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19 pages, 10165 KiB

Open AccessArticle

Experimental Guide for Compact Bow-Tie Femtosecond Solid-State Laser Development

by Vinícius Pereira Pinto, Giovana Trevisan Nogueira, Fátima Maria Mitsue Yasuoka and Jarbas Caiado de Castro Neto

Photonics 2025, 12(6), 548; https://doi.org/10.3390/photonics12060548 - 29 May 2025

Viewed by 488

Abstract

Bow-tie cavity configurations have gained significant attention due to their efficacy in facilitating stable resonator operation for applications requiring short pulse operation and high repetition rate pulses, offering versatility and reliability. While there is an extensive body of literature addressing the theoretical aspects [...] Read more.

Bow-tie cavity configurations have gained significant attention due to their efficacy in facilitating stable resonator operation for applications requiring short pulse operation and high repetition rate pulses, offering versatility and reliability. While there is an extensive body of literature addressing the theoretical aspects and applications of this laser configuration, there exists a gap in practical insights and systematic approaches guidance pertaining to the development and precision alignment of this laser type. The paper achieves this by compiling a range of analytical and optimization techniques for the bow-tie cavity configuration and delineating the necessary steps for the optimization required for continuous wave operation. This ultimately leads to the attainment of the pulsed regime through the Kerr Lens Mode-locking technique, offering a detailed account of the development, optimization, and performance evaluation of a Ti:Sapphire femtosecond laser cavity, using dispersion-compensating mirrors to produce a low-energy pulse of 1 nJ, a high repetition rate of 1 GHz, and a short pulse duration of 61 fs. This work can be useful for researchers and engineers seeking to embark on the development of compact and high-performance femtosecond lasers for a spectrum of applications, encompassing biomedical imaging, laser-assisted surgery, spectroscopy, and optical frequency combs. Full article

(This article belongs to the Section Lasers, Light Sources and Sensors)

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10 pages, 2638 KiB

Open AccessArticle

Highly Birefringent FBG Based on Femtosecond Laser-Induced Cladding Stress Region for Temperature and Strain Decoupling

by Kuikui Guo, Hao Wu, Yonghao Liang, Mingshen Su, Hongcheng Wang, Rang Chu, Fei Zhou and Ye Liu

Photonics 2025, 12(5), 502; https://doi.org/10.3390/photonics12050502 - 18 May 2025

Viewed by 517

Abstract

We present and demonstrate a highly birefringent fiber Bragg grating (Hi-Bi FBG) that was fabricated using a femtosecond laser to induce a sawtooth stress region near the FBG. The FBG is fabricated with a femtosecond laser point-by-point method, while the sawtooth stress region [...] Read more.

We present and demonstrate a highly birefringent fiber Bragg grating (Hi-Bi FBG) that was fabricated using a femtosecond laser to induce a sawtooth stress region near the FBG. The FBG is fabricated with a femtosecond laser point-by-point method, while the sawtooth stress region is generated in fiber cladding using the femtosecond laser along a sawtooth path. This sawtooth stressor can introduce an anisotropic and asymmetric refractive index profile in the cross-section of the fiber, resulting in additional birefringence up to 2.97 × 10⁻⁴ along the axial direction of the FBG. The central wavelengths of the Hi-Bi FBG at the fast and slow axes exhibit different sensitivities to temperature and strain, allowing simultaneous measurement of the strain and temperature by tracking the resonant wavelength shifts in the two axes. The experimental results show that the temperature sensitivities of the fast and slow axes are 10.32 pm/°C and 10.42 pm/°C, while the strain sensitivities are 0.91 pm/µε and 0.99 pm/µε. The accuracy of this proposed sensor in measuring strain and temperature is estimated to be 2.2 µε and 0.2 °C. This approach addresses the issue of cross-sensitivity between temperature and strain and offers some advantages of low cost, compact size, and significant potential for advancements in practical multi-parameter sensing applications. Full article

(This article belongs to the Special Issue Novel Advances in Optical Fiber Gratings)

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11 pages, 5329 KiB

Open AccessCommunication

Radiation-Induced Wavelength Shifts in Fiber Bragg Gratings Exposed to Gamma Rays and Neutrons in a Nuclear Reactor

by G. Berkovic, S. Zilberman, Y. London, M. Rosenfeld, E. Shafir, O. Ozeri, K. Ben-Meir, A. Krakovich and T. Makmal

Sensors 2025, 25(2), 323; https://doi.org/10.3390/s25020323 - 8 Jan 2025

Cited by 3 | Viewed by 984

Abstract

Fiber Bragg gratings (FBGs) inscribed by UV light and different femtosecond laser techniques (phase mask, point-by-point, and plane-by-plane) were exposed—in several irradiation cycles—to accumulated high doses of gamma rays (up to 124 MGy) and neutron fluence (8.7 × 10¹⁸/cm²) [...] Read more.

