavelength tunability was achieved by temperature tuning of the crystal indices of refraction. It is well known that a similar wavelength range can be addressed by tuning the pump wavelength rather than the crystal temperature [2]. In addition, pump tuning can be significantly faster than temperature tuning. In this context we also need a narrow band spectrum to control the spectral output of the optical parametric oscillator, which is based on Vernier spectral filtering in doubly-resonant cavities. Seger and his team exhibited single longitudinal mode operation in a microlaser tuned with transversally chirped volume Bragg grating (TC-VBG) near 1 μm [3]. We show how this concept can be applied to a different laser emitting at 2 μm.
关键词： Tunable laser,LWIR,Tm:YAP,Narrowband,Volume Bragg Grating
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) - High Peak Power Laser Diodes for Eye Safe LIDAR with Integrated Wavelength Locking Element
摘要： We report on the development of high peak-power broad-area laser diodes emitting in the 1.5 μm wavelength band for eye-safe LIDAR applications. The laser contain a monolithically integrated surface grating section for wavelength stabilization. The performance merits of the wavelength stabilized laser is benchmark against traditional Fabry-Pérot diodes fabricated within the same processing batch and having identical quantum-well design. The study demonstrates the efficacy of the surface-grating applied to broad-area lasers and the benefits rendered possible for decreasing the spectral linewidth and reducing the temperature drift of the wavelength. This type of high-power light source can improve the signal-to-noise ratio of eye-safe time-of-flight LIDARs in bright illumination conditions by making possible the use of narrow band-pass filters for reducing the ambient sunlight. Moreover, the same advantage to reject ambient signal is expected in other applications such as gated imaging [1], or when using a pulsed laser as the illuminator in high speed imaging applications. In addition, the variation in the emission wavelengths from wafer-to-wafer and from chip-to-chip is reduced compared to non-stabilized lasers.
关键词： high peak-power,broad-area laser diodes,1.5 μm wavelength,wavelength stabilization,eye-safe LIDAR,surface grating
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) - Semiconductors as Highly Efficient Single and Multicycle Terahertz Sources
摘要： The low- (0.1-2 THz) and mid-frequency (2-20 THz) bands of the THz range can be accessed by optical rectification (OR) in LiNbO3 (LN) [1] and organic crystals [2], respectively. The low -frequency band is optimally fitting for acceleration of charged particle beams. However, further increasing the THz pulse energy and field strength is challenging. Semiconductors can be used as highly efficient terahertz sources if the pumping wavelength sufficiently long to eliminate two- and three-photon pump absorption and the associated free-carrier absorption in the THz range. At such long infrared pump wavelengths tilted-pulse-front (TPF) pumping has to be used for phase matching. Comparing to LN this angle is advantageously small (<30°), and contact-grating (CG) is feasible. In our experiment we demonstrated more than two orders of magnitude higher pump-to-THz conversion efficiency than before [3], using a pump wavelength of 1.7 μm. 14 μJ THz pulse energy at 0.7% efficiency were measured with a prism shape ZnTe source [4]. We also realized a monolithic ZnTe CG THz source and demonstrated the generation of THz pulses with up to 3.9 μJ energy and 0.3% efficiency (Fig. 1a) [5]. We will discuss the prospects and basic design aspects of long-wavelength-pumped semiconductor THz sources, including optimal pumping and phase-matching conditions [6]. Our calculations show that single-cycle THz pulses can be generated with 15 GW/cm2 pump intensity, 150 fs pump pulse duration and 2 THz phase- matching frequency with more than 3% conversion efficiency from an 8 mm thick GaP source (Fig 1b). We will also present our latest results on GaP CG design for three different pump wavelengths (1.76, 2.06 and 2.2 μm), symmetric and Littrow configurations, and four different phase-matching frequencies from 1 to 4 THz. The expected first order diffraction efficiencies are 76-81% which can be increased to >90% with additional anti-reflection coating for the corresponding pump wavelength. GaP in combination with a flexible and efficient pump source technology, such as the dual-chirped OPA [7], and the CG technology can be a highly efficient and versatile source of multicycle THz pulses too [8]. Conversion efficiencies up to 3% were predicted for 5 mm crystal length (Fig 1c). Based on this, producing multicycle THz pulses with about 1.2 mJ energy from a GaP contact-grating source of about 1 cm2 area is feasible by using intensity-modulated pump pulses with 40 mJ energy from a dual-chirped OPA [7]. For an optimal combination of THz frequency, pump intensity, and crystal length, efficiencies as high as 8% can be expected.