Fiber Bragg gratings (FBGs) inscribed by UV light and different femtosecond laser techniques (phase mask, point-by-point, and plane-by-plane) were exposed—in several irradiation cycles—to accumulated high doses of gamma rays (up to 124 MGy) and neutron fluence (8.7 × 10¹⁸/cm²) in a research-grade nuclear reactor. The FBG peak wavelengths were measured continuously in order to monitor radiation-induced shifts. Gratings inscribed on pure silica core fibers using near-IR femtosecond pulses through a phase mask showed the smallest shifts (<30 pm), indicating that these FBGs are suitable for temperature measurement even under extreme ionizing radiation. In contrast, the pointwise inscribed femtosecond gratings and a UV-inscribed grating showed maximal shifts of around 100 pm and 400 pm, respectively. Radiation-induced red shifts are believed to arise from gamma radiation damage, which may partially recover after irradiation is stopped. At the highest neutron exposures, grating peak blue shifts started to appear, apparently due to fiber compaction. Full article

(This article belongs to the Special Issue Optical Fiber Sensors in Radiation Environments: 2nd Edition)

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13 pages, 5166 KiB

Open AccessArticle

Fiber Optic Micro-Hole Salinity Sensor Based on Femtosecond Laser Processing

by Chen Li, Chao Fan, Hao Wu, Xxx Sedao and Jiang Wang

Nanomaterials 2025, 15(1), 60; https://doi.org/10.3390/nano15010060 - 2 Jan 2025

Viewed by 1195

Abstract

This study presents a novel reflective fiber Fabry–Perot (F–P) salinity sensor. The sensor employs a femtosecond laser to fabricate an open liquid cavity, facilitating the unobstructed ingress and egress of the liquid, thereby enabling the direct involvement of the liquid in light transmission. [...] Read more.

This study presents a novel reflective fiber Fabry–Perot (F–P) salinity sensor. The sensor employs a femtosecond laser to fabricate an open liquid cavity, facilitating the unobstructed ingress and egress of the liquid, thereby enabling the direct involvement of the liquid in light transmission. Variations in the refractive index of the liquid induce corresponding changes in the effective refractive index of the optical path, which subsequently influences the output spectrum. The dimensions and quality of the optical fiber are meticulously regulated through a combination of femtosecond laser cutting and chemical polishing, significantly enhancing the mechanical strength and sensitivity of the sensor’s overall structure. Experimental results indicate that the sensor achieves salinity sensitivity of 0.288 nm/% within a salinity range of 0% to 25%. Furthermore, the temperature sensitivity is measured at a minimal 0.015 nm/°C, allowing us to neglect temperature effects. The device is characterized by its compact size, straightforward structure, high mechanical robustness, ease of production, and excellent reproducibility. It demonstrates considerable potential for sensing applications in the domains of biomedicine and chemical engineering. Full article

(This article belongs to the Special Issue Nonlinear Optics and Ultrafast Lasers in Nanosystems)

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16 pages, 2769 KiB

Open AccessArticle

A Reflective Terahertz Point Source Meta-Sensor with Asymmetric Meta-Atoms for High-Sensitivity Bio-Sensing

by Luwei Zheng, Kazuki Hara, Hironaru Murakami, Masayoshi Tonouchi and Kazunori Serita

Biosensors 2024, 14(12), 568; https://doi.org/10.3390/bios14120568 - 23 Nov 2024

Cited by 1 | Viewed by 1049

Abstract

Biosensors operating in the terahertz (THz) region are gaining substantial interest in biomedical analysis due to their significant potential for high-sensitivity trace-amount solution detection. However, progress in compact, high-sensitivity chips and methods for simple, rapid and trace-level measurements is limited by the spatial [...] Read more.

Biosensors operating in the terahertz (THz) region are gaining substantial interest in biomedical analysis due to their significant potential for high-sensitivity trace-amount solution detection. However, progress in compact, high-sensitivity chips and methods for simple, rapid and trace-level measurements is limited by the spatial resolution of THz waves and their strong absorption in polar solvents. In this work, a compact nonlinear optical crystal (NLOC)-based reflective THz biosensor with a few arrays of asymmetrical meta-atoms was developed. A near-field point THz source was locally generated at a femtosecond-laser-irradiation spot via optical rectification, exciting only the single central meta-atom, thereby inducing Fano resonance. The reflective resonance response demonstrated dependence on several aspects, including structure asymmetricity, geometrical size, excitation point position, thickness and array-period arrangement. DNA samples were examined using 1 μL applied to an effective sensing area of 0.234 mm² (484 μm × 484 μm) for performance evaluation. The developed Fano resonance sensor exhibited nearly double sensitivity compared to that of symmetrical sensors and one-gap split ring resonators. Thus, this study advances liquid-based sensing by enabling easy, rapid and trace-level measurements while also driving the development of compact and highly sensitive THz sensors for biological samples. Full article

(This article belongs to the Section Optical and Photonic Biosensors)

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14 pages, 7266 KiB

Open AccessArticle

Femtosecond Laser Introduced Cantilever Beam on Optical Fiber for Vibration Sensing

by Jin Qiu, Zijie Wang, Zhihong Ke, Tianlong Tao, Shuhui Liu, Quanrong Deng, Wei Huang and Weijun Tong

Sensors 2024, 24(23), 7479; https://doi.org/10.3390/s24237479 - 23 Nov 2024

Viewed by 1123

Abstract

An all-fiber vibration sensor based on the Fabry-Perot interferometer (FPI) is proposed and experimentally evaluated in this study. The sensor is fabricated by introducing a Fabry-Perot cavity to the single-mode fiber using femtosecond laser ablation. The cavity and the tail act together as [...] Read more.

An all-fiber vibration sensor based on the Fabry-Perot interferometer (FPI) is proposed and experimentally evaluated in this study. The sensor is fabricated by introducing a Fabry-Perot cavity to the single-mode fiber using femtosecond laser ablation. The cavity and the tail act together as a cantilever beam, which can be used as a vibration receiver. When mechanical vibrations are applied, the cavity length of the Fabry-Perot interferometer changes accordingly, altering the interference fringes. Due to the low moment of inertia of the fiber optic cantilever beam, the sensor can achieve broadband frequency responses and high vibration sensitivity without an external vibration receiver structure. The frequency range of sensor detection is 70 Hz–110 kHz, and the sensitivity of the sensor is 60 mV/V. The sensor’s signal-to-noise ratio (SNR) can reach 56 dB. The influence of the sensor parameters (cavity depth and fiber tail length) on the sensing performance are also investigated in this study. The sensor has the advantages of compact structure, high sensitivity, and wideband frequency response, which could be a promising candidate for vibration sensing. Full article

(This article belongs to the Special Issue Recent Advances in Micro- and Nanofiber-Optic Sensors)

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14 pages, 2519 KiB

Open AccessReview

Developments of Waveguide Lasers by Femtosecond Laser Direct–Writing Technology

by Yang Zhang, Boyan Yu, Zihao Zhang, Xinghao Duan and Junli Wang

Photonics 2024, 11(9), 803; https://doi.org/10.3390/photonics11090803 - 28 Aug 2024

Cited by 1 | Viewed by 3300

Abstract

Waveguide lasers have the advantages of miniature and compact structure and have broad application prospects in photonic integration and on–chip laboratories. The development of femtosecond laser direct–writing technology makes the processing of transparent materials more flexible and controllable. This paper mainly introduces a [...] Read more.

Waveguide lasers have the advantages of miniature and compact structure and have broad application prospects in photonic integration and on–chip laboratories. The development of femtosecond laser direct–writing technology makes the processing of transparent materials more flexible and controllable. This paper mainly introduces a waveguide laser based on femtosecond laser direct–writing technology. Firstly, the applications of femtosecond laser direct–writing technology in an optical waveguide are introduced, including the principles of femtosecond laser direct–writing technology, common optical wave scanning methods, and types of optical waveguides. After that, we summarize the development of a waveguide continuous–wave laser, a Q–switched laser and a mode–locked laser from visible to mid–infrared wavebands and analyze some new representative work. Finally, we explain the difficulty of compensating for dispersion in pulse waveguide lasers and summarize some new ideas that have been proposed to solve the problem. Full article

(This article belongs to the Special Issue New Perspectives in Ultrafast Intense Laser Science and Technology)

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15 pages, 3626 KiB

Open AccessArticle

Optical Fiber Probe with Integrated Micro-Optical Filter for Raman and Surface-Enhanced Raman Scattering Sensing

by Md Abdullah Al Mamun, Tomas Katkus, Anita Mahadevan-Jansen, Saulius Juodkazis and Paul R. Stoddart

Nanomaterials 2024, 14(16), 1345; https://doi.org/10.3390/nano14161345 - 14 Aug 2024

Cited by 1 | Viewed by 2553

Abstract

Optical fiber Raman and surface-enhanced Raman scattering (SERS) probes hold great promise for in vivo biosensing and in situ monitoring of hostile environments. However, the silica Raman scattering background generated within the optical fiber increases in proportion to the length of the fiber, [...] Read more.