关键词： Tilted-pulse-front pumping,Optical rectification,Terahertz sources,Semiconductors,Contact-grating,Conversion efficiency
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) - Investigation of Grating Assisted Mode-Selective Few-Mode Fused Fiber Couplers
摘要： Spatial division multiplexing (SDM) in form of mode division multiplexing (MDM) is one solution to keep up with the increasing data traffic demand [1]. MDM is based on using individual modes of a few-mode or multi-mode fiber as individual transmission channels and requires the addressing of individual modes at the input and output of the multimode fiber link. Here, among others, mode-selective fused fiber couplers based on evanescent coupling can be applied for addressing individual modes of fiber optic transmission links. In this case, light coupling occurs when the mode propagation constants are equal and this can be achieved e.g. by applying grating structures and, thus, compensate for the mismatch of the propagation constants of the modes to be coupled [2]. In this work, we will present our latest efforts towards the development of grating assisted mode-selective fused fiber couplers. In order to realize these, the fabrication process is divided into two steps. First, the asymmetric fused fiber couplers are fabricated by using an etching, fusing and tapering process of a step index single-mode (sm) fiber from Fibercore SM1500 (4.2/125) and a four mode step index few-mode (fm) fiber from OFS. The cross-section of a fabricated asymmetric fused fiber coupler with a parabolic shape at the taper waist is shown in Fig. 1a. Following this step the grating structure is inscribed into the core of the sm fiber using the amplitude mask method. The grating structure is applied in order to obtain mode-selective light coupling between the sm and fm fibers. The amplitude mask method for inscribing the grating structure is realized by using a bronze foil mask (Optofab) and a KrF-excimer laser (Atlex FBG, ATL Lasertechnik). Moreover, the process parameters (repetition rate, pulse energy and exposure time) are taken from previous investigations of inscribing LPGs into the highly germanium doped sm fiber [3]. In order to determine the required grating period for mode selective light coupling a CAD model was designed in RSOFT. The model takes the fiber parameters as well as the heating zone, the fiber extension and the degree of fusion (DOF) of the coupler fabrication process into account. In Fig. 1b an illustration of the CAD model of the fabricated asymmetric fused fiber coupler is shown. To determine the required grating period for mode-selective light coupling and to simulate the performance of the grating assisted mode-selective fiber coupler the beam propagation method was applied (BeamPROP-toolbox in RSOFT). As illustrated in Fig. 1c, mode-selective light coupling can be obtained between the LP11 mode of the fm fiber and the LP01 mode of the sm fiber for a grating period of 500 μm.
关键词： fused fiber couplers,mode division multiplexing,few-mode fiber,grating structures,spatial division multiplexing
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) - Analysis of Operation of Photonic Integrated Interrogators for Fiber Optic Sensor Networks
摘要： In this work we present and discuss our solutions of photonic integrated interrogators for application in a novel fiber-optic sensing system, dedicated to monitoring condition of a patient exposed to magnetic resonance imaging (MRI) scanning procedure. The monitoring system makes use of multiple fiber Bragg grating (FBG) based sensors, which offer the advantages of high sensitivity and immunity to strong magnetic fields and simultaneously do not affect the results of an MRI scan. Furthermore, the fact that many gratings can be inscribed within a single optical fiber simplifies the architecture of the sensing network.
关键词： fiber Bragg grating,MRI,fiber-optic sensing system,photonic integrated interrogators,monitoring system
更新于2025-09-12 10:27:22