Optical fiber Raman and surface-enhanced Raman scattering (SERS) probes hold great promise for in vivo biosensing and in situ monitoring of hostile environments. However, the silica Raman scattering background generated within the optical fiber increases in proportion to the length of the fiber, and it can swamp the signal from the target analyte. While filtering can be applied at the distal end of the fiber, the use of bulk optical elements has limited probe miniaturization to a diameter of 600 µm, which in turn limits the potential applications. To overcome this limitation, femtosecond laser micromachining was used to fabricate a prototype micro-optical filter, which was directly integrated on the tip of a 125 µm diameter double-clad fiber (DCF) probe. The outer surface of the microfilter was further modified with a nanostructured, SERS-active, plasmonic film that was used to demonstrate proof-of-concept performance with thiophenol as a test analyte. With further optimization of the associated spectroscopic system, this ultra-compact microprobe shows great promise for Raman and SERS optical fiber sensing. Full article

(This article belongs to the Special Issue Low Dimensional Materials Fabrication, Characterization and Applications)

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8 pages, 1830 KiB

Open AccessArticle

Femtosecond Laser-Written Small-Period Long-Period Fiber Grating for an L-Band Normal Dispersion Mode-Locked Fiber Laser

by Qianying Li, Peiyun Cheng, Rong Zhao and Xuewen Shu

Photonics 2024, 11(8), 693; https://doi.org/10.3390/photonics11080693 - 25 Jul 2024

Cited by 1 | Viewed by 1552

Abstract

We utilize a femtosecond laser-inscribed small-period long-period fiber grating (SP-LPFG) to induce a nonlinear polarization rotation (NPR) effect for mode-locking pulses in a normal dispersion erbium-doped fiber laser (EDFL). The SP-LPFG has a length of 2.5 mm and a period of 25 μm. [...] Read more.

We utilize a femtosecond laser-inscribed small-period long-period fiber grating (SP-LPFG) to induce a nonlinear polarization rotation (NPR) effect for mode-locking pulses in a normal dispersion erbium-doped fiber laser (EDFL). The SP-LPFG has a length of 2.5 mm and a period of 25 μm. At wavelengths of 1556 nm and 1561 nm, it exhibits polarization-dependent loss (PDL) values of 20 dB and 14.5 dB, respectively, sufficient to trigger the NPR mechanism. With the pump power increased to 500 mW, the laser achieves normal dispersion mode-locked pulses centered at 1575 nm in the L-band, with a 3 dB bandwidth of 1.35 nm and a pulse width of 1.61 ps. The radio frequency (RF) spectrum reveals an signal-to-noise ratio (SNR) of up to 63.6 dB, demonstrating the excellent stability of the laser operation. This SP-LPFG holds promising applications, paving the way for efficient, compact, and stable normal dispersion ultrafast fiber lasers. Full article

(This article belongs to the Special Issue Cutting-Edge Developments in Fiber Laser)

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17 pages, 13676 KiB

Open AccessArticle

A Near Fourier-Limited Pulse-Preserving Monochromator for Extreme-Ultraviolet Pulses in the Few-Fs Regime

by Yudong Yang, Tanja Neumann, Julia Hengster, Roland E. Mainz, Jakob Elsner, Oliver D. Mücke, Franz X. Kärtner and Thorsten Uphues

Photonics 2024, 11(6), 525; https://doi.org/10.3390/photonics11060525 - 1 Jun 2024

Viewed by 1321

Abstract

We present a pulse-preserving multilayer-based extreme-ultraviolet (XUV) monochromator providing ultra-narrow bandwidth (

Δ E < 0.6 eV

,

E_{c} = 92 eV

) and compact footprint (

28 \times 10 {cm}^{2}

) for easy integration into high-harmonic generation (HHG) or free-electron [...] Read more.

We present a pulse-preserving multilayer-based extreme-ultraviolet (XUV) monochromator providing ultra-narrow bandwidth (

Δ E < 0.6 eV

,

E_{c} = 92 eV

) and compact footprint (

28 \times 10 {cm}^{2}

) for easy integration into high-harmonic generation (HHG) or free-electron laser (FEL) sources. The temporal resolution of the novel design supports pulse durations of typical pump–probe setups in the femtosecond and attosecond regime, depending on the mirror design and focusing geometries over the tuning range of the monochromator. The theoretical design is analyzed and experimentally characterized in a laser-driven HHG setup. Full article

(This article belongs to the Special Issue Advances in Ultrafast Optics: From Fundamental Science to Applications)

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11 pages, 3112 KiB

Open AccessArticle

Long-Period Grating with Asymmetrical Modulation for Curvature Sensing

by Lan Su, Xin Qiu, Rui Guo, Youbo Jing, Chaoshan Yang and Shuhui Liu

Appl. Sci. 2024, 14(5), 1895; https://doi.org/10.3390/app14051895 - 25 Feb 2024

Cited by 3 | Viewed by 1463

Abstract

We propose and demonstrate a curvature sensor based on long-period fiber grating (LPFG) with asymmetric index modulation. The LPFG is fabricated in single-mode fiber with femtosecond laser micromachining. The grating structure is not introduced in the central fiber core, but is located off-axis [...] Read more.

We propose and demonstrate a curvature sensor based on long-period fiber grating (LPFG) with asymmetric index modulation. The LPFG is fabricated in single-mode fiber with femtosecond laser micromachining. The grating structure is not introduced in the central fiber core, but is located off-axis with a distance of a few micrometers. Experimental results indicate that the offset distance has direct influence on the grating spectra. By utilizing such an asymmetric structure, two-dimensional vector curvature sensing can be realized. For an LPFG with an offset distance of 6 μm, the curvature sensitivity is around 29 nm/m⁻¹ in the 0° and 180° direction and about 20 nm/m⁻¹ in the 90° and 270° direction. The difference in curvature sensitivity in different bending directions makes the sensor capable of distinguishing the curvature orientation. The temperature response of the sensor is also experimentally investigated, and results indicate that the sensor has a very low temperature cross-sensitivity of 0.003 m⁻¹/°C. The characteristics of high curvature sensitivity, two-dimensional bending direction identification, and compact structure make the device an ideal candidate to be applied in the field of power grid health monitoring and intelligent robotics. Full article

(This article belongs to the Special Issue Progress in Fiber Bragg Gratings Sensor)

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13 pages, 5542 KiB

Open AccessArticle

Fiber Bragg Grating Salinity Sensor Array Based on Fiber Tapering and HF Etching

by Gaochao Li, Yongjie Wang, Mengchao Yan, Tuanwei Xu, Ancun Shi, Yuanhui Liu, Xuechun Li and Fang Li

Photonics 2023, 10(12), 1315; https://doi.org/10.3390/photonics10121315 - 29 Nov 2023

Cited by 4 | Viewed by 1980

Abstract

We propose a seawater salinity sensor array based on a micro/nanofiber Bragg grating structures, which allows for the simultaneous measurement of temperature and salinity. The proposed sensing structure is fabricated through a process involving optical fiber tapering, femtosecond laser inscription, and chemical etching. [...] Read more.

We propose a seawater salinity sensor array based on a micro/nanofiber Bragg grating structures, which allows for the simultaneous measurement of temperature and salinity. The proposed sensing structure is fabricated through a process involving optical fiber tapering, femtosecond laser inscription, and chemical etching. The equivalent refractive index (RI) of this sensor structure is influenced by the surrounding RI, resulting in a Bragg characteristic wavelength shift that can be used for salinity sensing. The experimental results show that the salinity sensitivity for two cascaded sensor arrays is 8.39 pm/‰ and 7.71 pm/‰, while the temperature sensitivity is 8.28 pm/°C and 8.03 pm/°C, respectively. This sensor structure is compact, exhibits excellent linearity, and offers good repeatability. It holds great potential for applications in seawater environmental monitoring and quantitative studies of seawater dispersion characteristics. Full article

(This article belongs to the Special Issue Progress and Prospects in Optical Fiber Sensing)

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7 pages, 1871 KiB

Open AccessCommunication

Fs-Laser Fabricated Miniature Fabry–Perot Interferometer in a No-Core Fiber for High-Temperature Applications

by Chen Zhu, Osamah Alsalman and Jie Huang

Sensors 2023, 23(18), 7754; https://doi.org/10.3390/s23187754 - 8 Sep 2023

Cited by 5 | Viewed by 1956

Abstract

This paper reports a fiber in-line Fabry–Perot interferometer (FPI) fabricated in a no-core fiber using the direct femtosecond laser writing technique for high-temperature sensing applications. Two in-line reflectors are directly inscribed in a no-core fiber to construct a low-finesse FPI. Fringe visibility greater [...] Read more.

This paper reports a fiber in-line Fabry–Perot interferometer (FPI) fabricated in a no-core fiber using the direct femtosecond laser writing technique for high-temperature sensing applications. Two in-line reflectors are directly inscribed in a no-core fiber to construct a low-finesse FPI. Fringe visibility greater than 10 dB is obtained from the reflection spectra of the fabricated no-core fiber FPIs. Temperature responses of a prototype no-core fiber FPI are characterized up to 1000 °C. The proposed configuration is compact and easy to fabricate, making it attractive for sensing applications in high-temperature harsh environments. Full article

(This article belongs to the Special Issue Distributed and Single-Point Fiber Optic Sensors: Applications and Technology)

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19 pages, 17021 KiB

Open AccessArticle

Analysis and 3D Imaging of Multidimensional Complex THz Fields and 3D Diagnostics Using 3D Visualization via Light Field

by Michael Gerasimov, Adnan Haj Yahya, Vadim Patrick Nave, Egor Dyunin, Jacob Gerasimov and Aharon Friedman

Computation 2023, 11(8), 160; https://doi.org/10.3390/computation11080160 - 14 Aug 2023

Cited by 1 | Viewed by 1772

Abstract

We present a numerical platform for 3D imaging and general analysis of multidimensional complex THz fields. A special 3D visualization is obtained by converting electromagnetic (EM) radiation to a light field via the Wigner distribution function, which is known for discovering (revealing) hidden [...] Read more.

We present a numerical platform for 3D imaging and general analysis of multidimensional complex THz fields. A special 3D visualization is obtained by converting electromagnetic (EM) radiation to a light field via the Wigner distribution function, which is known for discovering (revealing) hidden details. This allows for 3D diagnostics using the simple techniques of geometrical optics, which significantly facilitates the whole analysis. This simulation was applied to a complex field composed of complex beams emitted as ultra-narrow femtosecond pulses. A method was developed for the generation of phase–amplitude and spectral characteristics of complex multimode radiation in a free-electron laser (FEL) operating under various parameters. The tool was successful at diagnosing an early design of the transmission line (TL) of an innovative accelerator at the Schlesinger Family Center for Compact Accelerators, Radiation Sources, and Applications. Full article

(This article belongs to the Special Issue Intelligent Computing, Modeling and its Applications)

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13 pages, 5560 KiB

Open AccessArticle

Exploring the Interpad Gap Region in Ultra-Fast Silicon Detectors: Insights into Isolation Structure and Electric Field Effects on Charge Multiplication

by Gordana Laštovička-Medin, Mateusz Rebarz, Jovana Doknic, Ivona Bozovic, Gregor Kramberger, Tomáš Laštovička and Jakob Andreasson

Sensors 2023, 23(15), 6746; https://doi.org/10.3390/s23156746 - 28 Jul 2023

Cited by 6 | Viewed by 3304

Abstract

We present an in-depth investigation of the interpad (IP) gap region in the ultra-fast silicon detector (UFSD) Type 10, utilizing a femtosecond laser beam and the transient current technique (TCT) as probing instruments. The sensor, fabricated in the trench-isolated TI-LGAD RD50 production batch [...] Read more.

We present an in-depth investigation of the interpad (IP) gap region in the ultra-fast silicon detector (UFSD) Type 10, utilizing a femtosecond laser beam and the transient current technique (TCT) as probing instruments. The sensor, fabricated in the trench-isolated TI-LGAD RD50 production batch at the FBK Foundry, enables a direct comparison between TI-LGAD and standard UFSD structures. This research aims to elucidate the isolation structure in the IP region and measure the IP distance between pads, comparing it to the nominal value provided by the vendor. Our findings reveal an unexpectedly strong signal induced near p-stops. This effect is amplified with increasing laser power, suggesting significant avalanche multiplication, and is also observed at moderate laser intensity and high HV bias. This investigation contributes valuable insights into the IP region’s isolation structure and electric field effects on charge collection, providing critical data for the development of advanced sensor technology for the Compact Muon Selenoid (CMS) experiment and other high-precision applications. Full article

(This article belongs to the Special Issue Radiation Sensors and Detectors: Materials, Principles and Applications)

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